Upregulation of circulating myomiR following short-term energy restriction is inversely associated with whole-body protein synthesis

The objective of the present investigation was to determine whether energy restriction (ER) influences expression of skeletal muscle specific microRNA in circulation (c-myomiR), and if changes in c-myomiR are associated with rates of whole-body protein synthesis. Sixteen older (64 ± 2 yrs) overweight (28.5 ± 1.2 kg·m^-2) males enrolled in this 35-day controlled feeding trial. A 7-day weight maintenance (WM) period was followed by 28 days of 30% ER. Whole-body protein turnover was determined from ¹⁵N-glycine enrichments in 24-hr urine collections, and c-myomiR (miR-1-3p, miR-133a-3p, miR-133b, and miR-206) expressions were assessed from serum samples using RT-qPCR at the conclusions of WM and ER. Participants lost 4.4 ± 0.3 kg body mass during ER (P < 0.05). Following 28 days of ER miR-133a and miR-133b expression was upregulated (P < 0.05) compared to WM. When all four c-myomiR were grouped as a c-myomiR Score (sum of the median fold change of all myomiR), overall expression of c-myomiR was higher (P < 0.05) at ER versus WM. Backward linear regression analysis of whole-body protein synthesis, breakdown, and carbohydrate, fat and protein oxidation determined protein synthesis to be the strongest predictor of c-myomiR Score. An inverse association (P < 0.05) was observed with ER c-myomiR Scores and whole-body protein synthesis (r = -0.729, r² = -0.530). Findings from the present investigation provide evidence that upregulation in c-myomiR expression profiles in response to short-term ER are associated with lower rates of whole-body protein synthesis.

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