SIRT1-activating Compounds Research Articles

Rejuvenating SIRT1 Activators

Whether the red wine component resveratrol directly activates the NAD(+)-dependent protein deacetylase SIRT1 has been debated. A recent study by Hubbard etal. (2013) strengthens the case that SIRT1-activating compounds (STACs) function as positive allosteric regulators of SIRT1 and thereby regulate mitochondrial function.

Activation of SIRT1 by Resveratrol requires lamin A

Resveratrol, a compound enriched in red grape skin, has been reported to increase lifespan in yeast, worms and flies and enhance healthspan in rodents. Beneficial effects of resveratrol have been reported in aging-related cataracts, bone loss, neurodegeneration, obesity and diabetes. Resveratrol induces multiple genes expression mimicking caloric restriction (CR), which is the most conserved longevity-promoting manipulation across species [1]. Resveratrol intake conferred metabolic changes similar as CR in obese individuals [2]. Short-term consumption of resveratrol achieved a similar effect of CR [3]. In 2004, David Sinclair's group from Harvard Medical School in Boston identified resveratrol for the first time as a “direct” activator of SIRT1 using a fluorophore-conjugated synthetic peptide as targets [4]. SIRT1 is a NAD+-dependent protein deacetylase and regulates various metabolic pathways. Loss of SIRT1 abolishes many beneficial effects of CR, while transgenic mice with additional copies of SIRT1 show phenotypes resembling CR [5]. Over the past several years, CR-mimicking properties of resveratrol and SIRT1 have attracted considerable efforts in searching for resveratrol mimics. Based on the same screening strategy, researchers in Sirtris Pharmaceuticals found more than 5,000 SIRT1-activating compounds (STACs). One of the most characterized is SRT1720, which exhibits more than 1000-fold increase in SIRT1-activating potential compared with resveratrol and elicits similar CR-mimicking beneficial effects as resveratrol does [6]. However, in 2005, two independent groups reported that resveratrol only specifically enhances SIRT1 activity towards the fluorophore-conjugated rather than the unmodified synthetic peptide. This notion was later confirmed by other independent groups, showing that resveratrol and SRT1720 do not confer any SIRT1 activation towards its full-length native target proteins, including p53 and PGC-1α [7]. Although whether and how resveratrol activates SIRT1 remain unclear, many of its in vivo benefits have been shown to be dependent on SIRT1. In the current issue of Cell Metabolism (Volume 16, Issue 6, 738-750, 5 December 2012), we reported thatlamin A directly binds to SIRT1 and serves as an endogenous activator of SIRT1. Resveratrol treatment activates SIRT1 in vivo, ameliorates progeroid features and extends lifespan in a Hutchinson-Gilford progeria syndrome (HGPS) mouse model, Zmpste24 null mice. Lamin A, encoded by the LMNA gene, is a major component of the nuclear lamina and nuclear matrix, a filamentous nucleoskeleton critical for maintenance of nuclear structure. In HGPS cells where substantial amount of lamin A is replaced with progerin [8], SIRT1 deacetylase activity was significantly reduced due to decreased association of SIRT1 with nuclear matrix. In vivo and in vitro experiments revealed that the binding of lamin A to SIRT1 protein is critical to SIRT1 activation. As only lamin A but not lamin C interacts with SIRT1, the C-terminal specific domain of lamin A is most likely responsible for the interaction; and the farnesylated carboxyl tail in progerin and prelamin A might interfere with the interaction as well as the activation of SIRT1. Although how resveratrol activates SIRT1 is still unclear, it is likely that the binding of lamin A with SIRT1 has an allosteric effect on SIRT1 conformation which exposes active site of SIRT1 deacetylase to it native substrates. In an effort to further investigate whether lamin A serves as a co-factor of resveratrol in the activation of SIRT1, we found that resveratrol alone does not activate SIRT1 towards its native target, e.g. full-length acetyl p53. Instead, resveratrol enhances the binding of SIRT1 to lamin A and thus increases SIRT1 deacetylase activity. One possible explanation is that resveratrol might modulate the SIRT1 conformation, thus increasing the binding of SIRT1 to lamin A and enhancing its deacetylase activity. An alternate explanation could be that resveratrol bridges new interacting domains of lamin A and SIRT1. In any case lamin A might serve as an allosteric effector of SIRT1. Given that the C-terminal 80 amino acids of lamin A exhibits higher potential in activating SIRT1, it is also possible that the remaining part of lamin A might impose a conformational barrier for SIRT1 activation, and resveratrol might lead to allosteric changes in the lamin A-SIRT1 complex and thus further activate SIRT1. Nevertheless, the present finding provides direct evidence that resveratrol works through Lamin A in activating SIRT1 and suggests a therapeutic strategy based on SIRT1 pathway for HGPS. Also provided is a screening strategy for SIRT1-activating/inhibiting compounds based on the interaction between lamin A and SIRT1 and SIRT1-activating property of lamin A. Since the increase in SIRT1 deacetylase activity also confers beneficial effects on various mouse models mimicking human metabolic or degenerative diseases, such as obesity, diabetes and Alzheimer Diseases, SIRT1-activating compounds could benefit human patients suffering from various metabolic and aging-related degenerative diseases. On the other hand, SIRT1 protein is found upregulated in various human cancers and SIRT1-inhibiting compounds can be used to treat human malignancies.

