CGRP accelerates the pathogenesis of neurological heterotopic ossification following spinal cord injury

Interactions between the heterotopic ossification (HO) and the neurological injuries have got lots of interest but still poorly understood. The present study aims to determine the effect of neuroinflammation related calcitonin gene-related protein (CGRP) on HO following spinal cord injury (SCI). C57Bl6 mice were anesthetized to make an SCI model, together with the ectopic injection of snake venom cardiotoxin (SVC) or CGRP protein into tibialis anterior (TA) muscles. The TA muscles were then harvested for radiologic, histologic, and immunohistology examinations to determine the formation of bone and the expression of CGRP. Fibro/adipogenic progenitors (FAPs) were isolated and cultured. CGRP protein was added into the medium and then detected for chondrogenic markers. The callus formed following SVC injection and SCI successfully, with much more formed in the group with SCI, as well as an increased level of CGRP. Similarly, the injection of CGRP directly was able to induce the formation of bone-like tissues in vivo. And, the additional CGRP protein was able to induce chondrogenic differentiation as shown in RT-PCT and immunofluorescence, in a dose-dependent manner. CGRP was able to induce chondrogenic differentiation of FAPs, which may be an important part of Neurological heterotopic ossification developing.