Apoptosis induced by t10,c12-conjugated linoleic acid is mediated by an atypical endoplasmic reticulum stress response

TRB3 Deletion Has a Limited Effect on Milk Fat Synthesis and Milk Fat Depression in C57BL/6N Mice

BACKGROUND

Regulation of the endoplasmic reticulum (ER) stress pathway is critical to mammary epithelial cell function throughout pregnancy, lactation, and involution. Treatment with trans-10, cis-12 conjugated linoleic acid (t10c12CLA) suppresses mammary lipogenesis and stimulates the ER stress pathway. The ER stress pathway includes tribbles pseudokinase 3 (TRB3), a protein that regulates cellular energy and insulin signaling.

OBJECTIVES

Our objective was to describe the effect of TRB3 deficiency on milk fat synthesis and determine if TRB3 deficiency protects against suppression of mammary lipogenesis.

METHODS

First, mammary Trb3 expression was observed throughout pregnancy and lactation using ancillary microarray data (n = 4/time point). Second, intake, litter growth, and milk clot fatty acid (FA) profile of Trb3 knockout (KO) C57BL/6N mice were compared with wild-type (WT) and heterozygous (HET) mice throughout first (n ≥ 8/group) and second (n ≥ 6/group) lactation. Lastly, the interaction between Trb3 genotype and 2 treatments that suppress mammary lipogenesis, t10c12CLA and high safflower oil (HO) diet, was investigated in a 2 × 2 factorial design (n ≥ 6/group).

RESULTS

Trb3 expression was higher during late pregnancy and lactation. Trb3 KO and HET mice had lower feed intake, dam weight, and litter growth throughout first, but not second, lactation than WT mice. Treatment with t10c12CLA decreased litter growth (28%; P < 0.0001) and feed intake (8%; P < 0.0001) regardless of Trb3 genotype. When fed the HO diet, Trb3 KO mice had 17% higher mammary de novo synthesized FAs (<16 carbons; P int = 0.002) than WT mice. Mammary ER stress and lipogenic genes were mostly unaltered by Trb3 deficiency.

CONCLUSIONS

Overall, TRB3 plays a minor role in regulating mammary lipogenesis, because Trb3 deficiency had only a limited protective effect against diet-induced suppression of lipogenesis.

High rumen degradable starch decreased goat milk fat via trans-10, cis-12 conjugated linoleic acid-mediated downregulation of lipogenesis genes, particularly, INSIG1

Background

Starch is an important substance that supplies energy to ruminants. To provide sufficient energy for high-yielding dairy ruminants, they are typically fed starch-enriched diets. However, starch-enriched diets have been proven to increase the risk of milk fat depression (MFD) in dairy cows. The starch present in ruminant diets could be divided into rumen-degradable starch (RDS) and rumen escaped starch (RES) according to their different degradation sites (rumen or intestine). Goats and cows have different sensitivities to MFD. Data regarding the potential roles of RDS in milk fat synthesis in the mammary tissue of dairy goats and in regulating the occurrence of MFD are limited.

Results

Eighteen Guanzhong dairy goats (day in milk = 185 ± 12 d) with similar parity, weight, and milk yield were selected and randomly assigned to one of three groups (n = 6), which were fed an LRDS diet (Low RDS = 20.52%), MRDS diet (Medium RDS = 22.15%), or HRDS diet (High RDS = 24.88%) for 5 weeks. Compared with that of the LRDS group, the milk fat contents in the MRDS and HRDS groups significantly decreased. The yields of short-, medium- and long-chain fatty acids decreased in the HRDS group. Furthermore, increased RDS significantly decreased ruminal B. fibrisolvens and Pseudobutyrivibrio abundances and increased the trans-10, cis-12 conjugated linoleic acid (CLA) and trans-10 C18:1 contents in the rumen fluid.

A multiomics study revealed that the HRDS diet affected mammary lipid metabolism down-regulation of ACSS2, MVD, AGPS, SCD5, FADS2, CERCAM, SC5D, HSD17B7, HSD17B12, ATM, TP53RK, GDF1 and LOC102177400. Remarkably, the significant decrease of INSIG1, whose expression was depressed by trans-10, cis-12 CLA, could reduce the activity of SREBP and, consequently, downregulate the downstream gene expression of SREBF1.

Conclusions

HRDS-induced goat MFD resulted from the downregulation of genes involved in lipogenesis, particularly, INSIG1. Specifically, even though the total starch content and the concentrate-to-fiber ratio were the same as those of the high-RDS diet, the low and medium RDS diets did not cause MFD in lactating goats.

