Demonstration of kynurenine aminotransferases I and II and characterization of kynurenic acid synthesis in cultured cerebral cortical neurons

Abstract

The present study characterizes the synthesis of kynurenic acid (KYNA) from exogenously added kynurenine and its regulation by extrinsic factors, in cultured cerebral cortical neurons and, for comparison, in astrocytes incubated under identical conditions. The neuronal culture showed positive immunostaining for both kynurenic acid aminotransferase (KAT) isoforms I and II. Neurons synthesized KYNA at a rate about 2.3 times higher than astrocytes. Neuronal, but not astrocytic, KYNA synthesis was lowered approximately 30% by ionotropic glutamate receptor agonists [(R,S)-3-hydroxy-5-methoxyloxasole-4-propionic acid (AMPA; 100 microM) and N-methyl-D-aspartic acid (NMDA; 100 microM)] and depolarizing agents [KCl (50 mM) and 4-aminopyridine (4-AP; 10 microM)]. Neuronal and astrocytic synthesis alike were vulnerable to inhibition exerted by the aminotransferase inhibitor aminooxyacetic acid (AOAA), glutamate (IC50: 31 and 85 microM, respectively), substrates of the L-amino transport system [leucine (Leu); IC50: 19 and 42 microM, respectively] and 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH; IC50: 19 and 28 microM, respectively). Glutamine (Gln), which is a metabolic precursor of glutamate in astrocytes and L-system substrate in both cell types, inhibited KYNA synthesis both in neurons and in astrocytes (IC50: 268 and 318 microM, respectively). alpha-Ketoisocaproic acid (KIC), a Leu transamination product that is produced mainly in astrocytes and shuttled to neurons to modulate intraneuronal concentration of glutamate, stimulated KYNA synthesis in neurons but did not affect the synthesis in astrocytes. In conclusion, this study is the first to demonstrate active, regulation-prone KYNA synthesis in neurons.

Prognostic impact ofTP53mutation status for adult patients with supratentorial World Health Organization Grade II astrocytoma or oligoastrocytoma

“…These experiments also revealed an uneven distribution of KAT II immunoreactivity within the astrocytes, both in terms of the intensity of staining as well as the ability to discern fine processes. Notably, however, although KAT II has been reported to exist in retinal ganglion cells (Rejdak et al,2004) and in cultured oligodendrocytes (Wejksza et al,2005) and cortical neurons (Rzeski et al,2005), we found no evidence for KAT II immunoreactivity in cells other than astrocytes in our survey of the entire rat brain.…”

Demonstration of Kynurenine Aminotransferases I and II and Characterization of Kynurenic Acid Synthesis in Oligodendrocyte Cell Line (OLN-93)

“…While KYNA synthesis has long been thought to take place exclusively in astrocytes, more recent evidence indicates that KYNA synthesizing enzymes can also be located in other cells of the CNS, e.g. in neurons (12).…”

Systemic L-Kynurenine sulfate administration disrupts object recognition memory, alters open field behavior and decreases c-Fos immunopositivity in C57Bl/6 mice

“…Certain kynurenines (e.g., KYNA) have been demonstrated to have neuroactive properties (Lapin, 1978; Perkins and Stone, 1982; Stone and Darlington, 2007; Vécsei et al, 2013). The de novo formation of KYNA from its precursor L-KYN is associated with the action of the kynurenine aminotransferases (KATs), and especially KAT II, which is located predominantly in the glial cells, but can also be found in the neurons (Guidetti et al, 1997; Rzeski et al, 2005; Lim et al, 2007). It is known mainly from in vitro studies that KYNA acts as a non-competitive antagonist on the α7 nicotinic acetylcholine (α7nACh) receptor at submicromolar level (Hilmas et al, 2001; Albuquerque and Schwarcz, 2013).…”