Impaired PPAR? activation by cadmium exacerbates infection-induced lung injury
Emerging data indicates an association between environmental heavy metal exposure and lung disease, including lower respiratory tract infections (LRTIs). Here, we show by single cell RNA-sequencing an increase in Pparg gene expression in lung macrophages from mice exposed to cadmium and/or infected with S. pneumoniae. However, the heavy metal cadmium or infection mediated an inhibitory post-translational modification of peroxisome proliferator-activated receptor ? (PPAR?) to exacerbate LRTIs. Cadmium and infection increased ERK activation to regulate PPAR? degradation in monocyte-derived macrophages. Mice harboring a conditional deletion of Pparg in monocyte-derived macrophages had more severe S. pneumoniae infection after cadmium exposure, showed greater lung injury, and had increased mortality. Inhibition of ERK activation with BVD-523 protected mice from lung injury after cadmium exposure or infection. Moreover, subjects residing in areas of high air cadmium levels had increased cadmium concentration in their BAL fluid and showed PPAR? inhibition that was mediated, at least in part, by ERK activation in isolated BAL cells. These observations suggest that impaired activation of PPAR? in monocyte-derived macrophages exacerbates lung injury and the severity of LRTIs. Overall design: 8- to 12-week-old male and female WT C57BL/6J mice were intratracheally administered 100 ng/kg of CdCl2 or saline, as a vehicle control. Mice were administered sterile saline or 10^3 Streptococcus pneumoniae (strain A66.1, type 3) i.t and were euthanized after 15 days. Bacterial infections were performed 5 days after cadmium exposure.