Aging differentially affects human skeletal muscle microRNA expression at rest and after an anabolic stimulus of resistance exercise and essential amino acids

Abstract

Sarcopenia, skeletal muscle loss during aging, is associated with increased falls, fractures, morbidity, and loss of independence. MicroRNAs (miRNAs) are novel posttranscriptional regulators. The role of miRNAs in cell size regulation after an anabolic stimulus in human skeletal muscle is unknown. We hypothesized that aging would be associated with a differential expression of skeletal muscle primary miRNA (pri-miRNA) and mature miRNA (miR). To test this hypothesis, we used real-time PCR and immunoblotting before and after an anabolic stimulus (resistance exercise + ingestion of a 20-g leucine-enriched essential amino acid solution) to measure the expression of muscle-specific miRNAs (miR-1, miR-133a, and miR-206), upstream regulators (MyoD and myogenin), and downstream targets [insulin-like growth factor-I, histone deacetylase-4, myocyte enhancing factor-2, and Ras homolog enriched in brain (Rheb)] in skeletal muscle of young and older men. Muscle biopsies were obtained at baseline and 3 and 6 h after exercise. At baseline, we found pri-miRNA-1-1, -1-2, -133a-1, and -133a-2 expression elevated in older compared with young men (P < 0.05). Pri-miRNA-1-2, -133a-1, and -133a-2 were reduced at 6 h after exercise only in the young men compared with baseline, whereas pri-miRNA-206 was elevated at different postexercise time points in older and young men (P < 0.05). Compared with baseline, miR-1 was reduced only in the young men, whereas Rheb protein was increased in both age groups after the anabolic stimulus (P < 0.05). We conclude that skeletal muscle primary and mature miRNA expression in young men is readily altered by an anabolic stimulus of resistance exercise + essential amino acid ingestion. However, aging is associated with higher basal skeletal muscle primary miRNA expression and a dysregulated miRNA response after the anabolic stimulus.

Figures

Fig. 1.

Basal expression of primary and mature microRNAs (miRNAs) in young and older men: primary miR-1-1, pri-miR-1-2, and mature miRNA miR-1 (A), pri-miR-133a-1, pri-miR-133a-2, and mature miR-133a (B), and pri-miR-206 and mature miR-206 (C). Values are means ± SE. *Significantly different from young (P ≤ 0.05).

Fig. 2.

Expression levels of pri-miR-1-1 (A), pri-miR-1-2 (B), and miR-1 (C) in young and older men after a potent anabolic stimulus [resistance exercise + essential amino acid (EAA) ingestion]. Values are means ± SE. *Significantly different from basal (P ≤ 0.05).

Fig. 3.

Expression levels of pri-miR-133a-1 (A), pri-miR-133a-2 (B), and miR-133a (C) in young and older men after a potent anabolic stimulus (resistance exercise + EAA ingestion). Values are means ± SE. *Significantly different from basal (P ≤ 0.05).

Fig. 4.

Expression levels of pri-miR-206 (A) and miR-206 (B) in young and older men after a potent anabolic stimulus (resistance exercise + EAA ingestion). Values are means ± SE. *Significantly different from basal (P ≤ 0.05). #Significantly different from young at corresponding time point (P ≤ 0.05).

Fig. 5.

MicroRNA processing and transporting factor expression levels for Drosha mRNA (A), Drosha protein (B), Exportin-5 mRNA (C), and Exportin-5 protein (D) in young and older men after a potent anabolic stimulus (resistance exercise + EAA ingestion). Values are means ± SE. *Significantly different from basal (P ≤ 0.05). **Significant main effect for time × age (P ≤ 0.05).