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Background: Endothelial mesenchymal transition (EndMT) is a key pathological event for vasculopathy, and is one of the early features and hallmarks of systemic scleroderma (SSc). It has been well-established that hypoxia contributes to EndMT. However, little is known about the effects of EndMT induced by hypoxia on the skin microvascular remodeling of SSc, as well as the underlying mechanism. Methods: Skin biopsy was performed for SSc patients and healthy controls, and skin tissues were collected for isobaric tags for the relative and absolute quantification (iTRAQ)-based proteomics and immunohistochemical test. Human microvascular endothelial cell line-1 (HMEC-1) cultured in hypoxic or normal conditions was treated by tamoxifen or bevacizumab. The expression of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF)-a, CD31, α-smooth muscle actin (α-SMA), VE-cadherin, and fibronectin were detected at both the protein and mRNA level.Results: The iTRAQ-based proteomics indicated the significantly upregulated HIF-1 signal in the skin tissues of SSc patients. The immunohistochemical results demonstrated the significant downregulation of endothelial cell (EC) marker CD31 and the distinct positive staining of interstitial cell (IC) marker α-SMA at sites that lined the vessel lumens in skin tissues of SSc. Meanwhile, the positive staining of HIF-1α, which is a key transcription factor in response to chronic hypoxia, and VEGF-a were found to be diffusely distributed in SSc skin tissues. Consistent with these observations, HMEC-1 cells cultured under hypoxic conditions exhibited a significant decrease in CD31 and VE-cadherin expression, alongside the marked increase in the expression of α-SMA and fibronectin, as well as the distinct upregulation of HIF-1α and VEGF-a, when compared with those under normal conditions. It is noteworthy that the inhibition of HIF-1α by tamoxifen effectively downregulated the hypoxic induction of VEGF-a and α-SMA, while rescuing the hypoxic suppression of CD31. In addition, the VEGF-a inhibitor bevacizumab treatment had the same effect on the hypoxic expression of α-SMA and CD31, as a tamoxifen intervention, but did not reduce HIF-1α. Conclusion: These results suggest that the HIF-1α/VEGF signaling pathway has a critical role in mediating the effect of hypoxia-induced EndMT on the skin microvascular remodeling of SSc.

Background: Endothelial mesenchymal transition (EndMT) is a key pathological event for vasculopathy which is one of the early features and hallmarks of systemic scleroderma (SSc). It is well established that hypoxia contributes to EndMT, however, little is known about the effects of EndMT induced by hypoxia on skin microvascular remodeling of SSc,as well as the underlying mechanism.Methods: Skin biopsy was down for SSc patients and healthy controls and skin tissues were collected for iTRAQ-based proteomics and Immunohistochemical test. Human microvascular endothelial cell line (HMEC-1) cultured with hypoxic or normal conditions, treated by either tamoxifen or bevacizumab. The expression of Hypoxia inducible factor-1α (HIF-1α) ,vascular endothelial growth factor (VEGF)-a, CD31, α-smooth muscle actin (α-SMA), VE-cadherin, fibronectin were detected at both protein and mRNA level.Results : The iTRAQ-based proteomics indicated significantly up-regulated HIF-1 sigaling in the skin tissues of SSc patients. Immunohistochemical results demonstrated a significant downregulation of the endothelial cell (EC) marker CD31 and a distinct positive staining of the interstitial cell (IC) marker α-SMA at sites lining the vessel lumens in the skin tissues of SSc. Meanwhile the positive staining of HIF-1α, a key transcription factor in response to chronic hypoxia, and VEGF-a were found to be diffusely distributed in SSc skin tissue. Consistent with these observations, HMEC-1 cells cultured under hypoxic conditions exhibited a significant decrease in CD31 and VE-cadherin expression, alongside a marked increase in the expression of α-SMA and fibronectin, as well as a distinct up-regulation of HIF-1α and VEGF-a, while comparing with them under normal condition. Of note, the inhibition of HIF-1α by tamoxifen effectively down-regulated the hypoxic induction VEGF-a, α-SMA, while rescuing hypoxic suppression of CD31. In addition, a VEGF-a inhibitor bevacizumab treatment had the same effect on the hypoxic expression of α-SMA and CD31 as tamoxifen intervention, but did not reduce HIF-1α.Conclusion: These results suggest that the HIF-1α/VEGF signaling pathway has a critical role in mediating the effect of hypoxia-induced EndMT on skin microvascular remodeling of SSc.