N-Terminal pyroglutamate formation of Aβ38 and Aβ40 enforces oligomer formation and potency to disrupt hippocampal long-term potentiation

Pyroglutamate (pGlu)-modified amyloid peptides have been identified in sporadic and familial forms of Alzheimer's disease (AD) and the inherited disorders familial British and Danish Dementia (FBD and FDD). In this study, we characterized the aggregation of amyloid-β protein Aβ37, Aβ38, Aβ40, Aβ42 and ADan species in vitro, which were modified by N-terminal pGlu (pGlu-Aβ3-x, pGlu-ADan) or possess the intact N-terminus (Aβ1-x, ADan). The pGlu-modification confers rapid formation of oligomers and short fibrillar aggregates. In accordance with these observations, the pGlu-modified Aβ38, Αβ40 and Αβ42 species inhibit hippocampal long term potentiation of synaptic response, but pGlu-Aβ3-42 showing the highest effect. Among the unmodified Aβ peptides, only Aβ1-42 exhibites such propensity, which was similar to pGlu-Aβ3-38 and pGlu-Aβ3-40. Likewise, the amyloidogenic peptide pGlu-ADan impaired synaptic potentiation more pronounced than N-terminal unmodified ADan. The results were validated using conditioned media from cultivated HEK293 cells, which express APP variants favoring the formation of Aβ1-x, Aβ3-x or N-truncated pGlu-Aβ3-x species. Hence, we show that the ability of different amyloid peptides to impair synaptic function apparently correlates to their potential to form oligomers as a common mechanism. The pGlu-modification is apparently mediating a higher surface hydrophobicity, as shown by 1-anilinonaphtalene-8-sulfonate fluorescence, which enforces potential to interfere with neuronal physiology.     

A meta-analysis and genome-wide association study of platelet count and mean platelet volume in african americans

Several genetic variants associated with platelet count and mean platelet volume (MPV) were recently reported in people of European ancestry. In this meta-analysis of 7 genome-wide association studies (GWAS) enrolling African Americans, our aim was to identify novel genetic variants associated with platelet count and MPV. For all cohorts, GWAS analysis was performed using additive models after adjusting for age, sex, and population stratification. For both platelet phenotypes, meta-analyses were conducted using inverse-variance weighted fixed-effect models. Platelet aggregation assays in whole blood were performed in the participants of the GeneSTAR cohort. Genetic variants in ten independent regions were associated with platelet count (N?=?16,388) with p<5×10(-8) of which 5 have not been associated with platelet count in previous GWAS. The novel genetic variants associated with platelet count were in the following regions (the most significant SNP, closest gene, and p-value): 6p22 (rs12526480, LRRC16A, p?=?9.1×10(-9)), 7q11 (rs13236689, CD36, p?=?2.8×10(-9)), 10q21 (rs7896518, JMJD1C, p?=?2.3×10(-12)), 11q13 (rs477895, BAD, p?=?4.9×10(-8)), and 20q13 (rs151361, SLMO2, p?=?9.4×10(-9)). Three of these loci (10q21, 11q13, and 20q13) were replicated in European Americans (N?=?14,909) and one (11q13) in Hispanic Americans (N?=?3,462). For MPV (N?=?4,531), genetic variants in 3 regions were significant at p<5×10(-8), two of which were also associated with platelet count. Previously reported regions that were also significant in this study were 6p21, 6q23, 7q22, 12q24, and 19p13 for platelet count and 7q22, 17q11, and 19p13 for MPV. The most significant SNP in 1 region was also associated with ADP-induced maximal platelet aggregation in whole blood (12q24). Thus through a meta-analysis of GWAS enrolling African Americans, we have identified 5 novel regions associated with platelet count of which 3 were replicated in other ethnic groups. In addition, we also found one region associated with platelet aggregation that may play a potential role in atherothrombosis.     

