A progeroid syndrome in mice is caused by defects in A-type lamins

Numerous studies of the underlying causes of ageing have been attempted by examining diseases associated with premature ageing, such as Werner's syndrome and Hutchinson-Gilford progeria syndrome (HGPS). HGPS is a rare genetic disorder resulting in phenotypes suggestive of accelerated ageing, including shortened stature, craniofacial disproportion, very thin skin, alopecia and osteoporosis, with death in the early teens predominantly due to atherosclerosis. However, recent reports suggest that developmental abnormalities may also be important in HGPS. Here we describe the derivation of mice carrying an autosomal recessive mutation in the lamin A gene (Lmna) encoding A-type lamins, major components of the nuclear lamina. Homozygous mice display defects consistent with HGPS, including a marked reduction in growth rate and death by 4 weeks of age. Pathologies in bone, muscle and skin are also consistent with progeria. The Lmna mutation resulted in nuclear morphology defects and decreased lifespan of homozygous fibroblasts, suggesting premature cell death. Here we present a mouse model for progeria that may elucidate mechanisms of ageing and development in certain tissue types, especially those developing from the mesenchymal cell lineage.     

Recurrent de novo point mutations in lamin A cause Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder characterized by features reminiscent of marked premature ageing. Here, we present evidence of mutations in lamin A (LMNA) as the cause of this disorder. The HGPS gene was initially localized to chromosome 1q by observing two cases of uniparental isodisomy of 1q-the inheritance of both copies of this material from one parent-and one case with a 6-megabase paternal interstitial deletion. Sequencing of LMNA, located in this interval and previously implicated in several other heritable disorders, revealed that 18 out of 20 classical cases of HGPS harboured an identical de novo (that is, newly arisen and not inherited) single-base substitution, G608G(GGC > GGT), within exon 11. One additional case was identified with a different substitution within the same codon. Both of these mutations result in activation of a cryptic splice site within exon 11, resulting in production of a protein product that deletes 50 amino acids near the carboxy terminus. Immunofluorescence of HGPS fibroblasts with antibodies directed against lamin A revealed that many cells show visible abnormalities of the nuclear membrane. The discovery of the molecular basis of this disease may shed light on the general phenomenon of human ageing.     

SIRT6 is a histone H3 lysine 9 deacetylase that modulates telomeric chromatin

The Sir2 deacetylase regulates chromatin silencing and lifespan in Saccharomyces cerevisiae. In mice, deficiency for the Sir2 family member SIRT6 leads to a shortened lifespan and a premature ageing-like phenotype. However, the molecular mechanisms of SIRT6 function are unclear. SIRT6 is a chromatin-associated protein, but no enzymatic activity of SIRT6 at chromatin has yet been detected, and the identity of physiological SIRT6 substrates is unknown. Here we show that the human SIRT6 protein is an NAD+-dependent, histone H3 lysine 9 (H3K9) deacetylase that modulates telomeric chromatin. SIRT6 associates specifically with telomeres, and SIRT6 depletion leads to telomere dysfunction with end-to-end chromosomal fusions and premature cellular senescence. Moreover, SIRT6-depleted cells exhibit abnormal telomere structures that resemble defects observed in Werner syndrome, a premature ageing disorder. At telomeric chromatin, SIRT6 deacetylates H3K9 and is required for the stable association of WRN, the factor that is mutated in Werner syndrome. We propose that SIRT6 contributes to the propagation of a specialized chromatin state at mammalian telomeres, which in turn is required for proper telomere metabolism and function. Our findings constitute the first identification of a physiological enzymatic activity of SIRT6, and link chromatin regulation by SIRT6 to telomere maintenance and a human premature ageing syndrome.     

Lamins and their genes

The nuclear lamina is an important nuclear structure. The studies on its peptides lamins and genes have made substantial progress in recent years. In this paper, the new achievements in studies of new lamin members and their functions, lamin genes and their origin and differentiation, are reviewed and discussed. Some research areas that deserve to be investigated further are put forward.     

