Modulation of Astrocytic Mitochondrial Function by Dichloroacetate Improves Survival and Motor Performance in Inherited Amyotrophic Lateral Sclerosis

Mitochondrial dysfunction is one of the pathogenic mechanisms that lead to neurodegeneration in Amyotrophic Lateral Sclerosis (ALS). Astrocytes expressing the ALS-linked SOD1G93A mutation display a decreased mitochondrial respiratory capacity associated to phenotypic changes that cause them to induce motor neuron death. Astrocyte-mediated toxicity can be prevented by mitochondria-targeted antioxidants, indicating a critical role of mitochondria in the neurotoxic phenotype. However, it is presently unknown whether drugs currently used to stimulate mitochondrial metabolism can also modulate ALS progression. Here, we tested the disease-modifying effect of dichloroacetate (DCA), an orphan drug that improves the functional status of mitochondria through the stimulation of the pyruvate dehydrogenase complex activity (PDH). Applied to astrocyte cultures isolated from rats expressing the SOD1G93A mutation, DCA reduced phosphorylation of PDH and improved mitochondrial coupling as expressed by the respiratory control ratio (RCR). Notably, DCA completely prevented the toxicity of SOD1G93A astrocytes to motor neurons in coculture conditions. Chronic administration of DCA (500 mg/L) in the drinking water of mice expressing the SOD1G93A mutation increased survival by 2 weeks compared to untreated mice. Systemic DCA also normalized the reduced RCR value measured in lumbar spinal cord tissue of diseased SOD1G93A mice. A remarkable effect of DCA was the improvement of grip strength performance at the end stage of the disease, which correlated with a recovery of the neuromuscular junction area in extensor digitorum longus muscles. Systemic DCA also decreased astrocyte reactivity and prevented motor neuron loss in SOD1G93A mice. Taken together, our results indicate that improvement of the mitochondrial redox status by DCA leads to a disease-modifying effect, further supporting the therapeutic potential of mitochondria-targeted drugs in ALS

DCA prevents SOD1^G93A astrocyte neurotoxicity to motor neurons.

<p>Motor neuron survival 72 h after plating either on non Tg or SOD1^G93A-bearing astrocytes pretreated with DCA or vehicle as indicated. Data are expressed as percentage of non Tg control, mean ± SEM from four independent experiments. *p<0.05, significantly different from non Tg control. **p<0.05, significantly different from SOD1^G93A control.</p

DCA improves mitochondrial function in the spinal cord of SOD1^G93A mice.

<p>Calculated respiratory control ratio (RCR) for spinal cord mitochondria from non Tg or SOD1^G93A mice treated with DCA or vehicle as indicated. Data are mean ± SEM from three independent experiments. *p<0.05, significantly different from non Tg control. **p<0.05, significantly different from SOD1^G93A control.</p

Site of action of dichloroacetate.

<p>DCA inhibits the mitochondrial enzyme PDH kinase, thereby maintaining the PDH complex in its unphosphorylated catalytically active state and facilitating the aerobic oxidation of glucose.</p

DCA reduces motor neuron loss and astrocyte reactivity in the spinal cord of SOD1^G93A mice.

<p>Representative Toluidine blue stain (left column) and GFAP immunofluorescence (red, right column) in anterior horn spinal cord sections from non Tg (top), SOD1^G93A control (middle) or DCA-treated SOD1^G93A (bottom) mice. Dotted lines in right column panels indicate the limit between grey and white matter. The graphs indicate the number of neuronal somas located in Rexed lamina IX (left) and the percentage of GFAP immunoreactive area in the ventral horn (right) in the indicated groups of animals. The corresponding measurement areas are drawn in the top. Data are mean ± SEM from at least three animals per group as indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034776#s4" target="_blank">Methods</a>. *p<0.05, significantly different from non Tg control, **p<0.05, significantly different from SOD1^G93A control. Scale bars: 50 µm.</p