Physicochemical and Biomechanical Stimuli in Cell-Based Articular Cartilage Repair

12 Pages·2015·1.26 MB·English

CurrRheumatolRep(2015)17:22
DOI10.1007/s11926-014-0493-9
OSTEOARTHRITIS(MBGOLDRING,SECTIONEDITOR)
Physicochemical and Biomechanical Stimuli in Cell-Based
Articular Cartilage Repair
HolgerJahr&CsabaMatta&AliMobasheri
Publishedonline:2April2015
#TheAuthor(s)2015.ThisarticleispublishedwithopenaccessatSpringerlink.com
Abstract Articularcartilageisauniqueload-bearingconnec- Cartilagebioengineering .Mesenchymalstemcell .
tivetissuewithalowintrinsiccapacityforrepairandregen- Intracellularsignalingpathways
eration. Its avascularity makes it relatively hypoxic and its
unique extracellular matrix is enriched with cations, which Abbreviations
increases the interstitial fluid osmolarity. Several physico- ACI Autologouschondrocyteimplantation
chemicalandbiomechanicalstimuliarereportedtoinfluence ALP Alkalinephosphatase
chondrocytemetabolismandmaybeutilizedforregenerative CCI Characterizedchondrocyteimplantation
medicalapproaches.Inthisreviewarticle,wesummarizethe Cn Calcineurin
most relevant stimuli and describe how ion channels may CREB cAMPresponseelementbindingprotein
contributetocartilagehomeostasis,withspecialemphasison CsA CyclosporineA
intracellularsignalingpathways.Wespecificallyfocusonthe ECM Extracellularmatrix
roleofcalciumsignalingasanessentialmechanotransduction ERK Extracellularsignal-regulatedkinase
componentandhighlighttheroleofphosphatasesignalingin FAK Focaladhesionkinase
thiscontext. FCD Fixedchargedensity
FTE Functionaltissueengineering
Keywords Articularcartilage .Cartilagerepair.Regenerative GAG Glycosaminoglycan
medicine .Autologouschondrocyteimplantation . HP Hydrostaticpressure
Chondrocytemetabolism .Functionaltissueengineering . MAPK Mitogen-activatedproteinkinase
ThisarticleispartoftheTopicalCollectiononOsteoarthritis
H.Jahr C.Matta
DepartmentofOrthopaedicSurgery,UniversityHospitalRWTH DepartmentofAnatomy,HistologyandEmbryology,Facultyof
AachenUniversity,Pauwelsstraße30,52074Aachen,Germany Medicine,UniversityofDebrecen,Nagyerdeikrt.98,
: : Debrecen4032,Hungary
H.Jahr C.Matta A.Mobasheri(*)
TheD-BOARDEuropeanConsortiumforBiomarkerDiscovery,
A.Mobasheri
Surrey,UK
ArthritisResearchUKCentreforSport,ExerciseandOsteoarthritis,
e-mail:[email protected]
ArthritisResearchUKPainCentre,MedicalResearchCounciland
ArthritisResearchUKCentreforMusculoskeletalAgeingResearch,
A.Mobasheri
UniversityofNottingham,Queen’sMedicalCentre,
e-mail:[email protected]
NottinghamNG72UH,UK
URL:http://www.d-board.eu/dboard/index.aspx
:
C.Matta A.Mobasheri A.Mobasheri
DepartmentofVeterinaryPreclinicalSciences,SchoolofVeterinary CenterofExcellenceinGenomicMedicineResearch(CEGMR),
Medicine,FacultyofHealthandMedicalSciences,Universityof KingFahdMedicalResearchCenter(KFMRC),KingAbdulAziz
Surrey,DukeofKentBuilding,Guildford,SurreyGU27XH,UK University,Jeddah21589,KingdomofSaudiArabia
22 Page2of12 CurrRheumatolRep(2015)17:22
MSC Mesenchymalstemcell signalingapparatusthatconvertvariousenvironmentalforces
NFAT NuclearfactorofactivatedTlymphocytes (e.g., deformation, shear stress and fluid flow, hydrostatic
OA Osteoarthritis pressure(HP),andextracellularionicmilieu(i.e.,OP)aswell
OP Osmoticpressure as magnetic and electric forces), into cellular responses. We
PEMF Pulsedelectromagneticfield provide a brief overview of how these forces might be
PG Proteoglycan exploitedtofacilitatecartilageregeneration,withspecialem-
PKA ProteinkinaseA phasisonintracellularsignaling,whichisoftenunderstudied
PKC ProteinkinaseC inthecontextofcartilagebioengineering.
RVD Regulatoryvolumedecrease
TRPV Transientreceptorpotentialvanilloidchannel
FF Fluidflow CartilagePathologies
Traumaticlocaldamage[13–15],usuallyinyoungerpatients,
Introduction andwhole jointerosion,asinosteoarthritis(OA) [16]inthe
elderly,arechallengingareasofregenerativeorthopedics[17].
Theuniquebiomechanicalpropertiesofarticularcartilageare Todate,thereisnosuccessfultargetedtherapythatwouldhalt
attributedtothestructure,composition,andorganizationofits orevenreverseOAprogression;currentmanagementinclud-
extracellular matrix (ECM) macromolecules. The cartilage inginflammatorymedications,totaljointreplacements,oran-
ECM is mainly composed of a collagen fiber network (type algesicsonlyallowpalliativetreatment[18(cid:129)].Thereisapress-
II collagen with type IX and XI) and large aggregating pro- ing need for targeted treatment options, ideally at the early,
teoglycans (PGs) entrapped within. The fixed negative asymptomatic stages of the disease. The earliest signs of ar-
charges on the glycosaminoglycan (GAG) side chains of ticularcartilagedegenerationduringOAarenetdepletionof
PGsattractcounteractingions,whichdrivethemovementof PGs [10, 19–21], subsequent loss of the collagen network
largeamountsofosmoticallyobligedwaterintothematrix[1]. [22],anddiminishedintrinsiccompressivestiffness,affecting
Thehighosmoticmilieuandthetissueswellingmaintainthe chondrocytedeformation,metabolicactivities,andelectrome-
hydrostatic pressure and viscoelastic properties of cartilage. chanical events within cartilage under body load [10, 23].
The highly sulfated GAG side chains of PGs, through Severity-dependentcataboliceventsduringthecourseofOA
attractingmobilecations,areresponsibleforthecharacteristi- reduceextracellularosmolarity,resultinginreducedviscoelas-
cally high negative fixed-charge density (FCD) [2]. tic tissueproperties, correspondingbiomechanicalinferiority
Intertwined collagens and PGs combine to create the tissue [5,24],andeventuallyincreaseddeformationofcartilageun-
rigidity by entrapping solutes and water, giving cartilage its dermechanicalload.Elevatedlevelsofinflammatorymedia-
uniquebiomechanicalproperties,towithstandlargecompres- tors that promote matrix degradation may also accompany
sive and shear forces without failing [3]. Articular cartilage thesechanges.
