NMR resonance assignment of the N-terminal GTPase domain of human Miro2 Bound to GTP

Miro2 and Miro1 are mitochondrial-associated proteins critical for regulating mitochondrial movement within the cell. Both Miro1 and Miro2 have roles in promoting neuron function, but recently Miro2 has been shown to have additional roles in response to nutrient starvation in tumor cells. Miro1 and 2 consist of two small GTPase domains flanking a pair of EF-hands. The N-terminal GTPase (nGTPase) domain is responsible for initiating mitochondrial trafficking and interactions with GCN1 in prostate cancer. The crystal structure of Miro1 nGTPase bound to GTP has been solved. However, no structural data is available for the nGTPase domain of Miro2. To better understand the similarities and differences in the functions of Miro1 and Miro2, we have initiated structural studies of Miro2. Here we report the backbone NMR chemical shift assignments of a 22 KDa construct of the nGTPase domain of Miro2 bound to GTP that includes residues 1-180 of the full-length protein. We affirm that the overall secondary structure of this complex closely resembles that of Miro1 nGTPase bound to GTP. Minor variations in the overall structures can be attributed to crystal packing interactions in the structure of Miro1. These NMR studies will form the foundation for future work identifying the specific interaction sites between Miro2 and its cellular binding partners.

Mechanism by which T7 bacteriophage protein Gp1.2 inhibits Escherichia coli dGTPase

Levels of the cellular dNTPs, the direct precursors for DNA synthesis, are important for DNA replication fidelity, cell cycle control, and resistance against viruses. Escherichia coli encodes a dGTPase (2'-deoxyguanosine-5'-triphosphate [dGTP] triphosphohydrolase [dGTPase]; dgt gene, Dgt) that establishes the normal dGTP level required for accurate DNA replication but also plays a role in protecting E. coli against bacteriophage T7 infection by limiting the dGTP required for viral DNA replication. T7 counteracts Dgt using an inhibitor, the gene 1.2 product (Gp1.2). This interaction is a useful model system for studying the ongoing evolutionary virus/host "arms race." We determined the structure of Gp1.2 by NMR spectroscopy and solved high-resolution cryo-electron microscopy structures of the Dgt-Gp1.2 complex also including either dGTP substrate or GTP coinhibitor bound in the active site. These structures reveal the mechanism by which Gp1.2 inhibits Dgt and indicate that Gp1.2 preferentially binds the GTP-bound form of Dgt. Biochemical assays reveal that the two inhibitors use different modes of inhibition and bind to Dgt in combination to yield enhanced inhibition. We thus propose an in vivo inhibition model wherein the Dgt-Gp1.2 complex equilibrates with GTP to fully inactivate Dgt, limiting dGTP hydrolysis and preserving the dGTP pool for viral DNA replication.

AAV9-Stathmin1 gene delivery improves disease phenotype in an intermediate mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a devastating infantile genetic disorder caused by the loss of survival motor neuron (SMN) protein that leads to premature death due to loss of motor neurons and muscle atrophy. The approval of an antisense oligonucleotide therapy for SMA was an important milestone in SMA research; however, effective next-generation therapeutics will likely require combinatorial SMN-dependent therapeutics and SMN-independent disease modifiers. A recent cross-disease transcriptomic analysis identified Stathmin-1 (STMN1), a tubulin-depolymerizing protein, as a potential disease modifier across different motor neuron diseases, including SMA. Here, we investigated whether viral-based delivery of STMN1 decreased disease severity in a well-characterized SMA mouse model. Intracerebroventricular delivery of scAAV9-STMN1 in SMA mice at P2 significantly increased survival and weight gain compared to untreated SMA mice without elevating Smn levels. scAAV9-STMN1 improved important hallmarks of disease, including motor function, NMJ pathology and motor neuron cell preservation. Furthermore, scAAV9-STMN1 treatment restored microtubule networks and tubulin expression without affecting tubulin stability. Our results show that scAAV9-STMN1 treatment improves SMA pathology possibly by increasing microtubule turnover leading to restored levels of stable microtubules. Overall, these data demonstrate that STMN1 can significantly reduce the SMA phenotype independent of restoring SMN protein and highlight the importance of developing SMN-independent therapeutics for the treatment of SMA.

Dark side of the epididymis: tails of sperm maturation

BACKGROUND

The Hermes body (HB) previously called the cytoplasmic droplet is a focal distension of the flagellar cytoplasm of epididymal spermatozoa consisting mainly of isolated flattened Golgi cisternae.

OBJECTIVE

To define a functional role for the HB of epididymal spermatozoa.

METHODS

Isolated fractions of HBs of epididymal spermatozoa were prepared and by quantitative tandem mass spectrometry revealed 1511 proteins.

RESULTS

The glucose transporter GLUT-3 was the most abundant protein followed by hexokinase 1, which along with the presence of all glycolytic enzymes suggested a role for the HB in glycolysis. Several TMED/p24 Golgi trafficking proteins were abundant with TMED7/p27 and TMED2/p24 defining the identity of the flattened cisternae within the HB as Golgi, along with the known Golgi proteins, GBF1, GOLPH3, Man2α1, and ManIIX. The Golgi trafficking protein TMED7/p27 via small 50-nm vesicles emanating from the Golgi cisternae was proposed to transport GLUT-3 to the plasma membrane for ATP production related to sperm motility. The internal membranes revealed abundant proteins not only of Golgi cisternae, but also of endoplasmic reticulum and endosomes. COPI and COPII coats, clathrin, SNAREs, annexins, atlastins, and GTPases were identified for vesicular trafficking and membrane fusion, in addition to ribosomes, stress proteins for protection, proteasome proteins involved in degradation, and cytoskeletal elements for migration of the HB along the flagellum. The biogenesis of the HB occurring at step 19 spermatids of the testis just prior to their release was uncovered as a key step in germ cell differentiation, where several proteins were expressed, some for the first time.

CONCLUSION

As epididymal spermatozoa undergo remodeling of their protein makeup through selective degradation of sperm proteins during epididymal transit, then remodeling as a consequence of new protein synthesis is not excluded by our observations.

