Absence of a reductase, NCB5OR, causes insulin-deficient diabetes

A functional map of phosphoprotein phosphatase regulation identifies an evolutionary conserved reductase for the catalytic metal ions

Serine/Threonine phosphoprotein phosphatases (PPPs, PP1-PP7) are conserved metalloenzymes and central to intracellular signaling in eukaryotes, but the details of their regulation is poorly understood. To address this, we performed genome-wide CRISPR knockout and focused base editor screens in PPP perturbed conditions to establish a high-resolution functional map of PPP regulation that pinpoints novel regulatory mechanisms. Through this, we identify the orphan reductase CYB5R4 as an evolutionarily conserved activator of PP4 and PP6, but not the closely related PP2A. Heme binding is essential for CYB5R4 function and mechanistically involves the reduction of the metal ions in the active site. Importantly, CYB5R4-mediated activation of PP4 is critical for cell viability when cells are treated with DNA damage-inducing agents known to cause oxidative stress. The discovery of a dedicated PPP reductase points to shared regulatory principles with protein tyrosine phosphatases, where specific enzymes dictate activity by regulating the active site redox state. In sum, our work provides a resource for understanding PPP function and the regulation of intracellular signaling.

Heme metabolism in nonerythroid cells

Heme is an iron-containing prosthetic group necessary for the function of several proteins termed "hemoproteins." Erythrocytes contain most of the body's heme in the form of hemoglobin and contain high concentrations of free heme. In nonerythroid cells, where cytosolic heme concentrations are 2 to 3 orders of magnitude lower, heme plays an essential and often overlooked role in a variety of cellular processes. Indeed, hemoproteins are found in almost every subcellular compartment and are integral in cellular operations such as oxidative phosphorylation, amino acid metabolism, xenobiotic metabolism, and transcriptional regulation. Growing evidence reveals the participation of heme in dynamic processes such as circadian rhythms, NO signaling, and the modulation of enzyme activity. This dynamic view of heme biology uncovers exciting possibilities as to how hemoproteins may participate in a range of physiologic systems. Here, we discuss how heme is regulated at the level of its synthesis, availability, redox state, transport, and degradation and highlight the implications for cellular function and whole organism physiology.

The N-terminal intrinsically disordered region of Ncb5or docks with the cytochrome b5 core to form a helical motif that is of ancient origin

NADH cytochrome b5 oxidoreductase (Ncb5or) is a cytosolic ferric reductase implicated in diabetes and neurological conditions. Ncb5or comprises cytochrome b5 (b5 ) and cytochrome b5 reductase (b5 R) domains separated by a CHORD-Sgt1 (CS) linker domain. Ncb5or redox activity depends on proper inter-domain interactions to mediate electron transfer from NADH or NADPH via FAD to heme. While full-length human Ncb5or has proven resistant to crystallization, we have succeeded in obtaining high-resolution atomic structures of the b5 domain and a construct containing the CS and b5 R domains (CS/b5 R). Ncb5or also contains an N-terminal intrinsically disordered region of 50 residues that has no homologs in other protein families in animals but features a distinctive, conserved L34 MDWIRL40 motif also present in reduced lateral root formation (RLF) protein in rice and increased recombination center 21 in baker's yeast, all attaching to a b5 domain. After unsuccessful attempts at crystallizing a human Ncb5or construct comprising the N-terminal region naturally fused to the b5 domain, we were able to obtain a high-resolution atomic structure of a recombinant rice RLF construct corresponding to residues 25-129 of human Ncb5or (52% sequence identity; 74% similarity). The structure reveals Trp120 (corresponding to invariant Trp37 in Ncb5or) to be part of an 11-residue α-helix (S116 QMDWLKLTRT126 ) packing against two of the four helices in the b5 domain that surround heme (α2 and α5). The Trp120 side chain forms a network of interactions with the side chains of four highly conserved residues corresponding to Tyr85 and Tyr88 (α2), Cys124 (α5), and Leu47 in Ncb5or. Circular dichroism measurements of human Ncb5or fragments further support a key role of Trp37 in nucleating the formation of the N-terminal helix, whose location in the N/b5 module suggests a role in regulating the function of this multi-domain redox enzyme. This study revealed for the first time an ancient origin of a helical motif in the N/b5 module as reflected by its existence in a class of cytochrome b5 proteins from three kingdoms among eukaryotes.

Vitamin E/Coenzyme Q-Dependent "Free Radical Reductases": Redox Regulators in Ferroptosis

Significance: Lipid peroxidation and its products, oxygenated polyunsaturated lipids, act as essential signals coordinating metabolism and physiology and can be deleterious to membranes when they accumulate in excessive amounts. Recent Advances: There is an emerging understanding that regulation of polyunsaturated fatty acid (PUFA) phospholipid peroxidation, particularly of PUFA-phosphatidylethanolamine, is important in a newly discovered type of regulated cell death, ferroptosis. Among the most recently described regulatory mechanisms is the ferroptosis suppressor protein, which controls the peroxidation process due to its ability to reduce coenzyme Q (CoQ). Critical Issues: In this study, we reviewed the most recent data in the context of the concept of free radical reductases formulated in the 1980-1990s and focused on enzymatic mechanisms of CoQ reduction in different membranes (e.g., mitochondrial, endoplasmic reticulum, and plasma membrane electron transporters) as well as TCA cycle components and cytosolic reductases capable of recycling the high antioxidant efficiency of the CoQ/vitamin E system. Future Directions: We highlight the importance of individual components of the free radical reductase network in regulating the ferroptotic program and defining the sensitivity/tolerance of cells to ferroptotic death. Complete deciphering of the interactive complexity of this system may be important for designing effective antiferroptotic modalities. Antioxid. Redox Signal. 40, 317-328.

Cytochrome b5 reductases: Redox regulators of cell homeostasis

The cytochrome-b5 reductase (CYB5R) family of flavoproteins is known to regulate reduction-oxidation (redox) balance in cells. The five enzyme members are highly compartmentalized at the subcellular level and function as "redox switches" enabling the reduction of several substrates, such as heme and coenzyme Q. Critical insight into the physiological and pathophysiological significance of CYB5R enzymes has been gleaned from several human genetic variants that cause congenital disease and a broad spectrum of chronic human diseases. Among the CYB5R genetic variants, CYB5R3 is well-characterized and deficiency in expression and activity is associated with type II methemoglobinemia, cancer, neurodegenerative disorders, diabetes, and cardiovascular disease. Importantly, pharmacological and genetic-based strategies are underway to target CYB5R3 to circumvent disease onset and mitigate severity. Despite our knowledge of CYB5R3 in human health and disease, the other reductases in the CYB5R family have been understudied, providing an opportunity to unravel critical function(s) for these enzymes in physiology and disease. In this review, we aim to provide the broad scientific community an up-to-date overview of the molecular, cellular, physiological, and pathophysiological roles of CYB5R proteins.

