Smith-Magenis syndrome protein RAI1 regulates body weight homeostasis through hypothalamic BDNF-producing neurons and neurotrophin downstream signalling

Abstract

Retinoic acid-induced 1 (RAI1) haploinsufficiency causes Smith-Magenis syndrome (SMS), a genetic disorder with symptoms including hyperphagia, hyperlipidemia, severe obesity, and autism phenotypes. Rai1 is a transcriptional regulator with a pan-neural expression pattern and hundreds of downstream targets. The mechanisms linking neural Rai1 to body weight regulation remain unclear. Here we find that hypothalamic brain-derived neurotrophic factor (Bdnf)-TrkB signalling is disrupted in SMS (Rai1+/-) mice. Selective Rai1 loss from all Bdnf-producing cells or from Bdnf-producing neurons in the paraventricular nucleus of the hypothalamus (PVH) induced obesity in mice. Electrophysiological recordings revealed that Rai1 ablation increased inhibitory synaptic transmission to PVHBdnf neurons and decreased intrinsic neuronal excitability. Chronic treatment of SMS mice with a partial agonist of tropomyosin receptor kinase B (TrkB), the cognate Bdnf receptor, delayed obesity onset. This treatment also partially rescued disrupted lipid profiles, insulin intolerance, and stereotypical repetitive behaviour in SMS mice. These data argue that Rai1 regulates body weight and metabolic function through hypothalamic Bdnf-producing neurons and that targeting TrkB signalling might improve associated SMS phenotypes.