DNA polymerase β contains a functional nuclear localization signal at its N-terminus

DNA polymerase β (pol β) requires nuclear localization to fulfil its DNA repair function. Although its small size has been interpreted to imply the absence of a need for active nuclear import, sequence and structural analysis suggests that a monopartite nuclear localization signal (NLS) may reside in the N-terminal lyase domain. Binding of this domain to Importin α1 (Impα1) was confirmed by gel filtration and NMR studies. Affinity was quantified by fluorescence polarization analysis of a fluorescein-tagged peptide corresponding to pol β residues 2–13. These studies indicate high affinity binding, characterized by a low micromolar K_d, that is selective for the murine Importin α1 (mImpα1) minor site, with the K_d strengthening to ∼140 nM for the full lyase domain (residues 2–87). A further reduction in K_d obtains in binding studies with human Importin α5 (hImpα5), which in some cases has been demonstrated to bind small domains connected to the NLS. The role of this NLS was confirmed by fluorescent imaging of wild-type and NLS-mutated pol β(R4S,K5S) in mouse embryonic fibroblasts lacking endogenous pol β. Together these data demonstrate that pol β contains a specific NLS sequence in the N-terminal lyase domain that promotes transport of the protein independent of its interaction partners. Active nuclear uptake allows development of a nuclear/cytosolic concentration gradient against a background of passive diffusion.

Dipeptidyl Peptidase-4 Inhibition With Saxagliptin Ameliorates Angiotensin II-Induced Cardiac Diastolic Dysfunction in Male Mice

Activation of the renin-angiotensin-aldosterone system is common in hypertension and obesity and contributes to cardiac diastolic dysfunction, a condition for which no treatment currently exists. In light of recent reports that antihyperglycemia incretin enhancing dipeptidyl peptidase (DPP)-4 inhibitors exert cardioprotective effects, we examined the hypothesis that DPP-4 inhibition with saxagliptin (Saxa) attenuates angiotensin II (Ang II)-induced cardiac diastolic dysfunction. Male C57BL/6J mice were infused with either Ang II (500 ng/kg/min) or vehicle for 3 weeks receiving either Saxa (10 mg/kg/d) or placebo during the final 2 weeks. Echocardiography revealed Ang II-induced diastolic dysfunction, evidenced by impaired septal wall motion and prolonged isovolumic relaxation, coincident with aortic stiffening. Ang II induced cardiac hypertrophy, coronary periarterial fibrosis, TRAF3-interacting protein 2 (TRAF3IP2)-dependent proinflammatory signaling [p-p65, p-c-Jun, interleukin (IL)-17, IL-18] associated with increased cardiac macrophage, but not T cell, gene expression. Flow cytometry revealed Ang II-induced increases of cardiac CD45+F4/80+CD11b+ and CD45+F4/80+CD11c+ macrophages and CD45+CD4+ lymphocytes. Treatment with Saxa reduced plasma DPP-4 activity and abrogated Ang II-induced cardiac diastolic dysfunction independent of aortic stiffening or blood pressure. Furthermore, Saxa attenuated Ang II-induced periarterial fibrosis and cardiac inflammation, but not hypertrophy or cardiac macrophage infiltration. Analysis of Saxa-induced changes in cardiac leukocytes revealed Saxa-dependent reduction of the Ang II-mediated increase of cardiac CD11c messenger RNA and increased cardiac CD8 gene expression and memory CD45+CD8+CD44+ lymphocytes. In summary, these results demonstrate that DPP-4 inhibition with Saxa prevents Ang II-induced cardiac diastolic dysfunction, fibrosis, and inflammation associated with unique shifts in CD11c-expressing leukocytes and CD8+ lymphocytes.

Dietary fat modulation of hepatic lipase variant -514 C/T for lipids: a crossover randomized dietary intervention trial in Caribbean Hispanics

The hepatic lipase (LIPC) locus is a well-established determinant of high-density lipoprotein cholesterol (HDL-C) concentrations, an association that is modified by dietary fat in observational studies. Dietary interventions are lacking. We investigated dietary modulation of LIPC rs1800588 (-514 C/T) for lipids and glucose using a randomized crossover design comparing a high-fat Western diet and a low-fat traditional Hispanic diet in individuals of Caribbean Hispanic descent (n = 42, 4 wk/phase). No significant gene-diet interactions were observed for HDL-C. However, differences in dietary response according to LIPC genotype were observed. In major allele carriers (CC/CT), HDL-C (mmol/l) was higher following the Western diet compared with the Hispanic diet: phase 1 (Western: 1.3 ± 0.03; Hispanic: 1.1 ± 0.04; P = 0.0004); phase 2 (Western: 1.4 ± 0.03; Hispanic: 1.2 ± 0.03; P = 0.0003). In contrast, HDL-C in TT individuals did not differ by diet. Only major allele carriers benefited from the higher-fat diet for HDL-C. Secondarily, we explored dietary fat quality and rs1800588 for HDL-C and triglycerides (TG) in a Boston Puerto Rican Health Study (BPRHS) subset matched for diabetes and obesity status (subset n = 384). In the BPRHS, saturated fat was unfavorably associated with HDL-C and TG in rs1800588 TT carriers. LIPC rs1800588 appears to modify plasma lipids in the context of dietary fat. This new evidence of genetic modulation of dietary responses may inform optimal and personalized dietary fat advice and reinforces the importance of studying genetic markers in diet and cardiometabolic health.

Lipoprotein lipase variants interact with polyunsaturated fatty acids for obesity traits in women: replication in two populations

BACKGROUND AND AIMS

Lipoprotein lipase (LPL) is a candidate gene for obesity based on its role in triglyceride hydrolysis and the partitioning of fatty acids towards storage or oxidation. Whether dietary fatty acids modify LPL associated obesity risk is unknown.

METHODS AND RESULTS

We examined five single nucleotide polymorphisms (SNPs) (rs320, rs2083637, rs17411031, rs13702, rs2197089) for potential interaction with dietary fatty acids for obesity traits in 1171 participants (333 men and 838 women, aged 45-75 y) of the Boston Puerto Rican Health Study (BPRHS). In women, SNP rs320 interacted with dietary polyunsaturated fatty acids (PUFA) for body mass index (BMI) (P = 0.002) and waist circumference (WC) (P = 0.001) respectively. Higher intake of PUFA was associated with lower BMI and WC in homozygotes of the major allele (TT) (P = 0.01 and 0.005) but not in minor allele carriers (TG and GG). These interactions were replicated in an independent population, African American women of the Atherosclerosis Risk in Communities (ARIC) study (n = 1334).

CONCLUSION

Dietary PUFA modulated the association of LPL rs320 with obesity traits in two independent populations. These interactions may be relevant to the dietary management of obesity, particularly in women.