Characterization and Molecular Mechanism of a Novel Cytochrome b5 Reductase with NAD(P)H Specificity from Mortierella alpina

The electron-transfer capabilities of cytochrome b₅ reductase (Cyt b₅R) and NADPH supply have been shown to be critical factors in microbial fatty acid synthesis. Unfortunately, Cyt b₅R substrate specificity is limited to the coenzyme NADH. In this study, we discovered that a novel Cyt b₅R from Mortierella alpina (MaCytb5RII) displays affinity for NADPH and NADH. The enzymatic characteristics of high-purity MaCytb5RII were determined with the K_m,NADPH and K_m,NADH being 0.42 and 0.07 mM, respectively. MaCytb5RII shows high specific activity at 4 °C and pH 9.0. We anchored the residues that interacted with the coenzymes using the homology models of MaCytb5Rs docking NAD(P)H and FAD. The enzyme activity analysis of the purified mutants MaCytb5RII_[S230N], MaCytb5RII_[Y242F], and MaCytb5RII_[S272A] revealed that Ser230 is essential for MaCytb5RII to have dual NAD(P)H dependence, whereas Tyr242 influences MaCytb5RII's NADPH affinity and Ala272 greatly decreases MaCytb5RII's NADH affinity.

Mutations in Hsp90 Cochaperones Result in a Wide Variety of Human Disorders

The Hsp90 molecular chaperone, along with a set of approximately 50 cochaperones, mediates the folding and activation of hundreds of cellular proteins in an ATP-dependent cycle. Cochaperones differ in how they interact with Hsp90 and their ability to modulate ATPase activity of Hsp90. Cochaperones often compete for the same binding site on Hsp90, and changes in levels of cochaperone expression that occur during neurodegeneration, cancer, or aging may result in altered Hsp90-cochaperone complexes and client activity. This review summarizes information about loss-of-function mutations of individual cochaperones and discusses the overall association of cochaperone alterations with a broad range of diseases. Cochaperone mutations result in ciliary or muscle defects, neurological development or degeneration disorders, and other disorders. In many cases, diseases were linked to defects in established cochaperone-client interactions. A better understanding of the functional consequences of defective cochaperones will provide new insights into their functions and may lead to specialized approaches to modulate Hsp90 functions and treat some of these human disorders.

Cholecystokinin-like peptide mediates satiety by inhibiting sugar attraction

Feeding is essential for animal survival and reproduction and is regulated by both internal states and external stimuli. However, little is known about how internal states influence the perception of external sensory cues that regulate feeding behavior. Here, we investigated the neuronal and molecular mechanisms behind nutritional state-mediated regulation of gustatory perception in control of feeding behavior in the brown planthopper and Drosophila. We found that feeding increases the expression of the cholecystokinin-like peptide, sulfakinin (SK), and the activity of a set of SK-expressing neurons. Starvation elevates the transcription of the sugar receptor Gr64f and SK negatively regulates the expression of Gr64f in both insects. Interestingly, we found that one of the two known SK receptors, CCKLR-17D3, is expressed by some of Gr64f-expressing neurons in the proboscis and proleg tarsi. Thus, we have identified SK as a neuropeptide signal in a neuronal circuitry that responds to food intake, and regulates feeding behavior by diminishing gustatory receptor gene expression and activity of sweet sensing GRNs. Our findings demonstrate one nutritional state-dependent pathway that modulates sweet perception and thereby feeding behavior, but our experiments cannot exclude further parallel pathways. Importantly, we show that the underlying mechanisms are conserved in the two distantly related insect species.

Food intake is critical for animal survival and reproduction and is regulated both by internal states that signal appetite or satiety, and by external sensory stimuli. It is well known that the internal nutritional state influences the strength of the chemosensory perception of food signals. Thus, both gustatory and olfactory signals of preferred food are strengthened in hungry animals. However, the molecular mechanisms behind satiety-mediated modulation of taste are still not known. We show here that cholecystokinin-like (SK) peptide in brown planthopper and Drosophila signals satiety and inhibits sugar attraction by lowering the activity of sweet-sensing gustatory neurons and transcription of a sugar receptor gene, Gr64f. We show that SK peptide signaling reflects the nutritional state and inhibits feeding behavior. Re-feeding after starvation increases SK peptide expression and spontaneous activity of SK producing neurons. Interestingly, we found that SK peptide negatively regulates the expression of the sweet gustatory receptor and that activation of SK producing neurons inhibits the activity of sweet-sensing gustatory neurons (GRNs). Furthermore, we found that one of the two known SK peptide receptors is expressed in some sweet-sensing GRNs in the proboscis and proleg tarsi. In summary, our findings provide a mechanism that is conserved in distantly related insects and which explains how feeding state modulates sweet perception to regulate feeding behavior. Thus, we have identified a neuropeptide signal and its neuronal circuitry that respond to satiety, and that regulate feeding behavior by inhibiting gustatory receptor gene expression and activity of sweet sensing GRNs.

A Genetic Map of the Response to DNA Damage in Human Cells

The response to DNA damage is critical for cellular homeostasis, tumor suppression, immunity, and gametogenesis. In order to provide an unbiased and global view of the DNA damage response in human cells, we undertook 31 CRISPR-Cas9 screens against 27 genotoxic agents in the retinal pigment epithelium-1 (RPE1) cell line. These screens identified 890 genes whose loss causes either sensitivity or resistance to DNA-damaging agents. Mining this dataset, we discovered that ERCC6L2 (which is mutated in a bone-marrow failure syndrome) codes for a canonical non-homologous end-joining pathway factor, that the RNA polymerase II component ELOF1 modulates the response to transcription-blocking agents, and that the cytotoxicity of the G-quadruplex ligand pyridostatin involves trapping topoisomerase II on DNA. This map of the DNA damage response provides a rich resource to study this fundamental cellular system and has implications for the development and use of genotoxic agents in cancer therapy.

Cyb5r3 links FoxO1-dependent mitochondrial dysfunction with β-cell failure

OBJECTIVE

Diabetes is characterized by pancreatic β-cell dedifferentiation. Dedifferentiating β cells inappropriately metabolize lipids over carbohydrates and exhibit impaired mitochondrial oxidative phosphorylation. However, the mechanism linking the β-cell's response to an adverse metabolic environment with impaired mitochondrial function remains unclear.

METHODS

Here we report that the oxidoreductase cytochrome b5 reductase 3 (Cyb5r3) links FoxO1 signaling to β-cell stimulus/secretion coupling by regulating mitochondrial function, reactive oxygen species generation, and nicotinamide actin dysfunction (NAD)/reduced nicotinamide actin dysfunction (NADH) ratios.

RESULTS

The expression of Cyb5r3 is decreased in FoxO1-deficient β cells. Mice with β-cell-specific deletion of Cyb5r3 have impaired insulin secretion, resulting in glucose intolerance and diet-induced hyperglycemia. Cyb5r3-deficient β cells have a blunted respiratory response to glucose and display extensive mitochondrial and secretory granule abnormalities, consistent with altered differentiation. Moreover, FoxO1 is unable to maintain expression of key differentiation markers in Cyb5r3-deficient β cells, suggesting that Cyb5r3 is required for FoxO1-dependent lineage stability.

CONCLUSIONS

The findings highlight a pathway linking FoxO1 to mitochondrial dysfunction that can mediate β-cell failure.

