Up-regulation of cholesterol 24-hydroxylase following hypoxia-ischemia in neonatal mouse brain

BACKGROUND: Maintenance of cholesterol homeostasis is crucial for brain development. Brain cholesterol relies on de novo synthesis and is cleared primarily by conversion to 24S-hydroxycholesterol (24S-HC) with brain-specific cholesterol 24-hydroxylase (CYP46A1). We aimed to investigate the impact of hypoxia-ischemia (HI) on brain cholesterol metabolism in the neonatal mice. METHODS: Postnatal day 9 C57BL/6 pups were subjected to HI using the Vannucci model. CYP46A1 expression was assessed by western blotting and its cellular localization was determined by immunofluorescence staining. The amount of brain cholesterol, 24S-HC in the cortex and in the serum was measured with ELISA. RESULTS: There was a transient cholesterol loss at 6hr after HI. CYP46A1 was significantly up-regulated at 6hr and 24hr following HI with a concomitant increase of 24S-HC in the ipsilateral cortex and in the serum. The serum levels of 24S-HC correlated with those in the brain, as well as with necrotic and apoptotic cell death evaluated by the expression of spectrin breakdown products and cleaved caspase-3 at 6hr and 24hr after HI. CONCLUSIONS: Enhanced cholesterol turnover by activation of CYP46A1 represents disrupted brain cholesterol homeostasis early after neonatal HI. 24S-HC might be a novel blood biomarker for severity of hypoxic-ischemic encephalopathy with potential clinical application.