Role of Rel A and IkappaB of nuclear factor kappaB in the release of interleukin-8 by cyclic mechanical strain in human alveolar type II epithelial cells A549.

BACKGROUND AND OBJECTIVE

Overdistention of the lung tissue during mechanical ventilation may initiate ventilator-induced lung injury (VILI). Release of cytokines, including IL-8, may be responsible for VILI, although the mechanisms remain unclear. This study aimed to determine whether stretch-induced IL-8 production is dependent on degradation of IkappaB (IkappaB) and the resulting Rel A translocation into the nucleus.

METHODS

A549 cells were exposed to cyclic stretch of varying amplitude, frequency and duration before the mRNA and protein level of IL-8 were measured. To observe the role of Rel A and IkappaB of nuclear factor kappaB, A549 cells were exposed to cyclic stretch for 5 min to 1 h. Real-time PCR and ELISA respectively were performed to detect mRNA and IL-8 protein. Rel A and IkappaBalpha were assessed by Western blot. Further confirmation was sought using a nuclear factor kappaB inhibitor (PDTC) before mechanical stretch.

RESULTS

A549 cells exposed to cyclic stretch produced IL-8 in a time- and strain-dependent manner, but there was no observed effect related to stretch frequency. Activation of Rel A and IkappaBalpha was detected 10 min after the initiation of stretch, peaked at 15 min and returned to baseline within 1 h. IL-8 production was partially inhibited by the presence of PDTC.

CONCLUSION

Cyclic mechanical stretch can activate Rel A translocation and IkappaBalpha degradation, thus inducing the secretion of IL-8 in alveolar epithelial type II cells. Pharmacological inhibition of Rel A and IkappaBalpha inhibits IL-8 mRNA and protein levels, suggesting novel approaches to prevent VILI.