The transcriptome characteristics of vestibular organs from delayed endolymphatic hydrops patients (Meniere's disease)

IL-1β promotes glutamate excitotoxicity: indications for the link between inflammatory and synaptic vesicle cycle in Ménière's disease

Ménière's disease (MD) is a complex inner ear disorder characterized by a range of symptoms, with its pathogenesis linked to immune-related mechanisms. Our previous research demonstrated that IL-1β maturation and release can trigger cell pyroptosis, exacerbating the severity of the endolymphatic hydrops in a mouse model; however, the specific mechanism through which IL-1β influences MD symptoms remains unclear. This study conducted on patients with MD examined changes in protein signatures in the vestibular end organs (VO) and endolymphatic sac (ES) using mass spectrometry. Gene ontology and protein pathway analyses showed that differentially expressed proteins in the ES are closely related to adhesion, whereas those in the VO are related to synapse processes. Additionally, the study found elevated expression of Glutaminase (GLS) in the VO of MD patients compared to controls. Further investigations revealed that IL-1β increased glutamate levels by upregulating GLS expression in HEI-OC1 cells. Treatment with a GLS inhibitor or an IL-1β receptor antagonist alleviated auditory-vestibular dysfunction and reduced glutamate levels in mice with endolymphatic hydrops. These findings collectively suggest that imbalanced neurotransmitter release and immune responses contribute to the pathology of MD, potentially explaining the hearing loss and vertigo associated with the disease and offering new avenues for therapeutic interventions.

Cytokine profiling and transcriptomics in mononuclear cells define immune variants in Meniere Disease

Meniere Disease (MD) is a chronic inner ear disorder characterized by vertigo attacks, sensorineural hearing loss, tinnitus, and aural fullness. Extensive evidence supporting the inflammatory etiology of MD has been found, therefore, by using transcriptome analysis, we aim to describe the inflammatory variants of MD. We performed Bulk RNAseq on 45 patients with definite MD and 15 healthy controls. MD patients were classified according to their basal levels of IL-1β into 2 groups: high and low. Differentially expression analysis was performed using the ExpHunter Suite, and cell type proportion was evaluated using the estimation algorithms xCell, ABIS, and CIBERSORTx. MD patients showed 15 differentially expressed genes (DEG) compared to controls. The top DEGs include IGHG1 (p = 1.64  ×  10-6) and IGLV3-21 (p = 6.28  ×  10-3), supporting a role in the adaptative immune response. Cytokine profiling defines a subgroup of patients with high levels of IL-1β with up-regulation of IL6 (p = 7.65  ×  10-8) and INHBA (p = 3.39  ×  10-7) genes. Transcriptomic data from peripheral blood mononuclear cells support a proinflammatory subgroup of MD patients with high levels of IL6 and an increase in naïve B-cells, and memory CD8+ T cells.

Human myelin protein P2: from crystallography to time-lapse membrane imaging and neuropathy-associated variants

Peripheral myelin protein 2 (P2) is a fatty acid-binding protein expressed in vertebrate peripheral nervous system myelin, as well as in human astrocytes. Suggested functions of P2 include membrane stacking and lipid transport. Mutations in the PMP2 gene, encoding P2, are associated with Charcot-Marie-Tooth disease (CMT). Recent studies have revealed three novel PMP2 mutations in CMT patients. To shed light on the structure and function of these P2 variants, we used X-ray and neutron crystallography, small-angle X-ray scattering, circular dichroism spectroscopy, computer simulations and lipid binding assays. The crystal and solution structures of the I50del, M114T and V115A variants of P2 showed minor differences to the wild-type protein, whereas their thermal stability was reduced. Vesicle aggregation assays revealed no change in membrane stacking characteristics, while the variants showed altered fatty acid binding. Time-lapse imaging of lipid bilayers indicated formation of double-membrane structures induced by P2, which could be related to its function in stacking of two myelin membrane surfaces in vivo. In order to better understand the links between structure, dynamics and function, the crystal structure of perdeuterated P2 was refined from room temperature data using neutrons and X-rays, and the results were compared to simulations and cryocooled crystal structures. Our data indicate similar properties for all known human P2 CMT variants; while crystal structures are nearly identical, thermal stability and function of CMT variants are impaired. Our data provide new insights into the structure-function relationships and dynamics of P2 in health and disease.