Genes influencing the regulation of ion transport across respiratory epithelium may encode potential targets for pharmacologic treatment of CF. Using the nasal potential difference (PD) as an indicator of changes in electrolyte transport, we have found in mice that a gene associated with the agouti locus influences the change in PD elicited by a chloride gradient. In a colony of mice derived from strains of 129/Sv and C57/BL/6, there are two apparent phenotypes: those that respond to a chloride gradient and those that don't. We have also found that mice carrying a mutation which reduces the amount of CFTR mRNA do not respond to a chloride gradient whereas mice homozygous for CFTR null mutations do not respond to chloride gradients as well as adenylate cyclase activation, a stimulation for CFTR channel activity. Furthermore, the change in PD evoke by the chloride gradient is sensitive to DPC. Together, these data indicate both responses are CFTR-dependent, but the ion transport mechanisms involved in each are different. Both responses are reduced or absent in CF, suggesting these are phenomena relevant to CF pathophysiology. The traits described do not appear to be single gene events, so we propose (Aim 1) to identify genes involved in these processed by mapping and cloning the gene linked to the agouti locus, as well as identify genes linked to markers dispersed throughout the mouse genome.
In Aim 2, we hope to better understand the relationship between CFTR and other channels in the response of the nasal involved. Also as part of this aim, we will examine the PD profiles of men with congenital bilateral absence of the vas deferens, as some of these are strikingly similarly to the mice with regards to the chloride gradient response. Evidence that the genes involve could be therapeutic targets would be gained if they could modify some aspect of disease. CF mice do not spontaneously develop airway disease, so Aim 3 will utilize a mode of airway infection to determine if mice with different nasal PD profiles respond different to infection, either in terms of inflammation or survival. Once the various murine genes are mapped, Aim 4 proposes to identify the location of the human homologues and determine if alleles of the human genes associate with different clinical traits, such as age of colonization, rate of decline in FEV/1, etc. In all, these aims should allow us to better understand electrolyte transport processes, and, hopefully, identify ways to control CF pathogenesis.
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