生长分化因子11：TGF-β超家族的新成员

生长分化因子11(growth differentiation factor 11,GDF11),是新近发现的TGF-β超家族成员,属于BMPs亚家族的一种分泌性蛋白.在早期胚胎发育中,GDF11通过负性调节作用,参与包括骨骼、肾脏、胰腺、视网膜、嗅神经等组织器官的形成和分化,是胚胎正常发育不可或缺的分子.近年来研究发现,GDF11有明显的改善大脑认知、逆转心肌肥厚、改善骨骼肌代谢等功能,显示出GDF11广泛的生物学活性和潜在的应用价值.然而,一项最新的研究报道得出与此相反的结果.本文从GDF11的发现、研究历程、结构、表达及表达调控、信号传导通路和功能方面概括GDF11的基本情况及研究现状,为今后的研究提供思路.     

生长分化因子-5与骨骼发育

生长分化因子属于骨形态发生蛋白信号分子高度保守的亚家族,对骨骼的发育具有至关重要的作用。近年报道表明：生长分化因子-5（growth／differentiation factor-5,GDF6）的羧端区域与GDF-6和-7高度同源。GDF6在治疗肌腱或韧带修复,椎间盘退变修复,软骨修复,骨折愈合等方面具有潜在应用价值。     

秀丽隐杆线虫模型在抗衰老研究中的应用

随着人口老龄化问题的凸显,衰老相关的研究越来越被重视。秀丽隐杆线虫（Caenorhabditis elegans）是抗衰老研究领域中非常重要的生物模型,具有生命周期短、易于培养和观察等优点,但与其他哺乳动物模型相比仍有一些局限性,如DNA甲基化的缺乏等。本文主要综述了秀丽隐杆线虫模型在抗衰老研究和药物筛选中的应用,包括抗衰老药物对线虫寿命和抗性的测定与评估、药物筛选以及健康衰老研究中的应用,并概括了该模型的优势和局限性,为秀丽隐杆线虫模型在抗衰老研究中的应用提供理论依据。     

转化生长因子5在发育性髋关节发育不良中的作用研究进展

发育性髋关节发育不良(developmental dysplasia of the hip,DDH)是一种主要因髋臼、股骨近端和关节囊等存在结构性畸形而导致的不稳定关节病变,进而发展成为髋关节的脱位。髋关节内软骨发育不良、骨骼及肌腱的异常均可导致髋关节结构的畸形,最终造成DDH。因此,早期预防与诊断是DDH治疗的关键。研究表明,DDH具有遗传基础,其易感基因包括GDF5、HOXD9、COL2AL、PAPPA2等,其中遗传因子转化生长因子5(growth differentiation factor 5,GDF5)对软骨细胞的增殖、分化具有重要作用,是当前研究治疗DDH的热点之一。因而,了解GDF5基因对软骨发育及分化的影响,对于DDH的发病机制和治疗具有重要意义。基于此,综述了国内外近期探讨的GDF5在基因层面上对DDH的影响,以及通过关节内注射重组人GDF5等基于GDF5的DDH治疗方案,以期为DDH的临床治疗提供新的策略。     

