Urinary exosomes are 40-100 nm vesicles containing protein, mRNA, and microRNA that may serve as biomarkers of renal dysfunction and structural injury. Currently, there is a need for more sensitive and specific biomarkers of renal injury and disease progression. Here we sought to identify the best exosome isolation methods for both proteomic analysis and RNA profiling as a first step for biomarker discovery. We used six different protocols; three were based on ultracentrifugation, one used a nanomembrane concentrator-based approach, and two utilized a commercial exosome precipitation reagent. The highest yield of exosomes was obtained using a modified exosome precipitation protocol, which also yielded the highest quantities of microRNA and mRNA and, therefore, is ideal for subsequent RNA profiling. This method is likewise suitable for downstream proteomic analyses if an ultracentrifuge is not available and/or a large number of samples are to be processed. Two of the ultracentrifugation methods, however, are better options for exosome isolation if an ultracentrifuge is available and few samples will be processed for proteomic analysis. Thus, our modified exosome precipitation method is a simple, fast, highly scalable, and effective alternative for the isolation of exosomes, and may facilitate the identification of exosomal biomarkers from urine.

We previously observed association between variants in the plasmacytoma variant translocation 1 gene (PVT1) and end-stage renal disease (ESRD) attributed to both type 1 and type 2 diabetes, and demonstrated PVT1 expression in a variety of renal cell types. While these findings suggest a role for PVT1 in the development of ESRD, potential mechanisms for involvement remain unknown. The goal of this study was to identify possible molecular mechanisms by which PVT1 may contribute to the development and progression of diabetic kidney disease. We knocked-down PVT1 expression in mesangial cells using RNA interference, and analyzed RNA and protein levels of fibronectin 1 (FN1), collagen, type IV, alpha 1 (COL4A1), transforming growth factor beta 1 (TGFB1) and plasminogen activator inhibitor-1 (SERPINE1 or PAI-1) by qPCR and ELISA, respectively. PVT1 expression was significantly upregulated by glucose treatment in human mesangial cells, as were levels of FN1, COL4A1, TGFB1, and PAI-1. Importantly, PVT1 knockdown significantly reduced mRNA and protein levels of the major ECM proteins, FN1 and COL4A1, and two key regulators of ECM proteins, TGFB1 and PAI-1. However, we observed a higher and more rapid reduction in levels of secreted FN1, COL4A1, and PAI-1 compared with TGFB1, suggesting that at least some of the PVT1 effects on ECM proteins may be independent of this cytokine. These results indicate that PVT1 may mediate the development and progression of diabetic nephropathy through mechanisms involving ECM accumulation.

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Diabetic nephropathy is the most common cause of chronic kidney failure and end-stage renal disease in the Western World. One of the major characteristics of this disease is the excessive accumulation of extracellular matrix (ECM) in the kidney glomeruli. While both environmental and genetic determinants are recognized for their role in the development of diabetic nephropathy, epigenetic factors, such as DNA methylation, long non-coding RNAs, and microRNAs, have also recently been found to underlie some of the biological mechanisms, including ECM accumulation, leading to the disease. We previously found that a long non-coding RNA, the plasmacytoma variant translocation 1 (PVT1), increases plasminogen activator inhibitor 1 (PAI-1) and transforming growth factor beta 1 (TGF-β1) in mesangial cells, the two main contributors to ECM accumulation in the glomeruli under hyperglycemic conditions, as well as fibronectin 1 (FN1), a major ECM component. Here, we report that miR-1207-5p, a PVT1-derived microRNA, is abundantly expressed in kidney cells, and is upregulated by glucose and TGF-β1. We also found that like PVT1, miR-1207-5p increases expression of TGF-β1, PAI-1, and FN1 but in a manner that is independent of its host gene. In addition, regulation of miR-1207-5p expression by glucose and TGFβ1 is independent of PVT1. These results provide evidence supporting important roles for miR-1207-5p and its host gene in the complex pathogenesis of diabetic nephropathy.

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