Evolutionary dynamics of finite populations in games with polymorphic fitness equilibria

The hawk-dove (HD) game, as defined by Maynard Smith [1982. Evolution and the Theory of Games. Cambridge University Press, Cambridge], allows for a polymorphic fitness equilibrium (PFE) to exist between its two pure strategies; this polymorphism is the attractor of the standard replicator dynamics [Taylor, P.D., Jonker, L., 1978. Evolutionarily stable strategies and game dynamics. Math. Biosci. 40, 145-156; Hofbauer, J., Sigmund, K., 1998. Evolutionary Games and Population Dynamics. Cambridge University Press, Cambridge] operating on an infinite population of pure-strategists. Here, we consider stochastic replicator dynamics, operating on a finite population of pure-strategists playing games similar to HD; in particular, we examine the transient behavior of the system, before it enters an absorbing state due to sampling error. Though stochastic replication prevents the population from fixing onto the PFE, selection always favors the under-represented strategy. Thus, we may naively expect that the mean population state (of the pre-absorption transient) will correspond to the PFE. The empirical results of Fogel et al. [1997. On the instability of evolutionary stable states. BioSystems 44, 135-152] show that the mean population state, in fact, deviates from the PFE with statistical significance. We provide theoretical results that explain their observations. We show that such deviation away from the PFE occurs when the selection pressures that surround the fitness-equilibrium point are asymmetric. Further, we analyze a Markov model to prove that a finite population will generate a distribution over population states that equilibrates selection-pressure asymmetry; the mean of this distribution is generally not the fitness-equilibrium state.     

The effects of inspiratory intrathoracic pressure production on the cardiovascular response to submaximal exercise in health and chronic heart failure

We sought to determine whether the normal inspiratory intrathoracic pressures (P(ITP)) produced during exercise contribute to the blunted cardiac output and locomotor limb blood flow responses observed in chronic heart failure (CHF). Five chronically instrumented dogs exercised on a treadmill at 2.5 mile/h at 5% grade while healthy or after the induction of tachycardia-induced CHF. We observed several key differences in the cardiovascular responses to changes in the inspiratory P(ITP) excursion between health and CHF; namely, 1) removing approximately 70% of the normally produced inspiratory P(ITP) excursion during exercise (with 15 cmH(2)O inspiratory positive pressure ventilation) significantly reduced stroke volume (SV) in healthy animals by 5 +/- 2% (P < 0.05) but significantly increased SV and cardiac output (Q(TOT)) in animals with CHF by 5 +/- 1% (P < 0.05); 2) doubling the magnitude of the inspiratory P(ITP) excursion had no effect on SV or Q(TOT) in healthy animals but significantly reduced steady-state Q(TOT) and SV in animals with CHF by -4 +/- 3% and -10 +/- 3%, respectively; 3) removing the majority of the normally produced inspiratory P(ITP) excursion had no effect on blood flow distribution in healthy animals but increased hindlimb blood flow (9 +/- 3%, P < 0.05) out of proportion to the increases in Q(TOT); and 4) the only similarity between healthy and CHF animals was that increasing the inspiratory P(ITP) excursion significantly reduced steady-state locomotor limb blood flow by 5 +/- 2% and 6 +/- 3%, respectively (P < 0.05 for both). We conclude that 1) the normally produced inspiratory P(ITP) excursions are required for a maximal SV response to submaximal exercise in healthy animals but detrimental to the SV and Q(TOT) responses to submaximal exercise in CHF, 2) the respiratory muscle ergoreflex tonically restrains locomotor limb blood flow during submaximal exercise in CHF, and 3) excessive inspiratory muscle work further compromises cardiac function and blood flow distribution in both health and CHF.     

