The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. ...Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year
–1
, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year
–1
, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.
Background: Visceral adiposity, more so than overall adiposity, is associated with chronic disease and mortality. There has been, to our knowledge, little research exploring the association between ...diet quality and visceral adipose tissue (VAT) among a mulitethnic population aged 18-80 y Objective: The primary objective of this cross-sectional analysis was to examine the association between diet quality Healthy Eating lndex-2010 (HEI-2010) scores and VAT among a multiethnic population of young, middle, and older aged adults in the United States. Secondary objectives were to repeat these analyses with overall adiposity and blood-based biomarkers for type 2 diabetes and cardiovascular disease risk as outcome measures. Methods: A total of 540 adults (dropped out: n = 4; age: 18-40 y, n = 220; 40-60 y, n= 183; 60-80 y, n = 133) were recruited across 3 sites (Honolulu County, San Francisco, and Baton Rouge) for the Shape Up! Adults study. Whole-body DXA, anthropometry, fasting blood draw, and questionnaires (food frequency, physical activity, and demographic characteristics) were completed. Linear regression was used to assess the associations between HEI-2010 tertiles and VAT and secondary outcome measures among all participants and age-specific strata, while adjusting for known confounders. Results: VAT, BMI (kg/m.sup.2), body fat percentage, total body fat, trunk fat, insulin, and insulin resistance were inversely related to diet quality (all P values < 0.004). When stratified by age, diet quality was inversely associated with VAT among participants aged 60-80 y (P < 0.006) and VAT/subcutaneous adipose tissue (SAT) among participants aged 40-60 y (P < 0.008). Conclusions: Higher-quality diet was associated with lower VAT, overall adiposity, and insulin resistance among this multiethnic population of young, middle, and older aged adults with ages ranging from 18 to 80 y More specifically, adherence to a high-quality diet may minimize VAT accumulation in adults aged 60-80 y and preferentially promote storage of SAT compared with VAT in adults aged 40-60 y This study was registered at clinicaltrials.gov as NCT03637855. Curr Dev Nutr 2020;4:nzaa090.
Thrombin activates protease-activated receptors (PARs) by specific cleavage of their amino-terminal exodomains to unmask a tethered ligand that binds intramolecularly to the body of the receptor to ...effect transmembrane signaling. Peptides that mimic such ligands are valuable as agonists for probing PAR function, but the tethered ligand peptide for PAR4, GYPGKF, lacks potency and is of limited utility. In a structure-activity analysis of PAR4 peptides, AYPGKF was ∼10-fold more potent than GYPGKF and, unlike GYPGKF, elicited PAR4-mediated responses comparable in magnitude to those elicited by thrombin. AYPGKF was relatively specific for PAR4 in part due to the tyrosine at position 2; substitution of phenylalanine orp-fluorophenylalanine at this position produced peptides that activated both PAR1 and PAR4. Because human platelets express both PAR1 and PAR4, it might be desirable to inhibit both receptors. Identifying a single agonist for both receptors raises the possibility that a single antagonist for both receptors might be developed. The AYPGKF peptide is a useful new tool for probing PAR4 function. For example, AYPGKF activated and desensitized PAR4 in platelets and, like thrombin, triggered phosphoinositide hydrolysis but not inhibition of adenylyl cyclase in PAR4-expressing cells. The latter shows that, unlike PAR1, PAR4 couples to Gq and not Gi.