absorbs stresses generated during joint loading and contrib-
utes to joint lubrication [1, 4]. An intact collagen network
restricts swelling and, in combination with sulfated GAGs, RegenerativeApproaches
determinestheosmoticpressure(OP)oftheextracellularfluid
aroundchondrocytes,whichrangesfrom350to480mOsmin Autologous chondrocyte implantation (ACI) [25] surpasses
healthycartilage[5]. existing procedures for treating focal defects, but is unable
The electrochemical properties of articular cartilage arise to fully restore functional hyaline cartilage ad integrum. A
fromtheflowof“free”electrolytes(e.g.,Na+,K+,Ca2+)pass- potentially better procedure for structurally repairing symp-
ingtherelatively“fixed”FCD(e.g.,SO 2−)distributedalong tomaticcartilagedefectsinthekneeischaracterizedchondro-
4
thePGs[6]resultinginelectrokineticphenomenaandcharge- cyteimplantation(CCI)whichhasamorefavorableoutcome
dependent osmotic swelling pressures (i.e., Donnan osmotic comparedtomicrofracturing[26].
pressure) [7–9]. The FCD permits tissue hydration, charged Amajorchallengeisthecomplexzonalstructureofcarti-
species transport, and other electrochemical responses [10]. lagetissue,whichisimportantforitsload-bearingproperties
Mow et al. postulated that the ECM is a mechanical signal [27–29]. The sparse available data indicate that mechanical
transducer,receivingloadingasinputtogenerateanoutputof propertiessignificantlyvarybetweenarticularcartilagezones
multiplebiophysicalsignals[11]. [30–32].Thelackofmechanicalhomogeneitymaybeimpor-
Interestingly,reportsonphysiologicallyrelevantvaluesof tantformechanosensation,signaltransduction,andchondro-
tensile or shear forces in natural cartilage or in tissue- cytephenotypicstability.
engineered constructs are sparse [12], as is the knowledge Another major challenge of present tissue engineering
about the molecular identity of the sensory components and strategies for cartilage repair is the limited integration of the
CurrRheumatolRep(2015)17:22 Page3of12 22
constructsintothesurroundinghosttissue[33],oftenresulting MechanicalStimulation
inlocalcelldeathatthedefectmargins[34].Thegoal,there-
fore, isto createtissuefunctionality prior toimplantationby Incomparisontotheratherlimitedevidenceforeffectsofmag-
enhancingtherateandqualityoftissuegrowththroughcreat- netic and electrical stimulation, a vast body of studies have
ing in vivo-like conditions in vitro. Various environmental describedtheconsequencesofmechanicalstimulationonartic-
stimuli for promoting cartilage regeneration are discussed in ular cartilage or chondrocytes in tissue engineering strategies
thefollowingsections. [18(cid:129)].Wereviewmainlycellularresponsesofchondrocytesand
aspectscloselyrelatedtoosmoticstress,suchascompression-
inducedchangesinHPandOP,asbothareessentialforstim-
StimulatingFunctionalCartilageTissueEngineering ulating chondrocyte physiology and useful for manipulating
chondrocytemetabolismandphenotype[53].
ElectricalStimulation Mechanicalstimulationisanimportantregulatorofchon-
drocyte metabolism that is required for maintaining normal
Mechanoelectricaltransductionphenomenaoccurringnatural- cartilage matrix properties [54, 55] and a well-established
ly within the cartilage due to the FCD have prompted the cue for improving mechanical properties of tissue-
development ofexperimentalelectricalstimulation protocols engineeredcartilage[27],asreviewedbyVunjak-Novakovic
for therapeutic cartilage repair [35, 36]. Therapeutic devices etal.[56]andLeeetal.[57].Aplethoraofbioreactorshave
involving electrical stimulation are increasingly entering the been developed in which mechanical forces are applied via
clinicalmarket[37],despiteratherdiscouragingearlyresults compression, HP, shear, multimodal compression and shear,
[38, 39]. More recently, Brighton et al. observed anabolic vibration, bi-axial tension, and friction [18(cid:129)]. While static
effects [40] that may hold potential to treat osteoarthritic le- loading of tissue-engineered cartilage constructs, in general,
sions[18(cid:129)].Ourcurrentappreciationofunderlyingmolecular results in suppression of ECM biosynthesis, intermittent dy-
mechanisms,however,isrudimentary. namicloadingisusuallybeneficialandincreasesthebiosyn-
thetic activity of chondrocytes. The cellular response to me-
chanical stimuli always depends on magnitude, frequency,
MagneticStimulation and duration of the stimulus, as well the relative timing of
the loading, the culture period, and the subpopulation of
SinceitsFDAapprovalin1979,pulsedelectromagneticfield chondrocytes.Importantly,thebalancedactivitiesofcatabolic
(PEMF)therapyhasbeenwidelyusedinorthopedicstotreat and anabolic factors may be needed to stimulate native-like
poorly healing fractures [41, 42(cid:129)]. Although the biology of ECMsynthesis[58,59].
howPEMFstimulatesboneformationisonlypartiallyunder-
stood[43]andmayoriginatefromstimulatingprogenitorcell IntrinsicMechanicalStimulationandSubstrateProperties Cyclic
differentiation[44],itsclinicalusehasprovidedarationalefor compression is required for chondrogenesis [60], while its
applying (P)EMF in musculoskeletal tissue engineering [45, impact on the intrinsic material properties of cartilage is an
46]. underappreciated aspect in tissue engineering. Using surface
Datafromrandomizedcontrolledtrialsnowsuggestthat topography,stiffness,orpatternstoinducemesenchymalstem
PEMF improves clinical scores and function even in pa- cell(MSC)proliferationordifferentiation[61]holdsalotof
tients with knee OA [47]. While (low-frequency) PEMF potentialforenhancingmusculoskeletalregeneration[62(cid:129)].
therapy barely influences the biosynthetic activity of hu- OurunderstandingofhowcellssensethestiffnessofECM
manOAchondrocytesinvitro[48],itincreasesPGrelease or biomimetic substrates is rudimentary. Emerging mecha-
in alginate culture [49]. PEMF increases anti-inflammatory nisms of biophysically induced signals include focal adhe-
effects in the human costal chondrocyte cell line T/C-28a2 sionsandcytoskeletalorRhoGTPasefunctions[63,64].Lo-
[50], and, like IGF-1, it augments chondroprotective anabolic calmatrixstiffnesscandeterminecelldevelopment,differen-
activitiessuchasPGsynthesisinhumanOAcartilageexplants, tiation, and regeneration through adhesion complexes [64]
possiblybycounteractingtheeffectsofIL-1βinearlystagesof withthe actin–myosincytoskeleton generatingintrinsic con-
OA[51].A study in ovariectomized rats, aiming at simu- tractile forces by “sensing” substrate properties via pre-
lating postmenopausal osteoarthritis, reported an interest- stretching through actin stress fibers; linking integrin trans-
ing systemic effect of PEMF therapy on estrogen metab- membrane receptors to ECM in mechanosensation enables
olism that reduced apoptosis and matrix metalloproteinase primarycellstoaltertheirfunctioninresponsetoexogenous
(MMP)13 expression in knee joint cartilage [52]. Howev- forces[65]oroxygentensionandlocalcelldensity[66].Ini-
er, since current evidence for PEMF as a disease- tial attempts suggest the feasibility of creating 3D stiffness
modifying OA therapy is still weak, further studies are gradients in hydrogels [67] to re-differentiate chondrocytes.
needed to elucidate its molecular basis. By manipulating substrate elasticity and adhesion density
22 Page4of12 CurrRheumatolRep(2015)17:22
[68],stiffnessmayaffectproliferationandRGDadhesionsite chondrocytes can be technically challenging [53], while OP
densityduringcellulardifferentiation.Whilethebandingpe- isrobustly defined as chemical. Unlike OP, tonicityis influ-
riodicityofcollagenfibersintheECMis67nm[69]andthe enced only by solutes that cannot cross the cell membrane.
