Myosin II activity regulates neurite outgrowth and guidance in response to chondroitin sulfate proteoglycans

Chondroitin sulfate proteoglycans (CSPGs) are major components of the extracellular matrix in the CNS that inhibit axonal regeneration after CNS injury. Signaling pathways in neurons triggered by CSPGs are still largely unknown. In this study, using well-characterized in vitro assays for neurite outgrowth and neurite guidance, we demonstrate a major role for myosin II in the response of neurons to CSPGs. We found that the phosphorylation of myosin II regulatory light chains is increased by CSPGs. Specific inhibition of myosin II activity with blebbistatin allows growing neurites to cross onto CSPG-rich areas and increases the length of neurites of neurons growing on CSPGs. Using specific gene knockdown, we demonstrate selective roles for myosin IIA and IIB in these processes. Time lapse microscopy and immunocytochemistry demonstrated that CSPGs also inhibit cell adhesion and cell spreading. Inhibition of myosin II selectively accelerated neurite initiation without altering cell adhesion and spreading on CSPGs.