Vasorin-deficient mice display disturbed vitamin D and mineral homeostasis in combination with a low bone mass phenotype.

Vasorin (Vasn) is a pleiotropic molecule involved in various physiological and pathological conditions, including cancer. Vasn has also been detected in bone cells of developing skeletal tissues but no function for Vasn in bone metabolism has been implicated yet. Therefore, this study aimed to investigate if Vasn plays a significant role in bone biology. First, we investigated tissue distribution of expression, using lacZ knock-in reporter mice. We detected clear Vasn expression in skeletal elements of postnatal mice. In particular, osteocytes and bone forming osteoblasts showed high expression of Vasn, while the bone marrow was devoid of signal. Vasn knockout mice ( ) displayed postnatal growth retardation and died after four weeks. MicroCT analysis of femurs from 22- to 25-day-old demonstrated reduced trabecular and cortical bone volume corresponding to a low bone mass phenotype. bone marrow cultures demonstrated that osteoclast differentiation and activity were not affected by deficiency. However, osteogenesis of bone marrow cultures was disturbed, resulting in lower numbers of alkaline phosphate positive colonies, impaired mineralization and lower expression of osteoblast marker genes. In addition to the bone phenotype, these mice developed a vitamin D-related phenotype with a strongly reduced circulating 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D3 and urinary loss of vitamin D binding protein. In conclusion, Vasn-deficient mice suffer from severe disturbances in bone metabolism and mineral homeostasis.