Longitudinal Cholesterol Level Fluctuations in CNS during Myelin Loss and Repair in a Genetic Mouse Model

Multiple sclerosis is caused by the inflammatory demyelination of the myelin sheath. Cholesterol is a significant lipid in the myelin sheath and is known as a rate-limiting factor for myelination. We first aimed to quantify cholesterol in the mouse brain and spinal cord samples during postnatal myelination, demyelination, and remyelination stages. Deuterated cholesterol spiked mouse brain and spinal cord tissues were subjected to Bligh and Dyer lipid extraction followed by trimethylsilyl derivatization. Cholesterol was quantified using GC-MS (SIM). Cholesterol in postnatal brain tissues at P1– P7 shows 2–3 mg/ g tissue range with a slight increase, and then it reaches almost double the concentration at P10. Interestingly, a similar trend can be observed in the spinal cord. The average cholesterol levels in the healthy mature mouse brains go from 10-16 mg/g tissue with a gradual increase over age. In contrast, the healthy mature spinal cord cholesterol levels do not gradually increase over age as in the brain. It stays in the same value range of 29-33 mg/g tissue. The total cholesterol levels per mg tissue are higher in the spinal cord, indicating a high neuronal density or the myelin density. Brain cholesterol levels in the demyelinated mice stay 8–9 mg/ g range, which becomes significantly lower compared to healthy mice and fails to restore the cholesterol levels during the remyelination stages. A similar trend of not restoring cholesterol levels is also observed in the spinal cord. However, the significant lowering of cholesterol is observed earlier in the demyelinated spinal cord than in the brain. Taken all together, this data suggests that the normal cholesterol synthesis pathway could be disturbed in demyelinated mice, as they do not produce enough brain cholesterol as healthy mice. These findings lead to further investigations of cholesterol pathway intermediates and metabolites to identify pathways that could promote remyelination.