Regulation of Pyruvate Dehydrogenase Kinase 4 in the Heart through Degradation by the Lon Protease in Response to Mitochondrial Substrate Availability

Abstract

Edited by George N. DeMartinoCardiac metabolic inflexibility is driven by robust up-regulation of pyruvate dehydrogenase kinase 4 (PDK4) and phosphorylation-dependent inhibition of pyruvate dehydrogenase (PDH) within a single day of feeding mice a high fat diet. In the current study, we have discovered that PDK4 is a short lived protein (t1 ⁄ 2 ϳ 1 h) and is specifically degraded by the mitochondrial protease Lon. Lon does not rapidly degrade PDK1 and -2, indicating specificity toward the PDK isoform that is a potent modulator of metabolic flexibility. Moreover, PDK4 degradation appears regulated by dissociation from the PDH complex dependent on the respiratory state and energetic substrate availability of mouse heart mitochondria. Finally, we demonstrate that pharmacologic inhibition of PDK4 promotes PDK4 degradation in vitro and in vivo. These findings reveal a novel strategy to manipulate PDH activity by selectively targeting PDK4 content through dissociation and proteolysis.Dynamic regulation of metabolism is required for cells to respond to nutrient availability and stress to support ATP production and anabolic processes. Misappropriated metabolic alterations can exert deleterious effects as evidenced in diabetes and in many cancers where the preference for a specific metabolic profile promotes the progression of disease (1, 2). The heart derives energy primarily from the oxidation of fatty acids. However, glucose utilization increases with enhanced availability and is essential for cardiac function, particularly in response to physiologic and pathophysiologic stress. Obesity and diabetes are characterized by heavy reliance of the heart on fatty acids for energy production and the inability to appropriately utilize glucose (1). Loss of metabolic flexibility is believed to underlie associated cardiovascular disease. In mouse models of diet-induced obesity, induction of cardiac metabolic inflexibility has long been attributed to insulin resistance and altered glucose transporter 4 expression and transport (1, 3). However, we have recently made the discovery that these events are preceded by diminished mitochondrial oxidation of glucose-derived pyruvate, occurring within the 1st day of high fat feeding (4).The mitochondrial enzyme pyruvate dehydrogenase (PDH) 2 commits glycolytically derived pyruvate for ATP production and is central to regulating the use of glucose relative to fatty acids for energy homeostasis. Cardiac PDH activity is regulated by various isoforms of pyruvate dehydrogenase kinase (PDK1, -2, and -4) and phosphatase (PDP1 and -2) with phosphorylation resulting in enzyme inhibition (5-7). We demonstrated that a selective increase in cardiac PDK4 expression and inhibition of PDH are responsible for the rapid diet-induced loss of mitochondrial pyruvate utilization and the ensuing development of insulin resistance in the heart (4). Given that PDK4-mediated inhibition of PDH is an initiating event in diet-induced metabolic inflexibility and PDH is a key site for control of glucose oxidation, it is ...

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“…It has been recently recognized that the increase in PDK4 protein levels is extremely rapid and occurs within the first day when feeding mice a high‐fat diet (Crewe et al. 2013, 2017). Likewise, the turnover of malonyl‐CoA, the allosteric inhibitor of CPT1, is very rapid in the heart (Reszko et al.…”

“…PDH is an important metabolic control point where the competition between carbohydrates and fatty acids as metabolic substrates is rapidly regulated in the heart (Lopaschuk et al 2010). It has been recently recognized that the increase in PDK4 protein levels is extremely rapid and occurs within the first day when feeding mice a high-fat diet (Crewe et al , 2017. Likewise, the turnover of malonyl-CoA, the allosteric inhibitor of CPT1, is very rapid in the heart (Reszko et al 2001), given the high expression of acetyl-CoA carboxylase (responsible for its synthesis) and malonyl-CoA decarboxylase (responsible for its degradation).…”

Coenzyme A–mediated degradation of pyruvate dehydrogenase kinase 4 promotes cardiac metabolic flexibility after high-fat feeding in mice

“…PDK4 degradation would therefore be essential to reduce PDK4 content upon return to a control diet. Evidence for such a pathway is provided by our previous findings that PDK4 has a short half-life relative to other PDK isoforms and is specifically degraded by the mitochondrial protease Lon (20). Moreover, we demonstrated that the rate of PDK4 turnover is reduced in the presence of fatty acids, indicating that protein degradation represents a previously underappreciated facet of PDK4 regulation and, in effect, cardiac PDH activity and metabolic flexibility (20).…”

“…Reductions in PDK4 protein content following transition to a low-fat diet indicate a role for PDK4 degradation. In a previous study, we demonstrated that degradation of PDK4 by the Lon protease requires dissociation of PDK4 from the PDH complex (20). We sought to determine metabolites that govern the inter-action of PDK4 with PDH and, ultimately, degradation of PDK4.…”

“…Dissociation of PDK4 from the PDH complex governs the susceptibility of PDK4 to degradation by the Lon protease (20). Metabolites promoting PDK4/PDH dissociation may therefore act as in vivo metabolic sensors linking the rate of PDK4 degradation to the nutritional needs of the cell.…”