Regulation of Glucose Metabolism by MuRF1 and Treatment of Myopathy in Diabetic Mice with Small Molecules Targeting MuRF1.

Siegfried Labeit,Volker Adams,Stephanie Hirner,Moldir Myrzabekova,Julijus Bogomolovas,Anselmo Moriscot,Thomas Scott Bowen,André Cruz

doi:10.3390/ijms22042225

Abstract

The muscle-specific ubiquitin ligase MuRF1 regulates muscle catabolism during chronic wasting states, although its roles in general metabolism are less-studied. Here, we metabolically profiled MuRF1-deficient knockout mice. We also included knockout mice for MuRF2 as its closely related gene homolog. MuRF1 and MuRF2-KO (knockout) mice have elevated serum glucose, elevated triglycerides, and reduced glucose tolerance. In addition, MuRF2-KO mice have a reduced tolerance to a fat-rich diet. Western blot and enzymatic studies on MuRF1-KO skeletal muscle showed perturbed FoxO-Akt signaling, elevated Akt-Ser-473 activation, and downregulated oxidative mitochondrial metabolism, indicating potential mechanisms for MuRF1,2-dependent glucose and fat metabolism regulation. Consistent with this, the adenoviral re-expression of MuRF1 in KO mice normalized Akt-Ser-473, serum glucose, and triglycerides. Finally, we tested the MuRF1/2 inhibitors MyoMed-205 and MyoMed-946 in a mouse model for type 2 diabetes mellitus (T2DM). After 28 days of treatment, T2DM mice developed progressive muscle weakness detected by wire hang tests, but this was attenuated by the MyoMed-205 treatment. While MyoMed-205 and MyoMed-946 had no significant effects on serum glucose, they did normalize the lymphocyte–granulocyte counts in diabetic sera as indicators of the immune response. Thus, small molecules directed to MuRF1 may be useful in attenuating skeletal muscle strength loss in T2DM conditions.

Highlights

As an initial survey for metabolic effects after MuRF1 and MuRF2 gene inactivation, we performed clinical chemistry on sera obtained from 16-h food-deprived MuRF1-KO, MuRF2-KO, and MuRF1-Tg mice, respectively
Consistent with MuRF1-mediated effects on the mitochondrial metabolism, we found that the re-expression of MuRF1 by AAV9 significantly elevated pyruvate dehydrogenase complex (PDC) activity when determined as described by Jeoung et al [25], (Figure 4C)
The results indicated that MuRF1 and MuRF2 catalyze the mono-ubiquitination of PDK2 in vitro (Figure 4D)

Summary

Introduction

Two ubiquitin ligases, MAFBx (“muscle atrophy F-box protein”, called atrogin-1) and MuRF1 (“muscle-specific RING finger protein-1”), and their relationship with muscle diseases, have been characterized in the most detail (for review, [11,12]). Both MAFBx and MuRF1 transcripts are markedly upregulated during muscle wasting states, thereby coupling enhanced muscle catabolism to UPS activation and promoting atrophy development by the downregulation of the IGF-1/Akt/mTOR pathway [13,14,15,16]. In addition to general muscle wasting, MAFBx and MuRF1 are upregulated by specific hormones and cytokines such as glucocorticoids [15], AT-II [17], and TNF-alpha [18], all factors known to promote muscle protein catabolism

Methods

Results

Conclusion