The deubiquitinase USP40 preserves endothelial integrity by targeting the heat shock protein HSP90

Endothelial cell (EC) barrier disruption and inflammation are the pathological hallmarks of vascular disorders and acute infectious diseases and related conditions, including the coronavirus disease 2019 (COVID-19) and sepsis. Ubiquitination plays a critical role in regulating the stability, intracellular trafficking, and enzymatic activity of proteins and is reversed by deubiquitinating enzymes (DUBs). The role of DUBs in endothelial biology is largely unknown. In this study, we report that USP40, a poorly characterized DUB, prevents EC barrier disruption through reductions in the activation of RhoA and phosphorylation of myosin light chain (MLC) and cofilin. Furthermore, USP40 reduces EC inflammation through the attenuation of NF-kappa B activation, ICAM1 expression, and leukocyte-EC adhesion. We further show that USP40 activity and expression are reduced in response to endotoxin challenge. Global depletion of USP40 and EC-targeted USP40 depletion in mice exacerbated experimental lung injury, whereas lentiviral gene transfer of USP40 protected against endotoxin-induced lung injury. Using an unbiased approach, we discovered that the protective effect of USP40 occurs through the targeting of heat shock protein 90 beta (HSP90 beta) for its deubiquitination and inactivation. Together, these data reveal a critical protective role of USP40 in vascular injury, identifying a unique mechanistic pathway that profoundly impacts endothelial function via DUBs. Vascular endothelial cells (ECs - cells that line the interior of blood vessels) play a vital role in maintaining the health of blood vessels and controlling inflammation. Damage or malfunction of these cells can lead to severe inflammatory diseases like acute lung injury and sepsis. The molecular mechanisms (processes at a molecular level) that control these cells' function are not completely understood. In this research, a new protein, USP40, was identified that helps safeguard ECs from inflammation and maintains their barrier function. This protein functions by deubiquitinating (removing ubiquitin, a small protein) and inactivating another protein, HSP90, thereby reducing its ability to instigate inflammation and disrupt the EC barrier. These results suggest that USP40 could be a potential treatment target for inflammatory diseases.This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.