2014 Human coronaviruses_ Viral and cellular factors involved in neuroinvasiveness and neuropathogenesis

2014·3.52 MB·English

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Virus Research

journal homepage: www.elsevier.com/locate/virusres

Review
Human coronaviruses: Viral and cellular factors involved in

neuroinvasiveness and neuropathogenesis

MarcDesforges∗,AlainLeCoupanec,JennyK.Stodola,MathieuMeessen-Pinard,
Pierre J.Talbot∗∗

LaboratoryofNeuroimmunovirology,INRS-InstitutArmand-Frappier,Institutnationaldelarecherchescientifique,UniversitéduQuébec,531boulevard

desPrairies,Laval,Québec,CanadaH7V1B7

a r t i c l e i n f o a b s t r a c t

Articlehistory: Amongthevariousrespiratoryvirusesinfectinghumanbeings,coronavirusesareimportantpathogens,
Availab leonlinexxx which usua lly infe ct the uppe r respi ratory tra ct, whe re they are mainly a sso ciated wit h common

colds.However,inmorevulnerablepopulations,suchasnewborns,infants,theelderlyandimmune-

Keywords: compromised individuals, these opportunistic pathogens can also affect the lower respiratory tract,
Humancoronavirus leadingtopne umonia,exa cerba tionsofasthm a,andvari ous types ofres pira toryd istresssynd rome.
Respira tory viral infection Theresp ira toryinvolve mentofhuman co ronaviru sesh asbeen clearly es tablishedsi ncethe1 960s.Nev-
Neuroinvasion
ertheless,foralmostthreedecadesnow,datareportedinthescientificliteraturehasalsodemonstrated
CNSinfection
that,likeitwasdescribedforotherhumanviruses,coronaviruseshaveneuroinvasivecapacitiessince
Neurologicaldiseases
theycanspreadfromtherespiratorytracttothecentralnervoussystem(CNS).Oncethere,infection

ofCNScells(neurotropism)couldleadtohumanhealthproblems,suchasencephalitisandlong-term

neurologicaldiseases.NeuroinvasivecoronavirusescoulddamagetheCNSasaresultofmisdirected

hostimmuneresponsesthatcouldbeassociatedwithautoimmunityinsusceptibleindividuals(virus-

inducedneuroimmunopathology)and/orviralreplication,whichdirectlyinducesdamagetoCNScells

(virus-inducedneuropathology).Givenalltheseproperties,ithasbeensuggestedthattheseopportunistic

humanrespiratorypathogenscouldbeassociatedwiththetriggeringortheexacerbationofneurologic

diseasesforwhichtheetiologyremainspoorlyunderstood.Herein,wepresenthostandviralfactors

thatparticipateintheregulationofthepossiblepathogenicprocessesassociatedwithCNSinfectionby

humancoronavirusesandwetrytodeciphertheintricateinterplaybetweenvirusandhosttargetcells

inordertocharacterizetheirroleintheviruslifecycleaswellasinthecapacityofthecelltorespondto

viralinvasion.

©2014ElsevierB.V.Allrightsreserved.

Contents
1. Introduction.......................................................................................................................................... 00

2. Coronaviruses:anoverview.......................................................................................................................... 00

2.1. Viralmoleculardeterminantsofpathogenesis............................................................................................... 00

2.2. Humancoronaviruses:recognizedrespiratorypathogens................................................................................... 00

3. Neuroinvasiveandneurotropicviruses.............................................................................................................. 00

3.1. Respiratoryviruseswithneuroinvasiveandneurotropicproperties:associatedneuropathologies........................................ 00

3.2. HumancoronavirusesintheCNS............................................................................................................. 00

3.2.1. Possiblemechanismsofcoronavirusesneuroinvasiveness........................................................................ 00

3.2.2. MechanismsofHCoV-inducedneurodegeneration:possibleassociatedneuropathologies....................................... 00

∗
Correspondingauthor.Tel.:[phone]x4342;fax:[phone].
∗∗
Correspondingauthor.Tel.:[phone]x4300;fax:[phone].

E-mailaddresses:[email protected](M.Desforges),[email protected](P.J.Talbot).

http://dx.doi.org/10.1016/j.virusres.2014.09.011
0168-1702/©2014ElsevierB.V.Allrightsreserved.

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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4. Conclusions........................................................................................................................................... 00

Acknowledgments.................................................................................................................................... 00

References............................................................................................................................................ 00

1. Introduction themselves also naturally neuroinvasive in humans and mice, a

possible association between the presence of ubiquitous human

Viral infections of the respiratory tract represent a major coronavirusesintheestablishmentortheexarcerbationofneuro-

problem for human and animal health around the world. These logicalhumanpathologieshasovertheyearsbeensuggested.

respiratoryinfectionsinducethemostcommonillnesses(Vareille Upuntilnow,noclearspecificassociationhaseverbeenmade

etal.,2011)andarealeadingcauseofmorbidityandmortalityin with any known human neuropathology. However, even though

humansworldwide,especiallychildren,theelderlyandimmune- themechanismbywhichtheyreachthehumanCNSisstilltobe

compromisedindividuals(Cesario,2012;IsonandHayden,2002; decrypted,atleastthreeofthesixcoronavirusesthatinfecthumans

Jartti et al., 2012; Sloots et al., 2008). The idea that viruses can wereshowntobeneuroinvasiveandneurotropicinhumans:HCoV-

cause respiratory tract infections has been demonstrated since 229EandHCoV-OC43(Arbouretal.,1999a,1999b,2000;Bonavia

the early 1930s (Jartti et al., 2012). Nevertheless, with the help etal.,1997),aswellasSARS-CoV(Guetal.,2005;Xuetal.,2005).

ofmoderndiagnostictools,asignificantnumberofnewrespira- Eventhoughthisassociationbetweencoronavirusinfectionof

toryviruseshavebeendiscoveredsincethebeginningofthe21st theCNSandhumandiseasesremainscircumstantialandeventoa

centuryanditisestimatedthatthereareabout200antigenically certaindegreecontroversial,thecurrentreviewaimsatpresenting

distinctvirusesabletocauseinfectionoftherespiratorytract,espe- interestingandimportantdatathatclearlyillustratesthenatural

ciallyininfantsandchildren(Brouardetal.,2007).Infact,itisnow neuroinvasivepotentialofthesehumanpathogensandunderlines

believedthatvirusescause95%ofrespiratorydiseasesinchildren thatfurtherresearchiswarrantedinordertobettercharacterizethe

and infants and about 30–40% in the elderly (Jartti et al., 2012). realimpactofcoronavirusinfectionofthehumanCNSonhuman

Amongthevariousrespiratoryviruses,coronavirusesareimpor- health.

tantpathogensofhumansandanimals.Mostofthecoronaviruses

thatinfecthumanbeingsusuallyreachtheupperrespiratorytract, 2. Coronaviruses:anoverview

wheretheyaremainlyassociatedwithsymptomsofcommoncolds.

