Introduction Persistent endoplasmic reticulum (ER) stress impairs early embryonic development by inducing apoptosis through C/EBP homologous protein (CHOP). Toll-like receptor 4 (TLR4), traditionally recognized for its role in innate immunity, has recently emerged as a modulator of intracellular stress responses. Lipopolysaccharide (LPS), a natural TLR4 agonist derived from Gram-negative bacteria, elicits both pro-inflammatory and cytoprotective effects depending on the cellular context and dosage. This study aimed to elucidate the role of TLR4 signaling in the regulation of CHOP-mediated apoptosis during porcine preimplantation development under ER stress. Methods Porcine embryos were treated with tunicamycin (TM, 5 nM) to induce ER stress and co-treated with LPS (10 μM) to activate TLR4 signaling. Developmental competence was assessed by blastocyst formation rates, total cell number, and markers of apoptosis and autophagy. Results LPS treatment significantly improved blastocyst formation rates compared to TM groups (TM: 37.50 ± 4.77% vs. TM+LPS: 52.89 ± 4.86%). Consistent with this improvement, the total cell number per blastocyst was significantly restored by LPS co-treatment (Control: 55.63 ± 2.15 vs. TM: 38.61 ± 2.57; TM+LPS: 48.84 ± 0.83), confirming enhanced cell proliferation under ER stress conditions. LPS co-treatment markedly reduced CHOP protein expression and suppressed ATF4 expression, indicating alleviation of PERK-ATF4-CHOP signaling. Additionally, autophagy and apoptosis were attenuated, as evidenced by a significantly decreased LC3-II/LC3-I ratio and a reduced number of TUNEL-positive cells. Notably, TLR4 knockdown abolished these LPS-mediated protective effects, confirming the requirement of TLR4 in mitigating ER stress-induced damage. Conclusion These findings demonstrated that LPS-mediated TLR4 signaling suppressed CHOP-induced apoptosis and autophagy under persistent ER stress, thereby improving embryonic viability. This study provides novel mechanistic insights into the non-canonical role of TLR4 in early embryonic development and highlights its therapeutic potential for improving in vitro embryo culture systems.
Lee et al. (Tue,) studied this question.