4-Phenylbutyric acid improves free fatty acid-induced hepatic insulin resistance in vivo

Plasma free fatty acids (FFAs) are elevated in obesity and can induce insulin resistance via endoplasmic reticulum (ER) stress. However, it is unknown whether hepatic insulin resistance caused by the elevation of plasma FFAs is alleviated by chemical chaperones. Rats received one of the following i.v. treatments for 48 h: saline, intralipid plus heparin (IH), IH plus the chemical chaperone 4-phenylbutyric acid (PBA), or PBA alone and a hyperinsulinemic-euglycemic clamp was performed during the last 2 h. PBA co-infusion normalized IH-induced peripheral insulin resistance, similar to our previous findings with an antioxidant and an IκBα kinase β (IKKβ) inhibitor. Different from our previous results with the antioxidant and IKKβ inhibitor, PBA also improved IH-induced hepatic insulin resistance in parallel with activation of Akt. Unexpectedly, IH did not induce markers of ER stress in the liver, but PBA prevented IH-induced elevation of phosphorylated eukaryotic initiation factor-2α protein in adipose tissue. PBA tended to decrease circulating fetuin-A and significantly increased circulating fibroblast growth factor 21 (FGF21) without affecting markers of activation of hepatic protein kinase C-δ or p38 mitogen-activated protein kinase that we have previously involved in hepatic insulin resistance in this model. In conclusion: (i) PBA prevented hepatic insulin resistance caused by prolonged plasma FFA elevation without affecting hepatic ER stress markers; (ii) the PBA effect is likely due to increased FGF21 and/or decreased fetuin-A, which directly signal to upregulate Akt activation.

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Hepatic Mitogen-Activated Protein Kinase Phosphatase 1 Selectively Regulates Glucose Metabolism and Energy Homeostasis

Molecular and Cellular Biology ◽

10.1128/mcb.00503-14 ◽

2014 ◽

Vol 35 (1) ◽

pp. 26-40 ◽

Cited By ~ 33

Author(s):

Ahmed Lawan ◽

Lei Zhang ◽

Florian Gatzke ◽

Kisuk Min ◽

Michael J. Jurczak ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Glucose Metabolism ◽

Energy Homeostasis ◽

Mitogen Activated Protein Kinase ◽

Hepatic Insulin Resistance ◽

Fibroblast Growth Factor 21 ◽

High Fat ◽

Mitogen Activated Protein ◽

Fat Feeding

The liver plays a critical role in glucose metabolism and communicates with peripheral tissues to maintain energy homeostasis. Obesity and insulin resistance are highly associated with nonalcoholic fatty liver disease (NAFLD). However, the precise molecular details of NAFLD remain incomplete. The p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK) regulate liver metabolism. However, the physiological contribution of MAPK phosphatase 1 (MKP-1) as a nuclear antagonist of both p38 MAPK and JNK in the liver is unknown. Here we show that hepatic MKP-1 becomes overexpressed following high-fat feeding. Liver-specific deletion of MKP-1 enhances gluconeogenesis and causes hepatic insulin resistance in chow-fed mice while selectively conferring protection from hepatosteatosis upon high-fat feeding. Further, hepatic MKP-1 regulates both interleukin-6 (IL-6) and fibroblast growth factor 21 (FGF21). Mice lacking hepatic MKP-1 exhibit reduced circulating IL-6 and FGF21 levels that were associated with impaired skeletal muscle mitochondrial oxidation and susceptibility to diet-induced obesity. Hence, hepatic MKP-1 serves as a selective regulator of MAPK-dependent signals that contributes to the maintenance of glucose homeostasis and peripheral tissue energy balance. These results also demonstrate that hepatic MKP-1 overexpression in obesity is causally linked to the promotion of hepatosteatosis.

