Ambient PM25 Plus High‐Fat Diet Exacerbated Kidney Injury in Mice by Activating Ferroptosis Mediated TGF‐β1/Smad2 Signaling Pathway

ABSTRACT The prevalence of chronic kidney disease (CKD) is on the rise globally, posing a significant public health concern. Numerous studies have indicated that the consumption of a high‐fat diet (HFD) can lead to renal injury, a condition closely linked to CKD. Additionally, research has shown that exposure to ambient PM2.5 is associated with an increased risk of CKD, suggesting that PM2.5 may serve as an environmental risk factor for CKD. However, the synergistic impact of PM2.5 and HFD on renal injury remains poorly understood. Therefore, the objective of our study was to investigate the combined effect of PM2.5 and HFD on renal injury. Male C57BL/6J mice were subjected to a 12‐week feeding regimen of either a normal diet or a HFD, while also being exposed to either saline or ambient PM2.5 through intratracheal instillation twice a week. Evaluation of renal function demonstrated that the HFD significantly elevated levels of serum blood urea nitrogen and serum creatinine. Furthermore, the combination of PM2.5 and HFD exhibited a synergistic effect, exacerbating the aforementioned indicators of kidney injury. Masson's trichrome staining revealed that both the HFD and/or PM2.5 induced renal fibrosis, with PM2.5 exacerbating the HFD‐induced renal fibrosis in the mice. In this study, Western blot analysis was conducted to examine the protein expressions of TGF‐β1 and p‐Smad2 in kidney tissues, which were found to be significantly increased in response to a HFD and/or exposure to PM2.5. Additionally, the impact of PM2.5 combined with HFD on renal ferroptosis was investigated. The results revealed that both HFD and PM2.5 led to an elevation in 4‐HNE concentration, a reduction in GSH content, a decrease in GPX4 protein expression, and an increase in ACSL4 protein expression in kidney tissues. Moreover, the combined exposure to PM2.5 and HFD exhibited a synergistic effect on GPX4 alterations in the kidney. Collectively, our findings suggest that the presence of PM2.5 exacerbates the renal injury, oxidative stress, and renal fibrosis induced by a HFD. This detrimental effect may be attributed to the activation of the ferroptosis‐mediated TGF‐β1/Smad2 signaling pathway.