Low dose ionizing irradiation suppresses cellular senescence in normal human fibroblasts

Purpose: Exposure to high dose ionizing radiation leads to premature cell senescence and suppression of cell proliferation. In contrast, low dose and low dose-rate gamma-irradiation can lead to stimulation of cell proliferation. We aimed to examine whether the low dose radiation-induced proliferation of normal human fibroblasts can lead to a progressive depletion of proliferation potential and to an early onset of senescence.

Materials and methods: Normal human embryonic lung fibroblasts (HELF-104) at passage 22–24 were gamma-irradiated with doses of 0 (sham-irradiation), 10, 30, 50, 90, 120, 150, 200, and 500 mGy as well as 1 and 2?Gy. After irradiation, the fraction of cells positively stained for senescence-associated β-galactosidase activity was measured weekly until the cell culture completely ceased to proliferate.

Results: We show that single irradiation of HELF-104 cells with 30 and 50 mGy resulted in deceleration of senescence. The suppression of senescence was observed during almost the entire length of the study up to a complete arrest of cell growth.

Conclusions: Our data, together with the previously published observation of delayed stimulation of proliferation in HELF-104 cells exposed to 30 mGy, suggest that low dose gamma-irradiation can increase the overall proliferative potential of normal human fibroblasts.     

Study on the roles of β-catenin in hydrogen peroxide-induced senescence in human skin fibroblasts

Oxidative stress is one of the most important causes of the cellular senescence process. Previous studies showed that β-catenin can regulate FoxO3a and this association was enhanced in cells exposed to oxidative stress. It has also been reported that β-catenin can regulate some senescence-related proteins. We propose that β-catenin may play a crucial role in senescence of normal human primary skin fibroblasts (NHSFs). Here, we explored the roles and mechanisms of β-catenin on H(2)O(2)-induced senescence in NHSFs. β-catenin expression was decreased in NHSFs after H(2)O(2) treatment. Overexpression of β-catenin in NHSFs led to a marked delay of many senescent phenotypes induced by H(2)O(2). Furthermore, overexpression of β-catenin in NHSFs can antagonise the alteration of reactive oxygen species accumulation and some senescence-related proteins expression induced by H(2)O(2) treatment. Our data demonstrated that β-catenin can protect NHSFs from H(2)O(2)-induced premature senescence by alleviating oxidative stress and regulating some senescence-related molecules.     

胚肾发育过程中诱骗受体2表达与细胞衰老的关系

目的通过研究诱骗受体2(DcR2)在小鼠胚肾发育过程中的定位和表达,探讨DcR2在胚肾发育中与细胞衰老的关系。 方法分别选取胚龄为12.5 d、16.5 d、20.5 d和出生后8w小鼠的肾脏组织,使用过碘酸雪夫(PAS)染色观察肾组织形态,定量RT-PCR检测肾组织DcR2 mRNA表达水平,免疫组织化学染色观察DcR2的表达分布,免疫荧光共染检测DcR2与近端肾小管标志绒毛蛋白villin、远端肾小管标志水通道蛋白2(AQP-2)、衰老标志P16、胞核形态标志物核纤层蛋白B1(LaminB1)、增殖标志Ki-67和增殖细胞核抗原(PCNA)的共表达关系。 结果随着胚肾的发育,胚肾组织中DcR2 mRNA及蛋白表达逐渐增多,且明显高于成年肾脏;DcR2特异性表达于肾小管,且与villin共表达,但不与AQP-2共表达;DcR2阳性细胞高表达P16,却低表达LaminB1、Ki-67和PCNA。 结论DcR2特异性表达于胚肾近端肾小管细胞,且表达水平随胚龄增长而增多。此外,DcR2阳性细胞具有衰老相关表型,提示DcR2可能在胚肾发育过程中通过调控细胞衰老而具有重要作用。     

Maladie rénale chronique et immunosénescence prématurée : données et perspectives

