PERIPHERAL MYELIN PROTEIN-22 IS EXPRESSED IN CNS MYELIN

Molecular Markers in Maternal Blood Exosomes Allow Early Detection of Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure can cause developmental abnormalities (fetal alcohol spectrum disorders; FASD), including small eyes, face and brain, and neurobehavioral deficits. These cannot be detected early in pregnancy with available imaging techniques. Early diagnosis could facilitate development of therapeutic interventions. Banked human fetal brains and eyes at 9−22 weeks’ gestation were paired with maternal blood samples, analyzed for morphometry, protein, and RNA expression, and apoptotic signaling. Alcohol (EtOH)-exposed (maternal self-report) fetuses were compared with unexposed controls matched for fetal age, sex, and maternal race. Fetal brain-derived exosomes (FB-E) were isolated from maternal blood and analyzed for protein, RNA, and apoptotic markers. EtOH use by mothers, assessed by self-report, was associated with reduced fetal eye diameter, brain size, and markers of synaptogenesis. Brain caspase-3 activity was increased. The reduction in eye and brain sizes were highly correlated with amount of EtOH intake and caspase-3 activity. Levels of several biomarkers in FB-E, most strikingly myelin basic protein (MBP; r > 0.9), correlated highly with morphological abnormalities. Reduction in FB-E MBP levels was highly correlated with EtOH exposure (p < 1.0 × 10−10). Although the morphological features of FAS appear long before they can be detected by live imaging, FB-E in the mother’s blood may contain markers, particularly MBP, that predict FASD.

Central Alteration in Peripheral Neuropathy of Trembler-J Mice: Hippocampal pmp22 Expression and Behavioral Profile in Anxiety Tests

Charcot–Marie–Tooth (CMT) type 1 disease is the most common human hereditary demyelinating neuropathy. Mutations in pmp22 cause about 70% of all CMT1. Trembler-J (TrJ/+) mice are an animal model of CMT1E, having the same spontaneous pmp22 mutation that is found in humans. We compared the behavior profile of TrJ/+ and +/+ (wild-type) in open-field and elevated-plus-maze anxiety tests. In these tests, TrJ/+ showed an exclusive head shake movement, a lower frequency of rearing, but a greater frequency of grooming. In elevated-plus-maze, TrJ/+ defecate more frequently, performed fewer total entries, and have fewer entries to closed arms. These hippocampus-associated behaviors in TrJ/+ are consistent with increased anxiety levels. The expression of pmp22 and soluble PMP22 were evaluated in E17-hippocampal neurons and adult hippocampus by in situ hybridization and successive immunohistochemistry. Likewise, the expression of pmp22 was confirmed by RT-qPCR in the entire isolated hippocampi of both genotypes. Moreover, the presence of aggregated PMP22 was evidenced in unmasked granular hippocampal adult neurons and shows genotypic differences. We showed for the first time a behavior profile trait associated with anxiety and a differential expression of pmp22/PMP22 in hippocampal neurons of TrJ/+ and +/+ mice, demonstrating the involvement at the central level in an animal model of peripheral neuropathy (CMT1E).

Central nervous system impairment detected by somatosensory evoked potentials in patients with Charcot-Marie-Tooth disease type 1A

Diseases related to peripheral myelin protein 22 (PMP22) have been implicated to involve the central nervous system (CNS). This study aimed to detect central nerve impairment using somatosensory evoked potentials (SSEPs) in patients with Charcot-Marie-Tooth disease (CMT) 1A. A total of 30 CMT1A patients and 26 healthy volunteers were included. Baseline characteristics, brain MRI and segmental SSEPs were collected from the participants. The peak latencies of N9, N13 and N20 were recorded, and central conduction velocity (CCT) was calculated and compared between groups. Significant differences were found in the peak latencies and amplitudes of N9, N13 and N20 between the two groups. CCT was significantly prolonged in the CMT group (7.05 ± 2.09 ms) compared to the control group (5.40 ± 1.79 ms) (p = 0.003). Six of 30 CMT patients had abnormal MRI signals, but no correlation with CCT was found. The central somatosensory pathway that carries SSEPs was impaired in CMT1A patients, which implies an important underlying role of PMP22 in the CNS.

