TUMOR PROMOTING ROLE OF EPIPLOIC ADIPOSE TISSUE IN COLON OF OBESE INDIVIDUALS IS MEDIATED VIA LIPID DROPLETS ASSOCIATED ADIPOSE TRIGLYCERIDE LIPASE (ATGL)

Obesity increases colon cancer risk, progression, recurrence, and mortality. Epiploic adipose tissue (EPAT), understudied fat appendages attached to the colon, has unique characteristics as compared to other fats (Gut, 2022) and can be a culprit in colon cancer linked to obesity, mechanisms of which are unexamined. To investigate the tumor-promoting role of EPAT and identify effective therapeutics, we developed a novel microphysiological system (MPS) comprised of human EPAT and colon cancer cells (Cancers, 2023). Moreover, we have shown elevated lipid droplets (LDs), intracellular lipid stores, in colon cancer cells, which provide fuel for tumor growth in obesity. LDs-associated enzyme, ATGL, exclusively responsible for fuel utilization stored in LDs (fatty acids, FA), is primarily expressed in adipocytes but also in the colon. Elevated ATGL levels in human colonic tumor are further augmented in obesity (Oncogenesis, 2021). We hypothesize that in obesity, adipocytes in EPAT release FA from their LDs via ATGL which are subsequently taken up by colon cancer cells, thereby stored in their LDs and utilized via ATGL for tumor growth. The aim of this study is to investigate therapeutic significance of targeting this LDs-ATGL mechanism in attenuating tumor-promoting role of EPAT in colon using EPAT-MPS model. Methods: Human samples: EPAT (obese and lean) individuals, human colon cancer TCGA; colon cancer cells: HT29-GFP, HT29, HCT116; EPAT-MPS: EPAT and colonic cancer cells sandwiched between adipose stromal cells, conditioned media from MPS (CM-EPAT); Obesity FA: Oleic acid and Palmitic Acid, 300 µM; Inhibitor: atglistatin, 50µM; Immunofluorescence; RNAseq (Illumina HiSeq 2500); Bioinformatics: RSEM/EBseq, Differentially Expressed Genes (DEGs), Ingenuity Pathway Analysis (IPA), Gene Set Enrichment Analysis (GSEA), R. Results: We demonstrated in EPAT-MPS that EPAT obtained from obese individuals (vs lean) has a tumor promoting role in the colon (4.9-fold increased HT29-GFP cell growth). Here, we found altered FA metabolism in HT29 cells treated by obese CM-EPAT (GSEA). This obese CM-EPAT (vs lean) stimulated LDs accumulation in colon cancer cells, similar to FA prevalent in obesity. Further, we assessed if inhibiting ATGL activity (blocking LDs utilization) will attenuate EPAT facilitated colon cancer growth. In colon cancer cells, DEGs mediated either with obese CM-EPAT or inhibited by atglistatin revealed that ATGL inhibition targets EPAT dependent pathways (IPA). Ultimately, in EPAT-MPS model, growth of HT29-GFP cells facilitated by obese EPAT is attenuated with ATGL inhibition. Conclusion: These findings underscore the tumor-promoting role of EPAT in obese colon cancer patients mediated by increased LDs utilization via ATGL. The study highlights the therapeutic significance of utilizing EPAT-MPS as a platform targeting these mechanisms.