1628-P: Role of CD38 in the Regulation of Muscle Stem Cell Functions in Aged Mice

Skeletal muscle repair and regeneration is a complex process and is known to be delayed with aging, diabetes and obesity. This is in part due to infiltration of inflammatory macrophages which can delay the recovery process. Both macrophages and satellite cells require nicotinamide adenine dinucleotide (NAD+) for their biological functions. Aging-induced decline in NAD+ have been shown to worsen insulin resistance and muscle dysfunction. CD38 is an ectoenzyme that degrades NAD+ and is increased in inflammatory macrophages in aging, obesity and other insulin-resistant states. However, how inhibition of CD38 affects satellite cell functions in aged or obese mice, remains unknown. Here, we utilized aged CD38 knockout mice to assess the role of this protein and NAD+ in the recovery process in injured muscle. CD38 KO mice were found to be resistant to diet-induced obesity and had improved insulin sensitivity. Our data show that genetic deletion of CD38 in aged mice increased NAD+ levels and thus enhanced muscle stem/satellite cells differentiation and promote myogenesis. Deletion of CD38 also resulted in an enhanced number of regenerating myofibers. Furthermore, we found that deletion of CD38 significantly reduces fibrosis of muscle and also improved limb grip strength. Pharmacological inhibition of CD38 in C2C12 myoblasts and ex-vivo primary myoblasts significantly increased NAD+ levels and also enhanced the differentiation of satellite cells into myoblasts and myofibers. We, therefore, examined the rescue effects of 78c (CD38i) on human recombinant CD38 (hCD38) inhibition of muscle stem cells. Administration of hCD38 inhibited expression of MyoD and MyoG in primary myoblasts, while this effect was rescued through 78c treatment. Taken together, these data demonstrate that restoration of NAD+ levels either through genetic deletion/pharmacological inhibition of CD38 can improve muscle stem cell functions and muscle regeneration and might promote muscle regeneration in obesity, type 2 diabetes, and aging. Disclosure A.Nawaz: None. K.Yaku: None. I.Jeelani: None. K.Tobe: Other Relationship; MSD K.K., Novo Nordisk Pharma Ltd., Takeda Pharmaceutical Company Limited, Daiichi Sankyo, Mitsubishi Tanabe Pharma Corporation, Suntory Global Corporation, Ltd.,, Taiho Pharmaceutical Co. Ltd., Japan Diabetes Foundation, Japan Association for Diabetes Education and Care. T.Nakagawa: None.