1625-P: Osteoprotection by FNIP1 Signaling in Skeletal Muscle

Abstract

Obesity is increasingly recognized to exert negative impact on bone mass. Skeletal muscle and bone are closely related throughout life, and muscle dysfunction can cause osteoporosis. Understanding of the crosstalk between muscle and bone could have implications for maintaining bone fitness in various disease states such as obesity. FNIP1 is emerging as key regulator of muscle metabolism acting via AMPK. However, the role of muscle FNIP1 in bone mass control is unknown. Using both gain- and loss-of function muscle-specific genetic models, we show that in addition to the known role in the regulation of mitochondrial function muscle fiber type, FNIP1 participates in muscle programs that govern bone homeostasis. FNIP1 KO mice showed a decrease in trabecular bone volume and bone mineral density, whereas muscle specific restoration of FNIP1 expression in KO mice (FNIP1Tg/KO) reversed the bone loss phenotypes. Femoral bending tests revealed a marked decrease in elastic modulus and maximum force in FNIP1 KO mice but increase in FNIP1 TgKO mice. Consistent with these findings, muscle cell-specific deletion of FNIP1 resulted in a pronounced bone structural and mechanical dysfunction. Using AMPKα1/α2 KO lines, we show that muscle FNIP1 exerts control actions upon bone homeostasis independently of AMPK. Through comprehensive RNA-seq and genomic analyses, we reveal that muscle FNIP1 deficiency induces IGF2 secretion, thereby driving an IGF2-depenent osteoclast program. Importantly, we also found that the muscle FNIP1-IGF2 regulatory circuit is associated with osteoporosis in humans. Thus, muscle FNIP1 is a critical safeguard of bone mass. These findings provide new therapeutic opportunities for enhancing muscle fitness to combat a variety of metabolic and musculoskeletal diseases. Disclosure M.Yan: None. Z.Xu: None. Y.Yin: None. T.Fu: None. Z.Zhou: None. L.Yang: None. Z.Gan: None.