Nitric oxide retards xanthine oxidase-mediated superoxide anion generation in Phalaenopsis flower: an implication of NO in the senescence and oxidative stress regulation

Senescence is a developmentally regulated and highly ordered sequence of events. Senescence leads to abscission of plant organs and eventually leads to death of a plant or part of it. Present study revealed that Phalaenopsis flower undergo senescence due to over activation of O₂ ^·−generating xanthine oxidase (XO), which consequently increases the concentrations of O₂ ^·− leading to enhanced oxidative damage and disturbed cellular redox environment as indicated by increased lipid peroxidation and DHA/AsA + DHA ratio, respectively. While activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and non-specific peroxidase (POD) were enhanced in sepals and petals of old flower, activities of catalase (CAT) and glutathione reductase (GR) were decreased. Exogenous application of nitric oxide (NO) retarded H₂O₂-induced senescence of Phalaenopsis flower by downregulating activity of XO and concentrations of O₂ ^·−, H₂O₂ and malondialdehyde (MDA, an index of lipid peroxidation). Exogenous application of NO also downregulated SOD activity and upregulated antioxidant enzymes involved in the detoxification of H₂O₂ (CAT and APX), and in the regulation of redox couples viz, monodehydroascorbate reductase (MDHAR) and GR, together with the modulation in non-protein thiol status and DHA/AsA + DHA ratio.     

Suitability of human mesenchymal stem cells for gene therapy depends on the expansion medium

Great hope is set in the use of mesenchymal stem cells for gene therapy and regenerative medicine. Since the frequency of this subpopulation of stem cells in bone marrow is low, mesenchymal stem cells are expanded ex vivo and manipulated prior to experimental or clinical use. Different methods for isolation and expansion are available, but the particular effect on the stem cell character is unclear. While the isolation of mesenchymal stem cells by density centrifugation followed by selection of the plastic adherent fraction is frequently used, the composition of expansion media differs. Thus, in the present study we cultured mesenchymal stem cells isolated from five healthy young volunteers in three widely used expansion media and performed a detailed analysis of the effect on morphology, proliferation, clonogenicity, passaging, differentiation and senescence. By this way we clearly show that the type of expansion medium used determines the stem cell character and time of senescence which is critical for future gene therapeutic and regenerative approaches using mesenchymal stem cells.     

过氧化氢参与烟草叶片衰老调节的研究（简报）

叶片衰老是一个复杂的过程．多年来人们对叶片衰老的机制开展了大量的研究。许多研究证明叶片中H2O2的迅速积累与叶片的衰老密切相关^[1-3],然而,H2O2的积累是衰老的结果还是作为信号启动衰老？H2O2作为植物细胞的信号分子,调控一系列重要的生理生化过程,如系统获得抗性（SAR）、细胞衰老与程序化死亡（PCD）、气孔关闭、根的生长、细胞壁的发育等^[4]。H2O2参与脱落酸（A—BA）、甲基茉莉酸（MJ）诱导的水稻叶片衰老,且H2O2产生早于叶片衰老^[2,5]。     

Senescence-related functional nuclear barrier by down-regulation of nucleo-cytoplasmic trafficking gene expression

One of the characteristic natures of senescent cells is the hypo- or irresponsiveness not only to growth factors but also to apoptotic stress. In the present study, we confirmed the inhibition of nuclear translocation of activated p-ERK1/2 and NF-kB p50 in response to growth stimuli or LPS in the senescent human diploid fibroblasts. In order to elucidate the underlying mechanism for the senescence-associated hypo-responsiveness, we carried out the comparison study for gene expression profiles through microarray analysis. In consequence, we observed the vast reduction in expression of nucleo-cytoplasmic trafficking genes in senescent cells, when compared with those in young cells. Expression levels of several nucleoporins, karyopherin α, karyopherin β, Ran, and Ran-regulating factors were confirmed to be down-regulated in senescent HDFs by using RT-PCR and Western blot methods. Taken together, these data suggest the operation of certain senescence-associated functional nuclear barriers by down-regulation of the nucleo-cytoplasmic trafficking genes in the senescent cells.     

