最大化寿命和健康跨度: 多种方法都融合在自噬

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Maximizing Longevity and Healthspan: Multiple Approaches All Converging on Autophagy

Our understanding of the molecular basis of aging has greatly increased over the past few decades. In this review, we provide an overview of the key signaling pathways associated with aging, and whose modulation has been shown to extend lifespan in a range of model organisms. We also describe how these pathways converge onto autophagy, a catabolic process that functions to recycle dysfunctional cellular material and maintains energy homeostasis. Finally, we consider various approaches of therapeutically modulating these longevity pathways, highlighting exercise as a potent geroprotector.

在过去的几十年里,我们对衰老的分子基础的了解大大增加了。在这篇综述中,我们提供了与衰老相关的关键信号通路的概述,它们的调节已被证明在一系列模式生物中延长寿命。我们也描述了这些通路如何汇聚到自噬,一个分解代谢过程,功能回收功能失调的细胞物质和维持能量稳态。最后,我们考虑了各种治疗性调节这些长寿途径的方法,强调运动是一种有效的老年保护剂。

Introduction

引言

In the past two decades, the molecular signatures of aging have been started to be uncovered. A remarkable conservation of these cell signaling pathways has been shown across various invertebrate and vertebrate species (Kenyon, 2010). Autophagy is a cellular process that has emerged as a nexus at which these various pathways have been shown to converge. Autophagy is the catabolic process by which the cell eliminates unnecessary cellular components to maintain energy homeostasis and prevent the build-up of toxic material. There are three forms of autophagy—macroautophagy, microautophagy, and chaperone-mediated autophagy. In this review, we will only discuss macroautophagy (which we will henceforth refer to simply as “autophagy”). This review will provide an overview of the cell signaling pathways that are associated with longevity, and discuss how they all converge onto autophagy. We will also discuss how established anti-aging approaches including exercise, caloric restriction, and pharmaceutical therapeutics affect these pathways to regulate autophagy in ways that are geroprotective and possibly longevity-enhancing.

在过去的二十年里,衰老的分子特征已经开始被发现。在各种无脊椎动物和脊椎动物物种中,这些细胞信号通路的保护显得尤为重要(凯尼恩,2010)。细胞自噬是一个细胞过程,已经成为各种途径汇聚的纽带。自噬是一种分解代谢过程,细胞通过消除不必要的细胞成分来维持能量稳态,防止有毒物质的积累。自噬有三种形式: 大自噬、微自噬和伴侣介导的自噬。在这篇综述中,我们将只讨论宏观自噬(我们今后将简称为“自噬”)。本综述将提供与寿命相关的细胞信号通路的概述,并讨论它们如何全部汇聚到自噬。我们还将讨论现有的抗衰老方法,包括运动、热量限制和药物治疗,如何影响这些途径,以调节自噬的方式保护老年人,并可能延长寿命。

Evidence That Autophagy is Associated With and Necessary for Longevity

自噬与长寿有关并且对长寿有必要的证据

Autophagic activity has been shown to decline with age in various animal models. For example, body-wide quantification of autophagic flux in Caenorhabditis elegans revealed a general decline in activity in various tissues, including the intestine and neurons (Chang et al., 2017). A similar decline in function has been observed in mammals. For example, electron microscopy analysis of aged mouse livers revealed a depression in the rate of autophagic vesicle formation (Terman, 1995).

在各种动物模型中,自噬活性已经显示出随着年龄的增长而下降。例如,全身自噬通量的定量分析显示,在秀丽隐桿线虫,包括肠和神经元在内的各种组织的活性普遍下降。在哺乳动物身上也观察到类似的功能衰退。例如,对老年小鼠肝脏的电子显微镜分析显示,自噬囊泡形成的速率下降(Terman,1995)。

Various groups have identified a necessary role of autophagy in mediating the effects of longevity-enhancing mutations. The Levine group was the first to demonstrate that inhibiting autophagy in a long-lived mutant model nullifies the longevity-promoting effects of the mutation. C. elegans worms that carry a loss-of-function mutation in their daf-2 gene [which encodes for a common single insulin/Insulin-like Growth Factor (IGF)-1 Receptor in this organism] live significantly longer than their wild-type counterparts. They demonstrated that RNAi-mediated knockdown of the autophagy gene bec-1 significantly reduced the lifespan of the daf-2 mutants, clearly identifying autophagy as a process that is required for the increased longevity of this mutant (Melendez et al., 2003).

不同的研究小组已经确定了自噬在介导长寿增强基因突变效应中的必要作用。Levine 小组是第一个证明在长寿的突变体模型中抑制自噬取消了突变的延长寿命作用的小组。携带 daf-2基因突变的线虫[编码该生物体中共同的胰岛素/胰岛素样生长因子 -1受体]比野生型线虫活得更长。他们证明,rna 干扰介导的自噬基因 bec-1的敲除显著降低了 daf-2突变体的寿命,清楚地确定了自噬作为延长该突变体寿命所需的过程(Melendez 等人,2003年)。

To demonstrate a causal relationship between autophagy and longevity, some groups have evaluated the effects of overexpressing autophagy genes. A positive relationship between autophagic activity and lifespan was first demonstrated in Drosophila. Neuron-specific overexpression of the Atg8a gene resulted both in an increase in lifespan and a reduction in the accumulation of toxic protein aggregates in neurons (Simonsen et al., 2008). Similarly, body-wide overexpression of Atg5 resulted in a significant increase in lifespan in mice (Pyo et al., 2013). Increase in autophagy via disruption of the beclin1-BCL2 complex has been shown to promote both healthspan and lifespan in mice (Fernandez et al., 2018).

