Rapid modulation of spine morphology by the 5-HT _2A serotonin receptor through kalirin-7 signaling

Abstract

The 5-HT2A serotonin receptor is the most abundant serotonin receptor subtype in the cortex and is predominantly expressed in pyramidal neurons. The 5-HT 2A receptor is a target of several hallucinogens, antipsychotics, anxiolytics, and antidepressants, and it has been associated with several psychiatric disorders, conditions that are also associated with aberrations in dendritic spine morphogenesis. However, the role of 5-HT 2A receptors in regulating dendritic spine morphogenesis in cortical neurons is unknown. Here we show that the 5-HT 2A receptor is present in a subset of spines, in addition to dendritic shafts. It colocalizes with PSD-95 and with multiple PDZ protein-1 (MUPP1) in a subset of dendritic spines of rat cortical pyramidal neurons. MUPP1 is enriched in postsynaptic density (PSD) fractions, is targeted to spines in pyramidal neurons, and enhances the localization of 5-HT 2A receptors to the cell periphery. 5-HT2A receptor activation by the 5-HT 2 receptor agonist DOI induced a transient increase in dendritic spine size, as well as phosphorylation of p21-activated kinase (PAK) in cultured cortical neurons. PAK is a downstream target of the neuronal Rac guanine nucleotide exchange factor (RacGEF) kalirin-7 that is important for spine remodeling. Kalirin-7 regulates dendritic spine morphogenesis in neurons but its role in neuromodulator signaling has not been investigated. We show that peptide interference that prevents the localization of kalirin-7 to the postsynaptic density disrupts DOI-induced PAK phosphorylation and spine morphogenesis. These results suggest a potential role for serotonin signaling in modulating spine morphology and kalirin-7's function at cortical synapses.GPCR ͉ neuromodulator ͉ PAK ͉ Rac ͉ synapse D endritic spine morphogenesis is an important component of structural plasticity in the mammalian forebrain. Changes in dendritic spine shape, size, and number underlie synaptic functional changes and accompany neuronal development, learning and memory, and behavior (1). Additionally, abnormal spine morphogenesis has been associated with many neurodevelopmental, neuropsychiatric, and neurodegenerative diseases, suggesting the importance of appropriate development, plasticity, and maintenance of these structures to neuronal function (2). Spine morphogenesis relies on alterations in the actin cytoskeleton, but the molecular mechanisms that regulate this process are just beginning to be uncovered. The role of neuromodulators, in particular of serotonin, in spine remodeling is not well understood.The 5-HT 2A receptor is the most abundantly expressed serotonin receptor subtype in the cortex, and it is predominantly expressed in pyramidal neurons (3-5). It is a target of several hallucinogens, antipsychotics, anxiolytics, and antidepressants, and it has been functionally and genetically associated with schizophrenia, autism, attention-deficit/hyperactivity disorder, and affective disorders (6-11). 5-HT 2A receptors are expressed late in development, coinciding with the period of synapto...

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