RGDepitopesoffibronectinfibersare≥73nm[70,71],cells Althoughchemicalloading(i.e.,OP)andmechanicalloading
are clearly sensitive to changes in interparticle spacing of (i.e.,HP)maynotbeexactlyequivalent[85],thecombination
about1nmoveracelllength[63], ofHPandOPproducegeneexpressionprofilesdifferentfrom
That MSC fate can be re-directed, even after weeks, by those with OP alone, each stimulus by itself often results in
switching the biophysical microenvironment [72(cid:129)(cid:129)] holds similar effects such as the stimulation of sulfated GAG syn-
promisesforseveralcartilage-relatedtissueengineeringappli- thesis[53].
cations. In contrast to generally unfavorable static compres- As OP is a state quantity, it changes during compressive
sion,staticpre-stretchingofbiomaterialsmaybeneficiallyal- jointloadingandoff-loading;withzone-dependentconcentra-
ter(stem)cellbehavior[73]throughregulationofepigenetic tionsofsulfatedGAGscausingOPgradientsinarticularcar-
events[74].Ameshworkofintermediatefilamentsandlamins tilage[86].Ineachzone,chondrocytesaresubjecttodifferent
physically links chromatin to the cytoskeleton-mediated ex- HPsandOPsduetoweightbearingandjointloading[53,32].
tracellularsignalreception[75,76].Mechanicalforcesarising ApplyingHPsfrom0to0.5MPaat0.5HzandOPsfrom300
frommatrixrigidityandnanotopographycanphysicallyaffect to450mOsmcanupregulateanabolicandcatabolicmolecules
thestructuralorganizationofthenucleus[77],possiblydirect- in all three major zones in a descending order of magnitude
lyalteringgeneexpressionandmechanicalproperties[63]. from the surface to the deep zone. Interestingly, HP off-
Incombinationwithmechanicalstimulation,incorporation loading maintains anabolic messenger RNAs (mRNAs) and
ofchemicalgroupssuchassulfatesmayimprovechondrocyte reducescatabolicmRNAs,whilehighOPretainsmainlycat-
proliferationwhileinhibitinghypertrophicdifferentiation[78, abolic mRNAs [53]. Superficial zone-derived cells are most
79].Byusingintrinsicbiomaterialcuestostimulatemigration, sensitive to changes in HP or OP [53], which may explain
cell-seeded scaffolds appear promising for cartilage repair. discrepancies between chondrocytes isolated from “normal”
Similar to MSCs, chondrocytes respond to HP, fluid flow and OAcartilage.The effects of OP on viscoelastic and
(FF) and the accompanyingshear stress, substrate strainand physical properties of chondrocytes are well described
stiffnessortopography,andelectromagneticfields[80].Fully [87]. Tonicity enhancer binding protein (TonEBP, also
synthetic hydrogels can provide independent control over known as nuclear factor of activated T cells (NFAT)5)
physicaland adhesive properties[81] for use incartilage re- stimulates multiple cellular pathways for adaptation to
generativemedicine[82]. osmotic stress [88, 89] and organic osmolyte-dependent
and independent pathways [90]. Physiological and path-
OsmoticStimulation ophysiological stimuli such as cytokines, growth factors,
receptor and integrin activation, contractile agonists,
Chondrocytes in cartilage represent cells under pressures of ions, and reactive oxygen species have been implicated
different natures, like deformation, hydrostatic pressure, ex- in the positive regulation of TonEBP expression and
tracellularioncomposition(i.e.,OP),andstreamingpotential activity in diverse cell types [91].
(i.e.,FF)[54].Further,theconceptisgenerallyacceptedthat Under standard FCS-containing expansion culture
matrixturnoverbychondrocytesisinfluencedbychangesto conditions, proliferation of human chondrocytes seems
theintracellularcomposition(e.g.,cellvolume,pH,andionic to be unhampered up to physiological osmolarity levels
content).Thepericellularmicroenvironmentfunctionsinsitu (i.e., ∼350–400 mOsm) [92, 93]. Proteomic analysis of
tomediatethechondrocyte(orchondron)responsestophys- serum-free expanded chondrocytes has confirmed a cut-
icochemicalchangesassociatedwithjointloading[83].Dur- off threshold of about 350 mOsm, above which cell
ingcompression-inducedchangesinOP,thepericellularma- cycle progression and proliferation appears compromised
trix exerts important functions through amplifying cell vol- [94, 95].
ume changes [84]; such findings argue in favor of using
chondrons, rather than isolated chondrocytes, for osmo- MolecularAspects Theresponsetoosmoticloadingseemsto
inducedcartilagetissueengineering. dependonthenatureoftheosmoticstimulationandthechon-
About15years ago [11],Mow etal.described thesome- drocyte phenotype, which is related to passage number and
timescounter-intuitiveeffectsofflow-inducedcompressionof pathologicalstate[96].Osmoticloadingdifferentiallyregulates
the ECM and hypothesized that this friction-drag effect is SOX9andCOL2A1mRNAstabilityposttranscriptionally[97].
likely of major importance for fluid flow through the ECM. Innucleuspulposuscells,NFAT5[98],togetherwithintracel-
ChangesinHPandOPareessentialforchondrocytephysiol- lularCa2+[99]andMEK/extracellularsignal-regulatedkinase
ogyandusefulformanipulatingtheirmetabolicfunctionand (ERK)signaling[100],controlcellfunction,survival,andsul-
phenotype [53]. Applying controlled HP to cartilage or fatedGAGsynthesis[101,102].Hyperosmoticstressinduces
CurrRheumatolRep(2015)17:22 Page5of12 22
volumechangesandCa2+transientsinchondrocytesbytrans- RegulationofPhosphatasesbyChemo-andBiomechanics
membraneionchannels,phospholipids,andG-proteincoupled
pathways[103]. CalcineurinasaPotentialTargetMolecule
Pritchard et al. [104] found that IL-1α alters the normal
volumetric and Ca2+ signaling response of porcine A precisely set balance between the activities of protein
chondrocytes to OP through mechanisms involving F-actin kinases and phosphoprotein phosphatases is crucial to
remodelingandRhoGTPases.HumanOAchondrocyteshave regulating chondrogenesis and maintaining the chondro-
a more positive membrane potential (i.e., −26±4 mV) than cyte phenotype. All of the major protein kinase families,
healthy cells and show reduced [Ca2+] independent protein including protein kinase A (PKA), PKC, mitogen-
o
kinase C (PKC)α-mediated hyperpolarization upon activated protein kinase (MAPK), and CaMK, as well
hyperosmoticstimulation[105]. as all major protein phosphatases (PP1, PP2A, and
Osmotic loading is known to modulate chondrocyte PP2B) play fundamental roles in molecular regulation
height, width, and volume in situ, and OP may modulate in chondrocytes [112]. These signaling pathways even-
cell shape in accordance with the primary collagen fibril tually converge on targets that are involved in defining
direction [106], as well as altering nuclear size and shape the chondrocyte phenotype, and they regulate cell shape,
[107]. Interestingly, osmotic sensitivity of nuclear shape proliferation, differentiation, and gene expression (via
and volume appeared to be independent of the actin cyto- transcriptional regulators such as Sox9, cAMP response
skeleton. While compression (and thus increased OP) re- element binding protein (CREB), and NFAT; see details
duces the ECM, cellular, nuclear, rER, and mitochondrial below).
