GENOTYPIC ANALYSIS OF RESPIRATORY MUCOUS SULFATION DEFECTS IN CYSTIC-FIBROSIS

Intracellular dysfunction of the cystic fibrosis transmembrane conduct ance regulator (CFTR) has been proposed to alter endosomal acidificati on, The most widely studied consequence of this defect has been altera tions in the biochemical properties of cystic fibrosis (CF) respirator y mucus glycoproteins. However, studies confirming the existence of mu cous processing defects in CF have been hindered by the lack of in viv o animal models by which to test these hypotheses in the absence of se condary effects of chronic bacterial infection. The human bronchial xe nograft model has been useful in evaluating the pathophysiologic diffe rences between CP and non-CF airway epithelium, in the absence of seco ndary disease effects such as goblet cell hyperplasia. In this study w e sought to compare the extent of sulfation within secreted mucus glyc oproteins from CF and non-CF human bronchial xenografts. Cumulative re sults of xenografts generated from 13 independent CF tissue samples de monstrated a statistically significant higher level of sulfation (1.7/-0.18, P < 0.026) as compared to non-CF paired controls. Such finding s add to the growing body of knowledge that primary defects in sulfati on exist in CF respiratory mucin. Correlation of genotype with the ext ent of mucus sulfation revealed two categories of CF tissues with stat istically different mucus sulfation profiles. Results from these studi es demonstrated a 2.0+/-0.15-fold higher level of mucus sulfation prod uced from xenografts of five defined CF genotypes as compared to non-C F controls (P < 0.004, n = 10), Interestingly, three CF samples for wh ich one mutant allele remained undefined (Delta F508/unknown or G551D/ unknown) demonstrated no statistical difference in the level of sulfat ion as compared with matched non-CF controls (n = 3). This as yet unkn own allele was not identified within a screen for the 26 most common C F mutations, These results provide preliminary evidence for allelic va riation within the CF population which may begin to elucidate the stru cture-function of CFTR with regards to intracellular mucus processing defects.