生长分化因子11对甲醛诱导的海马神经细胞凋亡的影响

目的探讨生长分化因子11（GDF11）对甲醛诱导的海马神经（HT22）细胞毒性的影响。 方法把HT22细胞分为对照组（细胞未做任何处理）、甲醛组（50、100、200 μmol/ L甲醛处理细胞）和GDF11+甲醛组（GDF11转染细胞后用100 μmol/L甲醛处理）。细胞计数试剂盒（CCK8）法检测HT22细胞的活力;蛋白免疫印迹法检测HT22细胞凋亡相关蛋白Bax以及Bcl-2的变化;caspase-3活性检测试剂盒检测HT22细胞内caspase-3活性;DCFDA染色流式细胞仪检测HT22细胞中活性氧（ROS）水平。三组间比较采用单因素方差分析,组间两两比较采用LSD-t检验。 结果与对照组比较,甲醛组HT22细胞活力（92.23±0.20比56.12±0.61）和Bcl-2蛋白表达（220.32±2.21比150.25±0.31）水平均降低,差异具有统计学意义（P均< 0.05）;而caspase-3活性（95.36±1.74比190.17±2.14）、Bax蛋白表达（132.19±1.21比150.17±1.06）和ROS水平（1099.32±75.47比2802.17±126.49）均升高,差异具有统计学意义（P均< 0.05）。GDF11转染HT22细胞后,与甲醛组比较,GDF11+甲醛组HT22细胞活力升高（56.12±0.61比83.11±1.64）,Bax蛋白表达（270.03±0.17比150.17±1.06）降低,Bcl-2蛋白表达（150.25±0.31比187.34±1.52）升高,caspase-3活性降低（190.17±2.14比105.31±4.12）和ROS水平降低（2802.17±126.49比1305.36±68.45）,差异具有统计学意义（P均< 0.05）。 结论GDF11能够逆转甲醛对HT22细胞凋亡的诱导作用以及降低甲醛对HT22细胞ROS水平的增加作用,此机制对防治甲醛的神经毒性具有重要意义。     

SIRT6:一个新的哺乳动物抗衰老因子

Sir2是一个在低等动物中被广泛研究的抗衰老蛋白因子。最新研究发现,哺乳动物Sir2的同源蛋白家族Sirtuin(SIRT)中的SIRT6在抗衰老过程中也发挥着重要作用,它的功能缺失将导致碱基切除修复(BER)受阻,而出现细胞对氧化损伤的敏感性增加、皮肤变薄等衰老症状,使人们对哺乳动物的衰老机制有了初步的认识。     

果蝇微小RNA及其在衰老过程中的作用

微小RNA（microRNA, miRNA）是一类长度在22 nt左右的内源非编码小RNA,广泛存在于动物、植物、病毒等多种有机体中,是机体正常衰老与疾病的重要调控因子。本文对果蝇不同生长时期miRNA的表达模式、主要衰老相关信号通路以及与衰老相关的miRNA进行了综述。在果蝇的不同发育时期均有特定的miRNA发挥重要作用,其表达模式与功能相关;miRNA参与了主要衰老分子信号通路的调控,如胰岛素/胰岛素样生长因子（IIS）通路和雷帕霉素靶蛋白（TOR）通路。研究表明,miRNA通过调控衰老相关信号通路中的靶基因,进而促进或延缓果蝇衰老,如miR-34, miR-8, miR-14, miR let7和miR-277等。因此,研究参与衰老调控的miRNA,为阐明衰老机制及抗衰老药物的设计奠定了基础。     

褪黑素延缓哺乳动物衰老的作用 及其机制的研究进展

褪黑素（melatonin）在哺乳动物中是主要由松果体分泌的一种多功能吲哚激素,具有抗氧化、调节睡眠、调节昼夜节律、增强免疫力、抑制肿瘤等作用,在哺乳动物的复杂衰老进程中发挥重要作用。本文从氧化应激和能量代谢两个方面综述了褪黑素在哺乳动物中延缓衰老的作用机制。褪黑素通过清除自由基、激发抗氧化作用以及保护线粒体功能从而减缓氧化应激;通过调节代谢感知、重建昼夜节律以及促进能量消耗调节能量代谢。最后对该领域今后可能的发展方向进行了展望。     

衰老的表观遗传调控机制

表观遗传通过调控基因表达影响众多生命过程。大量的证据表明,表观遗传在衰老调控中也发挥重要的作用。本文介绍表观遗传的3种主要机制对衰老的调控作用,及其对衰老的2个主要特征的影响。同时,介绍热量限制介导的抗衰老作用的表观遗传的调控机制,和3种重要的抗衰老活性小分子及其如何通过表观遗传相关机制发挥抗衰老作用。本文结果为进一步研究表观遗传在衰老调控中的作用,以及发展抗衰老干预措施提供了理论依据和重要的参考资料。     

