Toxoplasma gondii infection triggers ongoing inflammation mediated by increased intracellular Cl- concentration in airway epithelium

Cellular Senescence Contributes to Colonic Barrier Integrity Impairment Induced by Toxoplasma gondii Infection

Toxoplasma gondii (T. gondii) induces gut barrier integrity impairment, which is crucial to the establishment of long-term infection in hosts. Cellular senescence is an imperative event that drives disease progression. Several studies have indicated that T. gondii induces oxidative stress and cell cycle blockade in the tissues of hosts, suggesting cellular senescence induced by the parasite. Here, we explored whether cell senescence is involved in T. gondii-mediated colonic barrier integrity damage in mice. C57BL/6J mice were infected with 10 cysts of T. gondii. Senolytic therapy (dasatinib and quercetin, DQ, a combination therapy for reducing senescent cells) was given by oral gavage 4 weeks post-infection. Alcian blue staining, immunofluorescence, western blot, quantitative PCR (qPCR), and enzyme-linked immunosorbent assay (ELISA) were employed to evaluate the thickness of the colonic mucus layer, the expression profiles of genes and proteins related to tight junction function and cellular senescence in the colonic tissues, and the levels of serum lipopolysaccharides (LPS), respectively. T. gondii-infected mice exhibited deteriorated secreted mucus, shortened length, decreased expression of zonula occludens-1 (ZO-1) and occludin in the colon, accompanied by elevated levels of serum LPS. Moreover, the infection upregulated cell senescence-related markers (p16INK4A, p21CIP1) while inhibiting Lamin B1 expression. In addition, the expression levels of senescence-associated secretory phenotypes (SASPs), including IL-1β, TNF-α, IL-6, MMP9 and CXCL10, were upregulated post-infection. Notably, reducing cell senescence with DQ administration, significantly ameliorated the colonic pathological alterations induced by T. gondii infection. This study uncovers for the first time that cellular senescence contributes to the colonic barrier integrity damage induced by chronic T. gondii infection. Importantly, we provide evidence that senolytic therapy exerts a therapeutic effect on the intestinal pathological lesions.

SARS-CoV-2 envelope protein impairs airway epithelial barrier function and exacerbates airway inflammation via increased intracellular Cl- concentration

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection disrupts the epithelial barrier and triggers airway inflammation. The envelope (E) protein, a core virulence structural component of coronaviruses, may play a role in this process. Pathogens could interfere with transepithelial Cl- transport via impairment of the cystic fibrosis transmembrane conductance regulator (CFTR), which modulates nuclear factor κB (NF-κB) signaling. However, the pathological effects of SARS-CoV-2 E protein on airway epithelial barrier function, Cl- transport and the robust inflammatory response remain to be elucidated. Here, we have demonstrated that E protein down-regulated the expression of tight junctional proteins, leading to the disruption of the airway epithelial barrier. In addition, E protein triggered the activation of Toll-like receptor (TLR) 2/4 and downstream c-Jun N-terminal kinase (JNK) signaling, resulting in an increased intracellular Cl- concentration ([Cl-]i) via up-regulating phosphodiesterase 4D (PDE4D) expression in airway epithelial cells. This elevated [Cl-]i contributed to the heightened airway inflammation through promoting the phosphorylation of serum/glucocorticoid regulated kinase 1 (SGK1). Moreover, blockade of SGK1 or PDE4 alleviated the robust inflammatory response induced by E protein. Overall, these findings provide novel insights into the pathogenic role of SARS-CoV-2 E protein in airway epithelial damage and the ongoing airway inflammation during SARS-CoV-2 infection.