为了证明自噬与长寿之间的因果关系,一些研究小组评估了过度表达自噬基因的影响。自噬活性与寿命之间的正相关关系首次在果蝇身上得到证实。Atg8a 基因的神经元特异性过度表达导致了寿命的延长和神经元中毒性蛋白聚集体积累的减少(Simonsen 等人,2008年)。类似地,Atg5的全身过度表达导致了小鼠寿命的显著延长(Pyo 等人,2013)。通过破坏 beclin1-BCL2复合物增加自噬已被证明可以促进小鼠的健康寿命(Fernandez 等人,2018)。

Autophagy and the Hallmarks of Aging

自噬与衰老的标志

Guido Kroemer and colleagues have recently published an excellent overview of the molecular underpinnings of aging, in which they enumerate the following nine hallmarks of aging—genomic instability, telomere shortening, epigenetic alterations, loss of proteostasis, dysregulated nutrient sensing, mitochondrial dysfunction, cell senescence, stem cell loss, and altered intercellular communication (Lopez-Otin et al., 2013). Remarkably, autophagy has been shown to be intimately involved in nearly all of these processes. Autophagy can mitigate the effects of genomic instability by reducing the production of DNA-damaging reactive oxygen species (ROS) production, and by promoting the recycling of DNA repair proteins (Vessoni et al., 2013). Although autophagy is unable to revert or stall telomere attrition, recent work has shown that telomere dysfunction directly stimulates autophagy to promote the death of precancerous cells (Nassour et al., 2019). While autophagy is not thought to have a direct relationship with epigenetic alterations, it has canonical roles in maintaining proteostasis (Kern and Behl, 2019), nutrient sensing (Dagon et al., 2015), and mitochondrial health via mitophagy (Palikaras et al., 2018). While the relationship between autophagy and senescence is complex and requires further disentangling, autophagy has been shown to play an essential role in the maintenance of stem cells (Boya et al., 2018). Finally, autophagy maintains proper immune function (a key component of intercellular communication) by preserving phagocytic activity and controlling levels of inflammation (Cuervo and Macian, 2014). In summary, autophagy has been shown to counter the effects of the majority of the presented hallmarks of aging.

Guido Kroemer 和他的同事最近发表了一篇关于衰老的分子基础的优秀综述,其中他们列举了衰老的以下九个特征: 基因组不稳定、端粒缩短、表观遗传改变、蛋白质平衡失调、营养失调感知、线粒体功能障碍、细胞衰老、干细胞丢失和细胞间通讯改变(Lopez-Otin et al. 2013)。值得注意的是,自噬与几乎所有这些过程都密切相关。自噬可以减轻基因组不稳定的影响,通过减少生产的 DNA 损伤性活性氧类(ROS) ,并通过促进循环的 DNA 修复蛋白(Vessoni 等人,2013年)。虽然自噬不能恢复或阻止端粒的消耗,但最近的研究表明端粒功能障碍直接刺激自噬,从而促进癌前细胞的死亡(Nassour et al. 2019)。虽然自噬被认为与表观遗传改变没有直接关系,但它在维持蛋白质平衡(Kern and Behl,2019)、营养感知(Dagon et al. ,2015)和线粒体健康(mitophaggy,2018)方面有典型作用。虽然自噬和衰老之间的关系是复杂的,需要进一步的解释,自噬已被证明在干细胞的维持中发挥了重要作用(Boya 等人,2018)。最后,自噬通过保持吞噬活性和控制炎症水平来维持正常的免疫功能(细胞间通讯的关键组成部分)。总之,自噬已经被证明可以对抗大多数衰老特征的影响。

Longevity Pathways and Autophagy

长寿途径与细胞自噬

Four well-studied pathways that are known to regulate aging, and whose modulation has been shown to influence the rate of aging are Insulin/IGF-1, mechanistic target of rapamycin (mTOR), AMP-activating protein kinase (AMPK), and Sirtuin pathways (Kenyon, 2010). In this section, we will discuss the relationship between each of these pathways and longevity, their effects on autophagy, and the effects of aging and exercise on these pathways with respect to autophagy. Figure 1 illustrates how these various pathways converge onto, and activate, autophagy.

四种已知的调节衰老的研究得很好的途径是胰岛素/igf-1、雷帕霉素机械靶标(mTOR)、 AMPK 和 Sirtuin 途径(Kenyon,2010)。在这一部分,我们将讨论这些途径与长寿之间的关系,它们对自噬的影响,以及衰老和运动对这些途径在自噬方面的影响。图1说明了这些不同的通路是如何汇聚并激活自噬的。FIGURE 1 图1

Figure 1. The influence of exercise on cell signaling pathways that regulate autophagy. This figure shows how various pathways associated with longevity converge onto autophagy, and how exercise influences these pathways. Also indicated are the nodes upon which Metformin, Rapamycin, and Resveratrol are thought to act. Please see text for details.

图1。运动对调节自噬的细胞信号通路的影响。这幅图显示了与长寿相关的各种通路如何汇聚到自噬上,以及运动如何影响这些通路。还指出节点二甲双胍,雷帕霉素和白藜芦醇被认为是行动。详情请参阅文字。

Insulin/IGF-1 Signaling (IIS)

胰岛素/胰岛素样生长因子 -1信号通路(IIS)

IIS and Longevity

IIS 与寿命

The insulin/IGF-1 (IIS) pathway was the first pathway to be shown to affect aging (Kenyon et al., 1993). C. elegans worms with a loss-of-function mutation in their daf-2 gene experienced a >2-fold extension in lifespan compared to wild-type. Inhibition of this pathway in vertebrate models has also been shown to extend lifespan, but to a lesser degree and in a more inconsistent manner. Female 129/SvPas mice heterozygous for the IGF-1 receptor null allele (Igf1r+/−) have been shown to live significantly longer (33%) than wild-type females, while male mutant mice demonstrated no such lifespan enhancing benefits (Holzenberger et al., 2003). Subsequent work has demonstrated that these benefits are strain dependent, as female C57BL/6J Igf1r+/− mice experienced a more modest (albeit significant) increase in lifespan compared to wild-type controls (Xu et al., 2014). In contrast, both male and female fat-specific insulin receptor knockout (FIRKO) mice showed a significant increase in lifespan (Bluher et al., 2003), possibly indicating that insulin signaling is more relevant to longevity than IGF-1 signaling. Alternatively, perhaps these differences between C. elegans and mice can be attributed to the fact that daf-2 encodes for a receptor that shows significant homology to both the IGF-1 receptor and the insulin receptor (Kimura et al., 1997), suggesting that dual knockout (or knockdown) of these receptors is necessary to achieve enhanced lifespan extension. In support of this supposition is the finding that both male and female mice that are null for the insulin receptor substrate protein 1 (Irs1)experienced significant extensions in lifespan (Selman et al., 2011). Irs1 is an adaptor protein that mediates the actions of both insulin and IGF-1.

