The deacetylase Sirt1 is an essential regulator of Aire-mediated induction of central immunological tolerance.

Aire is a transcriptional regulator that induces the promiscuous expression of thousands of tissue-restricted antigens (TRAs) in medullary thymic epithelial cells (mTECs), a step critical for the induction of immunological self-tolerance. Studies have offered molecular insights into how Aire operates, but more comprehensive understanding of this process still remains elusive. Here we found abundant expression of the protein deacetylase Sirtuin-1 (Sirt1) in mature Aire(+) mTECs, wherein it was required for the expression of Aire-dependent TRA-encoding genes and the subsequent induction of immunological self-tolerance. Our study elucidates a previously unknown molecular mechanism for Aire-mediated transcriptional regulation and identifies a unique function for Sirt1 in preventing organ-specific autoimmunity.

The sirtuin SIRT6 regulates lifespan in male mice.

The significant increase in human lifespan during the past century confronts us with great medical challenges. To meet these challenges, the mechanisms that determine healthy ageing must be understood and controlled. Sirtuins are highly conserved deacetylases that have been shown to regulate lifespan in yeast, nematodes and fruitflies. However, the role of sirtuins in regulating worm and fly lifespan has recently become controversial. Moreover, the role of the seven mammalian sirtuins, SIRT1 to SIRT7 (homologues of the yeast sirtuin Sir2), in regulating lifespan is unclear. Here we show that male, but not female, transgenic mice overexpressing Sirt6 (ref. 4) have a significantly longer lifespan than wild-type mice. Gene expression analysis revealed significant differences between male Sirt6-transgenic mice and male wild-type mice: transgenic males displayed lower serum levels of insulin-like growth factor 1 (IGF1), higher levels of IGF-binding protein 1 and altered phosphorylation levels of major components of IGF1 signalling, a key pathway in the regulation of lifespan. This study shows the regulation of mammalian lifespan by a sirtuin family member and has important therapeutic implications for age-related diseases.

ModuleBlast: identifying activated sub-networks within and across species.

Identifying conserved and divergent response patterns in gene networks is becoming increasingly important. A common approach is integrating expression information with gene association networks in order to find groups of connected genes that are activated or repressed. In many cases, researchers are also interested in comparisons across species (or conditions). Finding an active sub-network is a hard problem and applying it across species requires further considerations (e.g. orthology information, expression data and networks from different sources). To address these challenges we devised ModuleBlast, which uses both expression and network topology to search for highly relevant sub-networks. We have applied ModuleBlast to expression and interaction data from mouse, macaque and human to study immune response and aging. The immune response analysis identified several relevant modules, consistent with recent findings on apoptosis and NFκB activation following infection. Temporal analysis of these data revealed cascades of modules that are dynamically activated within and across species. We have experimentally validated some of the novel hypotheses resulting from the analysis of the ModuleBlast results leading to new insights into the mechanisms used by a key mammalian aging protein.

The complex role of SIRT6 in carcinogenesis.

SIRT6, a member of the mammalian sirtuins family, functions as a mono-ADP-ribosyl transferase and NAD(+)-dependent deacylase of both acetyl groups and long-chain fatty acyl groups. SIRT6 regulates diverse cellular functions such as transcription, genome stability, telomere integrity, DNA repair, inflammation and metabolic related diseases such as diabetes, obesity and cancer. In this review, we will discuss the implication of SIRT6 in the biology of cancer and the relevance to organism homeostasis and lifespan.

Self-Assembled Cyclic d,l-α-Peptides as Generic Conformational Inhibitors of the α-Synuclein Aggregation and Toxicity: In Vitro and Mechanistic Studies.

