A recent University of Iowa study has uncovered that rare lung cells, known as pulmonary ionocytes, have an unexpected role in absorbing water and salt from the airway surface. This discovery challenges previous assumptions and could have implications for understanding cystic fibrosis.
These unique cells were once thought to only exist in the gills of freshwater fish and the skin of frogs. Their discovery in human lungs provide new insights into the causes of cystic fibrosis.
What Is Cystic Fibrosis?
Cystic fibrosis is a hereditary disorder impacting a specific protein in the body. Those with CF possess a malfunctioning protein that affects various bodily cells, tissues, as well as the glands responsible for producing mucus and sweat.
Ordinarily, mucus serves as a slippery protective layer for the linings of the airways, digestive system, and other organs. However, individuals with cystic fibrosis produce thick, adhesive mucus that can accumulate, resulting in blockages, harm, or infections in the affected organs. Inflammation further contributes to organ damage, particularly in the lungs and pancreas.
Symptoms could vary depending on the organs affected and the condition's severity. While some individuals exhibit minimal or no symptoms, others experience severe symptoms and even life-threatening complications.
Respiratory issues, known as pulmonary or respiratory problems, primarily involving severe lung infections, are the most prevalent and critical complications associated with CF. Furthermore, individuals with CF often encounter difficulties in maintaining proper nutrition due to challenges in nutrient absorption from food, potentially leading to growth delays.
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CFTR's Surprising Role in Lung Function
Cystic fibrosis is characterized by the absence or mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) protein in the lungs, which regulates salt and water balance on the lung's surface. Despite extensive research, the full structure and function of CFTR remain incompletely understood.
The University of Iowa's research, published in The Journal of Clinical Investigation, uncovered an unexpected role of CFTR. Prior studies primarily focused on CFTR proteins within airway secretory cells, where they secrete chloride ions into the airway's liquid lining, promoting rehydration and trapping of irritants and pathogens.
However, individuals with CF produce thick, sticky mucus that can block airways. In 2018, researchers discovered a previously unknown cell type, ionocytes, within the human lung, similar to those found in fish and frogs.
Experimental studies on cultured ionocytes revealed that CFTR proteins in ionocytes appear to absorb chloride ions, extracting moisture from the lung's liquid lining instead of secreting it. More ionocytes were associated with increased liquid absorption, not secretion.
This new understanding suggests that ionocytes mediate liquid absorption, while secretory cells manage liquid secretion. The divergent roles of CFTR in these cell types indicate that CF disrupts both liquid secretion and absorption, offering fresh insights into CF's pathology.
These findings may open doors to genetic therapies targeting ionocytes for future CF treatments, providing hope for improved management of the disease. However, further research is needed to understand the precise regulation of transport processes within ionocytes.
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