Loss of Prohibitin Membrane Scaffolds Impairs Mitochondrial Architecture and Leads to Tau Hyperphosphorylation and Neurodegeneration

Fusion and fission of mitochondria maintain the functional integrity of mitochondria and protect against neurodegeneration, but how mitochondrial dysfunctions trigger neuronal loss remains ill-defined. Prohibitins form large ring complexes in the inner membrane that are composed of PHB1 and PHB2 subunits and are thought to function as membrane scaffolds. In Caenorhabditis elegans, prohibitin genes affect aging by moderating fat metabolism and energy production. Knockdown experiments in mammalian cells link the function of prohibitins to membrane fusion, as they were found to stabilize the dynamin-like GTPase OPA1 (optic atrophy 1), which mediates mitochondrial inner membrane fusion and cristae morphogenesis. Mutations in OPA1 are associated with dominant optic atrophy characterized by the progressive loss of retinal ganglion cells, highlighting the importance of OPA1 function in neurons. Here, we show that neuron-specific inactivation of Phb2 in the mouse forebrain causes extensive neurodegeneration associated with behavioral impairments and cognitive deficiencies. We observe early onset tau hyperphosphorylation and filament formation in the hippocampus, demonstrating a direct link between mitochondrial defects and tau pathology. Loss of PHB2 impairs the stability of OPA1, affects mitochondrial ultrastructure, and induces the perinuclear clustering of mitochondria in hippocampal neurons. A destabilization of the mitochondrial genome and respiratory deficiencies manifest in aged neurons only, while the appearance of mitochondrial morphology defects correlates with tau hyperphosphorylation in the absence of PHB2. These results establish an essential role of prohibitin complexes for neuronal survival in vivo and demonstrate that OPA1 stability, mitochondrial fusion, and the maintenance of the mitochondrial genome in neurons depend on these scaffolding proteins. Moreover, our findings establish prohibitin-deficient mice as a novel genetic model for tau pathologies caused by a dysfunction of mitochondria and raise the possibility that tau pathologies are associated with other neurodegenerative disorders caused by deficiencies in mitochondrial dynamics.     

Decline of FoxP3+ Regulatory CD4 T Cells in Peripheral Blood of Children Heavily Exposed to Malaria

FoxP3+ regulatory CD4 T cells (T_regs) help to maintain the delicate balance between pathogen-specific immunity and immune-mediated pathology. Prior studies suggest that T_regs are induced by P. falciparum both in vivo and in vitro; however, the factors influencing T_reg homeostasis during acute and chronic infections, and their role in malaria immunopathogenesis, remain unclear. We assessed the frequency and phenotype of T_regs in well-characterized cohorts of children residing in a region of high malaria endemicity in Uganda. We found that both the frequency and absolute numbers of FoxP3+ T_regs in peripheral blood declined markedly with increasing prior malaria incidence. Longitudinal measurements confirmed that this decline occurred only among highly malaria-exposed children. The decline of T_regs from peripheral blood was accompanied by reduced in vitro induction of T_regs by parasite antigen and decreased expression of TNFR2 on T_regs among children who had intense prior exposure to malaria. While T_reg frequencies were not associated with protection from malaria, there was a trend toward reduced risk of symptomatic malaria once infected with P. falciparum among children with lower T_reg frequencies. These data demonstrate that chronic malaria exposure results in altered T_reg homeostasis, which may impact the development of antimalarial immunity in naturally exposed populations.     

Piscivore Responses to Enhancement of the Channelized Kissimmee River,Florida, U.S.A.

