New Findings r What is the central question of this study?The beneficial effects of glutamine supplementation are related to heat shock protein induction and reduced inflammation, but its effects on skeletal muscle function, heat shock protein expression and inflammatory factors after spinal cord injury (SCI) are unknown. r What is the main finding and its importance? Using a mouse model of SCI, glutamine supplementation for 7 days following SCI was associated with significant improvements in muscle force, fatigue resistance and maintenance of contractile proteins versus placebo. Lower protein levels of heat shock proteins, interleukin-6 and tumour necrosis factor-α after SCI suggest that reduced stress is experienced by skeletal muscles with glutamine. The findings support glutamine as a therapeutic intervention to moderate inflammation and accelerate recovery of muscle function after SCI.Spinal cord injury (SCI) results in loss of muscle function due to rapid breakdown of contractile proteins. Glutamine supplementation improves clinical outcomes, but its effects on muscle function after SCI are unknown. The benefits of glutamine in non-skeletal muscle tissues involve elevated heat shock protein (Hsp)70 and Hsp25, but the muscle response may differ because it is the largest contributor to plasma glutamine. We tested the hypothesis that glutamine preserves muscle function after SCI and that this is associated with increased heat shock protein and reduced inflammatory factors, interleukin-6 (IL-6) and tumour necrosis factor-α (TNFα). Changes in plantarflexor force, fatigability and total myofibrillar, Hsp70, Hsp25, IL-6 and TNFα muscle protein levels were measured 7 days after sham or spinal cord transection surgery in mice receiving daily placebo or glutamine. Compared with placebo, after SCI glutamine significantly attenuated the reductions in maximal isometric force (0.22 ± 0.01 versus 0.31 ± 0.03 N, respectively) and fatigue resistance (34 ± 4 versus 59 ± 4% of initial force, respectively). Glutamine significantly ameliorated the loss of myofibrillar protein with spinal cord transection. Spinal cord transection was associated with decreased Hsp70 and Hsp25 with glutamine only (45 ± 3 and 44 ± 5% of placebo, respectively). Glutamine significantly reduced spinal cord transection-associated increases in IL-6 and TNFα compared with placebo (38 ± 6 and 37 ± 8% of placebo, respectively). Functionally, early reductions in contractile protein, force and fatigue resistance after SCI were reversed with glutamine. Spinal cord transection-associated reductions in Hsp70, Hsp25, IL-6 and TNFα with glutamine versus placebo suggest lower stress C.C. and M.G. contributed equally to this work

Exercise accustomization may protect against statin‐associated losses in muscle force. Exercise‐induced increases in Hsp25 and αB‐crystallin may contribute to this protection by helping reduce muscle breakdown and oxidative stress. We tested the hypothesis that 1 or 3 days of prior exercise protects against statin‐induced muscle force loss and this will be associated with reduced contractile protein breakdown and oxidative stress. Mice received daily atorvastatin or saline for 14d, with/without wheel running (RW) (Novel & Sedentary (Sed)) and prior RW groups completed 1 or 3d of RW before saline or statin + RW. Plantarflexor force, fatigue, contractile proteins, protein carbonyls, and Hsp25 and αB‐crystallin protein were quantified. Statins reduced force in Sed, novel, and 1d RW groups vs saline (21, 35, & 21%, respectively, p<0.05), while 3d RW prevented statin‐associated force loss. Hsp25 and αB‐crystallin increased with RW vs. Sed, independent of statin treatment (p<0.05). Statins were associated with lower contractile protein levels in Sed and novel groups vs. saline (18 & 26%, respectively, p<0.05). Total protein carbonyls were lower than Sed‐saline in novel, 1d, & 3d RW groups with either treatment (p<0.05). Results suggest 3d prior exercise does not reduce oxidative stress vs. novel exercise, but may preserve contractile proteins and help prevent statin‐associated force loss with exercise.

Spinal cord injury (SCI) results in loss of muscle function due to rapid breakdown of contractile proteins. Glutamine (GLN) supplementation improves clinical outcomes, but its effects on muscle function after SCI are unknown. Improvements with GLN in non‐skeletal muscle tissues have been related to elevated heat shock protein 70 (Hsp70) and Hsp25, but the muscle response may differ since it is the largest contributor to plasma GLN. We tested the hypothesis that GLN preserves muscle function after SCI and this is associated with increased Hsp levels. Changes in plantarflexor mass, force, fatigability, and Hsp70 and 25 protein were measured 7 d after sham or spinal cord transection (ST) surgery in mice receiving daily placebo (PL) or GLN. ST reduced muscle mass with PL or GLN (p<0.05). Maximal isometric force relative to body mass was not different among groups, but GLN prevented greater fatigability seen with ST + PL (59±4 vs. 34±4% of initial force after 10 contractions, respectively, p<0.05). ST was associated with decreased Hsp70 and 25 with GLN only (49±3 and 44±5% of PL, respectively, p<0.05). Functionally, early increases in fatigability after SCI were reversed with GLN. ST‐associated reductions in Hsp70 and 25 with GLN vs. PL suggest lower stress in the muscle, possibly related to a reduced need to produce GLN. These findings support GLN as a therapeutic intervention to accelerate recovery of muscle function after SCI.

Functional overload (FO, removal of major synergists) induces muscle growth and increased strength and fatigue resistance. With FO, Hsp25 (rodent form of Hsp27) expression and phosphorylation is significantly increased in hypertrophying muscle suggesting its role in muscle adaptation to loading stressors. Since phosphorylation can modify stress‐related Hsp25 functions, we tested the hypothesis that overexpression of human Hsp27 (TG) or a nonphosphorylatable Hsp27 mutant (MUT) will respectively increase and decrease FO‐induced muscle growth and function vs. wild type (WT) mice. Plantaris (Plt) isometric force and fatigue were measured in vivo 14 or 30 d after FO or sham surgery. Plt mass increased ~ 2 fold with FO in all groups, but was lower in MUT than WT at 14d (p<0.05). Plt maximal isometric force was 30% lower in MUT than WT at 30d (p<0.05) and tended to be lower in TG than WT at 14 and 30d. Fatigue resistance was lower in MUT than WT at 14 and 30d (16 and 32% respectively) and 20% lower in TG than WT with Sham only (p<0.05). Results suggest that elevated Hsp27 levels do not alter muscle adaptation to FO; however, preventing Hsp27 phosphorylation attenuates adaptations in force and fatigability compared to WT with 14 or 30d of FO. This suggests Hsp27 phosphorylation dependent functions (e.g. reducing apoptosis) may be involved in processes that increase muscle strength and fatigue resistance. Funded by NIH R15AR060469