Abstract
BackgroundSystemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast. It is well known that vascular endothelial growth factor A (VEGF-A, hereafter referred to as VEGF) may induce a profibrotic phenotype on perivascular cells. Caveolin-1 (Cav-1) is involved in the regulation of VEGF signaling, playing a role in the transport of internalized VEGF receptor 2 (VEGFR2) toward degradation, thus decreasing VEGF signaling. In this work, we assessed the levels of Cav-1 in SSc bone marrow mesenchymal stem cells (SSc-MSCs), a pericyte surrogate, and correlate these results with VEGF signaling, focusing onpotential pathogenic pathways leading to fibrosis.ResultsWe explored the VEGF signaling assessing: (1) Cav-1 expression; (2) its co-localization with VEGFR2; (3) the activity of VEGFR2, by IF, immunoprecipitation, and western blot. In SSc-MSCs, Cav-1 levels were lower when compared to healthy controls (HC)-MSCs. Furthermore, the Cav-1/VEGFR2 co-localization and the ubiquitination of VEGFR2 were impaired in SSc-MSCs, suggesting a decreased degradation of the receptor and, as a consequence, the tyrosine phosphorylation of VEGFR2 and the PI3-kinase-Akt pathways were significantly increased when compared to HC. Furthermore, an increased connective tissue growth factor (CTGF) expression was observed in SSc-MSCs. Taken together, these data suggested the upregulation of VEGF signaling in SSc-MSCs. Furthermore, after silencing Cav-1 expression in HC-MSCs, an increased CTGF expression in HC-MSCs was observed, mirroring the results obtained in SSc-MSCs, and confirming the potential role that the lack of Cav-1 may play in the persistent VEGF signaling .ConclusionsDuring SSc, the lower levels of Cav-1 may contribute to the pathogenesis of fibrosis via an upregulation of the VEGF signaling in perivascular cells which are shifted to a profibrotic phenotype.
Highlights
Systemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast
Cav-1 levels are decreased in SSc-mesenchymal stem cells (MSCs) The immunofluorescence staining showed that in the unstimulated healthy controls (HC)-MSCs, Cav-1 was primarily expressed in the surface of cells and after treatment with Vascular endothelial growth factor A (VEGF) for 15 min, Cav-1 was internalized to the cytoplasm as shown by intracellular and perinuclear staining
Before VEGF treatment, in both limited SSc (lSSc)- and diffused systemic sclerosis (dSSc)-MSCs, independent from the duration of the disease, mRNA levels of Cav-1 were significantly lower when compared with basal HC-MSCs expression (Cav-1 mRNA levels: 0.45 in lSSc-MSCs and 0.49 in dSSc-MSCs, both vs. 1.21 in HC-MSCs, P
Summary
Systemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast. The use of lineage tracing, helped us to better define the myofibroblasts origin and evolution, confirming that pericytes and resident fibroblasts are the major, if not the only, source of myofibroblasts in at least one animal model of kidney fibrotic diseases [8,9,10]. On these bases, it might be important to assess if the molecular mechanisms involved in the differentiation of pericytes toward myofibroblasts may play a role in the pathological process leading to fibrosis during SSc
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