5‐HT7 Serotonin Receptor Increases Neurite Complexity of Hippocampal Neurons Through Novel PKA‐LIM Kinase 1 Dependent Mechanism

Abstract

Serotonin [5‐hydroxytryptamine (5‐HT)] containing neurons are critical in memory formation. Previously, we found that 5‐HT7R promotes neurite outgrowth in PC12 cells and dissociated hippocampal neurons. A serine/threonine kinase, LIM kinase 1 (LIMK1) is a novel cytoskeleton regulator that upon phosphorylation leads to increase in actin filament stability and promotion of neurite outgrowth. The purpose of this study is to determine whether genetic deletion of LIM kinase 1 (LIMK1) could suppress 5‐HT7R induced increase in neurite complexity in hippocampal neurons.Using Western blot analysis, we found that 5‐HT7R can induce phosphorylation of LIMK1 in PC12 cells. 5‐HT7R can activate adenylate cyclase and increase intracellular levels of cAMP. Stimulation of PC12 cells with forskolin induced adenylate cyclase (AC) mediated LIMK1 phosphorylation. Furthermore, pretreatment of 5‐HT7R‐transfected PC12 cells with PKA specific inhibitor reduced LIMK1 phosphorylation. These findings suggest that 5‐HT7R‐AC‐cAMP‐PKA could be a novel pathway that leads to LIMK1 phosphorylation. We found that 5‐HT7R protein is expressed in pyramidal neurons of CA3 hippocampal region. To further explore importance of 5‐HT7R‐LIMK1 phosphorylation in neurons, we will determine morphology of 5‐HT7R‐expressing CA3 neurons in organotypic slices of wild type and LIMK1 ‐/‐ mice.This project is supported by NIH R01 grant.