Immune Suppressive and Bone Inhibitory Effects of Prednisolone in Growing and Regenerating Zebrafish Tissues

Abstract

Glucocorticoids are widely used as therapeutic agents to treat immune-mediated diseases in humans because of their anti-inflammatory and immunosuppressive effects. However, glucocorticoids have various adverse effects, in particular rapid and pronounced bone loss associated with fractures in glucocorticoid-induced osteoporosis, a common form of secondary osteoporosis. In zebrafish, which are increasingly used to study processes of bone regeneration and disease, glucocorticoids show detrimental effects on bone tissue; however, the underlying cellular mechanisms are incompletely understood. Here, we show that treatment with the glucocorticoid prednisolone impacts on the number, activity and differentiation of osteoblasts, osteoclasts, and immune cells during ontogenetic growth, homeostasis, and regeneration of zebrafish bone. Macrophage numbers are reduced in both larval and adult tissues, correlating with decreased generation of myelomonocytes and enhanced apoptosis of these cells. In contrast, osteoblasts fail to proliferate, show decreased activity, and undergo incomplete differentiation. In addition, prednisolone treatment mitigates the number and recruitment of osteoclasts to sites of bone regeneration in adult fish. In combination, these effects delay bone growth and impair bone regeneration. Our study demonstrates the many-faceted effects of glucocorticoids in non-mammalian vertebrates and helps to further establish the zebrafish as a model to study glucocorticoid-induced osteoporosis. © 2017 American Society for Bone and Mineral Research.

Role of the immune response in initiating central nervous system regeneration in vertebrates: learning from the fish

“…In addition, the study provides evidence that macrophages are crucial early mediators of blastema formation (Petrie et al, 2014). Furthermore, a recent zebrafish study showed, that immune-suppressive treatment using prednisolone leads to decreased bone growth as well as impaired regeneration (Geurtzen et al, 2017). In a zebrafish model of peripheral axonal nerve injury, macrophages rapidly arrive at the lesion site where they engulf axonal debris and invade into the nerve following axon fragmentation (Rosenberg et al, 2012).…”

Molecular mechanisms of glucocorticoids on skeleton and bone regeneration after fracture

“…2007 , Oppedal & Goldsmith 2010 ). As in mammals, systemic GC treatment of zebrafish has complex effects, including suppression of the immune response, reduced osteoblast differentiation, and proliferation, and effects on osteoclast activity ( Geurtzen et al . 2017 ).…”

“…Tissue-specific manipulations of GR activity have not yet been performed in zebrafish, thus it has to date not been possible to ascertain which of the GC effects on bone, and in particular on osteoblasts, are direct. Interestingly however, in contrast to mammals, prednisolone treatment does not appear to induce osteoblast apoptosis in regenerating zebrafish fins ( Geurtzen et al . 2017 ).…”

Advances in treatment of glucocorticoid-induced osteoporosis

“…Local metabolism of glucocorticoids in bone cells is controlled by a pair of complementary enzymes, 11β-hydroxysteroid dehydrogenase types 1 and 2 (Hsd11b1 & Hsd11b2), which respectively activate or deactivate glucocorticoid action by metabolizing the interconversion of biologically active or inert forms[6, 7]. Additional pathways of glucocorticoid action are thought to be multiple, including inducing proapoptotic molecules in osteoblasts and osteocytes, and through antagonizing the osteoblastogenic Wnt pathway [4, 8, 9]. There continues to be active work into uncovering pathways of glucocorticoid mechanism at the cellular level[10], including recent claims of enhancing osteoblast activity through heat shock protein 90[11].…”