ARS | Publication request: Hepatic changes in metabolic gene expression in old ghrelin and ghrelin receptor knockout mice

Submitted to: Endocrine Journal
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2010
Publication Date: June 1, 2010
Citation: Rogers, N.H., Van Der Brug, M.P., Cookson, M.R., Sun, Y., Smith, R.G. 2010. Hepatic changes in metabolic gene expression in old ghrelin and ghrelin receptor knockout mice [abstract]. Endocrine Reviews. 31(3): P2-507.

Technical Abstract: Ghrelin knockout (GKO) and ghrelin receptor (growth hormone secretagogue receptor) knockout (GHSRKO) mice exhibit enhanced insulin sensitivity, but the mechanism is unclear. Insulin sensitivity declines with age and is inversely associated with accumulation of lipid in liver, a key glucoregulatory tissue. While the GHSR is not found in liver, central ghrelin can indirectly regulate peripheral metabolism. In an effort to clarify links between ghrelin status and insulin resistance, we performed in depth hepatic gene expression studies in older C57Bl/6J WT, GKO and GHSRKO mice. We first isolated hepatic RNA from 10 mo old WT and GHSRKO littermates (n=3) and globally assessed gene expression using microarrays (Illumina) and RNA-Sequencing (Illumina Genome Analyzer II). Both methods showed higher IGFBP2, and lower lipid droplet-associated proteins (cidea, cidec, S3-12), acetyl-coA carboxylase (ACC beta), and stearoyl-coA desaturase (scd1) expression in GHSRKO compared to WT mice. Moreover, RNA-seq methods revealed additional differentially expressed genes (underscoring array limitations). Genes more highly expressed in GHSRKO mice included insulin receptor (insr) and ampk alpha 2, while carnitine palmitoyl transferase (cpt1 alpha) abundance was lower. We next used real-time-PCR and 2-way ANOVAs to assess hepatic gene expression differences in 10 and 15 mo GKO and GHSRKO mice (each vs respective WT littermates). Whereas WT mice express markedly more (~40-fold) cidea at 15 mo compared to 10 mo of age, 15 mo GKO and GHSRKO mice show expression levels similar to the 10 mo WT mice (genotype x age interactions, p<0.001). Likewise, 15 mo WT mice express ~5-fold more PPAR y than 10 mo WT mice, but 15 mo knockout mice show only 2x more (GKO), or similar (GHSRKO) hepatic PPAR y as their 10 mo counterparts. Accordingly, older WT mice express more cidec, S3-12 and scd1, and less IGFBP2, but knockout mice again show attenuated age-related changes. In summary, comprehensive hepatic gene expression analyses reveal altered metabolic profiles in older mice that are dependent on ghrelin signaling, albeit indirectly. Key findings, such as increased insr expression in GHSRKO mice, offer enticing clues to help explain enhanced insulin sensitivity in mice lacking ghrelin or the ghrelin receptor.