Development of an Animal Model for Traumatic Brain Injury Augmentation of Heterotopic Ossification in Response to Local Injury

Abstract

Heterotopic ossification (HO) is the abnormal growth of bone in soft connective tissues that occurs as a frequent complication in individuals with traumatic brain injury (TBI) and in rare genetic disorders. Therefore, understanding the mechanisms behind ectopic bone formation in response to TBI is likely to have a significant impact on identification of novel therapeutic targets for HO treatment. In this study, we induced repetitive mild TBI (mTBI) using a weight drop model in mice and then stimulated HO formation via a local injury to the Achilles tendon or fibula. The amount of ectopic bone, as evaluated by micro-CT analyses, was increased by four-fold in the injured leg of mTBI mice compared to control mice. However, there was no evidence of HO formation in the uninjured leg of mTBI mice. Since tissue injury leads to the activation of hypoxia signaling, which is known to promote endochondral ossification, we evaluated the effect of IOX2, a chemical inhibitor of PHD2 and a known inducer of hypoxia signaling on HO development in response to fibular injury. IOX2 treatment increased HO volume by five-fold compared to vehicle. Since pericytes located in the endothelium of microvascular capillaries are known to function as multipotent tissue-resident progenitors, we determined if activation of hypoxia signaling promotes pericyte recruitment at the injury site. We found that markers of pericytes, NG2 and PDGFRβ, were abundantly expressed at the site of injury in IOX2 treated mice. Treatment of pericytes with IOX2 for 72 h stimulated expression of targets of hypoxia signaling (Vegf and Epo), as well as markers of chondrocyte differentiation (Col2α1 and Col10α1). Furthermore, serum collected from TBI mice was more effective in promoting the proliferation and differentiation of pericytes than control mouse serum. In conclusion, our data show that the hypoxic state at the injury site in soft tissues of TBI mice provides an environment leading to increased accumulation and activation of pericytes to form endochondral bone.

Prevascularization techniques for dental pulp regeneration: potential cell sources, intercellular communication and construction strategies

“…Studies have found that pericytes express surface markers of MSCs, namely, CD146 + , CD45 − , CD34 − , CD73 + , CD44 + and CD105 + ( Crisan et al, 2008 ; Wang et al, 2019 ; Manocha et al, 2022 ), and exhibit multidirectional differentiation ability similar to that of MSCs ( Farrington-Rock et al, 2004 ; Tsang et al, 2013 ; Chou et al, 2020 ; Kesavan et al, 2023 ). The MSCs residing in tissue are located in the pericyte niche in the microvasculature ( Murray et al, 2014 ) and express perivascular cell markers: CD146, desmin, NG2, and platelet-derived growth factor receptor (PDGFR) ( Crisan et al, 2008 ).…”

Molecular and Cellular Mechanisms of Bone and Cartilage Diseases

“…The next editor choice was a study by Bonifacio et al [ 5 ] that provided solid evidence for the beneficial effects of hyaluronic acid and amino acids on in vitro maturation and activation of human osteoblasts, suggesting that the use of hyaluronic acid and amino acid solutions as therapeutic agents for promoting bone regeneration and nonunion healing has considerable merit. Furthermore, given the lack of knowledge concerning the mechanism of heterotopic ossification in response to traumatic brain injury, Kesavan et al [ 6 ] report on the development of an animal model for traumatic brain injury augmentation of heterotopic ossification in response to local injury. In this model, a traumatic brain injury was induced by a weight-drop model in mice, and heterotopic ossification was then induced by local injury to the Achilles tendon or fibula in mice.…”