PAK1 positively regulates oligodendrocyte morphology and myelination.

The actin cytoskeleton is crucial for oligodendrocyte differentiation and myelination. Here we show that p21-activated kinase1 (PAK1), a well-known actin regulator, promotes oligodendrocyte morphological change and myelin production in the central nervous system. A combination of in vitro and in vivo models demonstrated that PAK1 is expressed throughout the oligodendrocyte lineage with highest expression in differentiated oligodendrocytes. Inhibiting PAK1 early in oligodendrocyte development decreased oligodendrocyte morphological complexity and altered F-actin spreading at the tips of oligodendrocyte progenitor cell processes. Constitutively activating AKT in oligodendrocytes in male and female mice, which leads to excessive myelin wrapping, increased PAK1 expression, suggesting an impact of PAK1 during active myelin wrapping. Furthermore, constitutively activating PAK1 in oligodendrocytes in zebrafish led to an increase in myelin internode length while inhibiting PAK1 during active myelination decreased internode length. As myelin parameters influence conduction velocity, these data suggest that PAK1 may influence communication within the CNS. These data support a model in which PAK1 is a positive regulator of CNS myelination. SIGNIFICANCE STATEMENT Myelin is a critical component of the central nervous system (CNS) that provides metabolic support to neurons and also facilitates communication between cells in the CNS. Recent data demonstrate that actin dynamics drives myelin wrapping but how actin is regulated during myelin wrapping is unknown. The authors investigate the role of the cytoskeletal modulator PAK1 during differentiation and myelination by oligodendrocytes, the myelinating cells of the CNS. They demonstrate that PAK1 promotes oligodendrocyte differentiation and myelination by modulating myelin internode length, thus playing a critical role in the function of the CNS.