Tae Woo Jung

Protectin DX ameliorates palmitate- or high-fat diet-induced insulin resistance and inflammation through an AMPK-PPARα-dependent pathway in mice

Protectin DX (PDX), a double lipoxygenase derivative of docosahexaenoic acid, has been reported to attenuate inflammation and insulin resistance. In the current study, we explored the effects of PDX on hyperlipidemia-induced insulin resistance and inflammation through AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα). PDX attenuated the impairment of insulin receptor substrate 1/Akt–mediated insulin signaling in palmitate-treated differentiated C2C12 cells and soleus skeletal muscle of HFD-fed mice. Furthermore, PDX treatment significantly ameliorated HFD-induced weight gain and improved glucose tolerance in mice. Nuclear factor kB nuclear translocation, inhibitory kBα phosphorylation, and expression of proinflammatory cytokines were markedly attenuated by PDX in both in vitro and in vivo models. PDX treatment markedly augmented AMPK phosphorylation and PPARα expression in C2C12 cells and in skeletal muscle of mice. AMPK- and PPARα-specific siRNAs significantly abrogated the suppressive effects of PDX on palmitate-induced insulin resistance and inflammation. Furthermore, PDX markedly stimulated the expression of genes related to fatty acid oxidation. These effects of PDX were significantly suppressed by AMPK and PPARα siRNAs. In conclusion, our results demonstrate that PDX ameliorates insulin resistance and inflammation and stimulates fatty acid oxidation through AMPK- and PPARα-mediated pathways in skeletal muscle.

Protectin DX suppresses hepatic gluconeogenesis through AMPK-HO-1-mediated inhibition of ER stress

Several studies have shown that protectins, which are ω-3 fatty acid-derived proresolution mediators, may improve insulin resistance. Recently, protectin DX (PDX) was documented to attenuate insulin resistance by stimulating IL-6 expression in skeletal muscle, thereby regulating hepatic gluconeogenesis. These findings made us investigate the direct effects of PDX on hepatic glucose metabolism in the context of diabetes. In the current study, we show that PDX regulates hepatic gluconeogenesis in a manner distinct from its indirect glucoregulatory activity via IL-6. We found that PDX stimulated AMP-activated protein kinase (AMPK) phosphorylation, thereby inducing heme oxygenase 1 (HO-1) expression. This induction blocked hepatic gluconeogenesis by suppressing endoplasmic reticulum (ER) stress in hepatocytes under hyperlipidemic conditions. These effects were significantly dampened by silencing AMPK or HO-1 expression with small interfering RNA (siRNA). We also demonstrated that administration of PDX to high fat diet (HFD)-fed mice resulted in increased hepatic AMPK phosphorylation and HO-1 expression, whereas hepatic ER stress was substantially attenuated. Furthermore, PDX treatment suppressed the expression of gluconeogenic genes, thereby decreasing blood glucose levels in HFD-fed mice. In conclusion, our findings suggest that PDX inhibits hepatic gluconeogenesis via AMPK-HO-1-dependent suppression of ER stress. Thus, PDX may be an effective therapeutic target for the treatment of insulin resistance and type 2 diabetes through the regulation of hepatic gluconeogenesis.

Phosphatidylcholine Causes Lipolysis and Apoptosis in Adipocytes through the Tumor Necrosis Factor Alpha-Dependent Pathway

A phosphatidylcholine (PPC) formulation has been used to treat cellulite; however, its underlying mechanism of action remains unclear. In this study, we demonstrated that PPC induces lipolysis and apoptosis in adipocytes, and evaluated a possible tumor necrosis factor alpha (TNFα)-dependent pathway, whereby PPC exerts these effects. For in vitro study, fully differentiated 3T3-L1 cells, mouse adipocytes were treated with various concentrations of PPC and cell apoptosis and lipolysis were assayed. For in vivo experiments, mice fed on a high-fat diet for 8 weeks were injected twice to abdominal subcutaneous fat tissues of either vehicle or PPC. We found that PPC induced lipolysis and apoptosis dose-dependently in fully differentiated 3T3-L1 cells. In addition, PPC augmented both expression and release of TNFα in a dose-dependent fashion. Induction of TNFα by PPC was associated with the stimulation of nuclear factor kappa B (NFκB)-mediated transcriptional activity. Small interfering RNA (siRNA)-mediated suppression of NFκB abrogated the effect of PPC on TNFα secretion. Suppression of TNFα with specific siRNA abrogated the effects of PPC on lipolysis and apoptosis. Through in vivo experiments, we demonstrated that PPC injection not only stimulated the local lipolysis and apoptosis, resulting in weight loss, but also induced TNFα mRNA expression and neutrophil infiltration. Furthermore, PPC injection prevented lipogenesis and suppressed the mRNA expression of adipokines (such as adiponectin and leptin), due to the down-sizing of adipocytes. In conclusion, we suggest that PPC induces lipolysis and apoptosis in adipocytes through TNFα-dependent pathways.