Characterization of the redox transition of the XRCC1 N-terminal domain

XRCC1, a scaffold protein involved in DNA repair, contains an N-terminal domain (X1NTD) that interacts specifically with DNA polymerase β. It was recently discovered that X1NTD contains a disulfide switch that allows it to adopt either of two metamorphic structures. In the present study, we demonstrate that formation of an N-terminal proline carbimate adduct resulting from the nonenzymatic reaction of Pro2 with CO2 is essential for stabilizing the oxidized structure, X1NTDox. The kinetic response of X1NTDred to H2O2, monitored by NMR, was determined to be very slow, consistent with involvement of the buried, kinetically trapped Cys12 residue, but was significantly accelerated by addition of protein disulfide isomerase or by Cu(2+). NMR analysis of a sample containing the pol β polymerase domain, and both the reduced and oxidized forms of X1NTD, indicates that the oxidized form binds to the enzyme 25-fold more tightly than the reduced form.

Estimating mineral changes in enamel formation by ashing/BSE and microCT

Enamel formation produces the most highly mineralized tissue in the human body. The growth of enamel crystallites is assisted by enamel proteins and proteinases. As enamel formation progresses from secretory to maturation stages, the composition of the matrix with its mineral and non-mineral components dynamically changes in an inverse fashion. We hypothesized that appropriately calibrated micro-computed tomography (µCT) technology is suitable to estimate the mineral content (weight and/or density) and volume comparable in accuracy with that for directly weighed and sectioned enamel. Different sets of mouse mandibular incisors of C57BL/6 mice were used for dissections and µCT reconstructions. Calibration phantoms corresponding to the range of enamel mineral densities were used. Secretory-stage enamel contained little mineral and was consequently too poor in contrast for enamel volumes to be accurately estimated by µCT. Maturation-stage enamel, however, showed remarkable correspondence for total mineral content per volume where comparisons were possible between and among the different analytical techniques used. The main advantages of the µCT approach are that it is non-destructive, time-efficient, and can monitor changes in mineral content of the most mature enamel, which is too physically hard to dissect away from the tooth.

The association between LRP-1 variants and chylomicron uptake after a high fat meal

BACKGROUND AND AIMS

In vitro studies suggest that low density lipoprotein receptor-related protein 1 (LRP1) plays a role in the secondary uptake of chylomicrons. In addition, in vivo studies using LRP-1 knockout mice show these animals exhibit delayed chylomicron clearance. Whether this is true in humans is unknown. We aimed to determine whether genetic variants in LRP-1 are associated with postprandial chylomicron uptake in humans given an oral fat challenge.

METHODS AND RESULTS

As many as 817 men and women (mean age +/- standard deviation = 48.4 +/- 16.4 years) forming the study population for the Genetics of Lipid Lowering Drugs Network (GOLDN) study ingested an oral fat load of 700 kilocalories per m² of body surface area at 83% fat, after an 8-h fast. Chylomicrons were measured by nuclear resonance spectroscopy (NMR) at fasting, and 3.5 and 6 h after the meal. 26 Single nucleotide polymorphisms (SNPs) in the LRP-1 gene were genotyped on the Affymetrix 6.0 array. Chylomicrons were, as expected, zero at fasting. Mixed linear models adjusted for age, sex, study site and pedigree tested for associations between LRP-1 SNPs and changes in chylomicron concentrations 3.5-6 h. A gene-based test across all 26 SNPs was conducted which corrected for the linkage disequilibrium (LD) between SNPs. 11 LRP-1 SNPs were significantly associated with the change in chylomicron concentration correction for multiple testing (Q < 0.05). The subsequent gene-based test, was also significant (P = 0.01).

CONCLUSION

These results require replication but strongly indicate the role of LRP1 in postprandial lipoprotein uptake and/or clearance.

Barrier formation: potential molecular mechanism of enamel fluorosis

Enamel fluorosis is an irreversible structural enamel defect following exposure to supraoptimal levels of fluoride during amelogenesis. We hypothesized that fluorosis is associated with excess release of protons during formation of hypermineralized lines in the mineralizing enamel matrix. We tested this concept by analyzing fluorotic enamel defects in wild-type mice and mice deficient in anion exchanger-2a,b (Ae2a,b), a transmembrane protein in maturation ameloblasts that exchanges extracellular Cl(-) for bicarbonate. Defects were more pronounced in fluorotic Ae2a,b (-/-) mice than in fluorotic heterozygous or wild-type mice. Phenotypes included a hypermineralized surface, extensive subsurface hypomineralization, and multiple hypermineralized lines in deeper enamel. Mineral content decreased in all fluoride-exposed and Ae2a,b(-/-) mice and was strongly correlated with Cl(-). Exposure of enamel surfaces underlying maturation-stage ameloblasts to pH indicator dyes suggested the presence of diffusion barriers in fluorotic enamel. These results support the concept that fluoride stimulates hypermineralization at the mineralization front. This causes increased release of protons, which ameloblasts respond to by secreting more bicarbonates at the expense of Cl(-) levels in enamel. The fluoride-induced hypermineralized lines may form barriers that impede diffusion of proteins and mineral ions into the subsurface layers, thereby delaying biomineralization and causing retention of enamel matrix proteins.

New paradigms on the transport functions of maturation-stage ameloblasts

Fully matured dental enamel is an architecturally and mechanically complex hydroxyapatite-based bioceramic devoid of most of the organic material that was essential in its making. Enamel formation is a staged process principally involving secretory and maturation stages, each associated with major changes in gene expression and cellular function. Cellular activities that define the maturation stage of amelogenesis include ion (e.g., calcium and phosphate) transport and storage, control of intracellular and extracellular pH (e.g., bicarbonate and hydrogen ion movements), and endocytosis. Recent studies on rodent amelogenesis have identified a multitude of gene products that appear to be linked to these cellular activities. This review describes the main cellular activities of these genes during the maturation stage of amelogenesis.

Modulation of cell-cell junctional complexes by matrix metalloproteinases

The ameloblast cell layer of the enamel organ is in contact with the forming enamel as it develops into the hardest substance in the body. Ameloblasts move in groups that slide by one another as the enamel layer thickens. Each ameloblast is responsible for the formation of one enamel rod, and the rods are the mineralized trail that moving ameloblasts leave behind. Matrix metalloproteinases (MMPs) facilitate cell movement in various tissues during development, and in this review we suggest that the tooth-specific MMP, enamelysin (MMP20), facilitates ameloblast movements during enamel development. Mmp20 null mice have thin brittle enamel with disrupted rod patterns that easily abrades from the underlying dentin. Strikingly, the Mmp20 null mouse enamel organ morphology is noticeably dysplastic during late-stage development, when MMP20 is no longer expressed. We suggest that in addition to its role of cleaving enamel matrix proteins, MMP20 also cleaves junctional complexes present on ameloblasts to foster the cell movement necessary for formation of the decussating enamel rod pattern. Therefore, inactivation of MMP20 would result in tight ameloblast cell-cell attachments that may cause maturation-stage enamel organ dysplasia. The tight ameloblast attachments would also preclude the ameloblast movement necessary to form decussating enamel rod patterns.

