AMPK dysregulation promotes diabetes-related reduction of superoxide and mitochondrial function

Abstract

Diabetic microvascular complications have been considered to be mediated by a glucose-driven increase in mitochondrial superoxide anion production. Here, we report that superoxide production was reduced in the kidneys of a steptozotocin-induced mouse model of type 1 diabetes, as assessed by in vivo real-time transcutaneous fluorescence, confocal microscopy, and electron paramagnetic resonance analysis. Reduction of mitochondrial biogenesis and phosphorylation of pyruvate dehydrogenase (PDH) were observed in kidneys from diabetic mice. These observations were consistent with an overall reduction of mitochondrial glucose oxidation. Activity of AMPK, the major energy-sensing enzyme, was reduced in kidneys from both diabetic mice and humans. Mitochondrial biogenesis, PDH activity, and mitochondrial complex activity were rescued by treatment with the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR). AICAR treatment induced superoxide production and was linked with glomerular matrix and albuminuria reduction in the diabetic kidney. Furthermore, diabetic heterozygous superoxide dismutase 2 (Sod2 +/-) mice had no evidence of increased renal disease, and Ampka2 -/-mice had increased albuminuria that was not reduced with AICAR treatment. Reduction of mitochondrial superoxide production with rotenone was sufficient to reduce AMPK phosphorylation in mouse kidneys. Taken together, these results demonstrate that diabetic kidneys have reduced superoxide and mitochondrial biogenesis and activation of AMPK enhances superoxide production and mitochondrial function while reducing disease activity. IntroductionComplications of diabetes, including retinopathy, neuropathy, and nephropathy, are responsible for considerable morbidity, and are experienced by a majority of individuals with diabetes over time. How elevated glucose levels initiate these complications remains unclear. The prevailing theory states that enhanced mitochondrial production of superoxide anion in response to elevated cellular glucose concentrations leads to pathological pathway activation and cell dysfunction (1, 2). Studies in cell culture systems demonstrated that addition of high glucose produced an increase in ROS that has been attributed to the mitochondrial electron transport chain (ETC). The currently accepted scheme is that chronically elevated glucose leads to increased ROS production by mitochondria, contributing to downstream cellular injury processes, and ultimately resulting in end-organ dysfunction and structural changes. Based on this theory, numerous strategies are being developed to interrupt the mitochondrial production of superoxide and inhibit downstream deleterious pathways.

AICAR ameliorates high-fat diet-associated pathophysiology in mouse and ex vivo models, independent of adiponectin

“…AICAR did not affect the total number of renal macrophages in the mouse model used, but rather shifted their phenotype towards resolution by reducing the percentage of CD11c + M1 macrophages. Collectively, this supports previous work from our group and others, demonstrating that AICAR attenuates both HFD-induced [12,13] and diabetes-induced [14,15] kidney disease. Importantly, in this study, we now also demonstrate that AICAR-mediated protection against kidney disease is independent of adiponectin.…”

“…In a subset of mice, dihydroethidium (DHE, 50 mg/kg) was administered by i.p. injection 16 h before the mice were killed to quantify renal superoxide levels by confocal imaging (n = 4 per group) [14]. Detailed protocols for liver function analysis, HPLC plasma creatinine analysis and renal superoxide measurements are described in ESM Methods.…”

“…Evidence from experimental models has shown that AICAR may attenuate metabolic [6][7][8], hepatic [9][10][11] and renal pathophysiology [12][13][14][15]. However, the use of AICAR could be compromised as some reports indicate that AICAR increases adiponectin production [13].…”

Deletion of Lkb1 in Renal Tubular Epithelial Cells Leads to CKD by Altering Metabolism

“…27 Several studies indicate that the AMPK, PPARa, and PGC1a pathways are important in fibrosis development. 29,[48][49][50][51] Data from the Duffield group suggest that microRNA 21 is an important upstream regulator of the pathway. 52 In conclusion, this study showed that selective deletion of Lkb1 in the kidney induced severe injury over time, characterized by dilated tubules and interstitial fibrosis.…”

50 years forward: mechanisms of hyperglycaemia-driven diabetic complications

“…The Brownlee hypothesis is an area of ongoing controversy and active investigation. A recent study has suggested that this excess of mitochondrial ROS may not be a universal finding [14], and there is increasing evidence of the importance of nonmitochondrial sources of ROS, including cytosolic production of ROS by NADPH oxidase [15]. Furthermore, although the polyol pathway has now been under active investigation for over 40 years, except for some limited data in neuropathy, agents that inhibit this pathway, such as aldose reductase inhibitors, have not been widely used in clinical practice.…”