volumes, the Golgi apparatus seems relatively resistant to The Ca2+-dependent serine/threonine phosphoprotein
intraorganelle water loss [108]. This may, at least partial- phosphatasecalcineurin(Cn;alsoknownasPP2B)hasbeen
ly, explain some of the observed posttranscriptional ef- identified as a potential target to improve the chondrocyte
fects of OP [97]. phenotype.The Cninhibitor FK506(also known asTacroli-
mus)increasestheexpressionofchondrogenicmarkersduring
Clinical Relevance Chondrocyte shrinkage by raised invitroexpansioninhypoosmoticculturemedium[113].Iso-
hyperosmotic pressure (≥480 mOsm) may protect cells. lationandexpansionofadulthumanarticularchondrocytesin
While most cell-based chondral repair strategies aim at culture medium of physiologic osmolarity (i.e., 380 mOsm)
re-differentiation of routinely expanded, dedifferentiated improves chondrogenic marker gene expression and ECM
chondrocytes, van der Windt et al. showed that dedif- productionthroughNFAT5[92].Interestingly,FK506within
ferentiation can be delayed by harvesting and expanding therangeof0.1and1000ng/mLincreasednotonlyCOL2A1
cells under elevated (i.e., physiological, 380 mOsm) os- but also COL10A1 expression, while in human OA cells
molarity [92]. Interestingly, combining physiological os- FK506suppressedtheosmolarity-inducedCOL10A1expres-
molarity with inhibition of calcineurin activity can in- sion [93]. Generally, similar anabolic and anti-hypertrophic
crease the expression of anabolic genes and suppress effects were observed in ex vivo cartilage explant cultures
catabolic genes, as well as hypertrophic markers, in hu- and non-OA chondrocytes. Similar data were reported with
man OA and “normal” chondrocytes [93] and may be a alternativeCninhibitors(i.e.,cyclosporineA,CsA)inhuman
promising strategy for improving cell-based chondral cells [114] and in the murine AT805-derived chondrogenic
defect repair. The clinical potential of applying osmolar- ATDC5 cell line [115], where FK506 increased PG content
ity to improve the chondrocyte phenotype is hard to inadose-dependentmannerwithoutelevatingalkalinephos-
predict from present in vitro data, given the depth zone phatase(ALP)activity.
dependence of osmotic responses [109] and the current TheexactmechanismunderlyingtheeffectsofCninhibi-
clinical practice of harvesting chondrocytes irrespective tionunderdifferentosmolaritiesisnotyetunderstood,butCn
of their original zonal location. is known to induce FGF18, which can suppress noggin and
The effects of OP, to a certain extent, also depend on facilitateBMP-relatedchondrogenesis-likeeffects[116].This
the culture model: in alginate, higher proliferation rates, pathwaymayinvolve,amongothers,NFAT4-mediatedinduc-
with diminished sulfated GAG production, were found at tion of BMP2 [117]. FK506, but not CsA, induces ATDC5
280 mOsm [110]. Of note, the pH is also osmolarity- differentiation [118], suggesting that FK506 promotes
i
dependent and its contribution to sulfated GAG produc- chondrogenic differentiation, at least partly, by Cn-
tion remains speculative. independent signaling routes. Since FK506 has been proven
Finite element modeling showed that charged tissues (or effective and safe as an anti-rheumatoid arthritis drug [119,
synthetic matrices) always support larger loads than un- 120], this approach may improve cell-based chondral repair
chargedtissues.Thisloadsupportderivesfromthreesources: strategies by interfering with adverse inflammatory or im-
intrinsicmatrixstiffness,HP,andOP[111]. munecell-mediatedeffects.
22 Page6of12 CurrRheumatolRep(2015)17:22
Cn–NFATSignalinginCartilagePathologies regulatorsofNFATactivityinchondrocyteshavebeeniden-
tifiedtodate.Notsurprisingly,pharmacologicalinhibitionof
Cnregulates the activityofNFAT familymembers ina spe- GSK-3β signaling increases cartilage degeneration in rats
cificandCa2+/calmodulin-dependentmanner[121].Forade- [132],whileFK506inthesamespeciesprotectsthecollage-
tailed overview of this vertebrate-specific phosphatase in nous ECM of articular cartilage against osteoarthritic wear-
chondrocyte physiology, the reader is referred elsewhere and-tearerosion[133].Atpresent,itisnotclearwhetherthese
[112]. NFATs have arisen from an ancient precursor with a effects are due to altered NFAT activity or other pathways
Reldomain,andCn–NFATsignalingmaybeanessentialpro- affected by the inhibitors of Cn (CsA or FK506) or GSK
cessduringvertebratedevelopment[122]. (GIN). Earlier studies suggest a link between osmolarity-
After the original study by Glimcher’s group had shown inducedsignalingpathwayssuchasMAPKorCa2+signaling
thatallfourNFATc1–4proteinsareexpressedinthecartilage and Cn–NFAT signaling, which may be integrated through
[123],Greenblattandcolleaguesrecentlyexpandedtheearlier NFAT5. NFAT activity and expression in chondrocytes
studiesofRangeretal.andWangetal.[123,124]bydemon- invitroseemsalsotobedependentonbothNotchandWnt5a
strating essential functions of NFATs (i.e., NFATc1 and signaling, at least in growth plate chondrocytes [134, 135],
NFATc2)inarticularcartilagehomeostasis[125].NFATshave and its relevance for articular chondrocytes, especially
thepotentialtolinkmanyextracellularsignalstothenuclear invivo,remainstobeshown.
transcriptionalmachinery[126]. Overall, in vivo and in vitro data from mice and humans
Greenblatt’s cartilage-specific NFATc1 and NFATc2 dou- stronglysuggestadynamiccontrolofNFATc2expressionin
ble mutant mice showed accelerated cartilage degeneration articularcartilageandacrucialroleofNFATfamilymembers
andexpressionofOAmarkers,suchasincreasedexpression in cartilage homeostasis and joint health. NFATs might be
of genes encoding proteases involved in ECM degradation involved in distinguishing articular from growth plate
suchasMMP13,ADAMTS-5,andhypertrophicchondrocyte chondrocytes, the origins of which are still not understood
markers, including COL10A1, and reduced expression of completely [136]. Novel small molecular compounds with
Sox9andPRG4,encodinglubricin.Intriguingly,NFATc1pro- higher specificities may make NFATs potential therapeutic
teinexpressionisrestrictedtothesuperficialzoneofarticular targets for cartilage regenerative medicine and anti-
cartilage, and its mRNA expression is reduced around carti- osteoarthritictreatmentregimes.
lagelesionsinhumanosteoarthriticpatients[125].Anumber
ofearlierinvitrostudiessuggestthatNFATsignalingmayalso TheRoleofPKAandPP2AinMechanicalStimulation
induce catabolic genes such as ADAMTS4 and 9 in andtheChondrocytePhenotype
chondrogeniccells[127,128],whicharefindingscontradic-
torytothe protectiveroles observedinvivo. While NFATc3 Amainfunctionofarticularcartilageistoabsorbshockduring
seemslessimportantforcartilagehomeostasis,itmaystillbe joint movements. Chondrocytes are sensitive to mechanical
relevantinchondrogenesis[117].Mostnotably,multiplepath- load, one of the most physiological stimuli that trigger the
waysco-regulatethesubcellularlocalizationofthefourCa2+- activation of key signaling molecules. Although appropriate
dependent NFAT proteins (NFATc1–4). In contrast, osmotic mechanicalstimuliareessentialforlimbdevelopment[137],
stress,ratherthanCa2+signalingprimarilyregulatesthemore differentiationofMSCs[138],andcartilageregenerationdur-
distantly related fifth family member NFAT5, as discussed ingOA[139],mechanotransductionpathwaysindifferentiat-
above. ingormaturechondrocytesarestillincompletelyunderstood
A recent study showed that lentiviral shRNA-mediated [140(cid:129)].
