Introduction: Adipose tissue, once thought an inert organ for energy storage, is now considered a complex tissue with an enormous impact on whole-body homeostasis and metabolism.1 The lymphatic system, which has only recently gained scientific attention, is a key participant in proper homeostasis and lipid-handling.2 However, the functional link between adipose tissue and the lymphatic system is still unresolved. Research in recent years has begun to clearly demonstrate the relationship between these two organs, thanks to the development of new cellular and molecular tools. The in vitro coculture model represents a promising tool to create a more physiologically relevant environment to further understand the complex cellular interactions in tissue.3,4
Aim: Therefore, we aimed to investigate the bi-directional interconnections between human adipocytes and human dermal lymphatic endothelial cells (HDLECs) using complex in vitro models.
Methods: To study the in vitro directional link, we have developed a VEGF-C-induced direct coculture model between adipocytes and HDLECs to investigate their morphological and functional changes using Confocal Microscopy. To observe the effect of conditioned media and adipogenic regulator - PPARG we have developed a single culture model and analyzed changes in the mRNA levels of lipolytic (FABP4, CD36, and CPT1A) and lymphatic markers (PROX1, PDPN, and CD31).
Results: Using complex in vitro models, molecular approaches, and imaging methods, we showed that HDLECs are able to stimulate basal lipolysis in adipocytes as well as uptake, metabolize, and store released fatty acids in the form of lipid droplets in the cytoplasm of HDLECs. 2-day cultivation of HDLECs in lipolytic conditioned media increased significantly the expression of lipid handling genes (CPT1A, CD36, FABP4). Later, we documented that adipocytes supported lymphangiogenesis in HDLECs in the presence of VEGF-C. Surprisingly, the absence of VEGF-C led to the formation of clusters of HDLECs in the presence of adipocytes. However, it still remains to be determined whether the proteases produced by adipocytes are indeed able to activate VEGF-C.
Conclusion: In conclusion, we have provided valuable evidence for a close functional interplay between human adipocytes and lymphatic endothelial cells using complex in vitro coculture models.