A Simulated Microgravity Environment Causes a Sustained Defect in Epithelial Barrier Function

Abstract

Intestinal epithelial cell (IEC) junctions constitute a robust barrier to invasion by viruses, bacteria and exposure to ingested agents. Previous studies showed that microgravity compromises the human immune system and increases enteropathogen virulence. However, the effects of microgravity on epithelial barrier function are poorly understood. The aims of this study were to identify if simulated microgravity alters intestinal epithelial barrier function (permeability), and susceptibility to barrier-disrupting agents. IECs (HT-29.cl19a) were cultured on microcarrier beads in simulated microgravity using a rotating wall vessel (RWV) for 18 days prior to seeding on semipermeable supports to measure ion flux (transepithelial electrical resistance (TER)) and FITC-dextran (FD4) permeability over 14 days. RWV cells showed delayed apical junction localization of the tight junction proteins, occludin and ZO-1. The alcohol metabolite, acetaldehyde, significantly decreased TER and reduced junctional ZO-1 localization, while increasing FD4 permeability in RWV cells compared with static, motion and flask control cells. In conclusion, simulated microgravity induced an underlying and sustained susceptibility to epithelial barrier disruption upon removal from the microgravity environment. This has implications for gastrointestinal homeostasis of astronauts in space, as well as their capability to withstand the effects of agents that compromise intestinal epithelial barrier function following return to Earth.

Factors implicating the validity and interpretation of mechanobiology studies in simulated microgravity environments

“…The duration that cells were exposed to simulated microgravity is an important experimental variable, which can range from 1 hour 116 to over 14 days. 105 There is increasing evidence that simulated microgravity exerts temporal effects due to cellular adaptation. For example, prolonged exposure to simulated microgravity (between 2 and 14 days) was shown to reduce dendritic T cell activation whereas short term exposition (<72 hours) increased dendritic cell maturation markers.…”

“…This can significantly reduce autocrine signaling and may be another factor behind apoptosis and lower cell numbers typically reported in simulated microgravity studies. For example, RWV (full vessel) culture of intestinal epithelial cells was shown to disrupt intestinal epithelial barrier integrity 105 and increased culture medium volume was found to reduce osteoblast fusion and mineralization (bone formation) 106 . In paracrine studies, cell‐conditioned medium extracted from s‐μg culture was reported to have a cross‐pathogenic effect on endothelial cell and smooth muscle cell proliferation and migration compared to normal gravity‐conditioned medium 107 .…”

“…The duration that cells were exposed to simulated microgravity is an important experimental variable, which can range from 1 hour 116 to over 14 days 105 . There is increasing evidence that simulated microgravity exerts temporal effects due to cellular adaptation.…”

Medicina humana espacial: Performance fisiológico y contramedidas para mejorar la salud del astronauta

“…Igualmente existen alteraciones en la motilidad, microbiota intestinal, metabolismo de glucosa y lípidos (89,90) , daño de las vellosidades intestinales e interrupción en las uniones celulares epiteliales por la expresión de la proteína proapoptótica Bax y disminución de Bcl2; alterando de esta manera su función defensiva, homeostasis y el riesgo de contraer enfermedades inflamatorias intestinales (76,91,92,93) por el aumento de citosinas y disminución de la inmunoglobulina secretora (IgA) (76) .…”

Inflammatory bowel disease and epithelial barrier function

“…Professor McCole's group, together with Dr Kim Prisk, investigated the previously little-understood effects of microgravity (low gravity environments, as would be experienced in outer space) on the epithelial cell barrier (5). Previous studies in the field of space biology have demonstrated that microgravity can have a negative impact on the human immune system, via suppression of multiple immune cells.…”