Recent updates in experimental protocols for endothelial cells

Epigenetic down-regulation of microRNA-126 in scleroderma endothelial cells is associated with impaired responses to VEGF and defective angiogenesis

Impaired angiogenesis in scleroderma (SSc) is a critical component of SSc pathology. MicroRNA‐126 (miR‐126) is expressed in endothelial cells (MVECs) where it regulates VEGF responses by repressing the negative regulators of VEGF, including the sprouty‐related protein‐1 (SPRED1), and phosphoinositide‐3 kinase regulatory subunit 2 (PIK3R2). MVECs were isolated from SSc skin and matched subjects (n = 6). MiR‐126 expression was measured by qPCR and in situ hybridization. Matrigel‐based tube assembly was used to test angiogenesis. MiR‐126 expression was inhibited by hsa‐miR‐126 inhibitor and enhanced by hsa‐miR‐126 Mimic. Epigenetic regulation of miR‐126 expression was examined by the addition of epigenetic inhibitors (Aza and TSA) to MVECs and by bisulphite genomic sequencing of DNA methylation of the miR‐126 promoter region. MiR‐126 expression, as well as EGFL7 (miR‐126 host gene), in SSc‐MVECs and skin, was significantly down‐regulated in association with increased expression of SPRED1 and PIK3R2 and diminished response to VEGF. Inhibition of miR‐126 in NL‐MVECs resulted in reduced angiogenic capacity, whereas overexpression of miR‐126 in SSc‐MVECs resulted in enhanced tube assembly. Addition of Aza and TSA normalized miR‐126 and EGFL7 expression levels in SSc‐MVECs. Heavy methylation in miR‐126/EGFL7 gene was noted. In conclusion, these results demonstrate that the down‐regulation of miR‐126 results in impaired VEGF responses.

Slit2/Robo4 axis may contribute to endothelial cell dysfunction and angiogenesis disturbance in systemic sclerosis

OBJECTIVE

In systemic sclerosis (SSc), early microvascular injury is followed by impaired angiogenesis and peripheral capillary loss. Here, we investigated the possible contribution of the neurovascular guidance molecule Slit2 and its Roundabout (Robo) receptors to SSc-related endothelial cell dysfunction.

METHODS

Circulating Slit2 levels were measured in patients with SSc and healthy controls. Slit2, Robo1 and Robo4 expression was investigated in SSc and healthy skin biopsies and explanted dermal microvascular endothelial cells (MVECs). Slit2/Robo4 function in MVEC angiogenesis was studied by cell viability, wound healing and capillary-like tube formation assays.

RESULTS

Circulating Slit2 was significantly increased in either SSc or patients with a very early diagnosis of SSc (VEDOSS) compared with controls. Interestingly, serum Slit2 levels were raised in patients with VEDOSS with nailfold videocapillaroscopy (NVC) abnormalities, while they were similar in VEDOSS with normal NVC and controls. In SSc, Slit2 and Robo4 expression was upregulated in clinically affected skin and explanted MVECs in respect to controls. The angiogenic performance of healthy MVECs was significantly reduced after challenge with recombinant human Slit2 or SSc sera. These inhibitory effects were significantly attenuated when SSc sera were preincubated with an anti-Slit2 blocking antibody. In vitro angiogenesis was severely compromised in SSc-MVECs and could be significantly ameliorated by Slit2 neutralisation or ROBO4 gene silencing. Slit2/Robo4 axis interfered with angiogenesis through the inhibition of Src kinase phosphorylation.

CONCLUSIONS

In SSc, increased circulating levels of Slit2 and activation of the Slit2/Robo4 antiangiogenic axis may contribute to peripheral microangiopathy since the very early phase of the disease.

Certainties and uncertainties concerning the contribution of pericytes to the pathogenesis of systemic sclerosis

The role of pericytes in systemic sclerosis (SSc) is unclear because of the difficulty in phenotyping them. They are mainly distributed in the pre-capillary, capillary and post-capillary abluminal side of non-muscular micro-vessels, express platelet-derived growth factor receptors (PDGFRs), and preside over vascular integrity and regeneration. By establishing close contact with many endothelial cells, a single pericyte can regulate ion influx, mechanical stress, leukocyte diapedesis, and platelet activation. Moreover, under pathological conditions such as SSc, pericytes may acquire a contractile phenotype and respond to various stimuli, including endothelin, angiotensin II and reactive oxygen species. The pericytes of SSc patients share some molecular patterns with myofibroblasts or fibroblasts, including A disintegrin and metalloproteinase domain 12 (ADAM-12), α-smooth muscle actin (α-SMA), the extra domain A (ED-A) variant of fibronectin, and Thy-1. Following stimulation with PDGF-β or transforming growth factor-β (TGF-β), pericytes may acquire a myofibroblast phenotype, and produce extracellular matrix or indirectly promote fibroblast activation. They may also contribute to fibrosis by means of epigenetic regulation. The pericyte plasmalemma is particularly rich in caveolae containing caveolin-1, a deficit of which has been associated with defective vessel tone control and lung fibrosis in mice. Consequently, dysfunctional pericytes may underlie the microangiopathy and fibrosis observed in SSc patients. However, given its variability in biological behaviour and the lack of a pan-pericyte marker, the exact role of these cells in SSc warrants further investigation.