Microtubule-associated Proteins 1 (MAP1) Promote Human Immunodeficiency Virus Type I (HIV-1) Intracytoplasmic Routing to the Nucleus

After cell entry, HIV undergoes rapid transport toward the nucleus using microtubules and microfilaments. Neither the cellular cytoplasmic components nor the viral proteins that interact to mediate transport have yet been identified. Using a yeast two-hybrid screen, we identified four cytoskeletal components as putative interaction partners for HIV-1 p24 capsid protein: MAP1A, MAP1S, CKAP1, and WIRE. Depletion of MAP1A/MAP1S in indicator cell lines and primary human macrophages led to a profound reduction in HIV-1 infectivity as a result of impaired retrograde trafficking, demonstrated by a characteristic accumulation of capsids away from the nuclear membrane, and an overall defect in nuclear import. MAP1A/MAP1S did not impact microtubule network integrity or cell morphology but contributed to microtubule stabilization, which was shown previously to facilitate infection. In addition, we found that MAP1 proteins interact with HIV-1 cores both in vitro and in infected cells and that interaction involves MAP1 light chain LC2. Depletion of MAP1 proteins reduced the association of HIV-1 capsids with both dynamic and stable microtubules, suggesting that MAP1 proteins help tether incoming viral capsids to the microtubular network, thus promoting cytoplasmic trafficking. This work shows for the first time that following entry into target cells, HIV-1 interacts with the cytoskeleton via its p24 capsid protein. Moreover, our results support a role for MAP1 proteins in promoting efficient retrograde trafficking of HIV-1 by stimulating the formation of stable microtubules and mediating the association of HIV-1 cores with microtubules.     

Mate Familiarity Affects Pairing Behaviour in a Long‐Term Monogamous Lizard: Evidence from Detailed Bio‐Logging and a 31‐Year Field Study

Long‐term monogamy is most prevalent in birds but is also found in lizards. We combined a 31‐year field study of the long‐lived, monogamous Australian sleepy lizard, Tiliqua rugosa, with continuous behavioural observations through GPS data logging, in 1 yr, to investigate the duration of pair bonds, rates of partner change and whether either the reproductive performance hypothesis or the mate familiarity hypothesis could explain this remarkable long‐term monogamy. The reproductive performance hypothesis predicts higher reproductive success in more experienced parents, whereas the mate familiarity hypothesis suggests that effects of partner familiarity select for partner retention and long‐term monogamy. Rates of partner change were below 34% over a 5‐yr period and most sleepy lizards formed long‐term pair bonds: 31 partnerships lasted for more than 15 yr, 110 for more than 10 yr, and the recorded maximum was 27 yr (ongoing). In the year when we conducted detailed observations, familiar pairs mated significantly earlier than unfamiliar pairs. Previous pairing experience (total number of years paired with previous partners) had no significant effect. Early mating often equates to higher reproductive success, and we infer that is the case in sleepy lizards. Early mating of familiar pairs was not due to better body condition. We propose two suggestions about the proximate mechanisms that may allow familiar pair partners to mate earlier than unfamiliar partners. First, they may have improved coordination of their reproductive sexual cycles to reach receptivity earlier and thereby maximise fertilisation success. Second, they may forage more efficiently, benefiting from effective information transfer and/or cooperative predator detection. Those ideas need empirical testing in the future. Regardless of the mechanism, our observations of sleepy lizard pairing behaviour support the mate familiarity hypothesis, but not the reproductive performance hypothesis, as an explanation for its long‐term monogamous mating system.     

Drug Effect Unveils Inter-head Cooperativity and Strain-dependent ADP Release in Fast Skeletal Actomyosin

