The NERP-4-SNAT2 axis regulates pancreatic ß-cell maintenance and function.

Insulin secretion from pancreatic ß cells is regulated by multiple stimuli, including nutrients, hormones, neuronal inputs, and local signalling. Amino acids modulate insulin secretion via amino acid transporters expressed on ß cells. The granin protein VGF has dual roles in ß cells: regulating secretory granule formation and functioning as a multiple peptide precursor. A VGF-derived peptide, neuroendocrine regulatory peptide-4 (NERP-4), increases Ca2+ influx in the pancreata of transgenic mice expressing apoaequorin, a Ca2+-induced bioluminescent protein complex. NERP-4 enhances glucose-stimulated insulin secretion from isolated human and mouse islets and ß-cell-derived MIN6-K8 cells. NERP-4 administration reverses the impairment of ß-cell maintenance and function in db/db mice by enhancing mitochondrial function and reducing metabolic stress. NERP-4 acts on sodium-coupled neutral amino acid transporter 2 (SNAT2), thereby increasing glutamine, alanine, and proline uptake into ß cells and stimulating insulin secretion. SNAT2 deletion and inhibition abolish the protective effects of NERP-4 on ß-cell maintenance. These findings demonstrate a novel autocrine mechanism of ß-cell maintenance and function that is mediated by the peptide-amino acid transporter axis.

An efficient selenium transport pathway of selenoprotein P utilizing a high-affinity ApoER2 receptor variant and being independent of selenocysteine lyase.

Selenoprotein P (SeP, encoded by the SELENOP gene) is a plasma protein that contains selenium in the form of selenocysteine residues (Sec, a cysteine analog containing selenium instead of sulfur). SeP functions for the transport of selenium to specific tissues in a receptor-dependent manner. Apolipoprotein E receptor 2 (ApoER2) has been identified as a SeP receptor. However, diverse variants of ApoER2 have been reported, and the details of its tissue specificity and the molecular mechanism of its efficiency remain unclear. In the present study, we found that human T lymphoma Jurkat cells have a high ability to utilize selenium via SeP, while this ability was low in human rhabdomyosarcoma cells. We identified an ApoER2 variant with a high affinity for SeP in Jurkat cells. This variant had a dissociation constant value of 0.67 nM and a highly glycosylated O-linked sugar domain. Moreover, the acidification of intracellular vesicles was necessary for selenium transport via SeP in both cell types. In rhabdomyosarcoma cells, SeP underwent proteolytic degradation in lysosomes and transported selenium in a Sec lyase-dependent manner. However, in Jurkat cells, SeP transported selenium in Sec lyase-independent manner. These findings indicate a preferential selenium transport pathway involving SeP and high-affinity ApoER2 in a Sec lyase-independent manner. Herein, we provide a novel dynamic transport pathway for selenium via SeP.

Identification of a novel endogenous long non-coding RNA that inhibits selenoprotein P translation.

Selenoprotein P (SELENOP) is a major plasma selenoprotein that contains 10 Sec residues, which is encoded by the UGA stop codon. The mRNA for SELENOP has the unique property of containing two Sec insertion sequence (SECIS) elements, which is located in the 3' untranslated region (3'UTR). Here, we coincidentally identified a novel gene, CCDC152, by sequence analysis. This gene was located in the antisense region of the SELENOP gene, including the 3'UTR region in the genome. We demonstrated that this novel gene functioned as a long non-coding RNA (lncRNA) that decreased SELENOP protein levels via translational rather than transcriptional, regulation. We found that the CCDC152 RNA interacted specifically and directly with the SELENOP mRNA and inhibited its binding to the SECIS-binding protein 2, resulting in the decrease of ribosome binding. We termed this novel gene product lncRNA inhibitor of SELENOP translation (L-IST). Finally, we found that epigallocatechin gallate upregulated L-IST in vitro and in vivo, to suppress SELENOP protein levels. Here, we provide a new regulatory mechanism of SELENOP translation by an endogenous long antisense ncRNA.

Distribution of oxidized DJ-1 in Parkinson's disease-related sites in the brain and in the peripheral tissues: effects of aging and a neurotoxin.

