The recruitment mechanisms and potential therapeutic targets of podocytes from parietal epithelial cells

Podocytes are differentiated postmitotic cells which cannot be replaced after podocyte injury. The mechanism of podocyte repopulation after injury has aroused wide concern. Parietal epithelial cells (PECs) are heterogeneous and only a specific subpopulation of PECs has the capacity to replace podocytes. Major progress has been achieved in recent years regarding the role and function of a subset of PECs which could transdifferentiate toward podocytes. Additionally, several factors, such as Notch, Wnt/ß-catenin, Wilms’ tumor-1, miR-193a and growth arrest-specific protein 1, have been shown to be involved in these processes. Finally, PECs serve as a potential therapeutic target in the conditions of podocyte loss. In this review, we discuss the latest observations and concepts about the recruitment of podocytes from PECs in glomerular diseases as well as newly identified mechanisms and the most recent treatments for this process.

C-peptide and islet transplantation improve glomerular filtration barrier in diabetic nephropathy rats

OBJECTIVES

Islet transplantation has been proved to be effective in delaying early stage of DN. This study was established to observe the mechanism of islet transplantation on early diabetic nephropathy (DN).

METHOD

The diabetes mellitus (DM) rat model was established by an injection of a single-dose streptozotocin. According to the treatment, the rats were randomly divided into 4 groups: the untreated DN rats (DN group); the C-peptide treated rats (CP group); the islet transplanted rats (IT group); the normal control rats (NC group). Renal function and structure of glomerular filtration barrier (GFB) were evaluated by urinalysis and histopathological examination, respectively. The renal fibrotic factors, TGF- β1 and CTGF, as well as the anti-renal fibrosis factor HGF were assessed by immunohistochemical staining and western blotting methods.

RESULTS

After C-peptide treatment and islet transplantation, the GFB structure was obviously improved. The blood glucose significantly decreased in the IT group. The 24h urine protein and glomerular basement membrane thickness decreased, the pathological changes of podocytes improved, TGF- β1 and CTGF decreased and HGF increased in the CP group and the IT group compared with that in the DN group (P < 0.05), especially in the IT group.

CONCLUSION

Islet transplantation could ameliorate the structure of GFB of early DN in a rat model, and the treatment effect was partly attributed to the restoration of C-peptide concentration. Suppressing the fibrosis system can be the potential mechanism of islet transplantation, which is independent of blood glucose control.

Let‑7a‑5p may participate in the pathogenesis of diabetic nephropathy through targeting HMGA2

Diabetic nephropathy (DN) is one of the most common complications of diabetes mellitus (DM), and has been demonstrated as one of the major causes of renal failure. In a previous study, it was noted that microRNA let-7a-5p was downregulated in DN; however, the underlying mechanism requires additional investigation. The aim of the present study was to investigate the roles of let-7a-5p in the pathogenesis of DN and its associated mechanism. The renal tissues of db/db and db/m mice, and renal mesangial cells treated with high concentrations of glucose were obtained; reverse transcription-quantitative polymerase chain reaction, and western blot analysis were applied to detect the expression of let-7a-5p and high-mobility group AT-hook 2 (HMGA2) in vivo and in vitro. In addition, renal mesangial cells cultured under high-glucose conditions (20 and 30 mmol/l) were transfected with either let-7a-5p mimics or let-7a-5p inhibitors. The effects of let-7a-5p on the proliferation and apoptosis of renal mesangial cells were examined using CCK-8 and flow cytometry methods. Additionally, cells were collected and the expression of phosphoinositide 3-kinase (PI3K), phosphorylated protein kinase B (p-AKT) and HMGA2 was analyzed with western blot analysis. Finally, a dual luciferase reporter assay was performed to confirm whether HMGA2 was a direct target of let-7a-5p. Let-7a-5p was significantly downregulated and HMGA2 was markedly upregulated in the tissue samples of DN mice and renal mesangial cells cultured under high-glucose conditions. In addition, transfection of let-7a-5p mimics induced a significant decrease in the proliferation and increase in the apoptosis of renal mesangial cells cultured under high-glucose conditions; transfection of let-7a-5p inhibitors exhibited the opposite effects. Furthermore, transfection of let-7a-5p mimics also led to the inhibition of the PI3K-AKT signaling pathway; transfection of let-7a-5p inhibitors may activate the PI3K-AKT signaling pathway through the increase in PI3K and AKT levels. Finally, a dual luciferase reporter assay confirmed that HMGA2 is a direct target of let-7a-5p. Let-7a-5p was downregulated in DN and may participate in the pathogenesis of DN via regulating HMGA2 expression and the PI3K-AKT signaling pathway.