VEGF‐R blockade causes endothelial cell apoptosis, expansion of surviving CD34⁺precursor cells and transdifferentiation to smooth muscle‐like and neuronal‐like cells

Abstract

Severe pulmonary hypertension (PH) is characterized by complex precapillary arteriolar lesions, which contain phenotypically altered smooth muscle (SM) and endothelial cells (EC). We have demonstrated that VEGF receptor blockade by SU5416 {3-[(2,4-dimethylpyrrol-5-yl)methylidenyl]-indolin 2-one} in combination with chronic hypoxia causes severe angioproliferative PH associated with arterial occlusion in rats. We postulate that endothelial-mesenchymal transdifferentiation can take place in the occlusive lesions and that endothelium-derived mesenchymal cells can further differentiate toward a SM phenotype. To examine this hypothesis, we incubated human pulmonary microvascular endothelial cells (HPMVEC) with SU5416 and analyzed these cells utilizing quantitative-PCR, immunofluorescent staining and flow cytometry analysis. In vitro studies in HPMVEC demonstrated that SU5416 suppressed PGI2S gene expression while potently inducing COX-2, VEGF, and TGF-beta1 expression; and caused transdifferentiation of mature vascular endothelial cells (defined by Dil-ac-LDL, Lectin and Factor VIII) to SM-like (as defined by expression of alpha-SM actin) "transitional" cells, coexpressing both endothelial and SM markers. SU5416 expanded the number of CD34 and/or c-kit positive cells and caused transdifferentiation of CD34 positive cells but not negative cells. In conclusion, our data show that SU5416 generated a selection pressure that killed some EC and expanded progenitor-like cells to transdifferentiate to SM-like and neuronal-like cells.

Inhibition of Thrombin Receptor Signaling on α-Smooth Muscle Actin + CD34 + Progenitors Leads to Repair After Murine Immune Vascular Injury

“…34 Although at their peak these cells numbered no more than 30 000/mL in the circulation, these were the cells that were recruited to the luminal aspect of the allograft and that accumulated in the expanding neointima. The coexpression of ␣-SMA with TF and endothelial proteins, such as CD31, P-selectin, and E-selectin, in the neointima has been previously documented by us 10 and by other groups working in IH 35 with the luminal cells described as pseudoendothelial by some. 36 These distinct CD45 ϩ ␣-SMA ϩ cells were only found circulating after allogeneic transplantation and not syngeneic transplantation, suggesting that the inflammatory environment generated by the ongoing alloresponse was responsible.…”

Genomic assessment of a multikinase inhibitor, sorafenib, in a rodent model of pulmonary hypertension

“…A recent follow-up study of exposure of human pulmonary microvascular ECs to hypoxia/SU-5416 provided additional insights into the pathophysiology of PH in this model (46,47). Cells expressing CD34 and c-kit constituted increasing propor- Fig.…”

Transforming growth factor-beta 1 (tgf-β1) induces angiogenesis through vascular endothelial growth factor (vegf)-mediated apoptosis

“…These findings are seemingly in contrast with the well-established concept that VEGF/flk-1 signaling is required for endothelial cell survival in vitro and in vivo (Gerber et al, 1998a;Gerber et al, 1998b;Lee et al, 2007;Sweeney et al, 2002). However, several reports have shown that inhibition of VEGF -flk-1 signaling by antibodies or chemical inhibitors of the receptor does not cause rapid apoptosis of cultured endothelial cells in the absence of a pro-apoptotic stimulus (Geng et al, 2001;Lu et al, 2005;Sakao et al, 2007). The genetic deficiency of VEGF in cultured endothelial cells results in apoptosis only after 72 h incubation in serum-free medium, a pro-apoptotic culture condition (Gerber et al, 1998a;Gerber et al, 1998b;Lee et al, 2007).…”