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Endoplasmic reticulum (ER) stress can be induced by various stimuli and triggers the unfolded protein response to activate intracellular signaling pathways that are mediated by 3 ER-resident sensors: inositol requiring protein-1α (IRE1α), PKR-like ER kinase (PERK), and activating transcription factor-6 (ATF6). In nonruminants, ER stress plays a critical role in hepatic insulin resistance. However, whether ER stress plays a role in nonesterified fatty acid (NEFA)-induced hepatic insulin resistance in dairy cows is still unknown. Experiments were conducted using primary bovine hepatocytes isolated from 5 healthy calves (body weight: 30–40 kg; 1 d old). First, hepatocytes were treated with NEFA (1.2 m M) for 0.5, 1, 2, 3, 5, 7, 9, or 12 h. Treatment with NEFA elevated abundance of phosphorylated IRE1α and PERK, and cleavage of ATF6, along with the ER stress-associated genes XBP1 , ATF4 , and DNAJC3 , resulting in both linear and quadratic effects. Furthermore, ER Tracker red staining and transmission electron microscopy results indicated that ER was dilated and degranulated in response to NEFA treatment, suggesting that ER stress was induced by NEFA treatment in bovine hepatocytes. Second, to assess the effect of ER stress on NEFA-induced insulin resistance, hepatocytes were treated with different concentrations of NEFA (0, 0.6, 1.2, or 2.4 m M) for 5 h with or without tauroursodeoxycholic acid (TUDCA, a canonical inhibitor of ER stress). Here, NEFA induced insulin resistance by increasing the abundance of insulin receptor substrate-1 (IRS1) phosphorylation at the inhibitory residue Ser 307 (S307) and decreasing the abundance of phosphorylated protein kinase B (AKT) and glycogen synthase kinase-3β (GSK3β) in a dose-dependent manner. This was accompanied by upregulation of an abundance of gluconeogenic genes [phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6-Pase)]. These detrimental effects of NEFA on insulin signaling could be reversed with TUDCA treatment, indicating a mechanistic link between ER stress and NEFA-induced insulin resistance. In a third experiment, pGPU6/GFP/Neo vectors containing short hairpin RNA targeting IRE1α were used to silence IRE1α transcription, and GSK2656157 (PERK phosphorylation inhibitor) and 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF; an inhibitor of ATF6) were used to block PERK and ATF6 branches, respectively. Notably, the silencing of the IRE1α branch improved NEFA-induced insulin resistance by decreasing phosphorylation of IRS1 (S307) and increasing phosphorylation of AKT and GSK3β, and reducing PEPCK and G6-Pase mRNA abundance, which was likely dependent on IRE1α kinase activity. Similarly, blockage of the PERK branch increased phosphorylation of AKT and GSK3β, and reduced PEPCK and G6-Pase mRNA abundance, but had no effect on phosphorylation of IRS1 (S307). However, results showed that inhibition of the ATF6 branch had no effects on phosphorylation of IRS1, AKT, and GSK3β, and instead found increasing PEPCK and G6-Pase mRNA abundance. Taken together, data in the present study found that impeding IRE1α and PERK signaling might aid in relieving hepatic insulin resistance. However, the more detailed mechanisms of how IRE1α and PERK signaling contribute to hepatic insulin resistance in dairy cows remain to be determined. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of guanidinoacetic acid (GAA) and betaine on growth performance, meat quality and metabolism of ducks. A total of 384-one-day-old Cherry Valley meat ducks (55.75 ± 0.55 g) were randomly assigned to four treatments with 6 replicates of 16 ducks. Ducks were fed a basal diet (control) or a test diet supplemented with 0.6 g GAA/kg, 2.0 g betaine/kg, or 0.6 g GAA/kg + 2.0 g betaine/kg. The results showed that compared with the control group, GAA and betaine improved feed conversation ratio from day 1 to 14 and 1 to 35 and body weight at 35 days of age (p <.05). GAA and betaine increased breast muscle percentage while reduced abdominal fat percentage, and drip loss and shear force of breast muscle (p <.05). GAA and betaine lowered free serine, methionine, tryptophan and total amino acid contents in muscles, increased free serine, aspartic acid, phenylalanine and tryptophan contents in plasma (p <.05). There was a synergistic effect on non-esterified fatty acid, lactic acid and uric acid between GAA and betaine. GAA and betaine increased the creatine kinase activity in plasma and creatine and ATP content in breast muscle, decreased the lactate dehydrogenase and L-arginine: glycine amidino transferase activities (p <.05). In conclusion, supplementation of GAA and betaine improved the growth performance and meat quality of ducks by accelerating energy metabolism. There was a synergistic effect on NEFA, LA and UA concentrations in plasma of ducks between GAA and betaine. Supplementing GAA and betaine improved the growth performance and meat quality of ducks. Adding GAA and betaine accelerated the energy metabolism of ducks. There was a synergistic effect on non-esterified fatty acid, lactic acid and uric acid concentrations in the plasma of ducks between GAA and betaine. [ABSTRACT FROM AUTHOR]