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Abstract 552: Aberrant Expression of MicroRNA-378a Induces Hepatic Insulin Resistance via Activation of ER Stress and the dsRNA Activated Protein Kinase PKR

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.37.suppl_1.552 ◽

2017 ◽

Vol 37 (suppl_1) ◽

Author(s):

Xiao Cheng ◽

Yongyan Song ◽

Qiaozhu Su

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Er Stress ◽

Target Genes ◽

Rna Binding ◽

Mrna Level ◽

Hepatic Insulin Resistance ◽

Stress Signaling ◽

Aberrant Expression ◽

Mitochondrial Fatty Acid

microRNAs(miRNAs) are noncoding RNAs with a length of 19 to 25 nt that are involved in posttranscriptional gene regulation by binding to the 3’-untranslated regions (3’-UTR) of target mRNA and impacting diverse cellular processes, including cell differentiation, energy metabolism and chronic inflammation. MicroRNA-378a (miR-378a) has been reported to be involved in adipose tissue browning and cancer development. However, its role in cellular stress signaling and hepatic insulin resistance has not yet been investigated. Here we reported that expression of hepatic miR-378a was upregulated by metabolic inflammatory inducers, such as high fructose feeding, bacterial lipopolysaccharide (LPS) and inflammatory cytokine TNFα. The elevated miR-378a subsequently targeted the 3’-UTR of PPARα which compromised mitochondrial fatty acid β-oxidation and induced mitochondrial and ER stress. miR-378a was further found to directly interacted with the dsRNA binding motifs within the dsRNA activated protein kinase PKR and activated the kinase to sustain the inflammatory stress and blunt the insulin signaling in hepatocytes. Genetic depletion of miR-378a rescued hepatocytes from mitochondrial and ER stress, systemic inflammation and insulin resistance induced by fructose and LPS. Conclusion: This study, for the first time, demonstrates that miR-378a is involved in mediating the metabolic inflammatory response in the onset of insulin resistance. This study further unveils a novel finding that miR-378a is capable of directly interacting with and activating a protein kinase PKR to sustain the stress signaling between mitochondria and ER. This discovery greatly broadens the physiological function of miR-378a by demonstrating that, in addition to regulate its target genes on the mRNA level, miRNA-378a is able to interact with RNA binding protein(s) and exerts its regulatory effect directly on the protein levels. Results from this study may provide rationale for using miR-378a as a pharmaceutical target in the treatment of insulin resistance.

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Activation of dsRNA-Dependent Protein Kinase R by MicroRNA-378 Sustains Metabolic Inflammation in Hepatic Insulin Resistance

10.2337/figshare.13491342.v1 ◽

2021 ◽

Author(s):

Hao Wang ◽

Yongyan Song ◽

Yuxin Wu ◽

Virender Kumar ◽

Ram I Mahato ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Er Stress ◽

Rna Binding ◽

Hepatic Insulin Resistance ◽

Protein Kinase R ◽

Dependent Protein Kinase ◽

Metabolic Inflammation ◽

Mitochondrial Fatty Acid ◽

Dependent Protein

<a>MicroRNAs (miRNAs) are noncoding small RNAs that regulate various pathophysiological cellular processes. Here we reported that expression of the miR-378 family was significantly induced by metabolic inflammatory inducers, a high-fructose diet, and inflammatory cytokine TNF</a>a. Hepatic miRNA profiling revealed that expression of miR-378a was highly upregulated which, in turn, targeted the 3’-UTR of PPARa mRNA, impaired mitochondrial fatty acid b-oxidation and induced mitochondrial and ER stress. More importantly, the upregulated miR-378a can directly bind to and activate the dsRNA-dependent protein kinase R (PKR) to sustain the metabolic stress. <i>In vivo</i>, genetic depletion of miR-378a prevented PKR activation, ameliorated inflammatory stress and insulin resistance. Counterbalancing the upregulated miR-378a using nanoparticles encapsulated with an anti-miR-378a oligonucleotide restored PPARa activity, inhibited PKR activation and ER stress, and improved insulin sensitivity in the fructose-fed mice. <i>Conclusion: </i>Our study delineated a novel mechanism of miRNA-378a in the pathogenesis of metabolic inflammation and insulin resistance through targeting metabolic signaling at both mRNA (e.g., PPARa) and protein (e.g., PKR) molecules. This novel finding of functional interaction between miRNAs (e.g., miR-378a) and cellular RNA binding protein(s) (e.g., PKR) is biologically significant as it greatly broadens the potential targets of miRNAs in cellular pathophysiological processes.

