No abstract

Cu, Zn superoxide dismutase (SOD1) has been detected within spinal cord mitochondria of mutant SOD1 transgenic mice, a model of familial ALS. The copper chaperone for SOD1 (CCS) provides SOD1 with copper, facilitates the conversion of immature apo-SOD1 to a mature holoform, and influences in yeast the cytosolic/ mitochondrial partitioning of SOD1. To determine how CCS affects G93A-SOD1-induced disease, we generated transgenic mice overexpressing CCS and crossed them to G93A-SOD1 or wild-type SOD1 transgenic mice. Both CCS transgenic mice and CCS/wild-type-SOD1 dual transgenic mice are neurologically normal. In contrast, CCS/G93A-SOD1 dual transgenic mice develop accelerated neurological deficits, with a mean survival of 36 days, compared with 242 days for G93A-SOD1 mice. Immuno-EM and subcellular fractionation studies on the spinal cord show that G93A-SOD1 is enriched within mitochondria in the presence of CCS overexpression. Our results indicate that CCS overexpression in G93A-SOD1 mice produces severe mitochondrial pathology and accelerates disease course.amyotrophic lateral sclerosis ͉ motor neuron ͉ neurodegeneration ͉ transgenic ͉ aggregation

Metabolic acidosis results in impaired renal tubular phosphate reabsorption and proximal tubular apical brush border membrane (BBM) sodium gradient-dependent phosphate transport (Na/Pi cotransport) activity. In the present study we investigated the cellular mechanisms responsible for decreased Na/Pi cotransport activity following six hours to 10 days of metabolic acidosis induced by ingestion of NH4Cl. Urinary Pi excretion was significantly increased and BBM Na/Pi cotransport activity was progressively and significantly decreased by 18% at six hours, 24% at 12 hours, 32% at 24 hours, and 61% after 10 days of metabolic acidosis. The progressive and time-dependent decreases in BBM cotransport activity were associated with progressive decreases in BBM NaPi-2 protein (43% at 12 hr, 54% at 24 hr and 66% at 10 days) and cortical NaPi-2 mRNA (22% at 12 hr, 54% at 24 hr and 56% at 10 days) abundance. Interestingly, following six hours of metabolic acidosis, there was a significant 29% decrease in BBM NaPi-2 protein abundance that was not associated with decreases in either cortical homogenate NaPi-2 protein or cortical NaPi-2 mRNA abundance. In additional studies we found that the effects of chronic metabolic acidosis on Na/Pi cotransport activity were independent of endogenous parathyroid hormone activity, but were somewhat dependent on dietary Pi intake. In rats fed a high or a normal Pi diet metabolic acidosis caused significant decreases in Na/Pi cotransport activity, NaPi-2 protein and NaPi-2 mRNA abundance, however, in rats fed a low Pi diet the inhibitory effect of metabolic acidosis on Na/Pi cotransport were minimal and not significant. These results indicate that in chronic (> or = 12 hr) metabolic acidosis the progressive decrease in BBM Na/Pi cotransport activity is most likely mediated by decrease in BBM NaPi-2 protein and cortical mRNA abundance. In contrast, in acute (< or = 6 hr) metabolic acidosis the decrease in BBM Na/Pi cotransport activity is likely mediated by changes in the trafficking of the NaPi-2 protein that is, enhanced internalization from and/or impaired delivery of the NaPi-2 protein to the apical BBM.

Mutations in the Cu/Zn superoxide dismutase (SOD1) gene cause one form of familial amyotrophic lateral sclerosis, a progressive disorder of motor neurons leading to weakness and death of affected individuals. Experiments using both transgenic mice expressing mutant SOD1 and SOD1 knock-out mice have demonstrated that disease is caused by a toxic gain of function and not by a loss of normal SOD1 activity. Precise mechanisms underlying mutant SOD1 toxicity are unclear but may involve abnormal interactions between zinc and SOD1. The metallothioneins (MTs) represent a family of zinc binding proteins that can function as zinc chaperones for apo-SOD1 in vitro. We hypothesized that manipulation of metallothioneins in vivo might alter the disease phenotype of transgenic mice expressing G93A SOD1 and therefore crossed this line with MT-I and MT-II or MT-III knock-out mice. G93A SOD1 mice deficient of either MT-I and MT-II or MT-III exhibited significant reductions in survival compared with G93A SOD1 mice. In addition, motor dysfunction was markedly accelerated in G93A SOD1 mice deficient in metallothioneins with regard to onset (MT-I and MT-II) or progression (MT-III). These results indicate that the disease course in G93A SOD1 mice is dependent on levels of metallothionein expression. Because MT-I and MT-II are expressed in glia whereas MT-III is found in neurons, these results also indicate that primary changes within non-neuronal cells can affect mutant SOD1-induced disease and do so in ways distinct from primary neuronal changes.

The identification of proteins which determine fat and lean body mass composition is critical to better understanding and treating human obesity. TDP-43 is a well-conserved RNA-binding protein known to regulate alternative splicing and recently implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). While TDP-43 knockout mice show early embryonic lethality, post-natal conditional knockout mice show weight loss, fat depletion, and rapid death, suggesting an important role for TDP-43 in regulating energy metabolism. Here we report, that over-expression of TDP-43 in transgenic mice can result in a phenotype characterized by increased fat deposition and adipocyte hypertrophy. In addition, TDP-43 over-expression in skeletal muscle results in increased steady state levels of Tbc1d1, a RAB-GTPase activating protein involved in Glucose 4 transporter (Glut4) translocation. Skeletal muscle fibers isolated from TDP-43 transgenic mice show altered Glut4 translocation in response to insulin and impaired insulin mediated glucose uptake. These results indicate that levels of TDP-43 regulate body fat composition and glucose homeostasis in vivo.