The Science Bit – Part 10: Pigs lead the way in Cystic Fibrosis research

1 04 2011

Cystic Fibrosis (CF) is a recessive genetic disorder that affects approximately 8,500 people in the UK. It’s the most common life-shortening inherited disease in the world, with around 1 in 20 people being a carrier for the condition.

CF is caused by a mutation in the gene for a protein called the cystic fibrosis transmembrane conductance regulator or (thankfully) CFTR for short. This protein, in its normal state, is a channel protein that controls the movement of salts from the inside of the cell to the fluid surrounding the cells in the lungs, pancreas and other affected organs. In the sweat glands, CFTR usually works by moving salt from the sweat on the skin back into the body. When CFTR does not work properly however, too much salt and not enough water accumulates in the lungs, pancreas etc, and remains on the skin. The lack of water means that the normally lubricating tissue fluid in these organs becomes thick and sticky mucus.

The most recognisable symptoms of CF are to do with the build up of mucus in the airways, which causes unrelenting, mucusy coughing and a difficulty in breathing. Bacteria thrive on the thickened mucus, so lung infections including pneumonia are common, leading to damage of the airways and general poor health because of the inability to exercise properly to maintain fitness.

Mutated CFTR has effects elsewhere in the body, too. In the intestines, severe, chronic constipation caused by a lack of water to soften stools in the bowel can often lead to infection and rectal prolapse. Food cannot be digested properly in the small intestine, so CF patients often have difficulty in maintaining their weight and growth is stunted. The bile ducts may become blocked and cause damage to the liver. Cystic Fibrosis-related diabetes may occur as a result of the blockage of insulin in the pancreas. 97% of CF men are infertile because of an absence of the vas deferens, the tube that supplies sperm to the penis.

Given all these complications, it’s perhaps not surprising that until only a few decades ago, an infant born with CF would have been lucky to reach its first birthday. Now, although still a relatively short life expectancy, a CF sufferer might live well into their 30s and 40s, and with a successful lung transplant, even longer. Advances in treatment, including respiratory therapy, antibiotics, physiotherapy, diet and lifestyle changes have all made significant improvements to the quality of life for CF patients. But while the symptoms of CF can now be more effectively managed, there is still no cure for the disease.

A key to finding a targeted cure for CF is to understand the genetic and molecular processes that go on at the cellular level. Recently, a team of researchers from the University of Iowa made an important discovery that brings us a little step closer to the end goal of curing this disease. Pigs.

Pigs have long been used as an animal model for human disease research because in many organ systems, they have a very similar anatomy. Of course, there is much about a pig that is different, but by genetically engineering a pig model that mimics the faulty CFTR gene, the research team have been able to discover that the mutated protein has the same pathological effects in their pig model as in humans. This breakthrough means that pigs may now be used in further research to more accurately pinpoint what exactly happens to the mutated CFTR protein, and to find a way to treat it or correct it.

Using their new model, the team, whose findings were published in Science Translational Medicine last week, have already identified that the faulty CFTR protein is “misprocessed” in the cell and ends up in the wrong place, compared to the normal protein. Now that we know that pigs are analogous to humans in the manifestation of CF, they can be used to test a variety of potential new treatments, including gene therapy techniques that replace the faulty gene with a working copy, and “corrector” drugs, which aim to move the faulty protein to its proper position in the cell. The development of a pig model for studying this disease opens new doors to finding a way to beat cystic fibrosis, and new hope to its victims.

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