Amrinone is a bipyridine compound with characteristic effects on the force-velocity relationship of fast skeletal muscle, including a reduction in the maximum shortening velocity and increased maximum isometric force. Here we performed experiments to elucidate the molecular mechanisms for these effects, with the additional aim to gain insight into the molecular mechanisms underlying the force-velocity relationship. In vitro motility assays established that amrinone reduces the sliding velocity of heavy meromyosin-propelled actin filaments by 30% at different ionic strengths of the assay solution. Stopped-flow studies of myofibrils, heavy meromyosin and myosin subfragment 1, showed that the effects on sliding speed were not because of a reduced rate of ATP-induced actomyosin dissociation because the rate of this process was increased by amrinone. Moreover, optical tweezers studies could not detect any amrinone-induced changes in the working stroke length. In contrast, the ADP affinity of acto-heavy meromyosin was increased about 2-fold by 1 mm amrinone. Similar effects were not observed for acto-subfragment 1. Together with the other findings, this suggests that the amrinone-induced reduction in sliding velocity is attributed to inhibition of a strain-dependent ADP release step. Modeling results show that such an effect may account for the amrinone-induced changes of the force-velocity relationship. The data emphasize the importance of the rate of a strain-dependent ADP release step in influencing the maximum sliding velocity in fast skeletal muscle. The data also lead us to discuss the possible importance of cooperative interactions between the two myosin heads in muscle contraction.Muscle contraction, as well as several other aspects of cell motility, results from cyclic interactions between myosin II motors and actin filaments. These force-generating interactions are driven by the hydrolysis of ATP at the myosin active site as outlined in Scheme 1 (1–3). In the absence of actin, the P_i and ADP release steps (k₄ and k₅) are rate-limiting for the entire cycle at high (>12 °C) and low temperatures, respectively (4–6). In the presence of actin, the rate of P_i release increases significantly, and the overall cycle is accelerated more than 2 orders of magnitude. The sliding velocity of myosin-propelled motors is generally believed to be rate-limited by actomyosin dissociation (rate constant k′₅, k′₆, or k′₂ in Scheme 1) (7). Alternatively, some studies (8, 9) have suggested that the sliding velocity is determined by the fraction of myosin heads in the weak-binding states, AM⁴ ATP and AM ADP P_i. However, it is worth emphasizing that K_T is very low under physiological conditions (1, 3) with low population of these states. For the same reason, the rate of dissociation of the AM complex is governed by K′₁ and k′₂.Open in a separate windowSCHEME 1.Simplified kinetics scheme for MgATP turnover by myosin (lower row) and actomyosin (upper row). Inorganic phosphate is denoted by P_i; MgATP is denoted by ATP, and MgADP is denoted by ADP; myosin is denoted by M. The states AM*ADP and AM ADP correspond to myosin heads with their nucleotide binding pocket in a partially closed and open conformation, respectively (7, 52). Rate constants are indicated by lowercase letters (rightward transitions, k₂ − k₅ and k′₂ − k′₅, or leftward transitions, k₋₂ − k₋₅ and k′₋₂ − k′₋₅) and equilibrium constants by uppercase letters (K₁, K′₁, K_T, K₃, K′₃, K₆, k′₆, and K_DP). The equilibrium constants are association constants except for simple bimolecular reactions where they are defined as k_i/k_−i.For the study of contractile mechanisms in both muscle and other types of cells, drugs may be useful as pharmacological tools affecting different transitions or states in the force-generating cycle. Whereas the use of drugs as tools may be less specific than site-directed mutagenesis, it also has advantages. The motor protein function may be studied in vivo, with maintained ordering of the protein components, e.g. as in the muscle sarcomere, allowing more insight into the relationship between specific molecular events and contractile properties of muscle. A drug that has been used quite extensively in this context is butanedione monoxime. The usefulness of this drug is based on firm characterization of its effect on actomyosin function on the molecular level (3, 10–13). More recently other drugs, like N-benzyl-p-toluene sulfonamide (14, 15) and blebbistatin (16), have been found to affect myosin function, and their effects at the molecular level have also been elucidated in some detail (14, 15, 17, 18). Both these drugs appear to affect the actomyosin interaction in a similar way as butanedione monoxime by inhibiting a step before (or very early in) the myosin