Trans10,cis12 conjugated linoleic acid inhibits proliferation and migration of ovarian cancer cells by inducing ER stress, autophagy, and modulation of Src

The goal of this study was to investigate the anti-cancer effects of Trans10,cis12 conjugated linoleic acid (t10,c12 CLA). MTT assays and QCM™ chemotaxis 96-wells were used to test the effect of t10,c12 CLA on the proliferation and migration and invasion of cancer cells. qPCR and Western Blotting were used to determine the expression of specific factors. RNA sequencing was conducted using the Illumina platform and apoptosis was measured using a flow cytometry assay. t10,c12 CLA (IC50, 7 μM) inhibited proliferation of ovarian cancer cell lines SKOV-3 and A2780. c9,t11 CLA did not attenuate the proliferation of these cells. Transcription of 165 genes was significantly repressed and 28 genes were elevated. Genes related to ER stress, ATF4, CHOP, and GADD34 were overexpressed whereas EDEM2 and Hsp90, genes required for proteasomal degradation of misfolded proteins, were downregulated upon treatment. While apoptosis was not detected, t10,c12 CLA treatment led to 9-fold increase in autophagolysosomes and higher levels of LC3-II. G1 cell cycle arrest in treated cells was correlated with phosphorylation of GSK3β and loss of β-catenin. microRNA miR184 and miR215 were upregulated. miR184 likely contributed to G1 arrest by downregulating E2F1. miR215 upregulation was correlated with increased expression of p27/Kip-1. t10,c12 CLA-mediated inhibition of invasion and migration correlated with decreased expression of PTP1b and decreased Src activation by inhibiting phosphorylation at Tyr416. Due to its ability to inhibit proliferation and migration, t10,c12 CLA should be considered for treatment of ovarian cancer.

Developmental regulation and induction of cytochrome P450 2W1, an enzyme expressed in colon tumors

Cytochrome P450 2W1 (CYP2W1) is expressed predominantly in colorectal and also in hepatic tumors, whereas the levels are insignificant in the corresponding normal human adult tissues. CYP2W1 has been proposed as an attractive target for colorectal cancer (CRC) therapy by exploiting its ability to activate duocarmycin prodrugs to cytotoxic metabolites. However, its endogenous function, regulation and developmental pattern of expression remain unexplored. Here we report the CYP2W1 developmental expression in the murine and human gastrointestinal tissues. The gene expression in the colon and small intestine commence at early stages of embryonic life and is completely silenced shortly after the birth. Immunohistochemical analysis of human fetal colon revealed that CYP2W1 expression is restricted to the crypt cells. The silencing of CYP2W1 after birth correlates with the increased methylation of CpG-rich regions in both murine and human CYP2W1 genes. Analysis of CYP2W1 expression in the colon adenocarcinoma cell line HCC2998 revealed that the gene expression can be induced by e.g. the antitumor agent imatinib, linoleic acid and its derivatives. The imatinib mediated induction of CYP2W1 suggests an adjuvant therapy to treatment with duocarmycins that thus would involve induction of tumor CYP2W1 levels followed by the CYP2W1 activated duocarmycin prodrugs. Taken together these data strongly support further exploration of CYP2W1 as a specific drug target in CRC.

Supplementation with conjugated linoeic acid decreases pig back fat deposition by inducing adipocyte apoptosis

Background

Conjugated linoleic acid (CLA), a C18 fatty acid with conjugated double bonds, has been shown to serve as a powerful anti-obesity agent by several research groups, although the precise mechanism remains elusive. Previous studies showed that CLA induced apoptosis in 3T3-L1 cells and in mice. The aim of this research was to clarify the role of CLA in adipocyte apoptosis in pigs, a relevant model for obesity research.

Results

Our results clearly show that back fat deposition of CLA-fed pigs was significantly lower than that of pigs in the control group. Moreover, some typical apoptotic cells were observed among the adipocytes of CLA-fed pigs. Furthermore, the CLA-fed pigs had reduced expression of the anti-apoptosis factor Bcl-2 and increased expression of the pro-apoptosis factors Bax and P53. Subsequently, increased cytochrome C was released from the mitochondria to the endochylema, and the caspase cascade was activated, resulting in cellular apoptosis. These results are consistent with the effects of Bcl-2 and Bax in regulating CLA-induced adipocyte apoptosis via the mitochondrial signaling pathway. However, the increased expression of tumor necrosis factor (TNF)-α and its receptor TNFR indicate that the effect of CLA might partly be through the death receptor signaling pathway in adipose cells.

Conclusions

Our study has demonstrated that CLA reduces pig body fat deposition, an outcome that is partly meditated by apoptosis of adipose cells, and that both the mitochondrial pathway and the death receptor pathway are involved in this effect.

