Insulin treatment reverses the increase in atrogin-1 expression in atrophied skeletal muscles of diabetic rats with acute joint inflammation

Clara Maria Pinheiro-Dardis,1 Vânia Ortega Gutierres,1 Renata Pires Assis,1 Sabrina Messa Peviani,2 Gabriel Borges Delfino,2 João Luiz Quagliotti Durigan,3 Tania de Fátima Salvini,2 Amanda Martins Baviera,1 Iguatemy Lourenço Brunetti1 1São Paulo State University (UNESP), School of Pharmaceutical Sciences, Department of Clinical Analysis, Araraquara, São Paulo, Brazil; 2Federal University of São Carlos (UFSCar), Department of Physical Therapy, São Carlos, São Paulo, Brazil; 3Physical Therapy Division, University of Brasilia, Brasilia, Federal District, Brazil 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 Ɩ-carrageenan (NCa) injection into the tibiotarsal joint – and groups with diabetes – diabetes (D), plus insulin (DI), saline (DS), or Ɩ-carrageenan (DCa) injection into the tibiotarsal joint, or Ɩ-carrageenan injection and treatment with insulin (DCaI). Three days after Ɩ-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 Ɩ-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. Keywords: diabetes mellitus, inflammation, muscle proteolysis, atrogenes, creatine kinase, NF-κB, insuli