Cystic fibrosis-associated liver disease: when will the future be now?

CFTR dysfunction predisposes to fibrotic liver disease in a murine model

Cystic fibrosis liver disease (CFLD) is a rapidly progressive biliary fibrosis, resembling primary sclerosing cholangitis that develops in 5-10% of patients with cystic fibrosis. Further research and evaluation of therapies are hampered by the lack of a mouse model for CFLD. Although primary sclerosing cholangitis is linked to both ulcerative colitis and loss of cystic fibrosis transmembrane conductance regulator (CFTR) ion channel function, induction of colitis with dextran sodium sulfate (DSS) in cftr(-/-) mice causes bile duct injury but no fibrosis. Since profibrogenic modifier genes are linked to CFLD, we examined whether subthreshhold doses of the profibrogenic xenobiotic 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), along with DSS-induced colitis, lead to bile duct injury and liver fibrosis in mice that harbor loss of CFTR function. Exon 10 heterozygous (cftr(+/-)) and homozygous (cftr(-/-)) mice treated with DDC demonstrated extensive mononuclear cell inflammation, bile duct proliferation, and periductular fibrosis. In contrast, wild-type (cftr(+/+)) littermates did not develop bile duct injury or fibrosis. Histological changes corresponded to increased levels of alkaline phosphatase, hydroxyproline, and expression of profibrogenic transcripts for transforming growth factor-β(1), transforming growth factor-β(2), procollagen α(1)(I), and tissue inhibitor of matrix metaloproteinase-1. Immunohistochemistry demonstrated fibrosis and activation of periductal fibrogenic cells based on positive staining for lysyl oxidase-like-2, α-smooth muscle actin, and collagen I. These data demonstrate that subthreshold doses of DDC, in conjunction with DSS-induced colitis, results in bile duct injury and periductal fibrosis in mice with partial or complete loss of CFTR function and may represent a useful model to study the pathogenic mechanisms by which CFTR dysfunction predisposes to fibrotic liver disease and potential therapies.