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

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.