胰岛素/胰岛素样生长因子 -1(IIS)途径是第一个被证明影响衰老的途径(Kenyon 等人,1993)。与野生型相比,秀丽线虫 daf-2基因功能缺失突变的寿命延长了2倍以上。在脊椎动物模型中,这一通路的抑制也被证明可以延长寿命,但程度较轻,而且方式更不一致。雌性129/SvPas 小鼠 IGF-1受体缺失等位基因(Igf1r +/-)的杂合子显示比野生型雌性小鼠活得更长(33%) ,而雄性突变小鼠则没有这种延长寿命的好处(Holzenberger 等人,2003年)。随后的研究表明,这些益处是依赖于应变的,因为雌性 C57BL/6J Igf1r +/-小鼠的寿命比野生型对照组有了更适度的延长(尽管显著)(Xu et al. ,2014)。相比之下,雄性和雌性脂肪特异性胰岛素受体基因敲除(FIRKO)小鼠的寿命都显著延长(Bluher et al. 2003) ,这可能表明胰岛素信号比 IGF-1信号更能延长寿命。另外,也许这些秀丽隐杆线虫和小鼠之间的差异可以归因于 daf-2编码一个受体,这个受体与 IGF-1受体和胰岛素受体有明显的同源性,这表明这些受体的双重敲除(或击倒)对延长寿命是必要的。支持这一假设的发现是,无论是雄性还是雌性小鼠的胰岛素受体底物蛋白1(Irs1)都经历了明显的寿命延长(Selman 等人,2011)。Irs1是一种调节胰岛素和 IGF-1作用的适配蛋白。

Effects of IIS on Autophagy

IIS 对细胞自噬的影响

The C. elegans daf-2 mutants exhibit a pronounced increase in autophagic activity compared to wild-type worms, indicating that the IIS pathway suppresses autophagy (Hansen et al., 2008). Indeed, activation of the IIS pathway is known to inhibit autophagy via the activation of mTORC1 and inhibition of FoxO signaling. FoxO proteins are transcription factors whose translocation to the nucleus is blocked via phosphorylation of Akt, which is a key kinase in the IIS pathway (Sandri et al., 2004). Under conditions of nutrient deprivation (and suppressed IIS), FoxO3 upregulates autophagy by promoting the expression of autophagy-related genes, including LC3, Bnip3, and Beclin1 (Mammucari et al., 2007Zhao et al., 2007).

与野生型蠕虫相比,线虫 daf-2突变体显示出自噬活性的显著增加,这表明 IIS 途径抑制了自噬(Hansen et al. 2008)。事实上,IIS 通路的激活通过 mTORC1的激活和 FoxO 信号的抑制来抑制自噬。FoxO 蛋白是一种转录因子,其转运到细胞核的过程通过 Akt 的磷酸化被阻断,Akt 是 IIS 途径中的一个关键激酶(Sandri 等,2004)。在营养缺乏(和抑制 IIS)条件下,FoxO3通过促进自噬相关基因的表达上调自噬,包括 LC3,Bnip3,和 Beclin1(Mammucari 等人,2007; 赵等人,2007)。

Effects of Age on IIS

年龄对 IIS 的影响

As people age they enter a stage known as somatopause, during which they experience a decline in circulating growth hormone (GH) and IGF-1 levels (Junnila et al., 2013). Somatopause has also been detected in other mammals (Bartke, 2008). Paradoxically, centenarians have been shown to have significantly lower levels of circulating IGF-1 (Bonafe et al., 2003). Additionally, the offspring of centenarians have been shown to have both lower levels of circulating IGF-1 and lower IGF-1 activity compared to controls whose parents both died relatively young (Vitale et al., 2012). Perhaps the potential negative effects of lower GH/IGF-1 levels (e.g., lower levels of anabolism) are offset by a less pronounced decline in systemic autophagic activity. In support of this idea, healthy centenarians have been shown to have significantly higher levels of circulating beclin-1 compared to both young patients who have experienced an acute myocardial infarction and healthy young controls (Emanuele et al., 2014). This observation has been independently confirmed in a recent study that also showed a general increase in the expression of genes in the autophagy-lysosomal pathway in centenarians (Xiao et al., 2018).

随着人们年龄的增长,他们进入一个被称为生长顶的阶段,在此期间他们经历循环生长激素(GH)和 IGF-1水平的下降(Junnila 等人,2013年)。在其他哺乳动物中也发现了生体层顶(Bartke,2008年)。矛盾的是,百岁老人的血液中 IGF-1的水平显著降低(Bonafe 等人,2003)。此外,百岁老人的后代已被证明,与父母相对年轻死亡的对照组相比,他们的血液中 IGF-1水平和 IGF-1活性都较低(Vitale 等人,2012年)。也许 GH/IGF-1水平降低的潜在负面影响(例如,合成代谢水平降低)被系统性自噬活性的降低所抵消。为了支持这个观点,健康的百岁老人已经被证明比那些经历过心肌梗死和健康的年轻对照组的年轻患者有更高水平的循环 beclin-1(Emanuele et al. 2014)。这一观察在最近的一项研究中得到了独立的证实,该研究还表明,在百岁老人的自噬-溶酶体途径中,基因的表达普遍增加(Xiao 等人,2018)。

Unlike IGF-1, circulating insulin levels generally increase with age. Aging is associated with hyperinsulinemia and insulin resistance that are caused by greater secretion of insulin in response to the same stimulus compared to younger individuals (Gumbiner et al., 1989). In contrast, centenarians have been shown to exhibit both a lower degree of insulin resistance and preserved β-cell function (Paolisso et al., 2001). Additionally, increased insulin sensitivity and lower mean fasting insulin levels have been observed in the offspring of nonagenarians compared to their partners (Rozing et al., 2010). A causal relationship between higher circulating insulin levels and decreased hepatic autophagy has been demonstrated in mice (Liu et al., 2009).

