AMPKα2 regulates fasting-induced hyperketonemia by suppressing SCOT ubiquitination and degradation

Ketone bodies serve as an energy source, especially in the absence of carbohydrates or in the extended exercise. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a crucial energy sensor that regulates lipid and glucose metabolism. However, whether AMPK regulates ketone metabolism in whole body is unclear even though AMPK regulates ketogenesis in liver. Prolonged resulted in a significant increase in blood and urine levels of ketone bodies in wild-type (WT) mice. Interestingly, fasting AMPKα2^-/- and AMPKα1^-/- mice exhibited significantly higher levels of ketone bodies in both blood and urine compared to fasting WT mice. BHB tolerance assays revealed that both AMPKα2^-/- and AMPKα1^-/- mice exhibited slower ketone consumption compared to WT mice, as indicated by higher blood BHB or urine BHB levels in the AMPKα2^-/- and AMPKα1^-/- mice even after the peak. Interestingly, fasting AMPKα2^-/- and AMPKα1^-/- mice exhibited significantly higher levels of ketone bodies in both blood and urine compared to fasting WT mice. . Specifically, AMPKα2^ΔMusc mice showed approximately a twofold increase in blood BHB levels, and AMPKα2^ΔMyo mice exhibited a 1.5-fold increase compared to their WT littermates after a 48-h fasting. However, blood BHB levels in AMPKα1^ΔMusc and AMPKα1^ΔMyo mice were as same as in WT mice. Notably, AMPKα2^ΔMusc mice demonstrated a slower rate of BHB consumption in the BHB tolerance assay, whereas AMPKα1^ΔMusc mice did not show such an effect. Declining rates of body weights and blood glucoses were similar among all the mice. Protein levels of SCOT, the rate-limiting enzyme of ketolysis, decreased in skeletal muscle of AMPKα2^-/- mice. Moreover, SCOT protein ubiquitination increased in C2C12 cells either transfected with kinase-dead AMPKα2 or subjected to AMPKα2 inhibition. AMPKα2 physiologically binds and stabilizes SCOT, which is dependent on AMPKα2 activity.