SIRT7 suppresses energy expenditure and thermogenesis by regulating brown adipose tissue functions in mice.

Brown adipose tissue plays a central role in the regulation of the energy balance by expending energy to produce heat. NAD+-dependent deacylase sirtuins have widely been recognized as positive regulators of brown adipose tissue thermogenesis. However, here we reveal that SIRT7, one of seven mammalian sirtuins, suppresses energy expenditure and thermogenesis by regulating brown adipose tissue functions. Whole-body and brown adipose tissue-specific Sirt7 knockout mice have higher body temperature and energy expenditure. SIRT7 deficiency increases the protein level of UCP1, a key regulator of brown adipose tissue thermogenesis. Mechanistically, we found that SIRT7 deacetylates insulin-like growth factor 2 mRNA-binding protein 2, an RNA-binding protein that inhibits the translation of Ucp1 mRNA, thereby enhancing its inhibitory action on Ucp1. Furthermore, SIRT7 attenuates the expression of batokine genes, such as fibroblast growth factor 21. In conclusion, we propose that SIRT7 serves as an energy-saving factor by suppressing brown adipose tissue functions.

Inactivation of Sirt6 ameliorates muscular dystrophy in mdx mice by releasing suppression of utrophin expression.

The NAD+-dependent SIRT1-7 family of protein deacetylases plays a vital role in various molecular pathways related to stress response, DNA repair, aging and metabolism. Increased activity of individual sirtuins often exerts beneficial effects in pathophysiological conditions whereas reduced activity is usually associated with disease conditions. Here, we demonstrate that SIRT6 deacetylates H3K56ac in myofibers to suppress expression of utrophin, a dystrophin-related protein stabilizing the sarcolemma in absence of dystrophin. Inactivation of Sirt6 in dystrophin-deficient mdx mice reduced damage of myofibers, ameliorated dystrophic muscle pathology, and improved muscle function, leading to attenuated activation of muscle stem cells (MuSCs). ChIP-seq and locus-specific recruitment of SIRT6 using a CRISPR-dCas9/gRNA approach revealed that SIRT6 is critical for removal of H3K56ac at the Downstream utrophin Enhancer (DUE), which is indispensable for utrophin expression. We conclude that epigenetic manipulation of utrophin expression is a promising approach for the treatment of Duchenne Muscular Dystrophy (DMD).

Sirt7 Deficiency Attenuates Neointimal Formation Following Vascular Injury by Modulating Vascular Smooth Muscle Cell Proliferation.

BACKGROUND: Sirt7 is a recently identified sirtuin and has important roles in various pathological conditions, including cancer progression and metabolic disorders. It has previously been reported that Sirt7 is a key molecule in acute myocardial wound healing and pressure overload-induced cardiac hypertrophy. In this study, the role of Sirt7 in neointimal formation after vascular injury is investigated.Methods and Results:Systemic (Sirt7-/-) and smooth muscle cell-specific Sirt7-deficient mice were subjected to femoral artery wire injury. Primary vascular smooth muscle cells (VSMCs) were isolated from the aorta of wild type (WT) and Sirt7-/-mice and their capacity for cell proliferation and migration was compared. Sirt7 expression was increased in vascular tissue at the sites of injury. Sirt7-/-mice demonstrated significant reduction in neointimal formation compared to WT mice. In vitro, Sirt7 deficiency attenuated the proliferation of serum-induced VSMCs. Serum stimulation-induced upregulation of cyclins and cyclin-dependent-kinase 2 (CDK2) was significantly attenuated in VSMCs of Sirt7-/-compared with WT mice. These changes were accompanied by enhanced expression of the microRNA 290-295 cluster, the translational negative regulator of CDK2, in VSMCs of Sirt7-/-mice. It was confirmed that smooth muscle cell-specific Sirt7-deficient mice showed significant reduction in neointima compared with control mice. CONCLUSIONS: Sirt7 deficiency attenuates neointimal formation after vascular injury. Given the predominant role in vascular neointimal formation, Sirt7 is a potentially suitable target for treatment of vascular diseases.

SIRT7-dependent deacetylation of NPM promotes p53 stabilization following UV-induced genotoxic stress.

Adaptation to different forms of environmental stress is crucial for maintaining essential cellular functions and survival. The nucleolus plays a decisive role as a signaling hub for coordinating cellular responses to various extrinsic and intrinsic cues. p53 levels are normally kept low in unstressed cells, mainly due to E3 ubiquitin ligase MDM2-mediated degradation. Under stress, nucleophosmin (NPM) relocates from the nucleolus to the nucleoplasm and binds MDM2, thereby preventing degradation of p53 and allowing cell-cycle arrest and DNA repair. Here, we demonstrate that the mammalian sirtuin SIRT7 is an essential component for the regulation of p53 stability during stress responses induced by ultraviolet (UV) irradiation. The catalytic activity of SIRT7 is substantially increased upon UV irradiation through ataxia telangiectasia mutated and Rad3 related (ATR)-mediated phosphorylation, which promotes efficient deacetylation of the SIRT7 target NPM. Deacetylation is required for stress-dependent relocation of NPM into the nucleoplasm and MDM2 binding, thereby preventing ubiquitination and degradation of p53. In the absence of SIRT7, stress-dependent stabilization of p53 is abrogated, both in vitro and in vivo, impairing cellular stress responses. The study uncovers an essential SIRT7-dependent mechanism for stabilization of the tumor suppressor p53 in response to genotoxic stress.

Cardiomyocyte Sirt (Sirtuin) 7 Ameliorates Stress-Induced Cardiac Hypertrophy by Interacting With and Deacetylating GATA4.

