Apoptotic mesenchymal stromal cells support osteoclastogenesis while inhibiting multinucleated giant cells formation in vitro

Paul Humbert,Pierre Layrolle,Yohann Couté,Meadhbh Á Brennan,Frédéric Blanchard,Bénédicte Brulin,Régis Brion,Céline Charrier,Julien De Lima,Annie Adrait,Valérie Trichet

doi:10.1038/s41598-021-91258-4

Abstract

In bone regeneration induced by the combination of mesenchymal stromal cells (MSCs) and calcium-phosphate (CaP) materials, osteoclasts emerge as a pivotal cell linking inflammation and bone formation. Favorable outcomes are observed despite short-term engraftments of implanted MSCs, highlighting their major paracrine function and the possible implication of cell death in modulating their secretions. In this work, we focused on the communication from MSCs towards osteoclasts-like cells in vitro. MSCs seeded on a CaP biomaterial or undergoing induced apoptosis produced a conditioned media favoring the development of osteoclasts from human CD14+ monocytes. On the contrary, MSCs’ apoptotic secretion inhibited the development of inflammatory multinucleated giant cells formed after IL-4 stimulation. Components of MSCs’ secretome before and after apoptotic stress were compared using mass spectrometry-based quantitative proteomics and a complementary immunoassay for major cytokines. CXCR-1 and CXCR-2 ligands, primarily IL-8/CXCL-8 but also the growth-regulated proteins CXCL-1, -2 or -3, were suggested as the major players of MSCs’ pro-osteoclastic effect. These findings support the hypothesis that osteoclasts are key players in bone regeneration and suggest that apoptosis plays an important role in MSCs’ effectiveness.

Highlights

In bone regeneration induced by the combination of mesenchymal stromal cells (MSCs) and calciumphosphate (CaP) materials, osteoclasts emerge as a pivotal cell linking inflammation and bone formation
Conditioned media (CM) from MSC/biphasic calcium phosphate (BCP) cultures had an even stronger effect leading to the formation of huge and strongly Target ACP5 (TRAP)+ multinucleated cells and this effect was consistent with three different MSC donors (Fig. 1B)
CM obtained on BCP granules without cells did not have any effect on osteoclasts either, confirming that MSC-secreted factors other than RANK-L were responsible for the phenotypical changes in osteoclasts

Summary

Introduction

In bone regeneration induced by the combination of mesenchymal stromal cells (MSCs) and calciumphosphate (CaP) materials, osteoclasts emerge as a pivotal cell linking inflammation and bone formation. The combination of culture-expanded autologous mesenchymal stromal cells (MSCs) from bone marrow and calcium-phosphate (CaP) materials has been increasingly studied for bone regeneration therapies. It has proven efficacy in preclinical m odels[1], in both ectopic and orthotopic sites, and in clinical trials for the treatment of non-unions[2,3] as well as maxilla-facial d efects[4]. A better understanding of the exact mechanism of osteoinduction by MSC-CaP therapies is essential to rationally design future cell-free approaches for bone regeneration and improve further patients care Both the biomaterial properties (including porosity, surface structure, chemical composition)[7] and the cells’ characteristics (including tissue of origin, passage, dose)[8,9] are important in modulating the host response and directing the outcome of implantation. Apoptosis itself is a source of immunomodulatory signals that could be involved in MSC-based t herapies[22]

Methods

Results

Discussion

Conclusion