Robust pan-junctional reinforcement preserves the gut epithelial barrier under mechanical stress

Epithelia are specialized tissue barriers that safeguard the organisms internal milieu from the hostile external environment, a function critically dependent on intercellular junctions. In the colon, this barrier is repeatedly challenged by mechanical distension from faeces and it is unknown whether and how the colon adapts to such stress, which could otherwise compromise barrier integrity. Here, we show that faeces-mediated mechanical distension triggers coordinated remodelling at cell- and tissue-scale, suggestive of mechanoadaptation. This response includes recruitment of junctional proteins at all three types of adhesive cell-cell junctions (tight junctions, adherens junctions and desmosomes). We identified two modes of recruitment: stable responders (ZO-1, E-cad, plakoglobin) with sustained junctional enrichment, and adaptive responders (desmoplakin, keratin 8) with progressive accumulation during distension. Distension was also accompanied by perijunctional recruitment and activation of non-muscle myosin II (NMMII). Through genetic, pharmacological, and mechanical perturbations, we demonstrated that NMMII activation is an early and critical step for mechanoadaptation. This process requires extracellular calcium influx, and Piezo1 activation is sufficient to trigger NMMII activation and junctional recruitment. Loss of NMMII function abrogated the junctional response to distension across all three junctional complexes, including desmosomes, resulting in disorganised junctions and barrier breach. Together, our findings uncover a robust physiological mechano-adaptive response of the adult colonic epithelium to an extrinsic mechanical stress, whereby coordinated reinforcement of all junctional complexes, controlled by myosin II and mechanosensitive calcium influx, plays an essential role in preserving intestinal barrier integrity.