power stroke, leading to the inhibition of actomyosin cross-bridge formation and force production.In contrast to the reduced isometric force, caused by the above mentioned drugs, the bipyridine compound amrinone (Fig. 1A) has been found to increase the isometric force production of fast intact skeletal muscles of the frog (19, 20) and mouse (21) and also of fast (but much less slow) skinned muscle fibers of the rat (22). In all the fast myosin preparations, the effect of about 1 mm amrinone on isometric force was associated with characteristic changes of the force-velocity relationship (Fig. 1B), including a reduced maximum velocity of shortening (19–22) and a reduced curvature of the force-velocity relationship (19–22). The latter effect was accompanied (20, 21) by a less pronounced deviation of the force-velocity relationship from the hyperbolic shape (23) at high loads. There have been different interpretations of the drug effects. It has been proposed (20–22) that amrinone might competitively inhibit the MgATP binding by myosin. However, more recently, results from in vitro motility assay experiments (24) challenged this idea. These results showed that amrinone reduces the sliding velocity (V_max) at saturating MgATP concentrations but not at MgATP concentrations close to, or below, the K_m value for the hyperbolic relationship between MgATP concentration and sliding velocity. Such a combination of effects is consistent with a reduced MgADP release rate (24) but not with competitive inhibition of substrate binding. However, effects of amrinone on the MgADP release rate have not been directly demonstrated. Additionally, in view of the uncertainty about what step actually determines the sliding velocity at saturating [MgATP] (see above and Refs. 7–9), it is of interest to consider other possible drug effects that could account for the data of Klinth et al. (24). These include the following: 1) an increased drag force, e.g. because of enhancement of weak actomyosin interactions; 2) a reduced step length; and 3) effects of the drug on the rate of MgATP-induced dissociation of actomyosin.Open in a separate windowFIGURE 1.A, structure of amrinone. B, experimental force-velocity data obtained in the presence (filled symbols) and absence (open symbols) of 1.1 mm amrinone. The data, from intact single frog muscle fibers, were obtained at 2 °C and fitted by Hill''s (42) hyperbola (lines) for data truncated at 80% of the maximum isometric force. Filled line, equation fitted to control data, a/P₀* = 0.185; P₀*/P₀ = 1.196. Dashed line, amrinone, a/P₀* = 0.347; P₀*/P₀ = 1.009. Force-velocity data were obtained in collaboration with Professor K. A. P. Edman. Same data as in Fig. 8 of Ref. 20. Note a decrease in maximum sliding velocity and curvature of the force-velocity relationship at low force, in response to amrinone. Also note that amrinone caused increased isometric force and a reduced deviation of the force-velocity relationship from the Hill''s hyperbola at high force. All changes of the force-velocity relationship were statistically significant (20), and similar changes were later also observed in intact mouse muscle and skinned rat muscle fibers. Data in Fig. 1 are published by agreement with Professor K. A. P. Edman.To differentiate between these hypotheses for the amrinone effects, and to gain more general insight into fundamental aspects of muscle function (e.g. mechanisms underlying the force-velocity relationship), we here study the molecular effects of amrinone on fast skeletal muscle myosin preparations in the presence and absence of actin.In vitro motility assay studies at different ionic strengths suggest that drag forces, caused by increased fraction of myosin heads in weak binding states, are not important for the effect of amrinone on sliding velocity. Likewise, optical tweezers studies showed no effect of the drug on the myosin step length. Finally, ideas that amrinone should reduce sliding velocity by reduced rate of MgATP-induced dissociation could be discarded because the drug actually increased the rate of this process. Instead, we found an amrinone-induced increase in the MgADP affinity of heavy meromyosin (HMM) in the presence of actin. Interestingly, similar effects of amrinone were not observed using myosin S1. As discussed below, this result and other results point to an amrinone-induced reduction in the rate of a strain-dependent MgADP release step. Simulations, using a model modified from that of Edman et al. (25), support this proposed mechanism of action. The results are discussed in relation to fundamental mechanisms underlying the force-velocity relationship of fast skeletal muscle, including which step determines shortening velocity and the possible importance of inter-head cooperativity.     

