Probing Histone Deacetylase 7 in Cystic Fibrosis iPSCs
Cystic fibrosis (CF) is the most common autosomal recessive disease in the Caucasion population affecting approximately 1 in 3000 births. The ΔF508 mutation in the cystic fibrosis transmembrane receptor CFTR is the predominant cause of CF. The mutant CFTR channel dysregulates ionic homeostasis of several essential ions, and causes the loss of cell surface conductance, elevated mucus levels, bronchial obstruction, bacterial infections, inflammation, premature lung failure and a shortened lifespan. Despite recent advancements in CF research, current treatments, such as antibiotics, mucolytics, dietary supplements, and asthma therapy slow disease progression by alleviating the symptoms, while not addressing the cause.
Due to the difficulty of obtaining primary pulmonary cells from patients, information regarding mutant ΔF508 CFTR behavior has been generated from immortalized cell lines containing artificial reporter constructs. Although these reporter constructs provide an opportunity to approach misfolding diseases like CF, artificial systems can dramatically differ from primary cell sources, which are very limiting. In addition to cell culture models, there are several CF mouse models available. However, many of these models only display the gastrointestinal symptoms associated with CF, but do not recapitulate the bronchial pathology responsible for premature lung failure.
By using potent and selective HDACi and selectively silencing expression of histone deacetylases, we have found that histone deacetylase 7 (HDAC7) plays a critical role in regulating the ΔF508 CFTR mutant. This application is aimed at understanding the molecular basis of how HDAC7 silencing impacts the cellular environment in manner that functionally trafficks the CFTR to the surface instead of being degraded. CF induced pluripotent stem cells (iPSCs) provide us with an opportunity to explore HDAC7 as a master regulator of ΔF508 CFTR function in an endogenous setting. By introducing a fluorescent protein reporter sensitive to select ions, we can monitor CFTR activity levels during propagation of iPSCs and differentiation to primary lung cells. We have shown that silencing HDAC7 changes the levels of several chaperone proteins that participate in CFTR regulation. We now would like to pursue what their roles are and how they relate to HDAC7 mediated pathways. By looking at genes directly associated HDAC7, transcriptional changes that occur in its absence, and proteins interacting with CFTR, we can distill a set of critical proteins/pathways responsible for rescuing ΔF508 CFTR function. In addition, iPSCs provide a unique opportunity to discern if environmental changes are carried from progenitor to terminally differentiated cells and to what extent. Ultimately, these studies will contribute to our ongoing understanding of pliable cellular systems and how subtle changes in pathways associated with pathogenic genes can have tremendous impact on disease severity.
The availability of primary lung cells from patients has been a limiting reagent in the efforts to approach diseases like Cystic Fibrosis. With the recent developments in induced pluripotent cells derived from patient skin cells, we have the opportunity to move the field into a more relevant endogenous setting, by generating primary lung cells from a renewable resource. The studies proposed in this application will yield information on how we can modulate key elements in the cellular environment to restore functionality to misfolded pathogenic proteins. Not only will be of benefit to the State of California, but to therapeutic approaches in general.