Aqueous Extract of Humulus japonicus Attenuates Hyperlipidemia and Fatty Liver in Obese Mice

In this study, the effects of Humulus japonicus (HJ) aqueous extract on 3T3-L1 preadipocytes and HepG2 cells (in vitro model) as well as on C57BL/6 mice fed on high-fat diet (HFD) (in vivo model) were evaluated. Mice fed on HFD for 12-weeks were taken the HJ water extract (HJW) at various doses, 50, 150, and 250 mg/kg, orally for 8 weeks. We have noticed the accumulation of fat globules in preadipocytes and HepG2 cells using Oil Red O staining. In addition, supplementation with HJW considerably inhibited the weight gain, lipid accumulation, and adipogenesis and decreased the size of subcutaneous adipocytes in 3T3-L1 adipocytes. Furthermore, treatment with HJW improved hyperlipidemia via decreasing the levels of serum triglyceride (TG) and low-density lipoproteins as well as the atherogenic index. Supplementation with HJW could attenuate HFD-induced lipid accumulation, increase the mRNA expressions of fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD1), and would elevate the levels of serum aspartate aminotransferase and alanine aminotransferase in mice liver. The levels of TG and FAS mRNA in HepG2 cells treated with palmitate were reduced in a dose-dependent manner. In sum, HJW could alleviate the HFD-induced obesity and decrease the dyslipidemia profiles; the keys that could contribute to cardiovascular and nonalcoholic liver diseases.

WISP1 promotes non-alcoholic fatty liver disease and skeletal muscle insulin resistance via TLR4/JNK signaling

Wnt1‐inducible signaling pathway protein‐1 (WISP1) is a Cyr61/CTGF/NOV (CCN) family matricellular protein involved in adipogenesis and low‐grade inflammation in obesity. However, the roles of WISP1 in hepatic steatosis and insulin resistance in skeletal muscle remain elusive. Mouse primary hepatocytes and differentiated mouse skeletal muscle cells (C2C12) were treated with various concentrations of WISP1 and the functions and signaling pathways were analyzed by Western blot analysis. In vivo transfection for WISP1 knockdown was also performed to examine the effects of WISP1 on hepatic steatosis and skeletal muscle insulin resistance. Knockdown of WISP1 in high‐fat diet‐fed C57BL/6 mice significantly reduced (0.45–0.5%; p < 0.05) inflammation and JNK phosphorylation (45–50%; P < 0.01) and attenuated hepatic steatosis (approximately 55%; p < 0.001) and skeletal muscle insulin resistance (30–40%; p < 0.05). Treatment with WISP1 significantly induced inflammation (hepatocytes: approximately 500%; p < 0.01, C2C12 cells: approximately 500%; p < 0.01) and JNK phosphorylation (hepatocytes: approximately 200%; p < 0.01, C2C12 cells: approximately 280%; p < 0.01) in mouse primary hepatocytes and C2C12 mouse skeletal muscle cells. Moreover, it increased lipogenesis‐associated gene expression (200–300%; p < 0.01) and accumulation of triglycerides (approximately 320%; p < 0.01) in hepatocytes, and suppressed insulin signaling (approximately 50%; p < 0.01) in C2C12 cells. These WISP1‐induced effects were significantly abrogated in NFκB‐, JNK‐, and TLR4‐knockdown hepatocytes (p < 0.05) and C2C12 cells (p < 0.05). These results indicate that WISP1 contributes to hepatic steatosis and skeletal muscle insulin resistance through a TLR4‐activated inflammation/JNK signaling pathway and could be a useful therapeutic target for treatment of non‐alcoholic fatty liver disease and type 2 diabetes.

Protective potential of glutathione peroxidase-1 gene against cocaine-induced acute hepatotoxic consequences in mice: Role of GPx-1 in cocaine-induced hepatotoxicity

Since the cocaine‐induced oxidative stress has been established to lead to hepatotoxicity, we examined the role of the glutathione peroxidase (GPx)‐1 gene in cocaine‐induced hepatotoxicity. Cocaine treatment significantly increased superoxide dismutase activity in as little as 1 hour, with a maximum level at 6 hours in wild‐type mice, while significantly decreasing GPx activity and subsequently inducing oxidative damage (i.e., reactive oxygen species, lipid peroxidation and protein carbonylation). These changes were more prominent in the mitochondrial fraction than in the cytosolic fraction. In contrast, genetic overexpression of GPx‐1 significantly attenuated cocaine‐induced oxidative damage in mice. Cocaine treatment significantly increased alanine aminotransferase and aspartate aminotransferase levels in the serum. Consistently, cocaine significantly enhanced cleaved caspase‐3 expression and intramitochondrial Ca2+, while significantly reducing mitochondrial transmembrane potential. Cocaine treatment potentiated cleavage of protein kinase C δ (PKC δ ), mitochondrial translocation of PKC δ , cytosolic release of cytochrome c and activation of caspase‐3, followed by hepatopathologic changes. These results were more prominent in GPx‐1 knockout than in wild‐type mice, and they were less pronounced in overexpressing transgenic than in non‐transgenic mice. Combined, our results suggest that the GPx‐1 gene possesses protective potential against mitochondrial oxidative burden, mitochondrial dysfunction and hepatic degeneration induced by cocaine and that the protective mechanisms are associated with anti‐apoptotic activity via inactivation of PKC δ .