DJ-1 plays an important role in antioxidant defenses, and a reactive cysteine at position 106 (Cys106) of DJ-1, a critical residue of its biological function, is oxidized under oxidative stress. DJ-1 oxidation has been reported in patients with Parkinson's disease (PD), but the relationship between DJ-1 oxidation and PD is still unclear. In the present study using specific antibody for Cys106-oxidized DJ-1 (oxDJ-1), we analyzed oxDJ-1 levels in the brain and peripheral tissues in young and aged mice and in a mouse model of PD induced using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). OxDJ-1 levels in the brain, heart, and skeletal muscle were high compared with other tissues. In the brain, oxDJ-1 was detected in PD-related brain sites such as the substantia nigra (SN) of the midbrain, olfactory bulb (OB), and striatum. In aged wild-type mice, oxDJ-1 levels in the OB, striatum, and heart tended to decrease, while those in the skeletal muscle increased significantly. Expression of dopamine-metabolizing enzymes significantly increased in the SN and OB of aged DJ-1-/- mice, accompanied by a complementary increase in glutathione peroxidase 1. MPTP treatment concordantly changed oxDJ-1 levels in PD-related brain sites and heart. These results indicate that the effects of physiological metabolism, aging, and neurotoxin change oxDJ-1 levels in PD-related brain sites, heart, and skeletal muscle where mitochondrial load is high, suggesting a substantial role of DJ-1 in antioxidant defenses and/or dopamine metabolism in these tissues.

Deficiency of the hepatokine selenoprotein P increases responsiveness to exercise in mice through upregulation of reactive oxygen species and AMP-activated protein kinase in muscle.

Exercise has numerous health-promoting effects in humans; however, individual responsiveness to exercise with regard to endurance or metabolic health differs markedly. This 'exercise resistance' is considered to be congenital, with no evident acquired causative factors. Here we show that the anti-oxidative hepatokine selenoprotein P (SeP) causes exercise resistance through its muscle receptor low-density lipoprotein receptor-related protein 1 (LRP1). SeP-deficient mice showed a 'super-endurance' phenotype after exercise training, as well as enhanced reactive oxygen species (ROS) production, AMP-activated protein kinase (AMPK) phosphorylation and peroxisome proliferative activated receptor γ coactivator (Ppargc)-1α (also known as PGC-1α; encoded by Ppargc1a) expression in skeletal muscle. Supplementation with the anti-oxidant N-acetylcysteine (NAC) reduced ROS production and the endurance capacity in SeP-deficient mice. SeP treatment impaired hydrogen-peroxide-induced adaptations through LRP1 in cultured myotubes and suppressed exercise-induced AMPK phosphorylation and Ppargc1a gene expression in mouse skeletal muscle-effects which were blunted in mice with a muscle-specific LRP1 deficiency. Furthermore, we found that increased amounts of circulating SeP predicted the ineffectiveness of training on endurance capacity in humans. Our study suggests that inhibitors of the SeP-LRP1 axis may function as exercise-enhancing drugs to treat diseases associated with a sedentary lifestyle.

Oxidation and interaction of DJ-1 with 20S proteasome in the erythrocytes of early stage Parkinson's disease patients.

Parkinson's disease (PD) is a progressive, age-related, neurodegenerative disorder, and oxidative stress is an important mediator in its pathogenesis. DJ-1, the product of the causative gene of a familial form of PD, plays a significant role in anti-oxidative defence to protect cells from oxidative stress. DJ-1 undergoes preferential oxidation at the cysteine residue at position 106 (Cys-106) under oxidative stress. Here, using specific antibodies against Cys-106-oxidized DJ-1 (oxDJ-1), it was found that the levels of oxDJ-1 in the erythrocytes of unmedicated PD patients (n = 88) were higher than in those of medicated PD patients (n = 62) and healthy control subjects (n = 33). Elevated oxDJ-1 levels were also observed in a non-human primate PD model. Biochemical analysis of oxDJ-1 in erythrocyte lysates showed that oxDJ-1 formed dimer and polymer forms, and that the latter interacts with 20S proteasome. These results clearly indicate a biochemical alteration in the blood of PD patients, which could be utilized as an early diagnosis marker for PD.

Genetic polymorphism at codon 546 of the human RAD17 contributes to the risk for esophageal squamous cell carcinoma.

