Transgenic Overexpression of Them1 in WAT Promotes Inflammation but not Insulin Resistance
Authors: Desai Anal , Ozdemir Cafer , Li Yingxia , Cohen David E. 
Published: November 2023

Background

In the setting of obesity, inflammation in white adipose tissue (WAT) may contribute to insulin resistance through the liberation of free fatty acids (FFA) and production of inflammatory cytokines. Thioesterase superfamily member 1 (Them1) is a fatty acyl‐CoA thioesterase that converts long chain fatty acyl‐CoAs to FFA and CoASH. It is highly expressed in brown adipose tissue (BAT), where it functions to suppress energy expenditure. Although basal levels in WAT are minimal, Them1 is upregulated in response to high fat feeding, suggesting a pathogenic role in insulin resistance. Them1−/−mice are resistant to high fat diet‐induced obesity and diabetes, exhibiting improved insulin sensitivity, an absence of macrophage infiltration in WAT and blunted inflammatory cytokine production. Whether these beneficial effects are primarily due to increased energy expenditure in BAT or the absence of Them1 in WAT is unknown.

Aim

This study was designed to assess whether transgenic overexpression of Them1 in WAT is sufficient to promote inflammation and insulin resistance.

Methods

We previously designed conditional Them1 transgenic (c‐Them 1Tg) mice with Cre recombinase‐dependent Them1 overexpression. Adipose‐specific Them1 transgenic (A‐Them 1Tg) mice were generated by breeding with Adiponectin‐cre mice on the same genetic background. Littermate c‐Them 1Tg were used as controls. Adipose‐specific overexpression of Them1 expression in WAT and BAT was confirmed by immunoblot analysis. Mice were fed chow or a high fat (60% of kcal) diet for 14 w. Body composition was determined by magnetic resonance spectroscopy. For tolerance tests (n=10 mice/group) to insulin (ITT) and glucose (GTT), plasma glucose concentrations were determined after fasting (6 h for ITT, 16 h for GTT) and periodically up to 120 min after i.p. injection of insulin (0.75 U/kg bw) or glucose (1 – 2 mg/g bw). Mice were allowed to recover for 7 d between tolerance tests. WAT was embedded in paraffin and subjected to H&E or immunostaining using an F4/80 antibody. mRNA levels were determined by quantitative real‐time PCR and plasma concentrations of TNFα were determined by ELISA.

Results

Whereas total body weights and compositions did not differ in A‐Them 1Tg mice compared with c‐Them 1Tg controls on chow diet, high fat feeding increased body weights, as well as fat and lean body mass more for A‐Them 1Tg mice. Increased macrophage infiltration was observed in both chow and high fat fed A‐Them 1Tg mice, an effect supported by increased F4/80 mRNA expression and immunostaining. Whereas plasma FFA concentrations did not differ, TNFα concentrations were higher in chow fed A‐Them 1Tg mice. No differences were observed for GTT and ITT between A‐them 1Tg and c‐Them 1Tg mice fed either diet.

Conclusion

Adipose tissue specific overexpression of Them 1 in WAT is sufficient to promote inflammation, but not insulin resistance. These findings suggest that Them1 promotes obesity‐associated insulin resistance primarily by suppressing energy expenditure in BAT.

Support or Funding Information

NIH DK056626 and DK103046