Trans-10, cis-12 conjugated linoleic acid reduces neutral lipid content and may affect cryotolerance of in vitro-produced crossbred bovine embryos

Background

Due to high neutral lipids accumulation in the cytoplasm, in vitro-produced embryos from Bos primigenius indicus and their crosses are more sensitive to chilling and cryopreservation than those from Bos primigenius taurus. The objective of the present study was to evaluate the effects of trans-10, cis-12 conjugated linoleic acid (CLA) on the development and cryotolerance of crossbred Bos primigenius taurus x Bos primigenius indicus embryos produced in vitro, and cultured in the presence of fetal calf serum. Bovine zygotes (n = 1,692) were randomly assigned to one of the following treatment groups: 1) Control, zygotes cultured in Charles Rosenkrans 2 amino acid (CR2aa) medium (n = 815) or 2) CLA, zygotes cultured in CR2aa medium supplemented with 100 μmol/L of trans-10, cis-12 CLA (n = 877). Embryo development (cleavage and blastocyst rates evaluated at days 3 and 8 of culture, respectively), lipid content at morula stage (day 5) and blastocyst cryotolerance (re-expansion and hatching rates, evaluated 24 and 72 h post-thawing, respectively) were compared between groups. Additionally, selected mRNA transcripts were measured by Real–Time PCR in blastocyst stage.

Results

The CLA treatment had no effect on cleavage and blastocyst rates, or on mRNA levels for genes related to cellular stress and apoptosis. On the other hand, abundance of mRNA for the 1-acylglycerol-3-phosphate 0-acyltransferase-encoding gene (AGPAT), which is involved in triglycerides synthesis, and consequently neutral lipid content, were reduced by CLA treatment. A significant increase was observed in the re-expansion rate of embryos cultured with trans-10, cis-12 CLA when compared to control (56.3 vs. 34.4%, respectively, P = 0.002). However, this difference was not observed in the hatching rate (16.5 vs. 14.0%, respectively, P = 0.62).

Conclusions

The supplementation with trans-10, cis-12 CLA isomer in culture medium reduced the lipid content of in vitro produced bovine embryos by reducing the gene expression of 1-acylglycerol 3-phosphate 0-acyltransferase (AGPAT) enzyme. However, a possible improvement in embryo cryotolerance in response to CLA, as suggested by increased blastocyst re-expansion rate, was not confirmed by hatching rates.

RedOx status, proteasome and APEH: insights into anticancer mechanisms of t10,c12-conjugated linoleic acid isomer on A375 melanoma cells

This study describes the investigation of the efficiency of conjugated linoleic acid (CLA) isomers in reducing cancer cells viability exploring the role of the oxidative stress and acylpeptide hydrolase (APEH)/proteasome mediated pathways on pro-apoptotic activity of the isomer trans10,cis12 (t10,c12)-CLA. The basal activity/expression levels of APEH and proteasome (β-5 subunit) were preliminarily measured in eight cancer cell lines and the functional relationship between these enzymes was clearly demonstrated through their strong positive correlation. t10,c12-CLA efficiently inhibited the activity of APEH and proteasome isoforms in cell-free assays and the negative correlation between cell viability and caspase 3 activity confirmed the pro-apoptotic role of this isomer. Finally, modulatory effects of t10,c12-CLA on cellular redox status (intracellular glutathione, mRNA levels of antioxidant/detoxifying enzymes activated through NF-E2-related factor 2, Nrf2, pathway) and on APEH/β-5 activity/expression levels, were investigated in A375 melanoma cells. Dose- and time-dependent variations of the considered parameters were established and the resulting pro-apoptotic effects were shown to be associated with an alteration of the redox status and a down-regulation of APEH/proteasome pathway. Therefore, our results support the idea that these events are involved in ROS-dependent apoptosis of t10,c12-CLA-treated A375 cells. The combined inhibition, triggered by t10,c12-CLA, via the modulation of APEH/proteasome and Nrf2 pathway for treating melanoma, is suggested as a subject for further in vivo studies.

S-adenosyl methionine prevents endothelial dysfunction by inducing heme oxygenase-1 in vascular endothelial cells

S-adenosyl methionine (SAM) is a key intermediate in the metabolism of sulfur amino acids and is a major methyl donor in the cell. Although the low plasma level of SAM has been associated with atherosclerosis, the effect of SAM administration on atherosclerosis is not known. Endothelial dysfunction is an early prerequisite for atherosclerosis. This study was undertaken to investigate the possible preventive effect of SAM on endothelial dysfunction and the molecular mechanism of its action. SAM treatment prevented endothelial dysfunction in high fat diet (HFD)-fed rats. In cultured human aortic endothelial cells, linoleic acid (LA) increased and SAM decreased cell apoptosis and endoplasmic reticulum stress. Both LA and SAM increased heme oxygenase-1 (HO-1) expression in an NF-E2-related factor 2-dependent manner. However, knockdown of HO-1 reversed only the SAM-induced preventive effect of cell apoptosis. The LA-induced HO-1 expression was dependent on PPARα, whereas SAM induced HO-1 in a PPAR-independent manner. These data demonstrate that SAM treatment prevents endothelial dysfunction in HFDfed animals by inducing HO-1 in vascular endothelial cells. In cultured endothelial cells, SAM-induced HO-1 was responsible for the observed prevention of cell apoptosis. We propose that SAM treatment may represent a new therapeutic strategy for atherosclerosis.