衰老的表观遗传调控机制北大核心CSCD

表观遗传通过调控基因表达影响众多生命过程。大量的证据表明,表观遗传在衰老调控中也发挥重要的作用。本文介绍表观遗传的3种主要机制对衰老的调控作用,及其对衰老的2个主要特征的影响。同时,介绍热量限制介导的抗衰老作用的表观遗传的调控机制,和3种重要的抗衰老活性小分子及其如何通过表观遗传相关机制发挥抗衰老作用。本文结果为进一步研究表观遗传在衰老调控中的作用,以及发展抗衰老干预措施提供了理论依据和重要的参考资料。     

Skeletal muscle-derived progenitors capable of differentiating into cardiomyocytes proliferate through myostatin-independent TGF-beta family signaling

The existence of skeletal muscle-derived stem cells (MDSCs) has been suggested in mammals; however, the signaling pathways controlling MDSC proliferation remain largely unknown. Here we report the isolation of myosphere-derived progenitor cells (MDPCs) that can give rise to beating cardiomyocytes from adult skeletal muscle. We identified that follistatin, an antagonist of TGF-β family members, was predominantly expressed in MDPCs, whereas myostatin was mainly expressed in myogenic cells and mature skeletal muscle. Although follistatin enhanced the replicative growth of MDPCs through Smad2/3 inactivation and cell cycle progression, disruption of myostatin did not increase the MDPC proliferation. By contrast, inhibition of activin A (ActA) or growth differentiation factor 11 (GDF11) signaling dramatically increased MDPC proliferation via down-regulation of p21 and increases in the levels of cdk2/4 and cyclin D1. Thus, follistatin may be an effective progenitor-enhancing agent neutralizing ActA and GDF11 signaling to regulate the growth of MDPCs in skeletal muscle.     

The role of GDF11 in aging and skeletal muscle,cardiac and bone homeostasis

GDF11 is a secreted factor in the TGFß family of cytokines. Its nearest neighbor evolutionarily is myostatin, a factor discovered as being a negative regulator of skeletal muscle growth. High profile studies several years ago suggested that GDF11 declines with age, and that restoration of systemic GDF11 to ‘youthful’ levels is beneficial for several age-related conditions. Particularly surprising was a report that supplementation of GDF11 aided skeletal muscle regeneration, as its homolog, myostatin, has the opposite role. Given this apparent contradiction in functionality, multiple independent labs sought to discern differences between the two factors and better elucidate age-related changes in circulating GDF11, with most failing to reproduce the initial finding of declining GDF11 levels, and, importantly, all subsequent studies examining the effects of GDF11 on skeletal muscle described an inhibitory effect on regeneration – and that higher doses induce skeletal muscle atrophy and cachexia. There have also been several studies examining the effect of GDF11 and/or the downstream ActRII pathway on cardiac function, along with several interesting reports on bone. A review of the GDF11 literature, as it relates in particular to aging and skeletal muscle, cardiac and bone biology, is presented.     

Autoregulation of neurogenesis by GDF11

In the olfactory epithelium (OE), generation of new neurons by neuronal progenitors is inhibited by a signal from neurons themselves. Here we provide evidence that this feedback inhibitory signal is growth and differentiation factor 11 (GDF11). Both GDF11 and its receptors are expressed by OE neurons and progenitors, and GDF11 inhibits OE neurogenesis in vitro by inducing p27(Kip1) and reversible cell cycle arrest in progenitors. Mice lacking functional GDF11 have more progenitors and neurons in the OE, whereas mice lacking follistatin, a GDF11 antagonist, show dramatically decreased neurogenesis. This negative autoregulatory action of GDF11 is strikingly like that of its homolog, GDF8/myostatin, in skeletal muscle, suggesting that similar strategies establish and maintain proper cell number during neural and muscular development.     