Sirtuins, aging and diseases

SIR2 and related genes (sirtuins) are NAD-dependent deacetylases that link metabolism, protein acetylation and aging in a variety of species. Sirtuins are also involved in the longevity conferred by dietary or calorie restriction (CR). The mammalian sirtuins SIRT1-7 are involved in changes in stress resistance and metabolism that are triggered by CR, which not only extends life span, but also protects against many diseases of aging. In this talk, I will describe how mamamlian SIRT1 impacts tissue metabolism and diseases by deacetylating nuclear transcription factors that govern key physiological pathways. I will also describe new data from several labs showing that the mitochondrial sirtuin SIRT3 suppresses reactive oxygen species (ROS) in mitochondria and thus links sirtuins, calorie restriction, ROS, mitochondria and aging. The effect of SIRT3 on mitochondrial generated ROS further regulates the key nuclear transcription factor HIF-1α, and may thus govern the metabolic reprogramming (Warburg effect) in cancer. Finally, I will touch upon recent progress in trying to understand the mechanism of action of SIRT1-activating compounds, which are currently in numerous human clinical trials. Supported by NIA & Glenn Foundation for Medical Research. LG consults for Sirtris/GSK.

Oral Resveratrol Reduces Neuronal Damage in a Model of Multiple Sclerosis

Neuronal loss in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), correlates with permanent neurological dysfunction. Current MS therapies have limited the ability to prevent neuronal damage. We examined whether oral therapy with SRT501, a pharmaceutical grade formulation of resveratrol, reduces neuronal loss during relapsing-remitting EAE. Resveratrol activates SIRT1, an NAD+-dependent deacetylase that promotes mitochondrial function. Oral SRT501 prevented neuronal loss during optic neuritis, an inflammatory optic nerve lesion in MS and EAE. SRT501 also suppressed neurological dysfunction during EAE remission, and spinal cords from SRT501-treated mice had significantly higher axonal density than vehicle-treated mice. Similar neuroprotection was mediated by SRT1720, another SIRT1-activating compound; and sirtinol, an SIRT1 inhibitor, attenuated SRT501 neuroprotective effects. SIRT1 activators did not prevent inflammation. These studies demonstrate that SRT501 attenuates neuronal damage and neurological dysfunction in EAE by a mechanism involving SIRT1 activation. SIRT1 activators are a potential oral therapy in MS.

