Socio-economic and Climate Factors Associated with Dengue Fever Spatial Heterogeneity: A Worked Example in New Caledonia

Background/Objectives

Understanding the factors underlying the spatio-temporal distribution of infectious diseases provides useful information regarding their prevention and control. Dengue fever spatio-temporal patterns result from complex interactions between the virus, the host, and the vector. These interactions can be influenced by environmental conditions. Our objectives were to analyse dengue fever spatial distribution over New Caledonia during epidemic years, to identify some of the main underlying factors, and to predict the spatial evolution of dengue fever under changing climatic conditions, at the 2100 horizon.

Methods

We used principal component analysis and support vector machines to analyse and model the influence of climate and socio-economic variables on the mean spatial distribution of 24,272 dengue cases reported from 1995 to 2012 in thirty-three communes of New Caledonia. We then modelled and estimated the future evolution of dengue incidence rates using a regional downscaling of future climate projections.

Results

The spatial distribution of dengue fever cases is highly heterogeneous. The variables most associated with this observed heterogeneity are the mean temperature, the mean number of people per premise, and the mean percentage of unemployed people, a variable highly correlated with people''s way of life. Rainfall does not seem to play an important role in the spatial distribution of dengue cases during epidemics. By the end of the 21st century, if temperature increases by approximately 3°C, mean incidence rates during epidemics could double.

Conclusion

In New Caledonia, a subtropical insular environment, both temperature and socio-economic conditions are influencing the spatial spread of dengue fever. Extension of this study to other countries worldwide should improve the knowledge about climate influence on dengue burden and about the complex interplay between different factors. This study presents a methodology that can be used as a step by step guide to model dengue spatial heterogeneity in other countries.     

Comparative aspects of in vitro proliferation of human and porcine lymphocytes exposed to mycotoxins

Mycotoxins are fungal secondary metabolites that elicit a wide spectrum of toxicological effects, including the alteration of normal immune function. In the present study we investigated the independent effect of four mycotoxins, aflatoxin B1 (AFB1), fumonisin B1 (FB1), deoxynivalenol (DON) and nivalenol (NIV), on lymphocyte proliferation using human and porcine lymphocytes. Human and porcine peripheral blood mononuclear cells and porcine splenocytes were cultured with increasing concentrations of mycotoxins for 72 hours and labelled in the last 24 hours with [methyl-3H]-thymidine. The results showed that increased concentrations of AFB1, DON and NIV affected the [methyl-3H]-thymidine cellular proliferation following mitogen stimulation in both species and cell types. Lower concentrations of mycotoxins enhanced cellular proliferation, which was more pronounced in human than in porcine cells, while higher concentrations caused a dose-dependent decrease. DON and NIV were the most potent mycotoxin in both species and both cell types. Based on the results of this in vitro study, high correlations were found between proliferation of human and porcine lymphocytes after mycotoxin exposure, especially for DON and NIV.     

The amyloid-beta precursor protein is phosphorylated via distinct pathways during differentiation, mitosis, stress, and degeneration

Phosphorylation of amyloid-beta precursor protein (APP) at Thr(668) is a normal process linked to neurite extension and anterograde transport of vesicular cargo. By contrast, increased phosphorylation of APP is a pathological trait of Alzheimer's disease. APP is overexpressed in Down's syndrome, a condition that occasionally leads to increased APP phosphorylation, in cultured cells. Whether phosphorylation of APP in normal versus high APP conditions occurs by similar or distinct signaling pathways is not known. Here, we addressed this problem using brainstem-derived neurons (CAD cells). CAD cells that ectopically overexpress APP frequently show features of degenerating neurons. We found that, in degenerating cells, APP is hyperphosphorylated and colocalizes with early endosomes. By contrast, in normal CAD cells, phosphorylated APP (pAPP) is excluded from endosomes, and localizes to the Golgi apparatus and to transport vesicles within the neurites. Whereas the neuritic APP is phosphorylated by c-Jun NH(2)-terminal kinase through a pathway that is modulated by glycogen synthase kinase 3beta, the endosomal pAPP in degenerated CAD cells results from activation of cyclin-dependent kinase 5. Additional signaling pathways, leading to APP phosphorylation, become active during stress and mitosis. We conclude that distinct pathways of APP phosphorylation operate in proliferating, differentiating, stressed, and degenerating neurons.     

