Interplay between Neuronal Metabolism and Signaling in Model Systems with Impaired α-Ketoglutarate Dehydrogenase...

The α-ketoglutarate dehydrogenase complex (KGDHC) serves as a master regulator of cell's molecular machinery. Beyond its classical role as a rate-limiting enzyme in the tricarboxylic acid (TCA) cycle, KGDHC has emerged as a critical redox sensor that can act as both a source and a target of reactive oxygen species (ROS), thereby regulating cellular redox homeostasis. This review summarizes evidence from genetically modified animal models and cell culture studies demonstrating that compromised KGDHC activity affects neuronal metabolism, redox homeostasis, and cellular signaling. KGDHC dysfunction causes mitochondrial failure, resulting in reduced ATP synthesis and activation of AMP-activated protein kinase (AMPK). Although inhibition of KGDHC reduces mitochondrial ROS formation, it also disrupts physiological ROS-dependent signaling mechanisms. In KGDHC-deficient mice, impaired ROS signaling and energy deficit decrease brain adaptability, increase susceptibility to neurotoxins, and disrupt crucial pathways by downregulating PGC-1α and Nrf2. These alterations result in suppression of antioxidant defences and lead to neuronal death in the hippocampus and memory impairment. Moreover, KGDHC dysfunction induces mitochondrial fragmentation and is strongly linked to excitotoxicity, further accelerating neuronal dysfunction. As observed in heterozygous models, even partial KGDHC deficiency can exacerbate persisting cellular and mitochondrial defects, leading to the development of more severe pathological conditions.