Objectives:

Adipose tissue is an important regulator of cardiovascular disease, also due to its resident immune cells, in particular macrophages. Recently, our development of adipoids (organoids consisting of adipocytes and immune cells) generated from visceral fat has made it possible to study the interactions between adipocytes and macrophages in a 3D model in vitro. However, as there are differences between the regional fat depots, in this study, we established and analyzed an immune-competent adipoid model generated from cardiac fat, hypothesizing that this model may better reflect the local pathways leading to immune-metabolism mediated cardiovascular diseases.

Methods:

Visceral and cardiac fat was removed from male wistar rats (400-500 g), mechanically minced, enzymatically digested and the stromal vascular fraction (SVF) isolated. The SVF were used to generate spheroids (containing 50 000 cells each), which were then differentiated by IBMX, dexamethasone, rosiglitazone and insulin to adipoids and further cultivated. Generated adipoids where analyzed via confocal microscopy and biomolecular analysis, specifically identifying neutral lipids and immune cells.

Results:

We successfully adapted the adipoid protocol to cardiac fat. The isolated SVF from cardiac fat showed distinct differences to the SVF from visceral fat. Nonetheless, cardiac fat derived adipoids showed mostly mononuclear lipid droplet formation as demonstrated by confocal microscopic analysis (LD540 staining). Additionally, independent differentiation of macrophages even without the addition of growth factors such as M-CSF could be demonstrated by F4/80 antibody staining. 3D cardiac fat derived adipoid could be kept in culture for over two weeks. 

Conclusion:

Our results show that it is possible to transfer the in vivo differences between visceral and cardiac fat to the 3D adipoid model in vitro. Immune-competent cardiac fat derived adipoids may be a valuable tool in order to investigate immune-metabolism mediated cardiovascular diseases, especially as those can also be generated from human tissue samples.