Establishment of induced pluripotent stem cell-derived white adipose tissue spheroid culture as a model system

Adipose tissue is one of the innervated specialized connective tissues found in mammals and is primarily known for its role in energy storage. Apart from energy storage, the functions of adipose tissue also include thermogenesis, immune defense, hormone secretion, and mechanical support. Due to its complex nature, modeling the adipose tissue in vitro plays a tremendous role in further deciphering the mechanisms behind the diseases and adipogenesis process. Here in this thesis, induced pluripotent stem cell (iPSC)-derived white adipose tissue spheroid culture as a model system was successfully established. After iPSCs and iPSC-derived neuromesodermal progenitors (NMPs) were characterized according to their molecular features, white adipose tissue (WAT) spheroids were generated using the appropriate differentiation protocol developed by our group. Then, mature WAT spheroids were characterized according to morphological structure, histological features, lipid accumulation capacities, protein expression, cellular viability, lipid content, relative mRNA expression, and ultrastructural features. After the characterization, the conditioned medium (CM) of the mature WAT spheroids was also characterized by transmission electron microscope and triglyceride content. According to the results, extracellular vesicle-like structures were detected in the CM of mature WAT spheroids alongside the high levels of triglyceride content. To further evaluate the effects of mature WAT spheroid CM as an indicator of functional adipose tissue, β-TC-6, and ASC52-telo cells were treated with the CM. The data showed that the CM supplementation to β-TC-6 cells increased insulin secretion, while no significant alternations were observed in terms of adipogenesis in ASC52-telo cells. As a last step, the response of mature WAT spheroids to LiCl, which is a lipolysis-inducing agent, was evaluated. Overall, the findings of this thesis highlight the generation of iPSC-derived WAT spheroids for the first time in literature as far as is known and the detailed characterization of both the spheroids and their secretome.