Date Published: January 19, 2010
Publisher: Public Library of Science
Author(s): Siva K. Panguluri, Shephali Bhatnagar, Akhilesh Kumar, John J. McCarthy, Apurva K. Srivastava, Nigel G. Cooper, Robert F. Lundy, Ashok Kumar, Gisela Nogales-Gadea. http://doi.org/10.1371/journal.pone.0008760
Abstract: Skeletal muscle wasting is a devastating complication of several physiological and pathophysiological conditions. Inflammatory cytokines play an important role in the loss of skeletal muscle mass in various chronic diseases. We have recently reported that proinflammatory cytokine TWEAK is a major muscle-wasting cytokine. Emerging evidence suggests that gene expression is regulated not only at transcriptional level but also at post-transcriptional level through the expression of specific non-coding microRNAs (miRs) which can affect the stability and/or translation of target mRNA. However, the role of miRs in skeletal muscle wasting is unknown.
Partial Text: Skeletal muscle wasting or atrophy is a major cause of human morbidity , , . Proinflammatory cytokines are the key mediators of muscle-wasting in various chronic conditions , . Besides directly inducing the degradation of selective muscle proteins , , elevated levels of inflammatory cytokines cause extracellular matrix abnormalities  and prevents the regeneration of skeletal muscle fibers by inhibiting the differentiation of muscle progenitor cells into myofibers , . Accumulating evidence suggests that bulk of the muscle protein degradation in atrophying skeletal muscle occurs through the activation of ubiquitin-proteasome system , , . In addition, it has been also found that muscle-wasting conditions involve the activation of nuclear-factor-kappa B (NF-κB), a proinflammatory transcription factor, which regulates the expression of large number of genes including the components of ubiquitin-proteasome system , . Specific inhibition of NF-κB activity has been found to attenuate loss of skeletal muscle mass in response to various catabolic stimuli including proinflammatory cytokines, tumor load, denervation, and unloading , , , .
We have previously shown that treatment of C2C12 myotubes with TWEAK augments the expression of muscle-specific E3 ubiquitin ligases atrogin and MuRF1 and augments the ubiquitination of select muscle proteins within 12–24h of treatment . In this study, we have performed mRNA and miRNA profiling after 18h of TWEAK treatment to detect the expression of both early and late responsive genes. To validate the effects of TWEAK on expression of various genes and miRs in vivo, we have also employed TWEAK-Tg mice. We have previously reported that transgenic mice expressing very high levels (>14 fold) of TWEAK in skeletal muscle died at perinatal/neonatal age . However, the mice which expressed relatively low levels of TWEAK (4–5 folds higher than littermate controls) survived and developed into adulthood. Our recent analysis of skeletal muscle revealed that TWEAK-Tg mice show significant muscle fiber atrophy at the age of 4–6 months (Mittal et al (2009), unpublished observation). Therefore, we used skeletal muscle from 6-months old TWEAK-Tg and their littermate control mice.