Crystal structures of the naturally fused CS and cytochrome b5 reductase (b5R) domains of Ncb5or reveal an expanded CS fold, extensive CS-b5R interactions and productive binding of the NAD(P)+ nicotinamide ring

Ncb5or (NADH-cytochrome b5 oxidoreductase), a cytosolic ferric reductase implicated in diabetes and neurological diseases, comprises three distinct domains, cytochrome b5 (b5) and cytochrome b5 reductase (b5R) domains separated by a CHORD-Sgt1 (CS) domain, and a novel 50-residue N-terminal region. Understanding how interdomain interactions in Ncb5or facilitate the shuttling of electrons from NAD(P)H to heme, and how the process compares with the microsomal b5 (Cyb5A) and b5R (Cyb5R3) system, is of interest. A high-resolution structure of the b5 domain (PDB entry 3lf5) has previously been reported, which exhibits substantial differences in comparison to Cyb5A. The structural characterization of a construct comprising the naturally fused CS and b5R domains with bound FAD and NAD+ (PDB entry 6mv1) or NADP+ (PDB entry 6mv2) is now reported. The structures reveal that the linker between the CS and b5R cores is more ordered than predicted, with much of it extending the β-sandwich motif of the CS domain. This limits the flexibility between the two domains, which recognize one another via a short β-sheet motif and a network of conserved side-chain hydrogen bonds, salt bridges and cation-π interactions. Notable differences in FAD-protein interactions in Ncb5or and Cyb5R3 provide insight into the selectivity for docking of their respective b5 redox partners. The structures also afford a structural explanation for the unusual ability of Ncb5or to utilize both NADH and NADPH, and represent the first examples of native, fully oxidized b5R family members in which the nicotinamide ring of NAD(P)+ resides in the active site. Finally, the structures, together with sequence alignments, show that the b5R domain is more closely related to single-domain Cyb5R proteins from plants, fungi and some protists than to Cyb5R3 from animals.

NCB5OR Deficiency in the Cerebellum and Midbrain Leads to Dehydration and Alterations in Thirst Response, Fasted Feeding Behavior, and Voluntary Exercise in Mice

Cytosolic NADH-cytochrome-b5-oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues. We have previously reported that global ablation of NCB5OR in mice results in early-onset lean diabetes with decreased serum leptin levels and increased metabolic and feeding activities. The conditional deletion of NCB5OR in the mouse cerebellum and midbrain (conditional knock out, CKO mice) results in local iron dyshomeostasis and altered locomotor activity. It has been established that lesion to or removal of the cerebellum leads to changes in nutrient organization, visceral response, feeding behavior, and body weight. This study assessed whether loss of NCB5OR in the cerebellum and midbrain altered feeding or metabolic activity and had an effect on serum T3, cortisol, prolactin, and leptin levels. Metabolic cage data revealed that 16 week old male CKO mice had elevated respiratory quotients and decreased respiratory water expulsion, decreased voluntary exercise, and altered feeding and drinking behavior compared to wild-type littermate controls. Most notably, male CKO mice displayed higher consumption of food during refeeding after a 48-h fast. Echo MRI revealed normal body composition but decreased total water content and hydration ratios in CKO mice. Increased serum osmolality measurements confirmed the dehydration status of male CKO mice. Serum leptin levels were significantly elevated in male CKO mice while prolactin, T3, and cortisol levels remain unchanged relative to wild-type controls, consistent with elevated transcript levels for leptin receptors (short form) in the male CKO mouse cerebellum. Taken together, these findings suggest altered feeding response post starvation as a result of NCB5OR deficiency in the cerebellum.

Molecular mechanism of metabolic NAD(P)H-dependent electron-transfer systems: The role of redox cofactors

NAD(P)H-dependent electron-transfer (ET) systems require three functional components: a flavin-containing NAD(P)H-dehydrogenase, one-electron carrier and metal-containing redox center. In principle, these ET systems consist of one-, two- and three-components, and the electron flux from pyridine nucleotide cofactors, NADPH or NADH to final electron acceptor follows a linear pathway: NAD(P)H → flavin → one-electron carrier → metal containing redox center. In each step ET is primarily controlled by one- and two-electron midpoint reduction potentials of protein-bound redox cofactors in which the redox-linked conformational changes during the catalytic cycle are required for the domain-domain interactions. These interactions play an effective ET reactions in the multi-component ET systems. The microsomal and mitochondrial cytochrome P450 (cyt P450) ET systems, nitric oxide synthase (NOS) isozymes, cytochrome b₅ (cyt b₅) ET systems and methionine synthase (MS) ET system include a combination of multi-domain, and their organizations display similarities as well as differences in their components. However, these ET systems are sharing of a similar mechanism. More recent structural information obtained by X-ray and cryo-electron microscopy (cryo-EM) analysis provides more detail for the mechanisms associated with multi-domain ET systems. Therefore, this review summarizes the roles of redox cofactors in the metabolic ET systems on the basis of one-electron redox potentials. In final Section, evolutionary aspects of NAD(P)H-dependent multi-domain ET systems will be discussed.

Overview of inactivating mutations in the protein-coding genome of the mouse reference strain C57BL/6J

Mice are extremely important as the premier model organism in human biomedical and mammalian genetic research. The genomes of several tens of mouse inbred strains have been sequenced. They have been compared to the genome of C57BL/6J, considered by convention as the reference genome. Based on a comparison of this reference genome with 36 other sequenced mouse strains, we generated an overview of all protein-coding genes that are deviant in this reference genome, compared with consensus protein-coding mouse gene sequences. We provide PROVEAN scores, reflecting the likelihood that these C57BL/6J proteins have lost function. We thus identified numerous abnormal proteins, and biological pathways, specifically present in C57BL/6J, suggesting the important caveats of this reference mouse strain, and linking candidate genes to some of the best-known phenotypes of this strain.

Loss of virulence in NAD(P)H cytochrome b5 oxidoreductase deficient Leishmania major

Leishmania promastigotes have the ability to synthesize essential polyunsaturated fatty acids de novo and can grow in lipid free media. Recently, we have shown that NAD(P)H cytochrome b5 oxidoreductase (Ncb5or) enzyme in Leishmania acts as the redox partner for Δ12 fatty acid desaturase, which catalyses the conversion of oleate to linoleate. So far, the exact role of Leishmania derived linoleate synthesis is still incomplete in the literature. The viability assay by flow cytometry as well as microscopic studies suggests that linoleate is an absolute requirement for Leishmania promastigote survival in delipidated media. Western blot analysis suggested that infection with log phase linoleate deficient mutant (KO) results in increased level of NF-κBp65, IκB and IKKβ phosphorylation in RAW264.7 cells. Similarly, the log phase KO infected RAW264.7 cells show dramatic increment of COX-2 expression and TNF-α secretion, compared to control or Ncb5or complement (CM) cell lines. The activation of inflammatory signaling pathways by KO mutant is significantly reduced when the RAW264.7 cells are pre-treated with BSA bound linoleate. Together, these findings confirmed that the leishmanial linoleate inhibits both COX-2 and TNF-α expression in macrophage via the inactivation of NF-κB signaling pathway. The stationary phase of KO promastigotes shows avirulence after infection in macrophages as well as inoculation into BALB/c mice; whereas CM cell lines show virulence. Collectively, these data provide strong evidence that de novo linoleate synthesis in Leishmania is an essential for parasite survival at extracellular promastigote stage as well as intracellular amastigote stage.

