An MCH neuroendocrine circuit in lateral hypothalamus for bone mass regulation

Neuroendocrine regulation is essential for maintaining metabolic homeostasis. However, whether neuroendocrine pathway influence bone metabolism is unelucidated. Here, we identify a central neuroendocrine circuit that directly controls osteogenesis. Using virus based tracing, weidentify that melanin concentrating hormone (MCH) expressing neuronsin the lateral hypothalamus (LH) are connected to the bone.Chemogenetic activation of MCH neurons in the LH induces osteogenesis, whereas inhibiting these neurons reduces osteogenesis.Meanwhile, MCH is released into the circulation upon chemogenetic activation of these neurons. Single cell sequencing reveals that blocking MCH neurons in the LH diminishes osteogenic differentiation of bone marrow stromal cells (BMSCs). Mechanistically, MCH promotes BMSC differentiation by activating MCHR1 via PKA signaling and activating MCHR1 by MCH agonists attenuate osteoporosis in mice. By elucidating a brain-bone connection that autonomously enhances osteogenesis, these findings uncover the neuroendocrinological mechanisms governing bone mass regulation. Overall design: Adult mice aged 6-8 weeks were anesthetized intraperitoneally using sodium pentobarbital (100 mg/kg) and gently secured to a stereotaxic frame (RWD Life Science, Shenzhen, China). A total volume of 200 nL of the virus suspension was loaded into a 1 ml-Hamilton syringe fitted with a needle made of glass electrode. The AAVs used were rAAV-hSyn-DIO-hM3D(Gq)-EGFP-WPRE-hGH polyA,rAAV-hSyn-DIO-EGFP-WPRE-hGH polyA rAAV-hSyn-DIO-hM4D(Gi)-EGFP-WPRE-hGH polyA, obtained from BrainVTA, Wuhan, China. The viral titer for all AAVs was maintained at 2.32-5.72E+12 PFU/mL. Mice(C57BL/6-Tg(Pmch-cre)1Rck/J) carrying genes specifically expressing CRE in pMCH cells come from JAXlab, The injection was performed at a rate of 20 nL/min into specific target locations (-0.58,0,-2.5 for the LH (bregma:-1.8 to -2.20 mm,lateral from midline:±1.27 to ±1.47 mm,depth:-4.55 to -4.75 mm). The surgical procedure adhered to the protocol outlined by Lowery and Majewska (reference 54). Following the surgery,a recovery period of at least 1 week was provided for the mice before commencing any experimental procedures. For chemogenetic activation and inhibition, clozapine-N-oxide (CNO) at a dosage of 1 mg/kg (MCE,34233-69-7) was administered intraperitoneally three weeks after viral expression. The injections were repeated every 48 hours for a duration of four weeks before serum and bone samples were collected for subsequent analysis. The AAV9 viruses were prepared in-house, ensuring their quality and consistency.