Histological methods to quantify changes of white and brown adipose tissue in response to a high content fat diet in mice

Background: Obesity is a major global health challenge associated with increased risk of metabolic, cardiovascular, and inflammatory diseases. White (WAT) and brown adipose tissue (BAT) are highly dynamic tissues, capable of morphological and functional adaptation in response to nutritional and metabolic changes. Methods: This study investigated histological alterations in WAT and BAT of Balb/c mice subjected to either a standard diet (STD) or high-fat diet (HFD) for 10 weeks. Adipocyte density, lipid vacuole size, macrophage infiltration and their immunophenotype were measured in WAT and BAT, while UCP1 expression was measured in BAT only. Four-mu m thick sections obtained from FFPE samples were H&E stained or immunostained with anti-UCP1, anti-Iba1 and anti-CD163. Results: In WAT from HFD-fed mice, a significant increase in adipocyte size and a decrease in cell density were observed, indicating hypertrophy without evident hyperplasia. BAT exhibited larger and more dispersed lipid droplets, reduced cell density, and decreased UCP1 immunoreactivity, consistent with a whitening process and impaired thermogenic function. Additionally, immunohistochemical analysis revealed changes in macrophage distribution in WAT, with a reduction in anti-inflammatory CD163 + cells and clustering of Iba1 + macrophages, suggesting a shift in macrophage polarization. Conclusions: These findings highlight the histological adaptability of adipose tissue under different dietary conditions and reinforce the importance of morphological analysis in understanding obesity-related tissue remodeling.