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.

Role of selenoprotein P expression in the function of pancreatic ß cells: Prevention of ferroptosis-like cell death and stress-induced nascent granule degradation.

Selenoprotein P (SELENOP) is a major selenium (Se)-containing protein (selenoprotein) in human plasma that is mainly synthesized in the liver. SELENOP transports Se to the cells, while SELENOP synthesized in peripheral tissues is incorporated in a paracrine/autocrine manner to maintain the levels of cellular selenoproteins, called the SELENOP cycle. Pancreatic ß cells, responsible for the synthesis and secretion of insulin, are known to express SELENOP. Here, using MIN6 cells as a mouse model for pancreatic ß cells and Selenop small interfering (si)RNA, we found that Selenop gene knockdown (KD) resulted in decreased cell viability, cellular pro/insulin levels, insulin secretion, and levels of several cellular selenoproteins, including glutathione peroxidase 4 (Gpx4) and selenoprotein K (Selenok). These dysfunctions induced by Selenop siRNA were recovered by the addition of Se. Ferroptosis-like cell death, regulated by Gpx4, was involved in the decrease of cell viability by Selenop KD, while stress-induced nascent granule degradation (SINGD), regulated by Selenok, was responsible for the decrease in proinsulin. SINGD was also observed in the pancreatic ß cells of Selenop knockout mice. These findings indicate a significant role of SELENOP expression for the function of pancreatic ß cells by maintaining the levels of cellular selenoproteins such as GPX4 and SELENOK.

Antioxidant action of persulfides and polysulfides against free radical-mediated lipid peroxidation.

Hydrogen sulfide, hydropersulfides, and hydropolysulfides have been revealed to play important physiological roles such as cell signaling and protection against oxidative stress, but the underlying mechanisms and dynamics of action remain elusive. It is generally accepted that these species act by two-electron redox mechanisms, while the involvement of one-electron redox chemistry has received less attention. In this study, the radical-scavenging activity of hydrogen persulfide, hydrogen polysulfides (HSnH n = 2-4), and diallyl- or dialkyl-sulfides (RSnR, n = 1-4) was measured. Furthermore, their antioxidant effects against free radical-mediated human plasma lipid peroxidation were assessed by measuring lipid hydroperoxides. It was found that disodium disulfide, trisulfide, and tetrasulfide acted as potent peroxyl radical scavengers, the rate constant for scavenging peroxyl radical being 3.5 × 105, 4.0 × 105, and 6.0 × 105 M-1 s-1 in PBS pH 7.4 at 37 °C respectively and that they inhibited plasma lipid peroxidation efficiently, the efficacy is increased with the catenation number. Disodium tetrasulfide was 1.5 times as reactive as Trolox toward peroxyl radical and inhibited plasma lipid peroxidation more efficiently than ascorbate and Trolox. On the other hand, diallyl- and dialkyl-sulfides did not exert significant radical-scavenging activity, nor did they inhibit lipid peroxidation efficiently, except for diallyl tetrasulfide, which suppressed plasma lipid peroxidation, despite less significantly than disodium tetrasulfide. Collectively, this study shows that hydrogen persulfide and hydrogen polysulfides act as potent radical-scavenging antioxidants and that, in addition to two-electron redox mechanisms, one electron redox reaction may also play important role in the in vivo defense against deleterious oxidative stress.

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.

Liver-expressed antimicrobial peptide 2 antagonizes the effect of ghrelin in rodents.

Ghrelin, a stomach-derived peptide, promotes feeding and growth hormone (GH) secretion. A recent study identified liver-expressed antimicrobial peptide 2 (LEAP2) as an endogenous inhibitor of ghrelin-induced GH secretion, but the effect of LEAP2 in the brain remained unknown. In this study, we showed that intracerebroventricular (i.c.v.) administration of LEAP2 to rats suppressed central ghrelin functions including Fos expression in the hypothalamic nuclei, promotion of food intake, blood glucose elevation, and body temperature reduction. LEAP2 did not inhibit neuropeptide Y (NPY)-induced food intake or des-acyl ghrelin-induced reduction in body temperature, indicating that the inhibitory effects of LEAP2 were specific for GHSR. Plasma LEAP2 levels varied according to feeding status and seemed to be dependent on the hepatic Leap2 expression. Furthermore, ghrelin suppressed the expression of hepatic Leap2 via AMPK activation. Together, these results reveal that LEAP2 inhibits central ghrelin functions and crosstalk between liver and stomach.

Impaired adaptation of energy intake induces severe obesity in aged mice on a high-fat diet.

