Generation of Functional Human Adipose Tissue in Mice from Primed Progenitor Cells.

Adipose tissue is used extensively in reconstructive and regenerative therapies, but transplanted fat often undergoes cell death, leading to inflammation, calcification and requirement for further revision surgery. Previously we have found that mesenchymal progenitor cells within human adipose tissue can proliferate in 3-dimensional culture under pro-angiogenic conditions. These cells (Primed ADipose progenitor cells=PADS) robustly differentiate into adipocytes in-vitro (ad-PADS). The goal of the present study is to determine whether ad-PADS can form structured adipose tissue in-vivo, with potential for use in surgical applications. Grafts formed from ad-PADS were compared to grafts formed from adipose tissue obtained by liposuction after implantation into nude mice. Graft volume was measured by micro-CT scanning, and the functionality of cells within the graft was assessed by quantifying circulating human adiponectin. The degree of graft vascularization by donor or host vessels, and the content of human or mouse adipocytes within the graft were measured using species-specific endothelial and adipocyte specific qRT-PCR probes, and histochemistry with mouse and human-specific lectins. Our results show that ad-PADS grafted subcutaneously into nude mice induce robust vascularization from the host, continue to increase in volume over time, express the human adipocyte marker PLIN1 at levels comparable to human adipose tissue, and secrete increasing amounts of human adiponectin into the mouse circulation. In contrast, grafts composed of adipose tissue fragments obtained by liposuction become less vascularized, develop regions of calcification and decreased content of PLIN1, and secrete lower amounts of adiponectin per unit volume. Enrichment of liposuction tissue with ad-PADS improves vascularization, indicating that ad-PADS may be pro-angiogenic. Mechanistically, ad-PADS express an extracellular matrix gene signature that includes elements previously associated with small vessel development (COL4A1). Thus, through the formation of a pro-angiogenic environment ad-PADS can form functional adipose tissue with capacity for long-term survival, and can potentially be used to improve outcomes in reconstructive and regenerative medicine.