However,beingopportunisticpathogens,theycanalsoaffectthe Coronaviruses display a characteristic crown-shaped appear-

lower respiratory tract in more vulnerable populations, such as ance, are widespread in nature and can infect several different

newborns,infants,theelderlyandimmune-compromisedindivid- species(Vabretetal.,2009),inwhichtheycausemainlyrespira-

uals,wheretheycanleadtopneumonia,exacerbationsofasthma, toryandentericpathologies,withneurotropicandneuroinvasive

respiratorydistresssyndromeorevensevereacuterespiratorysyn- properties in various hosts including humans, cats, pigs, rodents

drome (SARS) or Middle-East respiratory syndrome (MERS) (Raj and fowl (Buchmeier and Lane, 1999; Cavanagh, 2005; Talbot

etal.,2014;Vabretetal.,2009). et al., 2011). They form a group of enveloped viruses that have

Eventhoughtheairwayepithelialcellsoftherespiratorytract thelargestgenomeamongRNAviruses.Thisnon-segmented30kb

representafirstlineofdefenseagainstpathogens,theycanbecome positive-single-stranded polyadenylated RNA possesses 4 or 5

atargetforinfectionbyseveraldifferentrespiratoryviruses,asa genes encoding structural proteins (S, E, M, N; HE for several

wayforthemtopenetratethehumanhost.Severalinfectionsof membersoftheBetacoronavirusgenus)andseveralgenesencod-

epithelialcells,includingthosethatinvolvecoronaviruses,areself- ing non-structural proteins, mostly comprised in ORF1a and 1b,

limitedandtheinfectionremainslocalastheviruswillbecleared whichencodetwopolyproteins(pp1aandpp1ab)thatarecleaved

by the immune system in the respiratory tract, with minimal by two viral proteases to yield 15 to 16 non-structural proteins

clinical consequences. However, in some circumstances, oppor- (nsp),includingtheRNA-dependentRNApolymerase(RdRp),heli-

tunistic viral pathogens like the human coronaviruses can avoid case and exonuclease, which all play a role in viral replication

theimmuneresponseandcausemoresevererespiratorydiseases (Gorbalenyaetal.,2006;LaiandCavanagh,1997).

(Vareille et al., 2011) or even spread to other tissues, includ-

ing the central nervous system (CNS), where they could induce 2.1. Viralmoleculardeterminantsofpathogenesis

other types of pathologies (McGavern and Kang, 2011). Human

coronaviruses are molecularly related in structure and mode of Thespikeprotein(S)isalargetype1transmembraneglycosy-

replication with neuroinvasive animal coronaviruses (Brian and lated protein responsible for recognition of the cellular receptor

Baric,2005)suchasPHEV(porcinehemagglutinatingencephalitis used by the virus to infect a susceptible cell (Cavanagh, 1995).

virus)(Greigetal.,1962),FCoV(felinecoronavirus)(Foleyetal., Duringinfectionofsusceptiblehosts,theSproteinrepresentsan

2003), and MHV (mouse hepatitis virus) (Lampert et al., 1973), importantfactorofvirulenceasitappearstobeassociatedwith

whichhaveallbeenshowntoinvadetheCNSandinducedifferent mostofthecytotoxiceffectsthatleadtodegenerationofinfected

typesofneuropathologies.TheMHV,representsthebestdescribed cellsfollowinginfectionbydifferentcoronaviruses(Brisonetal.,

caseofcoronavirusesinvolvedinneurologicaldiseasesandseveral 2011,2014;Favreauetal.,2009,2012;Iaconoetal.,2006;Jacomy

excellentreviewshavehighlightedtheimportanceofbothviraland etal.,2010;Phillipsetal.,1999,2002).

hostfactorsintheprocess(BenderandWeiss,2010;Cowleyand Theenvelope(E)proteinisasmallstructuralproteinanchored

Weiss,2010;HoskingandLane,2010).MHVcanalsopersistinthe in the viral envelope and which has a role in the morphogene-

mouseCNSandinduceachronicdemyelinatingdisease,whichis sis,traffickingwithintheinfectedcellsandbuddingofthevirion,

partially immune-mediated, similar to what is observed in mul- andwhichappearsresponsibleforthecurvatureoftheviralenve-

tiple sclerosis (MS) in humans (Hosking and Lane, 2010; Weiss lope (Liu et al., 2007; Ruch and Machamer, 2012). Similarly to

andLeibowitz,2011).Therefore,theclosestructuralandbiologi- the S protein, but in a different manner, it also represents a

calrelatednessofhumancoronavirusestotheneurotropicanimal virulence factor: during infection of host cells, it appears to be

coronaviruseshasledtospeculationaboutpossibleinvolvement associatedwiththeinductionofthecellstressresponseandapo-

ofhumancoronavirusesinneurologicaldiseases.Becausetheyare ptosis (DeDiego et al., 2011; Nieto-Torres et al., 2014), and it

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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may be associated with disruption of the lung epithelium after morerecently,MERS-CoV,anewlyidentifiedBetacoronavirus(Zaki

a SARS-CoV infection (Teoh et al., 2010) and participate to the etal.,2012).

SARS-CoV-associated immunopathology in the respiratory tract The HCoV-229E, -OC43, -NL63 and -HKU1 strains all present

(Jimenez-Guardenoetal.,2014). aworldwidedistributionandgeneticvariability,astheyexistin

Themembrane(M)proteininteractswithalltheotherstructural different genotypes (Dominguez et al., 2012; Gerna et al., 2006;

proteins of the virus and therefore helps to shape and maintain Lauetal.,2011;Vabretetal.,2006;Vijgenetal.,2005;Wooetal.,

thestructureofthevirion(HogueandMachamer,2008;Neuman 2006). These four strains are endemic in humans and infections

etal.,2011).Duringinfectionofcells,thisproteincanparticipate mainlyoccursinwinterandearlyspring(Cabecaetal.,2013;Gaunt

inthevirus-inducedinhibitionofthetype1interferonresponseby etal.,2010;Larsonetal.,1980;Myint,1995),indifferentpartsof

theinfectedcells(Siuetal.,2009;Yangetal.,2013)andtherefore theworld(Chiuetal.,2005;Mackayetal.,2012;Theamboonlers

influencetheoutcomeofinfectionandcellfateafterinfection. et al., 2007; Vabret et al., 2009). Most of the times, they infect

Thenucleocapsid(N)proteinassociateswiththeviralgenome the upper respiratory tract, where they are mainly associated

andplaysanessentialroleinencapsidatingitinahelicalnucleo- with rhinitis, laryngitis or otitis but, as opportunistic pathogens,

capsid within the viral particle (Hogue and Machamer, 2008; in more vulnerable populations such as newborns, infants, the

MacneughtonandDavies,1978).ItalsoisanRNAchaperonethat elderlyandimmune-compromisedindividuals,theycanalsoreach

facilitatestemplateswitchingduringreplicationofthegenomeand the lower respiratory tract, where they could instead be associ-

transcriptionofthesgRNA(Zunigaetal.,2010,2007).TheNpro- ated with bronchitis, bronchiolitis, pneumonia, exacerbations of

teinofSARS-CoVwasshowntopartiallylocalizetothenucleolus asthma,respiratorydistresssyndrome(Talbotetal.,2008;Vabret

(You et al., 2005), and to deregulate the host cell cycle (Li et al., etal.,2009).

2005a). Moreover, like the M protein, the N protein of different The 2002–2003 SARS pandemic was caused by a coronavirus

coronavirusescanparticipateintheinhibitionoftype1interferon variantthatappearstohaveemergedfromabatreservoir(Lietal.,

responsebytheinfectedcellandintheinductionofapoptosis(Ding 2005b)toinfectpalmcivets,soldliveinopenmarkets,theinterme-

etal.,2014;Kopecky-Brombergetal.,2007;SurjitandLal,2008;Ye diaryreservoir,andthentohumans(Guanetal.,2003).Duringthis

etal.,2007). pandemic,atotalof8096probablecaseswerereportedandalmost

Thehemagglutinin-esterase(HE)isonlypresentinspeciesofthe 10%(774casesinmorethan30countries)oftheseresultedindeath

betacoronavirusgenus.LiketheSprotein,itisatype1transmem- (Bradenetal.,2013;Cherry,2004).Afteranincubationperiod,the

brane protein which forms homodimers (Hogue and Machamer, typicalclinicalportraitwasdescribedbyaflu-likesyndrome,fol-

