Abstract
Traditionally, myelin is viewed as insulation around axons, however, more recent studies have shown it also plays an important role in plasticity, axonal metabolism, and neuroimmune signaling. Myelin is a complex multi-protein structure composed of hundreds of proteins, with Myelin Basic Protein (MBP) being the most studied. MBP has two families: Classic-MBP that is necessary for activity driven compaction of myelin around axons, and Golli-MBP that is found in neurons, oligodendrocytes, and T-cells. Furthermore, Golli-MBP has been called a “molecular link” between the nervous and immune systems. In visual cortex specifically, myelin proteins interact with immune processes to affect experience-dependent plasticity. We studied myelin in human visual cortex using Western blotting to quantify Classic- and Golli-MBP expression in post-mortem tissue samples ranging in age from 20 days to 80 years. We found that Classic- and Golli-MBP have different patterns of change across the lifespan. Classic-MBP gradually increases to 42 years and then declines into aging. Golli-MBP has early developmental changes that are coincident with milestones in visual system sensitive period, and gradually increases into aging. There are three stages in the balance between Classic- and Golli-MBP expression, with Golli-MBP dominating early, then shifting to Classic-MBP, and back to Golli-MBP in aging. Also Golli-MBP has a wave of high inter-individual variability during childhood. These results about cortical MBP expression are timely because they compliment recent advances in MRI techniques that produce high resolution maps of cortical myelin in normal and diseased brain. In addition, the unique pattern of Golli-MBP expression across the lifespan suggests that it supports high levels of neuroimmune interaction in cortical development and in aging.
Highlights
The last decade has seen renewed interest in studying myelin in the cortex because it is involved in neuroplasticity, neurodegeneration, and neuroinflammation
We assessed the effect of PMI on expression of Classic- and Golli-Myelin Basic Protein (MBP) to determine if any samples needed to be removed because the PMI was too long
We found no correlation with PMI for either myelin protein (Classic: R = 0.307, n.s.; Golli: R = 0.143, n.s.) so all samples were included in the study
Summary
The last decade has seen renewed interest in studying myelin in the cortex because it is involved in neuroplasticity, neurodegeneration, and neuroinflammation. MBP makes up about 30% of all myelin proteins and is composed of two families, Classic- and Golli-MBP, each with multiple isoforms and post-translational modifications (Pribyl et al, 1996; Harauz et al, 2009; Harauz and Boggs, 2013) that individually contribute to myelination (Jacobs et al, 2005, 2009; Harauz et al, 2009). Classic-MBP isoforms (18.5–21.5 kDa in human) are found in mature oligodendrocytes and myelin sheaths, and have a key role in activity driven compaction of myelin around axons (Wake et al, 2011). Golli-MBP isoforms (33–35 kDa) are found in early developing oligodendrocytes, neurons and immune cells, with functions that extend beyond the myelin sheath and include regulating oligodendrocyte proliferation and migration (Paez et al, 2011). Golli-MBP is highly expressed prenatally in neurons and oligodendrocytes, even before the process of myelination begins (Tosic et al, 2002) and has been called a “molecular link” between the nervous and immune systems (Pribyl et al, 1993)
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