MECHANICALLY REGULATED YAP EXPRESSION ELICITS AGE-ASSOCIATED MORPHOLOGICAL CHANGES IN ASTROCYTES

The aging brain is associated with the accumulation of extracellular matrix (ECM) components, leading to stiffening of the ECM. The influence of these age-dependent altered mechanical properties on cellular functions in the CNS remains unclear. YAP/TAZ are the primary mechanotransduction transcription factors, responsible for ECM production, cell survival, and proliferation. We hypothesize that changes in the mechanical properties of the ECM are mediated by YAP, influencing astrocytic structure, function, and neuronal-glia communication in the aging brain.

To mimic the increasing stiffness of an aging brain, we synthesized synthetic scaffolds to examine (a) changes in YAP expression and nuclear localization, (b) changes in astrocyte morphology and function. Indeed, we observed an increase in nuclear YAP expression and a decrease in astrocyte complexity with increased substrate stiffness, effects that can be reversed by YAP knockdown. We further investigated whether Piezo1, a major mechanosensitive cation channel expressed on astrocytes, converts mechanical cues into YAP signaling, connecting extracellular cues with internal cellular mechanics, thereby mediating structural and functional changes. Piezo1 knockdown showed a similar increase in astrocyte complexity and a decrease in nuclear YAP. This was further supported by the use of Yoda1, a selective Piezo1 activator, which produced effects opposite to those observed in Piezo1 knockdowns. Lastly, combining Piezo1 and YAP manipulations with neuronal stimulation altered extracellular glutamate levels. These in vitro findings suggest that astrocytes, through mechanosensitive ion channels and nuclear YAP, undergo morphological changes in response to substrate stiffness that subsequently may influence age-related functions of neurons and astrocytes.