Growth differentiation factor 11 promotes differentiation of MSCs into endothelial‐like cells for angiogenesis

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor‐β super family. It has multiple effects on development, physiology and diseases. However, the role of GDF11 in the development of mesenchymal stem cells (MSCs) is not clear. To explore the effects of GDF11 on the differentiation and pro‐angiogenic activities of MSCs, mouse bone marrow–derived MSCs were engineered to overexpress GDF11 (MSC^GDF11) and their capacity for differentiation and paracrine actions were examined both in vitro and in vivo. Expression of endothelial markers CD31 and VEGFR2 at the levels of both mRNA and protein was significantly higher in MSC^GDF11 than control MSCs (MSC^Vector) during differentiation. More tube formation was observed in MSC^GDF11 as compared with controls. In an in vivo angiogenesis assay with Matrigel plug, MSC^GDF11 showed more differentiation into CD31⁺ endothelial‐like cells and better pro‐angiogenic activity as compared with MSC^Vector. Mechanistically, the enhanced differentiation by GDF11 involved activation of extracellular‐signal‐related kinase (ERK) and eukaryotic translation initiation factor 4E (EIF4E). Inhibition of either TGF‐β receptor or ERK diminished the effect of GDF11 on MSC differentiation. In summary, our study unveils the function of GDF11 in the pro‐angiogenic activities of MSCs by enhancing endothelial differentiation via the TGFβ‐R/ERK/EIF4E pathway.     

Transgenic over-expression of growth differentiation factor 11 propeptide in skeleton results in transformation of the seventh cervical vertebra into a thoracic vertebra

Growth differentiation factor 11 (GDF11) is one of the significant genes that control skeletal formation. Knockout of GDF11 function causes abnormal patterning of the anterior/posterior axial skeleton. The mRNA of GDF11 is initially translated to a precursor protein that undergoes a proteolytic cleavage to generate the C-terminal peptide or mature GDF11, and the N-terminal peptide named GDF11 propeptide. The propeptide can antagonize GDF11 activity in vitro. To investigate the effects of GDF11 propeptide on GDF11 function in vivo, we generated transgenic mice that over-express the propeptide cDNA in skeletal tissue. The transgenic mice showed formation of extra ribs on the seventh cervical vertebra (C7) as a result of transformation of the C7 vertebra into a thoracic vertebra. The GDF11 propeptide transgene mRNA was detected in tail tissue in embryos and was highly expressed in tail and calvaria bones after birth. A high frequency of C7 rib formation was noticed in the transgenic mouse line with a high level of transgene expression. The anterior boundaries of Hoxa-4 and Hoxa-5 mRNA in situ expressions showed cranial shifts from their normal prevertebra locations in transgenic embryos. These results demonstrated significant effects of GDF11 propeptide transgene on vertebral formation, which are likely occurring through depressing GDF11 function and altered locations of Hoxa-4 and Hoxa-5 expression.     

Ageing of the heart reversed by youthful systemic factors!

