Upregulation of cholesterol 24-hydroxylase following hypoxia–ischemia in neonatal mouse brain

Abstract

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.

CYP46A1 Activation by Efavirenz Leads to Behavioral Improvement without Significant Changes in Amyloid Plaque Load in the Brain of 5XFAD Mice

“…The former could be due to a decrease in the oxidative stress, the only factor that was found to upregulate CYP46A1 expression transcriptionally [64], and the latter could due to a partial restoration of a normal microglial function. The Iba1-CYP46A1 link is also supported by an increase in CYP46A1 expression in animal models of traumatic brain injury and hypoxia-ischemia [39,65,66], which are both characterized by an increase in oxidative stress [67,68].…”

The Evolution of Cholesterol-Rich Membrane in Oxygen Adaption: The Respiratory System as a Model

“…The increased hepatic activity of HIF2α by transient suppression of the Vhl Δ IE induced an increase in hepatic and circulating cholesterol by repression of CYP7A1 (Ramakrishnan et al, 2014). Brain hypoxia-ischemia in neonatal mice increased cortex HMGCR and CYP46A1 after 24 h (Lu et al, 2018), suggesting that brain cholesterol metabolism adaption in response to hypoxia. Interestingly, epigenetic studies performed in Andean highlanders suggest that high altitude hypobaric hypoxia exposure affected HIF2α methylation (Childebayeva et al, 2019), opening the possibility to HIF2α activation regulation and ultimately, cholesterol.…”

Serum 24S-hydroxycholesterol predicts long-term brain structural and functional outcomes after hypoxia-ischemia in neonatal mice

“…Our recent work suggests that the brain-derived cholesterol metabolite 24S-hydroxycholesterol (24S-HC) might be a promising candidate to serve as a novel lipid biomarker for the extent of HI brain injury. 4 24S-HC is produced exclusively in the brain by neuron-specific cytochrome P450 46A1 (CYP46A1 in human, cholesterol 24-hydroxylase, Cyp46a1 in mouse). This oxysterol is capable of crossing the blood–brain barrier (BBB) into circulation by concentration gradient (>100-fold) and is eventually excreted in bile in the liver.…”

“…This is the primary pathway for brain cholesterol elimination. 5–9 The hypothesis of using this oxysterol as an HI brain injury marker is made for several reasons: (1) 24S-HC is a cholesterol metabolite specific to the brain; 5 (2) HI-induced upregulation of Cyp46a1 mediates the increased formation of brain 24S-HC, leading to its concurrent elevation in the blood at 6 h and 24 h after HI; 4 (3) there is a co-localization of enhanced Cyp46a1 with apoptotic cell death as seen by the expression of cleaved-caspase 3 at 24 h after HI; 4 and (4) serum 24S-HC levels correlate well with HI-induced acute brain damage at 6 h and 24 h as evaluated by the buildup of spectrin breakdown products and cleaved-caspase 3, which indicate activation of calpain and caspase. 4 Therefore, higher serum 24S-HC reflects enhanced brain cholesterol turnover and probably ongoing neuronal death after neonatal HI.…”