Simulated Mars Gravity Impairs Intestinal Epithelial Barrier Integrity via Selective Modulation of Tight Junction...

Future long-duration human space missions will expose astronauts to chronically reduced gravitational loading, a condition associated with oxidative stress and epithelial barrier dysfunction. The intestinal epithelial barrier depends on tight junctions (TJs), yet the impact of partial gravity on TJ composition, assembly, and claudin organization remains poorly defined. Here, we show that differentiated intestinal epithelial monolayers exposed to simulated Mars gravity undergo TJ ultrastructural remodeling, characterized by loss of apical membrane "kissing points" and widening of the paracellular space, accompanied by impaired barrier function. Simulated Mars gravity also induces oxidative stress and accumulation of cytoplasmic and nuclear lipid droplets, consistent with altered membrane and lipid homeostasis. At the molecular level, simulated Mars gravity promotes selective TJ changes, with significant downregulation-but not mislocalization-of barrier-forming claudins CLDN1 and CLDN3 and the scaffolding protein ZO-1, while CLDN2, CLDN4, CLDN7, CLDN12, CLDN23, and OCLN remain unchanged. STAT3 activation, but not ERK or NF-κB signaling, may be associated with these alterations and is consistent with a stress-adaptive remodeling response to oxidative stress under simulated Mars gravity. Overall, these findings identify simulated Mars gravity as a disruptor of intestinal barrier homeostasis and highlight TJ remodeling as a target for countermeasures to preserve gut integrity during deep-space missions.