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Exogenous myelin basic protein promotes oligodendrocyte death via increased calcium influx
S F Tzeng1, G E Deibler, G H DeVries
1Department of Biochemistry and Molecular Biophysics, Medical College of Virginia, Richmond, USA.
Abstract:
Treatment of cultured oligodendrocytes (OLGs) with micromolar quantities of myelin basic protein (MBP) caused a rapid, MBP-dose-dependent cell death. In contrast, a 72-hr incubation of OLGs with MBP peptides (1-44, 47-87, 88-151, or 152-167) at comparable concentrations had no effect on cell viability. MBP and MBP peptides (1-44 and 88-151) have been shown to interact with ganglioside GM1 (Tzeng et al.: J Neurochem Res: 42:758-767, 1995). This interaction has been reported to increase calcium influx. Therefore, using the fluorescent dye Indo-1 and an ACAS laser cytometer, we examined the level of intracellular calcium in OLGs after MBP treatment. MBP was shown to provoke a rapid, dramatic, and sustained rise of intracellular calcium in most OLGs. The levels of elevated intracellular calcium were sustained and did not return to baseline even after 10 min. This increase of intracellular calcium was suppressed in the presence of EGTA, indicating that the [Ca2+]i rise was due to the entry of extracellular calcium. Incubation of cultured OLGs with MBP peptides (1-44 or 88-151) caused a modest and transitory elevation of intracellular calcium ions in a lower percentage of OLGs. The potent OLG cytotoxicity of intact MBP and the loss of potency after proteolysis raise the possibility that MBP proteolysis during demyelination protects OLGs from death.
Insights
Myelin basic protein (MBP) causes rapid oligodendrocyte (OLG) death by increasing intracellular calcium. Proteolysis of MBP may protect OLGs during demyelination, as MBP peptides do not induce cell death.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Oligodendrocytes (OLGs) are crucial for myelin sheath formation in the central nervous system.
- Myelin basic protein (MBP) is a major component of the myelin sheath.
- The role of MBP in oligodendrocyte survival and death is not fully understood.
Purpose of the Study:
- To investigate the effect of myelin basic protein (MBP) on oligodendrocyte (OLG) viability.
- To determine the mechanism by which MBP induces cell death, focusing on intracellular calcium levels.
- To explore the potential protective role of MBP proteolysis during demyelination.
Main Methods:
- Primary cultures of oligodendrocytes (OLGs) were treated with intact MBP and various MBP peptides.
- Cell viability was assessed after treatment.
- Intracellular calcium levels ([Ca2+]i) were measured using the fluorescent dye Indo-1 and an ACAS laser cytometer.
- The role of extracellular calcium in MBP-induced calcium influx was examined using EGTA.
Main Results:
- Intact MBP induced rapid, dose-dependent cell death in OLGs.
- MBP treatment caused a rapid, sustained, and dramatic rise in intracellular calcium in most OLGs, dependent on extracellular calcium.
- MBP peptides (1-44, 47-87, 88-151, 152-167) did not affect OLG viability at comparable concentrations.
- MBP peptides (1-44 and 88-151) caused only a modest and transient increase in intracellular calcium in a smaller percentage of OLGs.
Conclusions:
- Intact MBP is cytotoxic to oligodendrocytes (OLGs) primarily through a mechanism involving a rapid and sustained increase in intracellular calcium.
- MBP peptides lack the potent cytotoxicity of intact MBP, suggesting that proteolysis of MBP may mitigate its harmful effects.
- MBP proteolysis during demyelination could be a protective mechanism for oligodendrocytes, preventing cell death in conditions like multiple sclerosis.