与 IGF-1不同,循环胰岛素水平通常随着年龄的增长而增加。衰老与高胰岛素血症和胰岛素抵抗相关,这是由于相同刺激作用下较年轻的个体产生更多的胰岛素分泌而引起的(Gumbiner et al. ,1989)。相反,百岁老人表现出较低程度的胰岛素抵抗和保持 β 细胞功能(Paolisso et al. 2001)。此外,与他们的伴侣相比,90岁以上老人的后代胰岛素敏感性增加,平均空腹胰岛素水平降低。高循环胰岛素水平和减少小鼠肝脏自噬之间的因果关系已经得到证实(Liu 等人,2009)。

In summary, aging is associated with decreasing levels of autophagic activity that are partially the result of dysregulated IIS. Healthy centenarians, who do not experience the typical effects of normal aging, display both enhanced autophagy and better-preserved and regulated IIS.

综上所述,年龄增长与自噬活性降低有关,而自噬活性降低部分是由于 IIS 调节失调所致。健康的百岁老人,没有经历正常老化的典型影响,表现出增强的自噬和更好的保存和调节的 IIS。

Effects of Exercise on IIS

运动对 IIS 的影响

There is strong evidence to suggest that exercise promotes both healthspan and lifespan in worms (Chuang et al., 2016), flies (Piazza et al., 2009), and mammals (Cartee et al., 2016). In association, there is extensive evidence that indicates that exercise effectively suppresses insulin resistance and hyperinsulinemia (Ryan, 2000). Various population studies have shown inverse associations between physical activity and the incidence of type 2 diabetes mellitus, and both regular aerobic and resistance exercise have been recommended by the American Diabetes Association, especially for patients with type 2 diabetes (Colberg et al., 2016). Vigorous endurance exercise has been shown to decrease plasma insulin concentration and increase insulin sensitivity in subjects in their 60 s (Kirwan et al., 1993). A recent study has shown that a more gentle exercise regimen involving 20 min of resistance band exercise and 30 min of walking three times a week for 12 weeks is sufficient to improve insulin resistance in elderly women aged 70–80 years (Ha and Son, 2018). Mechanistically, one of the ways in which exercise is thought to increase insulin sensitivity is via contraction-stimulated glucose uptake, which involves the activation of AMPK. Importantly, exercise has also been shown to promote systemic autophagy (He et al., 2012). Perhaps acute exercise counteracts the autophagy-suppressing effects of IIS via the activation of autophagy promoters (such as AMPK), and regular exercise maintains long-term autophagic activity via preservation of insulin sensitivity and the consequent reduction in circulating insulin levels. Finally, the insulin sensitizing role of exercise-regulated myokines is discussed in a later section.

有强有力的证据表明,运动可以促进蠕虫(Chuang et al. ,2016)、苍蝇(Piazza et al. ,2009)和哺乳动物(Cartee et al. ,2016)的健康寿命。有大量证据表明,运动有效地抑制胰岛素抵抗和高胰岛素血症(Ryan,2000)。各种人群研究表明,体育活动与2型糖尿病发病率之间存在负相关关系,美国糖尿病协会建议定期进行有氧运动和抗阻运动,特别是对2型糖尿病患者。剧烈的耐力运动已被证明可以降低血浆胰岛素浓度和增加60岁受试者的胰岛素敏感性(Kirwan 等人,1993)。最近的一项研究表明,较为温和的运动方案包括20分钟的抗性带运动和30分钟的步行,每周三次,共12周,足以改善70-80岁老年妇女的胰岛素抗性(Ha and Son,2018)。机制上,运动被认为可以增加胰岛素敏感性的方法之一是通过收缩刺激葡萄糖摄取,其中包括 AMPK 的激活。重要的是,运动也被证明能促进系统性自噬(He et al. 2012)。也许急性运动通过激活自噬启动子(例如 AMPK)抵消了 IIS 的自噬抑制作用,定期运动通过保持胰岛素敏感性和随之降低的循环胰岛素水平维持长期的自噬活性。最后,运动调节肌浆网的胰岛素增敏作用将在后面部分讨论。

mTOR

mTOR and Longevity

mTOR 与长寿

As with the IIS pathway, inhibition of mTOR results in increased longevity. C. elegans deficient in TOR, like the previously-described daf-2 mutants, also displayed a doubling in lifespan (Vellai et al., 2003). Suppression of mTOR to ~25% of wild-type levels in mice carrying two hypomorphic mTOR alleles has also been shown to significantly extend median lifespan in both male and female mice (Wu et al., 2013). However, these mice experience lifespan extension of only ~20%, which approximately mirrors the lifespan extension seen in mice with suppressed IIS, as previously noted.