CSN5/Jab1 controls multiple events in the mammalian cell cycle

The COP9 signalosome (CSN) complex is critical for mammalian cell proliferation and survival, but it is not known how the CSN affects the cell cycle. In this study, MEFs lacking CSN5/Jab1 were generated using a CRE-flox system. MEFs ceased to proliferate upon elimination of CSN5/Jab1. Rescue experiments indicated that the JAMM domain of CSN5/Jab1 was essential. CSN5/Jab1-elimination enhanced the neddylation of cullins 1 and 4 and altered the expression of many factors including cyclin E and p53. CSN5/Jab1-elimination inhibited progression of the cell cycle at multiple points, seemed to initiate p53-independent senescence and increased the ploidy of cells. Thus, CSN5/Jab1 controls different events of the cell cycle, preventing senescence and endocycle as well as the proper progression of the somatic cell cycle.

Structured summary

MINT-8046253: Csn1 (uniprotkb:Q99LD4) physically interacts (MI:0914) with Csn5 (uniprotkb:O35864), Csn8 (uniprotkb:Q8VBV7), Csn3 (uniprotkb:O88543), Csn7b (uniprotkb:Q8BV13) and Csn6 (uniprotkb:O88545) by anti bait coimmunoprecipitation (MI:0006)     

Persistent p21 Expression after Nutlin-3a Removal Is Associated with Senescence-like Arrest in 4N Cells

Nutlin-3a is a preclinical drug that stabilizes p53 by blocking the interaction between p53 and MDM2. In our previous study, Nutlin-3a promoted a tetraploid G₁ arrest in two p53 wild-type cell lines (HCT116 and U2OS), and both cell lines underwent endoreduplication after Nutlin-3a removal. Endoreduplication gave rise to stable tetraploid clones resistant to therapy-induced apoptosis. Prior knowledge of whether cells are susceptible to Nutlin-induced endoreduplication and therapy resistance could help direct Nutlin-3a-based therapies. In the present study, Nutlin-3a promoted a tetraploid G₁ arrest in multiple p53 wild-type cell lines. However, some cell lines underwent endoreduplication to relatively high extents after Nutlin-3a removal whereas other cell lines did not. The resistance to endoreduplication observed in some cell lines was associated with a prolonged 4N arrest after Nutlin-3a removal. Knockdown of either p53 or p21 immediately after Nutlin-3a removal could drive endoreduplication in otherwise resistant 4N cells. Finally, 4N-arrested cells retained persistent p21 expression; expressed senescence-associated β-galactosidase; displayed an enlarged, flattened phenotype; and underwent a proliferation block that lasted at least 2 weeks after Nutlin-3a removal. These findings demonstrate that transient Nutlin-3a treatment can promote an apparently permanent proliferative block in 4N cells of certain cell lines associated with persistent p21 expression and resistance to endoreduplication.     

Senescence program in rice (Oryza sautiva L.) leaves: Analysis of the blade of the second leaf at the tissue and cellular levels

