Space Environmental Factor Impacts upon Murine Colon Microbiota and Mucosal Homeostasis

Abstract

<div><p>Astronaut intestinal health may be impacted by microgravity, radiation, and diet. The aim of this study was to characterize how high and low linear energy transfer (LET) radiation, microgravity, and elevated dietary iron affect colon microbiota (determined by 16S rDNA pyrosequencing) and colon function. Three independent experiments were conducted to achieve these goals: 1) fractionated low LET γ radiation (¹³⁷Cs, 3 Gy, RAD), high Fe diet (IRON) (650 mg/kg diet), and a combination of low LET γ radiation and high Fe diet (IRON+RAD) in male Sprague-Dawley rats; 2) high LET ³⁸Si particle exposure (0.050 Gy), 1/6 G partial weight bearing (PWB), and a combination of high LET³⁸Si particle exposure and PWB in female BalbC/ByJ mice; and 3) 13 d spaceflight in female C57BL/6 mice. Low LET radiation, IRON and spaceflight increased <i>Bacteroidetes</i> and decreased <i>Firmicutes</i>. RAD and IRON+RAD increased <i>Lactobacillales</i> and lowered <i>Clostridiales</i> compared to the control (CON) and IRON treatments. Low LET radiation, IRON, and spaceflight did not significantly affect diversity or richness, or elevate pathogenic genera. Spaceflight increased <i>Clostridiales</i> and decreased <i>Lactobacillales</i>, and similar trends were observed in the experiment using a ground-based model of microgravity, suggesting altered gravity may affect colonic microbiota. Although we noted no differences in colon epithelial injury or inflammation, spaceflight elevated TGFβ gene expression. Microbiota and mucosal characterization in these models is a first step in understanding the impact of the space environment on intestinal health.</p></div