Insulin Resistance Induced by Hyperinsulinemia Coincides with a Persistent Alteration at the Insulin Receptor Tyrosine Kinase Domain

Insulin resistance, the diminished response of target tissues to insulin, is associated with the metabolic syndrome and a predisposition towards diabetes in a growing proportion of the worldwide population. Under insulin resistant states, the cellular response of the insulin signaling pathway is diminished and the body typically responds by increasing serum insulin concentrations to maintain insulin signaling. Some evidence indicates that the increased insulin concentration may itself further dampen insulin response. If so, insulin resistance would worsen as the level of circulating insulin increases during compensation, which could contribute to the transition of insulin resistance to more severe disease. Here, we investigated the consequences of excess insulin exposure to insulin receptor (IR) activity. Cells chronically exposed to insulin show a diminished the level of IR tyrosine and serine autophosphorylation below that observed after short-term insulin exposure. The diminished IR response did not originate with IR internalization since IR amounts at the cell membrane were similar after short- and long-term insulin incubation. Förster resonance energy transfer between fluorophores attached to the IR tyrosine kinase (TK) domain showed that a change in the TK domain occurred upon prolonged, but not short-term, insulin exposure. Even though the altered ‘insulin refractory’ IR TK FRET and IR autophosphorylation levels returned to baseline (non-stimulated) levels after wash-out of the original insulin stimulus, subsequent short-term exposure to insulin caused immediate re-establishment of the insulin-refractory levels. This suggests that some cell-based ‘memory’ of chronic hyperinsulinemic exposure acts directly at the IR. An improved understanding of that memory may help define interventions to reset the IR to full insulin responsiveness and impede the progression of insulin resistance to more severe disease states.     

How much gene flow is needed to avoid inbreeding depression in wild tiger populations?

The number and size of tiger populations continue to decline owing to habitat loss, habitat fragmentation and poaching of tigers and their prey. As a result, tiger populations have become small and highly structured. Current populations have been isolated since the early 1970s or for approximately seven generations. The objective of this study is to explore how inbreeding may be affecting the persistence of remaining tiger populations and how dispersal, either natural or artificial, may reduce the potentially detrimental effect of inbreeding depression. We developed a tiger simulation model and used published levels of genetic load in mammals to simulate inbreeding depression. Following a 50 year period of population isolation, we introduced one to four dispersing male tigers per generation to explore how gene flow from nearby populations may reduce the negative impact of inbreeding depression. For the smallest populations, even four dispersing male tigers per generation did not increase population viability, and the likelihood of extinction is more than 90% within 30 years. Unless habitat connectivity is restored or animals are artificially introduced in the next 70 years, medium size wild populations are also likely to go extinct, with only four to five of the largest wild tiger populations likely to remain extant in this same period without intervention. To reduce the risk of local extinction, habitat connectivity must be pursued concurrently with efforts to increase population size (e.g. enhance habitat quality, increase habitat availability). It is critical that infrastructure development, dam construction and other similar projects are planned appropriately so that they do not erode the extent or quality of habitat for these populations so that they can truly serve as future source populations.     

Comparative pathobiology of Heterobasidion annosum during challenge on Pinus sylvestris and Arabidopsis roots: an analysis of defensin gene expression in two pathosystems

Heterobasidion annosum is widely known as a major root and butt rot pathogen of conifer trees, but little information is available on its interaction with the roots of herbaceous angiosperm plants. We investigated the infection biology of H. annosum during challenge with the angiosperm model Arabidopsis and monitored the host response after exposure to different hormone elicitors, chemicals (chitin, glucan and chitosan) and fungal species that represent diverse basidiomycete life strategies [e.g., pathogen (H. annosum), saprotroph (Stereum sanguinolentum) and mutualist (Lactarius rufus)]. The results revealed that the tree pathogen (H. annosum) and the saprotroph (S. sanguinolentum) could infect the Col-8 (Columbia) ecotype of Arabidopsis in laboratory inoculation experiments. Germinated H. annosum spores had appressorium-like penetration structures attached to the surface of the Arabidopsis roots. Subsequent invasive fungal growth led to the disintegration of the vascular region of the root tissues. Progression of root rot symptoms in Arabidopsis was similar to the infection development that was previously documented in Scots pine seedlings. Scots pine PsDef1 and Arabidopsis DEFLs (AT5G44973.1) and PDF1.2 were induced at the initial stage of the infection. However, differences in the expression patterns of the defensin gene homologs from the two plant groups were observed under various conditions, suggesting functional differences in their regulation. The potential use of the H. annosum–Arabidopsis pathosystem as a model for studying forest tree diseases is discussed.     

A PTCH1 Homolog Transcriptionally Activated by p53 Suppresses Hedgehog Signaling

The p53-mediated responses to DNA damage and the Hedgehog (Hh) signaling pathway are each recurrently dysregulated in many types of human cancer. Here we describe PTCH53, a p53 target gene that is homologous to the tumor suppressor gene PTCH1 and can function as a repressor of Hh pathway activation. PTCH53 (previously designated PTCHD4) was highly responsive to p53 in vitro and was among a small number of genes that were consistently expressed at reduced levels in diverse TP53 mutant cell lines and human tumors. Increased expression of PTCH53 inhibited canonical Hh signaling by the G protein-coupled receptor SMO. PTCH53 thus delineates a novel, inducible pathway by which p53 can repress tumorigenic Hh signals.     