SIRT1 Activation by Small Molecules: KINETIC AND BIOPHYSICAL EVIDENCE FOR DIRECT INTERACTION OF ENZYME AND ACTIVATOR

SIRT1 is a protein deacetylase that has emerged as a therapeutic target for the development of activators to treat diseases of aging. SIRT1-activating compounds (STACs) have been developed that produce biological effects consistent with direct SIRT1 activation. At the molecular level, the mechanism by which STACs activate SIRT1 remains elusive. In the studies reported herein, the mechanism of SIRT1 activation is examined using representative compounds chosen from a collection of STACs. These studies reveal that activation of SIRT1 by STACs is strongly dependent on structural features of the peptide substrate. Significantly, and in contrast to studies reporting that peptides must bear a fluorophore for their deacetylation to be accelerated, we find that some STACs can accelerate the SIRT1-catalyzed deacetylation of specific unlabeled peptides composed only of natural amino acids. These results, together with others of this study, are at odds with a recent claim that complex formation between STACs and fluorophore-labeled peptides plays a role in the activation of SIRT1 (Pacholec, M., Chrunyk, B., Cunningham, D., Flynn, D., Griffith, D., Griffor, M., Loulakis, P., Pabst, B., Qiu, X., Stockman, B., Thanabal, V., Varghese, A., Ward, J., Withka, J., and Ahn, K. (2010) J. Biol. Chem. 285, 8340–8351). Rather, the data suggest that STACs interact directly with SIRT1 and activate SIRT1-catalyzed deacetylation through an allosteric mechanism.

SIRT1 and caloric restriction: an insight into possible trade-offs between robustness and frailty

This review aims to summarize the importance of the mammalian nicotinamide adenine dinucleotide (NAD)-dependent deacetylase SIRT1 as a critical mediator that coordinates metabolic responses to caloric restriction and the recent progress in the development of SIRT1-targeted caloric restriction mimetics. It also discusses possible trade-offs between robustness and frailty in caloric restriction and the applicability of caloric restriction or SIRT1-targeted caloric restriction mimetics to humans. Loss-of-function and gain-of-function mouse studies have provided genetic evidence that SIRT1 is a key mediator that orchestrates the physiological response to caloric restriction. SIRT1-activating compounds function as potential caloric restriction mimetics, at least in part, through the activation of SIRT1 in vivo. Increasing SIRT1 dosage/activity is effective to provide significant protection from high-fat diet-induced metabolic complications, suggesting that SIRT1 activation likely promotes robustness in the regulation of metabolism. However, caloric restriction itself and caloric restriction mimicry through systemic SIRT1 activation might also generate frailty in response to unexpected environmental stimuli, such as bacterial and viral infections. It will be of great importance to understand the principles of systemic robustness and its spatial and temporal dynamics for the regulation of aging and longevity in mammals in order to achieve an optimal balance between robustness and frailty in our complex physiological system.

SIRT1 deacetylase protects against neurodegeneration in models for Alzheimer's disease and amyotrophic lateral sclerosis.

A progressive loss of neurons with age underlies a variety of debilitating neurological disorders, including Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), yet few effective treatments are currently available. The SIR2 gene promotes longevity in a variety of organisms and may underlie the health benefits of caloric restriction, a diet that delays aging and neurodegeneration in mammals. Here, we report that a human homologue of SIR2, SIRT1, is upregulated in mouse models for AD, ALS and in primary neurons challenged with neurotoxic insults. In cell-based models for AD/tauopathies and ALS, SIRT1 and resveratrol, a SIRT1-activating molecule, both promote neuronal survival. In the inducible p25 transgenic mouse, a model of AD and tauopathies, resveratrol reduced neurodegeneration in the hippocampus, prevented learning impairment, and decreased the acetylation of the known SIRT1 substrates PGC-1alpha and p53. Furthermore, injection of SIRT1 lentivirus in the hippocampus of p25 transgenic mice conferred significant protection against neurodegeneration. Thus, SIRT1 constitutes a unique molecular link between aging and human neurodegenerative disorders and provides a promising avenue for therapeutic intervention.