Cyclical mechanical stretch-induced apoptosis in myocytes from young rats but necrosis in myocytes from old rats

Mechanical load as stimulus for apoptosis and necrosis could be responsible for the loss of cardiomyocytes. Ventricular myocytes from young (3 mo) and old (14-24 mo) rats underwent cyclical mechanical stretch (CMS; 5% elongation, 1 Hz) for 24 h. Spontaneous apoptosis was in myocytes from young rats 0.33 +/- 0.12% and from old rats 1.05 +/- 0.35% [Tdt-mediated dUTP nick-end labeling (TUNEL) assay]; associated with a decrease of Bcl-2. CMS increased the apoptosis to 0.58 +/- 0.18% in myocytes from young rats. Western blot analysis showed that CMS reduced Bcl-2 and increased p53 (young rats). Bax was not changed by CMS. These were confirmed by cytochrome c release (31 +/- 13%) and by the enrichment of cytosolic nucleosomes (11 +/- 8%). CMS did not influence the apoptosis in myocytes from old rats (TUNEL assay, Bcl-2, Bax, or p53). CMS did not cause necrosis in myocytes from young rats. CMS increased the number of necrotic cells by showing the cell membrane rupture in myocytes from old rats (50 +/- 13% 5-hexadecanoylaminofluorescein-positive and 38 +/- 6% propidium iodide-positive cells) as well as by measuring the lactate dehydrogenase release. The results suggest that CMS-induced apoptosis in myocytes of young rats but necrosis in myocytes from old rats, which could be attributed to more stress sensitivity of cells from old rats.     

Selfish male‐determining element favors the transition from hermaphroditism to androdioecy

According to the current, widely accepted paradigm, the evolutionary transition from hermaphroditism toward separate sexes occurs in two successive steps: an initial, intermediate step in which unisexual individuals, male or female, sterility mutants coexist with hermaphrodites and a final step that definitively establishes dioecy. Two nonexclusive processes can drive this transition: inbreeding avoidance and reallocation of resources from one sexual function to the other. Here, we report results of controlled crosses between males and hermaphrodites in Phillyrea angustifolia, an androdioecious species with two mutually intercompatible, but intraincompatible groups of hermaphrodites. We observed different segregation patterns that can be explained by: (1) epistatic interactions between two unlinked diallelic loci, determining sex and mating compatibility, and (2) a mutation with pleiotropic effects: female sterility, full compatibility of males with both hermaphrodite incompatibility groups, and complete male‐biased sex‐ratio distortion in one of the two groups. Modeling shows that these mechanisms can explain the high frequency of males in populations of P. angustifolia and can promote the maintenance of androdioecy without requiring inbreeding depression or resource reallocation. We thus argue that segregation distortion establishes the right conditions for the evolution of cryptic dioecy and potentially initiates the evolution toward separate sexes.     

Mechanical deformation of ventricular myocytes modulates both TRPC6 and Kir2.3 channels

Cardiomyocytes respond to mechanical stretch with an increase [Ca2+]i. Here, we analyzed which ion channels could mediate this effect. Murine ventricular myocytes were attached to a glass coverslip and a cell-attached glass stylus sheared the upper cell part versus the attached cell bottom. At negative clamp potentials, stretch induced inward currents that increased with the extent of stretch and reversed within 2 min after relaxation from stretch. Stretch activated a nearly voltage-independent GsMTx-4-sensitive non-selective cation conductance Gns, antibodies against TRPC6 prevented Gns activation. In addition, stretch deactivated a Cs+-sensitive inwardly rectifying potassium conductance GK1, antibodies against Kir2.3 inhibited this effect. Immunolabeling localized TRPC6 and Kir2.3 in T-tubular membranes, and stretch-induced changes in membrane currents were absent in cells whose T-tubules had been removed. In absence of stretch, we could activate Gns and deactivate GK1 by 1-oleoyl-2-acetyl-sn-glycerol (OAG) and other amphipaths. We interpret that the function of TRPC6 and Kir2.3 channels is controlled by both tension and curvature of the surrounding lipid bilayer that are changed by incorporation of amphipaths. Stretch-activation of TRPC6 channels may increase Ca2+ influx directly and indirectly, by membrane depolarization (activation of voltage-gated Ca2+ channels) and by elevated [Na+]i (augmented Na+,Ca2+-exchange).     

Contemporary variations of immune responsiveness during range expansion of two invasive rodents in Senegal

Biological invasions provide unique opportunities for studying life history trait changes over contemporary time scales. As spatial spread may be related to changes in parasite communities, several hypotheses (such as the evolution of increased competitive ability (EICA) or EICA‐refined hypotheses) suggest immune changes in invasive species along invasion gradients. Although native hosts may be subject to similar changes in parasite selection pressures, their immune responses have been rarely investigated in invasion contexts. In this study, we evaluated immune variations for invasive house mice Mus musculus domesticus, invasive black rats Rattus rattus and native rodents Mastomys erythroleucus and Mastomys natalensis along well‐characterised invasion gradients in Senegal. We focused on antibody‐mediated (natural antibodies and complement) and inflammatory (haptoglobin) responses. One invasion route was considered for each invasive species, and environmental conditions were recorded. Natural‐antibody mediated responses increased between sites of long‐established invasion and recently invaded sites only in house mice. Both invasive species exhibited higher inflammatory responses at the invasion front than in sites of long‐established invasion. The immune responses of native species did not change with the presence of invasive species. These patterns of immune variations do not support the EICA and EICA refined hypotheses, and they rather suggest a higher risk of exposure to parasites on the invasion front. Altogether, these results provide a first basis to further assess the role of immune changes in invasion success.     