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Inhibition of eIF2α Dephosphorylation Protects Hepatocytes from Apoptosis by Alleviating ER Stress in Acute Liver Injury

BioMed Research International ◽

10.1155/2020/2626090 ◽

2020 ◽

Vol 2020 ◽

pp. 1-16

Author(s):

Yong-Jing Tang ◽

Huan Chen ◽

Yu Yi ◽

Gui-Mei Chen ◽

Fang-Wan Yang ◽

...

Keyword(s):

Liver Injury ◽

Er Stress ◽

Acute Liver Injury ◽

Initiation Factor ◽

Calcium Balance ◽

Hepatocyte Apoptosis ◽

Protein Kinase R ◽

Chemical Chaperone ◽

Initiation Factor 2 ◽

Phenylbutyric Acid

Objectives. Protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor 2 alpha (eIF2α) is an important factor along the main pathways for endoplasmic reticulum (ER) stress-mediated apoptosis. In this study, we investigated the effects of eIF2α phosphorylation on hepatocyte apoptosis and the ER stress mechanisms in acute liver injury. Methods. eIF2α phosphorylation and apoptosis under ER stress were monitored and measured in male BALB/c mice with acute liver injury and human hepatocyte line LO2 cells. Results. Carbon tetrachloride (CCl4) administration triggered ER stress and hepatocyte apoptosis, as well as eIF2α phosphorylation in mice. Inhibition of eIF2α dephosphorylation, as the pretreatment with 4-phenylbutyric acid (chemical chaperone, ER stress inhibitor), mitigated CCl4-induced intrahepatic ER stress, apoptosis, and liver injury. In an ER stress model of LO2 cells induced by thapsigargin (disrupting ER calcium balance), inhibition of eIF2α dephosphorylation reduced ER stress and apoptosis, while PERK knockdown reduced eIF2α phosphorylation and exacerbated ER stress and apoptosis. Conclusions. eIF2α phosphorylation is one of the mechanisms employed by ER stress for restoring cellular homeostasis. Inhibition of eIF2α dephosphorylation mitigates hepatocyte apoptosis by alleviating ER stress in acute liver injuries.

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Activation of dsRNA-Dependent Protein Kinase R by MicroRNA-378 Sustains Metabolic Inflammation in Hepatic Insulin Resistance

10.2337/figshare.13491342 ◽

2021 ◽

Author(s):

Hao Wang ◽

Yongyan Song ◽

Yuxin Wu ◽

Virender Kumar ◽

Ram I Mahato ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Er Stress ◽

Rna Binding ◽

Hepatic Insulin Resistance ◽

Protein Kinase R ◽

Dependent Protein Kinase ◽

Metabolic Inflammation ◽

Mitochondrial Fatty Acid ◽

Dependent Protein

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IL-24 Promotes Apoptosis through cAMP-Dependent PKA Pathways in Human Breast Cancer Cells

International Journal of Molecular Sciences ◽

10.3390/ijms19113561 ◽

2018 ◽

Vol 19 (11) ◽

pp. 3561 ◽

Cited By ~ 7

Author(s):

Leah Persaud ◽

Jason Mighty ◽

Xuelin Zhong ◽

Ashleigh Francis ◽

Marifer Mendez ◽

...

