Endoplasmic reticulum stress is involved in chronic chlorpyrifos-induced jejunal barrier injury in weaned mice.

Chlorpyrifos (CPF), a widely used organophosphate insecticide, can cause intestinal toxicity under chronic exposure conditions, but the upstream mechanisms underlying intestinal epithelial barrier-associated injury remain unclear. This study investigated whether endoplasmic reticulum stress (ERS) contributes to CPF-induced tight junction (TJ) alterations and intestinal epithelial injury. We used an 8-week drinking-water exposure model in weaned ICR mice with 30, 60, and 120 mg/L CPF and a MODE-K cell model, combined with pharmacological ERS modulation using 4-phenylbutyric acid (4-PBA) and tunicamycin (TM). Quantitative single-cell immunofluorescence was performed at 12, 24, and 48 h to assess temporal changes in TJ proteins and apoptosis-related markers. CPF induced jejunal villus atrophy, reduced the villus-to-crypt ratio, downregulated ZO-1, Occludin, and Claudin-1, impaired TJ structural integrity, increased the total protein levels of PERK, IRE1, and ATF6, and enhanced apoptosis-related alterations, including increased Bax and total Caspase-3 levels and decreased Bcl-2 levels. 4-PBA partially restored TJ protein expression and attenuated apoptosis-related alterations, whereas TM further aggravated TJ protein loss and apoptosis-related changes. Time-course analysis showed that TJ protein reductions were detectable before marked apoptosis-related changes and persisted at later time points. Collectively, chronic CPF exposure induced jejunal epithelial barrier-associated injury in weaned mice, accompanied by coordinated increases in the total protein levels of UPR sensors, TJ protein reductions, and enhanced apoptosis-related alterations. The opposing effects of 4-PBA and TM support the involvement of ERS in CPF-associated epithelial injury. These findings suggest that ERS contributes to progressive intestinal epithelial injury induced by CPF.