PhospholipaseA2: a key regulator of inflammatory signalling and a connector to fibrosis development in atherosclerosis

Atherosclerosis is a progressive inflammatory disease that takes place in the intima of the arterial wall. It is characterized by activation of endothelial cells, proliferation of smooth muscle cells and macrophages, accumulation of lipoproteins, deposition of extracellular matrix components and enhanced lipolytic enzyme activity. Phospholipase A(2) (PLA(2)) has been postulated to play an important role in the inflammatory process of atherosclerosis, but its molecular mechanism is uncertain. The secretory PLA(2) is expressed at increased levels in an atherosclerotic plaque and may hydrolyze low-density lipoproteins (LDL). This action promotes the production of pro-inflammatory lipids such as lysophospholipids, unsaturated fatty acids and eicosanoids. The current review highlights recent findings on how LDL-derived lipid mediators, generated by sPLA_2 modification of LDL, regulate pro-inflammatory activation and intracellular signaling in macrophages. Moreover, the review discusses how PLA_2 enzymes regulate signalling that promotes collagen accumulation and fibrotic plaque development. PLA_2 could therefore function as a connector between inflammation and fibrosis, the latter being an endpoint of chronic inflammation.     

GCK-MODY diabetes associated with protein misfolding, cellular self-association and degradation

GCK-MODY, dominantly inherited mild fasting hyperglycemia, has been associated with >600 different mutations in the glucokinase (GK)-encoding gene (GCK). When expressed as recombinant pancreatic proteins, some mutations result in enzymes with normal/near-normal catalytic properties. The molecular mechanism(s) of GCK-MODY due to these mutations has remained elusive. Here, we aimed to explore the molecular mechanisms for two such catalytically 'normal' GCK mutations (S263P and G264S) in the F260-L270 loop of GK. When stably overexpressed in HEK293 cells and MIN6 β-cells, the S263P- and G264S-encoded mutations generated misfolded proteins with an increased rate of degradation (S263P>G264S) by the protein quality control machinery, and a propensity to self-associate (G264S>S263P) and form dimers (SDS resistant) and aggregates (partly Triton X-100 insoluble), as determined by pulse-chase experiments and subcellular fractionation. Thus, the GCK-MODY mutations S263P and G264S lead to protein misfolding causing destabilization, cellular dimerization/aggregation and enhanced rate of degradation. In silico predicted conformational changes of the F260-L270 loop structure are considered to mediate the dimerization of both mutant proteins by a domain swapping mechanism. Thus, similar properties may represent the molecular mechanisms for additional unexplained GCK-MODY mutations, and may also contribute to the disease mechanism in other previously characterized GCK-MODY inactivating mutations.     

Impact of oncogenic driver mutations on feedback between the PI3K and MEK pathways in cancer cells

Inhibition of the PI3K (phosphoinositide 3-kinase)/Akt/mTORC1 (mammalian target of rapamycin complex 1) and Ras/MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase]/ERK pathways for cancer therapy has been pursued for over a decade with limited success. Emerging data have indicated that only discrete subsets of cancer patients have favourable responses to these inhibitors. This is due to genetic mutations that confer drug insensitivity and compensatory mechanisms. Therefore understanding of the feedback mechanisms that occur with respect to specific genetic mutations may aid identification of novel biomarkers that predict patient response. In the present paper, we show that feedback between the PI3K/Akt/mTORC1 and Ras/MEK/ERK pathways is cell-line-specific and highly dependent on the activating mutation of K-Ras or overexpression c-Met. We found that cell lines exhibited differential signalling and apoptotic responses to PD184352, a specific MEK inhibitor, and PI103, a second-generation class I PI3K inhibitor. We reveal that feedback from the PI3K/Akt/mTORC1 to the Ras/MEK/ERK pathway is present in cancer cells harbouring either K-Ras activating mutations or amplification of c-Met but not the wild-type counterparts. Moreover, we demonstrate that inhibition of protein phosphatase activity by OA (okadaic acid) restored PI103-mediated feedback in wild-type cells. Together, our results demonstrate a novel mechanism for feedback between the PI3K/Akt/mTORC1 and the Ras/MEK/ERK pathways that only occurs in K-Ras mutant and c-Met amplified cells but not the isogenic wild-type cells through a mechanism that may involve inhibition of a specific endogenous phosphatase(s) activity. We conclude that monitoring K-Ras and c-Met status are important biomarkers for determining the efficacy of PI103 and other PI3K/Akt inhibitors in cancer therapy.     

