UNRAVELLING MECHANISMSOF SCHWANN CELLS IN VESTIBULAR SCHWANNOMA AND THEIR IMPACT ON HEARING LOSS.

Vestibular schwannoma (VS) is a benign peripheral nerve tumour arising from Schwann cells (SCs) of the vestibulocochlear nerve (VN) and represents the most common tumour of the cerebellopontine angle. Although the loss of NF2/merlin is a well-established driver of schwannoma (SCH) formation, likely of the VS, the early biological events that promote SC transformation and the mechanisms underlying VS-associated sensorineural hearing loss (SNHL) remain largely unresolved. In the recent years, environmental cues such as electromagnetic fields (EMFs) have been suggested as one of the potential co-factor influencing SC behaviour, but their cellular impact and the molecular mechanisms behind their action are still poorly understood. In this regard, this thesis investigates the molecular and functional responses of human naïve SCs, SCH-derived SCs, and VN-derived SCs to chronic EMF exposure, combining primary cell culture, transcriptomics, immunocytochemistry, co-culture systems, and migration assays. Naïve hSCs were successfully isolated, purified, and characterized, showing that chronic EMFs transiently reduce proliferation but markedly enhance motility and cytoskeletal remodelling. RNA-seq analysis revealed EMF-dependent transcriptional deregulation affecting pathways associated with migration, oncogenic signalling, and hearing loss-related genes. Because of the limited availability of human VN and VS tissues, a physiologically relevant alternative model was established through the isolation and characterization of primary rat VN-derived SCs. These cells displayed a distinct molecular signature, confirming their suitability as an inner ear-specific experimental system. Therefore, the VN-derived SCs proved as a physiologically sound and experimentally reliable in vitro model to study that type of SCs specific of the VN. Importantly, this model enables the exploration of early SC-intrinsic alterations relevant to VS onset, including responses to environmental stressors such as EMFs, and allows the study of the glial mechanisms contributing to auditory nerve dysfunction and HL. Furthermore, the inflammatory microenvironment of SCH was explored through the setup of SC-macrophage co-culture paradigm. We found a significant cross-talk between SCs and monocytes: naïve SCs were shown to modulate monocytes and macrophages toward an anti-inflammatory phenotype, and in parallel tumour-derived SCs induced a stronger immunosuppressive M2-like reprogramming of macrophages. Chronic EMF exposure further affected macrophage polarization and enhanced the migratory response of SCH cells to macrophage-derived soluble factors. Overall, the findings collected in this thesis provide new insights into the mechanisms at the base of SC plasticity, and the immunobiology of SCH, giving further proof of the potential impact of EMFs on peripheral glial cells. Our study highlights the molecular pathways and microenvironmental interactions that may contribute to VS initiation and progression, offering a framework for future mechanistic, translational, and therapeutic studies.