The Power Struggle: Kynurenine Pathway Enzyme Knockouts and Brain Mitochondrial Respiration

Numerous illnesses, including neurological and mental disorders, have been associated with mitochondrial dysfunction. Disruptions in mitochondrial respiration and energy production have been linked to dysmetabolism of the tryptophan (Trp)-kynurenine (KYN) pathway, which produces a diverse array of bioactive metabolites. Kynurenic acid (KYNA) is a putative neuroprotectant. The exact mechanisms through which Trp-KYN metabolic dysregulation affects mitochondrial function remain largely unclear. This study investigates the impact of the genetic deletion of kynurenine aminotransferase (KAT) enzymes, which are responsible for KYNA synthesis, on mitochondrial function, specifically mitochondrial respiration and ATP synthesis, and its potential role in neuropsychiatric pathology. CRISPR/Cas9-induced knockout mouse strains kat1^-/-, kat2^-/-, and kat3^-/- were generated. Eight-to-ten-week-old male mice were used, and cerebral and hepatic respiration, complex I- and II-linked oxidative phosphorylation (CI and CII OXPHOS), and complex IV (CIV) activity were measured using high-resolution respirometry. Mitochondrial membrane potential changes were measured with Fluorescence-Sensor Blue and safranin dye. KAT knockout mice exhibited significantly lower cerebellar respiration (CI OXPHOS, CII OXPHOS, and CIV activity) compared to wild-type mice. Lower baseline respiration and attenuated OXPHOS activities were observed in the hippocampus and striatum, particularly in kat2^-/- and kat3^-/- mice. Non-neuronal tissues showed reduced CIV activity, while ADP-stimulated CI and CII OXPHOS remained unchanged. The deletion of the KAT genes significantly impairs mitochondrial respiration and ATP synthesis, potentially contributing to pathogenesis. This study highlights the importance of KYNA in mitochondrial function, offering new insights into potential therapeutic targets for various disorders. Targeting the KYN pathway could mitigate mitochondrial dysfunction in a variety of diseased conditions.