Fibrillar Amyloid-beta(1-42) Modifies Actin Organization Affecting the Cofilin Phosphorylation State: A Role for Rac1/cdc42 Effector Proteins and the Slingshot Phosphatase

The neuronal cytoskeleton regulates numerous processes that occur in normal homeostasis. Under pathological conditions such as those of Alzheimer's disease (AD), major alterations in cytoskeleton organization have been observed and changes in both microtubules and actin filaments have been reported. Many neurodegenerative consequences of AD are linked to the production and accumulation of amyloid peptides (A beta) and their oligomers, produced from the internal cleavage of the amyloid-beta protein precursor. We previously reported that fibrillar A beta(1-42) (fA beta) treatment of hippocampal neurons induced an increase in Rac1 and Cdc42 activities linking fA beta effects with changes in actin dynamics. Here we show fA beta-induces increased activity of PAK1 and cyclin-dependent kinase 5, and that p21-activated kinase (PAK1) activation targets the LIMK1-cofilin signaling pathway. Increased cofilin dephosphorylation under conditions of enhanced LIM-Kinase 1 (LIMK1) activity suggests that fA beta co-stimulates bifurcating pathways impacting cofilin phosphorylation. Overexpression of slingshot (SSH) prevents the augment of F-actin induced by fA beta after 24 h, suggesting that fA beta-induced changes in actin assembly involve both LIMK1 and SSH. These results suggest that fAb may alter the PAK1/LIMK1/cofilin axis and therefore actin organization in AD.