Immune senescence is associated with age-related diseases (i.e. infectious disease, cardiovascular diseases and cancers). Chronic kidney disease patients die prematurely when compared with general population, because of a higher occurrence of infections, cardiovascular events and cancer. These diseases are commonly observed in the elderly population and frequently associated with immune senescence. Indeed, chronic kidney disease causes a premature aging of the T lymphocyte compartment, widely related to a decrease in thymic function, a phenomenon that plays a key role in the onset of age-related diseases in chronic kidney disease patients. The degree of immune senescence also influences patients’ outcome after renal transplantation, particularly the risk of acute rejection and infections. Partial reversion of pre-transplant immune senescence is observed for some renal transplant patients. In conclusion, to reduce the increasing incidence of morbidity and mortality of chronic kidney disease patients, a better knowledge of uremia-induced immune senescence would help to pave the way to build clinical studies and promote innovative therapeutic approaches. We believe that therapeutic reversion and immune senescence prevention approaches will be part of the management of chronic kidney disease patients in the future.     

Arterial “inflammaging” drives vascular calcification in children on dialysis

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Decreased osteogenesis, increased cell senescence and elevated Dickkopf-1 secretion in human fracture non union stromal cells

The delicately orchestrated process of bone fracture healing is not always successful and long term non union of fractured bone occurs in 5–20% of all cases. Atrophic fracture non unions have been described as the most difficult to treat and this is thought to arise through a cellular and local failure of osteogenesis. However, little is known about the presence and osteogenic proficiency of cells in the local area of non union tissue. We have examined the growth and differentiation potential of cells isolated from human non union tissues compared with normal human bone marrow mesenchymal stromal cells (BMSC). We report the isolation and culture expansion of a population of non union stromal cells (NUSC) which have a CD profile similar to that of BMSC, i.e. CD34-ve, CD45-ve and CD105+ve. The NUSC demonstrated multipotentiality and differentiated to some extent along chondrogenic, adipogenic and osteogenic lineages. However, and importantly, the NUSC showed significantly reduced osteogenic differentiation and mineralization in vitro compared to BMSC. We also found increased levels of cell senescence in NUSC compared to BMSC based on culture growth kinetics and cell positivity for senescence associated beta galactosidase (SA-β-Gal) activity. The reduced capacity of NUSC to form osteoblasts was associated with significantly elevated secretion of Dickkopf-1 (Dkk-1) which is an important inhibitor of Wnt signalling during osteogenesis, compared to BMSC. Conversely, treating BMSC with levels of rhDkk-1 that were equivalent to those levels secreted by NUSC inhibited the capacity of BMSC to undergo osteogenesis. Treating BMSC with NUSC conditioned medium also inhibited the capacity of the BMSC to undergo osteogenic differentiation when compared to their treatment with BMSC conditioned medium. Our results suggest that the development of fracture non union is linked with a localised reduced capacity of cells to undergo osteogenesis, which in turn is associated with increased cell senescence and Dkk-1 secretion.     

Sex differences in the phagocytic and migratory activity of microglia and their impairment by palmitic acid

Sex differences in the incidence, clinical manifestation, disease course, and prognosis of neurological diseases, such as autism spectrum disorders or Alzheimer's disease, have been reported. Obesity has been postulated as a risk factor for cognitive decline and Alzheimer's disease and, during pregnancy, increases the risk of autism spectrum disorders in the offspring. Obesity is associated with increased serum and brain levels of free fatty acids, such as palmitic acid, which activate microglial cells triggering a potent inflammatory cascade. In this study, we have determined the effect of palmitic acid in the inflammatory profile, motility, and phagocytosis of primary male and female microglia, both in basal conditions and in the presence of a pro‐inflammatory stimulus (interferon‐γ). Male microglia in vitro showed higher migration than female microglia under basal and stimulated conditions. In contrast, female microglia had higher basal and stimulated phagocytic activity than male microglia. Palmitic acid did not affect basal migration or phagocytosis, but abolished the migration and phagocytic activity of male and female microglia in response to interferon‐γ. These findings extend previous observations of sex differences in microglia and suggest that palmitic acid impairs the protective responses of these cells.     