Aldehyde dehydrogenase 1a3 defines a subset of failing pancreatic β cells in diabetic mice

Insulin-producing β cells become dedifferentiated during diabetes progression. An impaired ability to select substrates for oxidative phosphorylation, or metabolic inflexibility, initiates progression from β-cell dysfunction to β-cell dedifferentiation. The identification of pathways involved in dedifferentiation may provide clues to its reversal. Here we isolate and functionally characterize failing β cells from various experimental models of diabetes and report a striking enrichment in the expression of aldehyde dehydrogenase 1 isoform A3 (ALDH(+)) as β cells become dedifferentiated. Flow-sorted ALDH(+) islet cells demonstrate impaired glucose-induced insulin secretion, are depleted of Foxo1 and MafA, and include a Neurogenin3-positive subset. RNA sequencing analysis demonstrates that ALDH(+) cells are characterized by: (i) impaired oxidative phosphorylation and mitochondrial complex I, IV and V; (ii) activated RICTOR; and (iii) progenitor cell markers. We propose that impaired mitochondrial function marks the progression from metabolic inflexibility to dedifferentiation in the natural history of β-cell failure.

Loss of NCB5OR in the cerebellum disturbs iron pathways, potentiates behavioral abnormalities, and exacerbates harmaline-induced tremor in mice

Iron dyshomeostasis has been implicated in many diseases, including a number of neurological conditions. Cytosolic NADH cytochrome b5 oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues and is capable of reducing ferric iron in vitro. We previously reported that global gene ablation of NCB5OR resulted in early-onset diabetes and altered iron homeostasis in mice. To further investigate the specific effects of NCB5OR deficiency on neural tissue without contributions from known phenotypes, we generated a conditional knockout (CKO) mouse that lacks NCB5OR only in the cerebellum and midbrain. Assessment of molecular markers in the cerebellum of CKO mice revealed changes in pathways associated with cellular and mitochondrial iron homeostasis. (59)Fe pulse-feeding experiments revealed cerebellum-specific increased or decreased uptake of iron by 7 and 16 weeks of age, respectively. Additionally, we characterized behavioral changes associated with loss of NCB5OR in the cerebellum and midbrain in the context of dietary iron deprivation-evoked generalized iron deficiency. Locomotor activity was reduced and complex motor task execution was altered in CKO mice treated with an iron deficient diet. A sucrose preference test revealed that the reward response was intact in CKO mice, but that iron deficient diet consumption altered sucrose preference in all mice. Detailed gait analysis revealed locomotor changes in CKO mice associated with dysfunctional proprioception and locomotor activation independent of dietary iron deficiency. Finally, we demonstrate that loss of NCB5OR in the cerebellum and midbrain exacerbated harmaline-induced tremor activity. Our findings suggest an essential role for NCB5OR in maintaining both iron homeostasis and the proper functioning of various locomotor pathways in the mouse cerebellum and midbrain.

The cytochrome b5 reductase HPO-19 is required for biosynthesis of polyunsaturated fatty acids in Caenorhabditis elegans

Polyunsaturated fatty acids (PUFAs) are fatty acids with backbones containing more than one double bond, which are introduced by a series of desaturases that insert double bonds at specific carbon atoms in the fatty acid chain. It has been established that desaturases need flavoprotein-NADH-dependent cytochrome b5 reductase (simplified as cytochrome b5 reductase) and cytochrome b5 to pass through electrons for activation. However, it has remained unclear how this multi-enzyme system works for distinct desaturases. The model organism Caenorhabditis elegans contains seven desaturases (FAT-1, -2, -3, -4, -5, -6, -7) for the biosynthesis of PUFAS, providing an excellent model in which to characterize different desaturation reactions. Here, we show that RNAi inactivation of predicted cytochrome b5 reductases hpo-19 and T05H4.4 led to increased levels of C18:1n-9 but decreased levels of PUFAs, small lipid droplets, decreased fat accumulation, reduced brood size and impaired development. Dietary supplementation with different fatty acids showed that HPO-19 and T05H4.4 likely affect the activity of FAT-1, FAT-2, FAT-3, and FAT-4 desaturases, suggesting that these four desaturases use the same cytochrome b5 reductase to function. Collectively, these findings indicate that cytochrome b5 reductase HPO-19/T05H4.4 is required for desaturation to biosynthesize PUFAs in C. elegans.

Adaptive human CDKAL1 variants underlie hormonal response variations at the enteroinsular axis

Recent analyses have identified positively selected loci that explain differences in immune responses, body forms, and adaptations to extreme climates, but variants that describe adaptations in energy-balance regulation remain underexplored. To identify variants that confer adaptations in energy-balance regulation, we explored the evolutionary history and functional associations of candidate variants in 207 genes. We screened single nucleotide polymorphisms in genes that had been associated with energy-balance regulation for unusual genetic patterns in human populations, followed by studying associations among selected variants and serum levels of GIP, insulin, and C-peptide in pregnant women after an oral glucose tolerance test. Our analysis indicated that 5′ variants in CDKAL1, CYB5R4, GAD2, and PPARG are marked with statistically significant signals of gene–environment interactions. Importantly, studies of serum hormone levels showed that variants in CDKAL1 are associated with glucose-induced GIP and insulin responses (p<0.05). On the other hand, a GAD2 variant exhibited a significant association with glucose-induced C-peptide response. In addition, simulation analysis indicated that a type 2 diabetes risk variant in CDKAL1 (rs7754840) was selected in East Asians ∼6,900 years ago. Taken together, these data indicated that variants in CDKAL1 and GAD2 were targets of prior environmental selection. Because the selection of the CDKAL1 variant overlapped with the selection of a cluster of GIP variants in the same population ∼11,800 to 2,000 years ago, we speculate that these regulatory genes at the human enteroinsular axis could be highly responsive to environmental selection in recent human history.

Impact on offspring methylation patterns of maternal gestational diabetes mellitus and intrauterine growth restraint suggest common genes and pathways linked to subsequent type 2 diabetes risk

Size at birth, postnatal weight gain, and adult risk for type 2 diabetes may reflect environmental exposures during developmental plasticity and may be mediated by epigenetics. Both low birth weight (BW), as a marker of fetal growth restraint, and high birth weight (BW), especially after gestational diabetes mellitus (GDM), have been linked to increased risk of adult type 2 diabetes. We assessed DNA methylation patterns using a bead chip in cord blood samples from infants of mothers with GDM (group 1) and infants with prenatal growth restraint indicated by rapid postnatal catch-up growth (group 2), compared with infants with normal postnatal growth (group 3). Seventy-five CpG loci were differentially methylated in groups 1 and 2 compared with the controls (group 3), representing 72 genes, many relevant to growth and diabetes. In replication studies using similar methodology, many of these differentially methylated regions were associated with levels of maternal glucose exposure below that defined by GDM [the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study] or were identified as changes observed after randomized periconceptional nutritional supplementation in a Gambian cohort characterized by maternal deprivation. These studies provide support for the concept that similar epigenetic modifications may underpin different prenatal exposures and potentially increase long-term risk for diseases such as type 2 diabetes.

