Mechanical contrast between brain and leptomeninges: Insights into leptomeningeal cell and astrocyte responses to mechanical stiffness alterations

Replicating the native mechanical environment of cells in vitro is essential for accurately capturing their physiological behaviour as it occurs in vivo. While astrocytes have been extensively studied within the brain, leptomeningeal cells (LMCs), which reside in the arachnoid and pia mater layers of the meninges, have received comparatively less attention despite their essential structural and immunological functions at the brain-meningeal interface. These two tissues are in direct contact yet exhibit stark differences in mechanical properties; the brain possesses a Young's modulus in the low kilopascal (kPa) range, whereas the leptomeninges exhibit stiffness in the low megapascal (MPa) range. This pronounced mechanical contrast raises critical questions regarding the mechanosensitivity of LMCs and their adaptive responses to different substrate stiffnesses. In this study, the mechanobiological responses of primary human LMCs and astrocytes were investigated when cultured on substrates that either replicated or deviated from their native mechanical environments. Nanoindentation, morphological analysis, and protein expression profiling were employed to assess mechanosensitive behaviours. The results demonstrate that both LMCs and astrocytes are responsive to mechanical stimuli, though their capacity to adapt varies. LMCs are particularly sensitive to changes in substrate stiffness, especially when the mechanical properties diverge from their native environment. In contrast, astrocytes maintain more stable behaviour across a wider range of stiffnesses. However, both cell types exhibit diminished physiological relevance when grown on rigid gigapascal (GPa) plastic surfaces, underscoring the importance of using physiologically relevant stiffness in vitro. These findings establish a foundational understanding of how LMCs respond to mechanical alterations in two-dimensional cultures that mimic both the native and non-native stiffness environments, providing new insight into the mechanosensitivity of this overlooked but functionally significant cell type. STATEMENT OF SIGNIFICANCE: The leptomeninges, made up of the pia and arachnoid layers, protect the brain while also regulating cerebrospinal fluid, immune responses, and blood flow, helping maintain overall brain function. Despite being in direct contact, the brain and leptomeninges exhibit starkly different mechanical properties. The brain has a Young's modulus in the low kPa range, whereas the leptomeninges are significantly stiffer, with a Young's modulus in the MPa range. This sharp mechanical contrast raises important questions about how LMCs respond to their mechanical environment. Given that LMCs remain an understudied cell population, understanding their response to mechanical cues could provide new insights into their role in brain function and disease.