Abstract / Summary
Sustained upregulation of hepatic gluconeogenesis is a major source of hyperglycemia in type 2 diabetes, and obesity is the primary driver. However, a substantial subset of obese individuals does not progress to diabetes, a condition termed metabolically healthy obesity, and the underlying mechanism has long remained unclear. ROS act both as physiological signals and as pathological drivers, but no molecular marker characterizes the transition between these two states, making it difficult to time antioxidant intervention against oxidative modification-mediated damage. Here we show that the activity of phosphoenolpyruvate carboxykinase 1 (PCK1), a key enzyme of gluconeogenesis, is redox-sensitive. Excess accumulated ROS induce reversible sulfenylation at cysteine 288, near the catalytic center, directly driving gluconeogenesis in the absence of insulin. We therefore propose a dual regulatory model of glucose metabolism signaled by hepatic oxidative load. At low oxidative load, ROS activate AMP-activated protein kinase (AMPK) via glutathionylation to promote glycolysis, whereas once the load accumulates, PCK1 is activated via sulfenylation to drive gluconeogenesis, accompanied by a decline in AMPK glutathionylation. Hepatic oxidative load therefore acts as a switch governing the direction of hepatic glucose flux. In diabetic mice, the two modifications show a complementary, stage-dependent distribution paralleling this accumulation, with AMPK glutathionylation predominating in the compensatory stage and PCK1 sulfenylation becoming dominant as the load accumulates further. Their reciprocal dynamic therefore serves as an early warning signal for the transition of ROS from physiological to pathological states. On this basis, we intervened as oxidative load began to accumulate, and found that lowering hepatic ROS prevented the oxidative activation of PCK1, suppressed gluconeogenesis and ameliorated hyperglycemia. These findings reveal that the key gluconeogenic enzyme is directly regulated by redox signals independently of insulin, providing a molecular basis for the heterogeneity of diabetes progression in obesity and for the precise timing of antioxidant intervention.