mSphere of Influence: Adenosine in Host Defense against Bacterial Pneumonia-Friend or Foe?

Efficacy of YAP1-gene Knockdown to Inhibit Alveolar-Epithelial-Cell Senescence and Alleviate Idiopathic Pulmonary Fibrosis (IPF)

BACKGROUND/AIM

The prevalence of idiopathic pulmonary fibrosis (IPF) increases with age and is associated with senescence of alveolar epithelial cells (AECs). AEC senescence in pulmonary cells mediates IPF. We herein aimed to determine if YAP1 gene knockdown, a member of the Hippo/YAP signal pathway, in the bleomycin (BLM)-induced mouse model of IPF, inhibits onset of senescence of AECs and alleviates IPF.

MATERIALS AND METHODS

Adeno-associated viruses (AAVs) expressing Yes-associated protein 1 (YAP1) short hairpin RNA (shRNA) were delivered into the lung of BLM-induced IPF mice via intratracheal injection, to knockdown the YAP1 gene in AECs. The mice were assigned to 4 groups: G1: control (normal mice); G2: IPF mice; G3: IPF + AAV/YAP1; G4: IPF + AAV/scramble. After 28 days, AECs were examined for senescence using H&E staining, Masson's trichrome Staining, senescence-associated ß-galactosidase (SA-β-gal) staining, western blotting and co-immunofluorescence staining, to determine the expression of YAP1, Smad-3 and p21, in order to determine the induction of senescence of ACEs.

RESULTS

The severity of IPF determined by H&E staining, Masson's staining and immunofluorescence (IF) staining was positively correlated with the senescence of AECs. Down-regulation of YAP1 expression of the Hippo-signaling pathway, determined by western blotting in AECs, alleviated pulmonary fibrosis as determined by Masson's staining. Down regulation of YAP1 expression reduced the senescence of AECs as determined by ß-galactosidase (SA-β-gal) staining, which alleviated the clinical symptoms of IPF mice, as determined by body weight and lung index.

CONCLUSION

Down-regulation of YAP1 expression in AECs inhibited AEC senescence which is thought to be the cause of IPF. Therefore, future studies can focus on inhibiting YAP1 to effectively treat IPF.

Host surface ectonucleotidase-CD73 and the opportunistic pathogen, Porphyromonas gingivalis, cross-modulation underlies a new homeostatic mechanism for chronic bacterial survival in human epithelial cells

Cell surface nucleotide-metabolizing enzyme, ectonucleotidase-CD73, has emerged as a central component of the cellular homeostatic-machinery that counterbalances the danger-molecule (extracellular-ATP)-driven proinflammatory response in immune cells. While the importance of CD73 in microbial host fitness and symbiosis is gradually being unraveled, there remains a significant gap in knowledge of CD73 and its putative role in epithelial cells. Here, we depict a novel host-pathogen adaptation mechanism where CD73 takes a center role in the intracellular persistence of Porphyromonas gingivalis, a major colonizer of oral mucosa, using human primary gingival epithelial cell (GEC) system. Temporal analyses revealed, upon invasion into the GECs, P. gingivalis can significantly elevate the host-surface CD73 activity and expression. The enhanced and active CD73 significantly increases P. gingivalis intracellular growth in the presence of substrate-AMP and simultaneously acts as a negative regulator of reactive oxygen species (ROS) generation upon eATP treatment. The inhibition of CD73 by siRNA or by a specific inhibitor markedly increases ROS production. Moreover, CD73 and P. gingivalis cross-signaling significantly modulates pro-inflammatory interleukin-6 (IL-6) in the GECs. Conversely, exogenous treatment of the infected GECs with IL-6 suppresses the intracellular bacteria via amplified ROS generation. However, the decreased bacterial levels can be restored by overexpressing functionally active CD73. Together, these findings illuminate how the local extracellular-purine-metabolism, in which CD73 serves as a core molecular switch, can alter intracellular microbial colonization resistance. Further, host-adaptive pathogens such as P. gingivalis can target host ectonucleotidases to disarm specific innate defenses for successful intracellular persistence in mucosal epithelia.