Chronic hypoxia reduces cold tolerance via hepatic ANGPTL3-driven mitochondrial damage and adipose thermogenesis suppression

Abstract Objective To investigate the role and mechanism of hepatic-derived angiopoietin-like 3 (ANGPTL3) in mediating reduced cold tolerance induced by chronic hypoxic exposure. Methods ① Male Sprague-Dawley (SD) rats (7 to 8 weeks old, weighing 220 to 260 g) were randomly divided into a normoxic group (N, housed at an ambient condition of altitude 308 m and 24.0±0.5 ℃) and a hypoxic group (H, housed in a hypobaric hypoxic chamber of simulating an altitude 5 800 m and 24.0±0.5 ℃), with 20 rats in each group. Twelve rats from each group were implanted intraperitoneally with temperature-sensing transponders for subsequent measurement of core body temperature (Tc). ② Male SD rats were randomly divided into (n=20 per group): a hypoxic (H) group and a hypoxic+ANGPTL3 inhibitor [Vupanorsen 2 mg/(kg·w)] intervention (H+V) group. Twelve rats from each group were implanted intraperitoneally with temperature-sensing transponders for subsequent Tc measurement. The rats in the H and H+V groups were all housed in a hypobaric hypoxic chamber (simulated altitude 5 800 m, 24.0±0.5 ℃). After 6 weeks, 8 non-implanted rats per group were anesthetized for blood and liver tissue collection. Serum aspartate aminotransferase (AST) level was measured using an automatic biochemical analyzer. Blood levels of hepatic factors were detected with ELISA. Hepatic mitochondrial morphology was assessed by transmission electron microscopy (TEM). Hepatic ANGPTL3 protein level was quantified by Western blotting. The 12 implanted rats from each group were exposed to either a hypoxic cold environment (5 800 m, 6 ℃ for 24 h) or a normoxic cold environment (308 m, -10 ℃ for 6 h). Tc was monitored using a physiological signal telemetry system to assess cold tolerance. Western blotting was used to detect the protein level uncoupling protein 1 (UCP1) in subcutaneous white adipose tissue as an indicator of browning potential. Results ① Compared to normothermic hypoxia (5 800 m, 24 ℃), the group H exhibited a significant Tc decrease during hypoxic cold exposure (5 800 m, 6 ℃) (P