Comprehensive lipidomic analysis reveals regulation of glyceride metabolism in rat visceral adipose tissue by high-altitude chronic hypoxia

Abstract

Adipose tissue plays a central role in energy substrate homeostasis and is a key regulator of lipid flow throughout these processes. As hypoxia affects lipid metabolism in adipose tissue, we aimed to investigate the effects of high-altitude chronic hypoxia on lipid metabolism in the adipose tissue of rats using a lipidomic analysis approach. Visceral adipose tissues from rats housed in a high-altitude hypoxia environment representing 4,300 m with 14.07% oxygen (hypoxia group) and from rats housed in a low-altitude normoxia environment representing 41 m with 20.95% oxygen (normoxia group) for 8 weeks were analyzed using an ultra-performance liquid chromatography-Orbitrap mass spectrometry system. After 8 weeks, the body weight and visceral adipose tissue weight of the hypoxia group were significantly decreased compared to those of the normoxia group (p < 0.05). The area and diameter of visceral adipose cells in the hypoxia group were significantly smaller than those of visceral adipose cells in the normoxia group (p < 0.05). The results of lipidomic analysis showed a total of 21 lipid classes and 819 lipid species. The total lipid concentration of the hypoxia group was lower than that in the normoxia group (p < 0.05). Concentrations of diacylglycerols and triacylglycerols in the hypoxia group were significantly lower than those in the normoxia group (p < 0.05). Using univariate and multivariate analyses, we identified 74 lipids that were significantly altered between the normoxia and hypoxia groups. These results demonstrate that high-altitude chronic hypoxia changes the metabolism of visceral adipose glycerides, which may potentially modulate other metabolic processes.

Fig 1. Changes in body weight, adipose tissue, and blood indexes in the hypoxia group versus the normoxia group.

Hemoglobin, (B) 0-week body weight, (C) 8-week body weight, (D) total food intake, (E) visceral adipose tissue weight. A: n = 5 rats per group. B-D: n = 6 rats per group. E: n = 4 rats per group. Independent-samples t-test was used for statistical analysis.

Fig 2. Changes in lipids in the hypoxia group versus the normoxia group.

Lipids were classified according to the guidelines of the International Lipid Classification and Nomenclature committee. (A) Number of lipid classes and lipid species, (B) total lipid molecular content, and (C and D) content of different lipid subgroups. Independent-samples t-test was used for the statistical analysis of data presented in panels B, C, and D.

Fig 3. Univariate and multivariate analyses of lipids in rat visceral adipose tissue.

(A) PCA score plot, (B) PLS-DA score plot, (C) PLS-DA permutation test, (D) OPLS-DA score plot, (E) OPLS-DA permutation test, and (F) volcano plot of the normoxia and hypoxia groups.Differences in lipid molecules with FC >1.5 or FC <0.67 and p-value <0.05 are represented by different colors. The rose-red dots in the figure represent significantly different lipids.

Fig 4. Effects of hypoxia on markers of lipolysis.

Haematoxylin and eosin staining, scale bar:10μm, (B) adipocyte diameter, and (C) adipocyte area changes in the visceral adipose tissue in the hypoxia group versus the normoxia group. The mRNA levels of lipolysis related-genes,including (D) adipose TG lipase (ATGL), and (E) hormone-sensitive lipase (HSL). (F) The content of NEFA. A-C: n = 3 rats per group.D-E: n = 6 rats per group. Independent-samples t-test was used for statistical analysis.

Fig 5. Analysis of significantly different lipids between the normoxia and hypoxia groups.

(A) DG carbon chain length analysis. (B) DG saturation analysis. (C) TG carbon chain length analysis. (D) TG saturation analysis. **p <0.01 versus the normoxia group; *p <0.05 versus the normoxia group.

Fig 6. Clustering and correlation analyses of lipids in rat visceral adipose tissue.

Correlation clustering heat map. Red represents positive correlation and purple represents negative correlation. Color intensity is related to the absolute value of the correlation coefficient; i.e., the higher the positive or negative correlation, the darker the color. (B) Hierarchical clustering heat map.