Biomechanical signals upregulate myogenic gene induction in the presence or absence of inflammation.
Inflammation of the muscle invariably leads to muscle cell damage and impaired regeneration. Biomechanical signals play a vital role in the regulation of myogenesis in healthy and inflamed muscle. We hypothesized that biomechanical signals counteract the actions of proinflammatory mediators and upregulate the basic helix-loop-helix and MADS box transcription enhancer factor 2 (MEF2) families of transcription factors, leading to increased myogenesis in inflamed muscle cells. For this purpose, C2C12 cells plated on collagenized silastic membranes were subjected to equibiaxial cyclic tensile strain (CTS) in the presence or absence of TNF-alpha, and the myogenic gene induction was examined over a period of 72 h. Exposure of cells to CTS resulted in a significant upregulation of mRNA expressions and synthesis of myogenic regulatory factors, MYOD1, myogenin (MYOG), MEF2A, and cyclin-dependent kinase inhibitor 1A (CDKN1A; p21) as well as muscle structural proteins like myosin heavy chain (MYHC) isoforms (MYH1, MYH2, and MYH4) and alpha-tropomyosin (TPM1), eventually leading to an increase in myotube formation. Contrarily, TNF-alpha suppressed the expression of all of the above differentiation-inducing factors in C2C12 cells. Further results revealed that simultaneous exposure of C2C12 cells to CTS and TNF-alpha abrogated the TNF-alpha-mediated downregulation of myogenic differentiation. In fact, the mRNA expression and protein synthesis of all myogenic factors (Myod1, Myog, Mef2a, Cdkn1a, Myh1, Myh2, Myh4, and Tpm1) were increased in stretched C2C12 cells despite the sustained presence of TNF-alpha. These results demonstrate that mechanotransduction regulates multiple signaling molecules involved in C2C12 cell differentiation. On one hand, these signals are potent transducers of myotube phenotype in myoblasts; on the other, these signals counteract catabolic actions of proinflammatory cytokines like TNF-alpha and allow the expression of myogenic genes to upregulate muscle cell differentiation.
Chandran
Ravi
R
Section of Oral Biology, The Ohio State University College of Dentistry, 305 W. 12th Ave., Columbus, OH 43210, USA.
Knobloch
Thomas J
TJ
Anghelina
Mirela
M
Agarwal
Sudha
S
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression; D007249:Inflammation / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D064326:MEF2 Transcription Factors; D040542:Mechanotransduction, Cellular / Q000235:genetics*; D051379:Mice; D024510:Muscle Development / Q000235:genetics*; D017570:MyoD Protein / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism*; D018006:Myogenic Regulatory Factors / Q000235:genetics / Q000378:metabolism*; D018008:Myogenin / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D013314:Stress, Mechanical; D013997:Time Factors; D014335:Tropomyosin / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D064326:MEF2 Transcription Factors; C578036:Mef2a protein, mouse; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; C503801:Myog protein, mouse; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D012333:RNA, Messenger; C490774:Tpm1 protein, mouse; D014335:Tropomyosin; D014409:Tumor Necrosis Factor-alpha; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D018995:Myosin Heavy Chains