Development and Initial Characterization of a Novel Ghrelin Receptor CRISPR/Cas9 Knockout Wistar Rat Model

BACKGROUND/OBJECTIVES: Ghrelin, a stomach-derived hormone implicated in numerous behaviors including feeding, reward, stress, and addictive behaviors, acts through binding to the growth hormone secretagogue receptor (GHSR). Here, we present the development, verification and initial characterization of a novel GHSR knockout (KO) Wistar rat model created with CRISPR genome editing. METHODS: Using CRISPR/Cas9, we developed a GHSR knockout (KO) in a Wistar background. Loss of GHSR mRNA expression was histologically verified using RNAscope in wild-type WT (n = 2) and KO (n = 2) rats. We tested the effects of intraperitoneal acyl-ghrelin administration on food consumption and plasma growth hormone (GH) concentrations in WT (n = 8) and KO (n = 8) rats. We also analyzed locomotion, food consumption, and body fat composition in these animals. Body weight was monitored from early development to adulthood. RESULTS: The RNAscope analysis revealed an abundance of GHSR mRNA expression in the hypothalamus, midbrain, and hippocampus in WTs, and no observed probe binding in KOs. Ghrelin administration increased plasma GH levels (p = 0.0067) and food consumption (p = 0.0448) in WT rats but not KOs. KO rats consumed less food overall at basal conditions and weighed significantly less compared with WTs throughout development (p = 0.0001). Compared with WTs, KOs presented higher concentrations of brown adipose tissue (BAT) (p = 0.0322). CONCLUSIONS: We have verified GHSR deletion in our KO model using histological, physiological, neuroendocrinological and behavioral measures. Our findings indicate that GHSR deletion in rats is not only associated with a lack of response to ghrelin, but also associated with decreases in daily food consumption and body growth, and increases in BAT. This GHSR KO Wistar rat model provides a novel tool for studying the role of the ghrelin system in obesity and in a wide range of medical and neuropsychiatric disorders.