Common defects of mitochondria and iron in neurodegeneration and diabetes (MIND): a paradigm worth exploring

A popular, if not centric, approach to the study of an event is to first consider that of the simplest cause. When dissecting the underlying mechanisms governing idiopathic diseases, this generally takes the form of an ab initio genetic approach. To date, this genetic 'smoking gun' has remained elusive in diabetes mellitus and for many affected by neurodegenerative diseases. With no single gene, or even subset of genes, conclusively causative in all cases, other approaches to the etiology and treatment of these diseases seem reasonable, including the correlation of a systems' predisposed sensitivity to particular influence. In the cases of diabetes mellitus and neurodegenerative diseases, overlapping themes of mitochondrial influence or dysfunction and iron dyshomeostasis are apparent and relatively consistent. This mini-review discusses the influence of mitochondrial function and iron homeostasis on diabetes mellitus and neurodegenerative disease, namely Alzheimer's disease. Also discussed is the incidence of diabetes accompanied by neuropathy and neurodegeneration along with neurodegenerative disorders prone to development of diabetes. Mouse models containing multiple facets of this overlap are also described alongside current molecular trends attributed to both diseases. As a way of approaching the idiopathic and complex nature of these diseases we are proposing the consideration of a MIND (mitochondria, iron, neurodegeneration, and diabetes) paradigm in which systemic metabolic influence, iron homeostasis, and respective genetic backgrounds play a central role in the development of disease.

Advancing animal models of human type 1 diabetes by engraftment of functional human tissues in immunodeficient mice

Despite decades of studying rodent models of type 1 diabetes (T1D), no therapy capable of preventing or curing T1D has successfully been translated from rodents to humans. This inability to translate otherwise promising therapies to clinical settings likely resides, to a major degree, from significant species-specific differences between rodent and human immune systems as well as species-related variances in islets in terms of their cellular composition, function, and gene expression. Indeed, taken collectively, these differences underscore the need to define interactions between the human immune system with human β cells. Immunodeficient mice engrafted with human immune systems and human β cells represent an interesting and promising opportunity to study these components in vivo. To meet this need, years of effort have been extended to develop mice depleted of undesirable components while at the same time, allowing the introduction of constituents necessary to recapitulate physiological settings as near as possible to human T1D. With this, these so-called "humanized mice" are currently being used as a preclinical bridge to facilitate identification and translation of novel discoveries to clinical settings.

Natural mutations lead to enhanced proteasomal degradation of human Ncb5or, a novel flavoheme reductase

NADH cytochrome b5 oxidoreductase (Ncb5or) protects β-cells against oxidative stress and lipotoxicity. The predominant phenotype of lean Ncb5or-null mouse is insulin-dependent diabetes due to β-cell death. This suggests the putative role of NCB5OR polymorphism in human diabetes. Therefore, we aimed to investigate the effect of natural missense mutations on the expression of human NCB5OR. Protein and mRNA levels of five non-synonymous coding variants were analyzed in transfected HEK293 and HepG2 cells. Although the mRNA levels were only slightly affected by the mutations, the amount of Ncb5or protein was largely reduced upon two Glu to Gly replacements in the third exon (p.E87G, p.E93G). These two mutations remarkably and synergistically shortened the half-life of Ncb5or and their effect could be attenuated by proteasome inhibitors. Our results strongly indicate that p.E87G, p.E93G mutations lead to enhanced proteasomal degradation due to manifest conformational alterations in the b5 domain. These data provide first evidence for natural mutations in NCB5OR gene resulting in decreased protein levels and hence having potential implications in human pathology.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

NAD(P)H cytochrome b5 oxidoreductase deficiency in Leishmania major results in impaired linoleate synthesis followed by increased oxidative stress and cell death

NAD(P)H cytochrome b(5) oxidoreductase (Ncb5or), comprising cytochrome b(5) and cytochrome b(5) reductase domains, is widely distributed in eukaryotic organisms. Although Ncb5or plays a crucial role in lipid metabolism of mice, so far no Ncb5or gene has been reported in the unicellular parasitic protozoa Leishmania species. We have cloned, expressed, and characterized Ncb5or gene from Leishmania major. Steady state catalysis and spectral studies show that NADH can quickly reduce the ferric state of the enzyme to the ferrous state and is able to donate an electron(s) to external acceptors. To elucidate its exact physiological role in Leishmania, we attempted to create NAD(P)H cytochrome b(5) oxidoreductase from L. major (LmNcb5or) knock-out mutants by targeted gene replacement technique. A free fatty acid profile in knock-out (KO) cells reveals marked deficiency in linoleate and linolenate when compared with wild type (WT) or overexpressing cells. KO culture has a higher percentage of dead cells compared with both WT and overexpressing cells. Increased O(2) uptake, uncoupling and ATP synthesis, and loss of mitochondrial membrane potential are evident in KO cells. Flow cytometric analysis reveals the presence of a higher concentration of intracellular H(2)O(2), indicative of increased oxidative stress in parasites lacking LmNcb5or. Cell death is significantly reduced when the KO cells are pretreated with BSA bound linoleate. Real time PCR studies demonstrate a higher Δ12 desaturase, superoxide dismutase, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA with a concomitant fall in Δ9 desaturase mRNA expression in LmNcb5or null cell line. Together these findings suggest that decreased linoleate synthesis, and increased oxidative stress and apoptosis are the major consequences of LmNcb5or deficiency in Leishmania.

Beta-Cell Injury in Ncb5or-null Mice is Exacerbated by Consumption of a High-Fat Diet

NADH-cytochrome b5 oxidoreductase (Ncb5or) in endoplasmic reticulum (ER) is involved in fatty acid metabolism, and Ncb5or(-/-) mice fed standard chow (SC) are insulin-sensitive but weigh less than wild type (WT) littermates. Ncb5or(-/-) mice develop hyperglycemia at about age 7 weeks due to β-cell dysfunction and loss associated with saturated fatty acid accumulation and manifestations of ER and oxidative stress. Here we report that when Ncb5or(-/-) mice born to heterozygous mothers fed a high fat (HF) diet continue to ingest HF, they weigh as much as SC-fed WT at age 5 weeks. By age 7 weeks, diabetes mellitus develops in all HF-fed vs. 68% of SC-fed Ncb5or(-/-) mice. Islet β-cell content in age 5-week Ncb5or(-/-) mice fed HF for 7 days is lower (53%) than for those fed SC (63%), and both are lower than for WT (75%, SC, vs. 69%, HF). Islet transcript levels for markers of mitochondrial biogenesis (PGC-1α) and ER stress (ATF6α) are higher in Ncb5or(-/-) than WT mice but not significantly affected by diet. Consuming a HF diet exacerbates Ncb5or(-/-) β-cell accumulation of intracellular saturated fatty acids and increases the frequency of ER distention from 11% (SC) to 47% (HF), thus accelerates β-cell injury in Ncb5or(-/-) mice.

Metformin prevents endoplasmic reticulum stress-induced apoptosis through AMPK-PI3K-c-Jun NH2 pathway

Type 2 diabetes mellitus is thought to be partially associated with endoplasmic reticulum (ER) stress toxicity on pancreatic beta cells and the result of decreased insulin synthesis and secretion. In this study, we showed that a well-known insulin sensitizer, metformin, directly protects against dysfunction and death of ER stress-induced NIT-1 cells (a mouse pancreatic beta cell line) via AMP-activated protein kinase (AMPK) and phosphatidylinositol-3 (PI3) kinase activation. We also showed that exposure of NIT-1 cells to metformin (5mM) increases cellular resistance against ER stress-induced NIT-1 cell dysfunction and death. AMPK and PI3 kinase inhibitors abolished the effect of metformin on cell function and death. Metformin-mediated protective effects on ER stress-induced apoptosis were not a result of an unfolded protein response or the induced inhibitors of apoptotic proteins. In addition, we showed that exposure of ER stressed-induced NIT-1 cells to metformin decreases the phosphorylation of c-Jun NH(2) terminal kinase (JNK). These data suggest that metformin is an important determinant of ER stress-induced apoptosis in NIT-1 cells and may have implications for ER stress-mediated pancreatic beta cell destruction via regulation of the AMPK-PI3 kinase-JNK pathway.