Perilipin polymorphism interacts with saturated fat and carbohydrates to modulate insulin resistance

BACKGROUND AND AIMS

Macronutrient intakes and genetic variants have been shown to interact to alter insulin resistance, but replications of gene-nutrient interactions across independent populations are rare, despite their critical importance in establishing credibility. We aimed to investigate a previously demonstrated saturated fat and carbohydrate interaction for insulin resistance for perilipin (PLIN1), a regulator of adipocyte metabolism.

METHODS AND RESULTS

We investigated the previously shown interaction for PLIN1 11482G > A (rs894160) on insulin resistance in US men (n = 462) and women (n = 508) (mean ± SD, 49 ± 16 years). In multivariable linear regression models, we found an interaction (P < 0.05) between the ratio of saturated fat to carbohydrate intake as a continuous variable and PLIN1 11482G > A for HOMA-IR (homeostasis model assessment of insulin resistance) in women. For carriers of the minor allele but not for non-carriers, as the ratio of saturated fat to carbohydrate intake increased, predicted HOMA-IR increased (P = 0.002). By dichotomizing the ratio of saturated fat to carbohydrate intake into high and low, we found significant interaction terms for insulin and HOMA-IR (P < 0.05). When the ratio of saturated fat to carbohydrate was high, insulin and HOMA-IR were higher in minor allele carriers (P = 0.004 and P = 0.003, respectively), but did not differ when the ratio was low. Similar patterns or trends were observed when saturated fat and carbohydrate were dichotomized into high and low as individual macronutrients.

CONCLUSIONS

Replication of the previously reported interaction between macronutrient intakes and PLIN1 genotype for insulin resistance reinforces the potential usefulness of applying genotype information in the dietary management of insulin resistance.

Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultrafast-heating calorimetry

Differential scanning calorimetry (DSC) is widely used to study the stability of amorphous solids, characterizing the kinetics of crystallization close to the glass-transition temperature T(g). We apply ultrafast DSC to the phase-change material Ge(2)Sb(2)Te(5) (GST) and show that if the range of heating rates is extended to more than 10(4) K s(-1), the analysis can cover a wider temperature range, up to the point where the crystal growth rate approaches its maximum. The growth rates that can be characterized are some four orders of magnitude higher than in conventional DSC, reaching values relevant for the application of GST as a data-storage medium. The kinetic coefficient for crystal growth has a strongly non-Arrhenius temperature dependence, revealing that supercooled liquid GST has a high fragility. Near T(g) there is evidence for decoupling of the crystal-growth kinetics from viscous flow, matching the behaviour for a fragile liquid suggested by studies on oxide and organic systems.

SIRT1 and CLOCK 3111T> C combined genotype is associated with evening preference and weight loss resistance in a behavioral therapy treatment for obesity

BACKGROUND

A new negative feedback loop has been proposed, which suggests connections between the circadian clock and SIRTUIN1 (SIRT1)-dependent functions associated with cell survival, development and metabolism.

OBJECTIVE

To develop a SIRT1 and circadian locomotor output cycles kaput (CLOCK) combined genotype and to assess its associations with the chronotype of subjects and their potential resistance to weight loss in a behavioral treatment for obesity based on a Mediterranean diet.

DESIGN

Overweight /obese subjects (n=1465), aged 20-65 years, who attended outpatient obesity clinics, were genotyped for SIRT1 (rs1467568) and CLOCK (3111T>C, rs1801260). Anthropometric, biochemical and dietary-intake variables were analyzed. Effectiveness of the program and weight loss progression during 30 weeks of treatment was assessed.

RESULTS

We found highly consistent associations between the morning/evening questionnaires across the different genotype categories. Subjects carrying minor alleles at SIRT1 and CLOCK loci (R group) displayed a higher resistance to weight loss and a lower weekly weight loss rate as compared with homozygotes for both major alleles (P group). Significant differences were found across genotypes in weight loss progression during the 30 weeks of treatment (P=0.039). Dietary habits indicated that R carriers had a lower intake of total carbohydrates and monounsaturated fats, and a higher intake of saturated fats than those carrying the intermediate (M) and the P genotype (P=0.02). Plasma ghrelin concentrations were also significantly higher in subjects carrying the R genotype.

CONCLUSION

Variants of both SIRT1 and CLOCK have an additive effect on resistance to weight loss that could be related to the chronotype of the subject, higher plasma levels of ghrelin and less adherence to Mediterranean diet patterns.

Differences in daily rhythms of wrist temperature between obese and normal-weight women: associations with metabolic syndrome features

The circadian rhythm of core body temperature is associated with widespread physiological effects. However, studies with other more practical temperature measures, such as wrist (WT) and proximal temperatures, are still scarce. The aim of this study was to investigate whether obesity is associated with differences in mean WT values or in its daily rhythmicity patterns. Daily patterns of cortisol, melatonin, and different metabolic syndrome (MetS) features were also analyzed in an attempt to clarify the potential association between chronodisruption and MetS. The study was conducted on 20 normal-weight women (age: 38 ± 11 yrs and BMI: 22 ± 2.6 kg/m(2)) and 50 obese women (age: 42 ± 10 yrs and BMI: 33.5 ± 3.2 kg/m(2)) (mean ± SEM). Skin temperature was measured over a 3-day period every 10 min with the "Thermochron iButton." Rhythmic parameters were obtained using an integrated package for time-series analysis, "Circadianware." Obese women displayed significantly lower mean WT (34.1°C ± 0.3°C) with a more flattened 24-h pattern, a lower-quality rhythm, and a higher intraday variability (IV). Particularly interesting were the marked differences between obese and normal-weight women in the secondary WT peak in the postprandial period (second-harmonic power [P2]), considered as a marker of chronodisruption and of metabolic alterations. WT rhythmicity characteristics were related to MetS features, obesity-related proteins, and circadian markers, such as melatonin. In summary, obese women displayed a lower-quality WT daily rhythm with a more flattened pattern (particularly in the postprandial period) and increased IV, which suggests a greater fragmentation of the rest/activity rhythm compared to normal-weight women. These 24-h changes were associated with higher MetS risk.

