Abstracts of the Canadian Nutrition Society's 2nd Annual Scientific Meeting / Résumés de la deuxième rencontre scientifique annuelle de la Société canadienne de nutrition

摘要

Defects in skeletal muscle integrity underlie diseases such as muscularndystrophy and obesity. In affected individuals, the inability tonmaintain skeletal muscle mass often worsens the diseases. The mammalianntarget of rapamycin complex one (mTORC1), through itsndownstream target S6K1, is involved in regulating mRNA translation,nprotein synthesis, and skeletal muscle mass. It does this in partnby preventing the recruitment of the mRNA translation inhibitor,nthe tumor suppressor programmed cell death 4 (PDCD4). Becausenit inhibits protein synthesis and cell cycle progression, PDCD4 maynregulate myogenesis. To examine this, L6 myoblasts were plated inna growth medium and upon reaching 90% confluency, they werenswitched to a differentiation medium. Differentiation was followednfor the next 5 days. We found that total PDCD4 level and its nuclearnaccumulation increased approximately 7.2-fold on day 1, and thenndecreased as differentiation progressed (p < 0.05). We hypothesizednthat the regulation of PDCD4 abundance during differentiation likelyninvolved S6K1. In testing this, we showed that siRNA-mediatednknockdown of S6K1 reversed the decrease in PDCD4 expressionnduring differentiation. In these cells, we observed a 10-fold decreasenin myosin heavy chain one (MHC 1), a contractile protein that is usednas a marker of differentiation. This indicated that PDCD4 regulationnwas vital for myogenesis. To specifically examine this, myoblastsnwere depleted of this protein by siRNA. Cells with depleted PDCD4nlevel showed delayed myoblast fusion and abnormal myotube lengthnrelative to control cells. In line with this, on day 3 of differentiation,nMHC 1 was detected in the nontransfected cells but not in cells depletednof PDCD4. By day 5 of differentiation, however, no significantndifference was found either in morphology or in MHC 1 abundance,nindicating that the cells were able to recover from the defects associatednwith PDCD4 depletion. In summary, our results unravel a linknbetween PDCD4 and skeletal myogenesis, and identify mTORC1/nS6K1/PDCD4 as a pathway that can be manipulated to promote musclenregeneration. (Supported by NSERC and York University.)