Signaling mechanisms in regenerative myogenesis.

191 Pages·2016·13.05 MB·English

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Electronic Theses and Dissertations
12-2014
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Sajedah M. Hindi 1986-
University of Louisville
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Hindi, Sajedah M. 1986-, "Signaling mechanisms in regenerative myogenesis." (2014). Electronic Theses
and Dissertations. Paper 1740.
https://doi.org/10.18297/etd/1740
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SIGNALING MECHANISMS IN REGENERATIVE MYOGENESIS

By

Sajedah M. Hindi, M.S.

A dissertation submitted to the Faculty of School of Medicine of the University of Louisville
in Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy

Department of Anatomical Sciences and Neurobiology,
University of Louisville
Louisville, Kentucky

December 2014

SIGNALING MECHANISMS IN REGENERATIVE MYOGENESIS

By

Sajedah M. Hindi, M.S.

A Dissertation Approved on

November 25, 2014

By the following Dissertation Committee:

________________________________________
Ashok Kumar, PhD.
Dissertation Director

________________________________________
Robert P. Friedland, M.D.

_________________________________________
Robert F. Lundy, PhD.

________________________________________
J. Patrick Moore, Ph.D.

_________________________________________
Jeffrey C. Petruska, Ph.D.
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To my parents
Mrs. Fatima J. Romman-Hindi and Dr. Mahmoud Y Hindi
for their support and unconditional love

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ACKNOWLEDGMENTS

Above all I thank God, the most gracious and most merciful of all

Thank you to my committee members; Dr. Robert Friedland, Dr. Robert Lundy, Dr. Patrick
Moore, Dr. Jeffery Petruska, and previously Dr. Theo Hagg, Thank you for your support and
critical advice!

I thank Dr. William Guido, Dr. Suresh Tyagi, Dr. Guillermo Rougier, Dr. Shihuan Kuang
and once more Dr. Robert Lundy and Dr. Theo Hagg for the impactful recommendation
letters for the NRSA and John M. Hunchens prize.

My lab members, currently and previously; Samara Carvalho, Kyle Bohnert, Dr. Shuichi
Sato, Dr. Marjan Tajrishi, Dr. Guangyan Xiong, Dr. Yuji Ogura, Dr. Jonghyun Shin, Dr.
Pradyut Paul, Dr. Saurabh Dahiya, Dr. Vivek Mishra, Dr. Shephali Bhatnagar, Dr. Sanjay
Gupta, and Dr. Hong Li. Thank you for creating a great working environment.

Thank you for the love and warmth of ASNB office staff; Ms. Donna Bottorff, Ms. Dana
Thomas, Ms. Barbara Hughes, Ms. Chris Ekstrom, and Ms. Camilla Harden.

Pradeepa Poudyal, my buddy, Thank you!

Thank You to the Kumar family: Savita Kumar, Aman Mann and the one and only, Eira
Mann!
My awesome family: My parents Mahmoud and Fatima Hindi, My siblings: Musa, Samiha,
Yousef, Lubna, Mohammad, and Balsam; and my four legged siblings: Mia, Dabdoob, Fried
Chicken, and M&Ms, I thank you every day…….I’ll tell you more later;)
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And last but most definite certainly not least, Dr. Ashok Kumar, my mentor, Thank You for
being!

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ABSTRACT

SIGNALING MECHANISMS IN REGENERATIVE MYOGENESIS

Sajedah M. Hindi

November 25, 2014

Skeletal muscle constitutes a highly plastic and malleable tissue that rapidly and profoundly
adapts to various environmental and physiological stimuli. This response takes place by
means of regulated signaling transduction which elicits changes in gene expression,
biochemical, and metabolic properties. Adult muscle is composed by alignment of multi-
nucleated, post mitotic muscle fibers formed during embryonic and neonatal development.
Residing in the niche of mature muscle fibers is a small population of undifferentiated
muscle progenitors termed satellite cells. Satellite cells are muscle stem cells that carry out
regenerative response in adult myofibers. Coordinated signaling emitting from terminally
differentiated muscle fibers and un-differentiated muscle progenitors sustains muscle
homeostasis. De-regulation in the components of this synchronized signaling machinery
manifests in deleterious disease states and myopathies.
The main focus of my research has been towards understanding the role of the
adaptor protein, tumor necrosis factor-associated factor 6 (TRAF6) in regulation of
regenerative myogenesis. Utilizing the Cre-loxP system, we generated TRAF6 muscle-
specific knock-out mice: TRAF6mko, and TRAF6 satellite cell-specific knock-out mice:
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TRAF6scko. Our findings displayed distinct roles of TRAF6 in differentiated
myofibers vs. satellite cells. Deletion of TRAF6 under the control of muscle creatine kinase
(MCK) promoter (differentiated muscle) led to improvement in muscle regeneration in wild-
type (WT) mice following induced muscle injury. This improvement was brought about by
prevalence of an anti-inflammatory environment characterized by reduced signaling from
inflammatory pathways such as NF-B and a domination of pro-regeneration M2c over pro-
inflammatory M1 macrophages. Regenerating muscle of TRAF6mko mice also displayed a
higher up-regulation in Notch signaling family proteins and target genes which in turn
enhanced the activation of satellite cells leading to accelerated regeneration. Similar results
were also observed upon deletion of TRAF6 in differentiated muscle of mdx mice (model
for Duchenne muscular dystrophy). However, mdx;TRAF6mko muscle later displayed
exacerbated signs of myopathy possibly due to diminished autophagy which has been
associated with progressive myopathy in mdx mice.
Employing the same models of muscle injury, our analysis revealed an absolute
requirement of TRAF6 in satellite cell function during regenerative myogenesis. Contrary to
its role in differentiated muscle, injured muscle of TRAF6scko mice displayed impaired
regeneration due to a cell-autonomous defect in TRAF6-deficient satellite cells. Deletion of
TRAF6 in satellite cells dramatically repressed the levels of Pax7 resulting in precocious
differentiation and progressive depletion of the satellite cell reservoir. Myopathy was further
exaggerated in dystrophic muscle of mdx;TRAF6scko due to satellite cell dysfunction. Our
results further demonstrate that TRAF6 regulates proliferation and self-renewal of satellite
cells through activation of mitogen-activated protein kinases (MAPKs) such as ERK1/2 and
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JNK and through modulating the levels of muscle specific microRNA’s: miR-1, miR-206,
and mir-133a.
The findings of this work highlight the importance of implementing a holistic
approach upon development of target-based therapies. Oversight of the fundamental roles of
targeted molecules has been associated with virulent outcomes. Developing a universal
understanding of the various implications of individual molecules maximizes therapeutic
potential.

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