Diabetic kidney disease (DKD) is associated with oxidative stress and mitochondrial injury. Myo-inositol oxygenase (MIOX), a tubular-specific enzyme, modulates redox imbalance and apoptosis in tubular cells in diabetes, but these mechanisms remain unclear. We investigated the role of MIOX in perturbation of mitochondrial quality control, including mitochondrial dynamics and autophagy/mitophagy, under highglucose (HG) ambience or a diabetic state. HK-2 or LLC-PK1 cells subjected to HG exhibited an upregulation of MIOX accompanied by mitochondrial fragmentation and depolarization, inhibition of autophagy/ mitophagy, and altered expression of mitochondrial dynamic and mitophagic proteins. Furthermore, dysfunctional mitochondria accumulated in the cytoplasm, which coincided with increased reactive oxygen species generation, Bax activation, cytochrome C release, and apoptosis. Overexpression of MIOX in LLC-PK1 cells enhanced the effects of HG, whereas MIOX siRNA or D-glucarate, an inhibitor of MIOX, partially reversed these perturbations. Moreover, decreasing the expression of MIOX under HG ambience increased PTEN-induced putative kinase 1 expression and the dependent mitofusin-2-Parkin interaction. In tubules of diabetic mice, increased MIOX expression and mitochondrial fragmentation and defective autophagy were observed. Dietary supplementation of D-glucarate in diabetic mice decreased MIOX expression, attenuated tubular damage, and improved renal functions. Notably, D-glucarate administration also partially attenuated mitochondrial fragmentation, oxidative stress, and apoptosis and restored autophagy/mitophagy in the tubular cells of these mice. These results suggest a novel mechanism linking MIOX to impaired mitochondrial quality control during tubular injury in the pathogenesis of DKD and suggest D-glucarate as a potential therapeutic agent for the amelioration of DKD.

BackgroundStudies have documented AKI with high-grade proteinuria in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In some patients, biopsies have revealed collapsing glomerulopathy, a distinct form of glomerular injury that has been associated with other viruses, including HIV. Previous patient reports have described patients of African ancestry who developed nephrotic-range proteinuria and AKI early in the course of disease.MethodsIn this patient series, we identified six patients with coronavirus disease 2019 (COVID-19), AKI, and nephrotic-range proteinuria. COVID-19 was diagnosed by a positive nasopharyngeal swab RT-PCR for SARS-CoV-2 infection. We examined biopsy specimens from one transplanted kidney and five native kidneys. Three of the six patients underwent genetic analysis of APOL1, the gene encoding the APOL1 protein, from DNA extracted from peripheral blood. In addition, we purified genomic DNA from paraffin-embedded tissue and performed APOL1 genotype analysis of one of the native biopsies and the donor kidney graft.ResultsAll six patients were of recent African ancestry. They developed COVID-19–associated AKI with podocytopathy, collapsing glomerulopathy, or both. Patients exhibited generally mild respiratory symptoms, and no patient required ventilator support. Genetic testing performed in three patients confirmed high-risk APOL1 genotypes. One APOL1 high-risk patient developed collapsing glomerulopathy in the engrafted kidney, which was transplanted from a donor who carried a low-risk APOL1 genotype; this contradicts current models of APOL1-mediated kidney injury, and suggests that intrinsic renal expression of APOL1 may not be the driver of nephrotoxicity and specifically, of podocyte injury.ConclusionsGlomerular disease presenting as proteinuria with or without AKI is an important presentation of COVID-19 infection and may be associated with a high-risk APOL1 genotype.

Renal tubular injury is increasingly being recognized as an early characteristic of diabetic nephropathy (DN). Mitochondrial dynamic alterations and redox protein p66Shc-mediated oxidative stress are both critical for ensuing diabetic tubular cell injury and apoptosis; whether these two processes are interlinked remains unclear. In the present study, we observed changes in mitochondrial morphology and expression of associated proteins in tubules of patients with DN. We demonstrated mitochondrial fragmentation as an important pathogenic feature of tubular cell injury that is linked to oxidative stress and p66Shc up-regulation. In renal proximal tubular cells, alterations in mitochondrial dynamics and expression of fission-fusion proteins were observed under high glucose (HG) ambience, along with p66Shc Ser36 phosphorylation. Gene ablation of p66Shc alleviated HG-induced mitochondrial fragmentation, down-regulated Fis1 and reduced p66Shc-Fis1 binding, increased Mfn1 expression, and disrupted interactions between Mfn1 and proapoptotic Bak. Overexpression of p66Shc exacerbated these changes, whereas overexpression of dominant-negative p66Shc Ser36 mutant had a marginal effect under HG, indicating that p66Shc phosphorylation as a prerequisite in the modulation of mitochondrial dynamics. Disrupted mitochondrial dynamics and enhanced Mfn1-Bak interactions modulated by p66Shc led to loss of mitochondrial voltage potential, cytochrome release, excessive ROS generation, and apoptosis. Taken together, these results link p66Shc to mitochondrial dynamic alterations in the pathogenesis of DN and unveil a novel mechanism by which p66Shc mediates HG-induced mitochondrial fragmentation and proapoptotic signaling that results in oxidative injury and apoptosis in the tubular compartment in human diabetic nephropathy.

Context.-Nodular, intercapillary glomerulosclerotic lesions resembling Kimmelstiel-Wilson nodules commonly observed in diabetic nephropathy can also be seen in patients without any clinical history or evidence of diabetes.Objectives.-To discuss the pathobiology of lesions reminiscent of diabetes nephropathy, including light-chain deposition disease, amyloidosis, immunotactoid nephropathy, the membranoproliferative form of glomerulonephritis, and idiopathic nodular glomerulosclerosis, and how to differentiate them from diabetic nephropathy.Data Sources.-Published literature and authors' personal experience.Conclusions.-The well-formed, intercapillary, nodular mesangial lesions, along with thickened glomerular basement membranes and tubular basement membranes, and hyaline arteriolosclerosis are virtually pathognomic of diabetic nephropathy. However, the pathologist must exclude lesions reminiscent of diabetic nephropathy by performing special stains on histologic sections, immunofluorescence, and electron microscopic studies.