Glycyrrhiza and Uncaria Hook contribute to protective effect of traditional Japanese medicine yokukansan against amyloid β oligomer-induced neuronal death

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan, a traditional Japanese (Kampo) medicine, composed of seven medicinal herbs has been traditionally used to treat neurosis, insomnia, and night crying and irritability in children. Recently, this medicine has been reported to improve the behavioral and psychological symptoms of dementia (BPSD) that often become problematic in patients with Alzheimer's disease (AD).

AIM OF THE STUDY

Amyloid β (Aβ) oligomers, which are extremely toxic to neurons, are involved in neurodegeneration in AD. In animals, yokukansan has been proven to improve memory impairments and BPSD-like behavior in transgenic mice overexpressing amyloid precursor protein and mice intracerebroventricularly injected with Aβ oligomers. These results suggest that yokukansan is potentially able to reduce the neurotoxicity of Aβ oligomers. Therefore, the present study aimed to explore the improving effects brought by yokukansan that consists of seven herbs for Aβ oligomer-induced neurotoxicity in vitro and to identify the candidate herbs in yokukansan's action.

MATERIALS AND METHODS

Primary cultured rat cortical neurons were used. Neurotoxicity induced by Aβ oligomers (3µM) and improving effects of yokukansan (300-1000 µg/mL) and its constituent herbs were evaluated in MTT assay, DNA fragmentation analysis, and electron microscopic analysis at 48h after treatment with Aβ oligomers and drugs. Moreover, changes in expression of genes related to endoplasmic reticulum (ER) stress and in caspase-3 activity that is the enzyme closely related to apoptosis were analyzed to investigate the underlying mechanisms.

RESULTS

Yokukansan ameliorated Aβ oligomer-induced neuronal damage in a dose-dependent manner in the MTT assay. This drug also suppressed DNA fragmentation caused by Aβ oligomers. Electron microscopic analysis suggested that yokukansan reduced karyopyknosis and the expansion of rough ER caused by Aβ oligomers. However, neither Aβ oligomers nor yokukansan affected the mRNA expression of any ER stress-related genes, including CHOP and GRP78. On the other hand, yokukansan dose-dependently suppressed Aβ oligomer-induced activation of caspase-3. Among the seven constituents of yokukansan, Glycyrrhiza and Uncaria Hook (60-200 µg/mL) suppressed Aβ oligomer-induced neuronal damage, DNA fragmentation, karyopyknosis, and caspase-3 activation to almost the same extent as yokukansan.

CONCLUSIONS

The present results suggest that yokukansan possesses an ameliorative effect against Aβ oligomer-induced neuronal apoptosis through the suppression of caspase-3 activation. Glycyrrhiza and Uncaria Hook may, at least in part, contribute to the neuroprotective effect of yokukansan. These mechanisms may underlie the improving effects of yokukansan on memory impairment and BPSD-like behaviors induced by Aβ oligomers.

Trans-10, cis 12-Conjugated Linoleic Acid-Induced Milk Fat Depression Is Associated with Inhibition of PPARγ Signaling and Inflammation in Murine Mammary Tissue

Exogenous trans-10, cis-12-CLA (CLA) reduces lipid synthesis in murine adipose and mammary (MG) tissues. However, genomewide alterations in MG and liver (LIV) associated with dietary CLA during lactation remain unknown. We fed mice (n = 5/diet) control or control + trans-10, cis-12-CLA (37 mg/day) between d 6 and d 10 postpartum. The 35,302 annotated murine exonic evidence-based oligo (MEEBO) microarray and quantitative RT-PCR were used for transcript profiling. Milk fat concentration was 44% lower on d 10 versus d 6 due to CLA. The CLA diet resulted in differential expression of 1,496 genes. Bioinformatics analyses underscored that a major effect of CLA on MG encompassed alterations in cellular signaling pathways and phospholipid species biosynthesis. Dietary CLA induced genes related to ER stress (Xbp1), apoptosis (Bcl2), and inflammation (Orm1, Saa2, and Cp). It also induced marked inhibition of PPAR γ signaling, including downregulation of Pparg and Srebf1 and several lipogenic target genes (Scd, Fasn, and Gpam). In LIV, CLA induced hepatic steatosis probably through perturbations in the mitochondrial functions and induction of ER stress. Overall, results from this study underscored the role of PPAR γ signaling on mammary lipogenic target regulation. The proinflammatory effect due to CLA could be related to inhibition of PPAR γ signaling.

