Poly(I:C) Challenge Alters Brain Expression of Oligodendroglia-Related Genes of Adult Progeny in a Mouse Model of Maternal Immune Activation

Background: Altered white matter connectivity, as evidenced by pervasive microstructural changes in myelination and axonal integrity in neuroimaging studies, has been implicated in the development of autism spectrum disorder (ASD) and related neurodevelopmental conditions such as schizophrenia. Despite an increasing appreciation that such white matter disconnectivity is linked to social behavior deficits, virtually no etiologically meaningful myelin-related genes have been identified in oligodendrocytes, the key myelinating cells in the CNS, to furnish an account on the causes. The impact of neurodevelopmental perturbations during pregnancy such as maternal immune activation (MIA) on these genes in memory-related neural networks has not been experimentally scrutinized.

Methods: In this study, a mouse model of MIA by the viral dsRNA analog poly(I:C) was employed to mimic the effects of inflammation during pregnancy. Transcriptional expression levels of selected myelin- or oligodendroglia-related genes implicated in schizophrenia or ASD development were analyzed by in situ hybridization (ISH) and quantitative real-time PCR (qRT-PCR) with brain samples from MIA and control groups. The analysis focused on SOX-10 (SRY-related HMG-box 10), MAG (myelin-associated glycoprotein), and Tf (transferrin) expression in the hippocampus and the surrounding memory-related cortical regions in either hemisphere.

Results: Specifically, ISH reveals that in the brain of prenatal poly(I:C)-exposed mouse offspring in the MIA model (gestation day 9), mRNA expression of the genes SOX10, MAG and Tf were generally reduced in the limbic system including the hippocampus, retrosplenial cortex and parahippocampal gyrus on either side of the hemispheres. qRT-PCR further confirms the reduction of SOX10, MAG, and Tf expression in the medial prefrontal cortex, sensory cortex, amygdala, and hippocampus.

Conclusions: Our present results provide direct evidence that prenatal exposure to poly(I:C) elicits profound and long-term changes in transcript level and spatial distribution of myelin-related genes in multiple neocortical and limbic regions, notably the hippocampus and its surrounding memory-related neural networks. Our work demonstrates the potential utility of oligodendroglia-related genes as biomarkers for modeling neurodevelopmental disorders, in agreement with the hypothesis that MIA during pregnancy could lead to compromised white matter connectivity in ASD.

Sialic Acids on Varicella-Zoster Virus Glycoprotein B Are Required for Cell-Cell Fusion

Varicella-zoster virus (VZV) is a member of the human Herpesvirus family that causes varicella (chicken pox) and zoster (shingles). VZV latently infects sensory ganglia and is also responsible for encephalomyelitis. Myelin-associated glycoprotein (MAG), a member of the sialic acid (SA)-binding immunoglobulin-like lectin family, is mainly expressed in neural tissues. VZV glycoprotein B (gB) associates with MAG and mediates membrane fusion during VZV entry into host cells. The SA requirements of MAG when associating with its ligands vary depending on the specific ligand, but it is unclear whether the SAs on gB are involved in the association with MAG. In this study, we found that SAs on gB are essential for the association with MAG as well as for membrane fusion during VZV infection. MAG with a point mutation in the SA-binding site did not bind to gB and did not mediate cell-cell fusion or VZV entry. Cell-cell fusion and VZV entry mediated by the gB-MAG interaction were blocked by sialidase treatment. N-glycosylation or O-glycosylation inhibitors also inhibited the fusion and entry mediated by gB-MAG interaction. Furthermore, gB with mutations in N-glycosylation sites, i.e. asparagine residues 557 and 686, did not associate with MAG, and the cell-cell fusion efficiency was low. Fusion between the viral envelope and cellular membrane is essential for host cell entry by herpesviruses. Therefore, these results suggest that SAs on gB play important roles in MAG-mediated VZV infection.

Nerve ultrasound findings in neuropathy associated with anti-myelin-associated glycoprotein antibodies

BACKGROUND AND PURPOSE

No systematic nerve ultrasound (US) studies on patients with neuropathy and anti-myelin-associated glycoprotein (anti-MAG) antibodies are available.

PATIENTS AND METHODS

Twenty-eight patients (18 men, 10 women, mean age 69.2 ± 10.9 years; mean disease duration 6.9 years) with anti-MAG neuropathy underwent nerve US. Echotexture, nerve cross-sectional area (CSA) and intra-nerve and inter-nerve CSA variability were assessed. The frequency (number of nerves with enlarged CSA, 'enlarged nerves sum score') and distribution (proximal versus distal, arms versus legs, symmetry) of US abnormalities were considered. Controls included two groups: four patients with immunoglobulin M (IgM) paraproteinaemic neuropathy without anti-MAG antibodies and five with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) associated with IgM paraprotein.

RESULTS

In all, 26/28 patients had increased CSA (23 with at least one nerve outside entrapment sites). Intra-nerve CSA variability was abnormal in 21/28 patients (in 14 for increased nerve CSA outside entrapment sites). Inter-nerve CSA variability was abnormal in 16 patients (of whom half for CSA increase out of entrapment sites). The enlarged nerves sum score in anti-MAG neuropathy patients was greater than in MAG-negative paraproteinaemic neuropathies and lower than in CIDP. Intra-nerve variability appeared instead similar in anti-MAG and controls. No correlation was found between US findings and Inflammatory Neuropathy Cause and Treatment Group (INCAT) disability score or disease duration.

DISCUSSION

Amongst the different measures to assess the US pattern (symmetry/asymmetry, proximal/distal distribution and sum score), the enlarged nerves sum score was the most useful for differentiating the three groups of patients with demyelinating neuropathies and may contribute to diagnosis in a typical cases.