2008)andwhichmayinteractwithdifferenttypesofacetylated lowedbyarespiratorysyndromefirstassociatedmainlywithcough

sialicacid(deGroot,2006).Itmaybeimportantearlyduringinfec- anddyspneabeforethe“real”severeacuterespiratorysyndrome

tionorduringthereleaseofviralparticlesfromtheinfectedcellsat (SARS)tookoverinabout20%ofthepatients(Vabretetal.,2009).

theendofthereplicationcycleofthebetacoronaviruses(Rottier, Furthermore,atypicalpathologicalportraitoftherespiratorytract

1990). Moreover, its acetyl-esterase activity strongly enhances showededema,hemorrhageandcongestionofthelungs,aswellas

the production of infectious virions, which can disseminate in pleuraleffusioninthethoraciccavityassociatedwithinfiltration

murinemixedprimaryCNScultures(Desforgesetal.,2013a).Coro- ofimmunecells(vandenBrandetal.,2014).Multipleorganfailure

naviruses also possess non-structural (ns) or accessory proteins wasalsoobservedinseveralSARS-CoV-infectedpatients(Guetal.,

thatappeartomainlyplayaroleinpathogenesisandinthevirus- 2005;Vabretetal.,2009).

hostinteractions(Narayananetal.,2008)aswellasinvirulence Recently,inthefallof2012,tenyearsaftertheSARSepisode,a

andtropismassociatedwiththecapacitytoreplicateindifferent SARS-likediseaseaffectedindividualsthattraveledfromtheAra-

celltypesandorgans(Cruzetal.,2011;Dedeurwaerderetal.,2013; bianPeninsulatotheUnitedKingdom.Usingmolecularsequencing,

Koetzneretal.,2010;Zhaoetal.,2013,2012,2011). it was rapidly shown that this new respiratory coronavirus was

geneticallydifferentthanSARS-CoVanditisnowrecognizedthat

thenewepidemiciscausedbyanewcoronavirusfromthegenus

2.2. Humancoronaviruses:recognizedrespiratorypathogens Betacoronavirus (Zaki et al., 2012), that was first named HCoV-

EMC(forHumanCoronavirus–ErasmusMedicalCenter),human

Humancoronaviruses(HCoV)werefirstisolatedinthemid-60s betacoronavirus2candNcoVornCoV(fornovelCoronavirus),and

frompatientswithupperrespiratorytractdisease(Myint,1995). thatisnowknownundertheofficialnameMERS-CoV:Middle-East

In 1965, Tyrrell and Bynoe isolated the first HCoV (B814 strain) RespiratorySyndromeCoronavirus(ColemanandFrieman,2013;

thatwasabletocauseacommoncoldinhumanvolunteersafter de Groot et al., 2013), which is the etiologic agent of a severe

intranasalinoculation(TyrrellandBynoe,1965).Shortlythereafter, lowerrespiratorytractinfectionthatresemblesSARSandwhich

Hamre and Procknow (1966) isolated the prototype HCoV-229E can be associated with gastrointestinal symptoms and possible

strain,andMcIntoshandcollaborators(1967)wereabletoiden- renalfailure(Rajetal.,2014).Likeothercoronavirusesthatinfect

tifyvariousviruses,whichcomprisethenowrecognizedprototype humans,MERS-CoVmostlikelyoriginatedfrombatsbeforeinfect-

HCoV-OC43 strain (Hamre and Procknow, 1966; McIntosh et al., inganintermediaryreservoir(probablythedromedarycamelin

1967). thatcase),andthusrepresentsazoonotictransmissiontohumans.

Up until the Severe Acute Respiratory Syndrome (SARS) However, human to human transmission has now been demon-

appearedinChinaduringthefallof2002andwasassociatedwith stratedinseveralcases(Assirietal.,2013b;Haagmansetal.,2014;

SARS-CoV(Drostenetal.,2003;Fouchieretal.,2003;Ksiazeketal., Raj et al., 2014). As of September 18th, 2014, the Public Health

2003),serologicalstudiesonlydistinguishedbetweentwogroups Agency of Canada revealed that the World Health Organization

ofHCoV,namelyHCoV-229E(previousgroup1,nowclassifiedin (WHO) has reported that the MERS-CoV has spread to at least

the Alphacoronavirus genus) and HCoV-OC43 (previous group 2, twenty-one different countries, where 841 laboratory-confirmed

nowclassifiedintheBetacoronavirusgenus).SincetheSARSout- cases of individuals (including 402 between April 11 and June

breakof2002,researchoncoronaviruseshaveenteredanewera, 9, 2014 in Saudi Arabia alone) have been identified as infected

whichledtotheidentificationofseveralnewcoronaviruses,includ- bytheMERS-CoV,with298beingfatal(PublicHealthAgencyof

ing three that infect humans. Namely, they are HCoV-NL63 (van Canada,2014).AsdothefourcirculatingstrainsofHCoV(Cabeca

derHoeketal.,2004)inthegenusAlphacoronavirus,HCoV-HKU1, et al., 2013; Vabret et al., 2009), both SARS-CoV and MERS-CoV

whichispartoftheBetacoronavirusgenus(Wooetal.,2005)and usuallyinducemore(Assirietal.,2013a;Huietal.,2014)severe

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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illnesses in vulnerable populations such as the elderly, infants, (Stensballeetal.,2003),isonesuchneuroinvasiverespiratoryagent

immune-compromisedindividualsorpatientswithcomorbidities thathasbeendetectedinthecerebrospinalfluid(CSF)ofpatients

(Peirisetal.,2004;Vabretetal.,2009). (Kawashimaetal.,2009;ZlatevaandVanRanst,2004)andthatwas

Overtheyears,thefourcirculatingHCoVhavebeenassociated associatedwithconvulsions(Morichietal.,2011),febrileseizures,

withpathologiesoutsidetherespiratorytract,suchasmyocardites andencephalitis(MillichapandWainwright,2009).Furthermore,

andmeningitis(RiskiandHovi,1980)andseverediarrhea(Gerna it was recently shown that RSV can spread from the airways to

etal.,1985;Restaetal.,1985),asseenwithanimalcoronaviruses. the CNS in mice after intranasal inoculation, and that it induces

Recent investigations on the HCoV as enteric pathogens demon- behavioralandcognitiveimpairments(Espinozaetal.,2013).

stratedthatalltheHCoVcanbefoundinstoolsamplesofchildren Measlesvirus(MV),isanothercommonvirusthatcausesadis-

with acute gastroenteritis but could not conclude on their “true easeoftherespiratoryairwaysassociatedwithfever,coughand

association”withdiseaseetiology(Esperetal.,2010;Riskuetal., congestion.However,MVinfectionalsoinducesothersymptoms

2010). As previously mentioned, different reports have also pre- includingacharacteristicrashandKoplik’sspots(O’Donnelland

sentedapossiblelinkbetweenthepresenceofHCoVwithinthe Rall, 2010) in the oral mucosa. A second type of rare but sig-

humancentralnervoussystem(CNS)andsomeneurologicaldisor- nificant sequelae is long-term CNS disease (O’Donnell and Rall,

ders(Arbouretal.,2000;Cristalloetal.,1997;Fazzinietal.,1992; 2010). Post-infectious encephalomyelitis (PIE) or acute dissemi-

