Partial prevention of glucocorticoid-induced osteocyte deterioration with osteocrin gene therapy

Glucocorticoid (GC)-induced osteoporosis and subsequent bone fragility are preceded by death and dysfunction at the cellular level. In particular, short-term glucocorticoid excess suppresses osteocyte remodeling of the surrounding bone mineral, causes apoptosis of osteoblasts and osteocytes, and disrupts homeostatic bone remodeling. Preventing apoptosis and preserving osteocyte morphology and function could be effective means of preventing bone loss during glucocorticoid excess. We hypothesized that osteocrin, which preserves osteocyte viability and morphology in other models where osteocyte defects exist, could prevent osteocyte death and dysfunction in a GC excess model. We used a liver-targeted adeno-associated virus (AAV8) to induce osteocrin overexpression in mice one week prior to implantation with prednisolone or placebo pellets. After 28 days, tissues were collected for micro-CT and histological analysis. GC excess caused the expected reduction in cortical bone thickness and osteocyte canalicular length in control AAV8-treated mice, and these effects were blunted in mice overexpressing osteocrin. However, GC-induced changes in cortical porosity, trabecular bone mass, and gene expression were not prevented by osteocrin. While the mechanism of osteocrin’s effects on osteocyte morphology warrants further investigation, this study does not support a role for this model of osteocrin supplementation to combat the full skeletal effects of GC excess.