iRhom2 loss alleviates renal injury in long-term PM2.5-exposed mice by suppression of inflammation and oxidative stress

Particulate matter (PM2.5) is a risk factor for organ injury and disease progression, such as lung, brain and liver. However, its effects on renal injury and the underlying molecular mechanism have not been understood. The inactive rhomboid protein 2 (iRhom2), also known as rhomboid family member 2 (Rhbdf2), is a necessary modulator for shedding of tumor necrosis factor-alpha (TNF-alpha) in immune cells, and has been explored in the pathogenesis of chronic renal diseases. In the present study, we found that compared to the wild type (iRhom2(+/+)) mice, iRhom2 knockout (iRhom2(-/-)) protected PM2.5-exposed mice from developing severe renal injury, accompanied with improved renal pathological changes and functions. iRhom2(-/-) mice exhibited reduced inflammatory response, as evidenced by the reduction of interleukin 1 beta (IL-1 beta), IL-6, tumor necrosis factor-alpha (TNF-alpha) and IL-18 in kidney samples, which might be, at least partly, through inactivating TNF-alpha converting enzyme/TNF-alpha receptors (TACE/TNFRs) and inhibitor of alpha/nuclear factor B-K (I kappa B alpha/NF-kappa B) signaling pathways. In addition, oxidative stress was also restrained by iRhom2(-/- )in kidney of PM2.5-exposed mice by enhancing heme oxygenase/nuclear factor erythroid 2-related factor 2 (HO-1/Nrf-2) expressions, and reducing phosphorylated c-Jun N-terminal kinase (JNK). In vitro, blockage of HO-1 or Nrf-2 rescued the inflammatory response and oxidative stress that were reduced by iRhom2 knockdown in PM2.5-incubated RAW264.7 cells. Similar results were observed in JNK activator-treated cells. Taken together, our findings indicated that iRhom2 played an essential role in regulating PM2.5-induced chronic renal damage, thus revealing a potential target for preventing chronic kidney diseases development.