Neuropathologic and biochemical changes during disease progression in liver X receptor beta-/- mice, a model of adult neuron disease.

In amyotrophic lateral sclerosis (ALS), there is selective degeneration of motor neurons that leads to paralysis and death. Although the etiology of ALS is unclear, its heterogeneity suggests that a combination of factors (endogenous and/or environmental) may induce progressive motor neuron stress that results in the activation of different cell death pathways. Alterations of brain cholesterol homeostasis have recently been considered as possible cofactors in many neurodegenerative disorders, including ALS. The liver X receptor beta (LXR beta) receptor is involved in lipogenesis and cholesterol metabolism, and we previously found that adult-onset motor neuron pathology occurs in LXR beta(-/-) mice. Here, we investigated neuromuscular alterations of LXR beta(-/-) mice from ages 3 to 24 months. Increased cholesterol levels, gliosis, and inflammation preceded motor neuron loss and clinical disease onset; the mice showed progressive motor neuron deficits starting from age 7 months. The numbers of motor neurons and neuromuscular junctions were decreased in 24-month-old mice, but neither paralysis nor reduced life span was observed. Moreover, other spinal neurons were also lost in these mice. These results suggest that LXR beta may inhibit neuroinflammation and maintain cholesterol homeostasis, and that LXR beta(-/-) represent a potential model for investigating the role of cholesterol in ALS and other neurodegenerative disorders.