Development of diabetes in lean Ncb5or-null mice is associated with manifestations of endoplasmic reticulum and oxidative stress in beta cells

NADH-cytochrome b5 oxidoreductase (Ncb5or) is an endoplasmic reticulum (ER)-associated redox enzyme involved in fatty acid metabolism, and phenotypic abnormalities of Ncb5or(-/-) mice include diabetes and lipoatrophy. These mice are lean and insulin-sensitive but become hyperglycemic at age 7 weeks as a result of β-cell dysfunction and loss. Here we examine early cellular and molecular events associated with manifestations of β-cell defects in Ncb5or(-/-) mice. We observe lower islet β-cell content in pancreata at age 4 weeks and prominent ER distention in β-cells by age 5 weeks. Ultrastructural changes progress rapidly in severity from age 5 to 6 weeks, and their frequency rises from 10% of β-cells at 5 weeks to 33% at 6 weeks. These changes correlate temporally with the onset of diabetes. ER stress responses and lipid load in Ncb5or(-/-) β-cells were assessed with isolated islets from mice at age 5 weeks. Expression levels of the stress marker protein Grp78/BiP and of phosphorylated eIF2α protein were found to be reduced, although their transcript levels did not decline. This pattern stands in contrast to the canonical unfolded protein response. Ncb5or(-/-) β-cells also accumulated higher intracellular levels of palmitate and other free fatty acids and exhibited greater reactive oxygen species production than wild-type cells. An alloxan-susceptible genetic background was found to confer accelerated onset of diabetes in Ncb5or(-/-) mice. These findings provide the first direct evidence that manifestations of diabetes in lean Ncb5or(-/-) mice involve saturated free fatty acid overload of β-cells and ER and oxidative stress responses.

Living without Oxygen: Anoxia-Responsive Gene Expression and Regulation

Many species of marine mollusks demonstrate exceptional capacities for long term survival without oxygen. Analysis of gene expression under anoxic conditions, including the subsequent translational responses, allows examination of the functional mechanisms that support and regulate natural anaerobiosis and permit noninjurious transitions between aerobic and anoxic states. Identification of stress-specific gene expression can provide important insights into the metabolic adaptations that are needed for anoxia tolerance, with potential applications to anoxia-intolerant systems. Various methods are available to do this, including high throughput microarray screening and construction and screening of cDNA libraries. Anoxia-responsive genes have been identified in mollusks; some have known functions in other organisms but were not previously linked with anoxia survival. In other cases, completely novel anoxia-responsive genes have been discovered, some that show known motifs or domains that hint at function. Selected genes are expressed at different times over an anoxia-recovery time course with their transcription and translation being actively regulated to ensure protein expression at the optimal time. An examination of transcript status over the course of anoxia exposure and subsequent aerobic recovery identifies genes, and the proteins that they encode, that enhance cell survival under oxygen-limited conditions. Analysis of data generated from non-mainstream model systems allows for insight into the response by cells to anoxia stress.

Ncb5or deficiency increases fatty acid catabolism and oxidative stress

The endoplasmic reticulum-associated NADH cytochrome b(5) oxidoreductase (Ncb5or) is widely distributed in animal tissues. Ncb5or(-/-) mice develop diabetes at age 7 weeks and have increased susceptibility to the diabetogenic oxidant streptozotocin. Ncb5or deficiency also results in lipoatrophy and increased hepatocyte sensitivity to cytotoxic effects of saturated fatty acids. Here we investigate the mechanisms of these phenomena in prediabetic Ncb5or(-/-) mice and find that, despite increased rates of fatty acid uptake and synthesis and higher stearoyl-CoA desaturase (SCD) expression, Ncb5or(-/-) liver accumulates less triacylglycerol (TAG) than wild type (WT). Increased fatty acid catabolism and oxidative stress are evident in Ncb5or(-/-) hepatocytes and reflect increased mitochondrial content, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) expression, fatty acid oxidation rates, oxidative stress response gene expression, and oxidized glutathione content. Ncb5or(-/-) hepatocytes readily incorporate exogenous fatty acids into TAG but accumulate more free fatty acids (FFA) and have greater palmitate-induced oxidative stress responses and cell death than WT, all of which are alleviated by co-incubation with oleate via TAG channeling. A high fat diet rich in palmitate and oleate stimulates both lipogenesis and fatty acid catabolism in Ncb5or(-/-) liver, resulting in TAG levels similar to WT but increased intracellular FFA accumulation. Hepatic SCD-specific activity is lower in Ncb5or(-/-) than in WT mice, although Ncb5or(-/-) liver has a greater increase in Scd1 mRNA and protein levels. Together, these findings suggest that increased FFA accumulation and catabolism and oxidative stress are major consequences of Ncb5or deficiency in liver.

Study of the individual cytochrome b5 and cytochrome b5 reductase domains of Ncb5or reveals a unique heme pocket and a possible role of the CS domain

NADH cytochrome b(5) oxidoreductase (Ncb5or) is found in animals and contains three domains similar to cytochrome b(5) (b(5)), CHORD-SGT1 (CS), and cytochrome b(5) reductase (b(5)R). Ncb5or has an important function, as suggested by the diabetes and lipoatrophy phenotypes in Ncb5or null mice. To elucidate the structural and functional properties of human Ncb5or, we generated its individual b(5) and b(5)R domains (Ncb5or-b(5) and Ncb5or-b(5)R, respectively) and compared them with human microsomal b(5) (Cyb5A) and b(5)R (Cyb5R3). A 1.25 Å x-ray crystal structure of Ncb5or-b(5) reveals nearly orthogonal planes of the imidazolyl rings of heme-ligating residues His(89) and His(112), consistent with a highly anisotropic low spin EPR spectrum. Ncb5or is the first member of the cytochrome b(5) family shown to have such a heme environment. Like other b(5) family members, Ncb5or-b(5) has two helix-loop-helix motifs surrounding heme. However, Ncb5or-b(5) differs from Cyb5A with respect to location of the second heme ligand (His(112)) and of polypeptide conformation in its vicinity. Electron transfer from Ncb5or-b(5)R to Ncb5or-b(5) is much less efficient than from Cyb5R3 to Cyb5A, possibly as a consequence of weaker electrostatic interactions. The CS linkage probably obviates the need for strong interactions between b(5) and b(5)R domains in Ncb5or. Studies with a construct combining the Ncb5or CS and b(5)R domains suggest that the CS domain facilitates docking of the b(5) and b(5)R domains. Trp(114) is an invariant surface residue in all known Ncb5or orthologs but appears not to contribute to electron transfer from the b(5)R domain to the b(5) domain.

