Vascular endothelial growth factor secretion and immunosuppression are distinct potency mechanisms of human bone marrow mesenchymal stromal cells

Abstract

Mesenchymal Stromal Cells (MSCs) are investigated as cellular therapeutics for Inflammatory Bowel Diseases and associated Perianal Fistula, although consistent efficacy remains a concern. Determining host factors that modulate MSCs’ potency including their secretion of angiogenic & wound healing factors, immunosuppression and anti-inflammatory properties are important determinants of their functionality. We investigated the mechanisms that regulate the secretion of angiogenic & wound healing factors and immune suppression of human bone marrow MSCs. Secretory analysis of MSCs focusing on eighteen angiogenic & wound healing secretory molecules identified the most abundancy of Vascular Endothelial Growth Factor-A(VEGF-A). MSC viability and secretion of other angiogenic factors are not dependent on VEGF-A secretion which exclude the autocrine role of VEGF-A on MSC’s fitness. However, combination of inflammatory cytokines IFNγand TNFαreduces MSC’s VEGF-A secretion. To identify the effect of intestinal microvasculature on MSCs’ potency, coculture analysis was performed between Human Large Intestine Microvascular Endothelial Cells(HLMVECs) and human bone marrow derived MSCs. HLMVECs do not attenuate MSCs’ viability despite blocking their VEGF-A secretion. In addition, HLMVECs neither attenuate MSC’s IFNγmediated upregulation of immunosuppressive enzyme Indoleamine 2,3-dioxygenase(IDO) nor abrogate suppression of T cell proliferation despite the attenuation of VEGF-A secretion. We found that HLMVECs express copious amounts of endothelial nitric oxide synthase (eNOS) and mechanistic analysis showed that pharmacological blocking reverses HLMVEC mediated attenuation of MSC’s VEGF-A secretion. Together these results suggest that secretion of VEGF-A and immunosuppression are separable functions of MSCs which are regulated by distinct mechanisms in the host.