Abstract 7: LPA/PKD-1-HDAC7-FoxO1 Signaling-mediated Endothelial CD36 Transcriptional Repression and Proarteriogenic Reprogramming

Abstract

Background: CD36 is a scavenger and antiangiogenic receptor that plays an important role in athero-thrombotic diseases, diabetes and cancer and contributes to obesity. Lysophosphatidic acid (LPA), a bioactive phospholipid signaling mediator, abolishes endothelial cell responses to antiangiogenic proteins containing thrombospondin type 1 homology domains by down-regulating endothelial CD36 transcription via protein kinase PKD-1 signaling. However, the precise mechanism as to how angiogenic signaling is integrated to regulate endothelial specific CD36 transcription remain unknown. Hypothesis: LPA represses CD36 transcription through PKD-1-mediated formation of a nuclear transcriptional complex in endothelial cells. Methods: Microvascular endothelial cells expressing CD36 were used for studying signaling and CD36 transcription by real time RT-qPCR, Western blotting, co-immunoprecipitation or avidin-biotin-conjugated DNA-binding assay; angiogenesis gene array was used for angiogenic gene profiling in response to LPA exposure. Spheroid-based angiogenesis assay, in vivo Matrigel assay and tumor angiogenesis model in CD36 deficiency and wild type mice were established to elucidate mechanisms of angiogenic signaling. Results: CD36 transcriptional repression involved PKD-1 signaling mediated formation of FoxO1-HDAC7 complex in the nucleus of endothelial cells. Unexpectedly, turning off CD36 transcription initiated reprogramming MVECs to express ephrin B2, a critical “molecular signature” involved in angiogenesis and arteriogenesis, and increased phosphorylation of Erk1/2, the MAP kinase important in arterial differentiation. PKD-1 signaling was also shown in tumor endothelium of Lewis lung carcinomas, along with low CD36 expression or CD36 deficiency. Angiogenic branching morphogenesis and in vivo angiogenesis were dependent on PKD-1 signaling. Conclusion: LPA/PKD1-HDAC7-FoxO1 signaling axis regulates endothelial CD36 transcription and mediates silencing of the antiangiogenic switch, resulting in proarteriogenic reprogramming. Targeting this signaling cascade could be a novel approach for cancer, diabetes, athero-thrombotic diseases and obesity.