与 IIS 通路一样,mTOR 的抑制作用可以延长寿命。线虫缺乏 TOR,像先前描述的 daf-2突变体一样,也表现出寿命加倍(Vellai 等人,2003)。在携带两个弱等位基因 mTOR 的小鼠中,抑制 mTOR 到野生型水平的25% 也被证明能显著延长雄性和雌性小鼠的中位寿命(Wu 等人,2013)。然而,这些老鼠的寿命只延长了20% ,这大致反映了在抑制了 IIS 的老鼠身上所看到的寿命延长。

Effects of mTOR on Autophagy

mTOR 对细胞自噬的影响

As in the case of the daf-2 mutants, inactivation of TOR signaling in C. elegans also resulted in increased levels of autophagy, and suppression of autophagy resulted in the reversal of these lifespan-increasing effects (Hansen et al., 2008). Mechanistically, mTOR (while in the mTORC1 complex) has been shown to inhibit autophagy in two ways—via direct phosphorylation and inhibition of the autophagy-initiating kinase Ulk1 (Kim et al., 2011), and by phosphorylating transcription factor EB (TFEB) to prevent it from entering the nucleus where it can promote the expression of various autophagy and lysosomal genes (Martina et al., 2012).

与 daf-2突变体的情况一样,秀丽隐杆线虫 TOR 信号的失活也导致了自噬水平的增加,而自噬的抑制导致了这些延长寿命效应的逆转(Hansen 等人,2008年)。机制上,mTOR (而在 mTORC1复合体中)已被证明可以通过两种方式抑制自噬-通过直接磷酸化和抑制自噬启动激酶 Ulk1(Kim 等人,2011年) ,以及通过磷酸化转录因子 EB (TFEB)阻止其进入细胞核,从而促进各种自噬和溶酶体基因的表达(Martina 等人,2012年)。

Effects of Age on mTOR

年龄对 mTOR 的影响

Full activation of mTORC1 requires both growth factors (such as insulin or IGF-1) and a supply of amino acids (such as leucine, methionine, and arginine) (Saxton and Sabatini, 2017). As discussed previously, aging is associated with hyperinsulinemia, suggesting that mTORC1 activity also increases with age. Additionally, recent work has shown that the methionine metabolite, homocysteine, can also activate mTORC1 (Khayati et al., 2017). Homocysteine has been shown by various groups to accumulate with age (Selhub, 1999Tucker et al., 2005Smith and Refsum, 2016Antikainen et al., 2017), also indicating a positive correlation between aging and mTORC1 activity. Increased mTORC1 activity would therefore serve as another reason for the general decline in autophagic activity seen with age.

mTORC1的完全激活需要生长因子(如胰岛素或 IGF-1)和供应氨基酸(如亮氨酸、蛋氨酸和精氨酸)(Saxton 和 Sabatini,2017)。正如前面讨论的,衰老与高胰岛素血症有关,这表明 mTORC1活性也随着年龄增加而增加。此外,最近的研究表明,蛋氨酸代谢物,同型半胱氨酸,也可以激活 mTORC1(Khayati et al. ,2017)。同型半胱氨酸已经被不同的人群证明会随着年龄而累积(Selhub,1999; Tucker 等人,2005; Smith and Refsum,2016; Antikainen 等人,2017) ,也表明了老化和 mTORC1活性之间的正相关。因此,mTORC1活性增加可能是自噬活性普遍下降的另一个原因,这种现象随着年龄的增长而出现。

Effects of Exercise on mTOR

运动对 mTOR 的影响

Exercise has been shown to inhibit the mTORC1 pathway by reversing the phosphorylation of TFEB (Medina et al., 2015). It does so by promoting the release of Ca2+ from lysosomes via MCOLN1 resulting in local activation of calcineurin, which in turn dephosphorylates TFEB to promote its entry into the nucleus where it binds to and activates the promoters of various autophagic and lysosomal genes. Therefore, perhaps some of the lifespan-extending effects of exercise can be attributed to its effect on TFEB nuclear localization.

运动可以通过逆转 TFEB 的磷酸化来抑制 mTORC1通路(Medina 等人,2015)。它通过促进通过 MCOLN1从溶酶体释放 Ca2 + 导致钙调神经磷酸酶的局部活化,而钙调神经磷酸酶又反过来促进 TFEB 进入细胞核,在那里它结合并激活各种自噬和溶酶体基因的启动子。因此,运动延长寿命的作用可能与其对 tmb 核定位的影响有关。

AMPK

AMPK and Longevity

AMPK 与长寿

A positive correlation between AMPK activity and longevity has been demonstrated in both invertebrate and vertebrate models. C. elegans worms that lack AMPK experienced a 12% reduction in lifespan compared to wild-type worms, whereas, AMPK overexpression resulted in a 13% increase in lifespan (Apfeld et al., 2004). Female mice chronically treated with Metformin, an anti-diabetic drug that activates AMPK, experienced maximum lifespan increase of ~10% compared to control mice (Anisimov et al., 2008).

在无脊椎动物和脊椎动物模型中,AMPK 活性与寿命呈正相关。与野生型蠕虫相比,缺乏 AMPK 的线虫寿命缩短了12% ,而 AMPK 过度表达导致寿命延长了13% (Apfeld 等人,2004)。长期使用二甲双胍(一种激活 AMPK 的抗糖尿病药物)的雌性小鼠,与对照组小鼠相比,寿命增加了10% 。

Effects of AMPK on Autophagy

AMPK 对细胞自噬的影响

AMPK is a potent promoter of autophagy. Under conditions of stress, AMPK has been shown to promote autophagy via phosphorylation and subsequent stabilization of the cyclin-dependent kinase inhibitor p27Kip1 (Liang et al., 2007). During glucose starvation, AMPK promotes autophagy by phosphorylating and activating the autophagy-initiating kinase Ulk1 (Kim et al., 2011). AMPK also promotes autophagy by directly and indirectly inhibiting mTORC1. AMPK directly phosphorylates raptor (which is a member of the mTORC1 complex) resulting in a suppression of mTORC1 kinase activity (Gwinn et al., 2008). AMPK indirectly suppresses mTORC1 by phosphorylating tuberous sclerosis complex 2 (TSC2) which enhances its GAP activity (Inoki et al., 2003).

