Downregulation of epithelial sodium channel (ENaC) activity in cystic fibrosis cells by epigenetic targeting

Abstract

The pathogenic mechanism of cystic fibrosis (CF) includes the functional interaction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein with the epithelial sodium channel (ENaC). The reduction of ENaC activity may constitute a therapeutic option for CF. This hypothesis was evaluated using drugs that target the protease-dependent activation of the ENaC channel and the transcriptional activity of its coding genes. To this aim we used: camostat, a protease inhibitor; S-adenosyl methionine (SAM), showed to induce DNA hypermethylation; curcumin, known to produce chromatin condensation. SAM and camostat are drugs already clinically used in other pathologies, while curcumin is a common dietary compound. The experimental systems used were CF and non-CF immortalized human bronchial epithelial cell lines as well as human bronchial primary epithelial cells. ENaC activity and SCNN1A, SCNN1B and SCNN1G gene expression were analyzed, in addition to SCNN1B promoter methylation. In both immortalized and primary cells, the inhibition of extracellular peptidases and the epigenetic manipulations reduced ENaC activity. Notably, the reduction in primary cells was much more effective. The SCNN1B appeared to be the best target to reduce ENaC activity, in respect to SCNN1A and SCNN1G. Indeed, SAM treatment resulted to be effective in inducing hypermethylation of SCNN1B gene promoter and in lowering its expression. Importantly, CFTR expression was unaffected, or even upregulated, after treatments. These results open the possibility of CF patients’ treatment by epigenetic targeting.

Therapeutic potential of phytochemicals for cystic fibrosis

“…Studies have suggested that imbalanced ion transport via CF epithelia may be mitigated by inhibiting ENaC. 80,81 Therefore, a reduction in ENaC activity may be an alternative approach for treating CF. Recently, a study suggested that the activity of ENaC may be downregulated by epigenetic modulation, which acts on both DNA methylation and chromatin condensation, as well as inhibition of extracellular peptidases.…”

“…Recently, a study suggested that the activity of ENaC may be downregulated by epigenetic modulation, which acts on both DNA methylation and chromatin condensation, as well as inhibition of extracellular peptidases. 81 In addition, previous research has suggested that curcumin may have an effect on CF airway cells, which it may inhibit expression of the ENaC gene. 81 Lastly, it should be noted that oxidative stress plays a crucial role in the pathogenesis of cystic fibrosis.…”

“…81 In addition, previous research has suggested that curcumin may have an effect on CF airway cells, which it may inhibit expression of the ENaC gene. 81 Lastly, it should be noted that oxidative stress plays a crucial role in the pathogenesis of cystic fibrosis. Due to the antioxidant properties of nano-formulated curcumin, a clinical study was recently conducted to investigate its effect on oxidative stress in patients with CF.…”

“…Mutated CFTR is incapable of protecting ENaC from proteolytic cleavage, which could activate ENaC channels. Studies have suggested that imbalanced ion transport via CF epithelia may be mitigated by inhibiting ENaC 80,81 . Therefore, a reduction in ENaC activity may be an alternative approach for treating CF.…”

Gene therapy for cystic fibrosis: Challenges and prospects

“…CFTR has also been proposed to inhibit ENaC activity through direct physical interactions, and dehydration of CF ASL is driven by ENaC ( Stutts et al, 1995 ). Thus, stimulation of alternative chloride channels ( Xu et al, 2005 ; Liu et al, 2015 ; Quesada and Dutzler, 2020 ) or inhibition of sodium absorption ( Blacona et al, 2022 ) may be able to compensate for the lack of CFTR-mediate Cl − secretion in CF airways or to maximize the efficacy of gene therapies aiming at CFTR . Notably, it was reported that proteasome modulation agent doxorubicin facilitated long-term functional inhibition of ENaC currents.…”