Mesenchymal Stem Cell Paracrine Activity Is Modulated by Platelet Lysate: Induction of an Inflammatory Response and Secretion of Factors Maintaining Macrophages in a Proinflammatory Phenotype

Abstract

Wound healing is achieved through distinct programmed phases: hemostasis, inflammation, mesenchymal cell proliferation and migration, and tissue remodeling. At the injury site, clot formation and platelet degranulation release cytokines and growth factors and actively participating in the healing process and regulating the migration of inflammatory cells, such as neutrophils, macrophages, and lymphocytes. We previously demonstrated that, in an inflammatory environment, prostaglandin E2 (PGE2) secreted by mesenchymal stem cells (MSCs) promoted the macrophage switch from a proinflammatory to a proresolving phenotype. Using an in vitro model, we here evaluated the role carried out by the two main players of the wound healing process, the platelet degranulation content mimicked by the platelet lysate (PL) and the inflammatory stimulus, on the modulation of mouse bone-marrow-derived MSC paracrine activity. We demonstrated that, in MSCs, PL induced nuclear factor kappaB (NF-κB) activation, expression of COX-2 and mPGE synthase, and PGE2 production; in an inflammatory microenvironment, PL increased the inflammatory response and promoted the secretion of the proinflammatory cytokine IL-6. We assayed on mouse primary macrophages the paracrine activity of MSCs exposed to the different microenvironments and we observed that PL-treated MSC-conditioned medium maintained macrophages in a proinflammatory state. The involved factors were granulocyte macrophage-colony stimulating factor induced by PL in MSCs and TNF-α induced by PL-MSC-conditioned medium in macrophages. Our findings indicate that PL triggers an inflammatory response in MSCs and induces the secretion of factors maintaining macrophages in a proinflammatory state thus enhancing the initial inflammatory response to the injury, a key element in the activation of wound healing.

Paracrine effects of mesenchymal stem cells on the activation of keratocytes

“…All of these factors are known to increase during corneal wound healing 22. This is in agreement with several papers describing the upregulation of IL-6, IL-8, MCP-1 and RANTES (regulated on activation, normal T cell expressed and secreted)in MSCs 23. MCP-1 is a key chemokine involved in macrophage recruitment, whereas IL-6 and IL-8 play important roles in the regulation of leukocyte infiltration during the wound repair process.…”

Secreted trophic factors of mesenchymal stem cells support neurovascular and musculoskeletal therapies

“…Several studies have found that the exposure of MSCs to proinflammatory factors, sometimes for as little as a few hours, can alter the gene and protein expression of MSCs for days afterwards [52]. Factors known to be secreted or bound to MSC membranes with anti-inflammatory activities (activation of Tregs/tolerogenic dendritic cell phenotype; pro-resolving/M2 macrophage activation; inhibition or proapoptosis of T cells, B cells, NK cells, or dendritic cells; decreasing cytokine production) include: purines, bone morphogenetic proteins (BMPs, specifically BMP-4), CD274, CCL2, Connexin 43, cyclooxygenase (COX)/prostaglandin (PG), CD95/CD95 ligand, galectins, heme oxygenase-1, human leukocyte antigen-G (HLA-G), IDO/kynurenine, interleukin-6 (IL-6), leukemia inhibitory factor (LIF), NO, TGF-β, tumor necrosis factor-inducible gene-6 (TSG6), and vascular endothelial growth factor (VEGF) [53]. …”

Mesenchymal stem cells – A new hope for radiotherapy-induced tissue damage?

“…MSCs have been the focus of intensive research efforts within the field of regenerative medicine: In various animal studies, MSCs were found to migrate to lesion sites and differentiate into tissuespecific functional cells [21][22][23]; they may also create a supporting microenvironment within organ damage by the secretion of cytokines, growth factors and other paracrine molecules, in turn supporting other cell types in the regeneration of tissue lesions [24][25][26][27][28]. To date, beneficial effects of MSCs regarding tissue damage have been most widely investigated for myocardial scars, cartilage and bone injuries, pulmonary damage, skin and nerve tissue lesions [29][30][31][32].…”