Afferent Visual Pathway Affection in Patients with PMP22 Deletion-Related Hereditary Neuropathy with Liability to Pressure Palsies

BACKGROUND

The PMP22 gene encodes a protein integral to peripheral myelin. Its deletion leads to hereditary neuropathy with liability to pressure palsies (HNPP). PMP22 is not expressed in the adult central nervous system, but previous studies suggest a role in CNS myelin development. The objective of this study was to identify potential structural and functional alterations in the afferent visual system in HNPP patients.

METHODS

Twenty HNPP patients and 18 matched healthy controls (HC) were recruited in a cross-sectional study. Participants underwent neurological examination including visual acuity, visual evoked potential (VEP) examination, optical coherence tomography (OCT), and magnetic resonance imaging with calculation of brain atrophy, regarding grey and white matter, and voxel based morphometry (VBM), in addition answered the National Eye Institute's 39-item Visual Functioning Questionnaire (NEI-VFQ). Thirteen patients and 6 HC were additionally examined with magnetic resonance spectroscopy (MRS).

RESULTS

All patients had normal visual acuity, but reported reduced peripheral vision in comparison to HC in the NEI-VFQ (p = 0.036). VEP latency was prolonged in patients (P100 = 103.7±5.7 ms) in comparison to healthy subjects (P100 = 99.7±4.2 ms, p = 0.007). In OCT, peripapillary retinal nerve fiber layer thickness RNFL was decreased in the nasal sector (90.0±15.5 vs. 101.8±16.5, p = 0.013), and lower nasal sector RNFL correlated with prolonged VEP latency (Rho = -0.405, p = 0.012). MRS revealed reduced tNAA (731.4±45.4 vs. 814.9±62.1, p = 0.017) and tCr (373.8±22.2 vs. 418.7±31.1, p = 0.002) in the visual cortex in patients vs. HC. Whole brain volume, grey and white matter volume, VBM and metabolites in a MRS sensory cortex control voxel did not differ significantly between patients and HC.

CONCLUSION

PMP22 deletion leads to functional, metabolic and macro-structural alterations in the afferent visual system of HNPP patients. Our data suggest a functional relevance of these changes for peripheral vision, which warrants further investigation and confirmation.

Temporal and spatial expression analysis of peripheral myelin protein 22 (Pmp22) in developing Xenopus

Peripheral myelin protein 22 (Pmp22), a member of the junction protein family Claudin/EMP/PMP22, contributes to the formation and maintenance of myelin sheaths in the peripheral nervous system. Apart from the establishment and maintenance of peripheral nerves, Pmp22 and its family member have also participated in a broad range of more general processes including cell cycle regulation and apoptosis during development. Pmp22 has been identified from several vertebrate species including mouse, human and zebrafish. However, Pmp22 has not been identified from Xenopus embryos yet. In this paper, we cloned Pmp22 from Xenopus laevis and evaluated its expression during embryogenesis. We found that Pmp22 was initially expressed in the mesoderm and cement gland during the neurula stage. At early tailbud stage, strong expression of Pmp22 was detected in the trigeminal and profundal ganglia as well as developing somites and branchial arches. Later in development, Pmp22 was expressed specifically in cranio-facial cartilage, roof plate and floor plate of the developing brain, otic vesicle and lens. Pmp22 is also strongly expressed in the developing trachea and lungs. Based on its expression in facial tissues, we propose that Pmp22 may be involved in the formation of head structure in addition to the maintenance of functional peripheral nerves in Xenopus embryos.

Systematic approaches to central nervous system myelin

Rapid signal propagation along vertebrate axons is facilitated by their insulation with myelin, a plasma membrane specialization of glial cells. The recent application of 'omics' approaches to the myelinating cells of the central nervous system, oligodendrocytes, revealed their mRNA signatures, enhanced our understanding of how myelination is regulated, and established that the protein composition of myelin is much more complex than previously thought. This review provides a meta-analysis of the > 1,200 proteins thus far identified by mass spectrometry in biochemically purified central nervous system myelin. Contaminating proteins are surprisingly infrequent according to bioinformatic prediction of subcellular localization and comparison with the transcriptional profile of oligodendrocytes. The integration of datasets also allowed the subcategorization of the myelin proteome into functional groups comprising genes that are coregulated during oligodendroglial differentiation. An unexpectedly large number of myelin-related genes cause-when mutated in humans-hereditary diseases affecting the physiology of the white matter. Systematic approaches to oligodendrocytes and myelin thus provide valuable resources for the molecular dissection of developmental myelination, glia-axonal interactions, leukodystrophies, and demyelinating diseases.