Stewartetal.,1992;Yehetal.,2004). natedencephalomyelitis(ADEM)occursin1of1000measlescases

inchildrenandadolescents.Measlesinclusionbodyencephalitis
3. Neuroinvasiveandneurotropicviruses (M IBE)isas econ dCNScompl icationth atcanaris eafte raMVinfec-

tioninimmune-compromisedpatients.Finally,subacutesclerosing
SeveralviruseshavetheabilitytoinvadetheCNS,wherethey
panencephalitis (SSPE) is a third form of CNS disease associated
can infect the resident cells, including the neurons. In fact, as
withMVinfection.Itisaslowprogressiveneurologicaldiseasethat
stated by Big and colleagues (Big et al., 2009), even though the
appears6–10yearsafterinfectioninabout4to11casesper100,000
incidence of viral infections of the CNS is not well defined, they
casesofmeasles(forreviewsee(Wilsonetal.,2013)).
arenotuncommonoccurencesinclinicalpracticeandanincreas-
Hendra virus (HeV) and Nipah virus (NiV) represent impor-
ing number of positive viral identifications are now made with
tant emerging viruses discovered in the 1990s (Escaffre et al.,
thehelpofmodernmoleculardiagnostics.Usingdifferentroutes
2013)andcauseacuteandsevererespiratorydiseaseinhumans,
ofentry,severaldifferentviruseshavebeenshowntobeableto
including necrotizing alveolitis with hemorrhage, pulmonary
penetratetheCNS(neuroinvasion),wheretheycaninfectneurons
edema and pneumonia (Escaffre et al., 2013). Neurological signs
andglialcells(neurotropism)andpossiblyinduceorparticipatein
of pathology include confusion, motor deficits, seizures, febrile
theinductionofneurologicaldiseases(neurovirulence)(Giraudon
encephaliticsyndrome,andreducedlevelofconsciousness.More-
and Bernard, 2010). In humans, a long list of viruses, for which
over, neuropsychiatric sequelae have been reported but it is not
the primary site of infection in human is not the CNS, possess
knownwhetherpost-infectiousencephalo-myelitisoccursfollow-
these “neuroproperties” and neuroviral infection often leads to
inginfection(Wong,2010).Theuseofanimalmodelsshowedthat
acuteencephalitis,whichcanbefataldependingonvirustropism
themainrouteofentryintotheCNSistheolfactorynerve(Munster
(Whitley and Gnann, 2002). For example, rabies virus (Hankins
etal.,2012).
andRosekrans,2004),herpessimplexvirus(HSV)(Aurelian,2005),
Influenzaviruscomesinthreetypes:A,B,andC.TypesAand
arthropod-borne flaviviruses such as West Nile virus (WNV) or
Baremostprevalentandcausetheflusyndrome,characterizedby
Japanese encephalitis virus (JEV) (Mackenzie et al., 2004; Neal,
chills,fever,headache,sorethroatandmusclepains(Zengetal.,
2014;Sipsetal.,2012)andenterovirusessuchaspoliovirus(PV)
2013),andareresponsibleforseasonalepidemicsthataffect3–5
andcoxsakievirus(CV)(Muelleretal.,2005;Rhoadesetal.,2011),
millionhumans,ofwhich250,000–500,000casesarelethaleach
affectmillionsofindividualsworldwideeachyearandcaninduce
year(Kuikenetal.,2012).MostinfectionsofinfluenzavirusAare
encephalitis,meningitisandparalysisinhumans.Chronichuman
localizedtotheupperrespiratorytractbutsomemoreseverecases
neurologicaldiseasesand/orsequelaemayalsobelinkedtoviral
mayresultinpneumonia(Nicholsonetal.,2003)andevencompli-
infection.Inacquiredimmunodeficiencysyndrome(AIDS)demen-
cationsinvolvingtheCNS(Jangetal.,2009).Severalstudieshave
tia and related disorders, human immunodeficiency virus (HIV)
shownthatinfluenzaAcanbeassociatedwithencephalitis,Reye’s
inducesneurodegeneration(Mattsonetal.,2005),whichcanresult
syndrome,febrileseizure,acutenecrotizingencephalopathy,and
inmotordysfunctionsandpossiblycognitiveimpairments(Nath
possiblyacutedisseminatedencephalomyelitis(ADEM)inhumans
and Berger, 2004). Progressive multifocal leukoencephalopathy
(MillichapandMillichap,2006;Ozkaleetal.,2012;Toovey,2008;
(PML)isahumandemyelinatingdisease(Gordonetal.,2000)where
Wangetal.,2010;Zengetal.,2013).Makinguseofmurinemod-
prolongedimmunosuppressionleadstoreactivationoflatentpoly-
els,ithasalsobeenshownthatinfluenzaAviruscouldreachthe
omaJCvirus(JCV)(Weissert,2011).HumanT-lymphotropicvirus
CNSthroughtheolfactorynerverouteandalterhippocampalmor-
(HTLV-1)causesprogressivetropicalspasticparaperesis/HTLV-1-
phologyorexpressionofsynapticregulatorygeneswhileimpairing
associatedmyelopathy(PTSP/HAM)in1–2%ofinfectedindividuals
cognitionandemotionalbehavior(Berakietal.,2005;Jurgensetal.,
(Kaplanetal.,1990)andHSV-1andhumanherpesvirus6(HHV-
2012).InfluenzaAviruswasalsodescribedasafactorwhichmay
6)wereproposedtocauseorexacerbateAlzheimer’sdisease(AD)
increasetheriskofParkinson’sdisease(PD)(Jangetal.,2009).
(Itzhakietal.,2004).
As previously mentioned, among these different respiratory
Respiratory viral agents also have the capacity to invade the
viruses that can reach the CNS where they could be associated
human CNS where they will infect resident cells and potentially
withneurologicalsymptomsinhumansandanimals,arethecoro-
be neurovirulent in inducing a neuropathology. Several of these
naviruses.
recognizedrespiratorypathogenscangainaccesstotheCNS,where

theycaneventuallycausehealthproblemsinhumans.
3.2. HumancoronavirusesintheCNS

3.1. Respiratoryviruseswithneuroinvasiveandneurotropic
prop erties:assoc iatedne urop athologies Coronaviruses that infect humans are not well characterized
concerning their capa city to invade and infe ct th e CNS. How-

Respiratorysyncytialvirus(RSV),themostcommonpathogen ever, the detection of coronaviral RNA in human brain samples

to cause lower respiratory tract infection in infants worldwide clearlydemonstratesthattheserespiratorypathogensarenaturally

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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Fig.1. PotentialrouteofinfectionusedbyHCoVforneuroinvasionintothehumancentralnervoussystem(CNS)andpossiblemechanismsofneurovirulence.(A)Following

infectionofhumanairways,humancoronavirusesmay,insomeconditions,passthroughtheepithelium,gainaccesstothebloodstreamandinfectmonocytes,whichare

activatedbytheinfection.Amongotherfactors,MMP9,whichincreasesBBBpermeabilityandTNF-alpha,whichleadstoup-regulationofICAM-1expressiononendothelial

cells,facilitatesthepassageofinfectedandactivatedmonocytesintotheCNS.OnceintheCNS,thesecellsproduceproinflammatorycytokines(suchasTNF-alpha)thatcan

damagetheoligodendrocytesand/ortheneurons.Infiltratedinfectedmonocyte-derivedmacrophages(ormicroglia)mayproducechemokines(CCL-5,CXCL10,CXCL11),

whichwillinducechemoattractionofactivatedTcellsand/orothermonocytes.Aftersensingtheinfection,astrocytesmayalsoproduceotherchemokines(CCL2,CCL5and

CXCL12)thatwillalsoparticipateintherecruitmentofmoreinfectedleukocytes.Humancoronavirusesmaythereforeinitiateanaberrantneuroinflammatoryloopwhich

willmediateanimmune-mediatedneuropathology(adaptedfromTalbotetal.,2008).(B)Followingintranasalinfectioninhuman,coronavirusesmayinfecttheolfactory

receptorneurons(ORN)andpassthroughtheneuroepitheliumoftheolfactorymucosatoreachthemitralcellsandtheolfactorynerve(ON)andgainaccesstotheolfactory

bulb(OB)andeventuallytothehippocampusandotherregionsofthebrain.