Interstitial Deletions at 6q14.1-q15 Associated with Obesity, Developmental Delay and a Distinct Clinical Phenotype

BACKGROUND: Interstitial deletions of the long arm of chromosome 6 have been described in several patients with obesity and a Prader-Willi-like phenotype. Haploinsufficiency of the SIM1 gene located at 6q16.3 is suggested as being responsible for the regulation of body weight. Here we report on 2 patients with interstitial deletions at 6q14.1-q15 presenting with obesity and symptoms strikingly similar to those reported for deletions involving the SIM1 gene despite not having a deletion of this gene. METHODS: Array comparative genomic hybridisation was used to diagnose 2 children with obesity and developmental delay, revealing 2 interstitial deletions at 6q14.1-q15 of 8.73 and 4.50 Mb, respectively, and a region of overlap of 4.2-Mb. RESULTS: The similar phenotype in the 2 patients was most likely due to a 4.2-Mb common microdeletion at 6q14.1-q15. Another patient has previously been described with an overlapping deletion. The 3 patients share several features, such as developmental delay, obesity, hernia, rounded face with full cheeks, epicanthal folds, short palpebral fissures, bulbous nose, large ears, and syndactyly between toes II and III. CONCLUSIONS: Together with a previously reported patient, our study suggests that the detected deletions may represent a novel clinically recognisable microdeletion syndrome caused by haploinsufficiency of dosage-sensitive genes in the 6q14.1-q15 region.

The flavoheme reductase Ncb5or protects cells against endoplasmic reticulum stress-induced lipotoxicity

NCB5OR is a novel flavoheme reductase with a cytochrome b5-like domain at the N-terminus and a cytochrome b5 reductase-like domain at the C terminus. Ncb5or knock-out mice develop insulin deficient diabetes and loss of white adipose tissue. Ncb5or(-/-) mice have impairment of Delta9 fatty acid desaturation with elevated ratios of palmitate to palmitoleate and stearate to oleate. In this study we assess the role of the endoplasmic reticulum (ER) stress response in mediating lipotoxicity in Ncb5or(-/-) mice. The ER stress response was assessed by induction of BiP, ATF3, ATF6, XBP-1, and C/EBP homologous protein (CHOP). Exposure to palmitate, but not oleate or mixtures of oleate and palmitate induced these markers of ER stress to a much greater extent in Ncb5or(-/-) hepatocytes than in wild-type cells. In contrast, Ncb5or(-/-) and Ncb5or(+/+) hepatocytes were equally sensitive to ER stress imposed by increasing concentrations of tunicamycin. In order to assess the role of ER stress in vivo, we prepared mice that lack both NCB5OR and CHOP, a proapoptotic transcription factor important in the ER stress response. Onset of hyperglycemia in the Chop(-/-);Ncb5or(-/-) mice was delayed two weeks beyond that observed in Chop(+/+);Ncb5or(-/-) mice. Taken together these results suggest that ER stress plays a critical role in palmitate-induced lipotoxicity both in vitro and in vivo.

Loss of Ncb5or results in impaired fatty acid desaturation, lipoatrophy, and diabetes

Targeted ablation of the novel flavoheme reductase Ncb5or knock-out (KO) results in progressive loss of pancreatic beta-cells and white adipose tissue over time. Lipoatrophy persisted in KO animals in which the confounding metabolic effects of diabetes were eliminated by islet transplantation (transplanted knockout (TKO)). Lipid profiles in livers prepared from TKO animals were markedly deficient in triglycerides and diacylglycerides. Despite enhanced expression of stearoyl-Co-A desaturase-1, levels of palmitoleic and oleic acids (Delta9 fatty acid desaturation) were decreased in TKO relative to wild type controls. Treatment of KO hepatocytes with palmitic acid reduced cell viability and increased apoptosis, a response blunted by co-incubation with oleic acid. The results presented here support the hypothesis that Ncb5or supplies electrons for fatty acid desaturation, offer new insight into the regulation of a crucial step in fatty acid biosynthesis, and provide a plausible explanation for both the diabetic and the lipoatrophic phenotype in Ncb5or(-/-) mice.

Identification of a major locus for islet inflammation and fibrosis in the spontaneously diabetic Torii rat

The pathogenesis of inflammation and fibrosis in the pancreatic islets in diabetes is largely unknown. Spontaneously diabetic Torii (SDT) rats exhibit inflammation and fibrosis in and around the islets during the development of the disease. We investigated genetic factors for diabetes, islet inflammation, and fibrosis in the SDT rat. We produced F1 and F2 rats by intercross between SDT and F344 rats, examined the onset of diabetes, glucose tolerance, and histology of the pancreas, and performed genetic analysis of these traits. We then established a congenic strain carrying the SDT allele at the strongest diabetogenic locus on the F344 genetic background and characterized glucose tolerance and histology of the pancreas. F1 rats showed glucose intolerance and inflammatory changes mainly in the islets. Genetic analysis of diabetes identified a major locus on chromosome 3, designated Dmsdt1, at which a dominantly acting SDT allele was involved. Quantitative trait locus (QTL) analysis of glucose tolerance revealed, in addition to Dmsdt1 [logarithm of odds (LOD) 5.3 near D3Mit12], three other loci, designated Dmsdt2 (LOD 4.2 at D8Rat46), Dmsdt3 (LOD 3.8 near D13Arb5), and Dmsdt4 (LOD 5.8 at D14Arb18). Analysis of a congenic strain for Dmsdt1 indicates that the dominantly acting SDT allele induces islet inflammation and fibrosis. Thus we have found a major locus on chromosome 3 for islet inflammation and fibrosis in the SDT rat. Identification of the genes responsible should provide insight into the pathogenesis of diabetes.

Genome-wide analysis of Rad52 foci reveals diverse mechanisms impacting recombination

To investigate the DNA damage response, we undertook a genome-wide study in Saccharomyces cerevisiae and identified 86 gene deletions that lead to increased levels of spontaneous Rad52 foci in proliferating diploid cells. More than half of the genes are conserved across species ranging from yeast to humans. Along with genes involved in DNA replication, repair, and chromatin remodeling, we found 22 previously uncharacterized open reading frames. Analysis of recombination rates and synthetic genetic interactions with rad52Δ suggests that multiple mechanisms are responsible for elevated levels of spontaneous Rad52 foci, including increased production of recombinogenic lesions, sister chromatid recombination defects, and improper focus assembly/disassembly. Our cell biological approach demonstrates the diversity of processes that converge on homologous recombination, protect against spontaneous DNA damage, and facilitate efficient repair.

Homologous recombination (HR) is a cellular process that permits efficient repair of both endogenous and exogenous DNA damage. Although the principal players in HR have been well characterized, the interplay of diverse processes with the HR pathway remains mysterious. Traditionally, genetic screens investigating HR have utilized genetic assays, such as survival following exposure to DNA damaging agents or alterations in the rate of the generation of recombinant products. In this work, we instead utilize a cell biology phenotype, the relocalization of the central HR protein Rad52 into subnuclear foci reflecting repair centers actively engaged in HR. This approach allows us to identify mutants that affect the kinetics of HR repair center assembly and disassembly regardless of the outcome of recombination. We identified 86 gene deletions that lead to increases in the levels of spontaneous foci in proliferating diploid cells, 22 of which were deletions of previously uncharacterized ORFs (designated IRC2–11, 13–16, 18–25). Genetic characterization of the mutants revealed a diversity of mechanisms that underlie the focus phenotype. These include increasing the generation of DNA lesions, blocking the completion of HR, and altering the kinetics of genetic recombination and the assembly/disassembly of the HR protein complexes.

