Novel designer receptors to probe GPCR signaling and physiology

Abstract

Muscarinic receptor-based designer receptors have as powerful novel tools to study G-proteincoupled receptor (GPCR) signaling and physiology. These new designer GPCRs, which are most frequently referred to as DREADDs (designer receptors exclusively activated by designer drug), are unable to bind acetylcholine, the endogenous muscarinic receptor agonist, but can be activated by clozapine-N-oxide (CNO), an otherwise pharmacologically inert compound, with high potency and efficacy. The various DREADDs differ primarily in their G protein coupling preference. More recently, an arrestin-biased DREADD has also been developed. The expression of DREADDs in distinct tissues or cell types has enabled researchers to study the outcome of selective stimulation of distinct GPCR (or arrestin) signaling pathways in a temporally and spatially controlled fashion in vivo. In this review, we provide an up-to-date snapshot of where this field currently stands and which important novel insights have been gained using this new technology.

Remote control of induced dopaminergic neurons in parkinsonian rats

“…On the other hand, the DREADD M3Dq, associated with the stimulatory Gq protein, elicits robust Ca 2+ mobilization and membrane depolarization, thus increasing the firing rate (37). DREADD receptor activity has been investigated in both non-neuronal and neuronal cells (37,38,42). However, it is unknown whether DA neuronal activity is responsive to DREADD-induced intracellular signaling.…”

“…This approach relies on the known ability of CNO to easily cross the blood-brain barrier when peripherally injected (42). Rats grafted with M3Dq-expressing iDA neurons or fibroblasts were subjected to 1 daily injection of CNO for 3 days (1 mg/kg) before testing of drug-induced turning behavior.…”

Hepatic Gi signaling regulates whole-body glucose homeostasis

“…For this reason, it is not possible to selectively stimulate native G i -coupled receptors in hepatocytes by simply administering receptor-selective agonists in vivo. To circumvent this limitation, we took advantage of the availability of a new class of designer GPCRs known as DREADDs (15,16,46). Importantly, DREADDs do not bind any endogenous ligands but can be selectively activated by CNO, a synthetic drug that is otherwise pharmacologically inert (15,16,46).…”

Ganglionic GFAP+ glial Gq-GPCR signaling enhances heart functions in vivo

“…However, the ability of sympathetic SGCs to regulate ganglionic neuronal activity has never been directly tested, likely due to the inability to selectively activate SGCs without also activating neurons. To overcome this obstacle, we took advantage of DREADD technology and generated Gfap-hM3Dq transgenic mice (16).The engineered GPCR approach has been used by others to identify novel signaling pathways that play critical physiological roles in vivo (52)(53)(54). For example, Jain et al used hM3Dq transgenic mice to demonstrate that Gq-GPCR signaling in pancreatic β cells led to activation of ERK1/2 and IRS2 signaling; this activation led to markedly improved β cell function (55).…”