Variation in x-box binding protein 1 (XBP1) expression and its dependent endoplasmic reticulum chaperones does not regulate adiponectin secretion in dairy cows

Tumor necrosis factor-α reduces adiponectin production by decreasing transcriptional activity of peroxisome proliferator-activated receptor-γ in calf adipocytes

Adiponectin (encoded by ADIPOQ) is an adipokine that orchestrates energy homeostasis by modulating glucose and fatty acid metabolism in peripheral tissues. During the periparturient period, dairy cows often develop adipose tissue inflammation and decreased plasma adiponectin levels. Proinflammatory cytokine tumor necrosis factor-α (TNF-α) plays a pivotal role in regulating the endocrine functions of adipocytes, but whether it affects adiponectin production in calf adipocytes remains obscure. Thus, the present study aimed to determine whether TNF-α could affect adiponectin production in calf adipocytes and to identify the underlying mechanism. Adipocytes isolated from Holstein calves were differentiated and used for (1) BODIPY493/503 staining; (2) treatment with 0.1 ng/mL TNF-α for different times (0, 8, 16, 24, or 48 h); (3) transfection with peroxisome proliferator-activated receptor-γ (PPARG) small interfering RNA for 48 h followed by treatment with or without 0.1 ng/mL TNF-α for 24 h; and (4) overexpression of PPARG for 48 h followed by treatment with or without 0.1 ng/mL TNF-α for 24 h. After differentiation, obvious lipid droplets and secretion of adiponectin were observed in adipocytes. Treatment with TNF-α did not alter mRNA abundance of ADIPOQ but reduced the total and high molecular weight (HMW) adiponectin content in the supernatant of adipocytes. Quantification of mRNA abundance of endoplasmic reticulum (ER)/Golgi resident chaperones involved in adiponectin assembly revealed that ER protein 44 (ERP44), ER oxidoreductase 1α (ERO1A), and disulfide bond-forming oxidoreductase A-like protein (GSTK1) were downregulated in TNF-α-treated adipocytes, while 78-kDa glucose-regulated protein and Golgi-localizing γ-adaptin ear homology domain ARF binding protein-1 were unaltered. Moreover, TNF-α diminished nuclear translocation of PPARγ and downregulated mRNA abundance of PPARG and its downstream target gene fatty acid synthase, suggesting that TNF-α suppressed the transcriptional activity of PPARγ. In the absence of TNF-α, overexpression of PPARG enhanced the total and HMW adiponectin content in supernatant and upregulated the mRNA abundance of ADIPOQ, ERP44, ERO1A, and GSTK1 in adipocytes. However, knockdown of PPARG reduced the total and HMW adiponectin content in supernatant and downregulated the mRNA abundance of ADIPOQ, ERP44, ERO1A, and GSTK1 in adipocytes. In the presence of TNF-α, overexpression of PPARG decreased, while knockdown of PPARG further exacerbated TNF-α-induced reductions in total and HMW adiponectin secretion and gene expression of ERP44, ERO1A, and GSTK1. Overall, TNF-α reduces adiponectin assembly in the calf adipocyte, which may be partly mediated by attenuation of PPARγ transcriptional activity. Thus, locally elevated levels of TNF-α in adipose tissue may be one reason for the decrease in circulating adiponectin in periparturient dairy cows.

Tumor necrosis factor-α promotes lipolysis and reduces insulin sensitivity by activating nuclear factor kappa B and c-Jun N-terminal kinase in primary bovine adipocytes