Nfatc2 knockdown in articular chondrocytes in vitro largely Although mechanosensitive ion channels, primary cil-
matches the in vivo phenotype and also upregulates pro- ia, and the actin cytoskeleton have all been implicated
inflammatory cytokines [129]. In tracheal cartilage, Ca 3.2 as mechanosensors in chondrocytes, downstream path-
V
T-type Ca2+ channels may be involved in Cn–NFAT-depen- ways are even less well characterized. Of the major
dentmodulationofSox9expression[130(cid:129)(cid:129)].Apreviousstudy signaling pathways, integrins and focal adhesion kinases
usingotherCninhibitorssuchasCsAhadalreadysuggested (FAKs), the ERK, and the PI 3-kinase/Akt pathways
theparticipationofCa2+channels[131]. have been reported [141]. It is of note that activation
Pharmacological inhibition of Cn by FK506 promotes of the cAMP–PKA–CREB axis following mechanical
chondrogenic marker expression in dedifferentiated human stimuli has been documented in different models [142].
adultchondrocytes,probablythroughupregulationofTGFβ1 PP2A also plays a regulatory role in p38 MAPK acti-
[113].NFATactivityseemstightlyregulatedbyupstreamsig- vation during cyclic strain [143]. Oscillating mechanical
naling pathways: both activators (Cn) and inhibitors (e.g., load promotes chondrogenesis and stimulates cartilage
GSK-3)canlinkalargenumberofmechanicalandbiochem- ECM production in chicken limb bud-derived
ical stimuli to this protein family, but few extracellular micromass cultures, and the observed effects can be
CurrRheumatolRep(2015)17:22 Page7of12 22
attributed to the activation of PKA/CREB–Sox9 signal- induced activation of protein kinases and/or phosphatases
ing and concurrent inhibition of the PP2A pathway mayberesponsible,atleastpartially,fortheseeffects.
[144]. Here, we propose that increased PKA activity
results in enhanced Sox9 and CREB phosphorylation
and nuclear translocation; these in turn facilitate CalciumSignalingIsanEssentialComponent
chondrogenic differentiation and ECM matrix produc- inMechanotransductionPathwaysinDifferentiating
tion. Given that PP2A is a negative regulator of chon- andMatureChondrocytes
drogenesis and balances the effects of PKA by dephos-
phorylating many common targets, its reduced activity Intracellular Ca2+ signaling and changes in cytosolic Ca2+
further enhances the chondrogenesis-promoting effects concentrationarecloselyrelatedtocellproliferationanddif-
of mechanical stimulation in this model. Interestingly, ferentiationinchondroprogenitorcells,andCa2+releasefrom
previous data also indicated a direct interplay between intracellular storesandinfluxthrough plasmamembraneion
PKA and PP2A during chondrogenesis [145] and channels are key factors controlling chondrogenesis [149].
strongly support the important role of reversible protein Various chondrocyte plasma membrane ion channels appear
phosphorylation in establishing and maintaining the to be regulated by mechanical stimuli, such as the big con-
chondrocyte phenotype. ductanceCa2+-activatedK+channel(BK-likechannel)[150]
Seriallypassagedarticularchondrocytes,deprivedoftheir orthetransientreceptorpotentialvanilloid4(TRPV4)cation
ECM, rapidly lose their characteristic phenotype. Signaling channel [151(cid:129)(cid:129)]. Mechanical load-induced Ca2+ influx and
events that control the re-differentiation of dedifferentiated subsequentalterationsinCa2+signalinghavebeendocument-
chondrocyteshaveonlypartiallybeenanalyzed.Chondrocyte ed in chondrocytes upon both compressive loading and HP
re-differentiationinmicromass culturesmay bemediatedby [152].Furthermore,cycliccompressionisknowntomodulate
PKC-dependentERK1/2regulation,whereaschondrocytede- cartilage matrix synthesis and catabolism through an
differentiation is under a separate control by PKCα and autocrine/paracrine purinergic pathway; compression-
ERK1/2 [146]. In a different study, p38 MAPK along with induced ATP release evokes Ca2+ transients via activation
PKCα activity was reported to be essential for chondrocyte ofP2XandP2Yreceptorsthatcauseacombinationofextra-
re-differentiation [147]. Since cyclic hydrostatic pressure cellularCa2+influxandintracellularCa2+releaseinagarose-
upregulates cartilage-specific gene expression during re- embeddedchondrocytes[101].HowexactlyCa2+signalingis
differentiation of dedifferentiated bovine articular coupled to mechanosensation in chondrocytes remains an
chondrocytes[148],one can speculate thatmechanicalload- openquestion.
Fig.1 Theeffectsofelectrical,
magnetic,andmechanical
stimulationonarticularcartilage
22 Page8of12 CurrRheumatolRep(2015)17:22
Apromisingcandidateforamechanosensoryorganelleon HumanandAnimalRightsandInformedConsent Thisarticledoes
notcontainanystudieswithhumanoranimalsubjectsperformedbyany
chondrocytesisthe primary (non-motile)cilium, first identi-
oftheauthors.
fiedonarticularchondrocytesalmost40yearsago[153].Tis-
suecompressionduringjointloadingcanleadtodeformation OpenAccess ThisarticleisdistributedunderthetermsoftheCreative
ofthecilium,whichinturnmaytriggersignalinginvolvedin CommonsAttributionLicensewhichpermitsanyuse,distribution,and
reproduction in any medium, provided the original author(s) and the
mechanotransductionpathways.Indeed,variousextracellular
sourcearecredited.
matrix receptors including integrins, as well as osmo- and
mechanosensitiveionchannelsincludingTRPV4,areknown
tobepresent onits surface [140(cid:129)].Inparticular, the primary
References
ciliumisnecessaryforcompression-inducedATPreleaseand
Ca2+signalingviaP2XandP2Ypurinergicreceptors,induc-
Papersofparticularinterest,publishedrecently,havebeen
ingaggrecanmRNAexpressionandsulfatedGAGsecretion
highlightedas:
in a 3D chondrocyte culture system [154]. These findings
(cid:129) Ofimportance
suggest that the primary cilium does not act as the initial
(cid:129)(cid:129)Ofmajorimportance
mechanosensorinthatmodel,leavingseveralopenquestions
regardingitsspecificroleinchondrocytemechanosensation.
1. MowVC,RatcliffeA,PooleAR.Cartilageanddiarthrodialjoints
as paradigms for hierarchical materials and structures.
Biomaterials.1992;13(2):67–97.
Conclusions 2. LesperanceLM, Gray ML, Burstein D. Determinationoffixed
chargedensity incartilage using nuclearmagnetic resonance. J
OrthopRes.1992;10(1):1–13.
