Low plasma adropin concentrations increase risks of weight gain and metabolic dysregulation in response to a high-sugar diet in male nonhuman primates

Abstract

Mouse studies linking adropin, a peptide hormone encoded by the energy homeostasis-associated (ENHO) gene, to biological clocks and to glucose and lipid metabolism suggest a potential therapeutic target for managing diseases of metabolism. However, adropin's roles in human metabolism are unclear. In silico expression profiling in a nonhuman primate diurnal transcriptome atlas (GSE98965) revealed a dynamic and diurnal pattern of ENHO expression. ENHO expression is abundant in brain, including ventromedial and lateral hypothalamic nuclei regulating appetite and autonomic function. Lower ENHO expression is present in liver, lung, kidney, ileum, and some endocrine glands. Hepatic ENHO expression associates with genes involved in glucose and lipid metabolism. Unsupervised hierarchical clustering identified 426 genes co-regulated with ENHO in liver, ileum, kidney medulla, and lung. Gene Ontology analysis of this cluster revealed enrichment for epigenetic silencing by histone H3K27 trimethylation and biological processes related to neural function. Dietary intervention experiments with 59 adult male rhesus macaques indicated low plasma adropin concentrations were positively correlated with fasting glucose, plasma leptin, and apolipoprotein C3 (APOC3) concentrations. During consumption of a high-sugar (fructose) diet, which induced 10% weight gain, animals with low adropin had larger increases of plasma leptin and more severe hyperglycemia. Declining adropin concentrations were correlated with increases of plasma APOC3 and triglycerides. In summary, peripheral ENHO expression associates with pathways related to epigenetic and neural functions, and carbohydrate and lipid metabolism, suggesting co-regulation in nonhuman primates. Low circulating adropin predicts increased weight gain and metabolic dysregulation during consumption of a high-sugar diet.

Keywords: apolipoprotein; circadian; dyslipidemia; epigenetics; glucose metabolism; insulin resistance; leptin; nutrition; obesity; type 2 diabetes.

Figure 1.

Relative ENHO expression in baboon tissues (A) and diurnal expression profile within tissues (B). The heat map in A is a single column that shows relative expression between tissues and is read from top to bottom. These data are derived from FPKM averaged over 24 h within each tissue. The heat maps in B show relative expression as a deviation from the 24-h mean (z-score) during a 24-h period within each tissue and should be read left (ZT0) to right (ZT24). The heat maps illustrate the diurnal profile of ENHO expression. Peak ENHO expression (red) is observed in the daytime in most tissues. Lights-on (day time) and lights-off (night time) are indicated by the yellow and black bars, respectively.

Figure 2.

Hepatic ENHO expression shares a dynamic expression profile with >1200 genes. A, diurnal profile of hepatic ENHO expression shown as a line graph. Meal times are indicated by green arrows. B, heat map comparing profile of ENHO expression (top) with genes ranked by their correlation coefficient (r, high to low when read from the top down) with ENHO. The coefficient of determination (R²) is shown to the right. Lights-on (day time) and lights-off (night time) are indicated by the yellow and black bar at the top of the figure. There are 1276 genes showing a marked positive association and whose expression is mutually inclusive (r < −0.7) with ENHO. For a similar number of genes, ENHO expression appears be mutually exclusive (ENHO is highly expressed as indicated by red coloring and their expression is repressed as indicated by blue coloring).

Figure 3.

Relationships between plasma adropin concentrations and fasting plasma concentrations of leptin (A), glucose (B), insulin (C), and ApoC3 (D) in male rhesus macaques (n = 59). Scatterplots present the relationships at baseline (chow-fed) and after 1 and 3 months of consuming fructose-sweetened beverages (300 kcal/day). Fasting plasma glucose concentrations exceeding 100 mg/dl (indicated with red symbols, orange shading in B) have been used as a diagnostic criteria for type 2 diabetes in rhesus macaques (38–41). Of the seven animals with fasting glucose >100 mg/dl after 3 months of fructose, four had glucose levels >100 mg/dl at baseline (>50%). The fasting glucose levels of the other three animal at baseline were higher (85, 83, and 92 mg/dl) relative to the group average (mean 80 mg/dl, S.D. 15 mg/dl).

Figure 4.

Relationships between fructose-induced changes in ApoA1 (A and B), TG (C and D), and ApoC3 (E and F). The data shown are for fructose-induced changes (Δ) after 1 month (A, C, and E) and 3 months (B, D, and F). The proportion of variance dependent on the variable (coefficient of determination, R² with p value) is shown in each graph.

Figure 5.

Lipid parameters in subpopulations of rhesus macaques exhibiting low, medium, or high responses of plasma adropin concentrations after 1 month of fructose consumption. Animals were ranked by changes of plasma adropin concentrations after 1 month of fructose consumption. They were then subdivided into three groups: high-responders, n = 20, green lines/symbols; mid-responders, n = 19, blue lines/symbols; and low-responders, n = 20, red lines/symbols. Shown are the averages for each time point based on the ranking at the 1-month time point. Plasma concentrations of the variable defined in the y axis label are shown in A, C, E, G, and H. Fructose-induced Δs of plasma concentrations of the variable defined in the y axis label (1- and 3-month values subtracted from baseline) are shown in B, D, F, H, and J. “High-responders” exhibit a marked increase in plasma adropin concentration at the 1-month time point (B). ***, p < 0.001 between all groups; #, p < 0.05 versus mid- and high-responders; *, p < 0.05; **, p < 0.01 versus low-responders (within time points). #, low- versus medium-responder, p < 0.05, versus high-responder, p < 0.01 (ANOVA with repeated measures).