Increased oxidative stress induces apoptosis in human cystic fibrosis cells.

Oxidative stress results in deleterious cell function in pathologies associated with inflammation. Here, we investigated the generation of superoxide anion as well as the anti-oxidant defense systems related to the isoforms of superoxide dismutases (SOD) in cystic fibrosis (CF) cells. Pro-apoptotic agents induced apoptosis in CF but not in control cells that was reduced by treatment with SOD mimetic. These effects were associated with increased superoxide anion production, sensitive to the inhibition of IκB-α phosphorylation, in pancreatic but not tracheal CF cells, and reduced upon inhibition of either mitochondrial complex I or NADPH oxidase. CF cells exhibited reduced expression, but not activity, of both Mn-SOD and Cu/Zn-SOD when compared to control cells. Although, expression of EC-SOD was similar in normal and CF cells, its activity was reduced in CF cells. We provide evidence that high levels of oxidative stress are associated with increased apoptosis in CFTR-mutated cells, the sources being different depending on the cell type. These observations underscore a reduced anti-oxidant defense mechanism, at least in part, via diminished EC-SOD activity and regulation of Cu/Zn-SOD and Mn-SOD expressions. These data point to new therapeutic possibilities in targeting anti-oxidant pathways to reduce oxidative stress and apoptosis in CF cells.

Mechanisms of the noxious inflammatory cycle in cystic fibrosis.

Multiple evidences indicate that inflammation is an event occurring prior to infection in patients with cystic fibrosis. The self-perpetuating inflammatory cycle may play a pathogenic part in this disease. The role of the NF-kappaB pathway in enhanced production of inflammatory mediators is well documented. The pathophysiologic mechanisms through which the intrinsic inflammatory response develops remain unclear. The unfolded mutated protein cystic fibrosis transmembrane conductance regulator (CFTRDeltaF508), accounting for this pathology, is retained in the endoplasmic reticulum (ER), induces a stress, and modifies calcium homeostasis. Furthermore, CFTR is implicated in the transport of glutathione, the major antioxidant element in cells. CFTR mutations can alter redox homeostasis and induce an oxidative stress. The disturbance of the redox balance may evoke NF-kappaB activation and, in addition, promote apoptosis. In this review, we examine the hypotheses of the integrated pathogenic processes leading to the intrinsic inflammatory response in cystic fibrosis.

Exaggerated apoptosis and NF-kappaB activation in pancreatic and tracheal cystic fibrosis cells.

The pathophysiologic mechanisms causing inflammation in cystic fibrosis (CF) remain obscure. The effects of proapoptotic agents on pancreatic and tracheal cell lines expressing wild-type CFTR (PANC-1 and NT-1, respectively) or the homozygous CFTRDeltaF508 mutation (CFPAC-1 and CFT-2, respectively) were assessed. An increased susceptibility to apoptosis was observed in CFPAC-1 and CFT-2 cells. Apoptosis was reduced by treatment with a pan-caspase inhibitor and by incubation at 27 degrees C, allowing recruitment of CFTR deltaF508 at the plasma membrane. Inhibition of CFTR function in wild-type cells induced an increase of apoptosis. Apoptosis in CFPAC-1, but not in CFT-2 cells, was associated with overexpression of the proinflammatory mediators interleukin-6 and interleukin-8. In CF cells, apoptosis was linked to NF-kappaB pathway activation. Conditioned medium from actinomycin D-treated CFPAC-1 cells produced an increase in apoptosis of wild-type cells, suggesting that proinflammatory mediators secreted by mutant cells promote apoptosis. This was confirmed through the induction of apoptosis in wild-type cells by exogenous interleukin-6 and interleukin-8. These results suggest that CFTR deltaF508 mutation, apoptosis, and activation of the NF-kappaB pathway contribute to the self-perpetuating inflammatory cycle, at least in pancreatic cells, and provide evidence that excessive apoptosis may account for the exaggerated proinflammatory response observed in CF patients.