AMPK 是自噬的强有力的促进剂。在应激条件下,AMPK 已被证明通过磷酸化促进自噬,并随后稳定周期蛋白依赖性激酶抑制剂 p27Kip1(Liang 等人,2007)。在葡萄糖饥饿期间,AMPK 通过磷酸化和激活自噬启动激酶 Ulk1来促进自噬。AMPK 还通过直接和间接抑制 mTORC1促进自噬。AMPK 直接磷酸化猛禽(是 mTORC1复合体的一个成员) ,导致 mTORC1激酶活性的抑制(Gwinn 等人,2008年)。AMPK 通过磷酸化结节性硬化症蛋白2(TSC2)间接抑制 mTORC1,增强其 GAP 活性(猪木等,2003)。

Effects of Age on AMPK

年龄对 AMPK 的影响

Aging has a potent inhibitory effect on AMPK activity. Although baseline AMPK activity was comparable between young and old rats, old rats displayed a severely compromised ability to respond to activators of AMPK. Acute stimulation of AMPK via either administration of the AMPK activator AICAR or exercise was severely blunted in skeletal muscle of old rats compared to young (Reznick et al., 2007).

衰老对 AMPK 活性有明显的抑制作用。虽然基线 AMPK 活性在年轻和老年大鼠之间具有可比性,但老年大鼠对 AMPK 活化因子的反应能力严重受损。通过 AMPK 激活剂 AICAR 或运动对 AMPK 的急性刺激与年轻大鼠相比在老年大鼠的骨骼肌中被严重钝化(Reznick et al. ,2007)。

Effects of Exercise on AMPK

运动对 AMPK 的影响

Various studies have demonstrated the ability of exercise to promote AMPK activation (Kjobsted et al., 2018). One of the ways in which it does so is by increasing the intracellular ratios of AMP:ATP and ADP:ATP (Gowans and Hardie, 2014). However, it should be noted that exercise has been shown to be unable to activate AMPK in aged tissue (Reznick et al., 2007). Therefore, perhaps in order for exercise to have an effect on autophagy via this pathway, it must be initiated early in life. Additionally, Reznick et al. subjected their rats to only 5 days of treadmill exercise. Perhaps a longer term exercise regimen would be able to overcome this inability to activate AMPK.

各种各样的研究已经证明了运动促进 AMPK 激活的能力(Kjobsted et al. ,2018)。其中一种方法是通过增加细胞内 AMP: ATP 和 ADP: ATP 的比率(Gowans 和 Hardie,2014)。然而,应该指出的是,运动已被证明不能激活老化组织中的 AMPK (Reznick 等人,2007)。因此,也许为了使运动通过这一途径对自噬产生影响,运动必须在生命早期就开始。此外,Reznick 等人只让他们的老鼠进行了5天的跑步机运动。也许一个长期的运动养生法可以克服这种无法激活 AMPK 的缺点。

Sirtuins

Sirtuins and Longevity

去乙酰化酶与长寿

Sirtuins are NAD+-dependent protein deacetylases whose increased activity has been linked to lifespan extension in both invertebrates and vertebrates. Increased gene dosage of sir-2.1 in C. elegans resulted in up to a 50% increase in lifespan (Tissenbaum and Guarente, 2001). Brain-specific overexpression of the mammalian ortholog of Sirt2—Sirt1—resulted in a significant increase in median lifespan (~16% for female mice, and ~9% for male mice) compared to wild-type controls (Satoh et al., 2013).

去乙酰化酶是 NAD + 依赖的蛋白质脱乙酰化酶,其活性的增加与无脊椎动物和脊椎动物的寿命延长有关。秀丽隐杆线虫基因剂量的增加导致寿命延长了50% (Tissenbaum 和 Guarente,2001)。与野生型对照组相比,sirt2ー sirt1ー哺乳动物的大脑特异性过表达导致中位寿命显著增加(雌性小鼠增加16% ,雄性小鼠增加9%)(Satoh 等,2013)。

Effects of Sirtuins on Autophagy

去乙酰化酶对细胞自噬的影响

Sirt1 has been shown to play a role in the regulation of autophagy via direct interaction with participants in the autophagic pathway, including Atg5, Atg7, and Atg8 (Lee et al., 2008). Sirt1−/− fibroblasts show suppressed autophagy in the context of starvation and a marked elevation of acetylation of key autophagy proteins. Therefore, Sirt1 promotes autophagy via the deacetylation of proteins involved in the autophagy pathway.

Sirt1已被证明通过与参与自噬途径的参与者直接互动,包括 atg 5,atg 7和 atg 8(Lee 等人,2008) ,在自噬调节中发挥作用。Sirt1-/-成纤维细胞在饥饿状态下表现出自噬的抑制和关键自噬蛋白乙酰化水平的显著升高。因此,Sirt1通过自噬途径中蛋白质的去乙酰化促进自噬。

Effects of Age on Sirtuins

年龄对去乙酰化酶的影响

A general decline in sirtuin function with age has been observed. Reduced Sirt1 activity has been observed in the liver, heart, kidney, and lung of aged rats compared to young controls (Braidy et al., 2011). This decline in activity has been attributed to lower levels of NAD+. Similarly, a decrease in Sirt1 expression has been detected in the arteries of both mice and humans (Donato et al., 2011).

随着年龄的增长,去乙酰化酶功能普遍下降。与年轻的对照组相比,老年大鼠的肝脏、心脏、肾脏和肺脏的 Sirt1活性降低了(Braidy 等人,2011年)。活动减少的原因是 NAD + 水平较低。同样,Sirt1的表达在小鼠和人类的动脉中都有所减少(Donato 等人,2011)。

Effects of Exercise on Sirtuins

运动对去乙酰化酶的影响

Exercise has been shown to be a potent activator of sirtuins. Old rats subjected to an 8-week long regimen of treadmill exercise experienced a significant increase in Sirt1 deacetylase activity compared to both young and sedentary old rats (Ferrara et al., 2008). Similarly, both old and young human subjects experienced a significant increase in skeletal muscle Sirt1 expression after just one bout of intense treadmill exercise (Bori et al., 2012).

