Abstract The gut microbiome has been implicated in host metabolism, endocrinology, and pathophysiology. Furthermore, several studies have shown that gut bacteria impact host growth, partially mediated through the growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis. Yet, no study to date has examined the specific role of GH on the gut microbiome. Our study thus characterized the adult gut microbial profile and intestinal phenotype in GH gene-disrupted (GH-/-) mice (a model of GH deficiency) and bovine GH transgenic (bGH) mice (a model of chronic, excess GH action) at 6 months of age. Both the GH-/- and bGH mice had altered microbial signatures, in opposing directions at the phylum and genus levels. For example, GH-/- mice had significantly reduced abundance in the Proteobacteria, Campylobacterota, and Actinobacteria phyla, whereas bGH mice exhibited a trending increase in those phyla compared with respective controls. Analysis of maturity of the microbial community demonstrated that lack of GH results in a significantly more immature microbiome while excess GH increases microbial maturity. Several common bacterial genera were shared, although in opposing directions, between the 2 mouse lines (e.g., decreased in GH-/- mice and increased in bGH mice), suggesting an association with GH. Similarly, metabolic pathways like acetate, butyrate, heme B, and folate biosynthesis were predicted to be impacted by GH. This study is the first to characterize the gut microbiome in mouse lines with altered GH action and indicates that GH may play a role in the growth of certain microbiota thus impacting microbial maturation and metabolic function.

Illumina-based amplicon sequencing suffers from the deleterious effects of highly homogenous nucleotide composition, limiting the number of high-quality reads generated per run. We attempted to alleviate this limitation by comparing the results obtained from 16S ribosomal DNA (16S rDNA) sequencing of mouse gut microbiomes using Illumina V3–V4 primers (Run 1) and custom primers that incorporate a heterogeneity spacer (0–7 nucleotides) upstream of the 16S priming region (Run 2). Overall, Run 2 had higher quality sequences, a more diverse microbial profile, and higher precision within, and variation between, experimental groups than Run 1. Our primer design offers a simple way to increase the quality of 16S rDNA sequencing and increases the number of useable reads generated per Illumina run.

The gut microbiome has an important role in host development, metabolism, growth, and aging. Recent research points toward potential crosstalk between the gut microbiota and the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis. Our laboratory previously showed that GH excess and deficiency are associated with an altered gut microbial composition in adult mice. Yet, no study to date has examined the influence of GH on the gut microbiome over time. Our study thus tracked the impact of excess GH action on the longitudinal changes in the gut microbial profile (i.e. abundance, diversity/maturity, predictive metabolic function, and short chain fatty acid [SCFAs] levels) of bovine GH (bGH) transgenic mice at 3, 6, and 12 months of age compared to littermate controls in the context of metabolism, intestinal phenotype, and premature aging. The bGH mice displayed age-dependent changes in microbial abundance, richness, and evenness. Microbial maturity was significantly explained by genotype and age. Moreover, several bacteria (i.e. Lactobacillus, Lachnospiraceae, Bifidobacterium, and Faecalibaculum), predictive metabolic pathways (such as SCFA, vitamin B12, folate, menaquinol, peptidoglycan, and heme B biosynthesis), and SCFA levels (acetate, butyrate, lactate, and propionate) were consistently altered across all three timepoints, differentiating the longitudinal bGH microbiome from controls. Of note, the bGH mice also had significantly impaired intestinal fat absorption with increased fecal output. Collectively, these findings suggest that excess GH alters the gut microbiome in an age-dependent manner with distinct longitudinal microbial and predicted metabolic pathway signatures.

Purpose Growth hormone (GH) has an important role in intestinal barrier function, and abnormalities in GH action have been associated with intestinal complications. Yet, the impact of altered GH on intestinal gross anatomy and morphology remains unclear. Methods This study investigated the influence of GH signaling on gross anatomy, morphology, and fibrosis by characterizing the small and large intestines in male and female bovine growth hormone transgenic (bGH) mice and GH receptor gene-disrupted (GHR−/−) mice at multiple timepoints. ResultsThe length, weight, and circumference of the small and large intestines were increased in bGH mice and decreased in GHR−/− mice across all ages. Colon circumference was significantly increased in bGH mice in a sex-dependent manner while significantly decreased in male GHR−/− mice. Villus height, crypt depth, and muscle thickness of the small intestine were generally increased in bGH mice and decreased in GHR−/− mice compared to controls with age-and sex-dependent exceptions. Colonic crypt depth and muscle thickness in bGH and GHR−/− mice were significantly altered in an age-and sex-dependent manner. Fibrosis was increased in the small intestine of bGH males at 4 months of age, but no significant differences were seen between genotypes at other timepoints. Conclusion This study observed notable opposing findings in the intestinal phenotype between mouse lines with GH action positively associated with intestinal gross anatomy (i.e. length, weight, and circumference). Moreover, GH action appears to alter morphology of the small and large intestines in an age-and sex-dependent manner.