Evaluation of the success of ecosystem restoration projects requires identification of appropriate ecological metrics. Comparison of reconstructed food webs (or subsets thereof) from restored and non‐restored habitats may be a valuable tool to evaluate restoration success because food webs help identify critical predator–prey relationships, keystone species, relative importance of direct and indirect trophic interactions, and other aspects of ecological function. We compared the diets of apex predatory fishes collected from enhanced and non‐enhanced portions of the channelized Kissimmee River, Florida, USA to determine whether food web structure responded to experimental hydrologic manipulations. Diets were reconstructed for black crappie (Pomoxis nigromaculatus), bowfin (Amia calva), chain pickerel (Esox niger), Florida gar (Lepisosteus platyrhincus), largemouth bass (Micropterus salmoides), and warmouth (Lepomis gulosus) collected from enhanced and non‐enhanced portions of the Kissimmee River. Prey eaten by apex predatory fishes in the enhanced portion of the Kissimmee River were quantitatively and qualitatively different from prey eaten in non‐enhanced portions of the river. Predators in the enhanced portion of the river had fewer empty stomachs, more prey items per individual, more prey types per individual, more fish prey per individual, greater overall richness of prey, and a multivariate suite of prey distinct from predators in non‐enhanced portions of the river. Results from hydrologic manipulations suggest that large‐scale restoration of hydrologic linkages between the main channel and floodplain habitats will positively affect food web structure and ecosystem function in the Kissimmee River.     

Substituted aminobenzimidazole pyrimidines as cyclin-dependent kinase inhibitors

A series of aminobenzimidazole-substituted pyrimidines were synthesized and evaluated for biochemical activity against CDK1. A high-speed parallel synthesis approach enabled the identification of a potent lead series having improved potency in the CDK1 assay (IC(50)<10nM). Cell cycle analysis showed that the compounds induced a G2/M block. Docking studies were carried out with a CDK1 homology model, and provide a rationale for the observed activities.     

Biodiversity among haptophyte algae

The division Haptophyta is represented only by about 300 extant species showing wide diversity in morphology, biochemistry and ecology. They have a world-wide distribution and are numerically important in phytoplankton populations in nearly all marine environments. Evidence from the geological record shows that they have been the major constituent of calcareous deposits since the Late Triassic and, as they have evolved quickly through time, their coccoliths have always shown wide morphological diversity. In today's oceans they occasionally produce extensive blooms, visible by satellite imagery, which have ecological impact. As a consequence of these blooms the haptophyte algae are now receiving greater attention, as their role in the global sulphur and carbon cycles may influence the world's climate, and their potential as nuisance bloom algae have implications for commercial fishing and the marine ecosystem. As it is likely that these organisms have always produced such blooms, these effects may have been in operation for the last 200 million years.     

Solving post-prandial reduction in performance by adaptive regurgitation in a freshwater fish

Foraging animals must balance benefits of food acquisition with costs induced by a post-prandial reduction in performance. Eating to satiation can lead to a reduction in locomotor and escape performance, which increases risk should a threat subsequently arises, but limiting feeding behaviour may be maladaptive if food intake is unnecessarily reduced in the prediction of threats that do not arise. The efficacy of the trade-off between continued and interrupted feeding therefore relies on information about the future risk, which is imperfect. Here, we find that black carp (Mylopharyngodon piceus) can balance this trade-off using an a posteriori strategy; by eating to satiation but regurgitating already ingested food when a threat arises. While degrees of satiation (DS) equal to or greater than 60% reduce elements of escape performance (turning angle, angular velocity, distance moved, linear velocity), at 40% DS or lower, performance in these tasks approaches levels comparable to that at 0% satiation. After experiencing a chasing event, we find that fish are able to regurgitate already ingested food, thereby changing the amount of food in their gastrointestinal tract to consistent levels that maintain high escape performance. Remarkably, regurgitation results in degrees of satiation between 40 and 60% DS, regardless of whether they had previously fed to 40, 60 or 100% DS. Using this response, fish are able to maximize food intake, but regurgitate extra food to maintain escape performance when they encounter a threat. This novel strategy may be effective for continual grazers and species with imperfect information about the level of threat in their environment.     

