MG53 Does Not Manifest the Development of Diabetes in db/db Mice

Abstract

MG53 is a member of the TRIM protein family that is predominantly expressed in striated muscles and participates in cell membrane repair. Controversy exists regarding MG53's role in insulin signaling and manifestation of diabetes. We generated db/db mice with either whole-body ablation or sustained elevation of MG53 in the bloodstream in order to evaluate the physiological function of MG53 in diabetes. To quantify the amount of MG53 protein in circulation, we developed a monoclonal antibody against MG53 with high specificity. Western blot using this antibody revealed lower or no change of serum MG53 levels in db/db mice or patients with diabetes compared with control subjects. Neither wholebody ablation of MG53 nor sustained elevation of MG53 in circulation altered insulin signaling and glucose handling in db/db mice. Instead, mice with ablation of MG53 were more susceptible to streptozotocin-induced dysfunctional handling of glucose compared with the wild-type littermates. Alkaline-induced corneal injury demonstrated delayed healing in db/db mice, which was restored by topical administration of recombinant human (rh)MG53. Daily intravenous administration of rhMG53 in rats at concentrations up to 10 mg/kg did not produce adverse effects on glucose handling. These findings challenge the hypothetical function of MG53 as a causative factor for the development of diabetes. Our data suggest that rhMG53 is a potentially safe and effective biologic to treat diabetic oculopathy in rodents.

MG53 is not a critical regulator of insulin signaling pathway in skeletal muscle

“…While we cannot exclude the possibility that different reagents may lead to different results, our data raise significant doubts about the involvement of MG53 in the regulation of insulin signaling. In addition, our data are consistent with recent reports from the Ma's lab who used alternative strategies to come to the same conclusions [16,19]. First, they showed using transgenic mice that sustained elevation of plasma MG53 levels does not compromise insulin signaling in skeletal muscle as well as glucose handling when mice were placed under high fat diet.…”

“…We tried to measure MG53 levels in plasma samples from these animals. However, western blot analyses led to the detection of MG53 at a lower size (data not shown) with doubts about the accuracy of the band for the MG53 signal in line with observations made by other groups [16][17][18].…”

Multi-Cellular Functions of MG53 in Muscle Calcium Signaling and Regeneration

“…This would also imply that the high levels of circulating MG53 present in tPA-MG53 mice could block the insulin pathway and greatly facilitate the development of diabetes. However, as mentioned above, tPA-MG53 mice live a healthy lifespan and when crossed with db/db mice, tPA-MG53/db/db mice are indistinguishable from db/db littermates in terms of growth rate, glucose tolerance test, and insulin tolerance test (Bian et al, 2019;Wang et al, 2020). These studies highlight the deep controversies surrounding the protein that will need to be resolved by future studies.…”

“…tPA-MG53 mice live a healthy lifespan with enhanced tissue repair and regeneration capacity (Yao et al, 2016;Bian et al, 2019). To test the role of elevated circulating MG53 in the development of diabetes, we crossed tPA-MG53 mice with db/db mice and found that tPA-MG53/db/db mice develop diabetes at a rate similar to its db/db littermates, suggesting overexpression of MG53 has negligible effects on the development of diabetes (Wang et al, 2020). A separate transgenic mouse model with overexpression of MG53 was generated by Ham and Mahoney (2013).…”

“…These observations have not been substantiated by other investigators, and many others failed to observe an upregulation of MG53 in diabetic animals and humans ( Ma et al, 2013 , 2015 , 2017 ; Xu et al, 2013 ; Yi et al, 2013 ; Yuan et al, 2013 ; Zabielski et al, 2016 ). Rather, serum samples from high fat diet induced diabetic mice ( Ma et al, 2015 ) and db/db mice ( Wang et al, 2020 ) showed reduced levels of MG53. It is also well-known that a loss of IRS-1 does not directly result in diabetes, owing to a robust compensatory mechanism among the different IRS subtypes ( Tamemoto et al, 1994 ; Terauchi et al, 1997 ; Laustsen et al, 2002 ).…”