METRNL attenuates lipid-induced inflammation and insulin resistance via AMPK or PPARδ-dependent pathways in skeletal muscle of mice

AbstractPhysical activity has many beneficial effects on metabolic disorders, such as obesity, insulin resistance, and diabetes. Meteorin-like protein (METRNL), a novel secreted protein homologous to the neurotrophin Metrn, is induced after exercise in the skeletal muscle. Herein, we investigated the effects of METRNL on lipid-mediated inflammation and insulin resistance in skeletal muscle via AMP-activated protein kinase (AMPK) or peroxisome proliferator-activated receptor δ (PPARδ). Treatment with METRNL suppressed inflammatory markers, such as nuclear factor κB (NFκB) nuclear translocation, inhibitory κBα (IκBα) phosphorylation, interleukin-6 (IL-6) expression, and pro-inflammatory cytokines (such as TNFα and MCP-1). METRNL treatment also attenuated the impaired insulin response both in palmitate-treated differentiated C2C12 cells and the skeletal muscle of high-fat diet (HFD)-fed mice. Furthermore, METRNL administration rescued glucose intolerance and reduced HFD-induced body weight gain in mice; however, METRNL did not affect calorie intake. METRNL treatment increased AMPK phosphorylation and PPARδ expression both in differentiated C2C12 cells and mouse skeletal muscle. siRNA-mediated suppression of AMPK and PPARδ abrogated the suppressive effects of METRNL on palmitate-induced inflammation and insulin resistance. Moreover, METRNL augmented the mRNA expression of fatty acid oxidation-associated genes, such as carnitine palmitoyltransferase 1 (CPT1), acyl-CoA oxidase (ACO), and fatty acid binding protein 3 (FABP3). siRNAs for AMPK and PPARδ reversed these changes. In the current study, we report for the first time that METRNL alleviates inflammation and insulin resistance and induces fatty acid oxidation through AMPK or PPARδ-dependent signaling in skeletal muscle.Metabolic disorders: A hormone treatment for diabetes and obesityTreatment with a hormone that is normally induced following exercise helps alleviate inflammation and insulin resistance in the muscles of obese mice, highlighting a potential new therapeutic strategy for diabetes and other metabolic disorders. Meteorin-like protein (METRNL) is a hormone produced by muscle cells after physical activity and on exposure to cold. A team led by Ji Hoon Jeong and Yong Kyoo Shin from Chung-Ang University
in Seoul, South Korea, observed that levels of METRNL are reduced in mice fed a high-fat diet and in mouse skeletal muscle cells chemically treated to become unresponsive to insulin. Administering METRNL to the cells or mice reduced levels of inflammation, resulting in improved insulin responses. However, these improvements occurred only when certain regulatory molecules were active, revealing a key pathway through which METRNL acts.

Protectin DX attenuates LPS-induced inflammation and insulin resistance in adipocytes via AMPK-mediated suppression of the NFκB pathway

Several studies have demonstrated that protectins, ω-3 fatty acid-derived proresolution mediators, may ameliorate inflammation. Recently, protectin DX (PDX) was also reported to attenuate inflammation and insulin resistance in several cell types. However, the effects of PDX on inflammation in adipocytes remain ambiguous. In this study, we found that PDX treatment suppressed adipogenesis and lipid accumulation during 3T3-L1 differentiation. Treatment of differentiated 3T3-L1 cells with PDX stimulated AMP-activated protein kinase (AMPK) phosphorylation in a dose-dependent manner. PDX-induced AMPK phosphorylation blocked lipopolysaccharide (LPS)-induced secretion of proinflammatory cytokines, such as tumor necrosis factor-α and monocyte chemoattractant protein-1. Treatment of 3T3-L1 cells with PDX alleviated LPS-induced NF-κB and inhibitory factor κB phosphorylation. Furthermore, PDX treatment diminished LPS-induced impairment of insulin signaling and insulin-stimulated glucose uptake, as well as fatty acid oxidation. These effects were decreased by silencing AMPK expression with small-interfering RNA. In conclusion, the current findings suggest that PDX attenuates inflammation and insulin resistance in adipocytes via an AMPK-dependent pathway, which in turn provides evidence that PDX has anti-inflammatory and antidiabetic effects in adipocytes.