Human M4 muscarinic receptor-based inhibitory designer receptor exclusively activated by designer drugs (hM4Di) (hM4Di)

hM4Di is a designer G protein-coupled receptor (GPCR) engineered from the human M4 muscarinic acetylcholine receptor, belonging to the class of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) (Urban & Roth, 2015, NIH). It is modified with two point mutations (Y113C and A203G) that abolish its affinity for the endogenous neurotransmitter acetylcholine while enabling high-affinity binding to synthetic ligands such as clozapine N-oxide (CNO) and deschloroclozapine (DCZ) (Armbruster et al., 2007, PNAS; Zhang et al., 2022, Nature). Upon activation, hM4Di engages the Gi/o signaling pathway, which induces neuronal hyperpolarization via G protein-coupled inwardly rectifying potassium (GIRK) channels and suppresses presynaptic neurotransmitter release (Stachniak et al., 2014, Neuron). This dual mechanism allows for the reversible and remote inhibition of specific neuronal populations, making it a cornerstone technology for mapping neural circuits (Roth Lab, Benchling). While primarily used in preclinical research, hM4Di is being developed as a therapeutic target for gene therapy to treat neurological conditions characterized by neuronal hyperexcitability, such as focal epilepsy, chronic pain, and spinal cord injury (Goossens et al., 2021, eNeuro; PatSnap).

Other names

hM4D(Gi)Gi-DREADDInhibitory DREADDhM4D

Activation of the Gi/o signaling pathway, leading to the opening of G protein-coupled inwardly rectifying potassium (GIRK) channels and inhibition of presynaptic neurotransmitter release (Urban & Roth, 2015, NIH; Stachniak et al., 2014, Neuron).