The influence of cell type-specific G-protein activity on GPCR-mediated signal transduction in adipose tissue (patho)physiology

• Applicant: Dr. Isabell Kaczmarek
• Subject Area: Pharmacology ; Biochemistry ; Cell Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574313154

The global prevalence of obesity and associated comorbidities is rapidly rising, which places a high burden on affected individuals and the healthcare system, leading to an urgent demand for novel targets in obesity prevention and treatment. Since more than 30 % of all clinically relevant drugs act on G protein-coupled receptors (GPCRs), this receptor superfamily represents a particularly promising target class. Despite all efforts, there are no drugs commercially available that directly target adipose tissue and, thus, reduce fat mass. With more than 160 GPCRs expressed in human adipose tissue, there is a large number of targets for drug development. However, the specific role in adipogenesis and adipocyte-specific functions (e.g. lipolysis) has only been sufficiently characterized for a limited number of GPCRs. Adipocytes can perform distinct functions depending on their cellular subtype. Using single cell RNAseq, adipocyte subtypes were identified that are characterized by different expression patterns of genes (system bias) involved in adipocyte-specific functions. Since GPCR signalling pathways modulate these functions, it is conclusive that GPCRs and effector proteins, such as G proteins, contribute to system bias in adipocyte subtypes. Thus, in individuals with obesity, GPCR-dependent, adipocyte-specific functions can be dysregulated via system bias. Therefore, I hypothesize that it is essential to understand the mechanisms of system bias in adipocyte subtypes of lean individuals and individuals with obesity in order to predict different modes of action and side effects of drugs and to develop more effective therapeutic approaches. In preliminary work, four GPCRs (Hcar2, Adora1, Ffar4 and Adrb1) were identified by RNAseq analysis that are highly and specifically expressed in primary human and mouse adipocytes. First, G-protein activation is analysed in a heterologous expression system with overexpression of receptor and G protein using bioluminescence resonance energy transfer (BRET). Subsequently, the GPCR-mediated, endogenous G-protein activity will be analyzed in adipocyte subtypes at the cell surface and cellular compartments using BRET. Thereto, the 3T3-L1 cell line with adipogenic potential is used. Here, specific 3T3-L1 adipocyte subtypes are defined by different differentiation stages and pathophysiologically hypertrophic conditions. Considering the identified G-protein activities, the effects of system bias on adipogenesis and adipocyte-specific functions will be investigated. This project will show how system bias influences the function of GPCRs in adipose tissue and, thus, leads to cell type-specific differences in signal transduction. The findings will essentially contribute to the prediction of pharmacodynamic responses and potential side effects leading to the development of more efficient therapeutic approaches.

• DFG Programme: WBP Position