Energy homeostasis targets chromosomal reconfiguration of the human GH1 locus
Hana Vakili, Yan Jin, Peter A. Cattini
Hana Vakili, Yan Jin, Peter A. Cattini
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Research Article Endocrinology

Energy homeostasis targets chromosomal reconfiguration of the human GH1 locus

Abstract

Levels of pituitary growth hormone (GH), a metabolic homeostatic factor with strong lipolytic activity, are decreased in obese individuals. GH declines prior to the onset of weight gain in response to excess caloric intake and hyperinsulinemia; however, the mechanism by which GH is reduced is not clear. We used transgenic mice expressing the human GH (hGH) gene, GH1, to assess the effect of high caloric intake on expression as well as the local chromosome structure of the intact GH1 locus. Animals exposed to 3 days of high caloric intake exhibited hyperinsulinemia without hyperglycemia and a decrease in both hGH synthesis and secretion, but no difference in endogenous production of murine GH. Efficient GH1 expression requires a long-range intrachromosomal interaction between remote enhancer sequences and the proximal promoter region through “looping” of intervening chromatin. High caloric intake disrupted this interaction and decreased both histone H3/H4 hyperacetylation and RNA polymerase II occupancy at the GH1 promoter. Incorporation of physical activity muted the effects of excess caloric intake on insulin levels, GH1 promoter hyperacetylation, chromosomal architecture, and expression. These results indicate that energy homeostasis alters postnatal hGH synthesis through dynamic changes in the 3-dimensional chromatin structure of the GH1 locus, including structures required for cell type specificity during development.

Authors

Hana Vakili, Yan Jin, Peter A. Cattini

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Figure 6

Disruption of the HS I/II–GH1 promoter region interaction by excess caloric intake.

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Disruption of the HS I/II–GH1 promoter region interaction by excess calo...
(A) 3C assay: crosslinking of the interacting chromatin with formaldehyde, digestion of DNA by an appropriate restriction enzyme, and ligation of digested cross-linked chromatin fragments that can be quantified by qPCR. (B) Effect of HFD versus LFD on long-range chromatin-chromatin interactions that permit efficient expression of pituitary GH1 in vivo. The map of Bgl II restriction fragments and positions of primers (arrows) used to determine and quantify the ligated products representing HS I/II and GH1 promoter physical interaction are shown below the locus. (C) Detection of combined Bgl II fragments resulting from physical interaction between HS I/II and the GH1 promoter in the presence or absence of ligase, assessed by PCR and agarose gel electrophoresis. (D and E) HS I/II–GH1 promoter association in (D) pituitary and (E) heart tissue from 171hGH/CS-TG mice fed HFD versus LFD for 3 days. Ligation frequency was calculated as (ligation product/loading control) – (nonligation product/loading control). Results (mean ± SEM) were obtained from 3 independent samples (in duplicate). Significance was assessed by t test (n = 6). ***P < 0.001.