Chymotrypsin C (caldecrin) is associated with enamel development

Two main proteases cleave enamel extracellular matrix proteins during amelogenesis. Matrix metalloprotease-20 (Mmp20) is the predominant enzyme expressed during the secretory stage, while kallikrein-related peptidase-4 (Klk4) is predominantly expressed during maturation. Mutations to both Mmp20 and Klk4 result in abnormal enamel phenotypes. During a recent whole-genome microarray analysis of rat incisor enamel organ cells derived from the secretory and maturation stages of amelogenesis, the serine protease chymotrypsin C (caldecrin, Ctrc) was identified as significantly up-regulated (> 11-fold) during enamel maturation. Prior reports indicate that Ctrc expression is pancreas-specific, albeit low levels were also noted in brain. We here report on the expression of Ctrc in the enamel organ. Quantitative PCR (qPCR) and Western blot analysis were used to confirm the expression of Ctrc in the developing enamel organ. The expression profile of Ctrc is similar to that of Klk4, increasing markedly during the maturation stage relative to the secretory stage, although levels of Ctrc mRNA are lower than for Klk4. The discovery of a new serine protease possibly involved in enamel development has important implications for our understanding of the factors that regulate enamel biomineralization.

Tolerance induced by apoptotic antigen-coupled leukocytes is induced by PD-L1+ and IL-10-producing splenic macrophages and maintained by T regulatory cells

Ag-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide Ags linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-coupled splenocytes [Ag-SP]) has been demonstrated to be a highly efficient method for inducing peripheral, Ag-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. In this study, we show that apoptotic Ag-SP accumulate in the splenic marginal zone, where their uptake by F4/80(+) macrophages induces production of IL-10, which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 that is essential for Ag-SP tolerance induction. Ag-SP infusion also induces T regulatory cells that are dispensable for tolerance induction but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. To our knowledge, we show for the first time that tolerance results from the synergistic effects of two distinct mechanisms, PD-L1-dependent T cell-intrinsic unresponsiveness and the activation of T regulatory cells. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting multiple sclerosis.

ADAM17_i33708A>G polymorphism interacts with dietary n-6 polyunsaturated fatty acids to modulate obesity risk in the Genetics of Lipid Lowering Drugs and Diet Network study

BACKGROUND AND AIMS

The disintegrin and metalloproteinase ADAM17, also known as tumor necrosis factor alpha converting enzyme, is expressed in adipocytes. Importantly, elevated levels of ADAM17 expression have been linked to obesity and insulin resistance. Therefore, the aim of this study was to evaluate the association of six ADAM17 single nucleotide polymorphisms (SNPs) (m1254A>G, i14121C>A, i33708A>G, i48827A>C, i53440C>T, and i62781G>T) with insulin-resistance phenotypes and obesity risk, and their potential interactions with dietary polyunsaturated fatty acids (PUFA).

METHODS AND RESULTS

ADAM17 SNPs were genotyped in 936 subjects (448 men/488 women) who participated in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) study. Anthropometrical and biochemical measurements were determined by standard procedures. PUFA intake was estimated using a validated questionnaire. G allele carriers at the ADAM17_m1254A>G polymorphism exhibited significantly higher risk of obesity (P=0.003), were shorter (P=0.017), had higher insulin (P=0.016), and lower HDL-C concentrations (P=0.027) than AA subjects. For the ADAM17_i33708A>G SNP, homozygotes for the A allele displayed higher risk of obesity (P=0.001), were heavier (P=0.011), had higher BMI (P=0.005), and higher waist measurements (P=0.023) than GG subjects. A significant gene-diet interaction was found (P=0.030), in which the deleterious association of the i33708A allele with obesity was observed in subjects with low intakes from (n-6) PUFA (P<0.001), whereas no differences in obesity risk were seen among subjects with high (n-6) PUFA intake (P>0.5)

CONCLUSION

These findings support that ADAM17 (m1254A>G and i33708A>G) SNPs may contribute to obesity risk. For the ADAM17_i33708A>G SNP, this risk may be further modulated by (n-6) PUFA intake.

Altered ion-responsive gene expression in Mmp20 null mice

During enamel maturation, hydroxyapatite crystallites expand in volume, releasing protons that acidify the developing enamel. This acidity is neutralized by the buffering activity of carbonic anhydrases and ion transporters. Less hydroxyapatite forms in matrix metalloproteinase-20 null (Mmp20(-/-)) mouse incisors, because enamel thickness is reduced by approximately 50%. We therefore asked if ion regulation was altered in Mmp20(-/-) mouse enamel. Staining of wild-type and Mmp20(-/-) incisors with pH indicators demonstrated that wild-type mice had pronounced changes in enamel pH as development progressed. These pH changes were greatly attenuated in Mmp20(-/-) mice. Expression of 4 ion-regulatory genes (Atp2b4, Slc4a2, Car6, Cftr) was significantly decreased in enamel organs from Mmp20(-/-) mice. Notably, expression of secreted carbonic anhydrase (Car6) was reduced to almost undetectable levels in the null enamel organ. In contrast, Odam and Klk4 expression was unaffected. We concluded that a feedback mechanism regulates ion-responsive gene expression during enamel development.

The effects of ABCG5/G8 polymorphisms on HDL-cholesterol concentrations depend on ABCA1 genetic variants in the Boston Puerto Rican Health Study

BACKGROUND AND AIMS

ATP-binding cassette transporters G5/G8 (ABCG5/G8) are associated with HDL-C concentrations. To assess whether the effect of ABCG5/G8 genetic variants on HDL-C concentrations is dependent on ATP-binding cassette transporters A1 (ABCA1), we studied potential interactions between single nucleotide polymorphisms (SNPs) at ABCG5/G8 (i7892T > C, 5U145A > C, T54CA > G, T400KC > A) and ABCA1 (i27943G > A, i48168G > A, K219RG > A, i125970G > C, 3U8995A > G) genes with HDL-C concentrations.

METHODS AND RESULTS

ABCG5/G8 and ABCA1 SNPs were genotyped in 788 subjects (228 men and 560 women) who participated in the Boston Puerto Rican Health Study. Biochemical measurements were determined by standard procedures. Genotyping was performed using TaqMan assays according to routine laboratory protocols. Significant gene-gene interactions for HDL-C were found between ABCG8 (5U145A > C, T54CA > G, T400KC > A) SNPs and ABCA1_i48168G > A genetic variant (P = 0.009, P = 0.042 and P = 0.036, respectively), in which carriers of the 5U145C and 54C alleles, and homozygotes for the T400 allele at ABCG8 genetic variants displayed lower HDL-C concentrations than homozygotes for the 5U145A and T54 alleles, and heterozygotes for the 400K allele at ABCG8 SNPs, only if they were also homozygous for the minor allele (A) at the aforementioned ABCA1 SNP.