neuroinvasiveinhumansandsuggeststhattheyestablishapersis- happenswhenagivenvirusinfectsneuronsintheperipheryand

tentinfectioninhumanCNS(Arbouretal.,2000).Furthermore,we uses the transport machinery within those cells in order to gain

have shown that these viruses are able to establish a persistent accesstotheCNS(Berthetal.,2009).

infectioninhumancellsrepresentativeoftheCNS(Arbouretal., In order to be neuroinvasive, human coronaviruses may use

1999a,1999b)andthatHCoV-OC43RNAcouldbedetectedforat bothCNSentryroutesfromtheperiphery.Thehematogenousroute

least a year in the CNS of infected mice that survived the acute involves the presence of a given virus in the blood where it can

encephalitis.Asignificantportionofthesesurvivingmiceexhib- eitherremainfreeforaperiodoftimebeforeitinfectsendothelial

itedabnormalreflexesshownbylimbclasping,presentedclinical cellsoftheblood–brainbarrier(BBB),orinfectleukocytesthatwill

signsofdecreasedactivityinanopenfieldtest,andhadasmaller becomeaviralreservoirfordisseminationtowardtheCNS.Both

hippocampusassociatedwithalossofhippocampalneurons,par- situationsdooccurduringhumanimmunodeficiencyvirus(HIV)

ticularlyintheCA1andCA3layers(Jacomyetal.,2006),similarto infection of the CNS, as infected leukocytes migrate through the

whatisseenafterneuroinvasionoftheCNSbytheinfluenzaAvirus blood–brainbarrier(BBB)(Kimetal.,2003),withdirectinfectionof

(Jurgensetal.,2012).Therefore,anapparentlyinnocuoushuman endothelialcellsoftheBBBhavingalsobeenreported(Argyrisetal.,

respiratorypathogenmaypersistinthehumanCNSanditwould 2007).Humancytomegalovirus(HCMV)(Bentzetal.,2006;Chan

thereforebepossiblethatsuchapersistentinfectionmaybecome et al., 2012), enteroviruses including poliovirus (Rhoades et al.,

a factor or co-factor of neuropathogenesis associated with long- 2011)andflaviviruses(Neal,2014)havealsobeenshowntoinfect

termneurologicalsequelaeingeneticallyorotherwisepredisposed different types of leukocytes and to use them as a reservoir for

individuals. hematogenousdisseminationtowardtheCNS.

Inthehumanairways,itisstillunclearwhattypeofdamage

3.2.1. Possiblemechanismsofcoronavirusesneuroinvasiveness maybeinducedbyHCoVinepithelialcellsoftherespiratorytract
Vi ruses m ay enter th e CNS through two distinct routes: after in fection.O ne repor ti ndicatedt hate xp erim entalintra nasal
hematogen ous d issemi natio n or neuronal retro grade dis semina- inocu lationofH CoV -229E tohuman volu nteersledto disruption
tion.Hematoge nousspreadin vol vesthepr esenceofa givenvirus ofthenasal ep ithelium,lea din gtoda mageofthe cili ate dcellsand
in th e bloodstream and ret rograde vira l spread t ow a rd the CNS to asi gnific antdecrease inthe nu mberof ce llsa ndtoa lowe red

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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Fig.2. HumancoronavirustransneuronalrouteofneuroinvasionthroughtheolfactorynerveandspreadintotheCNSinsusceptiblemice.Followingintranasalinfectionor

14day-oldsusceptiblemice,HCoV-OC43infectsfirsttheolfactorybulb(leftpanel)andthendisseminatetootherregionsofthebrain,includingthehippocampus(right

panel).Inbothregionsofthebrain,neuronsarethemaintargetofinfection.

frequency of cilium beating (Chilvers et al., 2001). On the other becomemacrophagesastheyinvadetissues,thisactivationsug-

hand,usingprimaryculturesofcellsfromthehumanrespiratory geststhatHCoV-229E-infectedmonocyteswouldservetofacilitate

tract, Dijkman and collaborators were able to further character- their passage toward other tissues including the CNS, especially

izetheinteractionbetweenHCoVandepithelialcellsanddetected in immune-compromised individuals, as this was observed for

no cytopathic effect. Even though they showed that after infec- murine cytomegalovirus (MCMV) (Reuter et al., 2004). The fact

tionallfourcirculatingHCoVstrainswerebuddingandreleased thatHCoV-229Ecouldonlyinfectpartiallyimmune-compromised

preferentiallyontheapicalsideofthecells,alowbutsignificant transgenic mice (Lassnig et al., 2005) suggests that, being an

amountofviruswasalsofoundtobereleasedfromthebasolat- opportunistic pathogen, HCoV-229E could take advantage of an

eral side (Dijkman et al., 2013). This suggests that, even though immune-suppressed environment and disseminate to the CNS

HCoV infection are, most of the time, self-restricted to the air- within susceptible individuals. The establishment of a persistent

waylumensincetheydonotinduceimportantdisruptionofthe infectioninahumanleukocyticcellline(Desforgesetal.,2007)is

epithelium,theymay,undercertaincircumstances,passthrough alsoconsistentwiththepossibilitythatmonocytes/macrophages

theepitheliumbarrierandgainaccesstothebloodstreamorlymph, serveasareservoirandvectorforthisneuroinvasiveHCoV(Arbour

where they can infect leukocytes and consequently disseminate etal.,2000).TheSARS-CoVwasalsoshowntoinfectmonocytes-

toward other tissues, including the CNS (Fig. 1A; adapted from macrophages(Guetal.,2005;Nichollsetal.,2006)anddendritic

Desforgesetal.,2007;Talbotetal.,2008)asithasbeensuggested cells, where it modulates innate immunity (Spiegel et al., 2006).

for other important human respiratory viruses; namely measles These cells could also serve as a reservoir for virus to reach and

virus(Wilsonetal.,2013),Nipahvirus(Mathieuetal.,2011)and maintainitselfintheCNS.OurresultsindicatethatHCoVareable

influenzaBvirus(Xuetal.,1998). toinfecthumanendothelialcellsoftheBBBinculture(unpublished

Infectionofhumanmonocytes/macrophagesbyHCoV-229Eand data).IthasalsobeenspeculatedthatSARS-CoVcoulddothesame

HCoV-OC43 was reported (Collins, 2002; Desforges et al., 2007) after viremia (Guo et al., 2008). Therefore, neuroinvasive coron-

andinfectionbyHCoV-229Eofhuman(Mesel-Lemoineetal.,2012) avirusesthatinfecthumanscouldusethehematogenousrouteto

andmurinedendriticcellsexpressingthehumanaminopeptidase penetrateintotheCNS.