Conformational studies of the manganese transport regulator (MntR) from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> using deuterium exchange mass spectrometry

The manganese transport regulator (MntR) of Bacillus subtilis is a metalloregulatory protein responsible for regulation of genes involved in manganese uptake by this organism. MntR belongs to the iron-responsive DtxR family, but is allosterically regulated by manganese and cadmium ions. Having previously characterized the metal binding affinities of this protein as well as the DNA-binding activation profiles for the relevant metal ions, we have focused the current study on investigating the structural changes of MntR in solution upon binding divalent transition metal ions. Deuterium exchange mass spectrometry was utilized to investigate the deuterium exchange dynamics between apo-MntR, Co²⁺-MntR, Cd²⁺-MntR, and Mn²⁺-MntR. Comparing the rates of deuteration of each metal-bound form of MntR reveals that the N-terminal DNA-binding motif is more mobile in solution than the C-terminal dimerization domain. Furthermore, significant protection from deuterium exchange is observed in the helices that contribute metal-chelating amino acids to form the metal binding site of MntR. In contrast, the bulk of the DNA-binding winged helix–turn–helix motif shows no difference in deuterium exchange upon metal binding. Mapping of the deuteration patterns onto the crystal structures of MntR yields insight into how metal binding affects the protein structure and complements earlier studies on the mechanism of MntR. Metal binding acts to rigidify MntR, thereby limiting the mobility of the protein and reducing the entropic cost of DNA binding. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Indomethacin inhibits thymic involution in mice with streptozotocin-induced diabetes

Diabetes is chronic disease that is accompanied by a rapid thymus involution. To investigate the factors responsible for thymic involution in a model of STZ-induced diabetes, mice were injected with STZ alone or in combination with the cyclooxygenase 2 inhibitor indomethacin (INDO). Thymus weight, glycemia and serum corticosterone were measured, and apoptosis in thymus and thymocyte cultures was analyzed by flow cytometry. Although earlier studies report that streptozotocin (STZ) is toxic to lymphoid tissues, in our experiments even massive doses of STZ did not negatively affect thymocyte cultures. Cultured thymocytes also seemed unaffected by high glucose concentrations, even after 24 h of exposure. Administration of INDO concomitantly with STZ reduced thymic involution but did not prevent the onset of hyperglycemia or reduce established hyperglycemia. When INDO was given before STZ, the same degree of thymic involution occurred; however, hyperglycemia was reduced, although normoglycemia was not restored. INDO also reduced serum corticosterone. Because thymocytes are known to be sensitive to glucocorticoids, this finding suggests that cyclooxygenase 2 inhibition may retard thymic involution by reducing serum glucocorticoids. In conclusion, our results show that STZ and hyperglycemia are not toxic to thymocytes and that cyclooxygenase 2-mediated mechanisms are involved in thymic involution during diabetes.     

Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/deuterium exchange

The structure of an AKAP docked to the dimerization/docking (D/D) domain of the type II (RIIalpha) isoform of protein kinase A (PKA) has been well characterized, but there currently is no detailed structural information of an AKAP docked to the type I (RIalpha) isoform. Dual-specific AKAP2 (D-AKAP2) binds in the nanomolar range to both isoforms and provided us with an opportunity to characterize the isoform-selective nature of AKAP binding using a common docked ligand. Hydrogen/deuterium (H/D) exchange combined with mass spectrometry (DXMS) was used to probe backbone structural changes of an alpha-helical A-kinase binding (AKB) motif from D-AKAP2 docked to both RIalpha and RIIalpha D/D domains. The region of protection upon complex formation and the magnitude of protection from H/D exchange were determined for both interacting partners in each complex. The backbone of the AKB ligand was more protected when bound to RIalpha compared to RIIalpha, suggesting an increased helical stabilization of the docked AKB ligand. This combined with a broader region of backbone protection induced by the AKAP on the docking surface of RIalpha indicated that there were more binding constraints for the AKB ligand when bound to RIalpha. This was in contrast to RIIalpha, which has a preformed, localized binding surface. These distinct modes of AKAP binding may contribute to the more discriminating nature of the RIalpha AKAP-docking surface. DXMS provides valuable structural information for understanding binding specificity in the absence of a high-resolution structure, and can readily be applied to other protein-ligand and protein-protein interactions.     

A conserved Glu-Arg salt bridge connects coevolved motifs that define the eukaryotic protein kinase fold

Eukaryotic protein kinases (EPKs) feature two coevolved structural segments, the Activation segment, which starts with the Asp-Phe-Gly (DFG) and ends with the Ala-Pro-Glu (APE) motifs, and the helical GHI subdomain that comprises αG-αH-αI helices. Eukaryotic-like kinases have a much shorter Activation segment and lack the GHI subdomain. They thus lack the conserved salt bridge interaction between the APE Glu and an Arg from the GHI subdomain, a hallmark signature of EPKs. Although the conservation of this salt bridge in EPKs is well known and its implication in diseases has been illustrated by polymorphism analysis, its function has not been carefully studied. In this work, we use murine cAMP-dependent protein kinase (protein kinase A) as the model enzyme (Glu208 and Arg280) to examine the role of these two residues. We showed that Ala replacement of either residue caused a 40- to 120-fold decrease in catalytic efficiency of the enzyme due to an increase in K(m)(ATP) and a decrease in k(cat). Crystal structures, as well as solution studies, also demonstrate that this ion pair contributes to the hydrophobic network and stability of the enzyme. We show that mutation of either Glu or Arg to Ala renders both mutant proteins less effective substrates for upstream kinase phosphoinositide-dependent kinase 1. We propose that the Glu208-Arg280 pair serves as a center hub of connectivity between these two structurally conserved elements in EPKs. Mutations of either residue disrupt communication not only between the two segments but also within the rest of the molecule, leading to altered catalytic activity and enzyme regulation.     

Calcium binding rigidifies the C2 domain and the intradomain interaction of GIVA phospholipase A2 as revealed by hydrogen/deuterium exchange mass spectrometry

The GIVA phospholipase A(2) (PLA(2)) contains two domains: a calcium-binding domain (C2) and a catalytic domain. These domains are linked via a flexible tether. GIVA PLA(2) activity is Ca(2+)-dependent in that calcium binding promotes protein docking to the phospholipid membrane. In addition, the catalytic domain has a lid that covers the active site, presumably regulating GIVA PLA(2) activity. We now present studies that explore the dynamics and conformational changes of this enzyme in solution utilizing peptide amide hydrogen/deuterium (H/D) exchange coupled with liquid chromatography-mass spectrometry (DXMS) to probe the solvent accessibility and backbone flexibility of the C2 domain, the catalytic domain, and the intact GIVA PLA(2). We also analyzed the changes in H/D exchange of the intact GIVA PLA(2) upon Ca(2+) binding. The DXMS results showed a fast H/D-exchanging lid and a slow exchanging central core. The C2 domain showed two distinct regions: a fast exchanging region facing away from the catalytic domain and a slow exchanging region present in the "cleft" region between the C2 and catalytic domains. The slow exchanging region of the C2 domain is in tight proximity to the catalytic domain. The effects of Ca(2+) binding on GIVA PLA(2) are localized in the C2 domain and suggest that binding of two distinct Ca(2+) ions causes tightening up of the regions that surround the anion hole at the tip of the C2 domain. This conformational change may be the initial step in GIVA PLA(2) activation.