Heme Oxygenase Activity Modulates Vascular Endothelial Growth Factor Synthesis in Vascular Smooth Muscle Cells

Abstract

Hypoxia, cytokines, and nitric oxide (NO) stimulate the generation of vascular endothelial growth factor (VEGF) and induce heme oxygenase-1 (HO-1) expression in vascular tissue. HO-1 degrades heme to carbon monoxide (CO), iron, and biliverdin, the latter being reduced to bilirubin by biliverdin reductase. In the present study, we investigated the role of HO-1 in the modulation of VEGF synthesis in rat vascular smooth muscle cells (VSMC). In VSMC stimulated with cytokines, inhibition of NO production significantly, but not completely, reduced VEGF release. In contrast, inhibition of HO activity by tin protoporphyrin IX (SnPPIX) totally prevented cytokine-induced increase in VEGF, despite an augmented synthesis of intracellular NO. Stimulation of HO-1 activity by hemin enhanced VEGF production; this effect was abrogated by blockade of the HO pathway. Similarly, VEGF synthesis induced by hypoxia was down-regulated by SnPPIX, but not by inhibitors of NO synthase. To elucidate further a direct involvement of HO-1 in the observed effects, we generated transfected cells that overexpressed the HO-1 gene. Notably, these cells synthesized significantly more VEGF protein than cells transfected with a control gene. Among the products of HO-1, biliverdin and bilirubin showed no effect, whereas iron ions inhibited VEGF synthesis. Exposure of cells to 1% CO resulted in a marked accumulation of VEGF (20-fold increase) over the basal level. Our data indicate that HO-1 activity influences the generation of VEGF in VSMC in both normoxic and hypoxic conditions. As CO and iron, respectively the inducer and the inhibitor of VEGF synthesis, are concomitantly produced during the degradation of heme, these data indicate that HO by-products may differentially modulate VEGF production.

Increased levels of plasma haemoxygenase-1 in prostate cancer

“…4,6,7 HO-1 may also be important in cardiovascular disease and in apoptosis, 5,9,19,20 and there is also evidence that HO-1 may be linked experimentally to angiogenesis via VEGF. [10][11][12]18,21 It is therefore notable that we report good correlations between HO-1 and VEGF (r40.52) (although we acknowledge the possibility of small number error) in the absence of cancer, but that this correlation in markedly weaker in the presence of cancer (r ¼ 0.12). The reasons for this are unclear although it is tempting to speculate a linked role for HO-1 and VEGF in physiology that is uncoupled in cancer.…”

“…[5][6][7] Other reports suggest roles for HO-1 in defence from viraemia, from oxidant stress, in inflammation and in cardiovascular disease. 8,9 Notably, there are several reports linking HO-1 with cancer, possibly via interactions with VEGF, 10,11 suggesting a role in angiogenesis. 12 Increased expression of HO-1 in prostate tissue and a prostate cancer cell line have been reported 13,14 but there are no reports of plasma HO-1 in this disease.…”

Potential role of heme oxygenase-1 in the progression of rat adjuvant arthritis

“…Thus, this enzyme has been shown to induce VEGF in cultured endothelial cells by an increased transcription likely dependent on CO generated by HO-1 activity. 53 In adjuvant arthritis, local induction of TNFa, COX-2 and PGE 2 , iNOS and NO as well as HO-1 preceded the elevation in VEGF. All these mediators may cooperate to induce VEGF during the established phase of this model.…”

Atorvastatin prevents hypoxia-induced inhibition of endothelial nitric oxide synthase expression but does not affect heme oxygenase-1 in human microvascular endothelial cells

“…Western blotting for HO-1 was done as described previously [8]. Activity of HO enzyme was measured by bilirubin generation as described previously [9].…”