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Sterol synthesis by myelinating cultures of mouse spinal cord
Abstract:
We studied the control of sterol synthesis during myelination of central nervous system in culture. Explants of fetal mouse spinal cord were cultured for 3-30 days in vitro (DIV). Myelination was visible by electron micriscopy at 3 DIV, and by bright-field light microscopy beginning at 6 DIV. All explants were heavily myelinated by 15 DIV. Specific activity of 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP) increased rapidly until 15 DIV. The rate of incorporation of [1-14C]acetate into sterol was greatest at 12 DIV, more than double that at 4 and 22 DIV. Specific activity of the mevalonate synthesizing enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) was greatest at 11 DIV, threefold greater than at 6 and 30 DIV. Previous studies in fibroblasts and other non-neural tissues had shown that deprivation of exogenous lipid caused a rapid increase in HMG CoA reductase activity. In contrast, when the spinal cord explants were incubated for 24 h in a lipid-deficient medium, there was either a marked decrease in specific activity of HMG CoA reductase (at 6, 15 and 30 DIV), or no change in enzyme activity (at 11 DIV).
Insights
Sterol synthesis control during central nervous system myelination differs from other tissues. Lipid deprivation decreased HMG CoA reductase activity in spinal cord cultures, contrary to expectations.
Area of Science:
- Neuroscience
- Developmental Biology
- Cellular Metabolism
Background:
- Myelination is a critical process in the central nervous system (CNS) involving the synthesis of lipids and sterols.
- Understanding the regulation of sterol synthesis during CNS myelination is crucial for comprehending developmental processes and potential therapeutic targets.
Purpose of the Study:
- To investigate the regulation of sterol synthesis during the myelination of the CNS in a cell culture model.
- To compare the control mechanisms of sterol synthesis in myelinating CNS tissue with those observed in non-neural tissues.
Main Methods:
- Culturing fetal mouse spinal cord explants for 3-30 days in vitro (DIV).
- Assessing myelination using electron and light microscopy.
- Measuring the specific activity of 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP) as a marker of myelination.
- Quantifying the incorporation of [1-14C]acetate into sterols.
- Determining the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), a key enzyme in sterol synthesis.
Main Results:
- Myelination was established by 15 DIV, with a corresponding rapid increase in CNP specific activity.
- Sterol synthesis, indicated by [1-14C]acetate incorporation, peaked around 12 DIV.
- HMG CoA reductase activity showed a significant peak at 11 DIV, threefold higher than at earlier or later time points.
- In contrast to non-neural tissues, lipid-deficient medium caused a decrease or no change in HMG CoA reductase activity in spinal cord explants.
Conclusions:
- Sterol synthesis during CNS myelination is regulated differently compared to non-neural cells.
- The typical response of increased HMG CoA reductase activity upon lipid deprivation is not observed in myelinating CNS tissue.
- These findings suggest unique regulatory mechanisms governing lipid metabolism during CNS development and myelination.