Editor's Note: Much of CF research focuses on the serous cells and how they function in the airways of the CF patient, since it is believed that the malfunctioning of these cells prevents the natural anti-bacterial substances from reaching the airway surface. This article describes the importance of replicating serous cells in the laboratory in order to find solutions for this problem.
Earlier in my career I became interested in the airway glands, which contain two cell types, mucus and serous. Mucous cells secrete mucins which provide airway mucous with its thick viscous properties. Among other things, serous cells secrete antibacterial substances such as lysozyme. As part of my thesis project, I developed methods for the culture of cow tracheal submucosal gland serous cells-the first established cell line of airway submucosal gland cells. Then, in 1990, Christian Sommerhof-a postdoctoral fellow working in my laboratory-and I developed techniques for the culture of human tracheobronchial gland cells. Unlike the cow gland cells which grew in culture as serous-like cells, our first human gland cultures exhibited features of both serous and mucous cells. Early during their life in culture, the human gland cells lost their distinguishing serous and mucous secretory granules; fortunately, however, they did retain a number of physiological functions and were quite useful for studies of ion transport.
The pathological changes present in the lungs of patients with CF-among which are mucus hypersecretion, hypertrophy of the tracheobronchial glands and dilation of gland ducts-suggested to Dr. Jonathan Widdicombe and I that the gland cells might be the most important cells in the pulmonary pathophysiology of CF. We began investigating the glands by asking the question: Is the defect in chloride ion transport present in gland cells? Our studies of the electrical properties of cultured gland cells confirmed for the first time that airway gland cells from patients with CF were abnormal in their ability to transport chloride ions.
Shortly after our studies were published, scientists at the University of Michigan showed that the airway gland serous cells are a major site of cystic fibrosis transconductance regulator (CFTR) in the lung. Together with our data, this suggests that therapies for CF should not ignore the gland cells. With this in mind and with generous funding from CFRI, my laboratory has begun collaborative studies with Drs. Frank Szoka and Jonathan Widdicombe aimed at correcting the defect in CF gland cells in laboratory cultures. It is our hope that successful results could one day be transferred from the "test tube" to the patient.
In addition, I am also studying other aspects of airway biology that are indirectly related to CF. One of these projects is the development of cultures of human airway gland cells that maintain differentiated or physiologic functions in culture, particularly that of mucin secretion. Recently, we have been successful in maintaining the differentiation of human airway gland mucous cells in culture and proving that they secrete mucins similar to those secreted in the native airway.
Several years ago when we were having difficulty inducing differentiation in our gland cell cultures, I explored the possibility of using lung cancer cell lines as a model for mucous gland cells. Although this has not worked out as well as I had hoped, we made an interesting discovery about one cell line, Calu-3 cells. This cell line has high levels of CFTR, forms confluent cell sheets in Ussing chambers which are used to test ion transport properties of tissues and cells and, according to Dr. Jeffrey Wine and his laboratory group, are some of the easiest cells to use in patch clamp studies. Several manuscripts reporting our studies as well as collaborative studies among the Widdicombe/Wine/ Finkbeiner laboratories have been recently or will soon be published. We expect that these cells will be used by CF investigators in a number of studies aimed at dissecting the cellular functions of CFTR.
Editor's Note: Dr. Walter E. Finkbeiner received his medical training at the University of Illinois. He became interested in pulmonary disease while studying the pulmonary function of patients with kyphoscoliosis, or curvature of the spine. Following an internship in surgery, Dr. Finkbeiner trained in pathology at the University of California, San Francisco, receiving additional training in pulmonary pathology from Dr. Martha Warnock of UCSF and the late Dr. Charles Carrington of Stanford University. After completing his pathology training, Dr. Finkbeiner studied pulmonary cell biology under Dr. Carol Basbaum, UCSF, where he received his Ph.D. in 1989. He is currently an Associate Professor of Pathology and Director of the Cystic Fibrosis Cell Culture Facility at UCSF.
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