运动已被证明是去乙酰化酶的有效催化剂。与年轻和久坐的老年大鼠相比,经过8周跑步机锻炼的老年大鼠经历了 Sirt1去乙酰化酶活性的显著增加(Ferrara 等人,2008年)。类似地,无论老年人还是年轻人,在一轮高强度跑步机运动后,骨骼肌 Sirt1的表达都显著增加(Bori 等人,2012年)。

Does Exercise Regulate Autophagy via the Regulation of Myokine Secretion?

运动是否通过调节肌浆网分泌来调节自噬?

There is emerging evidence that skeletal muscle can regulate both systemic physiology and aging via the release of so-called “myokines” (Demontis et al., 2013). As mentioned before, exercise has the effect of promoting insulin sensitivity, and there is evidence to suggest that this effect is partially mediated by the regulation of myokine secretion. One of the most extensively studied myokines is myostatin, which belongs to the TGF-β superfamily of ligands and is a potent inhibitor of muscle mass. Myostatin has also been suggested to be a promoter of insulin resistance, and aerobic exercise has the effect of suppressing circulating levels of myostatin (Hittel et al., 2010). Conversely, exercise has been shown to promote the secretion of the myokines IL-6, IL-15, Irisin, Metrnl, and myonectin, all of which have been associated with improved insulin sensitivity (Ellingsgaard et al., 2011Barra et al., 2012Bostrom et al., 2012Rao et al., 2014Gizaw et al., 2017Jung et al., 2018Pourranjbar et al., 2018). Myokines Metrnl (Jung et al., 2018), Irisin (Li et al., 20182019), and IL-15 (Nadeau et al., 2019) activate AMPK in skeletal muscle and cardiac tissue suggesting a possible mechanism to induce autophagy throughout muscle and possibly non-muscle tissue. The role of myokines in exercise-induced autophagy has not been extensively studied. Given the emerging importance of myokines in mediating the insulin sensitizing effects of exercise, we propose that this possible role is worthy of further examination.

有新出现的证据表明,骨骼肌可以通过释放所谓的“肌酸因子”来调节系统生理和衰老(Demontis et al. ,2013)。如前所述,运动有促进胰岛素敏感性的作用,有证据表明,这种作用是部分介导的调节肌氨酸的分泌。肌肉生长抑制素是研究最广泛的肌浆网蛋白之一,属于 tgf-β 超家族配体,是一种强有力的肌块抑制剂。肌肉生长抑制素也被认为是胰岛素抵抗的促进因子,有氧训练具有抑制循环中肌肉生长抑制素水平的作用。相反,运动已被证明促进肌浆网 IL-6,IL-15,Irisin,Metrnl,和 myonectin 的分泌,所有这些都与改善胰岛素敏感性有关(Ellingsgaard 等人,2011; Barra 等人,2012; Bostrom 等人,2012; Rao 等人,2014; Gizaw 等人,2017; Jung 等人,2018; Pourranjbar 等人,2018)。Myokines metnl (Jung 等人,2018) ,Irisin (Li 等人,2018,2019) ,和 IL-15(Nadeau 等人,2019)在骨骼肌和心脏组织中激活 AMPK,这表明可能的机制诱导整个肌肉和可能的非肌肉组织的自噬。肌浆网在运动诱导的自噬中的作用还没有被广泛研究。鉴于肌浆网在调节运动的胰岛素增敏作用方面的重要性,我们认为这种可能的作用值得进一步研究。

Pharmacological Agents, Exercise, or Diet?

药物,运动,还是饮食?

Various drug candidates have been identified that can modulate each of the above pathways described. These autophagy-promoting pharmacological agents have been discussed elsewhere (Vakifahmetoglu-Norberg et al., 2015). While these agents have shown varying success in preclinical settings, certain caveats associated with them must be noted, including that they typically target just one protein or pathway, and their potentially negative side-effects have not been thoroughly examined, particularly in the setting of human biology. Alternatively, non-pharmacological approaches such as exercise and dietary interventions (such as calorie restriction) have been shown to be potent autophagy activators that effectively target all of the previously described longevity pathways. Additionally, exercise (especially moderate exercise) has few, if any, adverse side effects.

各种候选药物已经确定,可以调节每一个上述途径描述。这些促进自噬的药理因子已经在其他地方进行了讨论(Vakifahmetoglu-Norberg 等人,2015)。虽然这些药物在临床前环境中取得了不同程度的成功,但必须注意与之相关的某些注意事项,包括它们通常只针对一种蛋白质或途径,而且它们潜在的负面副作用尚未得到彻底的研究,特别是在人类生物学环境中。另外,非药理学方法,如运动和饮食干预(如卡路里限制)已被证明是强有力的自噬激活剂,有效地针对所有以前描述的长寿途径。此外,运动(特别是适度运动)几乎没有副作用。

Among the best-studied autophagy promoting agents are Metformin, Rapamycin, and Resveratrol. Metformin is a drug that is used to treat type 2 diabetes. It has been shown to promote autophagy via activation of both AMPK and Sirt1 (Zhou et al., 2001Song et al., 2015), however it is also known to have various off-target effects such as inhibition of respiratory complex I. Similarly, Resveratrol has also been shown to activate AMPK and Sirt1 (Borra et al., 2005Vingtdeux et al., 2010). However, trials in clinical settings have produced murky and sometimes contradictory findings, as described in Bitterman and Chung (2015). Rapamycin indirectly activates autophagy by inhibiting mTORC1. It is currently being tested in clinical trials as a therapy for amyotrophic lateral sclerosis (ClinicalTrials.gov Identifier: NCT03359538). Although a potent promoter of autophagy, Rapamycin treatment is associated with various negative side-effects, including immunosuppression and the potential induction of insulin resistance via off-target inhibition of mTORC2 (Saxton and Sabatini, 2017).

