Calorie restriction delays cardiac senescence and improves cardiac function in obese diabetic rats

Molecular and Cellular Biochemistry - The aims of this study were to investigate the impact of caloric restriction (CR) on cardiac senescence in an animal model of diabetes and examine the signal...     

Single base substitution in OsCDC48 is responsible for premature senescence and death phenotype in rice

A premature senescence and death 128 (psd128) mutant was isolated from an ethyl methane sulfonate‐induced rice IR64 mutant bank. The premature senescence phenotype appeared at the six‐leaf stage and the plant died at the early heading stage. psd128 exhibited impaired chloroplast development with significantly reduced photosynthetic ability, chlorophyll and carotenoid contents, root vigor, soluble protein content and increased malonaldehyde content. Furthermore, the expression of senescence‐related genes was significantly altered in psd128. The mutant trait was controlled by a single recessive nuclear gene. Using map‐based strategy, the mutation Oryza sativa cell division cycle 48 (OsCDC48) was isolated and predicted to encode a putative AAA‐type ATPase with 809 amino‐acid residuals. A single base substitution at position C2347T in psd128 resulted in a premature stop codon. Functional complementation could rescue the mutant phenotype. In addition, RNA interference resulted in the premature senescence and death phenotype. OsCDC48 was expressed constitutively in the root, stem, leaf and panicle. Subcellular analysis indicated that OsCDC48:YFP fusion proteins were located both in the cytoplasm and nucleus. OsCDC48 was highly conserved with more than 90% identity in the protein levels among plant species. Our results indicated that the impaired function of OsCDC48 was responsible for the premature senescence and death phenotype.     

Mechanism of enhanced cardiac function in mice with hypertrophy induced by overexpressed Akt

Transgenic mice with cardiac-specific overexpression of active Akt (TG) not only exhibit hypertrophy but also show enhanced left ventricular (LV) function. In 3-4-month-old TG, heart/body weight was increased by 60% and LV ejection fraction was elevated (84 +/- 2%, p < 0.01) compared with nontransgenic littermates (wild type (WT)) (73 +/- 1%). An increase in isolated ventricular myocyte contractile function (% contraction) in TG compared with WT (6.1 +/- 0.2 versus 3.5 +/- 0.2%, p < 0.01) was associated with increased Fura-2 Ca2+ transients (396 +/- 50 versus 250 +/- 24 nmol/liter, p < 0.05). The rate of relaxation (+dL/dt) was also enhanced in TG (214 +/- 15 versus 98 +/- 18 microm/s, p < 0.01). L-type Ca2+ current (ICa) density was increased in TG compared with WT (-9.0 +/- 0.3 versus 7.2 +/- 0.3 pA/pF, p < 0.01). Sarcoplasmic reticulum Ca2+ ATPase 2a (SERCA2a) protein levels were increased (p < 0.05) by 6.6-fold in TG, which could be recapitulated in vitro by adenovirus-mediated overexpression of Akt in cultured adult ventricular myocytes. Conversely, inhibiting SERCA with either ryanodine or thapsigargin affected myocyte contraction and relaxation and Ca2+ channel kinetics more in TG than in WT. Thus, myocytes from mice with overexpressed Akt demonstrated enhanced contractility and relaxation, Fura-2 Ca2+ transients, and Ca2+ channel currents. Furthermore, increased protein expression of SERCA2a plays an important role in mediating enhanced LV function by Akt. Up-regulation of SERCA2a expression and enhanced LV myocyte contraction and relaxation in Akt-induced hypertrophy is opposite to the down-regulation of SERCA2a and reduced contractile function observed in many other forms of LV hypertrophy.     

Identification of 30 protein species involved in replicative senescence and stress-induced premature senescence

Exposure of human proliferative cells to subcytotoxic stress triggers stress-induced premature senescence (SIPS) which is characterized by many biomarkers of replicative senescence. Proteomic comparison of replicative senescence and stress-induced premature senescence indicates that, at the level of protein expression, stress-induced premature senescence and replicative senescence are different phenotypes sharing however similarities. In this study, we identified 30 proteins showing changes of expression level specific or common to replicative senescence and/or stress-induced premature senescence. These changes affect different cell functions, including energy metabolism, defense systems, maintenance of the redox potential, cell morphology and transduction pathways.     

