Non-Contrast microCT Analysis of Obese Adipose in Response to Cold-Exposure Reveals Sex-Specific Alterations

Abstract

In 2020, it was reported that obesity in the United States had increased by 12% from 1999 to 2018. While exercise and diet are optimal lifestyle modifications to curb obesity, drug-based therapeutics focus on glucagon-like peptide (GLP) modifiers. Alternatively, current research suggests that a specialized type of adipose, called thermogenic adipose, may help protect against obesity. Active thermogenic adipose can metabolize free fatty acids (FFAs) and carbohydrates to carry out non-shivering thermogenesis (NST), potentially providing a method for reducing excess energy stores. While brown adipose tissue (BAT) provides the primary thermogenic response, we hypothesized that exposing diet-induced obese (DIO) mice to colder temperatures would also diminish white adipose tissue (WAT) depots and suppress their inflammatory signature. To measure adipose response to cold in vivo, we applied a non-contrast microCT ({micro}CT) imaging analysis. Male and female mice were housed at thermoneutrality (TN) and fed a Western-style diet (WD) ad lib until they became obese. Once they reached this stage, the mice were subjected to a thermalshift (TS) and exposed to either room temperature (RT) of 22{degrees}C or a colder temperature of 18{degrees}C. The adipose response was then assessed in post-exposure tissues by histological analysis, proteomics, and molecular characterization to correlate phenotypic changes with our {micro}CT findings. Results from this analysis revealed a sex-specific response to cold exposure: thermogenic adipose was predominantly formed in the interscapular BAT (iBAT) of male mice, while female mice showed formation in their perigonadal WAT (pgWAT) and iBAT when exposed to 18{degrees}C. Furthermore, male mice exhibited a decline in serum glucose levels when subjected to 18{degrees}C, which was increased in TS female mice. Serum-free fatty acids (FFAs) were unaffected by either sex across different environmental conditions. Importantly, using a mass-spectrometry-based approach, we detected a reduction in pro-inflammatory cytokines in the conditioned media (CM) of pgWAT and iBAT from TS male mice compared to TN DIO male mice. Overall, our studies demonstrated a new {micro}CT-based analytical method to detect changes in obese adipose tissue and highlighted unique sex-specific responses to environmental exposure. Our findings suggest that thermogenic adipose may offer a promising avenue for combating obesity and reducing its pathologic characteristics.