Amplitude reduction and phase shifts of melatonin, cortisol and other circadian rhythms after a gradual advance of sleep and light exposure in humans

Background

The phase and amplitude of rhythms in physiology and behavior are generated by circadian oscillators and entrained to the 24-h day by exposure to the light-dark cycle and feedback from the sleep-wake cycle. The extent to which the phase and amplitude of multiple rhythms are similarly affected during altered timing of light exposure and the sleep-wake cycle has not been fully characterized.

Methodology/Principal Findings

We assessed the phase and amplitude of the rhythms of melatonin, core body temperature, cortisol, alertness, performance and sleep after a perturbation of entrainment by a gradual advance of the sleep-wake schedule (10 h in 5 days) and associated light-dark cycle in 14 healthy men. The light-dark cycle consisted either of moderate intensity ‘room’ light (∼90–150 lux) or moderate light supplemented with bright light (∼10,000 lux) for 5 to 8 hours following sleep. After the advance of the sleep-wake schedule in moderate light, no significant advance of the melatonin rhythm was observed whereas, after bright light supplementation the phase advance was 8.1 h (SEM 0.7 h). Individual differences in phase shifts correlated across variables. The amplitude of the melatonin rhythm assessed under constant conditions was reduced after moderate light by 54% (17–94%) and after bright light by 52% (range 12–84%), as compared to the amplitude at baseline in the presence of a sleep-wake cycle. Individual differences in amplitude reduction of the melatonin rhythm correlated with the amplitude of body temperature, cortisol and alertness.

Conclusions/Significance

Alterations in the timing of the sleep-wake cycle and associated bright or moderate light exposure can lead to changes in phase and reduction of circadian amplitude which are consistent across multiple variables but differ between individuals. These data have implications for our understanding of circadian organization and the negative health outcomes associated with shift-work, jet-lag and exposure to artificial light.     

Multiple novel nesprin-1 and nesprin-2 variants act as versatile tissue-specific intracellular scaffolds

Background

Nesprins (Nuclear envelope spectrin-repeat proteins) are a novel family of giant spectrin-repeat containing proteins. The nesprin-1 and nesprin-2 genes consist of 146 and 116 exons which encode proteins of ∼1mDa and ∼800 kDa is size respectively when all the exons are utilised in translation. However emerging data suggests that the nesprins have multiple alternative start and termination sites throughout their genes allowing the generation of smaller isoforms.

Results

In this study we set out to identify novel alternatively transcribed nesprin variants by screening the EST database and by using RACE analysis to identify cDNA ends. These two methods provided potential hits for alternative start and termination sites that were validated by PCR and DNA sequencing. We show that these alternative sites are not only expressed in a tissue specific manner but by combining different sites together it is possible to create a wide array of nesprin variants. By cloning and expressing small novel nesprin variants into human fibroblasts and U2OS cells we show localization to actin stress-fibres, focal adhesions, microtubules, the nucleolus, nuclear matrix and the nuclear envelope (NE). Furthermore we show that the sub-cellular localization of individual nesprin variants can vary depending on the cell type, suggesting any single nesprin variant may have different functions in different cell types.

Conclusions

These studies suggest nesprins act as highly versatile tissue specific intracellular protein scaffolds and identify potential novel functions for nesprins beyond cytoplasmic-nuclear coupling. These alternate functions may also account for the diverse range of disease phenotypes observed when these genes are mutated.     

In search of lost opportunities: Marcel Proyce and James Joust discuss doctors, diseases, life and death (a hypothetical conversation between Marcel Proust and James Joyce)

Two of the most influential thinkers of the last century, Marcel Proust (1871-1922) and James Joyce (1882-1941), met in 1922 but had little to say to each other. Had circumstances been different, what might they have said? They had much in common, including an interest in doctors and diseases, but from different perspectives. Although the meeting was a lost opportunity to explore the insights of two great analysts of the human condition, their lives and works provide a record rich in detail and timeless in relevance. From this, we construct what might have been overheard during a conversation between Marcel Proyce and James Joust almost a century ago.     

Mechanisms of alpha-defensin bactericidal action: comparative membrane disruption by Cryptdin-4 and its disulfide-null analogue