Sustained lipolysis and insulin resistance increase the risk of metabolic dysfunction in dairy cows during the transition period. Proinflammatory cytokines are key regulators of adipose tissue metabolism in nonruminants, but biological functions of these molecules in ruminants are not well known. Thus, the objective of this study was to investigate whether tumor necrosis factor-α (TNF-α) could affect insulin sensitivity and lipolysis in bovine adipocytes as well as the underlying mechanisms. Bovine adipocytes (obtained from the omental and mesenteric adipose depots) isolated from 5 Holstein female calves (1 d old) with similar body weight (median: 36.9 kg, range: 35.5-41.2 kg) were differentiated and used for (1) treatment with different concentrations of TNF-α (0, 0.1, 1, or 10 ng/mL) for 12 h; (2) pretreatment with 10 μM lipolytic agonist isoproterenol (ISO) for 3 h, followed by treatment with or without 10 ng/mL TNF-α for 12 h; and (3) pretreatment with the c-Jun N-terminal kinase (JNK) inhibitor SP600125 (20 μM for 2 h) and nuclear factor kappa B (NF-κB) inhibitor BAY 11-7082 (10 μM for 1 h) followed by treatment with or without 10 ng/mL TNF-α for 12 h. The TNF-α increased glycerol content in supernatant, decreased triglyceride content and insulin-stimulated phosphorylation of protein kinase B suggesting activation of lipolysis and impairment of insulin sensitivity. The TNF-α reduced cell viability, upregulated mRNA abundance of Caspase 3 (CASP3), an apoptosis marker, and increased activity of Caspase 3. In addition, increased phosphorylation of NF-κB and JNK, upregulation of mRNA abundance of interleukin-6 (IL-6), TNFA, and suppressor of cytokine signaling 3 (SOCS3) suggested that TNF-α activated NF-κB and JNK signaling pathways. Furthermore, ISO plus TNF-α-activated NF-κB and JNK signaling pathway to a greater extent than TNF-α alone. Combining TNF-α and ISO aggravated TNF-α-induced apoptosis, insulin insensitivity and lipolysis. In the absence of TNF-α, inhibition of NF-κB and JNK did not alter glycerol content in supernatant, triglyceride content or insulin-stimulated phosphorylation of protein kinase B. In the presence of TNF-α, inhibition of NF-κB and JNK alleviated TNF-α-induced apoptosis, insulin insensitivity and lipolysis. Overall, TNF-α impairs insulin sensitivity and induces lipolysis and apoptosis in bovine adipocytes, which may be partly mediated by activation of NF-κB and JNK. Thus, the data suggested that NF-κB and JNK are potential therapeutic targets for alleviating lipolysis dysregulation and insulin resistance in adipocytes.

Fibroblast growth factor-21 improves insulin action in nonlactating ewes

During metabolically demanding physiological states, ruminants and other mammals coordinate nutrient use among tissues by varying the set point of insulin action. This set point is regulated in part by metabolic hormones with some antagonizing (e.g., growth hormone and TNFα) and others potentiating (e.g., adiponectin) insulin action. Fibroblast growth factor-21 (FGF21) was recently identified as a sensitizing hormone in rodent and primate models of defective insulin action. FGF21 administration, however, failed to improve insulin action in dairy cows during the naturally occurring insulin resistance of lactation, raising the possibility that ruminants as a class of animals or lactation as a physiological state are unresponsive to FGF21. To start addressing this question, we asked whether FGF21 could improve insulin action in nonlactating ewes. Gene expression studies showed that the ovine FGF21 system resembles that of other species, with liver as the major site of FGF21 expression and adipose tissue as a target tissue based on high expression of the FGF21 receptor complex and activation of p44/42 extracellular signal-regulated kinase (ERK1/2) following exogenous FGF21 administration. FGF21 treatment for 13 days reduced plasma glucose and insulin over the entire treatment period and improved glucose disposal during a glucose tolerance test. FGF21 increased plasma adiponectin by day 3 of treatment but had no effect on the plasma concentrations of total, C16:0-, or C18:0-ceramide. Overall, these data confirm that the insulin-sensitizing effects of FGF21 are conserved in ruminants and raise the possibility that lactation is an FGF21-resistant state.

Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) influences adipocytes injuries through triggering XBP1 and activating mitochondria-mediated apoptosis

Obesity is an important public-health problem worldwide. This study aimed to determine effects of porphyromonas gingivalis lipopolysaccharide (Pg-LPS) on adipocytes injuries and explore associated mechanisms. Adipocytes were isolated from SD rats. pLVX-XBP1 (XBP1 over-expression) and pLVX-XBP1-RNAi (silencing XBP1) were structured and transfected into adipocytes. All adipocytes were divided into pLVX-NC, pLVX-XBP1, pLVX-NC+Pg-LPS and pLVX-XBP1+ Pg-LPS group. Oil-Red O staining was employed to identify isolated adipocytes. Quantitative real-time PCR (qRT-PCR) was used to examine gene transcription of IL-6, TNF-α, leptin, adiponectin. Western blotting was used to detect Bax and caspase-3 expression. Adipocytes were successfully isolated and identified with Oil-Red O staining. Both XBP1 mimic and XBP1 RNAi were effectively transfected into adipocytes with higher expressing efficacy. XBP1 over-expression significantly aggravated Pg-LPS induced inflammatory response compared to adipocytes without Pg-LPS treatment (p<0.05). Pg-LPS significantly enhanced leptin and inhibited adiponectin expression by up-regulating XBP1 expression (p<0.05). XBP1 silence significantly alleviated Pg-LPS induced inflammatory response and reduced leptin, enhanced adiponectin expression in Pg-LPS treated adipocytes compared to adipocytes without Pg-LPS treatment (p<0.05). Pg-LPS induced apoptosis of adipocytes by enhancing XBP1 expression and modulating Bcl-2/Bax pathway associated molecules. In conclusion, Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) induces adipocytes injuries through modulating XBP1 expression and initialling mitochondria-mediated apoptosis.

