Microcapsule - Mediated Tubulointerstitial Fibrosis Mediated By MicroRNAs

Renal fibrosis is inevitably progressive no matter what the initial insult is or whether the insult persists. In clinical settings, renal biopsy samples show that fibrotic lesions are initially local and scattered; however, expand and progress with the time being. In experimental fibrosis model induced by unilateral ureteral obstruction (UUO), the accelerated pathologic changes could hardly be explained by aggravated pressure caused by hydronephrosis after ligation. Here, we investigated whether injured tubular cells contributed to the progression of renal fibrosis. In this study, cultured recipient tubular cells underwent phenotype transition after incubation with conditioned media derived from TGF-pl-treated donor tubular cells. Thus, it was reasonable to speculate that some secretable molecules from injured tubules contribute to the progression of renal fibrosis. We reported that secreted miRNA-21 (miR-21) could serve as the molecule mediating cell-to-cell communication between tubular epithelial cells. MiR-21 was packaged into microvesicles (MVs), which was then delivered into recipient tubular cells. The exogenous miR-21 enhanced Akt signaling by target depression of PTEN protein, and promoted tubular phenotype transition. These results demonstrated that tubular cells could secret miR-21 and deliver it into recipient tubule by MVs where the exogenous miR-21 targeted PTEN protein, enhanced Akt signaling in recipient cells. MVs-mediated delivery of miR-21 among tubular epithelial cells might shed a new light on the mechanism of progressive renal fibrosis.Apoptosis contributes to tubulointerstitial fibrosis but its regulation in renal tubular cells remained unclear. MicroRNA (miRNA) is an endogenous non-coding small RNA that regulates cell proliferation, differentiation, metabolism and death. Here, in fibrotic kidney induced by unilateral ureteral obstruction (UUO), we demonstrated that miR-34a was markedly up-regulated in tubulointerstitial spaces. MiR-34a level in microvesicles isolated from kidney was markedly up-regulated after obstruction. However, the increase of miR-34a was not de novo synthesized by proximal tubular epithelial cells because it was not up-regulated in cultured tubular cells incubated with TGF-β1. On the contrary, miR-34a was up-regulated in TGF-β1-incubated fibroblasts. This miR-34a was secreted from activated fibroblasts and delivered through disrupted tubular basement membrane (TBM). Microvesicles released by activated fibroblasts acted as a vector for delivery of miR-34a from fibroblasts to tubular cells. The transported miR-34a induced apoptosis of tubular cells, which were then detached and excreted. MiR-34a regulates apoptosis by targeting Bcl-2 in tubular cells. Moreover, injection of exogenous miR-34a-containing microvesicles enhanced tubular cell apoptosis in mice kidney. This study suggests that miR-34a transported by microvesicles induces tubular cell apoptosis that contributes to renal fibrosis. This study highlights the importance of cell-to-cell communication in renal fibrosis, demonstrates a new mechanism concerning apoptosis in fibrosis and will probably provide new therapeutic targets of renal fibrosis.Chronic kidney disease is characterized by tubulointerstitial fibrosis. Disruption of the integrity of tubular basement membrane (TBM) contributes to renal fibrosis. Tissue plasminogen activator (tPA) is one of the major compotents in the matrix proteolytic network by activating matrix metalloproleinases (MMP)-9, which is the predicted target of miRNA (miR)-144. It was reported by anti-doping researchers that serum miR-144 was up-regulated by erythropoietin (EPO), which was reported to attenuate renal fibrosis. Serum miRNAs are probably encapsulated in microvesicle. Here, we investigated whether EPO protected the integrity of TBM to attenuate renal fibrosis by up-regulating miR-144 in serum micro vesicles, which then targeted fibroblasts’tPA expression and inhibited MMP-9 activation. In obstructed kidney induced by unilateral ureteral obstruction (UUO), administration of EPO attenuated TBM disruption, relieved the up-regulation of tPA expression and MMP-9 activity. MiR-144 level in serum microvesicles was up-regulated after EPO administration. The miR-144-containing microvesicles inhibited tPA expression and MMP-9 activity and attenuated TGF-01-induced up-regulation of tPA and activation of MMP-9 of renal fibroblasts. Moreover, administration of miR-144-containing microvesicles attenuated TBM disruption, relieved the up-regulation of tPA expression and MMP-9 activity in obstructed kidney. MiR-144 negatively regulated tPA expression and therefore interfered MMP-9 activition of fibroblasts. Ectopic expression of miR-144 aliviated, while inhibition of miR-144 facilitated TGF-β1-induced up-regulation of tPA and activation of MMP-9 of renal fibroblasts. These results suggest that EPO protects the integrity of TBM by up-regulating miR-144 level of serum microvesicles, which then inhibits the expression of tPA and activity of MMP-9 in fibroblast.