Role of LXRβ in oligodendrocytes in neuronal survival

We have reported that mice in which the liver X receptor β (LXRβ) gene is inactivated lose dopaminergic neurons in the substantia nigra and motor neurons in the ventral horn of the spinal cord. These mice develop progressive hind limb paralysis starting at 6 months of age. Since LXRβ is not expressed in either dopaminergic neurons or motor neurons, we have focused on LXRβ-expressing cells whose function is essential for neuron survival. We now report defects in oligodendrocyte maturation in the absence of LXRβ. At 4 months of age, long before motor neuron loss occurs, there was reduction in expression of the four following genes in oligodendrocytes: The monocarboxylate transporter 1 (MCT1), which is essential for metabolic support of motor neurons; BDNF, a motor neuron trophic factor; 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR), a rate-limiting enzyme in cholesterol synthesis; glutamine synthetase (GS), an enzyme crucial for the elimination of neurotoxic glutamate from synapses. Differentiation of ES cells from WT and LXRβ^-/- mice into motor neurons/oligodendrocytes revealed that LXRβ^-/- cultures showed less arborization of motor neurons and a reduced proportion of mature oligodendrocytes. Our study suggests that defects in glial cells can have profound effects on neuronal survival and that early defective oligodendrocyte maturation can lead to motor neuron death. The expression of LXRβ in oligodendrocytes should be investigated as a target for preventing neuronal loss in diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson's disease.