Keyword(s):

Breast Cancer ◽

Cell Death ◽

Protein Kinase ◽

Er Stress ◽

Cancer Cell ◽

Mitogen Activated Protein Kinase ◽

Initiation Factor ◽

Breast Cancer Cell Lines ◽

Extrinsic Pathway ◽

Eif2α Phosphorylation

Interleukin 24 (IL-24) is a tumor-suppressing protein, which inhibits angiogenesis and induces cancer cell-specific apoptosis. We have shown that IL-24 regulates apoptosis through phosphorylated eukaryotic initiation factor 2 alpha (eIF2α) during endoplasmic reticulum (ER) stress in cancer. Although multiple stresses converge on eIF2α phosphorylation, the cellular outcome is not always the same. In particular, ER stress-induced apoptosis is primarily regulated through the extent of eIF2α phosphorylation and activating transcription factor 4 (ATF4) action. Our studies show for the first time that cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) activation is required for IL-24-induced cell death in a variety of breast cancer cell lines and this event increases ATF4 activity. We demonstrate an undocumented role for PKA in regulating IL-24-induced cell death, whereby PKA stimulates phosphorylation of p38 mitogen-activated protein kinase and upregulates extrinsic apoptotic factors of the Fas/FasL signaling pathway and death receptor 4 expression. We also demonstrate that phosphorylation and nuclear import of tumor suppressor TP53 occurs downstream of IL-24-mediated PKA activation. These discoveries provide the first mechanistic insights into the function of PKA as a key regulator of the extrinsic pathway, ER stress, and TP53 activation triggered by IL-24.

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Initiation Factor 2B Activity Is Regulated by Protein Phosphatase 1, Which Is Activated by the Mitogen-activated Protein Kinase-dependent Pathway in Insulin-like Growth Factor 1-stimulated Neuronal Cells

Journal of Biological Chemistry ◽

10.1074/jbc.m212936200 ◽

2003 ◽

Vol 278 (19) ◽

pp. 16579-16586 ◽

Cited By ~ 20

Author(s):

Celia Quevedo ◽

Matilde Salinas ◽

Alberto Alcázar

Keyword(s):

Growth Factor ◽

Protein Kinase ◽

Protein Phosphatase ◽

Neuronal Cells ◽

Mitogen Activated Protein Kinase ◽

Protein Phosphatase 1 ◽

Initiation Factor ◽

Insulin Like Growth Factor ◽

Mitogen Activated Protein ◽

Dependent Pathway

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Palmitate Causes Endoplasmic Reticulum Stress and Apoptosis in Human Mesenchymal Stem Cells: Prevention by AMPK Activator

Endocrinology ◽

10.1210/en.2012-1418 ◽

2012 ◽

Vol 153 (11) ◽

pp. 5275-5284 ◽

Cited By ~ 41

Author(s):

Jun Lu ◽

Qinghua Wang ◽

Lianghu Huang ◽

Huiyue Dong ◽

Lingjing Lin ◽

...

Keyword(s):

Stem Cells ◽

Endoplasmic Reticulum ◽

Mesenchymal Stem Cells ◽

Protein Kinase ◽

Er Stress ◽

Human Mesenchymal Stem Cells ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Human Umbilical Cord ◽

Amp Activated Protein Kinase

Abstract Elevated circulating saturated fatty acids concentration is commonly associated with poorly controlled diabetes. The highly prevalent free fatty acid palmitate could induce apoptosis in various cell types, but little is known about its effects on human mesenchymal stem cells (MSCs). Here, we report that prolonged exposure to palmitate induces human bone marrow-derived MSC (hBM-MSC) and human umbilical cord-derived MSC apoptosis. We investigated the role of endoplasmic reticulum (ER) stress, which is known to promote cell apoptosis. Palmitate activated XBP1 splicing, elF2α (eukaryotic translation initiation factor 2α) phosphorylation, and CHOP, ATF4, BiP, and GRP94 transcription in hBM-MSCs. ERK1/2 and p38 MAPK phosphorylation were also induced by palmitate in hBM-MSCs. A selective p38 inhibitor inhibited palmitate activation of the ER stress, whereas the ERK1/2 inhibitors had no effect. The AMP-activated protein kinase activator aminoimidazole carboxamide ribonucleotide blocked palmitate-induced ER stress and apoptosis. These findings suggest that palmitate induces ER stress and ERK1/2 and p38 activation in hBM-MSCs, and AMP-activated protein kinase activator prevents the deleterious effects of palmitate by inhibiting ER stress and apoptosis.

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