CONCLUSIONS

The gene-gene interactions reported in the present study support the hypothesis that the effect of ABCG5/G8 genetic variants on HDL-C concentrations is dependent on ABCA1 expression. Replication of these analyses to further populations, particularly with low HDL-C, is clearly warranted.

Regulation of dental enamel shape and hardness

Epithelial-mesenchymal interactions guide tooth development through its early stages and establish the morphology of the dentin surface upon which enamel will be deposited. Starting with the onset of amelogenesis beneath the future cusp tips, the shape of the enamel layer covering the crown is determined by five growth parameters: the (1) appositional growth rate, (2) duration of appositional growth (at the cusp tip), (3) ameloblast extension rate, (4) duration of ameloblast extension, and (5) spreading rate of appositional termination. Appositional growth occurs at a mineralization front along the ameloblast distal membrane in which amorphous calcium phosphate (ACP) ribbons form and lengthen. The ACP ribbons convert into hydroxyapatite crystallites as the ribbons elongate. Appositional growth involves a secretory cycle that is reflected in a series of incremental lines. A potentially important function of enamel proteins is to ensure alignment of successive mineral increments on the tips of enamel ribbons deposited in the previous cycle, causing the crystallites to lengthen with each cycle. Enamel hardens in a maturation process that involves mineral deposition onto the sides of existing crystallites until they interlock with adjacent crystallites. Neutralization of acidity generated by hydroxyapatite formation is a key part of the mechanism. Here we review the growth parameters that determine the shape of the enamel crown as well as the mechanisms of enamel appositional growth and maturation.

Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at square root(sNN) = 200 GeV

This Letter presents the first measurement of event-by-event fluctuations of the elliptic flow parameter v(2) in Au+Au collisions at square root(s(NN))=200 GeV as a function of collision centrality. The relative nonstatistical fluctuations of the v(2) parameter are found to be approximately 40%. The results, including contributions from event-by-event elliptic flow fluctuations and from azimuthal correlations that are unrelated to the reaction plane (nonflow correlations), establish an upper limit on the magnitude of underlying elliptic flow fluctuations. This limit is consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results provide important constraints on models of the initial state and hydrodynamic evolution of relativistic heavy ion collisions.

A composite scoring of genotypes discriminates coronary heart disease risk beyond conventional risk factors in the Boston Puerto Rican Health Study

BACKGROUND AND AIMS

Using a genetic predisposition score (GPS), integrating the additive associations of a set of single nucleotide polymorphisms (SNPs) with CHD, we examined the consequences of the joint presence of a high GPS and conventional risk factors (CRFs).

METHODS AND RESULTS

We studied 11 SNPs at eight loci in 197 participants with prior CHD and 524 CHD-free subjects from the Boston Puerto Rican Health Study. Each polymorphism contributed 1 unit (high-risk allele homozygous), 0.5 units (heterozygous) and 0 units (low-risk allele homozygous) to the GPS. Odds ratio (OR) of CHD for those at high risk because of GPS (>5) and simultaneous presence of CRFs were estimated, compared with subjects at low risk, for both measurements. The mean score was higher in participants with prior CHD than those CHD-free (P=0.015), and the OR for CHD with a GPS>5 was 2.90 (P<0.001).The joint presence of a high GPS and each CRF was associated with higher risk of CHD. Compared to participants with high GPS, those with low GPS (<or=5) were protected against CHD even if they were smokers (OR=0.44), heavy drinkers (OR=0.43), displayed low physical activity (OR=0.35), had hypertension (OR=0.52) or hyperlipidemia (OR=0.34) (P values ranging from 0.004 to 0.023).

CONCLUSION

A simple genetic score of 11 polymorphisms may identify those subjects at increased risk of CHD beyond conventional risk factors.

High transverse momentum triggered correlations over a large pseudorapidity acceptance in Au + Au collisions at square root(s(NN)) = 200 GeV

A measurement of two-particle correlations with a high transverse momentum trigger particle (p(T)(trig) > 2.5 GeV/c) is presented for Au+Au collisions at square root(s(NN)) = 200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4 < Delta eta < 2). A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all Delta eta. As in p+p collisions, the near side is characterized by a peak of correlated partners at small angle relative to the trigger particle. However, in central Au+Au collisions an additional correlation extended in Delta eta and known as the "ridge" is found to reach at least |Delta eta| approximately = 4. The ridge yield is largely independent of Delta eta over the measured range, and it decreases towards more peripheral collisions. For the chosen (p(T)(trig) cut, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.

The effect of a novel intergenic polymorphism (rs11774572) on HDL-cholesterol concentrations depends on TaqIB polymorphism in the cholesterol ester transfer protein gene

BACKGROUND AND AIMS

Several genes have been shown to individually affect plasma lipoprotein metabolism in humans. Studies on gene-gene interactions could offer more insight into how genes affect lipid metabolism and may be useful in predicting lipid concentrations. We tested for gene-gene interactions between TaqIB SNP in the cholesterol ester transfer protein (CETP) and three novel single nucleotide polymorphisms (SNPs), namely rs11774572, rs7819412 and rs6995374 for their effect on metabolic syndrome (MetS) components and related traits.

METHODS AND RESULTS

The aforementioned SNPs were genotyped in 1002 subjects who participated in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) study. Lipids were measured by standard procedures and lipoprotein subfractions, by proton nuclear magnetic resonance spectroscopy. Polymorphism rs11774572 was significantly associated with MetS (P=0.020), mainly driven by the association of the C allele with lower HDL-C (P=0.043) and higher triglycerides (P=0.049) and insulin (P=0.040) concentrations than TT subjects. A significant interaction between SNPs rs11774572 and CETP-TaqIB SNPs was found for HDL-C concentrations (P=0.006) and for HDL (P=0.008) and LDL particle sizes (P=0.009), small LDL (P=0.004), and VLDL concentrations (P=0.021), in which TT homozygotes displayed higher HDL-C concentrations and for HDL and LDL particle sizes, and lower small LDL and VLDL concentrations than C carriers, if they were CETP B2 allele carriers (P values ranging from <0.001 to 0.001).

CONCLUSIONS

The rs11774572 polymorphism may play a role in the dyslipidemia that characterizes MetS. The interaction between rs11774572 and CETP-TaqIB SNPs on HDL-C concentrations provides some insights into the underlying mechanisms.

System size, energy, and centrality dependence of pseudorapidity distributions of charged particles in relativistic heavy-ion collisions

We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, sqrt[s_{NN}]=22.4, 62.4, and 200 GeV, over a wide range of pseudorapidity, using the PHOBOS detector. A comparison of Cu+Cu and Au+Au results shows that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same N{part}/2A rather than the same N_{part}. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies.

