Cytosolic and mitochondrial isoforms of NADP⁺‐dependent isocitrate dehydrogenases are expressed in cultured rat neurons, astrocytes, oligodendrocytes and microglial cells

Abstract

NADP + -dependent isocitrate dehydrogenases (ICDHs) are enzymes that reduce NADP + to NADPH using isocitrate as electron donor. Cytosolic and mitochondrial isoforms of ICDH have been described. Little is known on the expression of ICDHs in brain cells. We have cloned the rat mitochondrial ICDH (mICDH) in order to obtain the sequence information necessary to study the expression of ICDHs in brain cells by RT-PCR. The cDNA sequence of rat mICDH was highly homologous to that of mICDH cDNAs from other species. By RT-PCR the presence of mRNAs for both the cytosolic and the mitochondrial ICDHs was demonstrated for cultured rat neurons, astrocytes, oligodendrocytes and microglia. The expression of both ICDH isoenzymes was confirmed by western blot analysis using ICDH-isoenzyme specific antibodies as well as by determination of ICDH activities in cytosolic and mitochondrial fractions of the neural cell cultures. In astroglial and microglial cultures, the total ICDH activity was almost equally distributed between cytosolic and mitochondrial fractions. In contrast, in cultures of neurons and oligodendrocytes about 75% of total ICDH activity was present in the cytosolic fractions. Putative functions of ICDHs in cytosol and mitochondria of brain cells are discussed.

Two Hypomorphic Alleles of Mouse Ass1 as a New Animal Model of Citrullinemia Type I and Other Hyperammonemic Syndromes

“…It is tempting to suggest that a lower antioxidant capacity could be the result of a lower NADPH availability to sustain glutathione redox cycling. 46,47 Nitrative stress (evaluated as nitrotyrosine) in cerebella from mutant mice was significantly decreased when compared to controls (40% reduction in the less severe fold/fold mutants). The decreased protein nitration could result from the lower nNOS expression found in the cerebella of mutant mice and/or to other effects, not related directly to the NOS protein content, but rather to metabolite control of enzymatic activity within the tissue.…”

Activation of Neuronal Nitric Oxide Synthase in Cerebellum of Chronic Hepatic Encephalopathy Rats is Associated with Up-regulation of NADPH-Producing Pathway

“…NADPH is another substrate required for NOS activity. Although some amount of NADPH in the brain is produced by the malic enzymes and NADP + -dependent ICDH [58], PPP has been described to be the main metabolic route that generates NADPH in the brain [25,59]. Glucose-6-phosphate dehydrogenase is the rate-limiting enzyme of PPP, and therefore, a change in the level of this enzyme would be of direct consequence on PPP in the cells.…”

Metabolic and Antioxidant System Alterations in an Astrocytoma Cell Line Challenged with Mitochondrial DNA Deletion

“…Overexpression of either cytosolic or mitochondrial ICDH enhances the resistance to oxidative stress, whereas cells with decreased activity of either of the ICDH isoforms are more susceptible to oxidative stress [20]. The high activities of ICDHs in neural cells attest to their contribution to supplying NADPH for anabolic reactions and for GSH redox cycling, especially in the mitochondrial compartment [19][20][21][22].…”