27-Hydroxycholesterol exacerbates hepatic insulin resistance via plasma membrane cholesterol remodeling

Background and aims: Insulin resistance is a key driver of metabolic disorders, yet its molecular mechanisms remain elusive. This study identifies 27-hydroxycholesterol (27HC), a cholesterol-derived metabolite, and investigates its role in insulin resistance. Methods: Targeted metabolomics quantified absolute and relative levels of 27HC (27HC/cholesterol ratio) in patients, mice, and hepatocytes. Insulin resistant mouse models were established to characterize spatiotemporal dynamics of 27HC and related enzymes. Functional analyses assessed 27HC's effect on insulin signaling across multiple hepatocyte types. Transcriptomic analysis identified key effector pathways. Plasma membrane cholesterol accessibility was evaluated using biosensors and validated by cholesterol rescue. Membrane protein extraction, immunofluorescence, and flow cytometry were employed to assess the impact of 27HC on insulin receptor (IR) distribution and binding capacity. Results: Elevated 27HC levels were observed in patients with metabolic dysfunction-associated steatotic liver disease (MASLD), obese and type 2 diabetic mice (T2DM), and PA-treated HepG2 and primary hepatocytes, correlating with impaired insulin sensitivity. CYP27A1 was identified as the key enzyme regulating liver 27HC levels. In vitro studies demonstrated that 27HC disrupts insulin signaling in HepG2, AML12, and primary hepatocytes, whereas CYP27A1 knockdown restored IR responsiveness. 27HC suppresses SREBP2-dependent cholesterol biosynthesis, depleting accessible cholesterol in the plasma membrane, triggering IR mislocalization and signal attenuation. Liver-specific CYP27A1 silencing in mice fed a high-fat diet improved systemic insulin sensitivity and restored metabolic homeostasis. Conclusion: Our findings establish 27HC as a key effector linking cholesterol metabolism to insulin resistance and propose CYP27A1 inhibition as a potential therapeutic strategy for insulin resistance.