Development and application of human virtual excitable tissues and organs: from premature birth to sudden cardiac death

The electrical activity of cardiac and uterine tissues has been reconstructed by detailed computer models in the form of virtual tissues. Virtual tissues are biophysically and anatomically detailed, and represent quantitatively predictive models of the physiological and pathophysiological behaviours of tissue within an isolated organ. The cell excitation properties are quantitatively reproduced by equations that describe the kinetics of a few dozen proteins. These equations are derived from experimental measurements of membrane potentials, ionic currents, fluxes, and concentrations. Some of the measurements were taken from human cells and human ion channel proteins expressed in non-human cells, but they were mostly taken from cells of other animal species. Data on tissue geometry and architecture are obtained from the diffusion tensor magnetic resonance imaging of ex vivo or post mortem tissue, and are used to compute the spread of current in the tissue. Cardiac virtual tissues are well established and reproduce normal and pathological patterns of cardiac excitation within the atria or ventricles of the human heart. They have been applied to increase the understanding of normal cardiac electrophysiology, to evaluate the candidate mechanisms for re-entrant arrhythmias that lead to sudden cardiac death, and to predict the tissue level effects of mutant or pharmacologically-modified ion channels. The human full-term virtual uterus is still in development. This virtual tissue reproduces the in vitro behaviour of uterine tissue biopsies, and provides possible mechanisms for premature labour.     

Genetic regulation of embryo death and senescence

The survival of the preimplantation mammalian embryo depends not only on providing the proper conditions for normal development but also on acquiring the mechanisms by which embryos cope with adversity. The ability of the early conceptus to resist stress as development proceeds may be regulated by diverse factors such as the attainment of a cell death program and protective mechanisms involving stress-induced genes and/or cell cycle modulators. This paper reviews the recent research on the genetic regulation of early embryo cell death and senescence focussing on the bovine species where possible. The different modes of cell death will be explained, clarifying the confusing cell death terminology, by advocating the recommendations set forth by the Cell Death Nomenclature Committee to extend to the embryology research field. Specific pro-death and anti-death genes will be discussed with reference to their expression patterns during early mammalian embryogenesis.     

Modulated dispersion of activation and repolarization by premature beats in patients with cardiomyopathy at risk of sudden death

Premature beats can trigger ventricular arrhythmias in heart disease, but the mechanisms are not well defined. We studied the effect of premature beats on activation and repolarization dispersion in seven patients with cardiomyopathy (57 ± 10 yr, left ventricular ejection fraction 31 ± 7%). Activation time (AT), activation-recovery interval (ARI), and total repolarization time (TRT) were measured from 26 unipolar electrograms during right ventricle (RV) endocardial (early) to left ventricle epicardial (late) activation in response to RV apical extrastimulation (S1S2). Early TRT dispersion increased significantly with shorter S1S2 (1.0 ± 0.2 to 2.3 ± 0.4 ms/mm, P < 0.0001), with minimal change in late TRT dispersion (0.8 ± 0.1 to 1.0 ± 0.3 ms, P = 0.02). This was associated with an increase in early AT dispersion (1.0 ± 0.1 to 1.5 ± 0.2 ms/mm, P = 0.05) but no change in late AT dispersion (0.6 ± 0.1 to 0.7 ± 0.2 ms/mm, P = 0.4). Early and late ARI dispersion did not change with shorter S1S2. AT restitution slopes were similar between early and late sites, as was slope heterogeneity. ARI restitution slope was greater in early vs. late sites (1.3 ± 0.6 vs. 0.8 ± 0.6, P = 0.03), but slope heterogeneity was similar. With shorter S1S2, AT-ARI slopes became less negative (flattened) at both early (-0.4 ± 0.1 to +0.04 ± 0.2) and late (-1.5 ± 0.2 to +0.3 ± 0.2) sites, implying less activation-repolarization coupling. There was no difference in AT-ARI slopes between early and late sites at short S1S2. In conclusion, high-risk patients with cardiomyopathy have greater TRT dispersion at tightly coupled S1S2 due to greater AT dispersion and activation-repolarization uncoupling. Modulated dispersion is more pronounced at early vs. late activated sites, which may predispose to reentrant ventricular arrhythmias.     

Down-regulation of OsSAG12-1 results in enhanced senescence and pathogen-induced cell death in transgenic rice plants

Senescence is a highly regulated process accompanied by changes in gene expression. While the mRNA levels of most genes decline, the mRNA levels of specific genes (senescence associated genes, SAGs) increase during senescence. Arabidopsis SAG12 (AtSAG12) gene codes for papain-like cysteine protease. The promoter of AtSAG12 is SA-responsive and reported to be useful to delay senescence by expressing cytokinin biosynthesis gene isopentenyltransferase specifically during senescence in several plants including Arabidopsis, lettuce and rice. The physiological role of AtSAG12 is not known; the homozygous atsag12 mutant neither fails to develop senescence-associated vacuoles nor shows any morphological phenotype. Through BLAST search using AtSAG12 amino acid sequences as query, we identified a few putative homologues from rice genome (OsSAGs; Oryza sativa SAGs). OsSAG12-1 is the closest homologue of AtSAG12 with 64% similar amino acid composition. Expression of OsSAG12-1 is induced during senescence and pathogen-induced cell death. To evaluate the possible role of OsSAG12-1 we generated RNAi transgenic lines in Japonica rice cultivar TP309. The transgenic lines developed early senescence at varying levels and showed enhanced cell death when inoculated with bacterial pathogen Xanthomonas oryzae pv.oryzae. Our results suggest that OsSAG12-1 is a negative regulator of cell death in rice.     

