(#8389) Gpr139, a Modulator of Mu Opioid Receptor, is a Target of Sonic Hedgehog Signaling in Cholinergic Interneurons of the Adult Striatum and Modulates Cholinergic Activity

Neuroscience, 2021 (SFN)

Dustin R. Zuelke, Sonia Bernal, Aria Walls, and Andreas H. Kottmann

Cholinergic interneurons (CIN) are key components of striatal circuits. CIN have been implicated in various processes including learning, aging, addiction, and Parkinson’s disease (PD). The gold standard treatment for PD is dopamine (DA) substitution therapy with L-Dopa, which aims to mitigate the functional consequences of dopamine cell loss. However, long-term treatment leads to the development of debilitating L-Dopa induced dyskinesia (LID). We have previously shown that activation of the GPCR Smoothened (Smo) on CIN attenuates L-Dopa induced dyskinesia (LID) in rodent and macaque models of PD (Malave et al., 2021). The predominant source of the physiological ligand for CIN expressed Smo, Sonic Hedgehog (Shh), are ventral midbrain DA neurons (DAN) (Gonzalez et al., 2012). To elucidate possible mechanism(s) by which loss of Shh signaling from DAN might mediate CIN pathophysiology in PD, we identified CIN-specific downstream transcriptional targets of Smo. We utilized translating ribosome affinity purification (TRAP), to isolate mRNA selectively from CINs for RNAseq in mice with conditional ablation of Shh from DAN and controls. The results from the RNAseq analysis identified the orphan G-coupled receptor GPR139 as a potential target for further investigation. Subsequent experiments showed that striatal GPR139 expression is reduced in mice with conditional ablation of Shh from DAN compared to controls. GPR139 expression in the wild-type striatum reveals a prominent low (medial) to high (lateral) expression gradient that matches the expression gradient of the transcriptional effector of Shh signaling, Gli3. GPR139 is a cell autonomous negative modulator of endo-opioid signaling acting downstream of mu-opioid receptor (MOR) activation by morphine and fentanyl. Previous studies have shown morphine decreases ACh release, while antagonists of MOR increase striatal ACh. Further, antagonists of MOR were previously found to attenuate LID in animal models of PD. Thus, we hypothesized that Shh signaling might attenuate LID by modulating the CIN response to MOR activation. We used fiber photometry with DA- and ACh- sensors to monitor in vivo extracellular levels of DA and ACh combined with localized micro-fluid injection of drugs in the striatum and detected increased striatal ACh levels in response to GPR139 agonist. To test if this effect is cell autonomous, we performed acute, Cre-dependent CIN CRISPR knock-down of GPR139. Using this novel paradigm, we will present pharmacological epistasis experiments that investigate the molecular details of the modulation of MOR signaling by Smo in CIN and the effect of GPR139 pharmacology on LID.