Hedgehog Interaction Protein Acts in the Habenula to Regulate Nicotine Intake

Medial habenular (mHb) cholinergic neurons that project to the interpeduncular nucleus (IPn) regulate aversive behavioral responses to nicotine that protect against tobacco addiction. Little is known about the nicotine-evoked cellular or molecular adaptations in these neurons that influence the development of the smoking habit. Using in vivo calcium imaging and single-cell RNA sequencing, we show that a dose of nicotine that stimulates mHb neural activity evokes robust transcriptional plasticity in neuronal and non-neuronal cells in the mHb, including upregulated expression of Hedgehog-interacting protein (HHIP) in putative cholinergic neurons. Allelic variation in HHIP confers risk for smoking-related diseases including chronic obstructive pulmonary disease and lung cancer, but underlying mechanisms of action are unclear. Using Translating Ribosome Affinity Purification (TRAP) sequencing and RNAscope, we confirmed that Hhip transcripts are highly enriched in mHb cholinergic neurons. HHIP mutant mice exhibit hundreds of differentially expressed transcripts in the mHb and perturbed transcriptional responses to nicotine. Moreover, acute in vivo CRISPR/Cas9-mediated genomic cleavage of mHb Hhip attenuated noxious responses to nicotine and increased intravenous nicotine self-administration behavior in mice. In vitro knockdown of Hhip reduces intracellular calcium release to nicotine and increases Gli activity. These findings suggest that HHIP acts in the mHb to regulate nicotine intake and that HHIP alleles may increase vulnerability to smoking-related diseases by modulating mHb signaling and enhancing the addictive properties of tobacco. HHIP mutant x WT. Saline x Nicotine. Medial Habenular tissue.