Many peptides and proteins with large sequences and structural differences self-assemble into disease-causing amyloids that share very similar biochemical and biophysical characteristics, which may contribute to their cross-interaction. Here, we demonstrate how the self-assembled, cyclic d,l-α-peptide CP-2, which has similar structural and functional properties to those of amyloids, acts as a generic inhibitor of the Parkinson's disease associated α-synuclein (α-syn) aggregation to toxic oligomers by an "off-pathway" mechanism. We show that CP-2 interacts with the N-terminal and the non-amyloid-ß component region of α-syn, which are responsible for α-syn's membrane intercalation and self-assembly, thus changing the overall conformation of α-syn. CP-2 also remodels α-syn fibrils to nontoxic amorphous species and permeates cells through endosomes/lysosomes to reduce the accumulation and toxicity of intracellular α-syn in neuronal cells overexpressing α-syn. Our studies suggest that targeting the common structural conformation of amyloids may be a promising approach for developing new therapeutics for amyloidogenic diseases.

Sirtuin 6 protects the heart from hypoxic damage.

Sirtuin 6 (SIRT6) is a protein associated with prolonged life expectancy. We investigated whether life extension is associated with cardioprotection against hypoxia. The proposed study is to develop approaches to reduce hypoxic damage through the use of the sirtuin pathway and to elucidate the mechanism involved. For that purpose we subjected cardiomyocytes from transgenic mice (TG) with over-expression of SIRT6, to hypoxic stress in cell cultures. We hypothesized that cardiomyocytes from transgenic mice subjected to prolonged hypoxia may release survival factors or fewer damage markers to protect them from hypoxic stress compared with wild type (WT) mice. Lactate dehydrogenase (LDH) and creatine kinase (CK) released to the medium and propidium iodide (PI) binding, were markedly decreased following hypoxia in TG cardiomyocytes. The protective mechanism of SIRT6 over-expression includes the activation of pAMPKα pathway, the increased protein level of B-cell lymphoma 2 (Bcl2), the inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), the decrease of reactive oxygen species (ROS) and the reduction in the protein level of phospho-protein kinase B (pAkt) during hypoxia. Together, all these processes impede the necrosis/apoptosis pathways leading to the improved survival of cardiomyocytes following hypoxia, which might explain life extension.

Role of sirtuins in lifespan regulation is linked to methylation of nicotinamide.

Sirtuins, a family of histone deacetylases, have a fiercely debated role in regulating lifespan. In contrast with recent observations, here we find that overexpression of sir-2.1, the ortholog of mammalian SirT1, does extend Caenorhabditis elegans lifespan. Sirtuins mandatorily convert NAD(+) into nicotinamide (NAM). We here find that NAM and its metabolite, 1-methylnicotinamide (MNA), extend C. elegans lifespan, even in the absence of sir-2.1. We identify a previously unknown C. elegans nicotinamide-N-methyltransferase, encoded by a gene now named anmt-1, to generate MNA from NAM. Disruption and overexpression of anmt-1 have opposing effects on lifespan independent of sirtuins, with loss of anmt-1 fully inhibiting sir-2.1-mediated lifespan extension. MNA serves as a substrate for a newly identified aldehyde oxidase, GAD-3, to generate hydrogen peroxide, which acts as a mitohormetic reactive oxygen species signal to promote C. elegans longevity. Taken together, sirtuin-mediated lifespan extension depends on methylation of NAM, providing an unexpected mechanistic role for sirtuins beyond histone deacetylation.

SIRT6 exhibits nucleosome-dependent deacetylase activity.

The SIRT6 deacetylase is a key regulator of mammalian genome stability, metabolism and lifespan. Previous studies indicated that SIRT6 exhibits poor deacetylase activity in vitro. Here, we explored the specific conditions that allow SIRT6 to function as a significant deacetylase. We show that SIRT6 associates with the nucleosome and deacetylates histones H3 and H4 when they are packaged as nucleosomes, but not as free histones. In contrast, SIRT1 shows the opposite characteristics. Thus, our results show that SIRT6 activity is nucleosome dependent, and suggest that its binding to the nucleosome might convert it into an active structure.

SIRT6, a protein with many faces.

Sirtuins are NAD(+) dependent deacylases enzymes. There are seven mammalian sirtuins, SIRT1-SIRT7, which are localized to different cellular compartments and are capable of diverse catalytic activities. SIRT6 is a key regulator of healthy ageing. In the past decade our understanding of SIRT6 significantly increased in many different aspects. We know its cellular localization, catalytic activities, substrates and the pathways it is involved in. This review discusses the recent discoveries regarding the SIRT6 enzyme.