G-MDSCs promote aging-related cardiac fibrosis by activating myofibroblasts and preventing senescence

Aging is one of the most prominent risk factors for heart failure. Myeloid-derived suppressor cells (MDSCs) accumulate in aged tissue and have been confirmed to be associated with various aging-related diseases. However, the role of MDSCs in the aging heart remains unknown. Through RNA-seq and biochemical approaches, we found that granulocytic MDSCs (G-MDSCs) accumulated significantly in the aging heart compared with monocytic MDSCs (M-MDSCs). Therefore, we explored the effects of G-MDSCs on the aging heart. We found that the adoptive transfer of G-MDSCs of aging mice to young hearts resulted in cardiac diastolic dysfunction by inducing cardiac fibrosis, similar to that in aging hearts. S100A8/A9 derived from G-MDSCs induced inflammatory phenotypes and increased the osteopontin (OPN) level in fibroblasts. The upregulation of fibroblast growth factor 2 (FGF2) expression in fibroblasts mediated by G-MDSCs promoted antisenescence and antiapoptotic phenotypes of fibroblasts. SOX9 is the downstream gene of FGF2 and is required for FGF2-mediated and G-MDSC-mediated profibrotic effects. Interestingly, both FGF2 levels and SOX9 levels were upregulated in fibroblasts but not in G-MDSCs and were independent of S100A8/9. Therefore, a novel FGF2-SOX9 signaling axis that regulates fibroblast self-renewal and antiapoptotic phenotypes was identified. Our study revealed the mechanism by which G-MDSCs promote cardiac fibrosis via the secretion of S100A8/A9 and the regulation of FGF2-SOX9 signaling in fibroblasts during aging.Subject terms: Senescence, Cardiovascular diseases     

Estradiol improves cardiac and hepatic function after trauma-hemorrhage: role of enhanced heat shock protein expression

Although studies indicate that 17beta-estradiol administration after trauma-hemorrhage (T-H) improves cardiac and hepatic functions, the underlying mechanisms remain unclear. Because the induction of heat shock proteins (HSPs) can protect cardiac and hepatic functions, we hypothesized that these proteins contribute to the salutary effects of estradiol after T-H. To test this hypothesis, male Sprague-Dawley rats ( approximately 300 g) underwent laparotomy and hemorrhagic shock (35-40 mmHg for approximately 90 min) followed by resuscitation with four times the shed blood volume in the form of Ringer lactate. 17beta-estradiol (1 mg/kg body wt) was administered at the end of the resuscitation. Five hours after T-H and resuscitation there was a significant decrease in cardiac output, positive and negative maximal rate of left ventricular pressure. Liver function as determined by bile production and indocyanine green clearance was also compromised after T-H and resuscitation. This was accompanied by an increase in plasma alanine aminotransferase (ALT) levels and liver perfusate lactic dehydrogenase levels. Furthermore, circulating levels of TNF-alpha, IL-6, and IL-10 were also increased. In addition to decreased cardiac and hepatic function, there was an increase in cardiac HSP32 expression and a reduction in HSP60 expression after T-H. In the liver, HSP32 and HSP70 were increased after T-H. There was no change in heart HSP70 and liver HSP60 after T-H and resuscitation. Estradiol administration at the end of T-H and resuscitation increased heart/liver HSPs expression, ameliorated the impairment of heart/liver functions, and significantly prevented the increase in plasma levels of ALT, TNF-alpha, and IL-6. The ability of estradiol to induce HSPs expression in the heart and the liver suggests that HSPs, in part, mediate the salutary effects of 17beta-estradiol on organ functions after T-H.     

The evolution of premature reproductive senescence and menopause in human females

Reproductive senescence in human females takes place long before other body functions senesce. This fact presents an evolutionary dilemma since continued reproduction should generally be favored by natural selection. Two commonly proposed hypotheses to account for human menopause are (a) a recent increase in the human lifespan and (b) a switch to investment in close kin rather than direct reproduction. No support is found for the proposition that human lifespans have only recently increased. Data from Ache hunter-gatherers are used to test the kin selection hypothesis. Ache data do not support the proposition that females can gain greater fitness benefits in old age by helping kin rather than continuing to reproduce. Nevertheless, one crucial parameter in the model, when adjusted to the highest value within the measured 95% confidence interval, would lead to the evolution of reproductive senescence at about 53 years of age. Further investigation is necessary to determine whether the kin selection hypothesis of menopause can account for its current maintenance in most populations.     

