# WWP2 underlies ROS-induced granulosa cell apoptosis by promoting ubiquitination of BAK in polycystic ovary syndrome

## TL;DR

This study shows that reduced WWP2 activity in granulosa cells contributes to PCOS by increasing cell death through BAK ubiquitination.

## Contribution

The novel role of WWP2 in promoting BAK ubiquitination and mitigating ROS-induced apoptosis in PCOS is identified.

## Key findings

- WWP2 expression is significantly reduced in granulosa cells of PCOS patients.
- WWP2 overexpression reduces mitochondrial apoptosis and ROS in KGN cells.
- Disrupting BAK ubiquitination or knocking down WWP2 increases apoptosis and worsens PCOS symptoms in mice.

## Abstract

Granulosa cell (GC) apoptosis is intrinsically linked to the ovarian dysfunction of polycystic ovary syndrome (PCOS). Although oxidative stress and apoptosis in GCs have been detected in PCOS patients, how reactive oxygen species (ROS) links to GC apoptosis in PCOS remains to be further elucidated. Here, by integrating public single-cell RNA-seq data with clinical GC sample validation, we found that the expression of the E3 ubiquitin ligase WWP2 was significantly reduced, whereas its role in PCOS has not been previously reported. Notably, we first demonstrated that WWP2 overexpression can effectively antagonize mitochondrial apoptosis and ROS in KGNs. Mechanistically, oxidative stress weakened the interaction between WWP2 and BAK and reduced WWP2 expression, thereby suppressing BAK ubiquitination at Lys113. This inhibition impaired proteasomal degradation and consequently increased BAK protein levels. Consistently, disrupting BAK ubiquitination (BAK-K113R mutant) or knocking down WWP2 facilitated KGN apoptosis, and genetic ablation of Wwp2 in PCOS mice further aggravated GC apoptosis and hormonal disturbances. This study elucidates the molecular mechanism by which oxidative stress modulates GC mitochondrial apoptosis through WWP2-mediated BAK ubiquitination, and establishes WWP2 as a potential therapeutic target for PCOS.