NADPH oxidase and aging drive microglial activation,oxidative stress,and dopaminergic neurodegeneration following systemic LPS administration

Parkinson's disease is characterized by a progressive degeneration of substantia nigra (SN) dopaminergic neurons with age. We previously found that a single systemic lipopolysaccharide (LPS, 5 mg/kg, i.p.) injection caused a slow progressive loss of tyrosine hydroxylase immunoreactive (TH+IR) neurons in SN associated with increasing motor dysfunction. In this study, we investigated the role of NADPH oxidase (NOX) in inflammation‐mediated SN neurotoxicity. A comparison of control (NOX2^+/+) mice with NOX subunit gp91^phox‐deficient (NOX2^?/?) mice 10 months after LPS administration (5 mg/kg, i.p.) resulted in a 39% (P < 0.01) loss of TH+IR neurons in NOX2^+/+ mice, whereas NOX2^?/? mice did not show a significant decrease. Microglia (Iba1+IR) showed morphological activation in NOX2^+/+ mice, but not in NOX2^?/? mice at 1 hr. Treatment of NOX2^+/+ mice with LPS resulted in a 12‐fold increase in NOX2 mRNA in midbrain and 5.5–6.5‐fold increases in NOX2 protein (+IR) in SN compared with the saline controls. Brain reactive oxygen species (ROS), determined using diphenyliodonium histochemistry, was increased by LPS in SN between 1 hr and 20 months. Diphenyliodonium (DPI), an NOX inhibitor, blocked LPS‐induced activation of microglia and production of ROS, TNFα, IL‐1β, and MCP‐1. Although LPS increased microglial activation and ROS at all ages studied, saline control NOX2^+/+ mice showed age‐related increases in microglial activation, NOX, and ROS levels at 12 and 22 months of age. Together, these results suggest that NOX contributes to persistent microglial activation, ROS production, and dopaminergic neurodegeneration that persist and continue to increase with age. © 147.     

Estrogen modulates synaptic N-methyl-D-aspartate receptor subunit distribution in the aged hippocampus

Estrogen interacts with N-methyl-D-aspartate (NMDA) receptors to regulate multiple aspects of morphological and functional plasticity. In hippocampus, estrogen increases both dendritic spine density and synapse number, and NMDA antagonists block these effects. Thus, estrogen-mediated hippocampal plasticity may be of particular importance in the context of age-related changes in endocrine status and cognitive performance. NR1 levels per synapse are increased in CA1 by estrogen in aged rats but not young rats, although no information is available on estrogen-induced synaptic alterations in other NMDA receptor subunits that might impact function. Therefore, the present study was designed to investigate the effect of estrogen on the synaptic and subsynaptic distributions of the NMDA receptor subunits, NR2A and NR2B in CA1 pyramidal cells, within the context of aging. Our results demonstrated that the overall synaptic levels of NR2A and NR2B are similar in young and aged female rats, regardless of estrogen treatment. However, in the aged CA1, estrogen restores NR2B levels back to young levels in the lateral portions of the active synaptic zone. Thus, estrogen may impact the mobility of NMDA receptors across the synapse and, in the process, restore a more youthful synaptic profile. These findings have important implications for the mechanism of estrogen-induced alterations in NMDA receptor-mediated processes, particularly in the context of aging.     

Multiple measures of functionality exhibit progressive decline in a parallel, stochastic fashion in Drosophila Sod2 null mutants

Oxidative damage has been proposed as an important factor in the progression of pathological and non-pathological age-related functional declines. Here, we examine functional deterioration in short-lived flies mutant for the mitochondrial antioxidant Manganese Superoxide Dismutase (Sod2). We find that the decline of several functional measures of aging occurs, in an accelerated fashion, in Sod2 mutants. Olfactory behavior, locomotor ability and cardiac performance were all seen to decline rapidly in Sod2 mutants. On average, functional declines in Sod2 mutants occur in a pattern similar to that seen in late-life Drosophila with a normal complement of Sod2. In longitudinal experiments, however, we find that functional failures occur in every possible sequence in Sod2 mutants. Significantly, failure of these functional measures is not irreversible, as spontaneous functional recovery was sometimes observed. These findings support a model where ROS-related damage strikes at multiple organ systems in parallel, rather than a “chain of dominos” model, in which primary organ failure contributes to the deterioration of further organ systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.