可降解聚醚酯弹性体PTCG的合成及初步生物学评价

用熔融缩聚法合成聚对苯二甲酸丁二醇酯-co-聚对苯二甲酸环己烷二甲醇酯-b-聚乙二醇(PTCG)聚醚酯弹性体.按照ISO 10993标准,采用L929小鼠成纤细胞对其进行体外细胞毒性测试;以狗的血管平滑肌细胞 (SMCs)为模板细胞,测试细胞在材料表面的贴附性能.采用旋转成型/粒子洗出法制备三维血管支架,接种SMCs后在生物反应器上进行动态培养,探索PTCG作为组织工程血管支架材料的可行性.结果表明,合成的PTCG聚醚酯弹性体无细胞毒性;SMCs在PTCG薄膜表面贴附生长良好;所制备支架的孔径、孔隙率和力学性能等满足组织工程血管支架的要求;体外培养3 d后,大量SMCs长入血管支架并开始分化.     

Stem-cell ageing modified by the cyclin-dependent kinase inhibitor p16INK4a

Stem-cell ageing is thought to contribute to altered tissue maintenance and repair. Older humans experience increased bone marrow failure and poorer haematologic tolerance of cytotoxic injury. Haematopoietic stem cells (HSCs) in older mice have decreased per-cell repopulating activity, self-renewal and homing abilities, myeloid skewing of differentiation, and increased apoptosis with stress. Here we report that the cyclin-dependent kinase inhibitor p16INK4a, the level of which was previously noted to increase in other cell types with age, accumulates and modulates specific age-associated HSC functions. Notably, in the absence of p16INK4a, HSC repopulating defects and apoptosis were mitigated, improving the stress tolerance of cells and the survival of animals in successive transplants, a stem-cell-autonomous tissue regeneration model. Inhibition of p16INK4a may ameliorate the physiological impact of ageing on stem cells and thereby improve injury repair in aged tissue.     

Delayed ageing through damage protection by the Arf/p53 pathway

The tumour-suppressor pathway formed by the alternative reading frame protein of the Cdkn2a locus (Arf) and by p53 (also called Trp53) plays a central part in the detection and elimination of cellular damage, and this constitutes the basis of its potent cancer protection activity. Similar to cancer, ageing also results from the accumulation of damage and, therefore, we have reasoned that Arf/p53 could have anti-ageing activity by alleviating the load of age-associated damage. Here we show that genetically manipulated mice with increased, but otherwise normally regulated, levels of Arf and p53 present strong cancer resistance and have decreased levels of ageing-associated damage. These observations extend the protective role of Arf/p53 to ageing, revealing a previously unknown anti-ageing mechanism and providing a rationale for the co-evolution of cancer resistance and longevity.     

Intrinsic transition of embryonic stem-cell differentiation into neural progenitors

The neural fate is generally considered to be the intrinsic direction of embryonic stem (ES) cell differentiation. However, little is known about the intracellular mechanism that leads undifferentiated cells to adopt the neural fate in the absence of extrinsic inductive signals. Here we show that the zinc-finger nuclear protein Zfp521 is essential and sufficient for driving the intrinsic neural differentiation of mouse ES cells. In the absence of the neural differentiation inhibitor BMP4, strong Zfp521 expression is intrinsically induced in differentiating ES cells. Forced expression of Zfp521 enables the neural conversion of ES cells even in the presence of BMP4. Conversely, in differentiation culture, Zfp521-depleted ES cells do not undergo neural conversion but tend to halt at the epiblast state. Zfp521 directly activates early neural genes by working with the co-activator p300. Thus, the transition of ES cell differentiation from the epiblast state into neuroectodermal progenitors specifically depends on the cell-intrinsic expression and activator function of Zfp521.     

HMBA诱导人成骨肉瘤MG-63细胞分化过程中核基质蛋白表达变化

应用选择性抽提、双向聚丙烯酰胺凝胶电泳技术分析5mmol/LHMBA诱导处理前后人成骨肉瘤MG 63细胞核基质蛋白表达变化,鉴定与人成骨肉瘤细胞增殖分化相关的特异核基质蛋白.实验结果显示在HMBA诱导处理MG 63细胞分化过程中,核基质蛋白NMP 1、NMP 2、NMP 3、NMP 4、NMP 5、NMP 6和NMP 7等7个蛋白点表达发生显著变化.其中NMP 1仅在MG 63细胞中表达,NMP 6则为经HMBA诱导处理后新出现的蛋白质,NMP 2、NMP 7在HMBA诱导分化细胞中表达减弱,而NMP 3、NMP 4和NMP 5则在诱导分化后细胞中表达增强.首次表明在人成骨肉瘤MG 63细胞诱导分化过程中伴有核基质蛋白表达的差异,证实了与肿瘤细胞增殖分化相关的特异核基质蛋白的存在.这对于揭示核基质蛋白与细胞癌变和逆转的关系、阐明细胞增殖分化的基因表达调控原理,均具有重要意义.     

