Gwang-woong Go

A Form of the Metabolic Syndrome Associated with Mutations in DYRK1B

BACKGROUND Genetic analysis has been successful in identifying causative mutations for individual cardiovascular risk factors. Success has been more limited in mapping susceptibility genes for clusters of cardiovascular risk traits, such as those in the metabolic syndrome. METHODS We identified three large families with coinheritance of early-onset coronary artery disease, central obesity, hypertension, and diabetes. We used linkage analysis and whole-exome sequencing to identify the disease-causing gene. RESULTS A founder mutation was identified in DYRK1B, substituting cysteine for arginine at position 102 in the highly conserved kinase-like domain. The mutation precisely cosegregated with the clinical syndrome in all the affected family members and was absent in unaffected family members and unrelated controls. Functional characterization of the disease gene revealed that nonmutant protein encoded by DYRK1B inhibits the SHH (sonic hedgehog) and Wnt signaling pathways and consequently enhances adipogenesis. Furthermore, DYRK1B promoted the expression of the key gluconeogenic enzyme glucose-6-phosphatase. The R102C allele showed gain-of-function activities by potentiating these effects. A second mutation, substituting proline for histidine 90, was found to cosegregate with a similar clinical syndrome in an ethnically distinct family. CONCLUSIONS These findings indicate a role for DYRK1B in adipogenesis and glucose homeostasis and associate its altered function with an inherited form of the metabolic syndrome. (Funded by the National Institutes of Health.).

LRP6 Protein Regulates Low Density Lipoprotein (LDL) Receptor-mediated LDL Uptake

Background: Elevated serum LDL cholesterol is a major risk factor for atherosclerosis. Mechanisms that regulate LDL homeostasis are not well understood. Results: LRP6 forms a complex with LDLR and other endocytic proteins, and its knockdown or mutation impairs LDLR endocytosis. Conclusion: LRP6 regulates LDLR-dependent LDL uptake. Significance: LRP6 is a potential target for development of novel lipid-lowering drugs. Genetic variations in LRP6 gene are associated with high serum LDL cholesterol levels. We have previously shown that LDL clearance in peripheral B-lymphocytes of the LRP6R611C mutation carriers is significantly impaired. In this study we have examined the role of wild type LRP6 (LRP6WT) and LRP6R611C in LDL receptor (LDLR)-mediated LDL uptake. LDL binding and uptake were increased when LRP6WT was overexpressed and modestly reduced when it was knocked down in LDLR-deficient CHO (ldlA7) cells. These findings implicated LRP6 in LDLR-independent cellular LDL binding and uptake. However, LRP6 knockdown in wild type CHO cells resulted in a much greater decline in LDL binding and uptake compared with CHO-ldlA7 cells, suggesting impaired function of the LDLR. LDLR internalization was severely diminished when LRP6 was knocked down and was restored after LRP6 was reintroduced. Further analysis revealed that LRP6WT forms a complex with LDLR, clathrin, and ARH and undergoes a clathrin-mediated internalization after stimulation with LDL. LDLR and LRP6 internalizations as well as LDL uptake were all impaired in CHO-k1 cells expressing LRP6R611C. These studies identify LRP6 as a critical modulator of receptor-mediated LDL endocytosis and introduce a mechanism by which variation in LRP6 may contribute to high serum LDL levels.

Rare Nonconservative LRP6 Mutations Are Associated with Metabolic Syndrome

A rare mutation in LRP6 has been shown to underlie autosomal dominant coronary artery disease (CAD) and metabolic syndrome in an Iranian kindred. The prevalence and spectrum of LRP6 mutations in the disease population of the United States is not known. Two hundred white Americans with early onset familial CAD and metabolic syndrome and 2,000 healthy Northern European controls were screened for nonconservative mutations in LRP6. Three novel mutations were identified, which cosegregated with the metabolic traits in the kindreds of the affected subjects and none in the controls. All three mutations reside in the second propeller domain, which plays a critical role in ligand binding. Two of the mutations substituted highly conserved arginines in the second YWTD domain and the third substituted a conserved glycosylation site. The functional characterization of one of the variants showed that it impairs Wnt signaling and acts as a loss of function mutation.

The bacterial signalling molecule indole attenuates the virulence of the fungal pathogen Candida albicans.

Indole is a signalling molecule, produced by a number of Gram‐positive and Gram‐negative bacteria both in nature as well as clinical environments. Here, we explored the effect of bacterial indole and one of its main derivatives on the virulence of the fungal pathogen Candida albicans.

