Altered Mechanical Properties of Astrocytes Lacking <scp>MLC1</scp> : Implications for the Leukodystrophy <scp>MLC</scp>

Loss of function of the astrocyte protein MLC1 causes Megalencephalic Leukoencephalopathy with subcortical Cysts (MLC), a leukodystrophy characterized by white matter edema and slow neurological deterioration. MLC1 dysfunction leads to swelling of perivascular astrocyte endfeet and an impaired attachment of endfeet to blood vessels. In isolated primary astrocytes, loss of MLC1 hinders recovery of astrocytes from cell swelling, but the cellular function of MLC1 is not completely understood. MLC1 modulates gating of mechanosensitive ion channels involved in volume regulation. The cytoskeleton plays a crucial role in cell volume regulation, and interactions between the cytoskeleton and cell membrane affect the properties of mechanosensitive ion channels. Therefore, we investigated whether primary Mlc1-null mouse astrocytes show a disruption in their mechanical properties. We measured the mechanical properties of cultured primary astrocytes with an indentation technique and demonstrated that Mlc1-null astrocytes are softer than wild-type astrocytes. Proteomic analysis and western blots confirmed dysregulation of several cytoskeleton-related pathways in Mlc1-null astrocytes. Confocal imaging revealed that the organization of the actin cytoskeleton and microtubule acetylation are unaffected. Instead, in Mlc1-null astrocytes we observed a decrease in the number of focal adhesions, which aid in relaying mechanical forces between the cytoskeleton, cell membrane, and the extracellular matrix (ECM). Inversely, overexpression of MLC1 in HeLa cells led to an increase in focal adhesions. Together, our findings reveal that the mechanical properties of Mlc1-null astrocytes are altered, and that disrupted cytoskeleton-membrane-ECM interactions potentially play a role in the disease. Modulators of astrocyte mechanobiology might therefore hold promise for MLC therapy development.