Effect of 8-week leucine supplementation and resistance exercise training on muscle hypertrophy and satellite cell activation in rats

Abstract

We investigated the effects of regular leucine intake and/or resistance exercise training on skeletal muscle hypertrophy and satellite cell activity after the administration of different doses of leucine. Ten-week-old Sprague-Dawley rats were assigned to six groups (n = 7 per group): a control group (Con), two groups receiving either 10% (0.135 g/kg.wt) (Leu10) or 50% (0.675 g/kg.wt) (Leu50) leucine supplementation, and three exercise groups receiving 0% (Ex), 10% (Leu10Ex), and 50% (Leu50Ex) leucine supplementation. The rats performed ladder climbing exercises thrice per week for 8 weeks, and received leucine supplements at the same time daily. Muscle phenotypes were assessed by immunohistochemistry. MyoD, myogenin, and IGF1 protein levels were determined by western blot. The Leu50Ex group displayed significantly higher numbers of positive embryonic myosin fibers (0.35 ± 0.08, 250%) and myonuclei (3.29 ± 0.3, 118.7%) than all other groups. And exercise training groups increased the cross-sectional area, the number of satellite cells and protein expression of MyoD, myogenin, and IGF1alpha relative to the Control group (P < 0.05). However, Only leucine supplementation group did not increase skeletal muscle hypertrophy and satellite cell activity, regardless of the dose (P > 0.05). Leucine intake accompanied by regular exercise training may increase satellite cell activation in skeletal muscles, and improve muscle quality more effectively than continuous leucine ingestion alone.

Keywords: Embryonic myosin; Leucine; Resistance exercise; Satellite cell.

Figure 1

Climbing ladder exercise.

Figure 2

Immunohistochemical detection of satellite cells (Pax7, green). (A), laminin (antilaminin, red), (B), nuclei (DAPI, blue), and (C) merged. The two yellow circles represent satellite cells for which the green and blue signals exactly overlap. Scale bar = 100 μm.

Figure 3

Satellite cell (Pax7/Fiber) numbers in EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. * P < 0.05, significant difference from Con.

Figure 4

Myonuclear number (myonuclear/fiber) in EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. * P < 0.05, significant difference from Con.

Figure 5

Ratio of central nuclei in EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group.

Figure 6

Immunohistochemical detection of central nuclei. The two yellow circles represent central nuclei. Scale bar = 100 μm.

Figure 7

Immunohistochemical detection of the heavy chain of embryonic myosin. The two yellow arrows indicate embryonic myosin‐positive fibers. Scale bar = 100 μm.

Figure 8

Embryonic MHC in EDL muscles. MHC: myosin heavy chain, Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. ** P < 0.005, significant difference from Con, # P < 0.005, significant difference from Ex, ∬ P < 0.005, significant difference from Leu10Ex.

Figure 9

MyoD (A) and myogenin (B) protein expression in EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. * P < 0.05, significant difference from Con.

Figure 10

IGF‐1 protein expression in EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. * P < 0.05, significant difference from Con, ** P < 0.005, significant difference from Con.

Figure 11

Cross‐sectional areas of EDL muscles. Con: control group, Leu10: 10% leucine group, Leu50: 50% leucine group, Ex: exercise group, Leu10Ex: 10% leucine + exercise group, Leu50Ex: 50% leucine + exercise group. * P < 0.05, significant difference from Con.