Hong, J. W. | bioRxiv Science

bioRxiv2025

TMEM145 is a key component in stereociliary link structures of outer hair cells

Outer hair cells (OHCs) in the cochlea contain specialized stereociliary structures essential for auditory function. These include horizontal top connectors (HTCs), linking adjacent stereocilia and tectorial membrane-attachment crowns (TM-ACs), anchoring the tallest stereocilia to the tectorial membrane. The known molecular components of these structures, such as stereocilin, otogelin, otogelin-like, and tubby, lack transmembrane domains, suggesting the existence of anchoring proteins. This study identified TMEM145, a transmembrane protein with a Golgi dynamics (GOLD) domain, as a crucial OHC stereocilia component. TMEM145 was expressed in both OHCs and spiral ganglion neurons, with specific localization to TM-ACs and HTCs in OHCs. Tmem145 knockout (KO) mice exhibited profound hearing impairment at three weeks of age, with complete loss of distortion product otoacoustic emissions, indicating OHC dysfunction. Immunostaining and scanning electron microscopy revealed the absence of TM-ACs and HTCs in Tmem145 KO mice. In heterologous cell systems, TMEM145 interacted with stereocilin and tubby, facilitating their extracellular secretion. TMEM145 was undetectable in stereocilin KO and tubby mutant mice, indicating interdependence among these proteins. These findings establish TMEM145 as an essential membrane protein for the structural integrity of OHC stereocilia, providing insights into the molecular architecture of cochlear hair cells and their role in auditory function.

neuroscience↗

bioRxiv2023

Alteration of neural network and hippocampal slice activation through exosomes derived from 5XFAD nasal lavage fluid

Exosomes contain various intracellular biomarkers reflecting the condition of cells, organs, and subjects. Under neurodegenerative conditions, they contrive in detrimental neuronal communications leading to the initiation and propagation of neurodegenerative symptoms. Since the exosomes in olfactory fluid are readily accessible to collect in ample amount noninvasively and highly enriched in neural biomarkers, they can be a primary biomarker if we can verify precise pathophysiological information from them. Here we show that exosomes from nasal lavage fluid (NLF) of the neurodegeneration model animal, 5XFAD mice, induce the pathological network activity in neuronal cultures. We separated intact NLF exosomes from the 5XFAD and wild-type mice via a high-efficacy microfluidic system and applied them to the primary cortical neurons and organotypic hippocampal slice cultures (OHSC), whose neuronal activities were monitored by a high-density microelectrode array system. We found that NLF exosomes from 5XFAD mice increased the firing rate of neuronal spikes with augmentation of neuronal connectivity similar to the effect of pathological amyloid beta oligomer treatment. Furthermore, the current source densities, computed from the local field potentials, were elevated in OHSCs incubated with the exosomes, suggesting a pathological shift in synaptic and membrane currents. Those results demonstrate that NLF exosomes from neurodegeneration model can effectively modify neuronal networks and suggest that this property can serve as a functional biomarker for Alzheimers disease.

neuroscience↗