Organ-specific over-sulfation of glycosaminoglycans and altered extracellular matrix in a mouse model of cystic fibrosis

Abstract

Cystic fibrosis (CF) is a fatal inherited disease caused by the loss of function of a plasma membrane chloride channel-the cystic fibrosis transmembrane conductance regulator (CFTR). It is characterized by viscous mucous secretions which have abnormal glycosylation and sulfation. The development of a CFTR knockout mouse has allowed in vivo experiments aimed at investigating the over-sulfation phenomenon reported for CF glycoconjugates. Four CF and five control mice injected with [35S]sulfate were examined for differences in the sulfation of glycosaminoglycans (GAGs) synthesized by 12 tissues after 48 h. The liver and pancreas of CF mice incorporated significantly higher amounts of [35S]sulfate into GAGs (dpm/microg) than the controls, while the ileum, jejunum, colon, cecum, spleen, trachea, and gall bladder of CF mice exhibited higher incorporation levels that were not significant. The lung and nasal septum were not different, and the nasal mucosa of CF mice was significantly lower (P < 0.05). Structural analysis of the chondroitin/dermatan sulfate component by strong anion-exchange HPLC revealed that the liver and ileum of CF mice incorporated significantly more total sulfate than controls. However, for other organs, the explanation for higher isotope incorporation was a 40-50% higher specific activity of [35S]sulfate within GAGs. This finding implied different uptake kinetics of sulfate from the circulation or that CF mice have altered sulfate pools. CF mice also had altered proportions of chondroitin/dermatan sulfate to heparan sulfate in the ileum and gall bladder (P < 0.05). We conclude that extracellular matrix architecture in some CF organs may be abnormal and that sulfation of glycoconjugates by some organs and sulfate utilization in others have been affected by the loss of CFTR. This study provides the first in vivo evidence for an influence of CFTR on glycoconjugate sulfation and suggests other secondary manifestations of CFTR dysfunction associated with abnormalities of the extracellular matrix.