G Protein-coupled receptors (GPCR) are transmembrane proteins and are virtually expressed by all cell types of the body. More than 800 GPCRs are expressed in humans and regulate most of the physiological functions in the body, and they account for more than 40% of the currently available drugs in the market. Our lab's long-term goal is to unravel new mechanisms and develop GPCR based drugs for the treatment of metabolic disorders, including obesity, and type 2 diabetes.
Multiple tissues (adipose tissue, liver, skeletal muscle, pancreas, and brain) and cell-types work in tandem to maintain systemic energy homeostasis in mammals. Perturbations to this metabolic homeostasis can alter metabolic tissues' function and lead to several metabolic diseases, including obesity and type 2 diabetes, NAFLD, and cancer. Immune cells that reside in these metabolic tissues contribute significantly to disease phenotype by inducing low-grade chronic inflammation. Immune cells express numerous GPCRs, and they are known to regulate various immune cell functions. Thus, we are interested in understanding how different GPCR/G protein signaling pathways in the immune system can govern the function of various insulin-sensitive tissues, and use this information for the development of GPCR based pharmacological interventions for the treatment of obesity and T2D.
Since different GPCRs are expressed in multiple cell types, it is challenging to target individual GPCRs in specific cell types. Hence, we employ a chemogenetic technology called DREADD (Designer Receptors Exclusively Activated by Designer Drugs), where the receptor is activated only by a chemically inert compound called clozapine-N-oxide (CNO) (Figure 1). We express these DREADDs in specific immune cells in vivo using Cre-lox P system and challenge with different diets to assess the metabolic roles of different G-protein signaling pathways upon activation by CNO. Further, we employ a wide range of techniques including in vivo metabolic tests, co-culture systems, and high throughput sequencing analysis, including single-cell transcriptomics and metabolomics to assess GPCRs role in whole-body glucose homeostasis and energy metabolism.
Structure, activation and G protein coupling properties of muscarinic receptor based DREADDs. Two point mutations were introduced into the transmembrane core of the different muscarinic receptor-based DREADDs (marked by red crosses). These mutations prevent receptor activation by the endogenous ligand acetylcholine but allow for activation by clozapine-N-oxide (CNO). The Gq DREADD (GqD) is derived from the M3 receptor. In the Gs DREADD (GsD), the second and third intracellular loops of GqD were replaced with turkey beta1-adrenergic receptor sequence. The Gi DREADD (GiD) is derived from the M4 receptor. The G12 DREADD (G12D) was obtained by replacing the third intracellular loop of GqD with the corresponding GPR132 sequence.