Processes After Cold Exposure Leading to the Onset of Stroke

Background: The mortality from stroke is known to increase to a greater extent with the fall of temperature. Environmental factors may play a major role in triggering of the onset of stroke. There is a delay between cold exposure and the onset of stroke. This fact may reflect the complex mechanism after cold exposure. However, a precise process after cold exposure is not well documented. The purpose of this paper is to study the processes after cold exposure that affect human health, exploring the changes in both weather and gene expression. Methods and findings: We used ambulance data of patients provided by the city of Nagoya in Japan during a period from 2002 to 2005. The data included the daily number of patients of all ages, who were first transported by ambulance to a hospital and then diagnosed at the hospital with stroke or cerebral infarction. We used also gene expression data extracted from the database GEO (gene expression omnibus) maintained by The National Center for Biotechnology Information (NCBI). The method is based on random walks in the plane of two variables, mean temperature and relative humidity. We extracted random walks that correspond to paths after cold exposure leading to the onset of stroke and classified the characteristic feature of cooling and rewarming random walks. The increase of relative humidity was observed during these random walks, and suggested the importance of inflammatory system. To discuss a possible mechanism after cold exposure, we examined the gene expression data among the database GEO, and found the increase of cytokine-related genes, especially interleukin 6 signal transducer IL6st and interleukin receptors of IL17. These interleukins play an important role in inflammatory responses. Conclusion: The correspondence between the gene expressions of cytokines and "cooling and rewarming random walks" in the meteorological factors will provide a scheme that connects weather and disease, and will provide novel avenues for research in the prevention of stroke.