Mammalian alpha-defensins all have a conserved triple-stranded beta-sheet structure that is constrained by an invariant tridisulfide array, and the peptides exert bactericidal effects by permeabilizing the target cell envelope. Curiously, the disordered, disulfide-null variant of mouse alpha-defensin cryptdin-4 (Crp4), termed (6C/A)-Crp4, has bactericidal activity equal to or greater than that of the native peptide, providing a rationale for comparing the mechanisms by which the peptides interact with and disrupt phospholipid vesicles of defined composition. For both live Escherichia coli ML35 cells and model membranes, disordered (6C/A)-Crp4 induced leakage in a manner similar to that of Crp4 but had less overall membrane permeabilizing activity. Crp4 induction of the leakage of the fluorophore from electronegative liposomes was strongly dependent on vesicle lipid charge and composition, and the incorporation of cardiolipin into liposomes of low electronegative charge to mimic bacterial membrane composition conferred sensitivity to Crp4- and (6C/A)-Crp4-mediated vesicle lysis. Membrane perturbation studies using biomimetic lipid/polydiacetylene vesicles showed that Crp4 inserts more pronouncedly into membranes containing a high fraction of electronegative lipids or cardiolipin than (6C/A)-Crp4 does, correlating directly with measurements of induced leakage. Fluorescence resonance energy transfer experiments provided evidence that Crp4 translocates across highly charged or cardiolipin-containing membranes, in a process coupled with membrane permeabilization, but (6C/A)-Crp4 did not translocate across lipid bilayers and consistently displayed membrane surface association. Thus, despite the greater in vitro bactericidal activity of (6C/A)-Crp4, native, beta-sheet-containing Crp4 induces membrane permeabilization more effectively than disulfide-null Crp4 by translocating and forming transient membrane defects. (6C/A)-Crp4, on the other hand, appears to induce greater membrane disintegration.     

Why don't zebras have machine guns? Adaptation, selection, and constraints in evolutionary theory

In an influential paper, Stephen Jay Gould and Richard Lewontin (1979) contrasted selection-driven adaptation with phylogenetic, architectural, and developmental constraints as distinct causes of phenotypic evolution. In subsequent publications Gould (e.g., 1997a,b, 2002) has elaborated this distinction into one between a narrow "Darwinian Fundamentalist" emphasis on "external functionalist" processes, and a more inclusive "pluralist" emphasis on "internal structuralist" principles. Although theoretical integration of functionalist and structuralist explanations is the ultimate aim, natural selection and internal constraints are treated as distinct causes of evolutionary change. This distinction is now routinely taken for granted in the literature in evolutionary biology. I argue that this distinction is problematic because the effects attributed to non-selective constraints are more parsimoniously explained as the ordinary effects of selection itself. Although it may still be a useful shorthand to speak of phylogenetic, architectural, and developmental constraints on phenotypic evolution, it is important to understand that such "constraints" do not constitute an alternative set of causes of evolutionary change. The result of this analysis is a clearer understanding of the relationship between adaptation, selection and constraints as explanatory concepts in evolutionary theory.     

Commensal-induced regulatory T cells mediate protection against pathogen-stimulated NF-kappaB activation

Host defence against infection requires a range of innate and adaptive immune responses that may lead to tissue damage. Such immune-mediated pathologies can be controlled with appropriate T regulatory (Treg) activity. The aim of the present study was to determine the influence of gut microbiota composition on Treg cellular activity and NF-kappaB activation associated with infection. Mice consumed the commensal microbe Bifidobacterium infantis 35624 followed by infection with Salmonella typhimurium or injection with LPS. In vivo NF-kappaB activation was quantified using biophotonic imaging. CD4+CD25+Foxp3+ T cell phenotypes and cytokine levels were assessed using flow cytometry while CD4+ T cells were isolated using magnetic beads for adoptive transfer to na?ve animals. In vivo imaging revealed profound inhibition of infection and LPS induced NF-kappaB activity that preceded a reduction in S. typhimurium numbers and murine sickness behaviour scores in B. infantis-fed mice. In addition, pro-inflammatory cytokine secretion, T cell proliferation, and dendritic cell co-stimulatory molecule expression were significantly reduced. In contrast, CD4+CD25+Foxp3+ T cell numbers were significantly increased in the mucosa and spleen of mice fed B. infantis. Adoptive transfer of CD4+CD25+ T cells transferred the NF-kappaB inhibitory activity. Consumption of a single commensal micro-organism drives the generation and function of Treg cells which control excessive NF-kappaB activation in vivo. These cellular interactions provide the basis for a more complete understanding of the commensal-host-pathogen trilogue that contribute to host homeostatic mechanisms underpinning protection against aberrant activation of the innate immune system in response to a translocating pathogen or systemic LPS.     

Why is celiac disease so common in Ireland?

Celiac disease (gluten sensitive enteropathy) is a condition affecting the small bowel, characterized by permanent intolerance to dietary gluten, and giving rise to varying degrees of malabsorption and diarrhea. With the advent of sensitive screening tests, the condition is being increasingly diagnosed. Celiac disease is more common in the Irish and in those of Irish descent. Simoons (1978, 1981) hypothesized that the present-day prevalence of celiac disease across Europe is related to the interaction between genetic gradients, largely determined by the advance of agriculture, and historical patterns of cereal ingestion. This essay examines Simoons' hypothesis as it relates to Ireland, reviews the ethnic and genetic mix of those living on the island of Ireland and aspects of Irish dietary history, and considers how these factors may have combined to result in a high frequency of celiac disease.