Human RAD17, a human homolog of the Schizosaccharomyces pombe cell cycle checkpoint gene RAD17, plays a significant role in activating checkpoint signals in response to DNA damage. We evaluated the association of hRAD17 Leu546Arg (rs1045051), a missense single nucleotide polymorphism, with the risk of esophageal squamous cell carcinoma in relation to smoking and alcohol consumption history in 154 esophageal squamous cell carcinoma male patients and 695 cancer-free male controls by a case-control study conducted in Japan. The results showed that the hRAD17 Arg/Arg genotype compared to the Leu/Leu and Leu/Arg genotypes was significantly associated with the risk of the esophageal squamous cell carcinoma with an adjusted odds ratios of 2.22 (95% CI: 1.19-4.16 P=0.013). In stratified studies, the risk of esophageal squamous cell carcinoma was markedly higher in light drinkers (less than 23 g ethanol/day) with the Arg/Arg genotype than in heavy drinkers (excess of 23 g ethanol/day) with the Arg/Arg genotype (OR=2.83, 95% CI: 1.05-7.61, P=0.04). We concluded that the genetic variant of hRAD17 Leu546Arg polymorphism exerts a significant effect on esophageal squamous cell carcinoma risk among Japanese men.

An alpha-adrenergic agonist protects hearts by inducing Akt1-mediated autophagy.

Alpha-adrenergic agonists is known to be protective in cardiac myocytes from apoptosis induced by beta-adrenergic stimulation. Although there has been a recent focus on the role of cardiac autophagy in heart failure, its role in heart failure with adrenergic overload has not yet been elucidated. In the present study, we investigated the contribution of autophagy to cardiac failure during adrenergic overload both in vitro and in vivo. Neonatal rat cardiac myocytes overexpressing GFP-tagged LC3 were prepared and stimulated with the alpha1-adrenergic agonist, phenylephrine (PE), the beta-adrenergic agonist, isoproterenol (ISO), or norepinephrine (NE) in order to track changes in the formation of autophagosomes in vitro. All adrenergic stimulators increased cardiac autophagy by stimulating autophagic flux. Blocking autophagy by the knockdown of autophagy-related 5 (ATG5) exacerbated ISO-induced apoptosis and negated the anti-apoptotic effects of PE, which indicated the cardioprotective role of autophagy during adrenergic overload. PE-induced cardiac autophagy was mediated by the PI3-kinase/Akt pathway, but not by MEK/ERK, whereas both pathways mediated the anti-apoptotic effects of PE. Knock down of Akt1 was the most essential among the three Akt family members examined for the induction of cardiac autophagy. The four-week administration of PE kept the high level of cardiac autophagy without heart failure in vivo, whereas autophagy levels in a myocardium impaired by four-week persistent administration of ISO or NE were the same with the control state. These present study indicated that cardiac autophagy played a protective role during adrenergic overload and also that the Akt pathway could mediate cardiac autophagy for the anti-apoptotic effects of the alpha-adrenergic pathway.

Immunostaining of oxidized DJ-1 in human and mouse brains.

DJ-1, the product of a causative gene of a familial form of Parkinson disease, undergoes preferential oxidation of Cys106 (cysteine residue at position 106) under oxidative stress. Using specific monoclonal antibodies against Cys106 oxidized DJ-1 (oxDJ-1), we examined oxDJ-1 immunoreactivity in brain sections from DJ-1 knockout and wild-type mice and in human brain sections from cases classified into different Lewy body stages of Parkinson disease and Parkinson disease with dementia. Oxidized DJ-1 immunoreactivity was prominently observed in neuromelanin-containing neurons and neuron processes of the substantia nigra; Lewy bodies also showed oxDJ-1 immunoreactivity. Oxidized DJ-1 was also detected in astrocytes in the striatum, in neurons and glia in the red nucleus, and in the inferior olivary nucleus, all of which are related to regulation of movement. These observations suggest the relevance of DJ-1 oxidation to homeostasis in multiple brain regions, including neuromelanin-containing neurons of the substantia nigra, and raise the possibility that oxDJ-1 levels might change during the progression of Lewy body-associated neurodegenerative diseases.

Cytosolic p53 inhibits Parkin-mediated mitophagy and promotes mitochondrial dysfunction in the mouse heart.

Cumulative evidence indicates that mitochondrial dysfunction has a role in heart failure progression, but whether mitochondrial quality control mechanisms are involved in the development of cardiac dysfunction remains unclear. Here we show that cytosolic p53 impairs autophagic degradation of damaged mitochondria and facilitates mitochondrial dysfunction and heart failure in mice. Prevalence and induction of mitochondrial autophagy is attenuated by senescence or doxorubicin treatment in vitro and in vivo. We show that cytosolic p53 binds to Parkin and disturbs its translocation to damaged mitochondria and their subsequent clearance by mitophagy. p53-deficient mice show less decline of mitochondrial integrity and cardiac functional reserve with increasing age or after treatment with doxorubicin. Furthermore, overexpression of Parkin ameliorates the functional decline in aged hearts, and is accompanied by decreased senescence-associated ß-galactosidase activity and proinflammatory phenotypes. Thus, p53-mediated inhibition of mitophagy modulates cardiac dysfunction, raising the possibility that therapeutic activation of mitophagy by inhibiting cytosolic p53 may ameliorate heart failure and symptoms of cardiac ageing.

p53-TIGAR axis attenuates mitophagy to exacerbate cardiac damage after ischemia.

