FITM1 (fat storage inducing transmembrane protein 1) is a six-transmembrane domain protein localized to the endoplasmic reticulum that plays a crucial role in lipid droplet formation and triglyceride storage 1. The protein mediates the partitioning of cellular triglycerides into lipid droplets without affecting triglyceride biosynthesis itself 1. FITM1 expression is transcriptionally regulated by peroxisome proliferator-activated receptors (PPARs), linking lipid uptake to cellular lipid storage capacity 2. In skeletal muscle cells, FITM1 is upregulated by PGC-1α and contributes to the formation of smaller, more numerous lipid droplets while modestly increasing triglyceride levels 3. The protein shows tissue-specific expression patterns, being downregulated in pancreatic cancer where it serves as a prognostic marker associated with overall survival 4. FITM1 levels are also decreased in frequent exacerbation phenotypes of COPD, suggesting potential diagnostic utility 5. Additionally, FITM1 expression is reduced following ovariectomy in mice, indicating hormonal regulation 6. The protein represents a potential therapeutic target for nonalcoholic fatty liver disease due to its central role in lipid droplet biology and metabolism 7.