Cell (2013) 153: 828–839Age-associated changes in tissue maintenance and repair have severe consequences to human physiology. The signals and mechanisms that cause age-related tissue demise are unclear. A recently published study in Cell (Loffredo et al, 2013) proposes that blood-borne factors in the adult systemic environment are lost during ageing, which leads to cardiac hypertrophy. One such factor is GDF11. Exposure of aged mice to youthful systemic factors or GDF11 decreases cardiac hypertrophy of the heart.The ageing process is associated with a loss of tissue function through disrupted homeostatic and regenerative mechanisms (Liu and Rando, 2011). Throughout the life of any organism, the cells of the body experience various extrinsic and intrinsic changes that ultimately impact tissue function. The relative contribution of extrinsic factors and intrinsic modifications that can impact any cell is likely to be dependent on the function of the cell, its turnover throughout life and the environment in which it resides.The regenerative decline of many tissues observed during ageing is thought to be due to stem cell demise, regulated in part through changes in the composition of blood-borne factors present in the systemic environment. Parabiosis is an experimental paradigm used to study the role of blood-borne factors in many cellular processes (Finerty, 1952). In this technique, two mice are surgically joined and develop a shared blood circulation; therefore, the tissues of one mouse are exposed to its partner''s circulatory factors. Parabiosis studies involving adult and aged mice have revealed the presence of stimulatory and repressive blood-borne factors in the systemic environment that impact stem and progenitor cell function in response to injury (Conboy et al, 2005; Brack et al, 2007; Villeda et al, 2011; Ruckh et al, 2012). However, tissues that do not rely on stem cells also undergo age-dependent decline. For example, the cardiac muscle undergoes ventricular hypertrophy during ageing, often leading to diastolic heart failure due to the increased size of individual differentiated cardiac myocytes. Is this also regulated by the systemic environment and, if so, how?In their present work, Loffredo et al (2013) have tested the hypothesis that age-dependent changes in systemic factors promote cardiac hypertrophy. The authors report an age-dependent increase in cardiac myocyte size that is coupled to increased weight of the heart muscle. Remarkably, 4 weeks of parabiosis led to a significant reversion of age-induced cardiac hypertrophy. Importantly, these effects were gender-independent and did not arise from the parabiosis technique itself, or changes in blood pressure. The authors identified that the myocyte cross-sectional area was decreased in aged mice paired with adult mice, and thus blood-borne factors were acting directly on the terminally differentiated cell. In comparison, analysis of adult mice that were paired with aged mice for up to 10 weeks did not show any change in the size of myocyte or weight of the heart. Together, these results are consistent with the loss of youthful factors in the aged systemic milieu that repress myocyte size rather than the accumulation of hypertrophic factors during ageing. Loffredo et al (2013) also investigated the molecular nature of cardiac hypertrophy, using a few molecular markers of cardiac hypertrophy, such as brain natriuretic peptide (BNP) and atrial brain natriuretic peptide (ANP). From this result, the authors claim that circulatory factors can reverse some molecular aspects of cardiac ageing.Identification of the blood-borne factors that impact ageing is of obvious significance. The authors used an aptamer-based proteomic platform to hunt for the ‘fountain of youth.'' Aptamers are chemically modified nucleotides that act as highly specific protein binding reagents. They can be multiplexed and transformed into a quantifiable readout using a hybridization array. Using this method and by validating using western blots, the authors show that levels of growth differentiation factor 11 (GDF11), a TGFβ superfamily member, were consistently lower in aged compared to adult plasma.To test whether GDF11 was sufficient to reverse age-induced cardiac hypertrophy, recombinant GDF11 was delivered daily via intraperitoneal injection for 30 days to aged mice. GDF11 administration led to a significant decline in weight and left ventricular cross-sectional area of the aged heart, albeit not a complete reversion to that of an adult heart. That GDF11 did not achieve complete revision of hypertrophy may be due to technical reasons, such as non-uniform access of the injected protein to the cardiomyocytes, or biological reasons, such as non-overlapping signalling pathways that control cardiomyocyte size. Nevertheless, the fact that single growth factors can be injected into the blood stream to substantially decrease age-dependent cardiac hypertrophy is a tantalizing prospect for the treatment of human cardiac hypertrophy (Figure 1).Open in a separate windowFigure 1In adult mice, the presence of GDF11 in the systemic environment acts to restrain cardiac myocyte size. Loss of blood-borne GDF11 in aged mice drives cardiac myocyte hypertrophy. Exposure of aged mice to youthful systemic factors through parabiosis or injection of GDF11 reverses morphological and molecular markers (AMP and BNP) of age-induced cardiac hypertrophy.To test the utility of GDF11 treatment in reversing other models of cardiac hypertrophy, two different approaches were tested: (1) phenylephrine-induced hypertrophy of neonatal cardiomyocytes in vitro and (2) pressure overload, via aortic constriction of adult mouse heart. These two assays provided contrasting results; phenylephrine-induced hypertrophy as measured by protein synthesis rate (3H leucine incorporation) was prevented by prior incubation with GDF11 and its TGFβ superfamily member, Myostatin, whereas pressure overload hypertrophy was not mitigated by GFD11 treatment, administered after aortic constriction.Therefore, ageing-induced cardiac hypertrophy may have a distinct causality (decreased levels of GDF11) compared to acute models of hypertrophy in adult mice. It is also possible that additional cooperatively acting signalling pathways participate in adult hypertrophy. This would act to minimize any effects of GDF11 augmentation in adult mice. In addition, there may be a specific time window relative to hypertrophic stimuli, owing to which GDF11 treatment elicits a more favourable cellular outcome. The results presented by Loffredo et al (2013) illustrate the complexity of studying the mechanisms behind the disease pathology.Seeking to identify the source of GDF11, the authors measured GDF11 levels across different tissues. Its expression was most abundant in the adult spleen and decreased during ageing. Interestingly, GDF11 was also observed at the intercalated discs of aged hearts. A couple of questions arise from these observations. Is the adult spleen the source of cardiac GDF11 and why is the GDF11 that is located in aged hearts insufficient to protect from hypertrophy? Answering these questions will be experimentally challenging but nonetheless important.This report identifies a blood-borne factor that is abundantly expressed in adult mice and acts to repress cardiac hypertrophy. Circulatory factors have the potential to act on multiple cell types. The present study illustrates that systemic factors can influence the size of terminally differentiated cells. Does GDF11 regulate the cell size of other tissues? In contrast to the cardiac muscle, other tissues such as bone and skeletal muscle undergo atrophy during ageing; thus, it is unlikely that decreasing levels of GDF11 in the aged systemic environment function to increase the cell size of multiple tissues during ageing. However, there may be other positive roles of blood-borne GDF11 in younger mice. For example, the stimulatory effect of youthful systemic factors on tissue regeneration may involve GDF11.A picture is beginning to emerge whereby multiple factors found in adult (GDF11) and aged (TGFβ2, Complement C1q and CCL11) serum can alter cell function (Villeda et al, 2011; Naito et al, 2012; Loffredo et al, 2013). In addition, it is apparent that the aged niche becomes deregulated, leading to a loss of stem cell homeostasis (Chakkalakal et al, 2012). Future work should focus on understanding how distinct factors from the systemic environment and the microenvironment integrate to dictate cellular outcome across different tissues during ageing.     

