Enhanced erythropoiesis in mice exposed to low environmental temperature

Abstract

Summary Hematopoietic responses to environmental factors are not fully characterized. Polycythemia has been reported during exposure to low temperatures in ectothermic animals. The relationship between the causes of polycythemia and erythropoiesis during low-temperature exposure is not fully understood. In this study, we exposed C57BL/6 mice to 5°C and monitored the blood cell counts and erythropoiesis. The hematocrit level increased from 45.6% to 52.2% after 14 days. Likewise, the hemoglobin concentration, initially 15.1 gdL-1, rose to 16.0 gdL-1. The reticulocyte production index significantly increased from 4% to 8% after seven days. We examined the anatomy and cell composition of the spleens of the mice. On day 5, the spleens were approximately 6 mgg-1 of body weight, which was two-fold greater than the spleens on day 0. Flow cytometry showed four-fold more proerythroblasts on day 5, compared with day 0. Additionally, the number of late-stage mature erythroblasts increased on days 14. Erythropoietin mRNA levels increased in the kidneys, and hypoxia inducible genes were enhanced in the kidney. Our findings indicated that low ambient temperature is a novel erythropoietic stress, that induces polycythemia by enhanced erythropoiesis.