The phospholipase C inhibitor U73122 attenuates trans-10, cis-12 conjugated linoleic acid-mediated inflammatory signaling and insulin resistance in human adipocytes

We have demonstrated that trans-10, cis-12 conjugated linoleic acid (18:2t10,c12)-mediated delipidation of human adipocytes was dependent on increased intracellular calcium and activation of inflammatory signaling in human primary adipocytes. These data are consistent with the actions of diacylglycerol and inositol triphosphate derived from phospholipase C (PLC)-dependent cell signaling. To test the hypothesis that PLC was an upstream activator of these cellular responses to 18:2t10,c12, primary cultures of human adipocytes were pretreated with 1-[6-((17β-3-methoxyestra-1,3,5 (10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U73122), a universal PLC inhibitor, followed by 18:2t10,c12 treatment. U73122 attenuated 18:2t10,c12-mediated insulin resistance within 48 h and suppression of the mRNA levels of peroxisome proliferator-activated receptor (PPAR)γ, insulin-stimulated glucose transporter-4, acetyl-CoA carboxylase-1, and stearoyl-CoA desaturase-1, and the protein levels of PPARγ within 18-24 h. U73122 inhibited 18:2t10,c12-mediated induction of the inflammatory-related genes calcium/calmodulin-dependent protein kinase-β, cyclooxygenase-2, monocyte chemoattractant protein-1, interleukin (IL)-6, and IL-8, secretion of IL-6 and IL-8, and the activation of extracellular signal-related kinase, c-Jun N-terminal kinase, and c-Jun within 18-24 h. Moreover, 18:2t10,c12 increased the mRNA levels of heat shock proteins within 6-24 h and intracellular calcium concentrations within 3 min, which were inhibited by U73122. Lastly, 18:2t10,c12 increased the abundance of PLCγ1 in the plasma membrane within 3 min. Taken together, these data suggest that PLC plays an important role in 18:2t10,c12-mediated activation of intracellular calcium accumulation, inflammatory signaling, delipidation, and insulin resistance in human primary adipocytes.

Cross regulation of sirtuin 1, AMPK, and PPARγ in conjugated linoleic acid treated adipocytes

Trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) reduces triglyceride (TG) levels in adipocytes through multiple pathways, with AMP-activated protein kinase (AMPK) generally facilitating, and peroxisome proliferator-activated receptor γ (PPARγ) generally opposing these reductions. Sirtuin 1 (SIRT1), a histone/protein deacetylase that affects energy homeostasis, often functions coordinately with AMPK, and is capable of binding to PPARγ, thereby inhibiting its activity. This study investigated the role of SIRT1 in the response of 3T3-L1 adipocytes to t10c12 CLA by testing the following hypotheses: 1) SIRT1 is functionally required for robust TG reduction; and 2) SIRT1, AMPK, and PPARγ cross regulate each other. These experiments were performed by using activators, inhibitors, or siRNA knockdowns that affected these pathways in t10c12 CLA-treated 3T3-L1 adipocytes. Inhibition of SIRT1 amounts or activity using siRNA, sirtinol, nicotinamide, or etomoxir attenuated the amount of TG loss, while SIRT1 activator SRT1720 increased the TG loss. SRT1720 increased AMPK activity while sirtuin-specific inhibitors decreased AMPK activity. Reciprocally, an AMPK inhibitor reduced SIRT1 activity. Treatment with t10c12 CLA increased PPARγ phosphorylation in an AMPK-dependent manner and increased the amount of PPARγ bound to SIRT1. Reciprocally, a PPARγ agonist attenuated AMPK and SIRT1 activity levels. These results indicated SIRT1 increased TG loss and that cross regulation between SIRT1, AMPK, and PPARγ occurred in 3T3-L1 adipocytes treated with t10c12 CLA.

Short communication: Endoplasmic reticulum stress gene network expression in bovine mammary tissue during the lactation cycle

The endoplasmic reticulum (ER) has a crucial role in cellular metabolism. Recent studies in nonruminants discovered that components of the ER stress pathway, induced during the unfolded protein response, play critical roles in regulating lipogenesis. The bovine mammary gland faces extreme metabolic stress at the onset of lactation due primarily to the increase in flux through pathways associated with milk fat and protein synthesis. Our objective was to study, via quantitative real-time PCR, the expression of the ER stress pathway components P58IPK, PERK, XBP1, ATF4, ATF3, ATF6, CHOP, MBTPS1, GRP94, and BiP in mammary tissue (n=7 cows × 5 time points) collected at -15, 1, 15, 60, and 240 d relative to parturition. Expression of P58IPK and ATF4 increased to a peak at d 60, followed by a decrease by d 240 postpartum. Despite the decrease in expression by 240 d, P58IPK remained higher than prepartal levels (d -15). Expression patterns of ATF3 and CHOP were similar and peaked at d 15, followed by a decrease through d 240, at which point CHOP expression was still greater than prepartal levels. The sharp increase in milk production postpartum (d 15) as well as apoptosis during late lactation (240 d) may have induced a pseudo unfolded protein response state. This is supported by the similar expression patterns of P58IPK and PERK. In the context of lactation, however, transcriptional changes in the ER stress pathway at different stages of the lactation cycle are a normal aspect of the tissue's adaptation to the changing physiological state.

