Impaired PPAR gamma activation by cadmium exacerbates infection-induced lung injury

Emerging data indicate 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 Streptococcus pneumoniae. However, the heavy metal cadmium or infection mediated an inhibitory posttranslational modification of peroxisome proliferatoractivated receptor gamma (PPAR gamma) to exacerbate LRTIs. Cadmium and infection increased ERK activation to regulate PPAR gamma 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, individuals residing in areas of high air cadmium levels had increased cadmium concentration in their bronchoalveolar lavage (BAL) fluid, increased barrier dysfunction, and showed PPAR gamma inhibition that was mediated, at least in part, by ERK activation in isolated BAL cells. These observations suggest that impaired activation of PPAR gamma in monocyte-derived macrophages exacerbates lung injury and the severity of LRTIs.