Late endosomal/lysosomal accumulation of a neurotransmitter receptor in a cellular model of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a congenital and developmental malformation syndrome associated with defective cholesterol biosynthesis. It is characterized by accumulation of 7-dehydrocholesterol (the immediate biosynthetic precursor of cholesterol in the Kandutsch-Russell pathway) and an altered cholesterol to total sterol ratio. Because SLOS is associated with neurological malfunction, exploring the function and trafficking of neuronal receptors and their interaction with membrane lipids under these conditions assume significance. In this work, we generated a cellular model of SLOS in HEK-293 cells stably expressing the human serotonin(1A) receptor (an important neurotransmitter G-protein coupled receptor) using AY 9944, an inhibitor for the enzyme 3 beta-hydroxy-steroid- increment (7)-reductase (7-DHCR). Using a quantitative flow cytometry based assay, we show that the plasma membrane population of serotonin(1A) receptors was considerably reduced under these conditions without any change in total cellular expression of the receptor. Interestingly, the receptors were trafficked to sterol-enriched LysoTracker positive compartments, which accumulated under these conditions. To the best of our knowledge, our results constitute one of the first reports demonstrating intracellular accumulation and misregulated traffic of a neurotransmitter GPCR in SLOS-like conditions. We believe these results assume relevance in our overall understanding of the molecular basis underlying the functional relevance of neurotransmitter receptors in SLOS.

Automated summary

Smith-Lemli-Opitz syndrome is a disorder related to defective cholesterol biosynthesis leading to neurological dysfunction. Research has shown that in SLOS-like conditions, there is a reduction in the number of neurotransmitter receptors on the cell membrane, with trafficking of these receptors to sterol-enriched compartments.