Heterotopic ossification and the elucidation of pathologic differentiation

Abstract

Tissue regeneration following acute or persistent inflammation can manifest a spectrum of phenotypes ranging from the adaptive to the pathologic. Heterotopic Ossification (HO), the endochondral formation of bone within soft-tissue structures following severe injury serves as a prominent example of pathologic differentiation; and remains a persistent clinical issue incurring significant patient morbidity and expense to adequately diagnose and treat. The pathogenesis of HO provides an intriguing opportunity to better characterize the cellular and cell-signaling contributors to aberrant differentiation. Indeed, recent work has continued to resolve the unique cellular lineages, and causative pathways responsible for ectopic bone development yielding promising avenues for the development of novel therapeutic strategies shown to be successful in analogous animal models of HO development. This review details advances in the understanding of HO in the context of inciting inflammation, and explains how these advances inform the current standards of diagnosis and treatment.

Keywords: Bone morphogenetic protein receptors; Ectopic bone; Inflammation.

Fig. 1.

HO Development: (A) Traumatic etiologies for incitation of HO development. (B) Cellular Populations present at sites of characteristic HO Development. (C) Stages of HO development: cellular infiltration, chondrogenic differentiation, and finally mineralization and ossification.

Fig. 2.

Cell Signaling in tHO: (A) Cell signaling pathways implicated in cellular proliferation and differentiation responsible for HO development. (B) Diagramatic representation of cellular progression in developing HO lesions.