Utilizing Confocal Microscopy to Characterize Human and Mouse Adipose Tissue

Significant advances in our understanding of human obesity, endocrinology, and metabolism have been made possible by murine comparative models, in which anatomically analogous fat depots are utilized; however, current research has questioned how truly analogous these depots are. In this study, we assess the validity of the analogy from the perspective of cellular architecture. Whole tissue mounting, confocal microscopy, and image reconstruction software were used to characterize the three-dimensional structure of the inguinal fat pad in mice, gluteofemoral fat in humans, and subcutaneous adipose tissue of the human abdominal wall. Abdominal and gluteofemoral adipose tissue specimens from 12 human patients and bilateral inguinal fat pads from 12 mice were stained for adipocytes, blood vessels, and a putative marker for adipose-derived multipotent progenitor cells, cluster of differentiation 34 (CD34). Samples were whole-mounted and imaged with laser scanning confocal microscopy. Expectedly, human adipocytes were larger and demonstrated greater size heterogeneity. Mouse fat displayed significantly higher vascular density compared with human fat when normalized to adipocyte count. There was no significant difference in the concentration of CD34-positive (CD34 + ) stromal cells from either species. However, the mean distance between CD34 + stromal cells and blood vessels was significantly greater in human fat. Finally, mouse inguinal fat contained larger numbers of brown adipocytes than did human gluteofemoral or human abdominal fat. Overall, the basic architecture of human adipose tissue differs significantly from that of mice. Insofar as human gluteofemoral fat differs from human abdominal adipose tissue, it was closer to mouse inguinal fat, being its comparative developmental analog. These differences likely confer variance in functional properties between the two sources and thus must be considered when designing murine models of human disease.