Mitochondrial pyruvate carrier regulates autophagy, inflammation, and neurodegeneration in experimental models of Parkinsons disease

Pyruvate constitutes a critical branch point in cellular carbon metabolism. We have identified two proteins, Mpc1 and Mpc2, as essential for mitochondrial pyruvate transport in yeast, Drosophila, and humans. Mpc1 and Mpc2 associate to form an ~150-kilodalton complex in the inner mitochondrial membrane. Yeast and Drosophila mutants lacking MPC1 display impaired pyruvate metabolism, with an accumulation of upstream metabolites and a depletion of tricarboxylic acid cycle intermediates. Loss of yeast Mpc1 results in defective mitochondrial pyruvate uptake, and silencing of MPC1 or MPC2 in mammalian cells impairs pyruvate oxidation. A point mutation in MPC1 provides resistance to a known inhibitor of the mitochondrial pyruvate carrier. Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes. These data demonstrate that Mpc1 and Mpc2 form an essential part of the mitochondrial pyruvate carrier.

The human brain contains 100 billion neurons and probably one thousand times more synapses. Such a system can be analyzed at different complexity levels, from cognitive functions to molecular structure of ion channels. However, it remains extremely difficult to establish links between these different levels. An alternative strategy relies on the use of much simpler animals that can be easily manipulated. In 1974, S. Brenner introduced the nematode Caenorhabditis elegans as a model system. This worm has a simple nervous system that only contains 302 neurons and about 7,000 synapses. Forward genetic screens are powerful tools to identify genes required for specific neuron functions and behaviors. Moreover, studies of mutant phenotypes can identify the function of a protein in the nervous system. The data that have been obtained in C. elegans demonstrate a fascinating conservation of the molecular and cellular biology of the neuron between worms and mammals through more than 550 million years of evolution.

A murine cell line (BV-2) has been generated by infecting primary microglial cell cultures with a v-raf/v-myc oncogene carrying retrovirus (J2). BV-2 cells expressed nonspecific esterase activity, phagocytic ability and lacked peroxidase activity. Such cells secreted lysozyme and, following appropriate stimulation, also interleukin 1 and tumor necrosis factor. Furthermore, BV-2 cells exhibited spontaneous anti-Candida activity and acquired tumoricidal activity upon treatment with interferon-gamma. Phenotypically, BV-2 cells resulted positive for MAC1 and MAC2 antigens, and negative for MAC3, glial fibrillary acidic protein (GFAP) and galactocerebroside (GC) antigens. Since BV-2 cells retain most of the morphological, phenotypical and functional properties described for freshly isolated microglial cells, we can conclude that J2 virus infection has resulted in the immortalization of active microglial cells.