BackgroundThe healthy heart has a dynamic capacity to respond and adapt to changes in nutrient availability. Diabetes mellitus disrupts this metabolic flexibility and promotes cardiomyopathy through mechanisms that are not completely understood. Phosphofructokinase 2 (PFK‐2) is a primary regulator of cardiac glycolysis and substrate selection, yet its regulation under normal and pathological conditions is unknown. This study was undertaken to determine how changes in insulin signaling affect PFK‐2 content, activity, and cardiac metabolism.Methods and ResultsStreptozotocin‐induced diabetes mellitus, high‐fat diet feeding, and fasted mice were used to identify how decreased insulin signaling affects PFK‐2 and cardiac metabolism. Primary adult cardiomyocytes were used to define the mechanisms that regulate PFK‐2 degradation. Both type 1 diabetes mellitus and a high‐fat diet induced a significant decrease in cardiac PFK‐2 protein content without affecting its transcript levels. Overnight fasting also induced a decrease in PFK‐2, suggesting it is rapidly degraded in the absence of insulin signaling. An unbiased metabolomic study demonstrated that decreased PFK‐2 in fasted animals is accompanied by an increase in glycolytic intermediates upstream of phosphofructokianse‐1, whereas those downstream are diminished. Mechanistic studies using cardiomyocytes showed that, in the absence of insulin signaling, PFK‐2 is rapidly degraded via both proteasomal‐ and chaperone‐mediated autophagy.ConclusionsThe loss of PFK‐2 content as a result of reduced insulin signaling impairs the capacity to dynamically regulate glycolysis and elevates the levels of early glycolytic intermediates. Although this may be beneficial in the fasted state to conserve systemic glucose, it represents a pathological impairment in diabetes mellitus.

Introduction-As an insulin sensitive tissue, the heart decreases glucose usage during fasting. This response is mediated, in part, by decreasing phosphofructokinase-2 (PFK-2) activity and levels of its product fructose-2,6-bisphosphate. However, the importance of fructose-2,6bisphosphate in the fasting response on other metabolic pathways has not been evaluated.Objectives-The goal of this study is to determine how sustaining cardiac fructose-2,6bisphosphate levels during fasting affects the metabolomic profile.Methods-Control and transgenic mice expressing a constitutively active form of PFK-2 (Glyco Hi ) were subjected to either 12-hours fasting or regular feeding. Animals (n=4 per group) were used for whole-heart extraction, followed by GC-MS metabolic profiling and multivariate data analysis.Results-Principal component analysis displayed differences between Control and Glyco Hi groups under both fasting and fed conditions while a clear response to fasting was observed only for Control animals. However, pathway analysis revealed that these smaller changes in the Glyco Hi group were significantly associated with branched-chain amino acid (BCAA) metabolism (~40% increase in all BCAAs). Correlation network analysis demonstrated clear differences in response

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