Variability in expression of common fragile sites: in search of a new criterion

Summary Fragile sites are nonrandom, heritable sites on chromosomes that can be induced to form gaps, breaks, and rearrangements under specific conditions. There is currently no established criterion to define a common fragile site. We applied seven published criteria to our data from three groups of subjects: (1) three pairs of like-sexed twins, (2) four unaffected von HippelLindau (VHL) family members, and (3) six patients affected with VHL disease. Substantial differences were present in the numbers of sites considered positive by these criteria. While some of this variability can be attributed to technical factors, our data illustrate the problems in comparing results from different studies to assess the significance of fragile sites. A recently published criterion is based upon the Poisson distribution. We found this criterion to be flawed in its presentation, and furthermore, the Poisson distribution did not provide an adequate approximation to our data. We propose here an alternative approach based upon the negative binomial distribution.     

Apoptosis and other immune biomarkers predict influenza vaccine responsiveness

Despite the importance of the immune system in many diseases, there are currently no objective benchmarks of immunological health. In an effort to identifying such markers, we used influenza vaccination in 30 young (20–30 years) and 59 older subjects (60 to >89 years) as models for strong and weak immune responses, respectively, and assayed their serological responses to influenza strains as well as a wide variety of other parameters, including gene expression, antibodies to hemagglutinin peptides, serum cytokines, cell subset phenotypes and in vitro cytokine stimulation. Using machine learning, we identified nine variables that predict the antibody response with 84% accuracy. Two of these variables are involved in apoptosis, which positively associated with the response to vaccination and was confirmed to be a contributor to vaccine responsiveness in mice. The identification of these biomarkers provides new insights into what immune features may be most important for immune health.     

V3 loop truncations in HIV-1 envelope impart resistance to coreceptor inhibitors and enhanced sensitivity to neutralizing antibodies

The V1/V2 region and the V3 loop of the human immunodeficiency virus type I (HIV-1) envelope (Env) protein are targets for neutralizing antibodies and also play an important functional role, with the V3 loop largely determining whether a virus uses CCR5 (R5), CXCR4 (X4), or either coreceptor (R5X4) to infect cells. While the sequence of V3 is variable, its length is highly conserved. Structural studies indicate that V3 length may be important for interactions with the extracellular loops of the coreceptor. Consistent with this view, genetic truncation of the V3 loop is typically associated with loss of Env function. We removed approximately one-half of the V3 loop from three different HIV-1 strains, and found that only the Env protein from the R5X4 strain R3A retained some fusion activity. Loss of V1/V2 (DeltaV1/V2) was well tolerated by this virus. Passaging of virus with the truncated V3 loop resulted in the derivation of a virus strain that replicated with wild-type kinetics. This virus, termed TA1, retained the V3 loop truncation and acquired several adaptive changes in gp120 and gp41. TA1 could use CCR5 but not CXCR4 to infect cells, and was extremely sensitive to neutralization by HIV-1 positive human sera, and by antibodies to the CD4 binding site and to CD4-induced epitopes in the bridging sheet region of gp120. In addition, TA1 was completely resistant to CCR5 inhibitors, and was more dependent upon the N-terminal domain of CCR5, a region of the receptor that is thought to contact the bridging sheet of gp120 and the base of the V3 loop, and whose conformation may not be greatly affected by CCR5 inhibitors. These studies suggest that the V3 loop protects HIV from neutralization by antibodies prevalent in infected humans, that CCR5 inhibitors likely act by disrupting interactions between the V3 loop and the coreceptor, and that altered use of CCR5 by HIV-1 associated with increased sensitivity to changes in the N-terminal domain can be linked to high levels of resistance to these antiviral compounds.     

Endothelial cell telomere dysfunction induces senescence and results in vascular and metabolic impairments

In advanced age, increases in oxidative stress and inflammation impair endothelial function, which contributes to the development of cardiovascular disease (CVD). One plausible source of this oxidative stress and inflammation is an increase in the abundance of senescent endothelial cells. Cellular senescence is a cell cycle arrest that occurs in response to various damaging stimuli. In the present study, we tested the hypothesis that advanced age results in endothelial cell telomere dysfunction that induces senescence. In both human and mouse endothelial cells, advanced age resulted in an increased abundance of dysfunctional telomeres, characterized by activation of DNA damage signaling at telomeric DNA. To test whether this results in senescence, we selectively reduced the telomere shelterin protein telomere repeat binding factor 2 (Trf2) from endothelial cells of young mice. Trf2 reduction increased endothelial cell telomere dysfunction and resulted in cellular senescence. Furthermore, induction of endothelial cell telomere dysfunction increased inflammatory signaling and oxidative stress, resulting in impairments in endothelial function. Finally, we demonstrate that endothelial cell telomere dysfunction-induced senescence impairs glucose tolerance. This likely occurs through increases in inflammatory signaling in the liver and adipose tissue, as well as reductions in microvascular density and vasodilation to metabolic stimuli. Cumulatively, the findings of the present study identify age-related telomere dysfunction as a mechanism that leads to endothelial cell senescence. Furthermore, these data provide compelling evidence that senescent endothelial cells contribute to age-related increases in oxidative stress and inflammation that impair arterial and metabolic function.     