Impaired LRP6-TCF7L2 Activity Enhances Smooth Muscle Cell Plasticity and Causes Coronary Artery Disease

Mutations in Wnt-signaling coreceptor LRP6 have been linked to coronary artery disease (CAD) by unknown mechanisms. Here, we show that reduced LRP6 activity in LRP6(R611C) mice promotes loss of vascular smooth muscle cell (VSMC) differentiation, leading to aortic medial hyperplasia. Carotid injury augmented these effects and led to partial to total vascular obstruction. LRP6(R611C) mice on high-fat diet displayed dramatic obstructive CAD and exhibited an accelerated atherosclerotic burden on LDLR knockout background. Mechanistically, impaired LRP6 activity leads to enhanced non-canonical Wnt signaling, culminating in diminished TCF7L2 and increased Sp1-dependent activation of PDGF signaling. Wnt3a administration to LRP6(R611C) mice improved LRP6 activity, led to TCF7L2-dependent VSMC differentiation, and rescued post-carotid-injury neointima formation. These findings demonstrate the critical role of intact Wnt signaling in the vessel wall, establish a causal link between impaired LRP6/TCF7L2 activities and arterial disease, and identify Wnt signaling as a therapeutic target against CAD.

Nonalcoholic fatty liver disease induced by noncanonical Wnt and its rescue by Wnt3a

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease, which begins with isolated steatosis and advances to nonalcoholic steatohepatitis (NASH), steatofibrosis, and cirrhosis. The pathways involved in disease progression are not understood. Loss‐of‐function mutations in Wnt coreceptor LDL receptor‐related protein 6 (LRP6) underlie early‐onset atherosclerosis, metabolic risk factors, and NAFLD in humans by unknown mechanisms. We generated mice with the human disease‐associated LRP6R611C mutation and phenotypically characterized their liver. Homozygote LRP6R611C (LRP6mut/mut) mice exhibited both steatohepatitis and steatofibrosis. These traits were associated with increased activity of the noncanonical Wnt/Ras homolog family member A, Rho‐associated protein kinase 2, and PKC‐α/‐μ pathways. Accordingly, there was increased TGF‐β1 activity, coupled with enhanced expression of smooth muscle α‐actin and vimentin that colocalized with albumin in LRP6mut/mut mouse liver. LRP6 knockdown reprogramed HepG2 cells to express both these markers, linking impaired Wnt signaling with hepatocyte transdifferentiation. The causal link between altered Wnt signaling and NASH was established by normalization of the disease pathways and rescue of the liver traits by Wnt3a administration to LRP6mut/mut mice. Thus, this study identifies diverse disease pathways that underlie a spectrum of NASH‐related liver diseases and are linked by a single human genetic variant. LRP6 and noncanonical Wnt pathways are important potential therapeutic targets against NASH.—Wang, S., Song, K., Srivastava, R., Dong, C., Go, G.‐W., Li, N., Iwakiri, Y., Mani, A. Nonalcoholic fatty liver disease induced by noncanonical Wnt and its rescue by Wnt3a. FASEB J. 29, 3436‐3445 (2015). www.fasebj.org

Endothelial APLNR regulates tissue fatty acid uptake and is essential for apelin’s glucose-lowering effects

Inhibition of FABP4 rescues defective apelin signaling, decreases fatty acid accumulation, and promotes insulin sensitivity. An apelin a day keeps the doctor away Apelin is an atheroprotective protein, which promotes insulin sensitivity and metabolic health, but the details of its signaling are not well understood. Hwangbo et al. discovered that the apelin receptor is predominantly localized in endothelial cells of metabolic organs, such as muscle and adipose tissues, and that it functions, in part, by inhibiting fatty acid binding protein 4 (FABP4) activity. The authors also found that inhibition of FABP4 can reverse the metabolic disease phenotype associated with defective apelin signaling and thus improve fatty acid uptake, glucose utilization, and insulin sensitivity. Treatment of type 2 diabetes mellitus continues to pose an important clinical challenge, with most existing therapies lacking demonstrable ability to improve cardiovascular outcomes. The atheroprotective peptide apelin (APLN) enhances glucose utilization and improves insulin sensitivity. However, the mechanism of these effects remains poorly defined. We demonstrate that the expression of APLNR (APJ/AGTRL1), the only known receptor for apelin, is predominantly restricted to the endothelial cells (ECs) of multiple adult metabolic organs, including skeletal muscle and adipose tissue. Conditional endothelial-specific deletion of Aplnr (AplnrECKO) resulted in markedly impaired glucose utilization and abrogation of apelin-induced glucose lowering. Furthermore, we identified inactivation of Forkhead box protein O1 (FOXO1) and inhibition of endothelial expression of fatty acid (FA) binding protein 4 (FABP4) as key downstream signaling targets of apelin/APLNR signaling. Both the Apln−/− and AplnrECKO mice demonstrated increased endothelial FABP4 expression and excess tissue FA accumulation, whereas concurrent endothelial Foxo1 deletion or pharmacologic FABP4 inhibition rescued the excess FA accumulation phenotype of the Apln−/− mice. The impaired glucose utilization in the AplnrECKO mice was associated with excess FA accumulation in the skeletal muscle. Treatment of these mice with an FABP4 inhibitor abrogated these metabolic phenotypes. These findings provide mechanistic insights that could greatly expand the therapeutic repertoire for type 2 diabetes and related metabolic disorders.