Oleic acid attenuates trans-10,cis-12 conjugated linoleic acid-mediated inflammatory gene expression in human adipocytes

The weight loss supplement conjugated linoleic acid (CLA) consists of an equal mixture of trans-10,cis-12 (10,12) and cis-9,trans-11 (9,11) isomers. However, high levels of mixed CLA isomers, or the 10,12 isomer, causes chronic inflammation, lipodystrophy, or insulin resistance. We previously demonstrated that 10,12 CLA decreases de novo lipid synthesis along with the abundance and activity of stearoyl-CoA desaturase (SCD)-1, a δ-9 desaturase essential for the synthesis of monounsaturated fatty acids (MUFA). Thus, we hypothesized that the 10,12 CLA-mediated decrease in SCD-1, with the subsequent decrease in MUFA, was responsible for the observed effects. To test this hypothesis, 10,12 CLA-treated human adipocytes were supplemented with oleic acid for 12 h to 7 days, and inflammatory gene expression, insulin-stimulated glucose uptake, and lipid content were measured. Oleic acid reduced inflammatory gene expression in a dose-dependent manner, and restored the lipid content of 10,12 CLA-treated adipocytes without improving insulin-stimulated glucose uptake. In contrast, supplementation with stearic acid, a substrate for SCD-1, or 9,11 CLA did not prevent inflammatory gene expression by 10,12 CLA. Notably, 10,12 CLA impacted the expression of several G-protein coupled receptors that was attenuated by oleic acid. Collectively, these data show that oleic acid attenuates 10,12 CLA-induced inflammatory gene expression and lipid content, possibly by alleviating cell stress caused by the inhibition of MUFA needed for phospholipid and neutral lipid synthesis.

Nutrigenomics, rumen-derived bioactive fatty acids, and the regulation of milk fat synthesis

Mammary synthesis of milk fat continues to be an active research area, with significant advances in the regulation of lipid synthesis by bioactive fatty acids (FAs). The biohydrogenation theory established that diet-induced milk fat depression (MFD) in the dairy cow is caused by an inhibition of mammary synthesis of milk fat by specific FAs produced during ruminal biohydrogenation. The first such FA shown to affect milk fat synthesis was trans-10, cis-12 conjugated linoleic acid, and its effects have been well characterized, including dose-response relationships. During MFD, lipogenic capacity and transcription of key mammary lipogenic genes are coordinately down-regulated. Results provide strong evidence for sterol response element-binding protein-1 (SREBP1) and Spot 14 as biohydrogenation intermediate responsive lipogenic signaling pathway for ruminants and rodents. The study of MFD and its regulation by specific rumen-derived bioactive FAs represents a successful example of nutrigenomics in present-day animal nutrition research and offers several potential applications in animal agriculture.

Conjugated linoleic acid-induced apoptosis in mouse mammary tumor cells is mediated by both G protein coupled receptor-dependent activation of the AMP-activated protein kinase pathway and by oxidative stress

Conjugated linoleic acid (CLA) has shown chemopreventive activity in several tumorigenesis models, in part through induction of apoptosis. We previously demonstrated that the t10,c12 isomer of CLA induced apoptosis of TM4t mouse mammary tumor cells through both mitochondrial and endoplasmic reticulum (ER) stress pathways, and that the AMP-activated protein kinase (AMPK) played a critical role in the apoptotic effect. In the current study, we focused on the upstream pathways by which AMPK was activated, and additionally evaluated the contributing role of oxidative stress to apoptosis. CLA-induced activation of AMPK and/or induction of apoptosis were inhibited by infection of TM4t cells with an adenovirus expressing a peptide which blocks the interaction between the G protein coupled receptor (GPCR) and Gα(q), by the phospholipase C (PLC) inhibitor U73122, by the inositol trisphosphate (IP(3)) receptor inhibitor 2-APB, by the calcium/calmodulin-dependent protein kinase kinase α (CaMKK) inhibitor STO-609 and by the intracellular Ca(2+) chelator BAPTA-AM. This suggests that t10,c12-CLA may exert its apoptotic effect by stimulating GPCR through Gα(q) signaling, activation of phosphatidylinositol-PLC, followed by binding of the PLC-generated IP(3) to its receptor on the ER, triggering Ca(2+) release from the ER and finally stimulating the CaMKK-AMPK pathway. t10,c12-CLA also increased oxidative stress and lipid peroxidation, and antioxidants blocked its apoptotic effect, as well as the CLA-induced activation of p38 MAPK, a downstream effector of AMPK. Together these data elucidate two major pathways by which t10,c12-CLA induces apoptosis, and suggest a point of intersection of the two pathways both upstream and downstream of AMPK.

