Expression of mitochondrial tricarboxylate carrier TCC mRNA and protein in the rat brain

Molecular Cloning and Characterization of a Novel Human Putative Transmembrane Protein Homologous to Mouse Sideroflexin Associated with Sideroblastic Anemia

Sideroflexin1 (Sfxn1), the prototype of a novel family of evolutionarily conserved proteins present in eukaryotes, has been found mutated in mice with siderocytic anemia. It is speculated that this protein facilitates the transport of a component required for iron utilization into mitochondrial. During the large-scale sequencing analysis of a human fetal brain cDNA library, we isolated a cDNA encoding a novel sideroflexin protein (SFXN4), which showed 59% identity and 71% similarity to mouse sideroflexin4. According to the search of the human genome database, SFXN4 gene is mapped to chromosome 10q25-26 and spans more than 24.7kb of the genomic DNA. It is 1428 base pair in length and the putative protein contains 305 amino acids with a conserved predicted five-transmembrane-domains structure. RT-PCR result shows that the SFXN4 gene is expressed in many tissues.

Mitochondrial glutathione uptake: characterization in isolated brain mitochondria and astrocytes in culture

Glutathione in the mitochondria is an important determinant of cellular responses to oxidative stress. Mitochondrial glutathione is maintained by uptake from the cytosol, a process that has been little studied in brain cells. In the present study, measurements using isolated rat brain mitochondria showed a rapid uptake of [3H]-glutathione that was strongly influenced by the mitochondrial glutathione content. [3H]-glutathione incorporated into the mitochondria was not rapidly released. Uptake was inhibited by substrates and inhibitors for several known mitochondrial anion transporters. Citrate, isocitrate and benzene-1,2,3-tricarboxylate were particularly effective inhibitors, suggesting a possible role for a tricarboxylate carrier in the glutathione transport. The properties of uptake differed greatly from those reported previously for mitochondria from kidney and liver. In astrocytes in primary culture, diethylmaleate or hydrogen peroxide treatment resulted in depletion of cytosolic and mitochondrial glutathione. The pattern of restoration of glutathione content in the presence of glutathione precursors following treatment with diethylmaleate was consistent with uptake into mitochondria being controlled primarily by the glutathione gradient between the cytosol and mitochondria. However, following hydrogen peroxide treatment, recovery of glutathione in the mitochondria initially preceded comparable proportional restoration in the cytosol, suggesting the possibility of additional controls on glutathione uptake in some conditions.

Mitochondrial Transporters as Novel Targets for Intracellular Calcium Signaling

Ca2+signaling in mitochondria is important to tune mitochondrial function to a variety of extracellular stimuli. The main mechanism is Ca2+entry in mitochondria via the Ca2+uniporter followed by Ca2+activation of three dehydrogenases in the mitochondrial matrix. This results in increases in mitochondrial NADH/NAD ratios and ATP levels and increased substrate uptake by mitochondria. We review evidence gathered more than 20 years ago and recent work indicating that substrate uptake, mitochondrial NADH/NAD ratios, and ATP levels may be also activated in response to cytosolic Ca2+signals via a mechanism that does not require the entry of Ca2+in mitochondria, a mechanism depending on the activity of Ca2+-dependent mitochondrial carriers (CaMC). CaMCs fall into two groups, the aspartate-glutamate carriers (AGC) and the ATP-Mg/Picarriers, also named SCaMC (for short CaMC). The two mammalian AGCs, aralar and citrin, are members of the malate-aspartate NADH shuttle, and citrin, the liver AGC, is also a member of the urea cycle. Both types of CaMCs are activated by Ca2+in the intermembrane space and function together with the Ca2+uniporter in decoding the Ca2+signal into a mitochondrial response.

FLRT3, a cell surface molecule containing LRR repeats and a FNIII domain, promotes neurite outgrowth

The mature peripheral nervous system has the ability to survive and to regenerate its axons following axonal injury. After nerve injury, the distal axonal and myelin segment undergoes dissolution and absorption by the surrounding cellular environment, a process called Wallerian degeneration. Using cDNA microarrays, we isolated FLRT3 as one of the up-regulated genes expressed in the distal segment of the sciatic nerve 7 days after transection relative to those of the intact sciatic nerve. FLRT3 is a putative type I transmembrane protein containing 10 leucine-rich repeats, a fibronectin type III domain, and an intracellular tail. The neurons plated on CHO cells expressing FLRT3 extended significantly longer neurites than those plated on wild-type CHO cells, demonstrating that FLRT3 promotes neurite outgrowth. FLRT3 mRNA was especially abundant in the basal ganglia, the granular layer of cerebellum, and the hippocampus, except the CA1 region in the adult rat brain. Thus, FLRT3 may contribute to regeneration following axonal injury.