The effects of electrical, magnetic, and mechanical stimu-
3. MowVCYGW,HuiCF.Structureandfunctionofarticularcarti-
lationonarticularcartilagearesummarizedinFig.1.Data
lage and meniscus. Basic orthopaedic biomechanics and
are accumulating regarding the molecular identity of the mechanobiology. Philadelphia (PA): Lippincott Williams &
sensors and the mechanotransduction signaling apparatus Wilkins;2005.
in chondrocytes that convert the effects of external forces 4. MowVC,AteshianGA,SpilkerRL.Biomechanicsofdiarthrodial
joints: a review of twenty years of progress. J Biomech Eng.
to cellular responses. Diverse stimuli have been shown to
1993;115(4B):460–7.
exertchondroprotectiveeffects,butourcurrentknowledge
5. Maroudas AI. Balance between swelling pressure and collagen
isstillincompleteandabetterunderstandingofthemolec- tension in normal and degenerate cartilage. Nature.
ular identity and function of mechanotransduction path- 1976;260(5554):808–9.
ways is of crucial importance. It is very important to em- 6. LaiWM,MowVC,SunDD,AteshianGA.Ontheelectricpoten-
tials inside a charged soft hydrated biological tissue: streaming
phasize that the mechanical properties of native cartilage,
potential versus diffusion potential. J Biomech Eng.
and thus the responsiveness of chondrocytes to external 2000;122(4):336–46.
stimuli, vary widely and depend on joint location, depth 7. Bassett CA, Pawluk RJ. Electrical behavior of cartilage during
in the tissue, sample orientation, species, and donor age. loading.Science.1972;178(4064):982–3.
These differences have important implications for cell- 8. Buschmann MD, Grodzinsky AJ. A molecular model of
proteoglycan-associatedelectrostaticforcesincartilagemechan-
based regenerative approaches and should be considered ics.JBiomechEng.1995;117(2):179–92.
during data interpretation. Further research should aim at
9. ChenAC,NguyenTT,SahRL.Streamingpotentialsduringthe
understandingwhichload-inducedbiophysicalchangesare confined compression creep test of normal and proteoglycan-
most important for cartilage ECM regeneration and main- depletedcartilage.AnnBiomedEng.1997;25(2):269–77.
10. MowVC,GuoXE.Mechano-electrochemicalpropertiesofartic-
tenanceofthechondrocytephenotypetobenefitfunctional
ularcartilage:theirinhomogeneitiesandanisotropies.AnnuRev
cartilagetissueengineering. BiomedEng.2002;4:175–209.
11. MowVC,WangCC,HungCT.Theextracellularmatrix,intersti-
Acknowledgments C.M.issupportedbytheEuropeanUnionthrough tialfluidandionsasamechanicalsignaltransducerinarticular
aMarieCurieIntra-EuropeanFellowshipforcareerdevelopment(project cartilage.OsteoarthrCartil.1999;7(1):41–58.
number 625746; acronym: CHONDRION; FP7-PEOPLE-2013-IEF). 12. LittleCJ,BawolinNK,ChenX.Mechanicalpropertiesofnatural
A.M.isthecoordinatoroftheD-BOARDConsortium(EUFP7;HEAL cartilage and tissue-engineered constructs. Tissue Eng B Rev.
TH.2012.2.4.5-2,projectnumber305815).C.M.isamemberoftheD- 2011;17(4):213–27.
BOARD.H.J.isalsoamemberoftheD-BOARDandisindebtedtothe 13. SmithGD,KnutsenG,RichardsonJB.Aclinicalreviewofcarti-
START-ProgramoftheFacultyofMedicineoftheRWTHAachenand lagerepairtechniques.JBoneJointSurg(Br).2005;87(4):445–9.
theAachenInterdisciplinaryCenterforClinicalResearch(IZKF). 14. DomaradBR,BuschmannMT.Interviewingolderadults:increas-
ingthecredibilityofinterviewdata.JGerontolNurs.1995;21(9):
CompliancewithEthicsGuidelines 14–20.
15. JordanMA,VanThielGS,ChahalJ,NhoSJ.Operativetreatment
ConflictofInterest HolgerJahr,CsabaMatta,andAliMobasheride- ofchondraldefectsinthehipjoint:asystematicreview.CurrRev
clarenoconflictsofinterest. MusculoskeletMed.2012;5(3):244–53.
CurrRheumatolRep(2015)17:22 Page9of12 22
16. Zhang W, Moskowitz RW, Nuki G, Abramson S, Altman RD, integration during cartilage repair. A review. Eur Cell Mater.
ArdenN,etal.OARSIrecommendationsforthemanagementof 2008;16:26–39.
hip and knee osteoarthritis, part I: critical appraisal of existing 34. GilbertSJ,SinghraoSK,KhanIM,GonzalezLG,ThomsonBM,
treatment guidelines and systematic review of current research BurdonD,etal.Enhancedtissueintegrationduringcartilagere-
evidence.OsteoarthrCart.2007;15(9):981–1000. pairinvitrocanbeachievedbyinhibitingchondrocytedeathatthe
17. HeinegardD,SaxneT.Theroleofthecartilagematrixinosteoar- woundedge.TissueEngA.2009;15(7):1739–49.
thritis.NatRevRheumatol.2011;7(1):50–6. 35. Snyder MJ, Wilensky JA, Fortin JD. Current applications of
18.(cid:129) BradyMA,WaldmanSD,EthierCR.TheApplicationofmultiple electrotherapeutics in collagen healing. Pain Physician.
biophysicalcuestoengineerfunctionalneo-cartilagefortreatment 2002;5(2):172–81.
ofosteoarthritis(partI:cellularresponse).TissueEngPartBRev. 36. ZuzziDC,CicconeCdeC,NevesLM,MendoncaJS,JoazeiroPP,
2014.Thisrecentpaperhighlightsthefactthattissueengineering EsquisattoMA.Evaluationoftheeffectsofelectricalstimulation
strategiesandthedevelopmentof“smart”functionalizedbioma- oncartilagerepairinadultmalerats.TissueCell.2012;45(4):275–
terialsthatenablethedeliveryofgrowthfactorsorintegrationof 81.
conjugatednanoparticlesmaybenefitfromtargetingknownsignal 37. BalintR,CassidyNJ,CartmellSH.Electricalstimulation:anovel
transductionpathwaysincombinationwithexternalbiophysical toolfortissueengineering.TissueEngBRev.2013;19(1):48–57.
cues. 38. ArmstrongPF,BrightonCT,StarAM.Capacitivelycoupledelec-
19. GrodzinskyAJ,LevenstonME,JinM,FrankEH.Cartilagetissue tricalstimulationofbovinegrowthplatechondrocytesgrownin
remodelinginresponsetomechanicalforces.AnnuRevBiomed pelletform.JOrthopRes.1988;6(2):265–71.
Eng.2000;2:691–713. 39. Brighton CT, Jensen L, Pollack SR, Tolin BS, Clark CC.
20. BondesonJ,WainwrightS,HughesC,CatersonB.Theregulation Proliferative and synthetic response of bovine growth plate
oftheADAMTS4andADAMTS5aggrecanasesinosteoarthritis: chondrocytes tovarious capacitively coupled electrical fields.J
areview.ClinExpRheumatol.2008;26(1):139–45. OrthopRes.1989;7(5):759–65.
