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 kB(NF-kB)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.