WFIKKN1 and WFIKKN2 bind growth factors TGFβ1, BMP2 and BMP4 but do not inhibit their signalling activity

WFIKKN1 and WFIKKN2 are large extracellular multidomain proteins consisting of a WAP domain, a follistatin domain, an immunoglobulin domain, two Kunitz-type protease inhibitor domains and an NTR domain. Recent experiments have shown that both proteins have high affinity for growth and differentiation factor (GDF)8 and GDF11. Here we study the interaction of WFIKKN proteins with several additional representatives of the transforming growth factor (TGF)β family using SPR measurements. Analyses of SPR sensorgrams suggested that, in addition to GDF8 and GDF11, both WFIKKN proteins bind TGFβ1, bone morphogenetic protein (BMP)2 and BMP4 with relatively high affinity (K(d) ～ 10(-6) m). To assess the biological significance of these interactions we studied the effect of WFIKKN proteins on the activity of GDF8, GDF11, TGFβ1, BMP2 and BMP4 using reporter assays. These studies revealed that WFIKKN1 and WFIKKN2 inhibited the biological activity of GDF8 and GDF11 in the nanomolar range, whereas they did not inhibit the activities of TGFβ1, BMP2 and BMP4 even in the micromolar range. Our data indicate that WFIKKN proteins are antagonists of GDF8 and GDF11, but in the case of TGFβ1, BMP2 and BMP4 they function as growth factor binding proteins. It is suggested that the physical association of WFIKKN proteins with these growth factors may localize their action and thus help to establish growth factor gradients in the extracellular space.     

生长分化因子15及其特异性受体GFRAL信号通路

生长分化因子 15(growth differentiation factor 15,GDF15)属于转化生长因子 β(transforming growth factor β,TGF-β)超家族的成员之一,是与转化生长因子β家族成员同源性很低的新一类二聚体多肽.GDF15最初发现于活化的巨噬细胞中,可通过2种不同的细...