ABSTRACT
Hypothalamic neurons are main regulators of energy homeostasis. Neuronal function essentially depends on plasma membrane-located gangliosides. The present work demonstrates that hypothalamic integration of metabolic signals requires neuronal expression of glucosylceramide synthase (GCS; UDP-glucose:ceramide glucosyltransferase). As a major mechanism of central nervous system (CNS) metabolic control, we demonstrate that GCS-derived gangliosides interacting with leptin receptors (ObR) in the neuronal membrane modulate leptin-stimulated formation of signaling metabolites in hypothalamic neurons. Furthermore, ganglioside-depleted hypothalamic neurons fail to adapt their activity (c-Fos) in response to alterations in peripheral energy signals. Consequently, mice with inducible forebrain neuron-specific deletion of the UDP-glucose:ceramide glucosyltransferase gene (Ugcg) display obesity, hypothermia, and lower sympathetic activity. Recombinant adeno-associated virus (rAAV)-mediated Ugcg delivery to the arcuate nucleus (Arc) significantly ameliorated obesity, specifying gangliosides as seminal components for hypothalamic regulation of body energy homeostasis.
Subject(s)
Body Weight/physiology , Central Nervous System/cytology , Central Nervous System/enzymology , Glucosyltransferases/metabolism , Neurons/enzymology , Animals , Arcuate Nucleus of Hypothalamus/drug effects , Arcuate Nucleus of Hypothalamus/metabolism , Blotting, Western , Body Weight/drug effects , Body Weight/genetics , Cells, Cultured , Central Nervous System/drug effects , Dependovirus/genetics , Energy Metabolism/drug effects , Energy Metabolism/genetics , Fatty Acids, Nonesterified/blood , Female , Fluorescent Antibody Technique , Glucosyltransferases/genetics , Homeostasis/drug effects , Homeostasis/genetics , Hypothalamus/cytology , Hypothalamus/drug effects , Immunoprecipitation , Leptin/blood , Male , Mice , Mice, Mutant Strains , Motor Activity/drug effects , Motor Activity/genetics , Motor Activity/physiology , Neurons/drug effectsABSTRACT
Olfactory receptor neurons respond to odor stimulation with a receptor potential that results from the successive activation of cyclic AMP (cAMP)-gated, Ca(2+)-permeable channels and Ca(2+)-activated chloride channels. The cAMP-gated channels open at micromolar concentrations of their ligand and are subject to a Ca(2+)-dependent feedback inhibition by calmodulin. Attempts to understand the operation of these channels have been hampered by the fact that the channel protein is composed of three different subunits, CNGA2, CNGA4, and CNGB1b. Here, we explore the individual role that each subunit plays in the gating process. Using site-directed mutagenesis and patch clamp analysis, we identify three functional modules that govern channel operation: a module that opens the channel, a module that stabilizes the open state at low cAMP concentrations, and a module that mediates rapid Ca(2+)-dependent feedback inhibition. Each subunit could be assigned to one of these functions that, together, define the gating logic of the olfactory transduction channel.