Comparative metaproteomics and diversity analysis of human intestinal microbiota testifies for its temporal stability and expression of core functions

The human intestinal tract is colonized by microbial communities that show a subject-specific composition and a high-level temporal stability in healthy adults. To determine whether this is reflected at the functional level, we compared the faecal metaproteomes of healthy subjects over time using a novel high-throughput approach based on denaturing polyacrylamide gel electrophoresis and liquid chromatography-tandem mass spectrometry. The developed robust metaproteomics workflow and identification pipeline was used to study the composition and temporal stability of the intestinal metaproteome using faecal samples collected from 3 healthy subjects over a period of six to twelve months. The same samples were also subjected to DNA extraction and analysed for their microbial composition and diversity using the Human Intestinal Tract Chip, a validated phylogenetic microarray. Using metagenome and single genome sequence data out of the thousands of mass spectra generated per sample, approximately 1,000 peptides per sample were identified. Our results indicate that the faecal metaproteome is subject-specific and stable during a one-year period. A stable common core of approximately 1,000 proteins could be recognized in each of the subjects, indicating a common functional core that is mainly involved in carbohydrate transport and degradation. Additionally, a variety of surface proteins could be identified, including potential microbes-host interacting components such as flagellins and pili. Altogether, we observed a highly comparable subject-specific clustering of the metaproteomic and phylogenetic profiles, indicating that the distinct microbial activity is reflected by the individual composition.     

Do allopatric male Calopteryx virgo damselflies learn species recognition?

There is a growing amount of empirical evidence that premating reproductive isolation of two closely related species can be reinforced by natural selection arising from avoidance of maladaptive hybridization. However, as an alternative for this popular reinforcement theory, it has been suggested that learning to prefer conspecifics or to discriminate heterospecifics could cause a similar pattern of reinforced premating isolation, but this possibility is much less studied. Here, we report results of a field experiment in which we examined (i) whether allopatric Calopteryx virgo damselfly males that have not encountered heterospecific females of the congener C. splendens initially show discrimination, and (ii) whether C. virgo males learn to discriminate heterospecifics or learn to associate with conspecifics during repeated experimental presentation of females. Our experiment revealed that there was a statistically nonsignificant tendency for C. virgo males to show initial discrimination against heterospecific females but because we did not use sexually naïve individuals in our experiment, we were not able to separate the effect of innate or associative learning. More importantly, however, our study revealed that species discrimination might be further strengthened by learning, especially so that C. virgo males increase their association with conspecific females during repeated presentation trials. The role of learning to discriminate C. splendens females was less clear. We conclude that learning might play a role in species recognition also when individuals are not naïve but have already encountered potential conspecific mates.     

Variation in predator species abundance can cause variable selection pressure on warning signaling prey

Predation pressure is expected to drive visual warning signals to evolve toward conspicuousness. However, coloration of defended species varies tremendously and can at certain instances be considered as more camouflaged rather than conspicuous. Recent theoretical studies suggest that the variation in signal conspicuousness can be caused by variation (within or between species) in predators' willingness to attack defended prey or by the broadness of the predators' signal generalization. If some of the predator species are capable of coping with the secondary defenses of their prey, selection can favor reduced prey signal conspicuousness via reduced detectability or recognition. In this study, we combine data collected during three large-scale field experiments to assess whether variation in avian predator species (red kite, black kite, common buzzard, short-toed eagle, and booted eagle) affects the predation pressure on warningly and non-warningly colored artificial snakes. Predation pressure varied among locations and interestingly, if common buzzards were abundant, there were disadvantages to snakes possessing warning signaling. Our results indicate that predator community can have important consequences on the evolution of warning signals. Predators that ignore the warning signal and defense can be the key for the maintenance of variation in warning signal architecture and maintenance of inconspicuous signaling.     

Maternal Vitamin C Deficiency during Pregnancy Persistently Impairs Hippocampal Neurogenesis in Offspring of Guinea Pigs

