Developmentally inspired programming of adult human mesenchymal stromal cells toward stable chondrogenesis

Abstract

<p id="d1828297e265">The study offers a pharmacological solution to the challenging target of inducing stable chondrogenesis by human mesenchymal stromal cells (hMSCs), including protection against vascularization. Cells were reversed from the tendency to follow the default differentiation pathway, namely endochondral ossification and osteogenesis. Our findings open perspectives in articular cartilage regeneration, as well as in the establishment of hMSC-based models of cartilage development, physiology, and possibly pathology. Importantly, the results were achieved by mimicking molecular processes occurring during embryonic cartilage formation. This indicates that adult hMSCs share similarities with embryonic mesenchyme and validates the relevance to engineer developmental processes (“developmental engineering”) to control fate specification by adult stem/progenitor cell systems. </p><p class="first" id="d1828297e268">It is generally accepted that adult human bone marrow-derived mesenchymal stromal cells (hMSCs) are default committed toward osteogenesis. Even when induced to chondrogenesis, hMSCs typically form hypertrophic cartilage that undergoes endochondral ossification. Because embryonic mesenchyme is obviously competent to generate phenotypically stable cartilage, it is questioned whether there is a correspondence between mesenchymal progenitor compartments during development and in adulthood. Here we tested whether forcing specific early events of articular cartilage development can program hMSC fate toward stable chondrogenesis. Inspired by recent findings that spatial restriction of bone morphogenetic protein (BMP) signaling guides embryonic progenitors toward articular cartilage formation, we hypothesized that selective inhibition of BMP drives the phenotypic stability of hMSC-derived chondrocytes. Two BMP type I receptor-biased kinase inhibitors were screened in a microfluidic platform for their time- and dose-dependent effect on hMSC chondrogenesis. The different receptor selectivity profile of tested compounds allowed demonstration that transient blockade of both ALK2 and ALK3 receptors, while permissive to hMSC cartilage formation, is necessary and sufficient to maintain a stable chondrocyte phenotype. Remarkably, even upon compound removal, hMSCs were no longer competent to undergo hypertrophy in vitro and endochondral ossification in vivo, indicating the onset of a constitutive change. Our findings demonstrate that adult hMSCs effectively share properties of embryonic mesenchyme in the formation of transient but also of stable cartilage. This opens potential pharmacological strategies to articular cartilage regeneration and more broadly indicates the relevance of developmentally inspired protocols to control the fate of adult progenitor cell systems. </p>