Acute kidney injury (AKI) is a public health problem worldwide. Several therapeutic strategies have been made to accelerate recovery and improve renal survival. Recent studies have shown that human adult renal progenitor cells (ARPCs) participate in kidney repair processes, and may be used as a possible treatment to promote regeneration in acute kidney injury. Here, we show that human tubular ARPCs (tARPCs) protect physically injured or chemically damaged renal proximal tubular epithelial cells (RPTECs) by preventing cisplatin-induced apoptosis and enhancing proliferation of survived cells. tARPCs without toll-like receptor 2 (TLR2) expression or TLR2 blocking completely abrogated this regenerative effect. Only tARPCs, and not glomerular ARPCs, were able to induce tubular cell regeneration process and it occurred only after damage detection. Moreover, we have found that ARPCs secreted inhibin-A and decorin following the RPTEC damage and that these secreted factors were directly involved in cell regeneration process. Polysaccharide synthetic vesicles containing these molecules were constructed and co-cultured with cisplatin damaged RPTECs. These synthetic vesicles were not only incorporated into the cells, but they were also able to induce a substantial increase in cell number and viability. The findings of this study increase the knowledge of renal repair processes and may be the first step in the development of new specific therapeutic strategies for renal repair.

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Introduction and Aims: Acute kidney injury (AKI) is emerging as a public health problem worldwide. Several pharmacologic therapies that can accelerate recovery and improve survival have been attempted and were efficacious in experimental models but failed to manifest any substantial beneficial effect in clinical practice. Recent studies showed that adult renal progenitor cells (ARPCs) can participate in kidney repair processes and might be potentially used in the clinic to improve regeneration in acute and progressive kidney disease. Our aim was to study the influence of ARPCs on the regenerative process of cisplatin-injured renal proximal tubular epithelial cells (RPTECs) and validate some the ARPC-secreted molecules able to induce regenerative processes. Methods: CD133-positive ARPCs were isolated by magnetic sorting, starting from healthy sections of kidney removed for renal carcinoma. An in vitro model of cisplatin induced cell toxicity, in which RPTECs were co-cultured with ARPCs, was used. Caspase 3 expressions was studied to evaluate apoptosis. Cell proliferation induced by ARPCs was evaluated by BrdU proliferation assay. ELISA assays were performed to evaluate inhibin-A (INHB-A), decorin (DCN) and FGF2 chemokines. A natural polymer-based nanosystem for efficacious delivery of molecules was developed. INHB-A-loaded Polysaccharides Synthetic Vesicles (INHB-A-PSSV) and DCN-loaded Polysaccharides Synthetic Vesicles (DCN-PSSV) were synthesized by two steps methods: ionotropic pre-gelation of alginate core, followed by chitosan polyelectrolyte complexation. A microfluidic device was appositely fabricated in order to optimize the INHB-A and DCN-PSSV at interface-assembly process, in terms of polymers and INHB-A and DCN amount as well as vesicles size distribution. Cellular uptake and INHB-A-PSSV and DCN-PSSV effectiveness were tested. Results: We showed that the induction of tubular cell regeneration process was specific of tARPCs and occured only after that they detect the damage. On the contrary, glomerular ARPCs could not induce RPTEC regeneration. tARPCs protected RPTEC and HK2 cells from cisplatin toxicity by preventing cisplatin-induced apoptosis and enhancing proliferation of survived cells. Regenerative effect was completely abrogated blocking the Toll-like receptor 2 (TLR2), or using tARPC not expressing the TLR2. We found that INHB-A, DCN and FGF2 were secreted by ARPCs following the damage of RPTEC and that they were involved in the RPTEC regeneration. We showed that addition of INHB-A and DCN PSSV to cisplatin-treated RPTECs led to a substantial increase in cell number and viability after 3 days of culture. Remarkably, a very low dosage of functional loaded proteins (8 ng/25 ul) was sufficient to induce cell regeneration and the percentage of viable cells was similar to that of RPTECs without damage. Conclusions: We demonstrated that tARPCs have a regenerative effect on damaged RPTEC, by both preventing apoptosis and enhancing proliferation of surviving cells. They act by means of their secretoma, t...