Following experiments on mice, it has been shown that stem cells which respond after a severe injury in the lungs may be a source of rapidly dividing cells that lead to lung cancer. The experiments were conducted by an international group of researchers from the U.S.-based Duke University and Cancer Research UK.
"There are chemically resistant, local-tissue stem cells in the lung that only activate after severe injury," said Dr. Barry R. Stripp, professor of medicine and cell biology at Duke University Medical Center.
"Cigarette smoke contains a host of toxic chemicals, and smoking is one factor that we anticipate would stimulate these stem cells. Our findings demonstrate that, with severe injury, the resulting repair response leads to large numbers of proliferating cells that are derived from these rare stem cells," Stripp added.
The researchers said that the new finding may be related to the increased incidence of lung cancer in people with chronic disease states, in particular among cigarette smokers.
"On the positive side, I think that it might be possible to improve lung function in the context of disease if we could understand which pathways regulate lung stem cell activation and then target these pharmacologically," said lead author Dr. Adam Giangreco, from Cancer Research UK's Cambridge Research Institute.
"In terms of lung cancer susceptibility, however, our observation that stem cell activation leads to clonal expansion after injury could, in the context of additional mutations, promote the development of cancerous or precancerous lesions from activated stem cells," Giangreco added. or their study, the researchers used a chimeric mouse model, part wild-type and part with green fluorescent protein-tagged cells (GFP), so that the behaviour of different populations of duplicating lung cells could be evaluated with high-resolution imaging methods.
They gauged the extent to which GFP-positive and GFP-negative cells were mixed, and showed that the abundant population of progenitor cells that normally maintain the epithelial layer in the lung could be rapidly wiped out with a strong chemical, naphthalene. Then the rare proliferative cells became active and grew into large patches.
The research team used a unique whole-lung imaging method to examine and identify the location of stem cells in the lung tissue of mice, and determine the role they play in both healthy and damaged mouse lungs.
They observed that the stem cells, though don't appear to be involved in the normal maintenance of healthy or moderately injured lungs, do play a vital role in repairing severely damaged lungs.
Even though this repair mechanism is important for restoring lung function, the researchers say that it can come at a price.
An acquired mutation in that rare cell or its descendants leads to clonal patches of many identical cells. Secondary mutations in any one of these cells may provide the signals needed for unregulated cell growth and tumour progression.
"This work provides a plausible mechanism to account for this type of event that we previously didn't have," Stripp said.
The findings have been published in the online edition of the Proceedings of the National Academy of Sciences.