Megalencephalic leukoencephalopathy with subcortical cysts protein-1 regulates epidermal growth factor receptor signaling in astrocytes

Mutations in the MLC1 gene, which encodes a protein expressed in brain astrocytes, are the leading cause of MLC, a rare leukodystrophy characterized by macrocephaly, brain edema, subcortical cysts, myelin and astrocyte vacuolation. Although recent studies indicate that MLC1 protein is implicated in the regulation of cell volume changes, the exact role of MLC1 in brain physiology and in the pathogenesis of MLC disease remains to be clarified. In preliminary experiments, we observed that MLC1 was poorly expressed inhighly proliferating astrocytomacellswhencomparedwith primaryastrocytes, and thatmodulation ofMLC1 expression influenced astrocyte growth. Because volume changes are key events in cell proliferation and during brain development MLC1 expression is inversely correlated to astrocyte progenitor proliferation levels,we investigated the possible role for MLC1 in the control of astrocyte proliferation.We found that overexpression ofwild type but notmutantMLC1 in human astrocytomacells hampered cell growth by favoring epidermal growth factor receptor (EGFR) degradation and by inhibiting EGF-induced Ca⁺ entry, ERK1/2 and PLCγ1 activation, and calcium-activated KCa3.1 potassium channel function, all molecular pathways involved in astrocyte proliferation stimulation. Interestingly, MLC1 did not influence AKT, an EGFR-stimulated kinase involved in cell survival. Moreover, EGFR expressionwas higher inmacrophages derived fromMLC patients than fromhealthy individuals. Since reactive astrocytes proliferate and re-express EGFR in response to different pathological stimuli, the present findings provide new information on MLC pathogenesis and unravel an important role for MLC1 in other brain pathological conditions where astrocyte activation occurs.