Inhibition of stearoyl-CoA desaturase 1 expression induces CHOP-dependent cell death in human cancer cells

BACKGROUND

Cancer cells present a sustained de novo fatty acid synthesis with an increase of saturated and monounsaturated fatty acid (MUFA) production. This change in fatty acid metabolism is associated with overexpression of stearoyl-CoA desaturase 1 (Scd1), which catalyses the transformation of saturated fatty acids into monounsaturated fatty acids (e.g., oleic acid). Several reports demonstrated that inhibition of Scd1 led to the blocking of proliferation and induction of apoptosis in cancer cells. Nevertheless, mechanisms of cell death activation remain to be better understood.

PRINCIPAL FINDINGS

In this study, we demonstrated that Scd1 extinction by siRNA triggered abolition of de novo MUFA synthesis in cancer and non-cancer cells. Scd1 inhibition-activated cell death was only observed in cancer cells with induction of caspase 3 activity and PARP-cleavage. Exogenous supplementation with oleic acid did not reverse the Scd1 ablation-mediated cell death. In addition, Scd1 depletion induced unfolded protein response (UPR) hallmarks such as Xbp1 mRNA splicing, phosphorylation of eIF2α and increase of CHOP expression. However, the chaperone GRP78 expression, another UPR hallmark, was not affected by Scd1 knockdown in these cancer cells indicating a peculiar UPR activation. Finally, we showed that CHOP induction participated to cell death activation by Scd1 extinction. Indeed, overexpression of dominant negative CHOP construct and extinction of CHOP partially restored viability in Scd1-depleted cancer cells.

CONCLUSION

These results suggest that inhibition of de novo MUFA synthesis by Scd1 extinction could be a promising anti-cancer target by inducing cell death through UPR and CHOP activation.

Activated AMPK and prostaglandins are involved in the response to conjugated linoleic acid and are sufficient to cause lipid reductions in adipocytes

trans-10, cis-12 Conjugated linoleic acid (t10c12 CLA) reduces triglyceride levels in adipocytes. AMP-activated protein kinase (AMPK) and inflammation were recently demonstrated to be involved in the emerging pathways regulating this response. This study further investigated the role of AMPK and inflammation by testing the following hypotheses: (1) a moderate activation of AMPK and an inflammatory response are sufficient to reduce triglycerides, and (2) strong activation of AMPK is also sufficient. Experiments were performed by adding compounds that affect these pathways and by measuring their effects in 3T3-L1 adipocytes. A comparison of four AMPK activators (metformin, phenformin, TNF-α and t10c12 CLA) found a correlation between AMPK activity and triglyceride reduction. This correlation appeared to be modulated by the level of cyclo-oxygenase (COX)-2 mRNA produced. Inhibitors of the prostaglandin (PG) biosynthetic pathway interfered with t10c12 CLA's ability to reduce triglycerides. A combination of metformin and PGH2, or phenformin alone, efficiently reduced triglyceride levels in adipocytes. Microarray analysis indicated that the transcriptional responses to phenformin or t10c12 CLA were very similar, suggesting similar pathways were activated. 3T3-L1 fibroblasts were found to weakly induce the integrated stress response (ISR) in response to phenformin or t10c12 CLA and to respond robustly as they differentiated into adipocytes. This indicated that both chemicals required adipocytes at the same stage of differentiation to be competent for this response. These results support the above hypotheses and suggest compounds that moderately activate AMPK and increase PG levels or robustly activate AMPK in adipocytes may be beneficial for reducing adiposity.

Activation of the AMP-activated protein kinase-p38 MAP kinase pathway mediates apoptosis induced by conjugated linoleic acid in p53-mutant mouse mammary tumor cells