二甲双胍、雷帕霉素和白藜芦醇是研究得最好的自噬促进剂。二甲双胍是一种用于治疗2型糖尿病的药物。它已经被证明可以通过激活 AMPK 和 Sirt1来促进自噬(Zhou 等人,2001; Song 等人,2015) ,然而它也被认为具有各种非靶向作用,如抑制呼吸复合物 i。类似地,白藜芦醇也被证明可以激活 AMPK 和 Sirt1(Borra 等人,2005; Vingtdeux 等人,2010)。然而,正如比特曼和钟(2015)所描述的那样,在临床环境中的试验产生了模糊的、有时甚至是矛盾的结果。雷帕霉素通过抑制 mTORC1间接激活自噬。它目前正在临床试验中作为肌萎缩性嵴髓侧索硬化症的一种治疗方法( clinicaltrials.gov 标识符: NCT03359538)。虽然雷帕霉素是自噬的强有力的促进剂,但它的治疗却伴随着各种负面的副作用,包括免疫抑制和通过对 mTORC2的非靶向抑制而诱导的潜在的胰岛素抵抗。

In summary, although these and various other drugs have been shown to positively modulate autophagy and even have life-extending effects (Howitz et al., 2003Harrison et al., 2009) in animal models, there are many concerns about their potential translation to a human setting.

总之,尽管这些和其他各种药物已经被证明可以积极调节自噬,甚至在动物模型中具有延长生命的作用(Howitz 等人,2003; Harrison 等人,2009) ,但是对于它们在人类环境中的潜在转化还有许多担忧。

Calorie restriction (CR) is another intervention that has also been shown to promote longevity and beneficially modulate the previously described longevity pathways (Kenyon, 2010). Although CR holds much promise as a promoter of healthspan and lifespan, there are limited long-term studies on the effects of CR in humans. Additionally, it is not an advisable intervention for subjects wanting to maintain lean mass, such as patients with cancer-associated cachexia and elderly individuals with symptoms of sarcopenia (Galluzzi et al., 2017). Finally, life-long adherence to a CR diet, notwithstanding its potentially life-extending effects, is unlikely to be an attractive option for most people. However, in light of the therapeutic promise that CR holds, it is worth exploring alternative and more feasible ways in which it could be exploited. To that end, time-restricted feeding, which entails food consumption within a certain time window and is seen as a more easily adoptable alternative to CR, has been shown to impede the development of high fat-induced metabolic disorders such as obesity, dyslipidemia, and glucose intolerance (Chaix et al., 2019). Finally, recent studies have revealed an additive effect of exercise and CR in promoting mitochondrial health and increasing insulin sensitivity (Sharma et al., 2015Kitaoka et al., 2016).

卡路里限制是另一种已经被证明可以延长寿命并有利于调节之前描述的长寿途径的干预措施。尽管 CR 在促进健康、延长寿命方面有着广阔的应用前景,但长期研究 CR 对人类健康的影响还很有限。此外,它不是一个明智的干预对象希望保持瘦的质量,如患有癌症相关恶病质患者和老年人的症状 sarcopenia (Galluzzi 等人,2017年)。最后,终生坚持健康饮食,尽管它可能会延长寿命,但对大多数人来说不太可能是一个有吸引力的选择。然而,考虑到 CR 具有的治疗前景,值得探索其他更可行的开发途径。为了达到这个目的,时间限制的喂养,需要在一定的时间窗口内食用食物,被认为是一种更容易采用的代替 CR 的方法,已经被证明会阻碍高脂肪引起的代谢紊乱的发展,如肥胖、血脂异常和葡萄糖耐受不良。最后,最近的研究揭示了运动和 CR 在促进线粒体健康和提高胰岛素敏感性方面的叠加效应(Sharma 等,2015; Kitaoka 等,2016)。

Future Directions

未来方向

An important future research direction is a thorough assessment of the relative contribution of each of the pathways discussed in this review to autophagy regulation in individual organs and tissue systems. Significant effort has been made to show that organ-specific blockade of autophagy has deleterious effects, including skeletal muscle (Carnio et al., 2014), brain (Komatsu et al., 2007), and liver (Inami et al., 2011). However, few studies have evaluated the effects of this organ-specific inhibition on lifespan. Finally, it would be of equal importance to determine the effects of organ-specific induction of autophagy on organismal health and longevity.

一个重要的未来研究方向是彻底评估本文讨论的每个通路在个别器官和组织系统的自噬调节中的相对贡献。已经做了大量的努力来证明器官特异性阻断自噬具有有害的影响,包括骨骼肌(carino 等人,2014年) ,大脑(Komatsu 等人,2007年) ,和肝脏(Inami 等人,2011年)。然而,很少有研究评估这种器官特异性抑制对寿命的影响。最后,确定器官特异性诱导的自噬对生物体健康和长寿的影响也同样重要。

Conclusion

总结

In summary, autophagy has convincingly been shown to play a pivotal role in healthspan and lifespan extension. In this review, we have discussed various cell signaling pathways whose modulation has been shown to have beneficial effects on longevity, and how autophagy is a necessary mediator of these effects. We have also presented current pharmaceutical therapies, exercise and dietary restriction as effective ways to modulate many of these pathways to increase or preserve autophagic activity, thereby acting as a potent geroprotector.

总之,自噬已经令人信服地被证明在健康跨度和寿命延长方面发挥关键作用。在这篇综述中,我们已经讨论了各种细胞信号通路的调节已被证明对长寿有益的影响,以及自噬如何是这些影响的一个必要的介质。我们还介绍了目前的药物疗法,运动和饮食限制,作为调节许多这些途径,以增加或保存自噬活性,从而作为一个有效的老年保护者。

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