A Novel GH Deficient Rat Model Reveals Cross-Species Insights Into Aging

Abstract

Multiple studies in mice with genetically disrupted growth hormone (GH) signaling have demonstrated that such disruption results in reduced body size, robustly increased longevity (> 50% in some cases), and improvements across multiple health parameters. However, it remains unclear how generalizable these findings are across mammals. Evidence in rats is limited and inconsistent. These conflicting results highlight the need for further investigation into the role of GH signaling in longevity across species. To address this gap, we developed a novel GH-deficient rat model using CRISPR/Cas9 technology to introduce a 10 bp deletion in exon 3 of the gene encoding rat GH-releasing hormone (GHRH) yielding a non-functional GHRH product. Physiological characterization of GHRH knockout (KO) rats revealed that they were half the body weight of wild-type controls. Additionally, relative to controls, they displayed an increased percent body fat, enhanced insulin sensitivity, reduced circulating insulin-like growth factor I (IGF-I) concentration, and a decreased reliance on glucose oxidation for energy metabolism, as determined by indirect calorimetry. Analysis of the gut microbial community in adult GHRH-KO rats further revealed a less diverse male microbiome, but a more diverse female KO microbiome compared to controls. Collectively, these findings demonstrate that multiple aspects of the GH activity-deficient phenotype, well-documented in mice, are faithfully recapitulated in our rat model. Therefore, the GHRH-deficient rat model represents a valuable new tool for advancing our understanding of the role of GH signaling in aging processes.

Keywords: aging; endocrinology; gender differences; insulin/IGF‐1 signaling; lifespan; longevity; metabolic rate; rat models.

FIGURE 1

Development of a GHRH knockout rat model. DNA sequence chromatogram of the WT and mutant GHRH gene (a). Genotyping of tail DNA by PCR using primers spanning exon 3 of the gene coding for rat GHRH reveals a 10 bp deletion in mutant rats (b). mRNA abundance of Gh1 transcripts in the pituitary of 3–4 month‐old rats, with Actb used as an endogenous control. Representative image of adult female rats (d). Serum IGF‐1 levels, assessed by ELISA in 1‐year‐old male and female rats as indicated (e). Data presented as mean ± SEM with points representing individual rats. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 as determined by two‐tailed n‐test (c, e). N = 3–8 per group.

FIGURE 2

Physiological characteristics and microbiome features of GHRH deficient rats. Weekly bodyweights of male (a) or female (b) rats as indicated. Body composition—percent fat mass and lean mass—in 3‐month‐old male (c) and female (d) rats as indicated. 1 U/kg IPITT in ad‐lib fed male (e) or female (f) rats. Respiratory exchange ratio (RER; VCO₂/VO₂) calculated during indirect calorimetry experiments in male (g) and female (h) rats. Rates of glucose (GOX) and fat (FOX) oxidation, calculated as detailed in the methods section, in male and female rats (i). LEfSe results for analysis of differentially abundant taxa within the male (j) or female (k) gut microbiome. Preliminary survival analysis of GHRH‐KO rats (l). Data presented as mean ± SEM with points representing individual rats. *p < 0.05, **p < 0.01, ***p < 0.001 as determined by two‐way repeated measure ANOVA followed by Tukey HSD post hoc test (e, f, g, h) or by two‐tailed n‐test with the Welch correction applied (c, d, i). N = 4–11 per group. p‐values presented represent the main effect of genotype as determined by two‐way repeated measure ANOVA (a, b, g, h) or by log‐rank test (l). N = 4–10 (a–k) or N = 15–16 per group (7 male WT, 10 male GHRH‐KO, 9 female WT, and 5 female GHRH‐KO; [l]).