Identification of Mixed Lineage Leukemia 1(MLL1) Protein as a Coactivator of Heat Shock Factor 1(HSF1) Protein in Response to Heat Shock Protein 90 (HSP90) Inhibition

Heat shock protein 90 (HSP90) inhibition inhibits cancer cell proliferation through depleting client oncoproteins and shutting down multiple oncogenic pathways. Therefore, it is an attractive strategy for targeting human cancers. Several HSP90 inhibitors, including AUY922 and STA9090, show promising effects in clinical trials. However, the efficacy of HSP90 inhibitors may be limited by heat shock factor 1 (HSF1)-mediated feedback mechanisms. Here, we identify, through an siRNA screen, that the histone H3 lysine 4 methyltransferase MLL1 functions as a coactivator of HSF1 in response to HSP90 inhibition. MLL1 is recruited to the promoters of HSF1 target genes and regulates their expression in response to HSP90 inhibition. In addition, a striking combination effect is observed when MLL1 depletion is combined with HSP90 inhibition in various human cancer cell lines and tumor models. Thus, targeting MLL1 may block a HSF1-mediated feedback mechanism induced by HSP90 inhibition and provide a new avenue to enhance HSP90 inhibitor activity in human cancers.     

A Sero-epidemiological Study of Arboviral Fevers in Djibouti,Horn of Africa

Arboviral infections have repeatedly been reported in the republic of Djibouti, consistent with the fact that essential vectors for arboviral diseases are endemic in the region. However, there is a limited recent information regarding arbovirus circulation, and the associated risk predictors to human exposure are largely unknown. We performed, from November 2010 to February 2011 in the Djibouti city general population, a cross-sectional ELISA and sero-neutralisation-based sero-epidemiological analysis nested in a household cohort, which investigated the arboviral infection prevalence and risk factors, stratified by their vectors of transmission. Antibodies to dengue virus (21.8%) were the most frequent. Determinants of infection identified by multivariate analysis pointed to sociological and environmental exposure to the bite of Aedes mosquitoes. The population was broadly naïve against Chikungunya (2.6%) with risk factors mostly shared with dengue. The detection of limited virus circulation was followed by a significant Chikungunya outbreak a few months after our study. Antibodies to West Nile virus were infrequent (0.6%), but the distribution of cases faithfully followed previous mapping of infected Culex mosquitoes. The seroprevalence of Rift valley fever virus was 2.2%, and non-arboviral transmission was suggested. Finally, the study indicated the circulation of Toscana-related viruses (3.7%), and a limited number of cases suggested infection by tick-borne encephalitis or Alkhumra related viruses, which deserve further investigations to identify the viruses and vectors implicated. Overall, most of the arboviral cases'' predictors were statistically best described by the individuals'' housing space and neighborhood environmental characteristics, which correlated with the ecological actors of their respective transmission vectors'' survival in the local niche. This study has demonstrated autochthonous arboviral circulations in the republic of Djibouti, and provides an epidemiological inventory, with useful findings for risk mapping and future prevention and control programs.     

The Limited Utility of Multiunit Data in Differentiating Neuronal Population Activity

To date, single neuron recordings remain the gold standard for monitoring the activity of neuronal populations. Since obtaining single neuron recordings is not always possible, high frequency or ‘multiunit activity’ (MUA) is often used as a surrogate. Although MUA recordings allow one to monitor the activity of a large number of neurons, they do not allow identification of specific neuronal subtypes, the knowledge of which is often critical for understanding electrophysiological processes. Here, we explored whether prior knowledge of the single unit waveform of specific neuron types is sufficient to permit the use of MUA to monitor and distinguish differential activity of individual neuron types. We used an experimental and modeling approach to determine if components of the MUA can monitor medium spiny neurons (MSNs) and fast-spiking interneurons (FSIs) in the mouse dorsal striatum. We demonstrate that when well-isolated spikes are recorded, the MUA at frequencies greater than 100Hz is correlated with single unit spiking, highly dependent on the waveform of each neuron type, and accurately reflects the timing and spectral signature of each neuron. However, in the absence of well-isolated spikes (the norm in most MUA recordings), the MUA did not typically contain sufficient information to permit accurate prediction of the respective population activity of MSNs and FSIs. Thus, even under ideal conditions for the MUA to reliably predict the moment-to-moment activity of specific local neuronal ensembles, knowledge of the spike waveform of the underlying neuronal populations is necessary, but not sufficient.     

Cholesterol-lowering effect of non-viscous soluble dietary fiber Nutriose6 in moderately hypercholesterolemic hamsters

NUTRIOSE6 is a new wheat starch-based low-digestible carbohydrate. This study investigated the effect of this soluble non-viscous fiber on cholesterol metabolism. Hamsters fed with 0.25% cholesterol-enriched diet (CHO) were given graded amounts of NUTRIOSE6, i.e., 0% (cellulose, CHO), 3% (N3), 6% (N6) or 9% (N9) (w:w). As compared to CHO diet, 9% NUTRIOSE6 significantly lowered plasma and LDL cholesterol by 14.5 and 23.8%, respectively. The LDL-cholesterol lowering effect was also significant with the 6% dose (-21.4%). NUTRIOSE6 diets prevented hepatic cholesterol accumulation (-10 to -20%) and significantly decreased bile cholesterol (-47 to -68%) and phospholipids (-30 to -45%) concentrations. The 9% NUTRIOSE6 diet significantly decreased the rate of dietary cholesterol absorption (-25%) and markedly stimulated faecal neutral sterol (+81%) and bile salts (+220%) excretion. No significant change in cholesterol 7-alpha-hydroxylase or LDL-receptor activities was observed whereas 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity was reduced by 29%. Reduced cholesterol and bile salt absorptions and lowered cholesterol synthesis are likely mechanisms underlying the cholesterol lowering effect of NUTRIOSE6. Results suggest the use of NUTRIOSE6 as a new dietary cholesterol-lowering agent that should be tested in humans as treatment and evenly prevention of mild hypercholesterolemia.