During the IMMUNOBAT project, I was actively involved in a broad range of tasks. In the first two years, I contributed to the design, planning, and implementation of the clinical trial. My responsibilities included participant recruitment and medical screening, experimental testing, collection and processing of biological samples, dataset creation, data integration, and both statistical and computational analyses. I was also engaged in scientific writing and dissemination activities. Through these efforts, we successfully assessed 28 lean healthy participants and 24 participants with obesity. In addition, I supported the cold intervention study, in which 11 participants with obesity completed the protocol.
In the later phase of my fellowship, I focused more on the project’s in vitro experiments. Since the required infrastructure was initially lacking, I contributed to establishing a wet laboratory to enable these studies. The experimental work included processing hBAT samples for single-cell omics analyses and developing a new model of brown adipocytes, designed to investigate how chronic inflammation influences hBAT regulation.
As a result, we generated the largest single-cell atlas of hBAT to date, analyzing approximately 130,000 cells from samples obtained from 6 lean volunteers and 7 volunteers with obesity. This dataset provides unique insights into hBAT’s cellular composition, the regulatory pathways governing its function, the interactions between different cell types, and the differences between lean and obese individuals. Overall, we identified several thermogenic and non-thermogenic adipocyte populations, as well as diverse immune cell subpopulations. Interestingly, despite the reduced metabolic activity of hBAT in obesity, we found no major differences in overall cell composition between the two groups.
In addition, we developed the first immune single-cell atlas of human brown fat, comprising about 80,000 cells from 6 lean and 6 obese participants. This resource enables the study of which immune cells are present in hBAT and how they may influence its metabolic function in health and obesity. Notably, we found marked heterogeneity in immune cell composition across individuals. Importantly, we identified specific immune cell clusters (validation pending) that were associated with higher hBAT metabolic activity, highlighting potential cellular targets for improving hBAT function.
We also analyzed hBAT samples collected before and after one of the longest human cold-exposure interventions conducted to date (3 months). This provided novel insights into how immune cells, adipocytes, and other hBAT cell types adapt to prolonged cold exposure. Notably, there was substantial inter-individual variability in the cold-acclimation response. An interesting trend emerged: participants with higher BMI tended to show reduced hBAT metabolic activity after the intervention, whereas those with lower BMI showed an increase. When stratifying participants into two groups (BMI <31 kg/m² and BMI >37 kg/m²), we observed that individuals in the lower-BMI group generally increased hBAT metabolic activity, while those in the higher-BMI group decreased it. These findings suggest that cold acclimation may be more effective in individuals with obesity whose hBAT and mitochondrial dysfunction is not yet too advanced.
Finally, we established a new laboratory model: a 3D culture system of human primary brown adipocytes. This model enables controlled investigation of the mechanisms regulating hBAT function and has potential applications in future drug screening.
