Overexpression of V-ATPase B2 attenuates lung injury/fibrosis by stabilizing lysosomal membrane permeabilization and increasing collagen degradation

Abstract

Excessive oxidative stress causes lysosomal membrane permeabilization (LMP), which leads to cell death. Vacuolar ATPase (V-ATPase) is the enzyme responsible for pumping H⁺ into the cytosol and thus maintaining intracellular pH. Previously, we reported that V-ATPase B2 subunit expression is upregulated in the TiO₂-exposed lung epithelium. We investigated the role of the lysosomal V-ATPase B2 subunit in oxidative stress-induced alveolar epithelial cell death and in an experimental lung injury/fibrosis model. Overexpression of V-ATPase B2 increased lysosomal pH and lysosomal activities in the cells. In the presence of H₂O₂, overexpression of V-ATPase B2 increased survival, and silencing of V-ATPase B2 dramatically increased cell death. Overexpression of V-ATPase B2 diminished H₂O₂-triggered LMP, as evidenced by a reduction in acridine orange staining and leakage of cathepsin D from the lysosome to the cytoplasm. In addition, V-ATPase B2-overexpressing macrophages exhibited significantly enhanced uptake and degradation of collagen. V-ATPase B2-overexpressing transgenic mice showed significant inhibition of the bleomycin-induced increases in lung inflammation and fibrosis. We conclude that V-ATPase B2 is critical for maintaining lysosomal activities against excessive oxidative stress by stabilizing LMP. Our findings reveal a previously unknown role of this V-ATPase subunit in a lung injury and fibrosis model.

Lysoomal vacuolar ATPase B2 prevents oxidative stress-induced cell death and lung injury/fibrosis

An enzyme involved in maintaining the correct pH inside the lysosome, an organelle involved in disposal of cellular waste, also plays a critical role in preventing lung injury. Using human lung cells and mouse models of lung fibrosis, a team led by Sung Woo Park from Soonchunhyang University Bucheon Hospital, South Korea, showed that a overexpression of subunit of the vacuolar ATPase enzyme B2, which pumps protons into cellular compartments to create more acidic environments, helps to boost lysosomal activities that lead to prevent oxidative stress-induced cell death and alleviate experimental lung injury/fibrosis. In addition, V-ATPase B2 overexpressed macrophages increased collagen uptake and degradation activities. The findings point to the vacuolar ATPase, and its B2 subunit in particular, as a promising drug target for future treatments of pulmonary fibrosis.