Thrombosis of arteries and veins is fundamentally important in human diseases such as myocardial infarction, stroke, and venous thrombotic events. Thrombus formation in response to tissue factor (TF) ...is highly regulated and results from the complex interactions of pro-, anti-coagulant and fibrinolytic effectors. We have taken a mouse genetic approach to identify novel molecules and pathways that regulate the response to a thrombotic trigger. Previously, we observed that the wild-derived inbred mouse strain Cast/EiJ (Cast) was completely resistant to an otherwise lethal dose of TF in an in vivo model of pulmonary embolism (PE). TF-resistance was 100% in the F1 offspring of an intercross to a susceptible strain, C57Bl6/J (B6). To identify the gene(s) mediating TF-resistance, we performed genome-wide linkage analysis on 200 N2 generation animals from a Cast-B6 backcross and found several TF-resistance loci. One such locus was on the proximal end of chromosome 11 (chr11, rs3088940). At the chr11 marker, animals heterozygous for B6 and Cast alleles were significantly protected in the PE model (median survival times of 770 vs. 210 seconds, p<0.05). To confirm linkage, we measured TF-resistance in a congenic strain carrying the Cast chr11 on a B6 background (11C). We found that mice homozygous for Cast chr11 showed significant protection in the PE model; B6, 11C, and Cast strains demonstrated survival fractions of 0, 0.5, and 1 and median survival times of 225, 772 and >1200 seconds, respectively (p<0.0001). To explore the mechanism of TF-resistance and to identify potential candidate genes within the chr11 locus, we performed in vitro analyses of coagulation. Whole blood clotting times triggered with dilute TF were significantly prolonged in 11C mice as compared to B6 (53.7±0.4 vs. 48.9±0.4 sec, p<0.0001). To determine the contribution of platelets, we repeated dilute TF-triggered clotting in platelet poor plasma and found that clotting times remained prolonged in plasma from 11C animals as compared to B6 (52.2±0.5 vs. 46.7±0.9 sec, p<0.05). Next, we measured the aPTT and PT and found that while the PT was similar, the aPTT was prolonged in 11C versus B6 plasma (mean time 50.8±5.3 vs.44.8±6.4, p<0.05). Thus, 11C mice exhibited prolonged clotting times in whole blood and in plasma in response to dilute TF, and had prolonged aPTT. These findings suggested that the principal mechanism of protection was within the intrinsic pathway or in the thrombin feedback pathway. To further investigate, we measured the activity of factors II, V, VII, VIII, IX, X and XI using human factor deficient plasma. There were no significant differences in factor activity between 11C and B6 mice, with the exception of factor XI. Factor XI activity in 11C animals was reduced to 59.1% of B6 activity. These results were confirmed using a chromogenic substrate for factor XI. Activity was decreased in 11C mice as compared to B6 (EC50 values of 74.4±0.3 vs. 70.9±0.6, p<0.0001). The 40% absolute reduction in plasma factor XI activity suggests a potential mechanism for the observed resistance to thrombosis, and supports our theory that the defect lies in the intrinsic or feedback pathway. Since there are no obvious coagulation related genes on mouse chr11, we speculate that the Cast chr11 locus contains a gene(s) that increases the expression and/or activity of a novel inhibitor of factor XI activity, thereby mediating resistance to thrombus formation in vivo.
The risk of thrombosis differs between men and women; however, the mechanisms underlying this sex difference are unknown. We recently reported differences in thrombosis that are dependent on ...sexually-dimorphic patterns of growth hormone (GH) secretion and its subsequent effects on the expression of coagulation-related genes in the liver. Mice that are deficient in STAT5A and STAT5B are largely insensitive to growth hormone and demonstrate loss or reversal of sex-specific patterns of liver gene expression. Thus, genetic manipulation of STAT5 factors provides a means of probing the mechanism of GH-dependent sex differences in thrombosis. We analyzed mice with global (STAT5g) and liver-specific (STAT5c) disruptions of the Stat5a and Stat5b genes, and determined their susceptibility to thrombosis in vivo and coagulation in vitro. In an in vivo model of pulmonary embolism, control female mice were relatively protected from thrombosis compared to control males, demonstrating percent survival of 61.3% and 50.0% and median survival times of 1200 and 972 seconds, respectively. In contrast, STAT5g males and females showed similar susceptibility to pulmonary embolism and had significantly reduced survival compared to matched controls, with percentages of 12.5% and 11.1% and median survival times of 468 and 275 seconds, respectively. As with the global loss of STAT5AB, liver-specific disruption of STAT5AB resulted in reduced survival compared to control mice. In vitro coagulation studies of whole blood triggered with dilute tissue factor (TF 1:1000) revealed significantly longer clot times in control females compared to control males. In contrast, mice with either global or liver-specific disruption of STAT5AB showed similar whole blood clot times between males and females, but had significantly shorter clot times as compared to controls. Similar results were obtained from coagulation studies in platelet poor plasma, indicating that platelets or white blood cells do not play a major role in this phenotype. No significant differences were found between control and STAT5AB-deficient mice in the expression or activity of a panel of pro- or anti-coagulant factors. APC sensitivity ratios were also similar between control and STAT5g males and females. An in vitro clotting model was employed to measure thrombin-antithrombin (TAT) complexes, fibrinogen, and D-dimer levels over time. Clotting was triggered with a 1:10,000 dilution of TF and analyzed at two minute intervals for ten minutes. Levels of TAT and fibrinogen did not differ between genotypes throughout the time course. In contrast, D-dimer was decreased in STAT5AB-deficient mice at each interval with a 52% reduction present at four minutes and a 46% reduction remaining at ten minutes. These studies have shown that global and liver-specific loss of STAT5AB results in reduced survival in a pulmonary embolism model, in vivo and shorter clotting times, in vitro. Furthermore, STAT5AB -deficiency eliminated the relative protection from thrombosis afforded to control female mice. This observed increase in thrombosis was not due to significant changes in coagulation factor activity, APC resistance, fibrinogen levels, or thrombin generation. However, a major decrease in D-dimer levels suggests a defect in the fibrinolytic system. While future studies are aimed at further defining the mechanistic regulation of the fibrinolytic system by growth hormone and downstream mediators, the current findings demonstrate a novel role for STAT5AB as a significant regulator of sexdependent thrombosis.