Conjugated linoleic acid (CLA) inhibits tumorigenesis and tumor growth in most model systems, an effect mediated in part by its pro-apoptotic activity. We previously showed that trans-10,cis-12 CLA induced apoptosis of p53-mutant TM4t mouse mammary tumor cells through both mitochondrial and endoplasmic reticulum stress pathways. In the current study, we investigated the role of AMP-activated protein kinase (AMPK), a key player in fatty acid metabolism, in CLA-induced apoptosis in TM4t cells. We found that t10,c12-CLA increased phosphorylation of AMPK, and that CLA-induced apoptosis was enhanced by the AMPK agonist 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and inhibited by the AMPK inhibitor compound C. The increased AMPK activity was not due to nutrient/energy depletion since ATP levels did not change in CLA-treated cells, and knockdown of the upstream kinase LKB1 did not affect its activity. Furthermore, our data do not demonstrate a role for the AMPK-modulated mTOR pathway in CLA-induced apoptosis. Although CLA decreased mTOR levels, activity was only modestly decreased. Moreover, rapamycin, which completely blocked the activity of mTORC1 and mTORC2, did not induce apoptosis, and attenuated rather than enhanced CLA-induced apoptosis. Instead, the data suggest that CLA-induced apoptosis is mediated by the AMPK-p38 MAPK-Bim pathway: CLA-induced phosphorylation of AMPK and p38 MAPK, and increased expression of Bim, occurred with a similar time course as apoptosis; phosphorylation of p38 MAPK was blocked by compound C; the increased Bim expression was blocked by p38 MAPK siRNA; CLA-induced apoptosis was attenuated by the p38 inhibitor SB-203580 and by siRNAs directed against p38 MAPK or Bim.

Inflammation and insulin resistance induced by trans-10, cis-12 conjugated linoleic acid depend on intracellular calcium levels in primary cultures of human adipocytes

We previously demonstrated that trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) induced inflammation and insulin resistance in primary human adipocytes by activating nuclear factor kappaB (NFkappaB) and extracellular signal-related kinase (ERK) signaling. In this study, we demonstrated that the initial increase in intracellular calcium ([Ca2+]i) mediated by 10,12 CLA was attenuated by TMB-8, an inhibitor of calcium release from the endoplasmic reticulum (ER), by BAPTA, an intracellular calcium chelator, and by D609, a phospholipase C (PLC) inhibitor. Moreover, BAPTA, TMB-8, and D609 attenuated 10,12 CLA-mediated production of reactive oxygen species (ROS), activation of ERK1/2 and cJun-NH2-terminal kinase (JNK), and induction of inflammatory genes. 10,12 CLA-mediated binding of NFkappaB to the promoters of interleukin (IL)-8 and cyclooxygenase (COX)-2 and induction of calcium-calmodulin kinase II (CaMKII) beta were attenuated by TMB-8. KN-62, a CaMKII inhibitor, also suppressed 10,12 CLA-mediated ROS production and ERK1/2 and JNK activation. Additionally, KN-62 attenuated 10,12 CLA induction of inflammatory and integrated stress response genes, increase in prostaglandin F2alpha, and suppression of peroxisome proliferator activated receptor gamma protein levels and insulin-stimulated glucose uptake. These data suggest that 10,12 CLA increases inflammation and insulin resistance in human adipocytes, in part by increasing [Ca2+]i levels, particularly calcium from the ER.

Antiobesity mechanisms of action of conjugated linoleic acid

Conjugated linoleic acid (CLA), a family of fatty acids found in beef, dairy foods and dietary supplements, reduces adiposity in several animal models of obesity and some human studies. However, the isomer-specific antiobesity mechanisms of action of CLA are unclear, and its use in humans is controversial. This review will summarize in vivo and in vitro findings from the literature regarding potential mechanisms by which CLA reduces adiposity, including its impact on (a) energy metabolism, (b) adipogenesis, (c) inflammation, (d) lipid metabolism and (e) apoptosis.

Conjugated linoleic acid activates AMP-activated protein kinase and reduces adiposity more effectively when used with metformin in mice

Trans-10, cis-12 (t10c12) conjugated linoleic acid (CLA) reduces lipid levels in adipocytes, but the mechanisms involved are still emerging. The hypotheses of this study were that t10c12 CLA treatment activated AMP-activated protein kinase (AMPK) and that the effectiveness of a low dose of t10c12 CLA would be increased when combined with an AMPK activator. We demonstrated t10c12 CLA, directly or indirectly, activated AMPK and increased the amount of phosphorylated acetyl-CoA carboxylase (ACC) in 3T3-L1 adipocytes. Compound C, a potent inhibitor of AMPK, attenuated the phosphorylation of ACC, integrated stress response (ISR), inflammatory response, reduction in key lipogenic transcription factors, and triglyceride (TG) reduction that otherwise occurred in t10c12 CLA-treated adipocytes. Treatment of adipocytes or mice with a low dose of t10c12 CLA in conjunction with the AMPK activator metformin resulted in more TG loss than treatment with the individual chemicals. Additionally, although an inflammatory response was required for robust TG reduction, the combination of t10c12 CLA with AMPK activators had a similar TG loss with a reduced inflammatory response. A microarray analysis of the transcriptional response to either t10c12 CLA, metformin, or the combination, indicated the responses were very similar, with a correlation coefficient of 0.91 or better for genes in the ISR or lipid-related pathways. Altogether, these results support our hypotheses that t10c12 CLA activates AMPK, directly or indirectly, and that metformin increases the effectiveness of t10c12 CLA in reducing TG amounts in adipocytes.