Neuronal basis of age-related working memory decline

Many of the cognitive deficits of normal ageing (forgetfulness, distractibility, inflexibility and impaired executive functions) involve prefrontal cortex (PFC) dysfunction. The PFC guides behaviour and thought using working memory, which are essential functions in the information age. Many PFC neurons hold information in working memory through excitatory networks that can maintain persistent neuronal firing in the absence of external stimulation. This fragile process is highly dependent on the neurochemical environment. For example, elevated cyclic-AMP signalling reduces persistent firing by opening HCN and KCNQ potassium channels. It is not known if molecular changes associated with normal ageing alter the physiological properties of PFC neurons during working memory, as there have been no in vivo recordings, to our knowledge, from PFC neurons of aged monkeys. Here we characterize the first recordings of this kind, revealing a marked loss of PFC persistent firing with advancing age that can be rescued by restoring an optimal neurochemical environment. Recordings showed an age-related decline in the firing rate of DELAY neurons, whereas the firing of CUE neurons remained unchanged with age. The memory-related firing of aged DELAY neurons was partially restored to more youthful levels by inhibiting cAMP signalling, or by blocking HCN or KCNQ channels. These findings reveal the cellular basis of age-related cognitive decline in dorsolateral PFC, and demonstrate that physiological integrity can be rescued by addressing the molecular needs of PFC circuits.     

Ia binding ligands and cAMP stimulate nuclear translocation of PKC in B lymphocytes

Altered subcellular distribution and activity of protein kinase C (PKC) is associated with transmembrane signalling in a variety of systems in which receptor occupancy leads to increased hydrolysis of polyphosphoinositides. Here we report evidence that in B lymphocytes, cyclic-cAMP-generating signal transduction pathways can activate translocation of PKC from the cytosol to the nucleus. Elevated cAMP levels and translocation of PKC to the nucleus are induced by antibodies against Ia antigens in normal B lymphocytes. Further, cAMP analogues mediate the translocation of PKC to the nucleus of these cells. These findings suggest that in physiological situations, ligation of B-lymphocyte Ia molecules by helper T cells leads to increased cAMP production which in turn causes PKC translocation to the nucleus. In view of recent observations that antibodies against Ia antigens induce differentiation of B cells, we conclude that nuclear PKC may function in the regulation of gene expression.     

Inhibition of pluripotential embryonic stem cell differentiation by purified polypeptides

Murine embryonic stem (ES) cells are pluripotent cell lines established directly from the early embryo which can contribute differentiated progeny to all adult tissues, including the germ-cell lineage, after re-incorporation into the normal embryo. They provide both a cellular vector for the generation of transgenic animals and a useful system for the identification of polypeptide factors controlling differentiation processes in early development. In particular, medium conditioned by Buffalo rat liver cells contains a polypeptide factor, ES cell differentiation inhibitory activity (DIA), which specifically suppresses the spontaneous differentiation of ES cells in vitro, thereby permitting their growth as homogeneous stem cell populations in the absence of heterologous feeder cells. ES cell pluripotentiality, including the ability to give rise to functional gametes, is preserved after prolonged culture in Buffalo rat liver media as a source of DIA. Here, we report that purified DIA is related in structure and function to the recently identified hematopoietic regulatory factors human interleukin for DA cells and leukaemia inhibitory factor. DIA and human interleukin DA/leukaemia inhibitory factor have thus been identified as related multifunctional regulatory factors with distinct biological activities in both early embryonic and hematopoietic stem cell systems.     

Altered enzymes in ageing human fibroblasts

Diploid human fibroblasts accumulate heat labile enzymes during the final stages of their life-span in culture. The RNA base analogue 5-FU induces premature senescence, which is preceded by the appearance of altered enzyme. These observations support Orgel's "error catastrophe" theory of ageing.     

The future of ageing

Advances in our knowledge of age-associated diseases have far outpaced advances in our understanding of the fundamental ageing processes that underlie the vulnerability to these pathologies. If we are to increase human life expectancy beyond the fifteen-year limit that would result if today's leading causes of death were resolved, more attention must be paid to basic research on ageing. Determination of longevity must be distinguished from ageing to take us from the common question of why we age to a more revealing question that is rarely posed: why do we live as long as we do? But if the ability to intervene in ageing ever becomes a reality, it will be rife with unintended and undesirable consequences.