Regulation of sphingosine 1-phosphate (S1P) signaling for therapeutic arteriogenesis and tissue engineering

The development of effective strategies to stimulate neovascularization and to develop sustainable microvascular networks is a critically important clinical need with the potential to treat a wide variety of disease pathologies and to enhance overall healing outcomes. While current approaches to promote neovascularization of ischemic tissues have focused primarily on inducing angiogenesis, the sprouting of new capillaries from pre-existing vessels, this work focuses on the therapeutic induction of arteriogenesis, the process by which existing arterioles structurally remodel and enlarge, and/or new arterioles form from either new or existing capillaries.;Sphingosine 1-phosphate (S1P) and S1P receptors play a critical role in vascular development, signaling to both types of vascular cells: endothelial cells (ECs) and smooth muscle cells (SMCs). Exogenous delivery of S1P has been shown to enhance both proliferation and migration of ECs and SMCs via signaling through a family of G protein-coupled receptors (S1P1, S1P2, S1P3). However, the role of S1P receptor-specific signaling in network-level microvascular remodeling in adult tissues has yet to be elucidated.;The objective of this project was to investigate the fundamental mechanisms (S1P receptor-specific activation) by which sustained release of S1P stimulates microvascular growth and remodeling. Specifically, these studies aimed to investigate the effects of S1P receptor-selective activation in stimulating SMC proliferation, lumenal expansion of microvessels, and in enhancing functional length density of SMC-invested microvessels. S1P receptor-targeted compounds were encapsulated in high molecular weight (71 kDa) methyl ester-capped 50:50 poly(lactic-co-glycolic acid) (PLAGA) and delivered to the dorsal skinfold window chamber model of male C57BL/6 mice. The effects of local sustained release of these compounds, specifically changes in functional length density, arteriolar and venular diameter expansion, and the proliferation of SMA+ cells, were evaluated after 3 and 7 days. The sustained release of S1P promoted lumenal expansion of arterioles and venules by stimulating mural cell (pericytes and SMCs) proliferation. Because S1P1 and S1P 3 receptors are coupled to Gi proteins and are known to stimulate cell proliferation and migration, we hypothesized that selectively activating S1P1 and S1P3 would significantly enhance smooth muscle cell proliferation, resulting in increased arteriolar diameter expansion and functional length density. Indeed, the stimulation of both S1P1 and S1P3 (via delivery of agonist FTY720) acted synergistically to enhance arteriogenesis via an increase in functional length density and arteriolar and venular diameters. In contrast, selective inhibition of S1P 3 (via delivery of antagonist VPC01091) resulted in a significant reduction in length density and diameter expansion, as well decreased numbers of SMA+ vessels. The sustained release of S1P+JTE013 (S1P2 antagonist) significantly increased the diameter of arterioles compared to S1P treatment alone, and with no statistical difference to the robust effects of FTY720 treatment. On the other hand, the delivery of S1P+VPC44116 (S1P1, S1P3 antagonist) significantly reduced FTY720-stimulated increases in functional length density and diameter, as a result of selective inhibition of S1P1 and S1P3.;Taken together, these results demonstrate the effectiveness of S1P 1 and S1P3 receptor selective agonists (such as FTY720) in enhancing vascular growth, which supports their potential use for therapeutic stimulation of arteriogenesis.