# N-Homocysteinylation of HMGB1/2 Promotes Corpus Cavernosum Endothelial Senescence in Erectile Dysfunction

## TL;DR

This study reveals how homocysteine contributes to erectile dysfunction through a specific pathway involving endothelial cell aging and offers a new treatment approach.

## Contribution

The study identifies the MARS1-HTL axis as a novel mechanism linking homocysteine to endothelial senescence in age-related erectile dysfunction.

## Key findings

- Senescent endothelial cells show increased MARS1 activity, leading to homocysteine thiolactone production and N-homocysteinylation.
- N-homocysteinylation, not acetylation, drives HMGB1/2 release and amplifies the senescence-associated secretory phenotype.
- N-acetylcysteine reduces homocysteine thiolactone and improves erectile function in middle-aged individuals with high homocysteine.

## Abstract

Homocysteine (Hcy) is an age-related risk factor for erectile dysfunction (ED), with enhanced vascular toxicity in middle-aged and elderly individuals. However, folate-based Hcy-lowering therapies have shown limited efficacy, necessitating a reevaluation of its age-dependent pathogenic mechanism. Here, we demonstrate that senescent endothelial cells exhibit heightened responsiveness of methionyl-tRNA synthetase 1 (MARS1) to Hcy, promoting the production of homocysteine thiolactone (HTL) and widespread N-homocysteinylation (K-Hcy) of proteins. K-Hcy, rather than acetylation, drives cytoplasmic translocation and extracellular release of high mobility group box proteins 1 and 2 (HMGB1/2), amplifying the senescence-associated secretory phenotype (SASP). Competitive inhibition of MARS1 with N-acetylcysteine (NAC) attenuates endothelial senescence and improves erectile function in middle-aged individuals with hyperhomocysteinemia by reducing HTL, rather than Hcy itself, while synergizing with tadalafil. Collectively, our findings highlight the pivotal role of the age-dependent MARS1-HTL axis in the pathogenesis of homocysteine-induced ED, offering a promising therapeutic strategy for ED in the aging population.