XBP1 may determine the size of the ameloblast endoplasmic reticulum

Ameloblasts progress through defined stages of development as enamel forms on teeth. Pre-secretory ameloblasts give rise to tall columnar secretory ameloblasts that direct the enamel to achieve its full thickness. During the maturation stage, the ameloblasts shorten and direct the enamel to achieve its final hardened form. Here we ask how the volume of selected ameloblast organelles changes (percent volume per ameloblast) as ameloblasts progress through six defined developmental stages. We demonstrate that mitochondria volume peaks during late maturation, indicating that maturation-stage ameloblasts maintain a high level of metabolic activity. Also, the endoplasmic reticulum (ER) volume changes significantly as a function of developmental stage. This prompted us to ask if X-box-binding protein-1 (XBP1) plays a role in regulating ameloblast ER volume, as has been previously demonstrated for secretory acinar cells and for plasma cell differentiation. We demonstrate that Xbp1 expression correlates positively with percent volume of ameloblast ER.

Echocardiographic ratio indices in overtly healthy Boxer dogs screened for heart disease

BACKGROUND

Boxer dogs are routinely screened by echocardiography to exclude congenital and acquired heart disease. Individuals of a given breed may span a large range of body sizes, potentially invalidating linear regression of M-mode measurements against body weight. Echocardiographic ratio indices (ERIs) provide a novel method of characterizing echocardiographic differences between Boxers and other dog breeds.

HYPOTHESIS

ERIs obtained from overtly healthy Boxer dogs presented for cardiac screening will be different from ERIs established for normal non-Boxer dogs, and those differences will be unrelated to aortic velocity or systolic blood pressure.

ANIMALS

Eighty-one Boxers with no outward clinical signs of heart disease were studied.

METHODS

All dogs were examined by 2-dimensional, M-mode, and Doppler echocardiography. M-mode measurements were used to perform ERI calculations, and the indices in Boxers were compared between Boxers with varying severity of arrhythmia and those of normal non-Boxer dogs.

RESULTS

Differences in weight-based ERIs, which reflect increased thickness of the left ventricular free wall (LVW) and interventricular septum (IVS) and smaller aortic size, were found in overtly healthy Boxer dogs compared with normal non-Boxer dogs. ERIs of left atrial and LV cavity size in overtly healthy Boxers were not significantly different from those of non-Boxer dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Boxer dogs may have an increased relative thickness of the LVW and IVS that is independent of aortic size, aortic velocity, or arterial blood pressure, and this morphology should be taken into consideration when screening Boxers by echocardiography.

CD43 regulates Th2 differentiation and inflammation

CD43 is a highly glycosylated transmembrane protein that regulates T cell activation. CD43(-/-) T cells are hyperproliferative and the cytoplasmic tail of CD43 has been found to be sufficient to reconstitute wild-type proliferation levels, suggesting an intracellular mechanism. In this study, we report that upon TCR ligation CD43(-/-) T cells demonstrated no increase in tyrosine phosphorylation but a decreased calcium flux. Interestingly, CD43(-/-) T cells preferentially differentiated into Th2 cells in vitro, and CD43(-/-) T cells show increased GATA-3 translocation into the nucleus. In vivo, CD43(-/-) mice exhibited increased inflammation in two separate models of Th2-mediated allergic airway disease. In contrast, in Th1-mediated diabetes, nonobese diabetic CD43(-/-) mice did not significantly differ from wild-type mice in disease onset or progression. Th1-induced experimental autoimmune encephalomyelitis to MOG(35-55) was also normal in the CD43(-/-) mice. Nonetheless, the CD43(-/-) mice produced more IL-5 when restimulated with MOG(35-55) in vitro and demonstrated decreased delayed-type hypersensitivity responses. Together, these data demonstrate that although CD43(-/-) T cells preferentially differentiate into Th2 cells, this response is not sufficient to protect against Th1-mediated autoimmune responses.

Multi-peptide coupled-cell tolerance ameliorates ongoing relapsing EAE associated with multiple pathogenic autoreactivities

The probability that epitope spreading occurs in multiple sclerosis (MS) and the fact that patients have been shown to respond to multiple myelin epitopes concurrently makes the use of peptide-specific tolerance therapies targeting single epitopes problematic. To attempt to overcome this limitation, we have employed cocktails of peptides in the ECDI coupled-APC tolerance system in mice to determine if T cell responses to multiple autoepitopes can be targeted simultaneously. Preventative tolerance induced with splenocytes coupled with a peptide cocktail of four distinct encephalitogenic epitopes (PLP(139-151), PLP(178-191), MBP(84-104), and MOG(92-106)) inhibited initiation of active EAE induced with each individual peptide and by a mixture of the four peptides by preventing activation of autoreactive Th1 cells and subsequent infiltration of inflammatory cells into the CNS. Most relevant to treatment of clinical MS, therapeutic tolerance initiated by splenocytes coupled with the peptide cocktail administered at the peak of acute disease prevented clinical relapses due to epitope spreading and ameliorated a diverse disease induced with a mixture of the four peptides. Interestingly, therapeutic tolerance appeared to be mediated by a mechanism distinct from preventative tolerance, i.e. by significantly increasing the levels of production of the anti-inflammatory cytokines TGF-beta and/or IL-10 in both the periphery and the CNS.

System size, energy, pseudorapidity, and centrality dependence of elliptic flow

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

Energy dependence of directed flow over a wide range of pseudorapidity in Au + Au collisions at the BNL Relativistic Heavy Ion Collider

We report on measurements of directed flow as a function of pseudorapidity in Au + Au collisions at energies of square root of SNN = 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at the BNL Relativistic Heavy Ion Collider. These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.

System size and centrality dependence of charged hadron transverse momentum spectra in Au + Au and Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV

We present transverse momentum distributions of charged hadrons produced in Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < pT < 5.0 GeV/c at square root of SNN = 62.4 GeV and 0.25 < pT < 7.0 GeV/c at square root of SNN = 200 GeV, in a pseudorapidity range of 0.2 < eta < 1.4. The nuclear modification factor R(AA) is calculated relative to p + p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, R(AA) is observed to be systematically larger in Cu + Cu collisions compared to Au + Au. However, for the same number of participating nucleons, R(AA) is essentially the same in both systems over the measured range of pT, in spite of the significantly different geometries of the Cu + Cu and Au + Au systems.

