Deletion of the gene encoding G0/G 1 switch protein 2 (G0s2) alleviates high-fat-diet-induced weight gain and insulin resistance, and promotes browning of white adipose tissue in mice

Abstract

Aims/hypothesis: Obesity is a global epidemic resulting from increased energy intake, which alters energy homeostasis and results in an imbalance in fat storage and breakdown. G0/G1 switch gene 2 (G0s2) has been recently characterised in vitro as an inhibitor of adipose triglyceride lipase (ATGL), the rate-limiting step in fat catabolism. In the current study we aim to functionally characterise G0s2 within the physiological context of a mouse model.

Methods: We generated a mouse model in which G0s2 was deleted. The homozygous G0s2 knockout (G0s2 (-/-)) mice were studied over a period of 22 weeks. Metabolic variables were measured including body weight and body composition, food intake, glucose and insulin tolerance tests, energy metabolism and thermogenesis.

Results: We report that G0s2 inhibits ATGL and regulates lipolysis and energy metabolism in vivo. G0s2 (-/-) mice are lean, resistant to weight gain induced by a high-fat diet and are glucose tolerant and insulin sensitive. The white adipose tissue of G0s2 (-/-) mice has enhanced lipase activity and adipocytes showed enhanced stimulated lipolysis. Energy metabolism in the G0s2 (-/-) mice is shifted towards enhanced lipid metabolism and increased thermogenesis. G0s2 (-/-) mice showed enhanced cold tolerance and increased expression of thermoregulatory and oxidation genes within white adipose tissue, suggesting enhanced 'browning' of the white adipose tissue.

Conclusions/interpretation: Our data show that G0s2 is a physiological regulator of adiposity and energy metabolism and is a potential target in the treatment of obesity and insulin resistance.

Fig. 1

Effects of G0S2 deletion on weight gain. (A) schematic representation of the G0S2 knockout gene with locations of primers used for genotyping indicated. (B) PCR genotyping of G0S2 wt, heterozygote and knockout genes as described in methods (C) G0S2 expression levels in liver, fat and muscle tissues. (D) G0S2 protein levels in liver lysates. (E) comparison of body length of wt and KO mice. (F) comparison of body weights of male and female mice at 6-weeks on chow diet. n=11 for wt and 18 for KO male mice; n=6 for wt and 14 for female KO mice. (G) Body mass composition of 22 week old male wt and KO mice on chow diet. n=8 for wt and 7 for KO mice. H) percentage of weight gain of male mice housed on either chow or HFD for 22 weeks. n=8 for wt mice on both diets; n=13 on chow diet and n=12 for KO mice on HFD. Data are represented as mean ± SEM. * P<0.05, **P<0.001.

Fig. 2

TG accumulation in livers of G0S2^−/− mice. (A) Analysis of body organs in mice on chow and HFD. (B) Representative images of H&E staining of liver sections of mice on HFD. n=4 per genotype. (C) Liver triglyceride (D) Liver FFA levels of mice on chow and HFD. (E) gene expression analysis of lipogenic and oxidative genes in livers of mice on HFD normalized to cyclophilin. (F) gene expression levels of CPT1-α and PGC1-α normalized to cyclophilin. Values represent means ± SEM. n= 8 for wt and 11 for G0S2^−/− mice on chow diet; n= 5 for wt and 8 for G0S2^−/− mice on HFD. *P<0.05, ***P<0.0001.

Fig. 3

G0S2^−/− mice have decreased adipocytes size and enhanced lipase activity. (A) H&E staining of WAT, fat pads and BAT of mice on 22 weeks of HFD. (B) WAT area, (C) fat pad area, (D) BAT area. (E) TG hydrolase activity measured in visceral fat extracts of male mice on chow and HFD. (F) protein levels of ATGL and HSL in visceral lysates of wt and KO mice. Values represent means ± SEM. (n=4 per genotype for adipocyte area and n=6 per genotype for TG hydrolase activity). n=4 per genotype for protein levels. *P<0.05, **P<0.005.

Fig. 4

Deletion of G0S2 enhances lipolysis. In vitro lipolysis of differentiated adipocytes from 3 week old mice under basal and isoproterenol stimulated conditions. (A) Glycerol levels, (B) FFA levels under control and stimulated conditions. (n=9–10 mice per condition). (C) gene expression analysis of adipogenic differentiation markers. Data are normalized to cyclophilin. *P<0.05, **P<0.001, ***P<0.0001.

Fig. 5

Improved glucose and insulin sensitivity in G0S2^−/− mice. Blood glucose levels during IPGTT (A,B) and IPITT (C,D) in fasted mice on (A,C) chow diet and (B,D) HFD. Values represent means ± SEM. n= 8 for wt and 13 for G0S2^−/− mice *P<0.05, **P<0.001.

Fig. 6

Increased energy expenditure in G0S2^−/− mice. Mice were housed individually for 4 days in metabolic cages fed either chow or HFD (A) VO2 levels on HFD, (B) ambulatory activity of mice on HFD, (C) food intake on chow diet. Respiratory quotient in mice fed (D) chow, (E) HFD diet. Values represent means ± SEM. n=7 per genotype. *P<0.05.

Fig. 7

Increased thermogenicity and oxidation in G0S2^−/− mice Body temperature was measured indirectly as heat production in metabolic cages. (A) chow, (B) HFD. (C,D) Mice on chow diet were housed for 30 hours at 4°C and (C) rectal temperature, (D) Abdominal temperatures were recorded. (E–H) Mice on 9-week HFD were housed at 4°C for 8 hours and expression analysis of thermogenic genes at normal temperature (E) and 4°C (F) and oxidation genes at room temperature (G) and 4°C (H) were done. n=7–8 per genotype. *P<0.05,**P<0.001, ***P<0.0001.