Increased Oxidative Damage of RNA in Early-Stage Nephropathy in db/db Mice

Targeting RNA oxidation by ISG20-mediated degradation is a potential therapeutic strategy for acute kidney injury

Oxidative stress plays a central role in the pathophysiology of acute kidney injury (AKI). Although RNA is one of the most vulnerable cell components to oxidative damage, it is unclear whether RNA oxidation is involved in the pathogenesis of AKI. In this study, we found that the level of RNA oxidation was significantly enhanced in kidneys of patients with acute tubular necrosis (ATN) and in the renal tubular epithelial cells (TECs) of mice with AKI, and oxidized RNA overload resulted in TEC injury. We further identified interferon-stimulated gene 20 (ISG20) as a novel regulator of RNA oxidation in AKI. Tubule-specific deficiency of ISG20 significantly aggravated renal injury and RNA oxidation in the ischemia/reperfusion-induced AKI mouse model and ISG20 restricted RNA oxidation in an exoribonuclease activity-dependent manner. Importantly, overexpression of ISG20 protected against oxidized RNA overproduction and renal ischemia/reperfusion injury in mice and ameliorated subsequent protein aggresome accumulation, endoplasmic reticulum stress, and unfolded protein response. Thus, our findings provide direct evidence that RNA oxidation contributes to the pathogenesis of AKI and that ISG20 importantly participates in the degradation of oxidized RNA, suggesting that targeting ISG20-handled RNA oxidation may be an innovative therapeutic strategy for AKI.

Aerobic exercise training alleviates renal injury in db/db mice through inhibiting Nox4-mediated NLRP3 inflammasome activation

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease, with few therapeutic options available to slow its progression. Aerobic exercise training is an effective strategy for diabetes mellitus and its complications' prevention and treatment. The purpose of this study was to determine the effects of aerobic exercise training on diabetic kidney injury in db/db mice and to characterize the mechanism underlying the renal protective effects. The db/db mice were exercised 5 days a week for 60 min each day for 8 weeks at a speed of 5.6 m/min, after which renal function, morphology, oxidative stress, inflammation, fibrosis, and the expression of the Nox4/ROS/NF-κB/NLRP3 signaling pathway-related protein were assessed. Our results showed that aerobic exercise training significantly reduced body weight and microalbuminuria, improved renal function, and attenuated renal pathological changes in db/db mice independent of hyperglycemic state. Aerobic exercise training was also found to significantly improve oxidative stress and inflammation in the kidneys of db/db mice by decreasing the activity of complex I, the levels of MDA, 8-OHdG, Nox4, ROS, TNF-α, MCP-1, IL-6, and IL-18, increasing the activities of SOD and GSH-Px, the expression of klotho and NPHS2, and decreasing the phosphorylation of NF-κB p65 and IκBα, as well as the expression of NLRP3, ASC, caspase-1 p20, and IL-1β. Additionally, aerobic exercise training decreased TGF-β, collagen I, collagen IV, and α-SMA expression, thereby slowing the progression of kidney fibrosis in db/db mice. In conclusion, aerobic exercise training effectively reduces oxidative stress, inflammation, and renal fibrosis by modulating the Nox4/ROS/NF-κB/NLRP3 signaling pathway, implying that aerobic exercise training has significant potential to protect diabetic kidney injury and should be given more emphasis in DKD treatment.

Oxidative RNA Damage in the Pathogenesis and Treatment of Type 2 Diabetes

Excessive production of free radicals can induce cellular damage, which is associated with many diseases. RNA is more susceptible to oxidative damage than DNA due to its single-stranded structure, and lack of protective proteins. Yet, oxidative damage to RNAs received little attention. Accumulating evidence reveals that oxidized RNAs may be dysfunctional and play fundamental role in the occurrence and development of type 2 diabetes (T2D) and its complications. Oxidized guanine nucleoside, 8-oxo-7, 8-dihydroguanine (8-oxoGuo) is a biomarker of RNA oxidation that could be associated with prognosis in patients with T2D. Nowadays, some clinical trials used antioxidants for the treatment of T2D, though the pharmacological effects remained unclear. In this review, we overview the cellular handling mechanisms and the consequences of the oxidative RNA damage for the better understanding of pathogenesis of T2D and may provide new insights to better therapeutic strategy.

NADH/NAD+ Redox Imbalance and Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common and severe complication of diabetes mellitus. If left untreated, DKD can advance to end stage renal disease that requires either dialysis or kidney replacement. While numerous mechanisms underlie the pathogenesis of DKD, oxidative stress driven by NADH/NAD⁺ redox imbalance and mitochondrial dysfunction have been thought to be the major pathophysiological mechanism of DKD. In this review, the pathways that increase NADH generation and those that decrease NAD⁺ levels are overviewed. This is followed by discussion of the consequences of NADH/NAD⁺ redox imbalance including disruption of mitochondrial homeostasis and function. Approaches that can be applied to counteract DKD are then discussed, which include mitochondria-targeted antioxidants and mimetics of superoxide dismutase, caloric restriction, plant/herbal extracts or their isolated compounds. Finally, the review ends by pointing out that future studies are needed to dissect the role of each pathway involved in NADH-NAD⁺ metabolism so that novel strategies to restore NADH/NAD⁺ redox balance in the diabetic kidney could be designed to combat DKD.

Circulating Oxidative Stress Biomarkers in Clinical Studies on Type 2 Diabetes and Its Complications

Type 2 diabetes (T2DM) and its complications constitute a major worldwide public health problem, with high rates of morbidity and mortality. Biomarkers for predicting the occurrence and development of the disease may therefore offer benefits in terms of early diagnosis and intervention. This review provides an overview of human studies on circulating biomarkers of oxidative stress and antioxidant defence systems and discusses their usefulness from a clinical perspective. Most case-control studies documented an increase in biomarkers of oxidative lipid, protein, and nucleic acid damage in patients with prediabetes and in those with a diagnosis of T2DM compared to controls, and similar findings were reported in T2DM with micro- and macrovascular complications compared to those without. The inconsistence of the results regarding antioxidant defence systems renders difficulty to draw a general conclusion. The clinical relevance of biomarkers of oxidative lipid and protein damage for T2DM progression is uncertain, but prospective studies suggest that markers of oxidative nucleic acid damage such as 8-hydroxy-2'-deoxyguanosine and 8-hydroxyguanosine are promising for predicting macrovascular complications of T2DM. Emerging evidence also points out the relationship between serum PON1 and serum HO1 in T2DM and its complications. Overall, enhanced oxidative damage represents an underlying mechanism of glucose toxicity in T2DM and its related micro- and macrovascular complications suggesting that it may be considered as a potential additional target for pharmacotherapy. Therefore, further studies are needed to understand whether targeting oxidative stress may yield clinical benefits. In this view, the measurement of oxidative stress biomarkers in clinical trials deserves to be considered as an additional tool to currently used parameters to facilitate a more individualized treatment of T2DM in terms of drug choice and patient selection.