Influence of Aging and Calorie Restriction on Protein Metabolism and microRNA Expression.
Margolis, Lee M.
2017-04-14T13:37:44.544Z
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Abstract: Modulation in the expression of microRNA (miRNA), which are small non-coding RNA that regulate gene expression, has been identified as a potential mechanism controlling age-associated declines in skeletal muscle mass. Recently, miRNA have also been identified to be stable analytes present in circulation (c-miRNA), with alterations in c-miRNA expression profiles suggested to reflect the u... read morenderlying physiological state of skeletal muscle. The potential for c-miRNA to provide insight into physiological adaptations within skeletal muscle makes them a promising noninvasive marker to assess mechanisms regulating muscle mass. Three investigations were conducted to assess the influence of aging and dietary manipulation on expression of miRNA in circulation and skeletal muscle to determine the functional implications to alterations in miRNA expression profiles. The first investigation sought to determine the influence of aging on c-miRNA expression at rest and following acute resistance exercise in 18 younger (22 ± 1 yrs, n = 9) and older (74 ± 2 yrs, n = 9) male volunteers. Primary findings revealed that fasting c-miRNA expression profiles were significantly (P < 0.05) predictive of aging, with miR-19b-3p, miR-206 and miR-486 distinguishing between age groups. Following resistance exercise, principal component analysis revealed a divergent response in expression of 10 c-miRNA. Using Ingenuity Pathway Analysis to test c-miRNA-to-mRNA interactions in skeletal muscle, it was found that the response of c-miRNA to exercise was indicative of an anabolic response in younger but not older participants. These findings were corroborated with a positive association (P < 0.05) observed with the phosphorylation status of p-AktSer473 and p-70S6K1Thr389 and expression of miR-19a-3p, miR-19b-3p, miR-20a-5p, miR-26b-5p, miR-143-3p, and miR-195-5p. These data provide evidence that alterations of c-miRNA expression with aging may be reflective of underlying molecular mechanisms resulting in age-associated declines in skeletal muscle mass. The second investigation examined the relationship of circulating muscle specific microRNA (c-myomiR; miR-1-3p, miR-133a-3p, miR-133b, miR-206) to whole-body protein synthesis following 28 days of calorie restriction (CR) in 16 older (64 ± 2 yrs) overweight (28.5 ± 1.2 kg·m-2) males. Following CR, overall expression of c-myomiR increased (P < 0.05) compared to weight maintenance values, with c-myomiR inversely associated (r = -0.70, P < 0.05) with whole-body protein synthesis. Confirming these results, in vitro CR of C2C12 myotubes reduced protein synthesis 2.1 ± 0.2 fold, while myomiR expression in medium increased 2.9 ± 0.1 fold compared to controls. Results from in vivo and in vitro analysis suggest that increased expression of c-myomiR reflects lower rates of protein synthesis following CR. The final investigation assessed the influence of prolonged (16-wks) 40% CR consuming adequate (10%) or high (32%) protein milk-based diets on skeletal muscle mTORC1 signaling and expression of associated miRNA in 12-wk old male Sprague Dawley rats. Independent of dietary protein intake, CR resulted in lower (P < 0.05) muscle protein content, as well as phosphorylation and total Akt, mTOR, rpS6 and p70S6K compared to AL. Despite downregulations in mTORC1 signaling following CR, associated miRNA expression was not altered by either energy or protein intake. Overall, results from these studies suggest that aging results in modulations in c-miRNA profiles that may be further exacerbated by CR, as c-myomiR were upregulated following short-term CR and inversely associated with protein synthesis.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Biochemical and Molecular Nutrition.
Advisor: Roger Fielding.
Committee: Donato Rivas, James McClung, and Stefan Pasiakos.
Keywords: Molecular biology, and Nutrition.read less - ID:
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