Differential induction of IgE-mediated anaphylaxis after soluble vs. cell-bound tolerogenic peptide therapy of autoimmune encephalomyelitis

The ability of different forms of myelin peptides to induce tolerance for the treatment of preestablished murine experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, was evaluated. i.v. administration of myelin peptide-pulsed, ethylene carbodiimide-fixed syngeneic splenocytes, but not soluble myelin peptide monomers or oligomers, proved exceedingly effective at treating preestablished EAE, resulting in amelioration of disease progression. In addition to the lack of therapeutic efficacy of soluble peptide and peptide oligomer, administering them i.v. after the onset of clinical symptoms in many but not all peptide-induced EAE models led to a rapid-onset anaphylactic reaction characterized by respiratory distress, erythema, decreased body temperature, unresponsiveness, and, often, death. By using anti-IgE antibody treatments and mice with targeted mutations of the FcgammaRIII alpha-chain or the common gamma-chain of FcepsilonRI and FcgammaRI/III, we demonstrate that IgE crosslinking of FcepsilonRI appears to be necessary and sufficient for myelin peptide-induced anaphylaxis. The implications of these findings to myelin peptide/protein tolerance strategies for the treatment of multiple sclerosis are discussed.

Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at the BNL relativistic heavy ion collider

This Letter describes the measurement of the energy dependence of elliptic flow for charged particles in Au+Au collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider. Data taken at collision energies of square root of s(NN)=19.6, 62.4, 130, and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of eta(')=|eta|-y(beam), scale with approximate linearity throughout eta('), implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.

Centrality dependence of charged hadron transverse momentum spectra in Au+Au collisions from sqrt[s(NN)]=62.4 to 200 GeV

We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt[s(NN)]=62.4 GeV. The spectra are presented for transverse momenta 0.25<p(T)<4.5 GeV/c, in a pseudorapidity range of 0.2<eta<1.4. The nuclear modification factor R(AA) is calculated relative to p+p data at the same collision energy as a function of collision centrality. For 2<p(T)<4.5 GeV/c, R(AA) is found to be significantly larger than in Au+Au collisions at sqrt[s(NN)]= 130 and 200 GeV. In contrast to the large change in R(AA), we observe a very similar centrality evolution of the p(T) spectra at sqrt[s(NN)]=62.4 and 200 GeV. The dynamical origin of this surprising factorization of energy and centrality dependence of particle production in heavy-ion collisions remains to be understood.

Decreased mineral content in MMP-20 null mouse enamel is prominent during the maturation stage

During enamel development, matrix metalloproteinase-20 (MMP-20, enamelysin) is expressed early during the secretory stage as the enamel thickens, and kallikrein-4 (KLK-4, EMSP1) is expressed later during the maturation stage as the enamel hardens. Thus, we investigated whether the physical properties of the secretory-/maturation-stage MMP-20 null enamel were significantly different from those of controls. We demonstrated that although, in relative terms, the weight percent of mature mineral in the MMP-20 null mouse enamel was only 7-16% less than that in controls, overall the enamel mineral was reduced by about 50%, and its hardness was decreased by 37%. Percent mineral content by weight was assessed at 3 different developmental stages. Remarkably, the biggest difference in mineral content between MMP-20 null and controls occurred in the nearly mature enamel, when MMP-20 is normally no longer expressed. This suggests that MMP-20 acts either directly or indirectly to facilitate the removal of maturation-stage enamel proteins.

Pseudorapidity distribution of charged particles in d+Au collisions at sqrt[sNN]=200 GeV

The measured pseudorapidity distribution of primary charged particles in minimum-bias d+Au collisions at sqrt[s(NN)]=200 GeV is presented for the first time. This distribution falls off less rapidly in the gold direction as compared to the deuteron direction. The average value of the charged particle pseudorapidity density at midrapidity is <dN(ch)/d eta>|eta|< or =0.6)=9.4+/-0.7(syst) and the integrated primary charged particle multiplicity in the measured region is 82+/-6(syst). Estimates of the total charged particle production, based on extrapolations outside the measured pseudorapidity region, are also presented. The pseudorapidity distribution, normalized to the number of participants in d+Au collisions, is compared to those of Au+Au and p+(-)p systems at the same energy. The d+Au distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25<p(T)<6.0 GeV/c, in a pseudorapidity range of 0.2<eta<1.4 in the deuteron direction. The evolution of the spectra with collision centrality is presented in comparison to p+pmacr; collisions at the same collision energy. With increasing centrality, the yield at high transverse momenta increases more rapidly than the overall particle density, leading to a strong modification of the spectral shape. This change in spectral shape is qualitatively different from observations in Au+Au collisions at the same energy. The results provide important information for discriminating between different models for the suppression of high-p(T) hadrons observed in Au+Au collisions.

Effects of fluoride on rat dental enamel matrix proteinases

Enamel fluorosis is characterised by increased porosity and a delay in the removal of enamel matrix proteins as the enamel matures. Amelogenin is the primary matrix protein in secretory-stage dental enamel. As enamel matures, amelogenins are hydrolysed by a number of enamel proteinases, including matrix metalloproteinase-20 (MMP-20 or enamelysin) and serine proteinase. Here, the effect of ingested fluoride on the relative activity of proteinases in the enamel matrix and the specific effect of fluoride on MMP-20 activity were examined. Proteinase activity relative to total enamel matrix protein was measured by fluorescence assay of enamel matrix dissected from rats given 0, 50, or 100 parts per 10(6) fluoride in their drinking water. To determine the specific effect of fluoride on the activity of MMP-20, the hydrolysis of a full-length recombinant human amelogenin by recombinant MMP-20 (rMMP-20) in the presence of 0, 2, 5, 10 or 100 microM fluoride was compared by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis (PAGE). In addition, a fluorescent peptide assay was developed to quantify enzyme activity against the tyrosine-rich amelogenin peptide cleavage site. In the late maturation stage, total proteinase activity per unit protein was lower in the fluoride-exposed rats than in the control rats. This in vivo finding indicates that fluoride ingestion can alter the relative amount of active proteinase in mature enamel. Hydrolysis of amelogenin at neutral pH by rMMP-20 was reduced in the presence of 100 microM F. In the peptide assay, rMMP-20 activity was significantly reduced by concentrations of fluoride as low as 2 microM at pH 6, with no significant effect at pH 7.2. These in vitro assays show that micromolar concentrations of fluoride can alter metalloproteinase activity, particularly when the pH is reduced to 6.0. These studies suggest that the effects of fluoride on enamel matrix proteinase secretion or activity could be involved in the aetiology of fluorosis in enamel and other mineralising tissues.