Accurate quantification of dimethylamine (DMA) in human urine by gas chromatography-mass spectrometry as pentafluorobenzamide derivative: evaluation of the relationship between DMA and its precursor asymmetric dimethylarginine (ADMA) in health and disease

Dimethylamine [DMA, (CH(3))(2)NH)] is abundantly present in human urine. Main sources of urinary DMA have been reported to include trimethylamine N-oxide, a common food component, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is excreted in the urine in part unmetabolized and in part after hydrolysis to DMA by dimethylarginine dimethylaminohydrolase (DDAH). Here we describe a GC-MS method for the accurate and rapid quantification of DMA in human urine. The method involves use of (CD(3))(2)NH as internal standard, simultaneous derivatization with pentafluorobenzoyl chloride and extraction in toluene, and selected-ion monitoring of m/z 239 for DMA and m/z 245 for (CD(3))(2)NH in the electron ionization mode. GC-MS analysis of urine samples from 10 healthy volunteers revealed a DMA concentration of 264+/-173 microM equivalent to 10.1+/-1.64 micromol/mmol creatinine. GC-tandem MS analysis of the same urine samples revealed an ADMA concentration of 27.3+/-15.3 microM corresponding to 1.35+/-1.2 micromol/mmol creatinine. In these volunteers, a positive correlation (R=0.83919, P=0.0024) was found between urinary DMA and ADMA, with the DMA/ADMA molar ratio being 10.8+/-6.2. Elevated excretion rates of DMA (52.9+/-18.5 micromol/mmol creatinine) and ADMA (3.85+/-1.65 micromol/mmol creatinine) were found by the method in 49 patients suffering from coronary artery disease, with the DMA/ADMA molar ratio also being elevated (16.8+/-12.8). In 12 patients suffering from end-stage liver disease, excretion rates of DMA (47.8+/-19.7 micromol/mmol creatinine) and ADMA (5.6+/-1.5 micromol/mmol creatinine) were found to be elevated, with the DMA/ADMA molar ratio (9.17+/-4.2) being insignificantly lower (P=0.46). Between urinary DMA and ADMA there was a positive correlation (R=0.6655, P<0.0001) in coronary artery disease, but no correlation (R=0.27339) was found in end-stage liver disease.     

Localization,transmission, spontaneous mutations,and variation of function of the Dpp4 (Dipeptidyl-peptidase IV; CD26) gene in rats

Dipeptidyl-peptidase IV (DPPIV) is involved in endocrine and immune functions via cleavage of regulatory peptides with a N-terminal proline or alanine such as incretins, neuropeptide Y, or several chemokines. So far no systematic investigations on the localization and transmission of the Dpp4 gene or the natural variations of DPPIV-like enzymatic function in different rat strains have been conducted. Here we mapped the Dpp4 gene to rat chromosome 3 and describe a semi-dominant mode of inheritance for Dpp4 in a mutant F344/DuCrj(DPPIV-) rat substrain lacking endogenous DPPIV-like activity. This mutant F344/DuCrj(DPPIV-) rat substrain constantly exhibits a nearly complete lack of DPPIV-like enzymatic activity, while segregation of DPPIV-like enzymatic activity was observed in another DPPIV-negative F344/Crl(Ger/DPPIV-) rat substrain. Screening of 12 different inbred laboratory rat strains revealed dramatic differences in DPPIV-like activity ranging from 11 mU/microl (LEW/Ztm rats) to 40 mU/microl (BN/Ztm and DA/Ztm rats). A lack of DPPIV-like activity in F344 rats was associated with an improved glucose tolerance and blunted natural killer cell function, which indicates the pleiotropic functional role of DPPIV in vivo. Overall, the variations in DPPIV-like enzymatic activity probably represent important confounding factors in studies using rat models for research on regulatory peptides.     

Acute phase reactants add little to composite disease activity indices for rheumatoid arthritis: validation of a clinical activity score

Introduction  

Frequent assessments of rheumatoid arthritis (RA) disease activity allow timely adaptation of therapy, which is essential in preventing disease progression. However, values of acute phase reactants (APRs) are needed to calculate current composite activity indices, such as the Disease Activity Score (DAS)28, the DAS28-CRP (i.e. the DAS28 using C-reactive protein instead of erythrocyte sedimentation rate) and the Simplified Disease Activity Index (SDAI). We hypothesized that APRs make limited contribution to the SDAI, and that an SDAI-modification eliminating APRs – termed the Clinical Disease Activity Index (CDAI; i.e. the sum of tender and swollen joint counts [28 joints] and patient and physician global assessments [in cm]) – would have comparable validity in clinical cohorts.