Liver X Receptor Regulation of Glial Cell Functions in the CNS

In this review, we discuss the role of liver X receptors (LXRs) in glial cells (microglia, oligodendrocytes and astrocytes) in the central nervous system (CNS). LXRs are oxysterol-activated nuclear receptors that, in adults, regulate genes involved in cholesterol homeostasis, the modulation of inflammatory responses and glutamate homeostasis. The study of LXR knockout mice has revealed that LXR beta plays a key role in maintaining the health of dopaminergic neurons in the substantia nigra, large motor neurons in the spinal cord and retinal ganglion cells in the eye. In the peripheral nervous system (PNS), LXR beta is responsible for the health of the spiral ganglion neurons (SGNs) in the cochlea. In addition, LXRs are essential for the homeostasis of the cerebrospinal fluid (CSF), and in LXR alpha beta(-/-) mice, the lateral ventricles are empty and lined with lipid-laden cells. As LXR alpha beta(-/-) mice age, lipid vacuoles accumulate in astrocytes surrounding blood vessels. By seven months of age, motor coordination becomes impaired, and there is a loss of motor neurons in the spinal cord of LXR beta(-/-) mice. During development, migration of neurons in the cortex and cerebellum is retarded in LXR beta(-/-) mice. Since LXRs are not expressed in dopaminergic or motor neurons in adult mice, the neuroprotective effects of LXRs appear to come from LXRs in glial cells where they are expressed. However, despite the numerous neurological deficits in LXR-/- rodents, multiple sclerosis has the clear distinction of being the only human neurodegenerative disease in which defective LXR signaling has been identified. In this review, we summarize the regulation and functions of LXRs in glial cells and analyze how targeting LXRs in glial cells might, in the future, be used to treat neurodegenerative diseases and, perhaps, disorders caused by aberrant neuronal migration during development.

Automated summary

This review discusses the role of liver X receptors (LXRs) in glial cells in the central nervous system (CNS). LXRs regulate genes involved in cholesterol homeostasis, inflammatory responses, and glutamate homeostasis. Studies on LXR knockout mice have shown that LXR beta is crucial for the health of various types of neurons in both CNS and peripheral nervous system. LXRs are also important for cerebrospinal fluid homeostasis. Despite the neurological deficits observed in LXR-deficient rodents, defective LXR signaling has only been identified in multiple sclerosis among human neurodegenerative diseases. Targeting LXRs in glial cells may hold potential for treating neurodegenerative diseases and disorders caused by abnormal neuronal migration during development.