N(Wentworthetal.,2005)suggeststhatHCoVmayononehand ThesecondformofanyviralspreadtowardtheCNSisthrough

manipulatetheimmunesystemandontheotherhandusedendritic neuronal dissemination, where a given virus infects neurons in

cellstodisseminatetoothertissues,includingtheCNS,wherethey peripheryandusesthemachineryofactivetransportwithinthose

couldbeassociatedwithothertypeofpathologies. cellsinordertogainaccesstotheCNS(Berthetal.,2009).Afteran

Human primary monocytes are activated following HCoV- intranasal infection, both HCoV-OC43 (Jacomy and Talbot, 2003)

229E infection (Desforges et al., 2007). Since they eventually and SARS-CoV (McCray et al., 2007) were shown to infect the

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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M.Desforgesetal./VirusResearchxxx(2014)xxx–xxx 7

A B
Norm al cont ro ls OND MS Monospecific T cell clones
100 Normal controls MS
MALE
V
Co 80 120
e for 60 nes 100
osi(cid:2)v 40 of clo 6800
% brain p 20 Number 2400
0 0
OC43 229E Both HCoV Myelin

Normal controls OND MS
Cross reac(cid:2)ve T cell clones

100 FEMALE Normal controls MS
V
o 5
or C 80
(cid:2)ve f 60 es 4
% brain posi 2400 mber of clon 123
u
N
0 0
OC43 229E Both 229E OC43 MBP PLP

Fig.3. DetectionofcoronaviralRNAinhumanCNSandofHCoV-myelinantigenscross-reactiveTcellsinMSpatients.(A)Double-blindanalysisofninetyhumanbrainautopsy

samplesrevealedthepresenceofHCoV-229EandHCoV-OC43RNAinnormalcontrols,patientswithotherneurologicaldisorders(OND)andpatientswithmultiplesclerosis

(MS).TheproportionofbrainsamplesfromMSpatientscontainingHCoV-OC43RNAwassignificantlygreaterthanONDandnormalcontrols.RNAfrombothHCoVwasfound

moreofteninFemalebrainscomparedtomale.(B)MoremonospecificT-cellcloneswereisolatedfromMSpatientscomparedtonormalcontrolsandcross-reactiveT-cell

cloneswereisolatedonlyfromMSpatients.

AdaptedfromArbouretal,2000andBoucheretal.,2007.

respiratory tract in mice and to be neuroinvasive as HCoV-OC43 role,withvirusesthemostlikelyculpritingeneticallypredisposed

(Butler et al., 2006; St-Jean et al., 2004) and SARS-CoV (Netland individuals (Kurtzke, 1993). There is a presumption that several

etal.,2008)weredetectedintheCNSofsusceptiblemice.Inter- neurotropicvirusescouldbeinvolvedinMSpathogenesisbutthat

estingly,theneurotropicMHVstrainsofthemurinecoronavirus theymaydosothroughsimilardirectand/orindirectmechanisms

(MuCoV)alsoreachtheCNSthroughtheolfactorynerve(Barnett (Cusicketal.,2013;Gilden,2005;Kakalachevaetal.,2011;Talbot

and Perlman, 1993). Furthermore, as shown here in Fig. 2, once etal.,2001).However,researchhasnotyetledtoadirectlinkto

inthebrain,HCoV-OC43isabletodisseminatefromtheolfactory anyspecificvirusorothermicrobeswithMS.Associationofcoro-

bulbtootherregionsofthebrain,includingthecortexandthehip- naviruses with MS was suggested in numerous reports that are

pocampus, from which it appears to spread by a trans-neuronal reviewedelsewhere(Desforgesetal.,2013b).Oneofthesereports

routebeforeiteventuallyreachesthebrainstemandspinalcord demonstratedasignificantassociationofcoldswithMSexacerba-

(Desforgesetal.,2013b).Theseresultssuggestthatcoronaviruses tionsandasignificantassociationofHCoV-229EinfectioninMS

may also invade the human CNS from the external environment patients(HovanecandFlanagan,1983)andanotherreportonthe

throughtheneuroepitheliumoftheolfactorynerveandolfactory association of viral infections and MS (Sibley et al., 1985) com-

bulbbeforeinfectingtheresidentcellsofthebrain,andpotentially mentedthatseasonalHCoVinfectionpatternsdofittheobserved

thespinalcord(Fig.1B),asreviewedbyMoriandcolleaguesfor occurrenceofMSexacerbations.

someneuroinvasivehumanvirusessuchasinfluenzavirus,Her- WewerepreviouslyabletoconfirmthatHCoV-OC43andHCoV-

pessimplexvirus(HSV),andbornadiseasevirus(BDV)(Morietal., 229Earenaturallyneuroinvasiveinhumans.Indeed,viruseswere

2005). detectedinsomecontrolbrainsandinsomebrainscomingfrom

Like several human viruses listed previously in the present patientsdifferentneurologicaldiseases,includingAlzheimer’sand

review,coronavirusesthatinfecthumanbeingsarenaturallyneu- Parkinson’sdisease,therewasasignificantlyhigherprevalenceof

roinvasiveandneurotropicandpotentiallyneurovirulentasaresult HCoV-OC43inbrainsofMSpatients(Arbouretal.,2000)andviral

of misdirected host immune responses (virus-induced neuroim- RNAwasfoundmoreofteninfemalebrainsamples(Fig.3A).Even

munopathology) and/or viral replication, which directly induces thoughthisobservationisonlycircumstantial,itisinterestingto

damagetoCNScells(virus-inducedneuropathology). notethatMSismoreprevalentinwomenthaninmen(Boveand

Chitnis,2013).Moreover,thisdata,inassociationwiththeobserva-

3.2.2. MechanismsofHCoV-inducedneurodegeneration:possible tionthatautoreactiveTcellswereabletorecognizebothviraland
associ atedneuropa tho logies mye lin a ntigens in M S patie nts b ut no t i n controls duri ng in fec-
Eventh oughnodirectassociationhaseverbeenmadewiththe tionby HCoV-OC 43 and HCoV-2 29E (Bo uch eretal., 2007; Talbot
onsetof human neu rolog icaldiseases ,th epre sence ofHC oV-2 29E et al ., 1 996), sugges t tha t the immu ne respon se ma y part icipate
andH Co V-OC43 wasdetecte dinvario us neurologi cal diseasesin in the induct ionorex acer bati onofneu ropatholo gies suchasMS
hum ans,includin gPa rkinson’s dis ease(PD )andmultip lesclero sis in gen eticallyor ot herwisesusce pt ibleindividuals(F ig.3B ).F ur-
(MS)(Arb ouretal., 2000),asw ellasAD EM( Yeh etal.,200 4). th ermore, eve n t hough the use of the immunosup pres sive drug
M ultiple s cle ros is truly re pres en ts a hu man ne uro logical dis- cyclospori nAin HCoV-O C43- infe cte dmi ceresultedinafaster onset
ease where an infect ious a gent or ag en ts may play a trigge ring ofencephal iti s, suggestingarolefor Tcel lsinvira lc le aranc eand

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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8 M.Desforgesetal./VirusResearchxxx(2014)xxx–xxx

Fig.4. HCoVinfectioninducesincreasedproductionofproinflammatorycytokinesandneuronaldegenerationasaconsequenceofglutamateexcitotoxicity.Inphysiological

conditions,glutamateismainlysynthesizedbyneuronsandreleasedinthesynapticcleftastheprimaryexcitatoryneurotransmitteroftheCNSthatactivatestheligand-

dependantreceptorAMPAr(alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionocacidreceptor),whichallowstheentryofsodiumionsandthepassageofthenerve

impulseinthepost-synapticneuron,leadingtoactivationoftheNMDAreceptor(N-methyl-D-aspartatereceptor)thatallowstheentryofcalciumions.Duringinfection

ofneuronsbyHCoV-OC43,microglialcellsdetectthepresenceofvirusandproducepro-inflammatorycytokines(TNF-alpha,IL-1betaandIL-6)thatdown-regulatethe

astrocyticreceptorGLT-1(glutamatetransporter1)andpreventtheefficientrecaptureofglutamate.Thissituationdisturbstheregulationofglutamatehomeostasisandthe

excessofthisneurotransmitterinthesynapticcleftleadstoexcitotoxicityassociatedwithamassiveentryofcalciumwhicheventuallyleadstodegenerationofanddeath

ofneuronalcells.

survivalwithnorelatedimmunopathology(Jacomyetal.,2006),it glutamatetransporterGLT-1onastrocytesthatshouldrecapture

wasshownthatinrecombinationactivationgene(RAG)knock-out the excess of glutamate, which may generate glutamate excito-

mice, HCoV-OC43-induced encephalitis could be partially medi- toxicity(Carmenetal.,2009)andtherebycontributetoneuronal

ated by the T-cell response to infection (Butler et al., 2006). The degeneration(Fig.4;Brisonetal.,2011),whichcanbeassociated

participationofdifferenttypesofTcellshasbeenshowntoplaya withhind-limbparalysisandpossibledemyelination(Brisonetal.,

significantroleinthedemyelinatingneurologicaldiseaseinduced 2011;Jacomyetal.,2010).Theoutcomeoftheobserveddegenera-

bythemurineCoV,inparticularforstrainMHV-JHM(Matthews tionofneuronsmayeventuallybedeathoftheseessentialcells.

etal.,2002).Furthermore,usedasanexperimentalmodelofchronic Aspreviouslymentioned,infectionofneuronsbyitselfmayalso

viral infection associated with demyelination in the mouse CNS, participateintheprocessofcelldeathbydirectlygeneratingacyto-

thismurinecoronavirushasrecentlybeenshowntoreflectpartial toxicinsultrelatedtoviralreplicationand/ortotheinductionof

oxidativetissueinjuryfoundinMSlesioninhumans(Schuhetal., differentcelldeathpathways.

