Anti‐Inflammatory/Tissue Repair Macrophages Enhance the Cartilage‐Forming Capacity of Human Bone Marrow‐Derived Mesenchymal Stromal Cells

Abstract

Macrophages are key players in healing processes. However, little is known on their capacity to modulate the differentiation potential of mesenchymal stem/stromal cells (MSC). Here we investigated whether macrophages (Mf) with, respectively, pro-inflammatory and tissue-remodeling traits differentially modulate chondrogenesis of bone marrow derived-MSC (BM-MSC). We demonstrated that coculture in collagen scaffolds of BM-MSC with Mf derived from monocytes polarized with M-CSF (M-Mf), but not with GM-CSF (GM-Mf) resulted in significantly higher glycosaminoglycan (GAG) content than what would be expected from an equal number of BM-MSC alone (defined as chondro-induction). Moreover, type II collagen was expressed at significantly higher levels in BM-MSC/M-Mf as compared to BM-MSC/GM-Mf constructs, while type X collagen expression was unaffected. In order to understand the possible cellular mechanism accounting for chondro-induction, developing monoculture and coculture tissues were digested and the properties of the isolated BM-MSC analysed. We observed that as compared to monocultures, in coculture with M-Mf, BM-MSC decreased less markedly in number and exhibited higher clonogenic and chondrogenic capacity. Despite their chondro-inductive effect in vitro, M-Mf did not modulate the cartilage tissue maturation in subcutaneous pockets of nude mice, as evidenced by similar accumulation of type X collagen and calcified tissue. Our results demonstrate that coculture of BM-MSC with M-Mf results in synergistic cartilage tissue formation in vitro. Such effect seems to result from the survival of BM-MSC with high chondrogenic capacity. Studies in an orthotopic in vivo model are necessary to assess the clinical relevance of our findings in the context of cartilage repair.

Mesenchymal stromal cells’ role in tumor microenvironment: involvement of signaling pathways

“…Notably, MSC secretome screening revealed numerous growth factors that potentially contribute to tissue repair, such as ( i ) vascular endothelial growth factor (VEGF), which has angiogenic abilities and triggers endothelial differentiation in MSCs through VEGFR-2/Sox18 29 and Rho/myocardin-related transcription factor-dependent mechanisms, thereby promoting blood vessel repair 30,31 ; ( ii ) hepatocyte growth factor (HGF) that may play a role in MSC regenerative effects on the liver, as it promotes the differentiation and proliferation of hepatic-like cells and induces MSC-associated cytoprotective effects on hepatocytes in vivo 32-34 ; ( iii ) transforming growth factor-beta (TGF-β), whose involvement was reported in MSC-mediated heart repair, where it stimulated the differentiation of cardiomyocytes and promoted angiogenesis 35 ; ( iv ) angiopoietin-1, another pro-angiogenic factor involved in MSC-mediated improvement of cardiac function (36) and skin damage 37 ; ( v ) epidermal growth factor (EGF) that mediates MSC-associated protection of podocytes from high glucose-induced apoptosis 38 ; ( vi ) platelet-derived growth factor (PDGF), whose release by MSCs was reported to play a role in cardiac healing after myocardial injury by exerting a pro-migratory effect on resident cardiac stem cells 39 ; ( vii ) granulocyte-colony stimulating factor (G-CSF), whose release by MSCs is triggered by co-cultures with counter-inflammatory or tissue repair macrophages, enhanced by the MSC cartilage-forming capacity 40 ; and ( viii ) fibroblast growth factor (FGF), and cytoprotective factors that partly account for the therapeutic effects of MSCs in lung diseases 41 . Numerous other soluble factors are released by MSCs and contribute to the properties of these cells, including stem cell factor, MCP-3, CXCL8, CXCL9, CXCL16, CCL20, CCL25, IL-6, and IL-12 42-45 .…”

Extrinsic and Intrinsic Mechanisms by Which Mesenchymal Stem Cells Suppress the Immune System

“…80 Also, BM-MSCs treated with pro-inflammatory macrophages lead to an increase in GAG expression. 81 …”

Processing Volumes and Therapeutic Cellular Doses of Point of Care Bone Marrow Concentrates

“…In addition to neutrophils, cells from the mononuclear phagocyte system applied within BMC (mainly monocytes and macrophages) have also been reported to possess remarkable functions in tissue repair and regeneration depending on the environmental stimuli they receive [30] . Monocytes are naturally recruited at tissue repair sites two to three days after injury and rapidly differentiate to phagocytes which, similarly to the above mentioned endogenous pro-regenerative macrophages, might help to dampen inflammation and stimulate connective tissue synthesis [31] . Furthermore, mononuclear cells (mainly monocytes and leukocytes) have also been described to facilitate MSC chondrogenic differentiation as well as being able to give rise, in hypoxic conditions as those found in sites of inflammation, to a heterogeneous cell population expressing MSC-like phenotype with potential participation in the observed clinical results after BMC administration [32] .…”