The neuropeptide calcitonin gene-related peptide alpha is essential for bone healing

Abstract

Background Impaired fracture healing represents an ongoing clinical challenge, as treatment options remain limited. Calcitonin gene-related peptide (CGRP), a neuropeptide targeted by emerging anti-migraine drugs, is also expressed in sensory nerve fibres innervating bone tissue. Method Bone healing following a femoral osteotomy stabilized with an external fixator was analysed over 21 days in αCGRP-deficient and WT mice. Bone regeneration was evaluated by serum analysis, µCT analysis, histomorphometry and genome-wide expression analysis. Bone-marrow-derived osteoblasts and osteoclasts, as well as the CGRP antagonist olcegepant were employed for mechanistic studies. Findings WT mice with a femoral fracture display increased CGRP serum levels. αCGRP mRNA expression after skeletal injury is exclusively induced in callus tissue, but not in other organs. On protein level, CGRP and its receptor, calcitonin receptor-like receptor (CRLR) complexing with RAMP1, are differentially expressed in the callus during bone regeneration. On the other hand, αCGRP-deficient mice display profoundly impaired bone regeneration characterised by a striking reduction in the number of bone-forming osteoblasts and a high rate of incomplete callus bridging and non-union. As assessed by genome-wide expression analysis, CGRP induces the expression of specific genes linked to ossification, bone remodeling and adipogenesis. This suggests that CGRP receptor-dependent PPARγ signaling plays a central role in fracture healing. Interpretation This study demonstrates an essential role of αCGRP in orchestrating callus formation and identifies CGRP receptor agonism as a potential approach to stimulate bone regeneration. Moreover, as novel agents blocking CGRP or its receptor CRLR are currently introduced clinically for the treatment of migraine disorders, their potential negative impact on bone regeneration warrants clinical investigation. Funding This work was funded by grants from the Else-Kröner-Fresenius-Stiftung (EKFS), the Deutsche Forschungsgemeinschaft (DFG), and the Berlin Institute of Health (BIH).

CGRP Regulates the Age-Related Switch Between Osteoblast and Adipocyte Differentiation

“…As shown in Figure 1B , CGRP levels were lower in aged mice than in young mice. Given the vital role of CGRP in bone metabolism ( Irie et al, 2002 ; Schinke et al, 2004 ; Appelt et al, 2020 ) and that CGRP has been reported to stimulate the proliferation and osteogenic differentiation of rat-derived BMSCs ( Liang et al, 2015 ), we subsequently hypothesized that CGRP may be involved in regulating BMSC functions during the aging process in mice.…”

“…CGRP is a 37-residue neuropeptide primarily expressed in the central and peripheral nervous systems (Emeson et al, 1989(Emeson et al, , 1992. That CGRP plays a vital role in bone metabolism is supported by evidence showing that the lack of CGRP results in reduced bone formation and impaired bone regeneration in mice (Schinke et al, 2004;Appelt et al, 2020). To assess the expression of Calca (encoding α-CGRP) in bone tissue during aging, we conducted RT-qPCR analysis on total RNA extracted from the bone tissue of mice at 3, 6, 9, 12, 15, 18, 21, and 24 months of age (n = 5 per age group).…”

No pain, no gain: Will migraine therapies increase bone loss and impair fracture healing?

“…Finally, to determine whether the differentially regulated genes observed in fracture repair were altered due to the interaction of aCGRP with its receptor, CRLR, bone marrow cells were treated with recombinant aCGRP or olcegepant (CRLR antagonist), and many of the genes which were identified in genome wide analyses were significantly increased with aCGRP treatment and decreased with olcegepant treatment. Overall, the findings of Appelt, et al [1] compellingly demonstrate the important role of secreted aCGRP in fracture repair.…”

“…Over time, the meaning of this phrase has adapted À so too has our understanding of biology and medicine. In this issue of EBioMedicine, Appelt and colleagues [1] demonstrated that a neuropeptide, calcitonin gene-related peptide (CGRP), which is known to be involved in the pathogenesis of migraines (pain), is essential in fracture repair (gain). This begs the question whether the converse is also true.…”

“…With regard to fracture and CGRP, as recently summarized [6], several investigators have shown CGRP expression at the fracture site and reported correlative findings. Prior to the studies reported in this issue of EBioMedicine by Appelt et al [1] perhaps the best evidence Contents lists available at ScienceDirect EBioMedicine journal homepage: www.elsevier.com/locate/ebiom for a role of CGRP in fracture repair was a report that intraperitoneal injection with CGRP inhibitor significantly impaired fracture healing in a rat model, as demonstrated by a significant reduction in mineralized callus with an increase in cartilage [9]. In the current study, Appelt et al [1] first demonstrate that CGRP and its receptor, calcitonin receptor-like receptor (CRLR), are expressed during bone regeneration.…”