2014),underliningthepossibilitythatlongterminfectionofthe WhenpresentinthemurineCNS,HCoV-OC43infectsneurons

CNSbycoronavirusesmayinduceMS-likelesions.Thismayalso indifferentregionsofthebrain(Fig.2),beforereachingthespinal

applyforpersistenceofHCoVRNAinthehumanCNS(Arbouretal., cord.Infectionoftheseessentialcellsinducestheirdegeneration

2000),whichinsomeconditions,couldbeassociatedwithonsetor as observed by aberrant state of neurofilament phosphorylation

exacerbationofneuropathologies,includingMS. (Brison et al., 2011, 2014; Jacomy et al., 2010), a situation that

Making use of another mouse model, we showed that HCoV- oftenleadstocelldeathandthatcouldbedirectlyinducedbyviral

OC43 induced immune cell infiltration and cytokine production replication. Furthermore, using two model cell lines represent-

within the mouse CNS. This immune response was significantly ing differentiated human neurons, we were able to demonstrate

increasedafterinfectionbyvirusvariantswhichharbormutations thatprogrammedcelldeath(PCD)wasinducedafterHCoV-OC43

inthesurfaceviralglycoprotein(S),consequentofviralpersistent infection (Favreau et al., 2009, 2012) and that the inhibition of

infection of human neural cells (Jacomy et al., 2010), and which viralreplicationwasalsoindirectcorrelationwithincreasedcell

induce glutamate excitotoxicity (Brison et al., 2011, 2014). The survival,suggestingthatinfectionandproductionofprogenyinfec-

increasedcytokineproductionfollowinginfectionbytheS-mutant tiousvirusesdirectlyparticipateintheprocessofdegenerationand

virusesmayinducedirectdamagetoneurons(Amoretal.,2010) eventualdeathofneurons.Ourresultsindicatethattheunderly-

and/or disturb glutamate homeostasis by down-regulating the ing mechanisms appear to involve different cellular factors and

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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M.Desforgesetal./VirusResearchxxx(2014)xxx–xxx 9

Fig.5. Pathwaysofneuronaldegenerationandprogrammedcelldeath(PCD)activatedorpotentiallyinhibitedafterHCoV-OC43infectionofneuronalcells.Hallmarksof

apoptosis,includingtherelocalizationoftheactivatedpro-apoptoticproteinBAX(Bcl-2associatedproteinX)fromthecytosoltothemitochondrialmembrane,cytochrome

Creleasefrommitochondriatowardthecytosol,DNAfragmentationandactivationofcaspases-3and-9,areobservedduringinfectionofhumanneurons.However,

eventhoughvirusinducesBaxrelocalization,itmayinhibitclassicalapoptosisbyblockingBaxpro-apoptoticfunctionatthemitochondriaand/ordownstreamofcaspase

activation,suggestingacaspase-independenttypeofapoptosis.RelocalizationofthemitochondrialproteinAIF(apoptosis-inducingfactor)towardthenucleus(truncated

tAIF)isobservedafterinfectionandparticipatesinDNAfragmentation.AIFisknowntobeactivatedduringcaspase-independentapoptosis.However,AIFisalsoinvolved

inParthanatos,anotherformofPCDpotentiallyassociatedwithneurodegeneration.Astheyaresynthesizedbythepoly(ADP-ribose)polymerase(PARP)duringaneuronal

stress,includingduringHCoV-OC43infection,polymersofADP-ribose(PAR)mayrelocalizetowardmitochondriaandparticipateintheactivationandrelocalizationofAIF

towardthecytosolbeforeitreachesthenucleus.CyclophilinD(CypD)inhibitiondecreasesAIFreleasefrommitochondriaandabrogatescelldeathinducedbyinfection.AIF

releasefrommitochondriamaybeinducedthroughitstruncation(tAIF)byactivatedcalpain,whichisusuallyactivatedbyariseinthemitochondrialcalciumconcentration.

Thisincreaseincalciumconcentrationmaybelinkedwitheitheranimportantentryfromtheextracellularmilieu(forinstanceduringglutamateexcitotoxicity)orwitha

releaseofcalciumfromtheERfollowinginductionofERstress.HoweverHCoV-OC43mayinhibittheERstress-relatedpathwayininfectedneurons.InfectioninducesRIP1

geneexpressionandtheknock-downofthereceptorinteractingproteinkinase-1(RIP-1),significantlyincreasescellsurvival,suggestingthatnecroptosis,athirdformof

PCDwhichinvolvesRIP-1andRIP-3downstreamofthedeathreceptorfamily,mayplayaroleinHCoV-OC43-inducedneuronaldeath.Solidarrowsindicateexperimental

dataanddashedarrowsrepresentpossiblepathwaysbasedontheliterature(seetextfordetails).

pathways,includingcaspase-independentapoptosis,parthanatos thattheviralSglycoproteinisanimportantfactorofneuroviru-

and necroptosis, three forms of programmed cell death (PCD) lenceandneurodegenerationofinfectedcells(Brisonetal.,2011;

reviewedelsewherebytheNomenclatureCommitteeonCellDeath Favreauetal.,2009;Jacomyetal.,2010).Thiswassimilarlyshown

(NCCD)(Galluzzietal.,2012).Thesecelldeathpathwayscanact for the strains MHV-A59 and MHV–JHM of the MuCoV species,

separatelybutmayalsointeractinresponsetoastimulus(includ- themurinecounterpartofHCoV-OC43.Indeed,severalreportsand

ing a viral infection), as they share some of the cellular factors reviewshave,overtheyears,shownthattheSproteinofthisneu-

involvedintheoverallprocessthatleadstocelldeathandthatoften roinvasive and neurotropic murine coronavirus is a major factor

convergestowardmitochondria(Galluzzietal.,2012).Fig.5isaten- associatedwithneurovirulenceduringencephalitisandtheeven-

tativerepresentationofthevariouspathwaysandcellularfactors tualdemyelinatingdiseaseinsusceptiblemice(BenderandWeiss,

associatedwithPCDthatmaybeactivatedand/orinhibiteddur- 2010;HoskingandLane,2010).Wehavealsodemonstratedthat

ingHCoV-OC43infectionofneurons.Itisbasedonourdata(Brison theHEproteinisanimportantfactorfortheproductionofinfec-

et al., 2011; Favreau et al., 2009, 2012; Jacomy et al., 2010) and tiousHCoV-OC43,suggestinganattenuationoftheeventualspread

on the scientific literature that describes some molecular path- intotheCNSofvirusesmadedeficientinfullyactiveHEprotein

ways(parthanatos,necroptosisandapoptosis)andcellularfactors, (Desforgesetal.,2013a).Therefore,astheinfectionofneuronalcells

includingcalciumoverload,endoplasmicreticulumstress,excito- andproductionofinfectiousvirusapparentlydirectlyparticipate

toxicity,poly(ADP-ribose)polymerase(PARP)andcalpaininvolved intheinductionofneuronaldeath,theHEproteinofHCoV-OC43

inmitochondrialdysfunctionandeventualneurodegenerationand could play a role in neurovirulence of HCoV-OC43, like it does

neuronalcelldeath(Calietal.,2011;Galluzzietal.,2012;Kaiser for MHV (Kazi et al., 2005). In recent years, several coronavirus

etal.,2013). accessoryproteins,includingtheTGEVprotein7andtheMHVns2

Virus-cellinteractionsarealwaysimportantintheregulation proteinhavebeenextensivelystudiedandarenowconsideredas

ofcellresponsetoinfection.ForHCoV-OC43,weclearlyshowed importantviralfactorsofvirulenceimplicatedinpathogenesisas