The reductase NCB5OR is responsive to the redox status in beta-cells and is not involved in the ER stress response

The novel reductase NCB5OR (NADPH cytochrome b5 oxidoreductase) resides in the ER (endoplasmic reticulum) and may protect cells against ER stress. Levels of BiP (immunoglobulin heavy-chain-binding protein), CHOP (CCAAT/enhancer-binding protein homologous protein) and XBP-1 (X-box-binding protein-1) did not differ in WT (wild-type) and KO (Ncb5or-null) tissues or MEFs (mouse embryonic fibroblasts), and XBP-1 remained unspliced. MEFs treated with inducers of ER stress demonstrated no change in Ncb5or expression and expression of ER-stress-induced genes was not enhanced. Induction of ER stress in beta-cell lines did not change Ncb5or expression or promoter activity. Transfection with Ncb5or-specific siRNA (small interfering RNA) yielded similar results. Microarray analysis of mRNA from islets and liver of WT and KO animals revealed no significant changes in ER-stress-response genes. Induction of oxidative stress in betaTC3 cells did not alter Ncb5or mRNA levels or promoter activity. However, KO islets were more sensitive to streptozotocin when compared with WT islets. MEFs incubated with nitric oxide donors showed no difference in cell viability or levels of nitrite produced. No significant differences in mRNA expression of antioxidant enzymes were observed when comparing WT and KO tissues; however, microarray analysis of islets indicated slightly enhanced expression of some antioxidant enzymes in the KO islets. Short-term tBHQ (t-butylhydroquinone) treatment increased Ncb5or promoter activity, although longer incubation times yielded a dose-dependent decrease in activity. This response appears to be due to a consensus ARE (antioxidant-response element) present in the Ncb5or promoter. In summary, NCB5OR does not appear to be involved in ER stress, although it may be involved in maintaining or regulating the redox status in beta-cells.

Large-scale molecular analysis of a 34 Mb interval on chromosome 6q: major refinement of the RP25 interval

A large scale bioinformatics and molecular analysis of a 34 Mb interval on chromosome 6q12 was undertaken as part of our ongoing study to identify the gene responsible for an autosomal recessive retinitis pigmentosa (arRP) locus, RP25. Extensive bioinformatics analysis indicated in excess of 110 genes within the region and we also noted unfinished sequence on chromosome 6q in the Human Genome Database, between 58 and 61.2 Mb. Forty three genes within the RP25 interval were considered as good candidates for mutation screening. Direct sequence analysis of the selected genes in 7 Spanish families with arRP revealed a total of 244 sequence variants, of which 67 were novel but none were pathogenic. This, together with previous reports, excludes 60 genes within the interval ( approximately 55%) as disease causing for RP. To investigate if copy number variation (CNV) exists within RP25, a comparative genomic hybridization (CGH) analysis was performed on a consanguineous family. A clone from the tiling path array, chr6tp-19C7, spanning approximately 100-Kb was found to be deleted in all affected members of the family, leading to a major refinement of the interval. This will eventually have a significant impact on cloning of the RP25 gene.

Endoplasmic reticulum stress signaling in disease

The extracellular space is an environment hostile to unmodified polypeptides. For this reason, many eukaryotic proteins destined for exposure to this environment through secretion or display at the cell surface require maturation steps within a specialized organelle, the endoplasmic reticulum (ER). A complex homeostatic mechanism, known as the unfolded protein response (UPR), has evolved to link the load of newly synthesized proteins with the capacity of the ER to mature them. It has become apparent that dysfunction of the UPR plays an important role in some human diseases, especially those involving tissues dedicated to extracellular protein synthesis. Diabetes mellitus is an example of such a disease, since the demands for constantly varying levels of insulin synthesis make pancreatic beta-cells dependent on efficient UPR signaling. Furthermore, recent discoveries in this field indicate that the importance of the UPR in diabetes is not restricted to the beta-cell but is also involved in peripheral insulin resistance. This review addresses aspects of the UPR currently understood to be involved in human disease, including their role in diabetes mellitus, atherosclerosis, and neoplasia.

Promoter characterization and transcriptional regulation of Ncb5or, a novel reductase necessary for pancreatic beta-cell maintenance

Ncb5or is a ubiquitously expressed gene required for beta-cell survival in mice. Examination of mouse tissues demonstrated high levels of expression in the pancreas, heart and kidney. A transcription start site was identified 149 bp upstream from the start codon and transient expression analysis in betaTC3 cells indicated the presence of a core promoter located within 348 bp upstream of this site. Deletion of Region C (-216/-157) resulted in a significant decrease in promoter activity and specific nucleotides located in a region designated C2 were demonstrated to be critical for complex binding. Deletion of Region D (-60/-33), which contains multiple consensus Sp1 sites, resulted in an additional loss of promoter activity. The data presented here identify and characterize the previously unknown promoter of Ncb5or, a reductase critical for beta-cell survival.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Protein Tyrosine Phosphatases as Targets of the Combined Insulinomimetic Effects of Zinc and Oxidants

Zinc ions have an insulin-like (insulinomimetic) effect. A particularly sensitive target of zinc ions is protein tyrosine phosphatase 1B (PTP 1B), a key regulator of the phosphorylation state of the insulin receptor. Modulation of insulin signaling by zinc chelating agents and the recognition of temporal and spatial fluctuations of zinc suggest a physiological role of zinc in insulin signal transduction. Tyrosine phosphatases seem to be regulated jointly by insulin-induced redox (hydrogen peroxide) signaling, which results in their oxidative inactivation, and by their zinc inhibition after oxidative zinc release from other proteins. In diabetes, the significant oxidative stress and associated changes in zinc metabolism modify the cell's response and sensitivity to insulin. Zinc deficiency activates stress pathways and may result in a loss of tyrosine phosphatase control, thereby causing insulin resistance.

Variation in NCB5OR: studies of relationships to type 2 diabetes, maturity-onset diabetes of the young, and gestational diabetes mellitus

Recent data show that homozygous Ncb5or(-/-) knock-out mice present with an early-onset nonautoimmune diabetes phenotype. Furthermore, genome-wide scans have reported linkage to the chromosome 6q14.2 region close to the human NCB5OR. We therefore considered NCB5OR to be a biological and positional candidate gene and examined the coding region of NCB5OR in 120 type 2 diabetic patients and 63 patients with maturity-onset diabetes of the young using denaturing high-performance liquid chromatography. We identified a total of 22 novel nucleotide variants. Three variants [IVS5+7del(CT), Gln187Arg, and His223Arg] were genotyped in a case-control design comprising 1,246 subjects (717 type 2 diabetic patients and 529 subjects with normal glucose tolerance). In addition, four rare variants were investigated for cosegregation with diabetes in multiplex type 2 diabetic families. The IVS5+7del(CT) variant was associated with common late-onset type 2 diabetes; however, we failed to relate this variant to any diabetes-related quantitative traits among the 529 control subjects. Thus, variation in the coding region of NCB5OR is not a major contributor in the pathogenesis of nonautoimmune diabetes.