While having the highest vitamin C (VitC) concentrations in the body, specific functions of VitC in the brain have only recently been acknowledged. We have shown that postnatal VitC deficiency in guinea pigs causes impairment of hippocampal memory function and leads to 30% less neurons. This study investigates how prenatal VitC deficiency affects postnatal hippocampal development and if any such effect can be reversed by postnatal VitC repletion. Eighty pregnant Dunkin Hartley guinea pig dams were randomized into weight stratified groups receiving High (900 mg) or Low (100 mg) VitC per kg diet. Newborn pups (n = 157) were randomized into a total of four postnatal feeding regimens: High/High (Control); High/Low (Depleted), Low/Low (Deficient); and Low/High (Repleted). Proliferation and migration of newborn cells in the dentate gyrus was assessed by BrdU labeling and hippocampal volumes were determined by stereology. Prenatal VitC deficiency resulted in a significant reduction in postnatal hippocampal volume (P<0.001) which was not reversed by postnatal repletion. There was no difference in postnatal cellular proliferation and survival rates in the hippocampus between dietary groups, however, migration of newborn cells into the granular layer of the hippocampus dentate gyrus was significantly reduced in prenatally deficient animals (P<0.01). We conclude that a prenatal VitC deficiency in guinea pigs leads to persistent impairment of postnatal hippocampal development which is not alleviated by postnatal repletion. Our findings place attention on a yet unrecognized consequence of marginal VitC deficiency during pregnancy.     

Catalytic activation of human glucokinase by substrate binding: residue contacts involved in the binding of D-glucose to the super-open form and conformational transitions

alpha-D-Glucose activates glucokinase (EC 2.7.1.1) on its binding to the active site by inducing a global hysteretic conformational change. Using intrinsic tryptophan fluorescence as a probe on the alpha-D-glucose induced conformational changes in the pancreatic isoform 1 of human glucokinase, key residues involved in the process were identified by site-directed mutagenesis. Single-site W-->F mutations enabled the assignment of the fluorescence enhancement (DeltaF/F(0)) mainly to W99 and W167 in flexible loop structures, but the biphasic time course of DeltaF/F(0) is variably influenced by all tryptophan residues. The human glucokinase-alpha-D-glucose association (K(d) = 4.8 +/- 0.1 mm at 25 degrees C) is driven by a favourable entropy change (DeltaS = 150 +/- 10 J.mol(-1).K(-1)). Although X-ray crystallographic studies have revealed the alpha-d-glucose binding residues in the closed state, the contact residues that make essential contributions to its binding to the super-open conformation remain unidentified. In the present study, we combined functional mutagenesis with structural dynamic analyses to identify residue contacts involved in the initial binding of alpha-d-glucose and conformational transitions. The mutations N204A, D205A or E256A/K in the L-domain resulted in enzyme forms that did not bind alpha-D-glucose at 200 mm and were essentially catalytically inactive. Our data support a molecular dynamic model in which a concerted binding of alpha-D-glucose to N204, N231 and E256 in the super-open conformation induces local torsional stresses at N204/D205 propagating towards a closed conformation, involving structural changes in the highly flexible interdomain connecting region II (R192-N204), helix 5 (V181-R191), helix 6 (D205-Y215) and the C-terminal helix 17 (R447-K460).     

The genetic liability to disability retirement: a 30-year follow-up study of 24,000 Finnish twins

Background

No previous studies on the effect of genetic factors on the liability to disability retirement have been carried out. The main aim of this study was to investigate the contribution of genetic factors on disability retirement due to the most common medical causes, including depressive disorders.

Methods

The study sample consisted of 24 043 participants (49.7% women) consisting of 11 186 complete same-sex twin pairs including 3519 monozygotic (MZ) and 7667dizygotic (DZ) pairs. Information on retirement events during 1.1.1975–31.12.2004, including disability pensions (DPs) with diagnoses, was obtained from the Finnish nationwide official pension registers. Correlations in liability for MZ and DZ twins and discrete time correlated frailty model were used to investigate the genetic liability to age at disability retirement.

Results

The 30 year cumulative incidence of disability retirement was 20%. Under the best fitting genetic models, the heritability estimate for DPs due to any medical cause was 0.36 (95% CI 0.32–0.40), due to musculoskeletal disorders 0.37 (0.30–0.43), cardiovascular diseases 0.48 (0.39–0.57), mental disorders 0.42 (0.35–0.49) and all other reasons 0.24 (0.17–0.31). The effect of genetic factors decreased with increasing age of retirement. For DP due to depressive disorders, 28% of the variance was explained by environmental factors shared by family members (95% CI 21–36) and 58% of the variance by the age interval specific environmental factors (95% CI 44–71).

Conclusions

A moderate genetic contribution to the variation of disability retirement due to any medical cause was found. The genetic effects appeared to be stronger at younger ages of disability retirement suggesting the increasing influence of environmental factors not shared with family members with increasing age. Familial aggregation in DPs due to depressive disorders was best explained by the common environmental factors and genetic factors were not needed to account for the pattern of familial aggregation.