# Biliary elimination of cholesterol can be modulated by hepatocyte mitochondrial Aquaporin-8 in mice

## TL;DR

This study shows that a protein called AQP8 in liver cells can influence how cholesterol is removed from the body through bile in mice.

## Contribution

The study reveals a new role for mitochondrial AQP8 in modulating biliary cholesterol excretion via regulation of ABCG5 and SREBP-2.

## Key findings

- Knockdown of mtAQP8 reduces SREBP-2 and ABCG5 expression, decreasing biliary cholesterol excretion.
- Expression of hAQP8 increases SREBP-2, LXR, and ABCG5, enhancing biliary cholesterol excretion.
- Mitochondrial antioxidants prevent upregulation of SREBP-2 and ABCG5, blocking increased cholesterol excretion.

## Abstract

Sterol regulatory element-binding protein (SREBP) transcription factors directly or indirectly regulate key genes involved in hepatic cholesterol homeostasis, including biliary elimination. The ATP-binding cassette transporter G5 (ABCG5), located in hepatocyte canalicular plasma membranes, strongly controls the excretion of unesterified cholesterol into bile. Recently, we demonstrated in cultured hepatocytes that mitochondrial aquaporin-8 (mtAQP8), a channel protein capable of conducting H2O2, is involved in SREBP-controlled cholesterol synthesis. In this study, we evaluated whether hepatic mtAQP8 participates in modulating the biliary elimination of cholesterol. Using C57BL/6 mice, we found that adenovirus-induced mtAQP8 knockdown significantly downregulated the expression of sterol regulatory element-binding protein-2 (SREBP-2) and, through liver X receptor (LXR), that of ABCG5, which in turn decreased biliary cholesterol excretion. In contrast, mice with adenovirus-mediated mitochondrial human AQP8 (hAQP8) expression significantly increased the expressions of SREBP-2, LXR, and ABCG5 and, consequently, the biliary excretion of cholesterol. A mitochondrial-targeted antioxidant, which has been shown to quench mitochondrial H2O2 release, did not affect mitochondrial hAQP8 expression, but prevented upregulation of SREBP-2, ABCG5, and biliary cholesterol excretion. Our data further support the involvement of mtAQP8 in hepatic cholesterol metabolism, suggesting that it modulates biliary cholesterol elimination through ABCG5 gene expression.

The online version contains supplementary material available at 10.1038/s41598-026-39058-6.