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The kidneys consume a large amount of energy to regulate volume status and blood pressure and to excrete uremic toxins. The identification of factors that cause energy mismatch in the setting of chronic kidney disease (CKD) and the development of interventions aimed at improving this mismatch are key research imperatives. Although the critical cellular energy sensor 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is known to be inactivated in CKD, the mechanism of AMPK dysregulation is unknown. In a mouse model of CKD, metabolome analysis confirmed a decrease in AMPK activation in the kidneys despite a high AMP: ATP ratio, suggesting that AMPK did not sense energy depletion. Similar AMPK inactivation was found in heart and skeletal muscle in CKD mice. Several uremic factors were shown to inactivate AMPK in vitro and in ex vivo preparations of kidney tissue. The specific AMPK activator A-769662, which bypasses the AMP sensing mechanism, ameliorated fibrosis and improved energy status in the kidneys of CKD mice, whereas an AMP analog did not. We further demonstrated that a low-protein diet activated AMPK independent of the AMP sensing mechanism, leading to improvement in energy metabolism and kidney fibrosis. These results suggest that a failure to sense AMP is the key mechanism underlying the vicious cycle of energy depletion and CKD progression and direct AMPK activation may be a novel therapeutic approach in CKD., (Copyright © 2018 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Cells are frequently exposed to hypoxia in physiological and pathophysiological conditions in organisms. Control of energy metabolism is one of the critical functions of the hypoxic response. Hypoxia-Inducible Factor (HIF) is a central transcription factor that regulates the hypoxic response. HIF prolyl-hydroxylase PHDs are the enzymes that hydroxylate the α subunit of HIF and negatively regulate its expression. To further understand the physiological role of PHD3, proteomics were used to identify PHD3-interacting proteins, and pyruvate dehydrogenase (PDH)-E1β was identified as such a protein. PDH catalyzes the conversion of pyruvate to acetyl-coA, thus playing a key role in cellular energy metabolism. PDH activity was significantly decreased in PHD3-depleted MCF7 breast cancer cells and PHD3(-/-) MEFs. PHD3 depletion did not affect the expression of the PDH-E1α, E1β, and E2 subunits, or the phosphorylation status of E1α, but destabilized the PDH complex (PDC), resulting in less functional PDC. Finally, PHD3(-/-) cells were resistant to cell death in prolonged hypoxia with decreased production of ROS. Taken together, the study reveals that PHD3 regulates PDH activity in cells by physically interacting with PDC., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Pharmacologic activation of the heterodimeric HIF transcription factor appears promising as a strategy to treat diseases, such as anemia, myocardial infarction, and stroke, in which tissue hypoxia is a prominent feature. HIF accumulation is normally linked to oxygen availability because an oxygen-dependent posttranslational modification (prolyl hydroxylation) marks the HIFalpha subunit for polyubiquitination and destruction. Three enzymes (PHD1, PHD2, and PHD3) capable of catalyzing this reaction have been identified, although PHD2 (also called Egln1) appears to be the primary HIF prolyl hydroxylase in cell culture experiments. We found that conditional inactivation of PHD2 in mice is sufficient to activate a subset of HIF target genes, including erythropoietin, leading to striking increases in red blood cell production. Mice lacking PHD2 exhibit premature mortality associated with marked venous congestion and dilated cardiomyopathy. The latter is likely the result of hyperviscosity syndrome and volume overload, although a direct effect of chronic, high-level HIF stimulation on cardiac myocytes cannot be excluded.