Long-Term Insulin Treatment Alters Muscle-Related Protein in OLETF Rat Skeletal Muscle

Purpose: The objective of this study was to investigate molecular and physiological changes in response to long-term insulin glargine treatment in the skeletal muscle of Otsuka Long-Evans Tokushima Fatty (OLETF) rats.

Methods: Protein changes in the skeletal muscle of type 2 diabetic rats was detected by Western blot analysis, and muscle fiber type composition was assessed by real-time PCR.

Results: Insulin glargine (1 U/kg) treatment in OLETF rats (OLETF-G) for 24 weeks were changed in blood glucose levels in intraperitoneal glucose tolerance tests compared with age-matched, untreated OLETF rats (OLETF-C), and the area under the curve was significantly decreased for OLETF-G rats compared with OLETF-C rats (P < 0.05). The protein levels of myosin heavy chain (MHC) isoforms were altered in gastrocnemius muscle of OLETF rats, and the proportions of MHC type I and II fibers were lower and higher, respectively, in OLETF-G compared with OLETF-C rats. Activation of myokines (interleukin [IL]-6, IL-15, fibronectin type III domain containing 5 [FNDC5]/irisin, and myostatin) in gastrocnemius muscle was significantly inhibited in OLETF-G compared with OLETF-C rats (P < 0.05). Moreover, myogenin determination gene D and myogenin levels were decreased, while insulin-like growth factor-I levels were increased, in the skeletal muscle of OLETF-G rats (P < 0.05). Insulin glargine treatment significantly increased the phosphorylation levels of 5’-AMP-activated protein kinase, sirtuin 1, and peroxisome proliferator-activated receptor γ coactivator 1α.

Conclusions: Our results suggest that long-term insulin glargine treatment can effectively alter protein expression in the gastrocnemius muscle of OLETF rats.