A time to fast,a time to feast: The crosstalk between metabolism and the circadian clock

The cyclic environmental conditions brought about by the 24 h rotation of the earth have allowed the evolution of endogenous circadian clocks that control the temporal alignment of behaviour and physiology, including the uptake and processing of nutrients. Both metabolic and circadian regulatory systems are built upon a complex feedback network connecting centres of the central nervous system and different peripheral tissues. Emerging evidence suggests that circadian clock function is closely linked to metabolic homeostasis and that rhythm disruption can contribute to the development of metabolic disease. At the same time, metabolic processes feed back into the circadian clock, affecting clock gene expression and timing of behaviour. In this review, we summarize the experimental evidence for this bimodal interaction, with a focus on the molecular mechanisms mediating this exchange, and outline the implications for clock-based and metabolic diseases.     

EF domains are sufficient for nongenomic mineralocorticoid receptor actions

The mineralocorticoid receptor (MR) is important for salt homeostasis and reno-cardiovascular pathophysiology. Signaling mechanisms include, besides classical genomic pathways, nongenomic pathways with putative pathophysiological relevance involving the mitogen-activated protein kinases ERK1/2. We determined the MR domains required for nongenomic signaling and their potential to elicit pathophysiological effects in cultured cells under defined conditions. The expression of full-length human MR or truncated MR consisting of the domains CDEF (MR CDEF), DEF (MR DEF), or EF (MR EF) renders cells responsive for the MR ligand aldosterone with respect to nongenomic ERK1/2 phosphorylation, whereas only full-length MR and MR CDEF conferred genomic responsiveness. ERK1/2 phosphorylation depends on the EGF receptor and cSRC kinase. MR EF expression is sufficient to evoke the aldosterone-induced increase of collagen III levels, similar to full-length MR expression. Our data suggest that nongenomic MR signaling is mediated by the EF domains and present the first proof of principle showing that nongenomic signaling can be sufficient for some pathophysiological effects. The minimum amino acid motif required for nongenomic MR signaling and its importance in various effects have yet to be determined.     

CREB expression in cardiac fibroblasts and CREM expression in ventricular myocytes

Activation of gene expression by the cAMP-dependent signaling pathway is regulated by members of the cAMP response element binding protein (CREB) family consisting of CREB, CREM, and ATF-1. It is decisively for the understanding of the heart function as to which type of heart cells expresses CREB and/or CREM. Ventricular myocytes and fibroblasts of young (3 months) and old (24 months) rat hearts were separately investigated to analyse CREB, CREM, and phospho-CREB. Western blot showed CREB expression exclusively in fibroblasts but CREM was predominantly detected in ventricular myocytes. CREB-positive nuclei in heart sections were only revealed in fibroblasts. CREB was activated by forskolin (10 microM), PMA (500 nM), and cyclical mechanical strain (1 Hz, 5% elongation) in fibroblasts. The number of CREB-positive myocytes in old rats was larger than in young rats. But CREB could not be activated by forskolin (10 microM) in all myocytes. Our results suggest that the expression of CREB depends on the cell type and the age of the animal. We discuss that modulation of gene expression as it occurs with a age could be affected by the change within the CREB family members.     

Cyclical mechanical stretch modulates expression of collagen I and collagen III by PKC and tyrosine kinase in cardiac fibroblasts

Mechanical load and chemical factors as stimuli for the different pattern of the extracellular matrix (ECM) could be responsible for cardiac dysfunction. Since fibroblasts can both synthesize and degrade ECM, ventricular fibroblasts from adult rat hearts underwent cyclical mechanical stretch (CMS; 0.33 Hz) by three different elongations (3%, 6%, 9%) and four different serum concentrations (0%, 0.5%, 5%, 10%) within 24 h. Expression of collagen I and III, as well as matrix metalloproteinase-2 (MMP-2), tissue inhibitor of MMP-2 (TIMP-2), and colligin were analyzed by RNase protection assay. In the absence of serum, 9% CMS increased the mRNA of collagen I by 1.70-fold and collagen III by 1.64-fold. This increase was prevented by the inhibition either of PKC or of tyrosine kinase but not of PKA. Inhibition of PKC or tyrosine kinase itself reduced the expression of collagen I and collagen III mRNA. The mRNA of MMP-2, TIMP-2, and colligin showed the same tendency by stretch. Combined with 10% serum, 6% CMS reduced the mRNA of collagen I (0.62-fold) and collagen III (0.79-fold). Inhibition of PKC or tyrosine kinase, but not of PKA, prevented the reduction of collagen I and collagen III mRNA in 10% serum. The results show that the response of fibroblasts to CMS depends on the serum concentration. At least two signaling pathways are involved in the stretch-induced ECM regulation. Myocardial fibrosis due to ECM remodeling contributes to the dysfunction of the failing heart, which might be attributed to changes in hemodynamic loading.     

Innate attractiveness and associative learnability of odors can be dissociated in larval Drosophila

We investigate olfactory associative learning in larval Drosophila. A reciprocal training design is used, such that one group of animals receives a reward in the presence of odor X but not in the presence of odor Y (Train: X+ // Y), whereas another group is trained reciprocally (Train: X // Y+). After training, differences in odor preference between these reciprocally trained groups in a choice test (Test: X - Y) reflect associative learning. The current study, after showing which odor pairs can be used for such learning experiments, 1) introduces a one-odor version of such reciprocal paradigm that allows estimating the learnability of single odors. Regarding this reciprocal one-odor paradigm, we show that 2) paired presentations of an odor with a reward increase odor preference above baseline, whereas unpaired presentations of odor and reward decrease odor preference below baseline; this suggests that odors can become predictive either of reward or of reward absence. Furthermore, we show that 3) innate attractiveness and associative learnability can be dissociated. These data deepen our understanding of odor-reward learning in larval Drosophila on the behavioral level, and thus foster its neurogenetic analysis.