Cellular origin and microRNA profiles of circulating extracellular vesicles in different stages of diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes and the main cause of end-stage renal disease. Extracellular vesicles (EVs) are small cell-derived vesicles that can alter disease progression by microRNA (miRNA) transfer.

METHODS

In this study, we aimed to characterize the cellular origin and miRNA content of EVs in plasma samples of type 2 diabetes patients at various stages of DN. Type 2 diabetes patients were classified in three groups: normoalbuminuria, microalbuminuria and macroalbuminuria. The concentration and cellular origin of plasma EVs were measured by flow cytometry. A total of 752 EV miRNAs were profiled in 18 subjects and differentially expressed miRNAs were validated.

RESULTS

Diabetic patients with microalbuminuria and/or macroalbuminuria showed elevated concentrations of total EVs and EVs from endothelial cells, platelets, leucocytes and erythrocytes compared with diabetic controls. miR-99a-5p was upregulated in macroalbuminuric patients compared with normoalbuminuric and microalbuminuric patients. Transfection of miR-99a-5p in cultured human podocytes downregulated mammalian target of rapamycin (mTOR) protein expression and downregulated the podocyte injury marker vimentin.

CONCLUSIONS

Type 2 diabetes patients with microalbuminuria and macroalbuminuria display differential EV profiles. miR-99a-5p expression is elevated in EVs from macroalbuminuria and mTOR is its validated mRNA target.

Urinary mitochondrial DNA associates with delayed graft function following renal transplantation

BACKGROUND

Ischaemia-reperfusion (IR) injury is an important determinant of delayed graft function (DGF) affecting allograft function. Mitochondrial DNA (mtDNA) is released upon cell death and platelet activation into the extracellular environment and has been suggested to be a biomarker in several diseases. Whether extracellular mtDNA accumulates in plasma and/or urine upon renal IR and predisposes DGF is unknown.

METHODS

C57BL/6J wild-type mice were subjected to renal IR. In addition, an observational case-control study was set up enrolling 43 patients who underwent kidney transplantation. One day post-IR in mice and a few days following renal transplantation in human, blood and urine were collected. Patients were stratified into DGF and non-DGF groups.

RESULTS

mtDNA-encoded genes accumulate in urine and plasma in both mice subjected to renal IR injury and in humans following renal transplantation. In human renal transplant recipients, cold ischaemia time and renal function correlate with urinary mtDNA levels. Urinary mtDNA levels but not urinary nuclear DNA levels were significantly higher in the DGF group compared with the non-DGF group. Multiple receiver operating characteristic curves revealed significant diagnostic performance for mtDNA-encoded genes cytochrome c oxidase III (COXIII); nicotinamide adenine dinucleotide hydrogen subunit 1 (NADH-deh); mitochondrially encoded, mitochondrially encoded nicotinamide adenine dinucleotide dehydrogenase 2 (MT-ND2) with an area under the curve of, respectively, 0.71 [P = 0.03; 95% confidence interval (CI) 0.54-0.89], 0.75 (P = 0.01; 95% CI 0.58-0.91) and 0.74 (P = 0.02; 95% CI 0.58-0.89).

CONCLUSIONS

These data suggest that renal ischaemia time determines the level of mtDNA accumulation in urine, which associates with renal allograft function and the diagnosis of DGF following renal transplantation.

Platelet inhibition by ticagrelor is protective against diabetic nephropathy in mice

Diabetic nephropathy (DN) is a major complication of diabetes and is associated with high risk for cardiovascular mortality, which is partially related to elevated platelet activity. Platelets are also active players in inflammation and fibrosis. In this study, we examine the effect of ticagrelor-induced platelet inhibition on the development of DN. DN was induced by unilateral nephrectomy followed by streptozotocin injections for 5 days. Mice received ticagrelor (300 mg/kg) or vehicle every other day, for 16 weeks. Experimental groups: non-diabetic control, diabetic control, non-diabetic ticagrelor, and diabetic ticagrelor. Ticagrelor treatment in diabetic mice lowered urinary albumin excretion, it prevented diabetes-induced mesangial matrix expansion, podocyte effacement, and glomerular endothelial cell injury, which includes loss of endothelial fenestrations, ICAM-1 expression, and PECAM expression. In addition, ticagrelor treatment prevented collagen IV deposition and macrophage infiltration in the tubulointerstitium and these diabetic mice showed lower systemic and tubular inflammation and tubular apoptosis. This tubular protection is likely to be a result of protection to the glomerular endothelium by ticagrelor, which reduces albuminuria and albumin toxicity to the tubules and reduced tubular and interstitial inflammation and fibrosis. In conclusion, ticagrelor-induced platelet inhibition protects against renal injury in diabetic mice, likely by protecting the glomerular endothelial cells.

NLRX1 does not play a role in diabetes nor the development of diabetic nephropathy induced by multiple low doses of streptozotocin

Diabetic nephropathy (DN) is a microvascular complication of diabetes mellitus that results in both tubular and glomerular injury. Low-grade inflammation and oxidative stress are two mechanisms known to drive the progression of DN. Nucleotide-binding leucine-rich repeat containing family member X1 (NLRX1) is an innate immune receptor, uniquely located in mitochondria, that has been found to regulate inflammatory responses and to dampen renal oxidative stress by regulating oxidative phosphorylation. For this reason, we investigated the role of NLRX1 in the development of DN in a Type 1 Diabetes mouse model. We analyzed the effect of NLRX1 deficiency on diabetes development and the accompanied renal damage, inflammation, and fibrosis. We found that multiple low doses of streptozotocin induced body weight loss, polydipsia, hyperglycemia, glycosuria, and a mild DN phenotype in wildtype and NLRX1-deficient mice, without significant differences between these mouse strains. Despite increased NLRX1 expression in diabetic wildtype mice, NLRX1 deficiency did not affect the diabetic phenotype induced by streptozotocin treatment, as reflected by similar levels of polyuria, microalbuminuria, and increased renal markers of oxidative stress and inflammation in wildtype and NLRX1-deficient mice. The present findings show that NLRX1 does not mediate the development of streptozotocin-induced diabetes and diabetic-induced nephropathy in mice after multiple low doses of streptozotocin. This data implies that, while NLRX1 can be triggered by cellular stress, its regulatory and functional effects may be dependent on the specific physiological conditions. In the case of DN, NLRX1 may be neither helpful nor harmful, but rather a marker of metabolic stress.