Fibroblast growth factor-21 (FGF21) administration to early-lactating dairy cows. I. Effects on signaling and indices of insulin action

Modern dairy cows rely on hormonally driven mechanisms to coordinate the metabolic adaptations needed to meet the energy and nutrient deficits of early lactation. In the case of glucose, dairy cows cope with its scarcity during early lactation via reduced plasma concentrations of insulin and the insulin sensitizing hormone adiponectin and increased insulin resistance. Reduced insulin action promotes diversion of available glucose to the mammary gland but increases susceptibility to diseases if excessive. In earlier work, we reported that the insulin sensitizing hormone fibroblast growth factor-21 (FGF21) is increased in periparturient dairy cows and identified liver and adipose tissue as possible targets. These observations raised the possibility that FGF21 acts directly on these tissues to limit the insulin resistance of early lactation. To test this hypothesis, dairy cows were randomly assigned on d 12.6 ± 2.2 (± standard error) of lactation to receive either excipient (n = 6) or recombinant human FGF21 (n = 7), first as an FGF21 bolus of 3 mg/kg of body weight, followed 2 d later by a constant i.v. infusion of FGF21 at the rate of 6.3 mg/kg of metabolic body weight for 9 consecutive days. Biopsies of liver and adipose tissue were collected during the bolus phase of the experiment and used to analyze FGF21 signaling by Western blotting and expression of its receptor components by quantitative PCR. Bolus FGF21 administration caused a 4-fold increase in p44/42 MAPK (ERK1/2) activation in adipose tissue but had no effect on AKT and signal transducer and activator of transcription-3 (STAT3) signaling. The liver expressed negligible levels of the preferred FGF21 receptor FGFR1c and failed to mount any FGF21 signaling response. The FGF21 administered as a bolus had no effect on plasma glucose or insulin and did not stimulate an acute release of adiponectin from adipose tissue. Similarly, FGF21 infusion had no effect on plasma levels of glucose or insulin measured over the 9-d infusion or on glucose disposal during an i.v. glucose tolerance test performed on d 8 of infusion. Finally, the chronic FGF21 infusion had no effect on indices of adiponectin production, including plasma adiponectin and adipose tissue mRNA abundance of adiponectin and the endoplasmic reticulum chaperones ERO1A and DSBA-L involved in the assembly of adiponectin into multimeric complexes. These data show that human FGF21 does not act as an insulin sensitizer during the energy and glucose deficit of early lactation but do not rule out such a role in other physiological states.

XBP1 inhibits mesangial cell apoptosis in response to oxidative stress via the PTEN/AKT pathway in diabetic nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus (DM) that frequently results in renal disease, and is characterized by a variety of symptoms, including albuminuria. It has been shown that apoptosis of glomerular mesangial cells (MCs) can aggravate albuminuria and contribute to the development of diabetic glomerulosclerosis. Hence, determination of the mechanisms leading to MC apoptosis may help us gain insights into the pathogenesis of DN. As our understanding of the role of high glucose (HG) in MC apoptosis remains elusive, we explored the interplay between X‐box binding protein 1 (XBP1) and MC apoptosis in this study. XBP1 was observed to be downregulated both in vivo and in vitro. Treatment of XBP1‐overexpressing cells with HG resulted in a decrease of reactive oxygen species (ROS) and a suppression of cell apoptosis, concomitant with decreases in cleaved caspase‐3 and Bax. Subsequent analyses demonstrated that XBP1 overexpression inhibited the expression of phosphatase and tensin homolog deleted on chromosome ten (PTEN) and enhanced the activation of AKT in MCs exposed to HG. In addition, XBP1‐induced injuries in MC were reversed by overexpression of PTEN, and XBP1 inhibited apoptosis, which was mediated by the activated PTEN/AKT signaling pathway. Thus, our data indicate that XBP1 can activate the PTEN/AKT signaling pathway, thereby alleviating oxidative stress caused by HG or MC apoptosis. These findings suggest that XBP1 may have potential in the development of treatment methods for DN.