21. MalemudCJ,PapayRS,HeringTM,HolderbaumD,Goldberg 40. BrightonCT,WangW,ClarkCC.Theeffectofelectricalfieldson
VM, Haqqi TM. Phenotypic modulation of newly synthesized geneandproteinexpressioninhumanosteoarthriticcartilageex-
proteoglycans in human cartilage and chondrocytes.Osteoarthr plants.JBoneJointSurgAm.2008;90(4):833–48.
Cart.1995;3(4):227–38. 41. Assiotis A, Sachinis NP, Chalidis BE. Pulsed electromagnetic
fieldsforthetreatmentoftibialdelayedunionsandnonunions.
22. NelsonF,BillinghurstRC,PidouxI,ReinerA,LangworthyM,
Aprospectiveclinicalstudyandreviewoftheliterature.JOrthop
McDermott M, et al. Early post-traumatic osteoarthritis-like
SurgRes.2012;7:24.
changesinhumanarticularcartilagefollowingruptureofthean-
teriorcruciateligament.OsteoarthrCart.2006;14(2):114–9. 42.(cid:129) HannemannPF,MommersEH,SchotsJP,BrinkPR,PoezeM.
Theeffectsoflow-intensitypulsedultrasoundandpulsedelectro-
23. WilliamsonAK,ChenAC,SahRL.Compressivepropertiesand
magneticfieldsbonegrowthstimulationinacutefractures:asys-
function-compositionrelationshipsofdevelopingbovinearticular
cartilage.JOrthopRes.2001;19(6):1113–21. tematicreviewandmeta-analysisofrandomizedcontrolledtrials.
ArchOrthopTraumaSurg.2014;134(8):1093–106.doi:10.1007/
24. BankRA,SoudryM,MaroudasA,MizrahiJ,TeKoppeleJM.The
s00402-014-2014-8.Thisrecentpaperisasystematicreviewand
increasedswellingandinstantaneousdeformationofosteoarthritic
meta-analysisthatsuggestslow-intensitypulsedultrasoundand
cartilageishighlycorrelatedwithcollagendegradation.Arthritis
Rheum.2000;43(10):2202–10. pulsedelectromagneticfieldscanbebeneficialinthetreatmentof
acutefractures.
25. Brittberg M, Lindahl A, Nilsson A, Ohlsson C, Isaksson O,
43. ChalidisB,SachinisN,AssiotisA,MaccauroG.Stimulationof
PetersonL.Treatmentofdeepcartilagedefectsinthekneewith
boneformationandfracturehealingwithpulsedelectromagnetic
autologous chondrocyte transplantation. N Engl J Med.
fields: biologic responses and clinical implications. Int J
1994;331(14):889–95. ImmunopatholPharmacol.2011;24(1Suppl2):17–20.
26. SarisDB,VanlauweJ,VictorJ,HasplM,BohnsackM,FortemsY,
44. JansenJH,vanderJagtOP,PuntBJ,VerhaarJA,vanLeeuwenJP,
et al. Characterized chondrocyte implantation results in better
WeinansH,etal.Stimulationofosteogenicdifferentiationinhu-
structuralrepair when treatingsymptomatic cartilage defects of
man osteoprogenitor cells by pulsed electromagnetic fields: an
the knee in a randomized controlled trial versus microfracture.
invitrostudy.BMCMusculoskeletDisord.2010;11:188.
AmJSportsMed.2008;36(2):235–46.
45. DiniL,AbbroL.Bioeffectsofmoderate-intensitystaticmagnetic
27. KockL,vanDonkelaarCC,ItoK.Tissueengineeringoffunction- fieldsoncellcultures.Micron.2005;36(3):195–217.
al articular cartilage: the current status. Cell Tissue Res.
46. Fini M, GiavaresiG,CarpiA, NicoliniA,Setti S, GiardinoR.
2012;347(3):613–27.
Effectsofpulsedelectromagneticfieldsonarticularhyalinecarti-
28. Mansour JM, Welter JF. Multimodal evaluation of tissue- lage: review of experimental and clinical studies. Biomed
engineeredcartilage.JMedBiolEng.2013;33(1):1–16. Pharmacother.2005;59(7):388–94.
29. MiotS,ScandiuccideFreitasP,WirzD,DanielsAU,SimsTJ, 47. Vavken P, Arrich F, Schuhfried O,DorotkaR.Effectiveness of
HollanderAP,etal.Cartilagetissueengineeringbyexpandedgoat pulsedelectromagneticfieldtherapyinthemanagementofosteo-
articularchondrocytes.JOrthopRes.2006;24(5):1078–85. arthritis of the knee: a meta-analysis of randomized controlled
30. WaldmanSD,GrynpasMD,PilliarRM,KandelRA.Theuseof trials.JRehabilMed.2009;41(6):406–11.
specific chondrocyte populations to modulate the properties of 48. Sadoghi P, Leithner A, Dorotka R, Vavken P. Effect of pulsed
tissue-engineeredcartilage.JOrthopRes.2003;21(1):132–8. electromagneticfieldsonthebioactivityofhumanosteoarthritic
31. DarlingEM,AthanasiouKA.Retainingzonalchondrocytephe- chondrocytes.Orthopedics.2013;36(3):e360–5.
notype by means of novel growth environments. Tissue Eng. 49. FioravantiA,NerucciF,CollodelG,MarkollR,MarcolongoR.
2005;11(3–4):395–403. Biochemical and morphological study of human articular
32. Darling EM, Hu JC, Athanasiou KA. Zonal and topographical chondrocytescultivatedinthepresenceofpulsedsignaltherapy.
differencesinarticularcartilagegeneexpression.JOrthopRes. AnnRheumDis.2002;61(11):1032–3.
2004;22(6):1182–7. 50. VincenziF,TargaM,CorciuloC,GessiS,MerighiS,SettiS,etal.
33. Khan IM, Gilbert SJ, Singhrao SK, Duance VC, Archer CW. Pulsedelectromagneticfieldsincreasedtheanti-inflammatoryef-
Cartilage integration: evaluation of the reasons for failure of fectofA(2)AandA(3)adenosinereceptorsinhumanT/C-28a2
22 Page10of12 CurrRheumatolRep(2015)17:22
chondrocytesandhFOB1.19osteoblasts.PLoSOne.2013;8(5): 70. LittleWC,SmithML,EbneterU,VogelV.Assaytomechanically
e65561. tuneandopticallyprobefibrillarfibronectinconformationsfrom
51. OngaroA,PellatiA,MasieriFF,CarusoA,SettiS,CadossiR, fullyrelaxedtobreakage.MatrixBiol.2008;27(5):451–61.
etal.Chondroprotectiveeffectsofpulsedelectromagneticfields 71. Smith ML, Gourdon D, Little WC, Kubow KE, Eguiluz RA,
on human cartilage explants. Bioelectromagnetics. 2011;32(7): Luna-MorrisS, et al.Force-inducedunfoldingoffibronectin in
543–51. the extracellular matrix of living cells. PLoS Biol. 2007;5(10):
52. LuoQ,LiSS,HeC,HeH,YangL,DengL.Pulseelectromagnetic e268.
fieldseffectsonserumE2levels,chondrocyteapoptosis,andma- 72.(cid:129)(cid:129)LeeJ,AbdeenAA,KilianKA.Rewiringmesenchymalstemcell
trix metalloproteinase-13 expression in ovariectomized rats. lineagespecificationbyswitchingthebiophysicalmicroenviron-
RheumatolInt.2009;29(8):927–35. ment. Sci Rep. 2014;4:5188. doi:10.1038/srep05188. This
53. MizunoS,OgawaR.Usingchangesinhydrostaticandosmotic importantnewstudydemonstratesthatMSCsremainsusceptible
pressuretomanipulatemetabolicfunctioninchondrocytes.AmJ to the biophysical properties of the extracellular matrix—even
PhysiolCellPhysiol.2011;300(6):C1234–45. after several weeks of culture—and can redirect lineage
