How an Emerging Disease in Dogs is Shedding Light on Cystic Fibrosis
A canine gallbladder disease that involves the accumulation of abnormal mucus similar to that seen in human cystic fibrosis (CF) patients is caused by improper expression of the gene associated with CF in humans. The finding could have implications for human CF patients as well as for animal models of CF.
The disease, gallbladder mucocele formation, is caused by the slow accumulation of thick, dehydrated mucus that interferes with normal gallbladder function and eventually leads to obstruction and rupture. Mucocele formation is seen primarily in purebred dogs – in the U.S. it’s most common in Shetland sheepdogs, whereas in the U.K. border terriers are most impacted.
“We really only started seeing this disease about 20 years ago in a handful of breeds,” says Jody Gookin, professor of small animal internal medicine at North Carolina State University and corresponding author of the research. “What captured my attention was how similar these gallbladders looked to those in animal models of CF.”
The thick immobile mucus associated with CF in humans stems from a defect in a gene called CFTR, which is responsible for depositing channels in epithelial cells that then secrete chloride and water. These channels lubricate the cell surface, keeping mucus moist and moveable. In CF, the absence of these lubricating channels means that the mucus dehydrates and clogs lungs and intestines. But in human patients, gallbladders don’t fill up with dehydrated mucus.
“There are no recorded instances of naturally occurring CF in any non-human species,” Gookin says. “But when researchers study CF in animal models by knocking out the CFTR gene, those animals often develop the same gallbladder pathology that we see in dogs with mucocele formation. “That led us to wonder whether dogs with mucoceles had a mutation in CFTR – but they didn’t. What they did have was a failure of CFTR to function.”
Gookin performed whole genome sequencing on blood collected from eight Shetland sheepdogs with gallbladder mucocele formation and compared the location and frequency of variants in the CFTR gene to 115 dogs from 12 breeds at high risk for mucocele formation and 2,519 dogs from 340 breeds considered low risk for mucocele formation. There were no significant differences between the groups. Additionally, the dogs with mucocele formation did not have mutations in CFTR in locations where humans with CF do.
“What that means is that somehow these dogs are acquiring a dysfunction of the CFTR channel that is not based on a defect in the gene,” Gookin says. “It could be due to the influence of other genes and environmental factors that influence CFTR function. Our next steps will be looking at the entire genome of these dogs to see if there are other mutations that could be a factor – if there’s something else in their genome that makes them susceptible to developing this disease.
“The most eye-opening piece for me is the idea that it is possible to develop a CF-like disease that isn’t caused by a mutation in the CFTR gene. Identifying the underlying cause of CFTR dysfunction in dogs with mucocele formation has important implications for people where similar factors might contribute to CF-like diseases – or reveal new treatment targets for CF.”
The research appears in Gastrointestinal and Liver Physiology and was supported by the Morris Animal Foundation (grant D17CA-068) and the National Institutes of Health (grants T35OD011070 and K01 OD027058). Research techs Jenny Holmes and Stephen Stauffer; veterinary student Nicole Torres-Machado; former veterinary student Bryanna Meredith; postdoctoral scholar Michael Vandewege; radiologist Gabriela Seiler; small animal surgeon Kyle Matthews; and Dean of the College of Veterinary Medicine Kathryn Meurs are NC State co-authors. Steven Friedenberg of the University of Minnesota St. Paul and Lane Clark of the University of Missouri, Columbia, also contributed to the work.
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Note to editors: An abstract follows.
“Acquired dysfunction of CFTR underlies cystic fibrosis-like disease of the canine gallbladder”
Authors: Jody Gookin, Jenny Holmes, Stephen Stauffer, Nicole Torres-Machado, Bryanna Meredith, Michael Vandewege, Gabriela Seiler, Kyle Matthews, Kathryn Meurs, North Carolina State University; Steven Friedenberg, University of Minnesota St. Paul; Lane Clark, University of Missouri, Columbia
Published: July 23, 2024 in Gastrointestinal and Liver Physiology
Abstract:
Mucocele formation in dogs is a unique and enigmatic muco-obstructive disease of the gallbladder caused by amassment of abnormal mucus that bears striking pathological similarity to cystic fibrosis. We investigated the role of CFTR in the pathogenesis of this disease. The location and frequency of disease-associated variants in the coding region of CFTR was compared using whole genome sequence data from 2,642 dogs representing breeds at low-risk, high-risk, or with confirmed disease. Expression, localization, and ion transport activity of CFTR was quantified in control and mucocele gallbladders by NanoString, Western blotting, immunofluorescence imaging, and studies in Ussing chambers. Our results establish significant loss of CFTR-dependent anion secretion by mucocele gallbladder mucosa. A significantly lower quantity of CFTR protein was demonstrated relative to E-cadherin in mucocele compared to control gallbladder mucosa. Immunofluorescence identified CFTR along the apical membrane of epithelial cells in control gallbladders but not in mucocele gallbladder epithelium. Decreases in mRNA copy number for CFTR was accompanied by decreases in mRNA for the Cl- /HCO3 – exchanger SLC26A3, K+ channels (KCNQ1, KCNN4), and vasoactive intestinal polypeptide receptor (VIPR1) which suggest a driving force for change in secretory function of gallbladder epithelial cells in the pathogenesis of mucocele formation. There were no significant differences in CFTR gene variant frequency, type, or predicted impact comparing low risk, high risk, and definitively diagnosed groups of dogs. This study describes a unique, naturally occurring muco-obstructive disease of the canine gallbladder, with uncanny similarity to cystic fibrosis, and driven by underlying failure of CFTR function.
This post was originally published in NC State News.
