Comprehensive and quantitative analysis of white and brown adipose tissue by shotgun lipidomics

Michal Grzybek, Alessandra Palladini, Vasileia I.Alexaki, Michal A.Surma, Kai Simons, Triantafyllos Chavakis, Christian Klose, Ünal Coskun

The two main forms of adipose tissue (AT) are white adipose tissue (WAT), which functions primarily as an energy reservoir, and brown adipose tissue (BAT), which contributes to thermoregulation. AT lipidomics analyses have reported differences between BAT and WAT and demonstrated remodeling upon exercise or cold exposure. However, these studies applied generic methods of lipid extraction and measurement rather than techniques tailored to these tissues. Grzybek, Palladini, et al. present a shotgun lipidomics method for the analysis for ATs with an unprecedented coverage of more than 300 lipid species. With their method, they not only observe clear differences between BAT and WAT lipidomes, but also amongst WAT subtypes, i.e. gonadal and inguinal subcutaneous ATs.

Objective: Shotgun lipidomics enables an extensive analysis of lipids from tissues and fluids. Each specimen requires appropriate extraction and processing procedures to ensure good coverage and reproducible quantification of the lipidome. Adipose tissue (AT) has become a research focus with regard to its involvement in obesity-related pathologies. However, the quantification of the AT lipidome is particularly challenging due to the predominance of triacylglycerides, which elicit high ion suppression of the remaining lipid classes.

Methods: We present a new and validated method for shotgun lipidomics of AT, which tailors the lipid extraction procedure to the target specimen and features high reproducibility with a linear dynamic range of at least 4 orders of magnitude for all lipid classes.

Results: Utilizing this method, we observed tissue-specific and diet-related differences in three AT types (brown, gonadal, inguinal subcutaneous) from lean and obese mice. Brown AT exhibited a distinct lipidomic profile with the greatest lipid class diversity and responded to high-fat diet by altering its lipid composition, which shifted towards that of white AT. Moreover, diet-induced obesity promoted an overall remodeling of the lipidome, where all three AT types featured a significant increase in longer and more unsaturated triacylglyceride and phospholipid species.

Conclusions: The here presented method facilitates reproducible systematic lipidomic profiling of AT and could be integrated with further –omics approaches used in (pre-) clinical research, in order to advance the understanding of the molecular metabolic dynamics involved in the pathogenesis of obesity-associated disorders.