High-fat diet (HFD) feeding induces inflammation in various tissues, including the nodose ganglion and hypothalamus, resulting in obesity and metabolic disorders. In this study, we investigated the effect of short-term HFD on aged and young mice. Aged mice easily gained weight during short-term HFD feeding, and required many days to adapt their energy intake. One-day HFD in aged mice induced inflammation in the distal colon, but not in the nodose ganglion or hypothalamus. The anorexic effect of glucagon-like peptide-1 (GLP-1) was attenuated in aged mice. Intraperitoneal administration of GLP-1 did not induce expression of genes that regulate feeding in the hypothalamus of aged mice. mRNA expression of the gene encoding the GLP-1 receptor (Glp1r) in the nodose ganglion was significantly lower in aged mice than in young mice. Our findings suggest that adaptation of energy intake regulation was attenuated in aged mice, causing them to become obese in response to short-term HFD feeding.

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.

Analysis of peripheral ghrelin signaling via the vagus nerve in ghrelin receptor-restored GHSR-null mice.

The vagus nerve connects peripheral organs to the central nervous system (CNS), and gastrointestinal hormones transmit their signals to the CNS via the vagal afferent nerve. Ghrelin, a gastric-derived orexigenic peptide, stimulates food intake by transmitting starvation signals via the vagus nerve. To understand peripheral ghrelin signaling via the vagus nerve, we investigated the ghrelin receptor (GHSR)-null mouse. For this purpose, we tried to produce mice in which GHSR was selectively expressed in the hindbrain and vagus nerve. GHSR was expressed in some nodose ganglion neurons in these mice, but GHSR-expressing neurons were less abundant than in wild-type mice. Intraperitoneal administration of ghrelin did not induce food intake or growth hormone release, but did increase blood glucose levels. Our findings suggest that the abundance of GHSR-expressing neurons in the nodose ganglion is critical for peripheral administration of ghrelin-induced food intake and growth hormone release via the vagus nerve.

Selenoprotein P-neutralizing antibodies improve insulin secretion and glucose sensitivity in type 2 diabetes mouse models.

Selenoprotein P (SeP) functions as a selenium (Se)-supply protein. SeP is identified as a hepatokine, promoting insulin resistance in type 2 diabetes. Thus, the suppression of Se-supply activity of SeP might improve glucose metabolism. Here, we develop an anti-human SeP monoclonal antibody AE2 as with neutralizing activity against SeP. Administration of AE2 to mice significantly improves glucose intolerance and insulin resistance that are induced by human SeP administration. Furthermore, excess SeP administration significantly decreases pancreas insulin levels and high glucose-induced insulin secretion, which are improved by AE2 administration. Epitope mapping reveals that AE2 recognizes a region of human SeP adjacent to the first histidine-rich region (FHR). A polyclonal antibody against the mouse SeP FHR improves glucose intolerance and insulin secretion in a mouse model of diabetes. This report describes a novel molecular strategy for the development of type 2 diabetes therapeutics targeting SeP.

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.

D-Glutamate is metabolized in the heart mitochondria.

D-Amino acids are enantiomers of L-amino acids and have recently been recognized as biomarkers and bioactive substances in mammals, including humans. In the present study, we investigated functions of the novel mammalian mitochondrial protein 9030617O03Rik and showed decreased expression under conditions of heart failure. Genomic sequence analyses showed partial homology with a bacterial aspartate/glutamate/hydantoin racemase. Subsequent determinations of all free amino acid concentrations in 9030617O03Rik-deficient mice showed high accumulations of D-glutamate in heart tissues. This is the first time that a significant amount of D-glutamate was detected in mammalian tissue. Further analysis of D-glutamate metabolism indicated that 9030617O03Rik is a D-glutamate cyclase that converts D-glutamate to 5-oxo-D-proline. Hence, this protein is the first identified enzyme responsible for mammalian D-glutamate metabolism, as confirmed in cloning analyses. These findings suggest that D-glutamate and 5-oxo-D-proline have bioactivities in mammals through the metabolism by D-glutamate cyclase.

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.

Enhancement of lipid peroxidation and its amelioration by vitamin E in a subject with mutations in the SBP2 gene.

Selenocysteine (Sec) insertion sequence-binding protein 2 (SBP2) is essential for the biosynthesis of Sec-containing proteins, termed selenoproteins. Subjects with mutations in the SBP2 gene have decreased levels of several selenoproteins, resulting in a complex phenotype. Selenoproteins play a significant role in antioxidative defense, and deficiencies in these proteins can lead to increased oxidative stress. However, lipid peroxidation and the effects of antioxidants in subjects with SBP2 gene mutations have not been studied. In the present study, we evaluated the lipid peroxidation products in the blood of a subject (the proband) with mutations in the SBP2 gene. We found that the proband had higher levels of free radical-mediated lipid peroxidation products, such as 7ß-hydroxycholesterol, than the control subjects. Treatment of the proband with vitamin E (α-tocopherol acetate, 100 mg/day), a lipid-soluble antioxidant, for 2 years reduced lipid peroxidation product levels to those of control subjects. Withdrawal of vitamin E treatment for 7 months resulted in an increase in lipid peroxidation products. Collectively, these results clearly indicate that free radical-mediated oxidative stress is increased in the subject with SBP2 gene mutations and that vitamin E treatment effectively inhibits the generation of lipid peroxidation products.

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.