Confocal microscopy image of intestinal organoids, self-organizing "mini guts" grown in cell culture from isolated single stem cells. Stained for nuclei (blue), proliferating cells (red) and nuclear lamina protein Lamin A/C (green). Image credit: Ilya Lukonin (CC-BY-NC-ND)
Cigarette smoking is one of the most significant and preventable health risks linked to a variety of diseases, including cancers. Cigarettes release over 5,000 chemicals when they burn, and at least 70 of them cause cancer.
Nicotine is a highly addictive component of cigarettes. Whilst it is not carcinogenic, it has been shown to affect various properties of many cell types, including stem cells. Stem cells function as a repair system and can be found in many tissues or organs. They can both self-renew and differentiate into specialized cell types. For example, intestinal stem cells (ISCs) are crucial for maintaining the structure of the intestines. However, when dysregulated they can lead to the development of tumors.
To find out how nicotine affects ISCs in mice, Isotani et al. exposed the animals and ISCs from mice grown in a laboratory to nicotine. Mice were fed 200 μg/ml (which emulates active smoking) for more than 8 weeks in their drinking water. They then used a technique known as immunohistochemistry as well as an organoid forming assay to study the behavior of the cells in the intestine of mice.
The results showed that exposure to nicotine caused ISCs in the small intestines of the treated mice to divide faster, which increased the number of these cells both in mice and in isolated cells. More specifically, nicotine activated a signaling pathway linked to cell growth, which caused the cells to multiply uncontrollably. When this signaling pathway was experimentally blocked, the ISCs were no longer overactive, and the mice did not develop any tumors.
In addition, Isotani et al. found that secretory cells, called Paneth cells, which are located near ISCs and have previously been shown to affect the growth rate of ISCs, did not show any changes to these pathways and their cell growth. This suggests that changes to the pathways affecting ISCs are not linked to Paneth cells.
To develop therapeutic strategies against nicotine-related diseases, including intestinal tumors, it is essential to understand how nicotine influences ISCs behavior. The results highlight the critical role of specific pathways in regulating the growth of ISCs and the formation of intestinal tumors linked to smoking. A next step would be to validate the therapeutic potential of drugs that can inhibit pathways linked to ISC growth.
