The Arp2/3 complex maintains gut epithelial integrity under mechanical challenge

Epithelia are specialized and selective tissue barriers that separate the organism's interior from the external environment. Among adult tissues, the gut epithelium must withstand microbial and biochemical insults but also mechanical stresses imposed by luminal contents and gastrointestinal motility. In addition, the continuous renewal of the intestinal epithelium creates tension^1,2 that must be withstood by cell-cell junctions and the actomyosin cytoskeleton to preserve barrier integrity.^{3,4,5,6,7,8,9,10,11,12} Despite these continuous challenges, the intestinal epithelium maintains a robust barrier function, though the underlying mechanisms remain poorly understood. Among the multiple actin regulators present at cell-cell junctions, the Arp2/3 complex acts as a mechanosensitive nucleator of F-actin at adherens junctions¹³ and is critical for maintaining cell adhesions in vitro^14,15,16,17 and in C. elegans intestinal¹⁸ and Drosophila notum¹⁹ epithelial cells. Here, we identify the actin nucleator Arp2/3 complex as a critical regulator of intestinal epithelial integrity under mechanical stress. Using a gut epithelium-specific, inducible Arpc4 knockout mouse model, we show that Arp2/3 loss of function leads to increased intestinal permeability, epithelial fracturing, and, ultimately, lethality. Arp2/3 depletion disrupts tight junction protein localization, compromising epithelial stability and making it prone to functional failure. Using ex vivo cultured intestinal slices and intestinal epithelial organoids, we found that these functional defects require mechanical challenge and elevated actomyosin contractility to manifest. Together, our findings establish Arp2/3 as a key regulator of intestinal epithelial homeostasis, ensuring tight junction stability, thus highlighting potential therapeutic targets for disorders associated with barrier dysfunction and inflammation.