Inhibition of tumor suppressor p53 is cardioprotective against ischemic injury and provides resistance to subsequent cardiac remodeling. We investigated p53-mediated expansion of ischemic damage with a focus on mitochondrial integrity in association with autophagy and apoptosis. p53(-/-) heart showed that autophagic flux was promoted under ischemia without a change in cardiac tissue ATP content. Electron micrographs revealed that ischemic border zone in p53(-/-) mice had 5-fold greater numbers of autophagic vacuoles containing mitochondria, indicating the occurrence of mitophagy, with an apparent reduction of abnormal mitochondria compared with those in WT mice. Analysis of autophagic mediators acting downstream of p53 revealed that TIGAR (TP53-induced glycolysis and apoptosis regulator) was exclusively up-regulated in ischemic myocardium. TIGAR(-/-) mice exhibited the promotion of mitophagy followed by decrease of abnormal mitochondria and resistance to ischemic injury, consistent with the phenotype of p53(-/-) mice. In p53(-/-) and TIGAR(-/-) ischemic myocardium, ROS production was elevated and followed by Bnip3 activation which is an initiator of mitophagy. Furthermore, the activation of Bnip3 and mitophagy due to p53/TIGAR inhibition were reversed with antioxidant N-acetyl-cysteine, indicating that this adaptive response requires ROS signal. Inhibition of mitophagy using chloroquine in p53(-/-) or TIGAR(-/-) mice exacerbated accumulation of damaged mitochondria to the level of wild-type mice and attenuated cardioprotective action. These findings indicate that p53/TIGAR-mediated inhibition of myocyte mitophagy is responsible for impairment of mitochondrial integrity and subsequent apoptosis, the process of which is closely involved in p53-mediated ventricular remodeling after myocardial infarction.

p53 promotes cardiac dysfunction in diabetic mellitus caused by excessive mitochondrial respiration-mediated reactive oxygen species generation and lipid accumulation.

BACKGROUND: Diabetic cardiomyopathy is characterized by energetic dysregulation caused by glucotoxicity, lipotoxicity, and mitochondrial alterations. p53 and its downstream mitochondrial assembly protein, synthesis of cytochrome c oxidase 2 (SCO2), are important regulators of mitochondrial respiration, whereas the involvement in diabetic cardiomyopathy remains to be determined. METHODS AND RESULTS: The role of p53 and SCO2 in energy metabolism was examined in both type I (streptozotocin [STZ] administration) and type II diabetic (db/db) mice. Cardiac expressions of p53 and SCO2 in 4-week STZ diabetic mice were upregulated (185% and 152% versus controls, respectively, P<0.01), with a marked decrease in cardiac performance. Mitochondrial oxygen consumption was increased (136% versus control, P<0.01) in parallel with augmentation of mitochondrial cytochrome c oxidase (complex IV) activity. Reactive oxygen species (ROS)-damaged myocytes and lipid accumulation were increased in association with membrane-localization of fatty acid translocase protein FAT/CD36. Antioxidant tempol reduced the increased expressions of p53 and SCO2 in STZ-diabetic hearts and normalized alterations in mitochondrial oxygen consumption, lipid accumulation, and cardiac dysfunction. Similar results were observed in db/db mice, whereas in p53-deficient or SCO2-deficient diabetic mice, the cardiac and metabolic abnormalities were prevented. Overexpression of SCO2 in cardiac myocytes increased mitochondrial ROS and fatty acid accumulation, whereas knockdown of SCO2 ameliorated them. CONCLUSIONS: Myocardial p53/SCO2 signal is activated by diabetes-mediated ROS generation to increase mitochondrial oxygen consumption, resulting in excessive generation of mitochondria-derived ROS and lipid accumulation in association with cardiac dysfunction.

TP53 codon 72 polymorphism is associated with pancreatic cancer risk in males, smokers and drinkers.

