RESUMO
BACKGROUND: The aim of this study was to evaluate the changes in biomarkers of skeletal muscle proteolysis (atrogin-1, muscle RING finger-1 protein [MuRF-1]) and inflammation (nuclear factor kappa-B) in skeletal muscles of rats under two catabolic conditions, diabetes mellitus (DM) and acute joint inflammation, and the effects of insulin therapy. MATERIALS AND METHODS: Male Wistar rats were divided into groups without diabetes - normal (N), saline (NS), or ι-carrageenan (NCa) injection into the tibiotarsal joint - and groups with diabetes - diabetes (D), plus insulin (DI), saline (DS), or ι-carrageenan (DCa) injection into the tibiotarsal joint, or ι-carrageenan injection and treatment with insulin (DCaI). Three days after ι-carrageenan injection (17 days after diabetes induction), tibialis anterior (TA) and soleus (SO) skeletal muscles were used for analysis. RESULTS: DM alone caused a significant decrease in the mass of TA and SO muscles, even with low levels of atrogenes (atrogin-1, MuRF-1), which could be interpreted as an adaptive mechanism to spare muscle proteins under this catabolic condition. The loss of muscle mass was exacerbated when ι-carrageenan was administered in the joints of diabetic rats, in association with increased expression of atrogin-1, MuRF-1, and nuclear factor kappa-B. Treatment with insulin prevented the increase in atrogin-1 (TA, SO) and the loss of muscle mass (SO) in diabetic-carrageenan rats; in comparison with TA, SO muscle was more responsive to the anabolic actions of insulin. CONCLUSION: Acute joint inflammation overcame the adaptive mechanism in diabetic rats to prevent excessive loss of muscle mass, worsening the catabolic state. The treatment of diabetic-carrageenan rats with insulin prevented the loss of skeletal muscle mass mainly via atrogin-1 inhibition. Under the condition of DM and inflammation, muscles with the prevalence of slow-twitch, type 1 fibers were more responsive to insulin treatment, recovering the ability to grow.
RESUMO
OBJECTIVE: The aim of this work was to investigate the effects of electrical stimulation (ES) of denervated muscles of rat in neuromuscular performance, muscle atrophy, and fibrosis formation. DESIGN: Wistar rats were divided into normal (N), 7- or 15-day denervation (D7d and D15d), D7d or D15d plus ES (DES7d and DES15d, respectively). Sciatic nerves were crushed causing muscle denervation. Two hundred muscle contractions were electrically induced daily by surface electrodes, considering muscle chronaxie. Sciatic functional index was used to determine neuromuscular performance during walking. The muscle fiber cross-sectional area and percentage of connective tissue were assessed by light microscopy. Molecular markers of extracellular matrix production and remodeling were evaluated. Metalloproteinase (MMP) activity was assessed by zymography, and TWEAK, Fn14, myostatin, and transforming growth factor (TGF)-ß gene expressions were determined by real-time PCR. RESULTS: Electrical stimulation impaired natural recovery of walking at 15 days. In addition, ES induced fibrosis and accentuated muscle atrophy in denervated muscles. Although ES reduced the accumulation of TWEAK and myostatin expressions, it up-regulated Fn14 and TGF-ß in a time-dependent manner. Electrical stimulation also increased the activity of MMP-2 compared to the other groups (P < 0.05). CONCLUSIONS: Electrical stimulation applied to denervated muscles induced muscle fibrosis and atrophy, as well as loss of performance. The TWEAK/Fn14 system, TGF-beta/myostatin pathway, and MMP activity seem to be involved in these deleterious changes.