Targeted deletion of Puma attenuates cardiomyocyte death and improves cardiac function during ischemia-reperfusion

The p53-upregulated modulator of apoptosis (Puma), a BH3-only member of the Bcl-2 protein family, is required for p53-dependent and -independent forms of apoptosis and has been implicated in the pathomechanism of several diseases, including cancer, acquired immunodeficiency syndrome, and ischemic brain disease. The role of Puma in cardiomyocyte death, however, has not been analyzed. On the basis of the ability of Puma to integrate diverse cell death stimuli, we hypothesized that Puma might be critical for cardiomyocyte death upon ischemia-reperfusion (I/R) of the heart. Here we show that hypoxia-reoxygenation of isolated cardiomyocytes led to an increase in Puma mRNA and protein levels. Moreover, if Puma was delivered by an adenoviral construct, cardiomyocytes died by apoptosis. Under ATP-depleted conditions, however, Puma overexpression primarily induced necrosis, suggesting that Puma is involved in the development of both types of cell death. Consistent with these findings, targeted deletion of Puma in a mouse model attenuated both apoptosis and necrosis. When the Langendorff ex vivo I/R model was used, infarcts were approximately 50% smaller in Puma(-/-) than in wild-type mice. As a result, after I/R, cardiac function was significantly better preserved in Puma(-/-) mice than in their wild-type littermates. Our study thus establishes Puma as an essential mediator of cardiomyocyte death upon I/R injury and offers a novel therapeutic target to limit cell loss in ischemic heart disease.     

Processes of protoplast senescence and death in flax fibers: An ultrastructural analysis

Plant fibers represent specialized cells that perform a mechanical function. Their development includes the following phases, typical for the most plant cells: determination, extension growth, specialization, senescence, and death. Ultrastructural analysis of these cells has been carried out at the late phases of their development (senescence and dying off) using flax phloem fibers, a classical object for the analysis of sclerenchyma fiber formation. The results of the performed analysis show that flax fiber protoplasts remain viable until the end of a vegetation season. The ultrastructural analysis of flax phloem fibers has not revealed any typical apoptosis features. Gradual degradation of the cytoplasm starts during the active thickening of a secondary cell wall and occurs via the intensification of autolytic processes, causing a partial loss of cell content. The rupture of tonoplast is the final stage. The obtained data allow us to suppose that the protoplast dying off occurs during process of the senescence, and its program is similar to the cell death program realized in the xylem fibers of woody plants.     

Early postnatal cardiac changes and premature death in transgenic mice overexpressing a mutant form of serum response factor

Serum response factor (SRF) is a key regulator of a number of extracellular signal-regulated genes important for cell growth and differentiation. A form of the SRF gene with a double mutation (dmSRF) was generated. This mutation reduced the binding activity of SRF protein to the serum response element and reduced the capability of SRF to activate the atrial natriuretic factor promoter that contains the serum response element. Cardiac-specific overexpression of dmSRF attenuated the total SRF binding activity and resulted in remarkable morphologic changes in the heart of the transgenic mice. These mice had dilated atrial and ventricular chambers, and their ventricular wall thicknesses were only 1/2 to 1/3 the thickness of that of nontransgenic mice. Also these mice had smaller cardiac myocytes and had less myofibrils in their myocytes relative to nontransgenic mice. Altered gene expression and slight interstitial fibrosis were observed in the myocardium of the transgenic mice. All the transgenic mice died within the first 12 days after birth, because of the early onset of severe, dilated cardiomyopathy. These results indicate that dmSRF overexpression in the heart apparently alters cardiac gene expression and blocks normal postnatal cardiac growth and development.     

Nek6 suppresses the premature senescence of human cancer cells induced by camptothecin and doxorubicin treatment

Cellular senescence plays an important role in tumor suppression. The mitotic kinase Nek6 has recently been shown to be overexpressed in various cancers and has been implicated in tumorigenesis. Previously, we reported that the down-regulation of Nek6 expression was required for p53-induced senescence. In this study, we examined the effect of Nek6 overexpression on the premature senescence of cancer cells induced by the anticancer drugs camptothecin (CPT) and doxorubicin (DOX). We found that CPT- and DOX-induced morphology changes and increases in senescence-associated β-galactosidase staining were significantly inhibited in EJ human bladder cancer cells and H1299 human lung cancer cells overexpressing HA-Nek6. DOX-induced G2/M cell cycle arrest and the reduction in cyclin B and cdc2 levels after DOX treatment were significantly reduced by Nek6 overexpression. In addition, an increase in the intracellular levels of ROS in response to DOX was also inhibited in cells overexpressing Nek6. These results suggest that the increased expression of Nek6 renders cancer cells resistant to premature senescence, and targeting Nek6 could be an efficient strategy for cancer treatment.