Pinus Densiflora Bark Extract (PineXol) Decreases Adiposity in Mice by Down-Regulation of Hepatic De Novo Lipogenesis and Adipogenesis in White Adipose Tissue

PineXol, extracted from Korean red pine bark, has beneficial effects, such as antioxidant, antiinflammatory, and antilipogenic activities in vitro. We tested the hypothesis that PineXol supplementation could have anti-obesity effects on mice fed a high-fat diet (HFD). Four-week-old male C57BL/6 mice were fed normal chow (18% kcal from fat) or a HFD (60% kcal from fat). HFD-fed animals were also subjected to PineXol treatment at a dose of 10 or 50 mg/kg body weight (BW) (PX10 or PX50, respectively) body weight. The body weight and body fat mass in the PX50 group were statistically lower than those in the HFD group (p < 0.05 and p < 0.001, respectively). The concentration of hepatic triglycerides, total cholesterol, and low-density lipoprotein cholesterol were reduced in the PX50 group compared with the HFD group (p < 0.01). Acetyl CoA carboxylase (p < 0.01), elongase of very long chain fatty acids 6 (p < 0.01), stearoyl CoA desaturase 1 (p < 0.05), microsomal triglyceride transfer protein (p < 0.01), and sterol regulatory element-binding protein 1 (p < 0.05) were significantly decreased in the PX50 group compared with that in the HFD group. In white adipose tissue, CCAATenhancer-binding protein alpha (p < 0.05), peroxisome proliferator-activated receptor gamma (p < 0.001), and perilipin (p < 0.01) were decreased in the PX50 group compared with those in the HFD group. Therefore, the current study implies the potential of PineXol for the prevention and/or amelioration of obesity, in part by inhibition of both hepatic lipid synthesis and adipogenesis in white adipose tissue.

Effect of Mechanically Deboned Chicken Meat Hydrolysates on the Physicochemical Properties of Imitation Fish Paste

This study investigated on the effects of adding mechanically deboned chicken meat (MDCM) hydrolysates on the quality properties of imitation fish paste (IFP) during storage. IFP was prepared from Alaska Pollack, spent laying hens surimi and protein hydrolysates which were enzymatically extracted from MDCM. The study was designed as a 3×4 factorial design with three MDCM hydrolysate content groups (0%, 0.4%, and 0.8%) and four storage times (0, 2, 4, and 6 weeks). Addition of MDCM hydrolysates increased crude fat content but lowered water content (p<0.05). The breaking force of IFP, an indicator of gel formation, increased in treated groups compared to control (p<0.05). Angiotensin I-converting enzyme (ACE) activity was inhibited and free radical scavenging activity increased with increasing MDCM hydrolysate content (p<0.05). In conclusion, the addition of MDCM to IFP improves gel characteristics. Additionally, protein hydrolysates from MDCM serve as a potential source of ACE inhibiting peptides.

Meat Quality Traits of Pigs Finished on Food Waste

Despite the benefits associated with the use of food waste (FW), there are mixed consumer perceptions regarding pork quality harvested from pigs fed FW. Twenty crossbred pigs were selected for the present study. Ten pigs were fed a conventional diet (control group), and the other 10 pigs were given a conventional diet and FW (FW group) during different growth stages. Meat quality in the FW group showed deteriorative qualities with higher lightness and yellowness synonymous to pale soft exudative meat. Drip loss in the experimental group was significantly higher than that in the control group (p<0.01). The contents of polyunsaturated fatty acids in the FW group were higher and those of saturated and monounsaturated fatty acids were lower than those in the control group. The contents of thiobarbituric acid were significantly different between the control and FW groups (p<0.05). There was also a significant difference between the control and FW groups in terms of off-flavor (p<0.05) after sensory evaluation. To conclude, the off-flavor noted, including other inferior pork quality traits, in the FW group implies that FW should not be used as swine feed.