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011
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C57Bl/6 BALB/c CD1
A ATCC ATCC ATCC
100 100 100
ns2-KO ns2-KO ns2-KO
al 80 80 80
v
urvi 60 60 60
s
e 40 40 40
c
mi 20 20 20
%
0 0 0
0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 20 25

dpi dpi dpi
B BALB/c ATCC CD1 AnsT5C-CKO
ns5-KO ns5-KO-10x
100 100 ns5- KO-100x

al 80 80
v
viur 60 60
s
e 40 40
c
mi 20 20
%
0 0
0 5 10 15 20 25 0 5 10 15 20 25
dpi dpi
Fig.6. ImportanceofHCoV-OC43non-structuralaccessoryproteinsasneurovirulencefactorsininfectedmicedependsofthemousestrain.Groupsof20mice(A)ofthree

differentstrainswereinfectedbytheintracerebralroutewithreferencewild-typeHCoV-OC43(ATCC)orwithamutantdeletedforthens2accessoryprotein(ns2-KO)and
(B)withr eferenc ewil d-typeH CoV -OC 43(ATCC)or with amut antdelete dforthen s5accessory protein (n s5-K O ).Infecti onwith ten tim es(n s5-KO-10 ×)orev enahund red
tim es(n s5-KO-100 ×)moren s5mutantv irusled to are du cedneu rovirul enc eco mpa redtowil dtypev irus(ATC C).Surviv alwa sev aluate ddailyovera pe riodo f 21days.

Resultsarerepresentativeoftwoindependentexperiments.

theyareabletocounteracthost-cellresponseassociatedwiththe (virus-inducedneuropathology).Inacuteencephalitis,viralrepli-

activationofRNAseLandthetype1interferonresponse(Cruzetal., cationoccursinthebraintissueitself,possiblycausingdestructive

2011;Zhaoetal.,2013,2012,2011).Ourmorerecentworkonthe lesions of the nervous tissue (Talbot et al., 2011). As previously

on-goingcharacterizationofHCoVinteractionswiththecellsfrom mentioned, chronic human neurological diseases may also be

theCNShasledustodeterminethattwooftheseaccessorypro- linkedtoviralinfection.However,inseveralcasesofthesechronic

teins(ns2andns5),producedduringinfectionofsusceptiblecells diseases,itisveryhardtoascertainaroleforanygivenvirus,inpart

byHCoV-OC43,playasignificantroleinvirulenceandpathogenesis duetothedifficultyofestablishingthetimeatwhichtheseviruses

inthemouseCNS(Fig.6)partiallybymodulatingvirusproduction becomeinvolved.Also,thefourKoch’spostulatesdictatewhether

(datanotshown). aparticularinfectiousagentcausesaspecificdisease(Koch,1942).

Asmentionedabove,SARS-CoVisalsoneuroinvasiveandneu- However,severalviralinfections,especiallyslowviralinfections

rotropicinhumans(Guetal.,2005;Xuetal.,2005)anditcould related to diseases that are rare manifestations of an infection,

therefore be associated with the development of a neurological representsituationswhereKoch’spostulatesneedtobemodified

symptomsasinfectedneuronswereshowntobenecroticinhuman (FredericksandRelman,1996;Hill,1965).Aseriesofnewcriteria,

brain of deceased patients (Gu et al., 2005). Furthermore, the adaptedfromSirAustinBradfordHill’sforcausation(Hill,1965),

involvement of SARS-CoV in CNS infections was underscored by waselaboratedbyGiovannoniandcollaborators(Giovannonietal.,

thefindingsthatmadeuseoftransgenicmousemodelsexpressing 2006) and should replace Koch’s postulates when one wants to

thehumanangiotensin-convertingenzyme-2(thecellularreceptor evaluatetherelevanceofanygivenvirusinrelationto,forexam-

usedbySARS-CoVtoinfectsusceptiblecells).Indeed,usingthese ple,MSetiology(Giovannonietal.,2006)oranyotherlong-term

mice,itwasshownthatSARS-CoVcouldinvadetheCNSafteran humanneurologicaldiseasespotentiallyrelatedtoaviralinfection

intranasalinfectionprimarilythroughtheolfactorybulb(Netland aswell,includinginfectionbyhumancoronaviruses.

etal.,2008)orevenafteranintra-peritonealinfection(Tsengetal.,

2007),withconcomitantneuronalloss(Netlandetal.,2008;Tseng 4. Conclusions
etal.,2 007); aphenomen onthatca neve ntuallyle ad to neurol ogical

problems.Toourknowledge,thereexistnoreportsonthedetec- Respiratoryhumancoronavirusesarenaturallyneuroinvasive
tionofHCo V- HKU 1,HCoV-NL 63and MER S-C oVinth eh uma nCNS. and neurotropi c, with potential neur opa thological consequences
On t he other hand, neurologica l sym ptoms ha ve bee n descr ibed ing eneticallyor other wisesusce ptibleindividuals, withorwith-
ina ssoc iation with bothHCoV-H KU1andH CoV-N L63( Severance ou tadditional en vironment alinsults.Ev enthought heiru se ofthe
et al.,2011)a ndar ecen treport,whi chev aluatedME RS-CoVcell hem atogenous or transneuro nal rout e to gain acc ess t o th e C NS
tro pis m, sug gest t hat, am ong sev eral ce ll lines re presentativ e of in humanbein gs remainsto be elucid ate d,the ir pres en cein the
different tissues ando rgans,t hisviru ssee msto beabletoinfe ct hu manCN Sisno wareco gni zed fact.Furthe rmor e,knowle dg eof
theneuro n-comm itte dhuma nce llline NT2(F uk -W ooCh an etal., mechan isms a nd co n sequences of co ronavirus inte ractions wi th
201 3). the nervous syste m is essential to better unde rstand poten tially
Based on several pieces of evidence presented herein, we path ological consequ en cesandd esi gninte rventionstr ategiesthat
hypothes ize that neu roinvas ive coronavi ruses could particip ate areappropri atetoencepha litis orexac erbationsof othertype sof
in the dama ge o f the human CNS as a resu lt of misdirected neu rologicaldis ea sesforwhich a givenvirusis inv olved .Inth at
ho st im mune re spo nse s (virus- induc ed ne uroimm un opathology) regard,theH ill’scrite riaa dapted b yGiov anno ni andcollab ora tors
and/ orviralre plication,w hichdirectlyin ducesdamagetoCNScells mayre pres enta highlyr elevant too ltoevaluate the relevanceof

Pleasecitethisarticleinpressas:Desforges,M.,etal.,Humancoronaviruses:Viralandcellularfactorsinvolvedinneuroinvasiveness

andneuropathogenesis.VirusRes.(2014),http://dx.doi.org/10.1016/j.virusres.2014.09.011