Abstract
BackgroundHypoxia is a major driving force in vascularization and vascular remodeling. Pharmacological inhibition of prolyl hydroxylases (PHDs) leads to an oxygen-independent and long-lasting activation of hypoxia-inducible factors (HIFs). Whereas effects of HIF-stabilization on transcriptional responses have been thoroughly investigated in endothelial cells, the molecular details of cytoskeletal changes elicited by PHD-inhibition remain largely unknown. To investigate this important aspect of PHD-inhibition, we used a spheroid-on-matrix cell culture model.ResultsMicrovascular endothelial cells (glEND.2) were organized into spheroids. Migration of cells from the spheroids was quantified and analyzed by immunocytochemistry. The PHD inhibitor dimethyloxalyl glycine (DMOG) induced F-actin stress fiber formation in migrating cells, but only weakly affected microvascular endothelial cells firmly attached in a monolayer. Compared to control spheroids, the residual spheroids were larger upon PHD inhibition and contained more cells with tight VE-cadherin positive cell-cell contacts. Morphological alterations were dependent on stabilization of HIF-1α and not HIF-2α as shown in cells with stable knockdown of HIF-α isoforms. DMOG-treated endothelial cells exhibited a reduction of immunoreactive Rac-1 at the migrating front, concomitant with a diminished Rac-1 activity, whereas total Rac-1 protein remained unchanged. Two chemically distinct Rac-1 inhibitors mimicked the effects of DMOG in terms of F-actin fiber formation and orientation, as well as stabilization of residual spheroids. Furthermore, phosphorylation of p21-activated kinase PAK downstream of Rac-1 was reduced by DMOG in a HIF-1α-dependent manner. Stabilization of cell-cell contacts associated with decreased Rac-1 activity was also confirmed in human umbilical vein endothelial cells.ConclusionsOur data demonstrates that PHD inhibition induces HIF-1α-dependent cytoskeletal remodeling in endothelial cells, which is mediated essentially by a reduction in Rac-1 signaling.
Highlights
Hypoxia is a major driving force in vascularization and vascular remodeling [1]
Using stable Hypoxia-inducible transcription factor (HIF)-1α- or HIF-2α-deficient glomerular endothelial cells, we demonstrate that cytoskeletal alterations by Prolyl hydroxylase domain enzyme (PHD) inhibition are HIF-1α dependent
dimethyloxalyl glycine (DMOG) modulates endothelial migration and cell-cell contacts within spheroids Murine glomerular microvascular endothelial cells were organized into spheroids overnight and were plated on glass plates coated with collagen IV in the presence or absence of the PHD inhibitor DMOG, which leads to the stabilization of HIF-α transcription factors
Summary
Hypoxia is a major driving force in vascularization and vascular remodeling [1]. Many of the genes involved in the regulation of vascular homeostasis are direct or indirect targets of hypoxia-induced transcription factors (HIFs) known as crucial mediators of the cellular response to hypoxia [2,3]. Angiogenesis as a response to activation of HIF transcription factors has been investigated in many studies related to tumor vascularization (for review see [1,8,9]) and in context of atherosclerosis [10], or wound healing [11]. Apart from HIF-dependent transcriptional regulation of angiogenic factors, molecular effects of PHD inhibition on the vasculature have not been studied extensively. Whereas effects of HIF-stabilization on transcriptional responses have been thoroughly investigated in endothelial cells, the molecular details of cytoskeletal changes elicited by PHD-inhibition remain largely unknown. To investigate this important aspect of PHD-inhibition, we used a spheroid-on-matrix cell culture model
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