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Temporal expression pattern of peripheral myelin protein 22 during in vivo and in vitro myelination
L Notterpek1, G J Snipes, E M Shooter
1Department of Neurobiology, Stanford University School of Medicine, California 94305, USA. notterpe@cmgm.stanford.edu
Abstract:
Peripheral myelin protein 22 (PMP22) was initially described as a minor component of peripheral myelin. Mutations affecting the PMP22 gene cause demyelinating neuropathies, supporting a role for the protein in PNS myelination. Furthermore, PMP22 carries the L2/HNK-1 carbohydrate epitope suggesting an adhesion/recognition function. Despite advances in characterizing the PMP22 gene, the specific role(s) of the protein in myelin remains unknown. In this study we determined the temporal expression pattern of PMP22 in comparison to galactocerebroside (GalC) and myelin associated glycoprotein (MAG), early constituents of PNS myelin, and to protein zero (P0) and myelin basic protein (MBP), late components of myelin. In sciatic nerve lysates, PMP22 was detected at postnatal day 3, after MAG, but before MBP expression. The same results were obtained in cocultures of dorsal root ganglion neurons and Schwann cells (SCs). Low levels of PMP22 were found in early, anti-MAG and anti-GalC immunoreactive, myelinating cocultures. However, PMP22 could only be detected in the SC plasma membrane after basal lamina formation. In long-term myelinating cocultures PMP22 levels continued to increase and the protein was found in anti-P0 and anti-MBP immunoreactive myelin segments. Furthermore, PMP22, MBP, and P0 protein levels were greatly enhanced by progesterone treatment of the cocultures. The highest levels of PMP22 expression were associated with late stages of myelination; however the presence of the protein in nonmyelinating SCs and in SCs commencing myelination supports multiple roles for PMP22 in peripheral nerve biology.
Insights
Peripheral myelin protein 22 (PMP22) expression increases during peripheral nervous system myelination, appearing after MAG but before MBP. Its presence in non-myelinating and myelinating Schwann cells suggests diverse roles in nerve biology.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Peripheral myelin protein 22 (PMP22) is a key component of peripheral myelin, with mutations linked to demyelinating neuropathies.
- PMP22's function in myelination and its precise roles within the peripheral nervous system (PNS) remain incompletely understood.
- The protein's association with the L2/HNK-1 carbohydrate epitope suggests potential adhesion or recognition functions.
Purpose of the Study:
- To elucidate the temporal expression pattern of PMP22 during peripheral nerve development.
- To compare PMP22 expression with established early (MAG, GalC) and late (P0, MBP) myelin components.
- To investigate the influence of progesterone on PMP22 expression in myelinating cultures.
Main Methods:
- Analysis of PMP22 expression in sciatic nerve lysates at different postnatal days.
- Coculture systems of dorsal root ganglion neurons and Schwann cells (SCs) to model myelination.
- Immunohistochemical detection of PMP22, MAG, GalC, P0, and MBP in cultured SCs and myelin segments.
- Assessment of PMP22, MBP, and P0 protein levels following progesterone treatment.
Main Results:
- PMP22 was detected postnatally after MAG but preceding MBP expression in sciatic nerves.
- In neuron-SC cocultures, PMP22 was observed in the SC plasma membrane after basal lamina formation and increased with myelination.
- PMP22 expression correlated with late myelination stages and was found in segments positive for P0 and MBP.
- Progesterone treatment significantly enhanced PMP22, MBP, and P0 protein levels.
Conclusions:
- PMP22 expression is temporally regulated during PNS myelination, with peak levels at later stages.
- The presence of PMP22 in both non-myelinating and myelinating SCs indicates multifaceted roles beyond just myelination.
- Progesterone may play a role in modulating PMP22 and other myelin protein expression.