Summary Previously, we showed that all greening mesophyll cells in the coleoptiles of rice (Oryza sauva L. cv. Nippon-bare) follow the identical program of senescence, which features the early degradation of chloroplast DNA (cpDNA) and subsequent nuclear condensation and disorganization. Following the coleoptile study, we analyzed the senescence-associated changes in the blade of the second leaf of rice at the tissue and cellular levels. Under the experimental conditions, the second leaf started to elongate rapidly 2 days after sowing and emerged on day 3. The blade of the second leaf completed its growth on day 4, although the sheath continued to grow until day 7. The amount of soluble protein and chlorophyll (Chl) per blade reached a maximum on day 7, and then declined. When blades were divided into three parts (the tip, mid-region, and base), levels of both soluble protein and Chl in the tip segment peaked earlier and decreased at a faster rate than in the other parts, demonstrating a longitudinal gradient of senescence from the tip to the base of the blade. In cross sections through the center of the tip and base segments, all the mesophyll cells senesced synchronously. They passed through the following steps in order: (i) degradation of cpDNA, (ii) decrease in the size of the chloroplast with degeneration of the chloroplast inner membranes, and (iii) condensation and disorganization of the nuclei. Although some differences were shown between the coleoptile and the second leaf in the timing and rate of each event, the order of those senescence-related events was conserved, suggesting an identical program of senescence exists in rice leaves.Abbreviations Chl chlorophyll - cpDNA chloroplast DNA - cpnucleoid chloroplast nucleoid - DAPI 4,6-diamidino-2-phenylindole - DiOC₇ 3,3-dihexyloxacarbocyanine iodide - VB vascular bundle - VIMPCS video-intensified microscope photon-counting system     

Interaction of checkpoint kinase 1 and the X-linked inhibitor of apoptosis during mitosis

Senescence marker protein-30 (SMP30) was originally identified as a novel protein in the rat liver, the expression of which decreases androgen-independently with aging. We have now characterized a unique property of SMP30, the hydrolysis of diisopropyl phosphorofluoridate (DFP), which is similar to the chemical warfare nerve agents sarine, soman and tabun. Hydrolysis of DFP was stimulated equally well by 1 mM MgCl₂, MnCl₂ or CoCl₂, to a lesser extent by 1 mM CdCl₂ but not at all by 1 mM CaCl₂. No ⁴⁵Ca²⁺-binding activity was detected for purified SMP30, suggesting that SMP30 is not a calcium-binding protein, as others previously stated. Despite the sequence similarity between SMP30 and a serum paraoxonase (PON), the inability of SMP30 to hydrolyze PON-specific substrates such as paraoxon, dihydrocoumarin, γ-nonalactone, and δ-dodecanolactone indicate that SMP30 is distinct from the PON family. We previously established SMP30 knockout mice and have now tested DFPase activity in their livers. The livers from wild-type mice contained readily detectable DFPase activity, whereas no such enzyme activity was found in livers from SMP30 knockout mice. Moreover, the hepatocytes of SMP30 knockout mice were far more susceptible to DFP-induced cytotoxicity than those from the wild-type. These results indicate that SMP30 is a unique DFP hydrolyzing enzyme in the liver and has an important detoxification effect on DFP. Consequently, a reduction of SMP30 expression might account for the age-associated deterioration of cellular functions and enhanced susceptibility to harmful stimuli in aged tissue.     

An analysis of replicative senescence in dermal fibroblasts derived from chronic leg wounds predicts that telomerase therapy would fail to reverse their disease-specific cellular and proteolytic phenotype

The accumulation of senescent fibroblasts within tissues has been suggested to play an important role in mediating impaired dermal wound healing, which is a major clinical problem in the aged population. The concept that replicative senescence in wound fibroblasts results in reduced proliferation and the failure of refractory wounds to respond to treatment has therefore been proposed. However, in the chronic wounds of aged patients the precise relationship between the observed alteration in cellular responses with aging and replicative senescence remains to be determined. Using assays to assess cellular proliferation, senescence-associated staining beta-galactosidase, telomere length, and extracellular matrix reorganizational ability, chronic wound fibroblasts demonstrated no evidence of senescence. Furthermore, analysis of in vitro senesced fibroblasts demonstrated cellular responses that were distinct and, in many cases, diametrically opposed from those exhibited by chronic wound fibroblasts. Forced expression of telomerase within senescent fibroblasts reversed the senescent cellular phenotype, inhibiting extracellular matrix reorganizational ability, attachment, and matrix metalloproteinase production and thus produced cells with impaired key wound healing properties. It would appear therefore that the distinct phenotype of chronic wound fibroblasts is not simply due to the aging process, mediated through replicative senescence, but instead reflects disease-specific cellular alterations of the fibroblasts themselves.