The mitochondrial CIC (citrate carrier) catalyses the efflux of citrate from the mitochondrial matrix in exchange for cytosolic malate. In the present paper we show that CIC mRNA and protein markedly increase in lipopolysaccharide-activated immune cells. Moreover, CIC gene silencing and CIC activity inhibition significantly reduce production of NO, reactive oxygen species and prostaglandins. These results demonstrate for the first time that CIC has a critical role in inflammation.

The inner membranes of mitochondria contain a family of carrier proteins that are responsible for the transport in and out of the mitochondrial matrix of substrates, products, co-factors and biosynthetic precursors that are essential for the function and activities of the organelle. This family of proteins is characterized by containing three tandem homologous sequence repeats of approximately 100 amino acids, each folded into two transmembrane alpha-helices linked by an extensive polar loop. Each repeat contains a characteristic conserved sequence. These features have been used to determine the extent of the family in genome sequences. The genome of Saccharomyces cerevisiae contains 34 members of the family. The identity of five of them was known before the determination of the genome sequence, but the functions of the remaining family members were not. This review describes how the functions of 15 of these previously unknown transport proteins have been determined by a strategy that consists of expressing the genes in Escherichia coli or Saccharomyces cerevisiae, reconstituting the gene products into liposomes and establishing their functions by transport assay. Genetic and biochemical evidence as well as phylogenetic considerations have guided the choice of substrates that were tested in the transport assays. The physiological roles of these carriers have been verified by genetic experiments. Various pieces of evidence point to the functions of six additional members of the family, but these proposals await confirmation by transport assay. The sequences of many of the newly identified yeast carriers have been used to characterize orthologs in other species, and in man five diseases are presently known to be caused by defects in specific mitochondrial carrier genes. The roles of eight yeast mitochondrial carriers remain to be established.

The mitochondrial carriers are a family of transport proteins that, with a few exceptions, are found in the inner membranes of mitochondria. They shuttle metabolites and cofactors through this membrane, and connect cytoplasmic functions with others in the matrix. SAM (S-adenosylmethionine) has to be transported into the mitochondria where it is converted into S-adenosylhomocysteine in methylation reactions of DNA, RNA and proteins. The transport of SAM has been investigated in rat liver mitochondria, but no protein has ever been associated with this activity. By using information derived from the phylogenetically distant yeast mitochondrial carrier for SAM and from related human expressed sequence tags, a human cDNA sequence was completed. This sequence was overexpressed in bacteria, and its product was purified, reconstituted into phospholipid vesicles and identified from its transport properties as the human mitochondrial SAM carrier (SAMC). Unlike the yeast orthologue, SAMC catalysed virtually only countertransport, exhibited a higher transport affinity for SAM and was strongly inhibited by tannic acid and Bromocresol Purple. SAMC was found to be expressed in all human tissues examined and was localized to the mitochondria. The physiological role of SAMC is probably to exchange cytosolic SAM for mitochondrial S-adenosylhomocysteine. This is the first report describing the identification and characterization of the human SAMC and its gene.

Up-regulation of heme oxygenase (HO-1) by either cobalt protoporphyrin (CoPP) or human gene transfer improves vascular and renal function by several mechanisms, including increases in antioxidant levels and decreases in reactive oxygen species (ROS) in vascular and renal tissue. The purpose of the present study was to determine the effect of HO-1 overexpression on mitochondrial transporters, cytochrome c oxidase, and anti-apoptotic proteins in diabetic rats (streptozotocin, (STZ)-induced type 1 diabetes). Renal mitochondrial carnitine, deoxynucleotide, and ADP/ATP carriers were significantly reduced in diabetic compared with nondiabetic rats ( p < 0.05). The citrate carrier was not significantly decreased in diabetic tissue. CoPP administration produced a robust increase in carnitine, citrate, deoxynucleotide, dicarboxylate, and ADP/ATP carriers and no significant change in oxoglutarate and aspartate/ glutamate carriers. The increase in mitochondrial carriers (MCs) was associated with a significant increase in cytochrome c oxidase activity. The administration of tin mesoporphyrin (SnMP), an inhibitor of HO-1 activity, prevented the restoration of MCs in diabetic rats. Human HO-1 cDNA transfer into diabetic rats increased both HO-1 protein and activity, and restored mitochondrial ADP/ ATP and deoxynucleotide carriers. The increase in HO-1 by CoPP administration was associated with a significant increase in the phosphorylation of AKT and levels of BcL-XL proteins. These observations in experimental diabetes suggest that the cytoprotective mechanism of HO-1 against oxidative stress involves an increase in the levels of MCs and anti-apoptotic proteins as well as in cytochrome c oxidase activity.The heme-heme oxygenase (HO), 4 HO-1 and HO-2, isoforms, are viewed as having a major role in the formation of carbon monoxide (CO) and bilirubin, and in heme breakdown (1-3). The fact that HO-1 is strongly induced by its substrate, heme, and by oxidant stress, in conjunction with the robust ability of HO-1 to guard against oxidative insult (4, 5), suggests a countervailing system to oxidative stress injury. HO-1 is a regulator of endothelial cell integrity and oxidative stress (4 -6). Up-regulation of HO-1 by pharmacological agents, including cobalt protoporphyrin (CoPP), has been shown to increase superoxide dismutase and to decrease reactive oxygen species (ROS) and NAD(P)H oxidase activity in vitro and in vivo (7-9). In earlier studies, we, as well as others, have demonstrated that overexpression of the HO-1 gene in human, rabbit, and rat endothelial cells not only renders the cells resistant to agents that elicit oxidative stress but also enhances cell growth (6) and angiogenesis (10, 11) via HO-1-derived CO (12). More recently, up-regulation of HO-1 has been shown to prevent endothelial cell death and sloughing in diabetic rats (8).Mitochondrially generated ROS have been well documented in diabetes (13,14). Hyperglycemia-mediated local formation of ROS is considered to be a major contributing factor to renal and vascula...