Background: Excessive intrapancreatic fat deposition (IPFD) exacerbates acute pancreatitis (AP). Fat storage-inducing transmembrane protein 2 (FIT2) regulates lipid droplet (LD) homeostasis and hydrolyzes long-chain acyl-coenzyme A (LC-CoA). FIT2 deficiency results in LC-CoA accumulation, which activates calcium channels and triggers calcium signalling. However, the mechanistic link between FIT2, lipid metabolism and AP pathogenesis remains poorly understood.
Methods: Hamsters and mice were fed a high-fat diet (HFD) for 6 and 12 weeks, respectively, to induce fatty pancreas; controls received standard chow diet. AP was induced in HFD and control mice by 7 intraperitoneal injections of caerulein (50 µg/kg) at hourly intervals (HFD-AP and CER-AP). The severity of AP was assessed by histological and biochemical indices. Pancreatic tissues underwent RNA sequencing and targeted LC-CoA metabolomics, with enrichment analysis via DAVID. In vitro, 266-6 pancreatic acinar cells were transfected with shRNA or plasmid to knockdown or overexpress FIT2. LD formation was induced by oleic acid and quantified using BODIPY staining. Freshly isolated acinar cells were treated with LC-CoA to assess viability and calcium signalling via fluorescence assays. Key mRNA and protein levels were quantified by RT-qPCR and Western blotting.
Results: In HFD-fed rodents, excessive IPFD led to fatty pancreas with abnormal LD accumulation and increased FIT2 protein expression. Similarly, oleic acid treatment enhanced both the number and size of LDs in acinar cells. Transcriptomic and metabolomic analyses revealed dysregulated lipid metabolism, with altered expression of LD-associated genes and a positive correlation between LD abundance and FIT2 levels. Compared with CER-AP mice versus chow diet controls, the HFD-AP exhibited dramatic decrease of pancreatic FIT2 expression and LD content; similar findings were replicated in oleic acid treated acinar cells upon stimulation by pancreatitis toxins. Enrichment analysis indicated metabolic reprogramming, with upregulation of LC-CoA synthases (Acsl4, Acsl5) and downregulation of β-oxidation enzymes (Cpt1a, Acox1) in HFD-AP. Targeted metabolomics confirmed LC-CoA accumulation. Functionally, LC-CoA dose-dependently induced enlarged sustained calcium plateau and increased cell death in acinar cells. Furthermore, acinar cells from HFD-fed mice exhibited exacerbated calcium overload in response to pancreatitis toxins.
Conclusions: FIT2 and LC-CoA play a critical role in IPFD and AP progression, warranting further investigation.