Tumor protein p53 (TP53) is the best-known tumor suppressor gene and plays a crucial role in carcinogenesis. The TP53 Arg 72 Pro polymorphism has been reported to be a risk factor for several types of cancer, but its association with pancreatic cancer has not been fully evaluated. Therefore, we investigated the effects of this polymorphism on pancreatic cancer in relation to smoking and drinking habits by examining the distribution of the SNP genotypes in 226 pancreatic cancer patients and 448 healthy controls. The frequencies of Arg/Arg, Arg/Pro and Pro/Pro were found to be 37, 49 and 15% in the pancreatic cancer cases and 44, 46 and 10% in the controls, respectively. Compared to the controls with the Arg/Arg genotype, cases with Pro/Pro homozygosity exhibited a significantly increased risk [adjusted odds ratio (OR)=1.70; 95% confidence interval (CI) 1.01-2.88]. In stratified studies, the association was particularly strong in males (OR=2.62; 95% CI 1.32-5.23), particularly in those smoking in excess of 20 pack-years and drinking in excess of 23 g ethanol/day (OR=5.02; 95% CI 1.12-22.51). We found that the TP53 Pro/Pro genotype compared to the Arg/Arg genotype had a profound effect on pancreatic cancer risk among males, particularly among heavy smokers and excessive alcohol drinkers.

p53 and TIGAR regulate cardiac myocyte energy homeostasis under hypoxic stress.

Bioenergetic homeostasis is altered in heart failure and may play an important role in pathogenesis. p53 has been implicated in heart failure, and although its role in regulating tumorigenesis is well characterized, its activities on cellular metabolism are just beginning to be understood. We investigated the role of p53 and its transcriptional target gene TP53-induced glycolysis and apoptosis regulator (TIGAR) in myocardial energy metabolism under conditions simulating ischemia that can lead to heart failure. Expression of p53 and TIGAR was markedly upregulated after myocardial infarction, and apoptotic myocytes were decreased by 42% in p53-deficient mouse hearts compared with those in wild-type mice. To examine the effect of p53 on energy metabolism, cardiac myocytes were exposed to hypoxia. Hypoxia induced p53 and TIGAR expression in a p53-dependent manner. Knockdown of p53 or TIGAR increased glycolysis with elevated fructose-2,6-bisphosphate levels and reduced myocyte apoptosis. Hypoxic stress decreased phosphocreatine content and the mitochondrial membrane potential of myocytes without changes in ATP content, the effects of which were prevented by the knockdown of TIGAR. Inhibition of glycolysis by 2-deoxyglucose blocked these bioenergetic effects and TIGAR siRNA-mediated prevention of apoptosis, and, in contrast, overexpression of TIGAR reduced glucose utilization and increased apoptosis. Our data demonstrate that p53 and TIGAR inhibit glycolysis in hypoxic myocytes and that inhibition of glycolysis is closely involved in apoptosis, suggesting that p53 and TIGAR are significant mediators of cellular energy homeostasis and cell death under ischemic stress.

Missense polymorphisms of PTPRJ and PTPN13 genes affect susceptibility to a variety of human cancers.

PURPOSE: We investigated the association between incidence of various cancers and four single nucleotide polymorphisms (SNPs), two each in two protein tyrosine phosphatase (PTP) genes, PTPRJ and PTPN13, by a case-control study conducted in Japan. METHODS: The study samples comprised 819 cancer-free controls and 569 cancer cases including lung, head and neck, colorectal, and esophageal cancers. RESULTS: Compared with the major homozygotes at the Arg326Gln SNP in PTPRJ, a likely homologue of the mouse SCC1 (susceptible to colon cancer), Arg/Gln or Gln/Gln genotypes exhibited an increased colorectal cancer risk with adjusted odds ratios (aOR) of 1.71 (P = 0.021) and 3.74 (P = 4.14 x 10(-4)), respectively. Increased risks were observed with one or more of the combination genotypes of Gln276Pro and Arg326Gln in PTPRJ for most cancer types (aOR range 10.13-55.08, Bonferroni-corrected P = 0.0454-7.20 x 10(-9)). In the PTPN13, major homozygotes of Ile1522Met showed an increased risk for lung squamous cell carcinomas (aOR 1.86), compared to the heterozygotes. Increased risks were observed with at least one of the combination genotypes of the two SNPs, Ile1522Met and Tyr2081Asp, for all but esophageal cancer examined (aOR 3.36-13.75), compared with double heterozygotes. Moreover, these high risks were seen also when all cancer cases were combined (aOR 1.81-6.84). CONCLUSIONS: PTPRJ and PTPN13 SNPs were found to influence susceptibility to a wide spectrum of cancers. Because allelic frequencies of these SNPs are relatively common in many ethnic groups, these findings are worthy of further study.