54. UrbanJP.Thechondrocyte:acellunderpressure.BrJRheumatol. specificationinresponsetochangesinthemicroenvironment.
1994;33(10):901–8. 73. LiuC,BaekS,KimJ,VaskoE,PyneR,ChanC.Effectofstatic
55. Holmvall K, Camper L, Johansson S, Kimura JH, Lundgren- pre-stretchinduced surfaceanisotropy onorientation of mesen-
AkerlundE.Chondrocyteandchondrosarcomacellintegrinswith chymalstemcells.CellMolBioeng.2014;7(1):106–21.
affinity for collagen type II and their response to mechanical 74. LiY, Chu JS, KurpinskiK,LiX,BautistaDM, YangL,etal.
stress.ExpCellRes.1995;221(2):496–503. Biophysical regulation of histone acetylation in mesenchymal
56. Vunjak-NovakovicG,GoldsteinS.Biomechanicalprinciplesof stemcells.BiophysJ.2011;100(8):1902–9.
cartilageandbonetissueengineering.Basicorthopaedicbiome- 75. Wang N, Tytell JD, Ingber DE. Mechanotransduction at a dis-
chanicsandmechano-biology.LippincottWilliamsandWilkins; tance:mechanicallycouplingtheextracellularmatrixwiththenu-
2005. cleus.NatRevMolCellBiol.2009;10(1):75–82.
57. LeeC,GradS,WimmerM,AliniM.mechanicalstimuliinartic-
76. GieniRS,HendzelMJ.MechanotransductionfromtheECMto
ular cartilage tissue engineering. Topicsin Tissue Engineering.
the genome: are the pieces now in place? J Cell Biochem.
2006. 2008;104(6):1964–87.
58. Vanderploeg EJ, Wilson CG, Levenston ME. Articular
77. CrispM,LiuQ,RouxK,RattnerJB,ShanahanC,BurkeB,etal.
chondrocytesderivedfromdistincttissuezonesdifferentiallyre-
Couplingofthenucleusandcytoplasm:roleoftheLINCcom-
spond to in vitro oscillatory tensile loading. Osteoarthr Cart. plex.JCellBiol.2006;172(1):41–53.
2008;16(10):1228–36.
78. SteinmetzNJ,BryantSJ.Chondroitinsulfateanddynamicloading
59. Li Z, Yao S, Alini M, Grad S. Different response of articular
alter chondrogenesis of human MSCs in PEG hydrogels.
chondrocyte subpopulations tosurface motion. OsteoarthrCart. BiotechnolBioeng.2012;109(10):2671–82.
2007;15(9):1034–41.
79. MhannaR,KashyapA,PalazzoloG,Vallmajo-MartinQ,Becher
60. GradS,EglinD,AliniM,StoddartMJ.Physicalstimulationof
J,MollerS,etal.Chondrocytecultureinthreedimensionalalgi-
chondrogenic cells in vitro: a review. Clin Orthop Relat Res.
nate sulfate hydrogels promotes proliferation whilemaintaining
2011;469(10):2764–72.
expressionofchondrogenicmarkers.TissueEngA.2014;20(9–
61. Unadkat HV, Hulsman M, Cornelissen K, Papenburg BJ,
10):1454–64.
TruckenmullerRK,CarpenterAE,etal.Analgorithm-basedto-
80. GoveyPM,LoiselleAE,DonahueHJ.Biophysicalregulationof
pographical biomaterials library to instruct cell fate. Proc Natl
AcadSciUSA.2011;108(40):16565–70. stemcelldifferentiation.CurrOsteoporosRep.2013;11(2):83–91.
62.(cid:129) ParkS,ImGI.Stemcellresponsestonanotopography.JBiomed 81. Trappmann B, Chen CS. How cells sense extracellular matrix
stiffness: a material’s perspective. Curr Opin Biotechnol.
MaterResA.2014.Thisreviewprovidesanoverviewoftheeffects
2013;24(5):948–53.
ofnanotopographyoncellbehaviorinthecontextofmusculoskel-
82. BreulsRG,JiyaTU,SmitTH.Scaffoldstiffnessinfluencescell
etalregeneration.
behavior: opportunities for skeletal tissue engineering. Open
63. YimEK,SheetzMP.Force-dependentcellsignalinginstemcell
OrthopJ.2008;2:103–9.
differentiation.StemCellResTher.2012;3(5):41.
64. DischerDE,JanmeyP,WangYL.Tissuecellsfeelandrespondto 83. Hing WA, Sherwin AF, Poole CA. The influence of the
thestiffnessoftheirsubstrate.Science.2005;310(5751):1139–43. pericellular microenvironment on the chondrocyte response to
65. JanmeyPA,WellsRG,AssoianRK,McCullochCA.Fromtissue osmoticchallenge.OsteoarthrCart.2002;10(4):297–307.
mechanics to transcription factors. Differentiation. 2013;86(3): 84. Likhitpanichkul M, Guo XE, Mow VC. The effect of matrix
112–20. tension-compressionnonlinearityandfixednegativechargeson
66. CigogniniD,LomasA,KumarP,SatyamA,EnglishA,AzeemA, chondrocyteresponsesincartilage.MolCellBiomech.2005;2(4):
etal.Engineeringinvitromicroenvironmentsforcellbasedther- 191–204.
apiesanddrugdiscovery.DrugDiscovToday.2013;18(21–22): 85. LaiWM,GuWY,MowVC.Ontheconditionalequivalenceof
1099–108. chemicalloadingandmechanicalloadingonarticularcartilage.J
67. OrsiG,FagnanoM,DeMariaC,MontemurroF,VozziG.Anew Biomech.1998;31(12):1181–5.
3Dconcentrationgradientmakeranditsapplicationinbuilding 86. SchneidermanR,KeretD,MaroudasA.Effectsofmechanicaland
hydrogelswitha3Dstiffnessgradient.JTissueEngRegenMed. osmoticpressureontherateofglycosaminoglycansynthesisinthe
2014. humanadultfemoralheadcartilage:aninvitrostudy.JOrthop
68. SchuhE,HofmannS,StokK,NotbohmH,MullerR,RotterN. Res.1986;4(4):393–408.
Chondrocyte redifferentiationin 3D: the effect ofadhesionsite 87. Guilak F, Erickson GR, Ting-Beall HP. Theeffects of osmotic
density and substrate elasticity. J Biomed Mater Res A. stress on the viscoelastic and physical properties of articular
2012;100(1):38–47. chondrocytes.BiophysJ.2002;82(2):720–7.
69. JiangF,HorberH,HowardJ,MullerDJ.Assemblyofcollagen 88. CheungCY,KoBC.NFAT5incellularadaptationtohypertonic
into microribbons: effects ofpHand electrolytes. J Struct Biol. stress—regulations and functional significance. J Mol Signal.
2004;148(3):268–78. 2013;8(1):5.