# Endothelial CYB5R1 is a Coenzyme Q reductase that suppresses ferroptosis and atherosclerosis

## TL;DR

This study shows that CYB5R1 in endothelial cells prevents a type of cell death called ferroptosis, which is linked to atherosclerosis, and introduces a new drug candidate to treat it.

## Contribution

CYB5R1 is newly identified as a CoQ-dependent redox regulator suppressing ferroptosis and atherosclerosis, with a novel small molecule therapeutic developed.

## Key findings

- CYB5R1 acts as a CoQ-dependent redox cycler that suppresses ferroptosis in endothelial cells.
- Disruption of CYB5R1-CoQ coupling increases hydrogen peroxide and ferroptosis, worsening atherosclerosis.
- The compound CP50 upregulates CYB5R1, prevents GPX4 degradation, and inhibits atherogenesis in mice.

## Abstract

Spatial-temporal coordination of oxidoreductase substrate specificity and turnover regulates redox-mediated signaling, shaping physiological and pathological outcomes. Here, we reveal novel actions of cytochrome b5 reductase 1 (CYB5R1) when localized to the outer mitochondrial membrane of endothelial cells. Specifically, CYB5R1 functions as a Coenzyme Q (CoQ)–dependent redox cycler, protecting against iron-dependent lipid oxidation or ferroptosis. CYB5R1 catalyzes CoQ redox cycling via electron transfer reactions that suppresses both lipid hydroperoxide accumulation and ferroptosis. CoQ-insufficiency or disruption of CYB5R1-CoQ coupling impairs these reactions, leading to elevated hydrogen peroxide production and initiating a ferroptotic cascade. Ferroptosis plays a pathogenic role in atherogenesis, and we report that both global and endothelial-specific CYB5R1 knockout significantly exacerbate plaque formation. Through a rational chemical library design and screening, we synthesized and tested CP50, a quinone–nitroalkene hybrid that upregulates CYB5R1, prevents glutathione peroxidase-4 (GPX4) degradation, limits lipid oxidation, confers potent anti-ferroptotic activity and in a murine model, profoundly inhibit atherogenesis. These findings a) establish CYB5R1 as a novel mitochondrial “redox rheostat” that governs endothelial ferroptotic susceptibility through substrate redox regulation and b) reveals a safe small molecule therapeutic strategy that can impact a broad range of diseases.