Clinical implication of cellular senescence on CFTR expression.

Background: Cystic fibrosis trans-membrane conductance regulator (CFTR) is a cAMP-modulated chloride/bicarbonate channel with different functions in various organs and tissues. Patients with CF are characterized by recurrent infections and by chronic neutrophilic airway inflammation as well as increased levels of neutrophil elastase (NE) in the airways. NE triggers cell cycle arrest that can lead to senescence. Moreover, it is well demonstrated that the CFTR expression get decreasing from embryogenesis to adult/elder age. Transcriptional, posttranscriptional and epigenetic regulatory mechanisms play a key role in decreasing the CFTR expression during life and recent evidences show that some CFTR-regulating microRNAs, i.e, mir-494, is up regulated during cell senescence. Cellular senescence is a permanent cell cycle arrest. In young cells it can be induced by different stimuli both exogenous and endogenous such as the physiological shortening of telomeres, the activation of oncogenes as well as oxidative stress. Furthermore, senescent cells are associated with modifications in the gene expression profile based on transcriptional, posttranscriptional and epigenetic regulatory mechanisms. Aims: To assess whether CFTR might be involved in cellular senescence and understand its role in the cellular senescence. Methods: To induce premature senescence, IMR90 cells at PDL34 were treated with 100 M diethylmaleate (DEM) (Sigma-Aldrich) in complete medium on alternate days for ten days. Western Blot and Real Time-PCR analysis were performed to assess either the CFTR and the microRNAs expression in: i) IMR90 cells at different population doubling levels (PDL); ii) IMR90 cells at different days after DEM treatment. Results:We found that: i) the CFTR expressions significantly decreased in IMR90 cells during replicative senescence (PDL58 versus PDL35); ii) the CFTR expression significantly decreased in IMR90 cells after DEM treatment; iii) there was an inverse relationship between CFTR and miRNA 494 expression either in IMR90 cells during replicative senescence and in IMR90 cells after DEM treatment. Conclusions: Our preliminary data show that CFTR is physiologically down-regulated during cellular senescence and this may (at least partially) depend on the up-regulation of miR-494. To better investigate the role of CFTR in cellular senescence, we are performing the over-expression of CFTR protein in pre-senescent/senescent IMR90 and the silencing of CFTR in IMR90 young cells. Furthermore, we are now validating such results on primary epithelial nasal cells from different subjects.