Signaling by the human serotonin1A receptor is impaired in cellular model of Smith–Lemli–Opitz Syndrome

Abstract

The Smith-Lemli-Opitz Syndrome (SLOS) is a congenital and developmental malformation syndrome associated with defective cholesterol biosynthesis. SLOS is clinically diagnosed by reduced plasma levels of cholesterol along with elevated levels of 7-dehydrocholesterol (and its positional isomer 8-dehydrocholesterol) and the ratio of their concentrations to that of cholesterol. Since SLOS is associated with neurological deformities and malfunction, exploring the function of neuronal receptors and their interaction with membrane cholesterol under these conditions assumes significance. We have earlier shown the requirement of membrane cholesterol for the ligand binding function of an important neurotransmitter G-protein coupled receptor, the serotonin(1A) receptor. In the present work, we have generated a cellular model of SLOS using CHO cells stably expressing the human serotonin(1A) receptor. This was achieved by metabolically inhibiting the biosynthesis of cholesterol, utilizing a specific inhibitor (AY 9944) of the enzyme required in the final step of cholesterol biosynthesis. We utilized this cellular model to monitor the function of the human serotonin(1A) receptor under SLOS-like condition. Our results show that ligand binding activity, G-protein coupling and downstream signaling of serotonin(1A) receptors are impaired in SLOS-like condition, although the membrane receptor level does not exhibit any reduction. Importantly, metabolic replenishment of cholesterol using serum partially restored the ligand binding activity of the serotonin(1A) receptor. These results are potentially useful in developing strategies for the future treatment of the disease since intake of dietary cholesterol is the only feasible treatment for SLOS patients.

Malformation syndromes caused by disorders of cholesterol synthesis

“…In a retrospective study that included 14 SLOS patients treated with cholesterol and simvastatin, Haas et al ( 107 ) reported a decrease in dehydrocholesterol levels and improvement of the dehydrocholesterol-cholesterol ratio but did not observe an increase in cholesterol levels. Fractional cholesterol syn-cholesterol in restoring ligand binding to solubilized hippocampal serotonin1A receptors ( 139 ), and serotonin1A receptor signaling is impaired in AY9944-treated cells ( 140 ). These in vitro fi ndings may be mechanistically related to the observation by Waage-Baudet et al ( 141 ) of abnormal serotonergic development in Dhcr7 mutant embryos and are especially intriguing given the high frequency of autistic symptoms in SLOS patients ( 53,56 ).…”

Molecular rheology of neuronal membranes explored using a molecular rotor: Implications for receptor function

“…An important aspect of our results is that the interaction between cholesterol and the serotonin1A receptor appears to be stringent, since immediate biosynthetic precursors of cholesterol (differing with cholesterol merely in a double bond) were not able to maintain receptor function (Paila et al, 2008;Singh et al, 2009). In addition, we recently showed that the requirement of cholesterol for receptor function is diastereospecific, but not enantiospecific (Jafurulla et al, 2014).…”

“…In this overall context, we have demonstrated the requirement of membrane cholesterol in modulating the function of the serotonin1A receptor Chattopadhyay, 2004, 2006;Paila et al, 2008;Paila and Chattopadhyay, 2010;Shrivastava et al, 2010;Jafurulla and Chattopadhyay, 2013). A continuing effort in our laboratory has been to explore how to correlate these cholesterol-dependent functional changes of the serotonin1A receptor with alterations in membrane organization and dynamics (Mukherjee et al, 2007;Saxena et al, 2008;Singh et al, 2012).…”

HGM2008 structural proteomics symposium abstracts

“…Importantly, recently reported crystal structures of GPCRs have shown structural evidence of cholesterol binding sites [5,6]. Previous work from our laboratory has demonstrated that membrane cholesterol is required for the function of the serotonin1A receptor, a representative GPCR [4], and this dependence could be an important determinant in diseases such as the Smith-Lemli-Opitz syndrome [7]. In order to gain insight into interaction of cholesterol with the serotonin1A receptor, we recently analyzed putative cholesterol binding sites from protein databases in the serotonin1A receptor.…”