Osteocalcin-dependent and -independent metabolic dysregulation in a mouse model of Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a rare bone fragility disorder. Previously, in a severe OI mouse model (Col1a1^Jrt/+), a sex- and age-dependent metabolic phenotype was observed, correlating with elevated levels of the bone-derived hormone osteocalcin (OCN). This hormone is known to play a crucial role in managing energy metabolism, including glucose regulation and fat mass. In fact, upon high-fat diet (HFD) exposure, OI mice developed a metabolic syndrome linked to sex and OCN. To assess OCN's role in OI, Col1a1^Jrt/+ mice were crossed with OCN-deficient mice (Bglap). Under regular chow and HFD conditions, both OCN-dependent and OCN-independent metabolic alterations were identified. OCN-dependent processes were adipose tissue, liver, and insulin metabolism in a sex-, age-, and diet-dependent manner. OCN-independent traits included the pancreas in juvenile mice, HFD-induced pancreatic insulin levels and glucose intolerance, besides overall growth, fertility, and bone phenotype. Notably, increased juvenile energy expenditure was OCN-independent, while HFD-induced changes were OCN-driven. These findings demonstrate OCN's role in shaping the metabolic phenotype while revealing distinct OCN-independent effects, emphasizing the complex genetic regulation of metabolism in OI.