# GRK5 is required for adipocyte differentiation through ERK activation

## TL;DR

This study shows that GRK5 is essential for fat cell development by activating the IGF-1 receptor/ERK pathway, offering a potential target for obesity treatment.

## Contribution

The study identifies GRK5's role in adipocyte differentiation via IGF-1/ERK signaling and introduces a small molecule GRK5 inhibitor.

## Key findings

- GRK5 knockout pre-adipocytes failed to mature into adipocytes with suppressed gene expression.
- IGF-1 signaling was among the top dysregulated pathways in GRK5 KO cells.
- A small molecule GRK5 inhibitor reduced 3T3-L1 adipogenesis.

## Abstract

Previous studies have identified G protein-coupled receptor (GPCR) kinase 5 (GRK5) as a genetic factor contributing to obesity pathogenesis, but the underlying mechanism remains unclear. We demonstrate here that Grk5 mRNA is more abundant in stromal vascular fractions of mouse white adipose tissue, the fraction that contains adipose progenitor cells, or committed pre-adipocytes, than in adipocyte fractions. Thus, we generated a GRK5 knockout (KO) 3T3-L1 pre-adipocyte to further investigate the mechanistic role of GRK5 in regulating adipocyte differentiation. During adipogenic stimulation, GRK5 KO pre-adipocytes were unable to achieve mature adipocyte morphology and lipid accumulation compared to wildtype cells coupled with suppressed adipogenic and lipogenic gene expression. Beside GPCR signaling, RNA sequencing and pathway analysis identified insulin-like growth factor 1 (IGF-1) signaling to be one of the top 5 significantly dysregulated pathways in GRK5 KO cells. GRK5 KO cells also displayed decreased insulin-stimulated ERK phosphorylation, a downstream target of insulin-stimulated IGF-1 receptor activation, suggesting that GRK5 acts through this critical pathway to impact 3T3-L1 adipocyte differentiation. To find a more translational approach, we identified a new small molecule GRK5 inhibitor that was able to reduce 3T3-L1 adipogenesis. These data suggest that GRK5 is required for adipocyte differentiation through IGF-1 receptor/ERK activation and may be a promising translational target for obesity.