The transcription factor HoxB5 stimulates vascular remodelling in a cytokine-dependent manner.

AIMS: Proper blood vessel formation is essential in health and is often dysregulated in ischaemic diseases. Therefore, regulatory mechanisms that control angiogenesis and arteriogenesis are required to improve treatment of ischaemic diseases. The aim of this study was to investigate the role of homeobox transcription factor HoxB5 overexpression during revascularization in ischaemic disease. METHODS AND RESULTS: To assess the effect of HoxB5 overexpression on blood vessel formation in vivo, we subjected C57BL/6 mice to femoral artery ligation with local intramuscular injection of HoxB5 or green fluorescent protein control adenoviral vectors. Laser Doppler perfusion imaging revealed that HoxB5 enhanced perfusion restoration in mice and immunohistochemistry analysis revealed increased capillary density. To identify a potential mechanism of HoxB5 in blood vessel formation, a 'proteome-profiler' array was performed. HoxB5 overexpression in endothelial cells increased the expression of pro-inflammatory molecules such as monocyte chemotactic protein-1 (MCP-1) and interleukin-6 (IL-6) in vitro and in vivo. Functionally, HoxB5 enhanced monocyte as well as endothelial cell migration in vitro and increased leucocyte infiltration into ischaemic tissues. HoxB5-induced migration of monocytes was antagonized by the presence of an MCP-1 blocking antibody. CONCLUSIONS: Our data suggest that overexpression of HoxB5 enhances blood vessel perfusion in vivo by up-regulation of MCP-1 and IL-6 as well as in enhanced leucocyte infiltration and blood vessel remodelling.

Inflammatory neovascularization during graft-versus-host disease is regulated by αv integrin and miR-100.

Acute graft-versus-host disease (GvHD) is a complex process involving endothelial damage and neovascularization. Better understanding of the pathophysiology of neovascularization during GvHD could help to target this process while leaving T-cell function intact. Under ischemic conditions, neovascularization is regulated by different micro RNAs (miRs), which potentially play a role in inflamed hypoxic GvHD target organs. We observed strong neovascularization in the murine inflamed intestinal tract (IT) during GvHD. Positron emission tomography imaging demonstrated abundant αvß3 integrin expression within intestinal neovascularization areas. To interfere with neovascularization, we targeted αv integrin-expressing endothelial cells, which blocked their accumulation in the IT and reduced GvHD severity independent of immune reconstitution and graft-versus-tumor effects. Additionally, enhanced neovascularization and αv integrin expression correlated with GvHD severity in humans. Expression analysis of miRs in the inflamed IT of mice developing GvHD identified miR-100 as significantly downregulated. Inactivation of miR-100 enhanced GvHD indicating a protective role for miR-100 via blocking inflammatory neovascularization. Our data from the mouse model and patients indicate that inflammatory neovascularization is a central event during intestinal GvHD that can be inhibited by targeting αv integrin. We identify negative regulation of GvHD-related neovascularization by miR-100, which indicates common pathomechanistic features of GvHD and ischemia.

MicroRNA-100 regulates neovascularization by suppression of mammalian target of rapamycin in endothelial and vascular smooth muscle cells.

BACKGROUND: The adaptive growth of blood vessels is an important protective mechanism in cardiovascular disease. However, the underlying regulatory mechanisms of this process are only partly understood. Recently, small endogenous RNAs (microRNAs [miRNAs]) were found to play an important role in embryonic and postnatal vascular development. Here, we used miRNA transcriptome analysis after induction of hind-limb ischemia in mice to screen for miRNAs involved in adaptive blood vessel growth following arterial occlusion. METHODS AND RESULTS: Using miRNA arrays, we explored the miRNA expression profile during adaptive neovascularization. We describe specific changes in miRNA expression patterns and show that miRNA-100 is significantly downregulated after induction of hind-limb ischemia in mice. Our data demonstrate that miR-100 modulates proliferation, tube formation, and sprouting activity of endothelial cells and migration of vascular smooth muscle cells and functions as an endogenous repressor of the serine/threonine protein kinase mammalian target of rapamycin (mTOR). Whereas miR-100 inhibition increased mTOR levels in endothelial cells, overexpression of miR-100 reduced mTOR expression and consequently attenuated cellular proliferation. Supporting this notion, overexpression of an mTOR construct lacking the miRNA binding site rescued the inhibitory effect of miR-100 on cell proliferation. Accordingly, miR-100 inhibition by specific antagomirs in vivo stimulated angiogenesis and resulted in functional improvement of perfusion after femoral artery occlusion in mice. In contrast, treatment with the mTOR inhibitor rapamycin had the opposite effect. CONCLUSIONS: Our data demonstrate that miR-100 has an antiangiogenic function and represses mTOR signaling in endothelial and vascular smooth muscle cells. Inhibition of miR-100 could be a novel approach for the modulation of blood vessel growth and other mTOR-dependent processes.