In skeletal muscle, myoblast differentiation results in the formation of multinucleated myofibers. Although recent studies have shown that unfolded protein responses (UPRs) play an important role in intracellular remodeling and contribute to skeletal muscle differentiation, the involvement of IRE1–XBP1 signaling, a major UPR signaling pathway, remains unclear. This study aimed to investigate the effect of the IRE1–XBP1 pathway on skeletal muscle differentiation. In C2C12 cells, knockdown of IRE1 and XBP1 in cells remarkably suppressed differentiation. In addition, apoptosis and autophagy were dramatically enhanced in the XBP1-knockdown cells, highlighting the participation of IRE1–XBP1 in cell survival maintenance with differentiation stimuli during skeletal muscle differentiation. In myogenic cells, we demonstrated that the expression of CDK5 (cyclin-dependent kinase 5) is regulated by XBP1s, and we propose that XBP1 regulates the expression of MyoD family genes via the induction of CDK5. In conclusion, this study revealed that IRE1–XBP1 signaling plays critical roles in cell viability and the expression of differentiation-related genes in predifferentiated myoblasts and during the early differentiation phase.

Hot, humid weather causes heat stress (HS) in broiler chickens, which can lead to high mortality. A recent study found that HS causes endoplasmic reticulum (ER) stress. However, the possible involvement of ER stress in HS-induced physiological alterations in broiler chickens is unclear. This study aimed to evaluate the effect of the dietary supplementation of 4-phenylbutyric acid (4-PBA), an alleviator of ER stress, in acute HS-exposed young broiler chickens. Twenty-eight 14-day-old male broiler chickens (ROSS 308) were divided into two groups and fed either a control diet or a diet containing 4-PBA (5.25 g per kg of diet feed) for 10 days. At 24 days old, each group of chickens was kept in thermoneutral (24 ± 0.5 °C) or acute HS (36 ± 0.5 °C) conditions for 2 h. The results showed that thermoneutral birds supplemented with 4-PBA exhibited no negative effects in terms of broiler body weight gain and tissue weight compared to non-supplemental birds. HS increased body temperature in both the control and 4-PBA groups, but the elevation was significantly lower in the 4-PBA group than in the control group. The plasma non-esterified fatty acid concentration was significantly increased by HS treatment in non-supplemental groups, while the increase was partially attenuated in the 4-PBA group. Moreover, 4-PBA prevented HS-induced gene elevation of the ER stress markers GRP78 and GRP94 in the skeletal muscle. These findings suggest that the 4-PBA effect may be specific to the skeletal muscle in HS-exposed birds and that 4-PBA supplementation attenuated HS-induced muscle ER stress, which could be associated with a supplementation of the body temperature elevation and lipolysis.

Objective: Palmitic acid (PA), the most abundant saturated free fatty acids, induces apoptosis in bovine mammary epithelial cells (MECs). It is suggested that oxidative stress and endoplasmic reticulum (ER) stress are key mechanisms underlying PA-induced cell death. This study aimed to investigate the interaction between ER stress and oxidative stress during PA-induced cell death in mammary alveolar cell-T (MAC-T) cells. Additionally, we examined whether L-citrulline can protect against PA-induced damage of MAC-T cells.Methods: MAC-T cells were treated with 4-phenyl butyric acid (4-PBA) or N-acetyl-Lcysteine (NAC) to inhibit PA-induced ER stress and oxidative stress, respectively. MAC-T cells were pretreated with or without L-citrulline for 48 h followed by PA treatment. Cell viability was measured with MTT assays. Intracellular reactive oxygen species (ROS) levels in MAC-T cells were assessed using 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluores cein diacetate acetyl ester dye. Real-time quantitative polymerase chain reaction was used to explore the regulation of genes associated with oxidative stress, and ER stress genes. Western blotting analysis was also carried out.Results: 4-PBA significantly reduced PA-induced mRNA expressions of activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), nuclear factor (erythroid-derived 2)-like 2 (NRF2), and intracellular ROS levels. Furthermore, NAC dramatically reduced PA-induced ROS levels and the mRNA expressions of NRF2, ATF4, and CHOP. L-citrulline pretreatment effectively rescued cell viability decreased by PA. Moreover, L-citrulline pretreatment significantly downregulated the PA-induced upregulation of GRP78, ATF4, and CHOP mRNA expression, and protein expression of p-PERK and cleaved caspase-3. PA increased intracellular ROS levels and NRF2 mRNA expression, whereas L-citrulline pretreatment remarkably reduced these levels.Conclusion: Both ER and oxidative stresses interact during PA-induced cell death in MAC-T cells, and L-citrulline could attenuate this cell death by inhibiting ER and oxidative stresses. Therefore, L-citrulline may be a promising supplement for protecting against PA-induced cell death in bovine MECs during the lactation period of dairy cows.

This study investigated the protective effects of ursodeoxycholic acid (UDCA) against PA‐induced apoptosis in the MAC‐T bovine mammary epithelial cell (bMEC) line by assessing the level of cell viability, oxidative stress indicators, and expression of endoplasmic reticulum (ER) stress markers. MAC‐T cells were pretreated with UDCA at 25, 50, and 100 μM before exposure to PA at 300 μM. UDCA was noncytotoxic at these concentrations and significantly improved cell viability, which was reduced by PA. UDCA pretreatment notably decreased PA‐induced expression of GRP78, XBP1s, ATF4, and CHOP mRNA, indicating reduced ER stress. Moreover, UDCA substantially lowered PA‐induced reactive oxygen species production and dichlorofluorescein fluorescence intensities. Although PA treatment elevated GSSG levels and disrupted redox balance by decreasing both the total GSH/GSSG and reduced GSH/GSSG ratios, UDCA effectively counteracted these effects. Specifically, UDCA reduced PA‐induced GSSG levels and restored redox balance by increasing both total and reduced GSH/GSSG ratios. These findings suggest that UDCA mitigates PA‐induced apoptosis in MAC‐T cells by enhancing redox homeostasis. Therefore, incorporating UDCA into dairy cow feed could help reduce PA‐induced cellular stress and improve milk production during periods of negative energy balance.

Exposure to chronic heat stress not only reduces body weight gain in growing broilers, but also enhances fat deposition. To elucidate this effect, numerous studies have investigated the changes in the liver, the primary site of de novo fat synthesis in avian species, and a marked increase in fat accumulation has been observed under chronic heat stress. However, the impact of heat stress on adipose tissue remains largely unclear. To investigate alterations in adipose tissue following heat-exposure, we reared growing broilers in a high-temperature environment (32 °C) for 14 d. Despite the decreased feed intake, the ratio of abdominal fat to body weight in the heat-exposed group remained comparable to that in the control group. Furthermore, the heat-exposed group exhibited a marked decrease in plasma free fatty acid concentrations. Transcriptome analysis of abdominal fat from heat-exposed and control groups indicated 459 differentially expressed genes. In the heat-exposed group, genes associated with lipid synthesis showed increased expression in the adipose tissue. Heat stimulation induced the expression of the lipoprotein lipase gene in cultured primary adipocytes. These results suggest that chronic heat exposure promotes lipoprotein lipase expression and triglyceride biosynthesis in the adipose tissue of growing broilers.