Global fold and backbone dynamics of the hepatitis C virus E2 glycoprotein transmembrane domain determined by NMR

E1 and E2 are two hepatitis C viral envelope glycoproteins that assemble into a heterodimer that is essential for membrane fusion and penetration into the target cell. Both extracellular and transmembrane (TM) glycoprotein domains contribute to this interaction, but study of TM–TM interactions has been limited because synthesis and structural characterization of these highly hydrophobic segments present significant challenges. In this NMR study, by successful expression and purification of the E2 transmembrane domain as a fusion construct we have determined the global fold and characterized backbone motions for this peptide incorporated in phospholipid micelles. Backbone resonance frequencies, relaxation rates and solvent exposure measurements concur in showing this domain to adopt a helical conformation, with two helical segments spanning residues 717–726 and 732–746 connected by an unstructured linker containing the charged residues D728 and R730 involved in E1 binding. Although this linker exhibits increased local motions on the ps timescale, the dominating contribution to its relaxation is the global tumbling motion with an estimated correlation time of 12.3 ns. The positioning of the helix–linker–helix architecture within the mixed micelle was established by paramagnetic NMR spectroscopy and phospholipid-peptide cross relaxation measurements. These indicate that while the helices traverse the hydrophobic interior of the micelle, the linker lies closer to the micelle perimeter to accommodate its charged residues. These results lay the groundwork for structure determination of the E1/E2 complex and a molecular understanding of glycoprotein heterodimerization.     

Eating Frequency is Associated With Energy Intake but Not Obesity in Midlife Women

Midlife women tend to gain weight with age, thus increasing risk of chronic disease. The purpose of this study was to examine associations between overweight/obesity and behavioral factors, including eating frequency, in a cross‐sectional national sample of midlife women (n = 1,099) (mean age = 49.7 years, and BMI = 27.7 kg/m²). Eating behaviors and food and nutrient intakes were based on a mailed 1‐day food record. BMI was calculated from self‐reported height and weight, and level of physical activity was assessed by self‐reported questionnaire. After exclusion of low‐energy reporters (32% of sample), eating frequency was not associated with overweight/obesity (P > 0.05) and was not different between BMI groups (normal, 5.21 ± 1.79; overweight, 5.16 ± 1.74; obese, 5.12 ± 1.68, P = 0.769). Adjusted logistic regression showed that eating frequency, snacking frequency, breakfast consumption, eating after 10 pm and consuming meals with children or other adults were not significantly associated with overweight/obesity. Total energy intake increased as eating frequency increased in all BMI groups, however, obese women had greater energy intake compared to normal weight women who consumed the same number of meals and snacks. Intake of fruit and vegetables, whole grains, dietary fiber, dairy, and added sugars also increased as eating frequency increased. While eating frequency was not associated with overweight/obesity, it was associated with energy intake. Thus, addressing total energy intake rather than eating frequency may be more appropriate to prevent weight gain among midlife women.     

Role of cytoskeletal elements in the recruitment of Cx43-GFP and Cx26-YFP into gap junctions

Cytoskeletal elements may be important in connexin transport to the cell surface, cell surface gap junction plaque formation and/or gap junction internalization. In this study, fluorescence recovery after photobleaching was used to examine the role of microfilaments and microtubules in the recruitment and coalescence of green fluorescent protein-tagged Cx43 (Cx43-GFP) or yellow fluorescent tagged-Cx26 (Cx26-YFP) into gap junctions in NRK cells. In untreated cells, both Cx26-YFP and Cx43-GFP were recruited into gap junctions within photobleached areas of cell-cell contact within 2 hrs. However, disruption of microfilaments with cytochalasin B inhibited the recruitment and assembly of both Cx26-YFP and Cx43-GFP into gap junctions within photobleached areas. Surprisingly, disruption of microtubules with nocodazole inhibited the recruitment of Cx43-GFP into gap junctions but had limited effect on the transport and clustering of Cx26-YFP into gap junctions within the photobleached regions of cell-cell contact. These results suggest that the recruitment of Cx43-GFP and Cx26-YFP to the cell surface or their lateral clustering into gap junctions plaques is dependent in part on the presence of intact actin microfilaments while Cx43-GFP was more dependent on intact microtubules than Cx26-YFP.