Lysophosphatidic acid suppresses endothelial cell CD36 expression and promotes angiogenesis via a PKD-1–dependent signaling pathway

Abstract

In pathologic settings including retinal ischemia and malignant tumors, robust angiogenesis occurs despite the presence in the microenvironment of antiangiogenic proteins containing thrombospondin structural homology (TSR) domains. We hypothesized that antiangiogenesis mediated by TSR-containing proteins could be blunted by localized downregulation of their cognate receptor on microvascular endothelial cells (MVECs), CD36. Through screening a panel of endothelial cell agonists, we found that lysophosphatidic acid (LPA) dramatically down-regulated CD36 surface expression on primary MVECs. LPA is a lipid-signaling mediator known to have proangiogenic activity, but the mechanisms are largely unknown. We observed that LPA caused CD36 down-regulation in a doseand time-dependent manner and was long lasting. Down IntroductionAngiogenesis, the growth of new blood vessels from existing microvasculature, is essential for organ growth and tissue repair. Under normal conditions, angiogenesis is tightly regulated by a dynamic balance between proangiogenic and antiangiogenic signaling pathways. Loss of balance between these pathways can occur as a consequence of many diseases and can lead to either inadequate or excess angiogenesis. The latter contributes to tumor progression, diabetic retinopathy, macular degeneration, and rheumatoid arthritis. 1,2 We have been interested in an endogenous antiangiogenic pathway triggered by proteins containing a conserved domain first identified in the platelet and matrix glycoprotein thrombospondin-1 (TSP-1). 3,4 This domain, called the TSP type 1 repeat (TSR), is also found in TSP-2, 5 in vasculostatin, 6,7 and in other antiangiogenic proteins and has been shown to exert its activity by binding to a specific receptor, CD36, expressed on microvascular endothelial cells (MVECs). 8 The antiangiogenic activities of TSP-1 and -2 and vasculostatin are absent or significantly reduced in cd36 knockout mice. [4][5][6] CD36 is a widely expressed cell surface glycoprotein with 2 major classes of ligand in addition to TSR-containing proteins. 9,10 On adipocytes, myocytes, specialized neurosensory cells, and gut epithelium, CD36 functions as a transporter and/or sensor of free fatty acids. On phagocytic cells and platelets, CD36 functions in the innate immune response as a scavenger receptor, facilitating binding and internalization of numerous endogenous and exogenous danger signals, including oxidized LDL. In these contexts CD36 has been shown to play a role in chronic inflammation, atherosclerosis, arterial thrombosis, and insulin resistance. [11][12][13] The mechanisms by which CD36 inhibits angiogenesis are based on its ability to transduce signals in MVECs that "turn off" proangiogenic responses and "turn on" antiangiogenic responses in newly formed microvasculature. TSR-CD36 interactions on MVECs inhibit cell migration and tube formation and induce apoptosis by recruiting and activating specific SRC-family and MAPKs, including Fyn, p38, and JNK, directly activating caspases, and inducing expres...

Lysophosphatidic Acid and Sphingosine-1-Phosphate: A Concise Review of Biological Function and Applications for Tissue Engineering

“…LPA also induces SMC dedifferentiation 50 and may lower expression of CD36 by endothelial cells. 51,52 Consistent with its role in Rho-ROCK signaling, LPA sensitizes murine aortic endothelial cells to oscillatory shear…”

Thrombospondin-1 modulates VEGF signaling via CD36 by recruiting SHP-1 to VEGFR2 complex in microvascular endothelial cells

“…Fluorescence images were taken from 4 randomly chosen areas and tube formation analyzed by ImageJ software (National Institutes of Health), as previously described. 6 In vivo VEGFR2 phosphorylation assay C57BL/6 wild-type and cd36 null mice 25 were anesthetized with ketamine (100 mg/kg) and xylazine (10 mg/kg) and then injected with 1 mg VEGF in 100 mL saline or saline alone via the jugular vein. Lung tissue was harvested 5 minutes after injection, minced in liquid nitrogen, and then lysed in 1 mL buffer, as for immunoprecipitation, for 5 mintues.…”

“…It functions as a negative regulator of angiogenesis 1,[3][4][5] and therefore plays a role in tumor growth, inflammation, wound healing, and other pathological processes requiring neovascularization. 6,7 Binding of TSP-1 or TSR proteins to CD36 inhibits growth factor-induced proangiogenic signals that mediate endothelial cell proliferation, migration, and tube formation, and instead generates antiangiogenic signals that lead to apoptosis. 4,8 In vivo, CD36 null mice exhibit an increase in vessel density in the brain, an organ in which early angiogenesis is modulated by high levels of TSP-1, increased tumor angiogenesis in subcutaneously injected TSP-expressing tumor cells, and a lack of response to antiangiogenic effect of TSP-1 in in vivo angiogenesis assays.…”

Lysophosphatidic Acid Protects Human Mesenchymal Stromal Cells from Differentiation-Dependent Vulnerability to Apoptosis

“…These data have significant implications for cell-based therapies for tissue repair, with potential applications for two unique treatment strategies. In one case, LPA, which has mitogenic effects on endothelial cells, 49 could be used to promote survival and VEGF secretion in undifferentiated MSC to further enhance angiogenesis for a natural wound healing response. This approach may markedly enhance the efficacy of MSC when implanted to drive neovascularization for use in advanced vascular disease, slow healing wounds, or promoting collateralization during bone repair.…”