Salvinorin A reduces mechanical allodynia and spinal neuronal hyperexcitability induced by peripheral formalin injection

ABSTRACT: BACKGROUND: Salvinorin A (SA), the main active component of Salvia Divinorum, is a non-nitrogenous kappa opioid receptor (KOR) agonist. It has been shown to reduce acute pain and to exert potent antinflammatory effects. This study assesses the effects and the mode of action of SA on formalin-induced persistent pain in mice. Specifically, the SA effects on long-term behavioural dysfuctions and changes in neuronal activity occurring at spinal level, after single peripheral formalin injection, have been investigated. Moreover, the involvement of microglial and glial cells in formalin-induced chronic pain condition and in SA-mediated effects has been evaluated. RESULTS: Formalin induced a significant decrease of mechanical withdrawal threshold at the injected and contralateral paw as well as an increase in the duration and frequency, and a rapid decrease in the onset of evoked activity of the nociceptive neurons 7 days after formalin injection. SA daily treatment significantly reduced mechanical allodynia in KOR and cannabinoid receptor 1 (CB1R) sensitive manner. SA treatment also normalized the spinal evoked activity. SA significantly reduced the formalin-mediated microglia and astrocytes activation and modulated pro and anti-inflammatory mediators in the spinal cord. CONCLUSION: SA is effective in reducing formalin-induced mechanical allodynia and spinal neuronal hyperactivity. Our findings suggest that SA reduces glial activation and contributes in the establishment of dysfunctions associated with chronic pain with mechanisms involving KOR and CB1R. SA may provide a new lead compound for developing anti-allodynic agents via KOR and CB1R activation.     

C2-alpha-lactylthiamin diphosphate is an intermediate on the pathway of thiamin diphosphate-dependent pyruvate decarboxylation. Evidence on enzymes and models

Thiamin diphosphate (ThDP)-dependent decarboxylations are usually assumed to proceed by a series of covalent intermediates, the first one being the C2-trimethylthiazolium adduct with pyruvate, C2-alpha-lactylthiamin diphosphate (LThDP). Herein is addressed whether such an intermediate is kinetically competent with the enzymatic turnover numbers. In model studies it is shown that the first-order rate constant for decarboxylation can indeed exceed 50 s(-1) in tetrahydrofuran as solvent, approximately 10(3) times faster than achieved in previous model systems. When racemic LThDP was exposed to the E91D yeast pyruvate decarboxylase variant, or to the E1 subunit of the pyruvate dehydrogenase complex (PDHc-E1) from Escherichia coli, it was partitioned between reversion to pyruvate and decarboxylation. Under steady-state conditions, the rate of these reactions is severely limited by the release of ThDP from the enzyme. Under pre-steady-state conditions, the rate constant for decarboxylation on exposure of LThDP to the E1 subunit of the pyruvate dehydrogenase complex was 0.4 s(-1), still more than a 100-fold slower than the turnover number. Because these experiments include binding, decarboxylation, and oxidation (for detection purposes), this is a lower limit on the rate constant for decarboxylation. The reasons for this slow reaction most likely include a slow conformational change of the free LThDP to the V conformation enforced by the enzyme. Between the results from model studies and those from the two enzymes, it is proposed that LThDP is indeed on the decarboxylation pathway of the two enzymes studied, and once LThDP is bound the protein needs to provide little assistance other than a low polarity environment.