Clinical reports suggest significant sex differences in risk for thrombosis-related diseases such as myocardial infarction, stroke, and venous thromboembolism. However, little is known about ...mechanism for such differences. There is a well-described sexual dimorphism in liver protein synthesis that is growth hormone (GH) dependent. GH secretion from the pituitary is itself highly sexually dimorphic with males (M) secreting in a pulsatile (P) and females (F) a continuous (C) fashion. These patterns induce M- and F-specific signatures of liver gene expression. In the past, we and others have observed significant sex differences in murine thrombosis models. Given that most coagulation proteases and inhibitors are synthesized or modified in the liver, we aimed to test whether sex-specific GH secretion patterns contribute to the observed sex differences in thrombosis. We measured whole blood clotting times (WCT), thrombosis susceptibility in the thromboplastin-mediated pulmonary embolism (PE) model, and hemostasis in the tail bleeding time (BT) model in M and F control (WT) and GH-deficient “little” (LIT) mice. We observed that WT Fs had longer WCTs (mean time 61.38 vs. 56.72 sec) and were significantly protected in the PE model (median survival 232.5 vs 165 sec) as compared to M. There were no differences in the BT model across all experiments. Interestingly, F and M LIT animals both had significantly prolonged WCTs (67.56 and 67.30 sec, respectively) and were substantially protected in the PE model (median survival 900 and 1200 sec) as compared to WT. Next, LIT animals were injected twice daily with GH to simulate the P pattern of GH secretion (LIT+). This resulted in a significant shortening of the F and M WCTs back to WT M levels (53.16 and 50.97 sec). A group of F WT animals were also injected with M pattern GH (WT+). This too resulted in significant shortening of the F WCTs (54.10 sec). To explore for possible mechanisms underlying these differences, we measured activity of coagulation factors II, V, VII, VIII, IX, X, and XI. The average of all factor activity levels was significantly higher in WT M vs F (100 vs. 81.99%), significantly lower and in both M and F LIT (60.85 and 57.97%), and increased to WT M levels in M and F LIT+ animals (106.6 and 99%). To determine whether these changes were mediated by changes in liver gene expression, we measured a panel of 30 coagulation protease and inhibitor genes in liver and vascular tissue by Taqman®. Surprisingly, we found no significant differences in coagulation factor expression, but found that expression of TFPI was significantly increased in F vs M WT vasculature (9431 vs. 7678 gene copy number (GCN)). Expression was increased in M and F LIT animals (10350 and 11710 GCN) and fell to below WT levels in M and F LIT+ animals (4534 and 4194 GCN). These results indicate that sex differences in thrombosis in mice are at least in part mediated by sex differences in GH secretion with F mice relatively protected as compared to M. M and F GH-deficient LIT mice are similarly protected as compared to WT M. Repletion of GH in a P pattern reverts M and F LIT and F WT mice to WT M levels. Finally, P GH secretion may promote increased thrombosis through inhibition of TFPI in the vasculature. This represents a novel mechanism underlying these sex-differences in thrombosis mediated by sexually dimorphic GH secretion and its effect on regulation of TFPI in the vasculature.
Platelets are critical in haemostasis and in arterial thrombosis, which causes heart attacks and other events triggered by abnormal clotting. The coagulation protease thrombin is a potent activator ...of platelets ex vivo.
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