Sirt (Sirtuin) 7, the most recently identified mammalian sirtuin, has been shown to contribute to appropriate wound healing processes after acute cardiovascular insult. However, its role in the development of cardiac remodeling after pressure overload is unclear. Cardiomyocyte-specific Sirt7-knockout and control mice were subjected to pressure overload induced by transverse aortic constriction. Cardiac hypertrophy and functions were then examined in these mice. Sirt7 protein expression was increased in myocardial tissue after pressure overload. Transverse aortic constriction-induced increases in heart weight/tibial length were significantly augmented in cardiomyocyte-specific Sirt7-knockout mice compared with those of control mice. Histological analysis showed that the cardiomyocyte cross-sectional area and fibrosis area were significantly larger in cardiomyocyte-specific Sirt7-deficient mice. Cardiac contractile functions were markedly decreased in cardiomyocyte-specific Sirt7-deficient mice. Mechanistically, we found that Sirt7 interacted directly with GATA4 and that the exacerbation of phenylephrine-induced cardiac hypertrophy by Sirt7 knockdown was decreased by GATA4 knockdown. Sirt7 deacetylated GATA4 in cardiomyocytes and regulated its transcriptional activity. Interestingly, we demonstrated that treatment with nicotinamide mononucleotide, a known key NAD+ intermediate, ameliorated agonist-induced cardiac hypertrophies in a Sirt7-dependent manner in vitro. Sirt7 deficiency in cardiomyocytes promotes cardiomyocyte hypertrophy in response to pressure overload. Sirt7 exerts its antihypertrophic effect by interacting with and promoting deacetylation of GATA4.

Sirt7 inhibits Sirt1-mediated activation of Suv39h1.

Sirtuins regulate a variety of cellular processes through protein deacetylation. The best-known member of mammalian sirtuin family, Sirt1, plays important roles in the maintenance of cellular homeostasis by regulating cell metabolism, differentiation and stress responses, among others. Sirt1 activity requires tight regulation to meet specific cellular requirements, which is achieved at different levels and by specific mechanisms. Recently, a regulatory loop between Sirt1 and another sirtuin, Sirt7, was identified. Sirt7 inhibits Sirt1 autodeacetylation at K230 and activation thereby preventing Sirt1-mediated repression of adipocyte differentiation by inhibition of the PPARγ gene. Here, we extend the regulatory complexity of Sirt7-dependent restriction of Sirt1 activity by demonstrating that Sirt7 reduces activation of a previously described prominent Sirt1 target, the histone methyltransferase Suv39h1. We show that removal of the acetyl-group at K230 in Sirt1 due to the absence of Sirt7 leads to hyperactivation of Sirt1 and thereby to constantly increased activity of Suv39h1.

SIRT7 has a critical role in bone formation by regulating lysine acylation of SP7/Osterix.

SP7/Osterix (OSX) is a master regulatory transcription factor that activates a variety of genes during differentiation of osteoblasts. However, the influence of post-translational modifications on the regulation of its transactivation activity is largely unknown. Here, we report that sirtuins, which are NAD(+)-dependent deacylases, regulate lysine deacylation-mediated transactivation of OSX. Germline Sirt7 knockout mice develop severe osteopenia characterized by decreased bone formation and an increase of osteoclasts. Similarly, osteoblast-specific Sirt7 knockout mice showed attenuated bone formation. Interaction of SIRT7 with OSX leads to the activation of transactivation by OSX without altering its protein expression. Deacylation of lysine (K) 368 in the C-terminal region of OSX by SIRT7 promote its N-terminal transactivation activity. In addition, SIRT7-mediated deacylation of K368 also facilitates depropionylation of OSX by SIRT1, thereby increasing OSX transactivation activity. In conclusion, our findings suggest that SIRT7 has a critical role in bone formation by regulating acylation of OSX.

Sirtuins in the Cardiovascular System: Potential Targets in Pediatric Cardiology.

Cardiovascular diseases represent a major cause of death and morbidity. Cardiac and vascular pathologies develop predominantly in the aged population in part due to lifelong exposure to numerous risk factors but are also found in children and during adolescence. In comparison to adults, much has to be learned about the molecular pathways driving cardiovascular diseases in the pediatric population. Sirtuins are highly conserved enzymes that play pivotal roles in ensuring cardiac homeostasis under physiological and stress conditions. In this review, we discuss novel findings about the biological functions of these molecules in the cardiovascular system and their possible involvement in pediatric cardiovascular diseases.

SIRT6-dependent cysteine monoubiquitination in the PRE-SET domain of Suv39h1 regulates the NF-κB pathway.

Sirtuins are NAD+-dependent deacetylases that facilitate cellular stress response. They include SirT6, which protects genome stability and regulates metabolic homeostasis through gene silencing, and whose loss induces an accelerated aging phenotype directly linked to hyperactivation of the NF-κB pathway. Here we show that SirT6 binds to the H3K9me3-specific histone methyltransferase Suv39h1 and induces monoubiquitination of conserved cysteines in the PRE-SET domain of Suv39h1. Following activation of NF-κB signaling Suv39h1 is released from the IκBα locus, subsequently repressing the NF-κB pathway. We propose that SirT6 attenuates the NF-κB pathway through IκBα upregulation via cysteine monoubiquitination and chromatin eviction of Suv39h1. We suggest a mechanism based on SirT6-mediated enhancement of a negative feedback loop that restricts the NF-κB pathway.

Exosomal tetraspanins mediate cancer metastasis by altering host microenvironment.

The metastases of malignant tumors develop through a cascade of events. The establishment of a pre-metastatic micro-environment is initiated by communication between tumors and host. Exosomes come into focus as the most potent intercellular communicators playing a pivotal role in this process. Cancer cells release exosomes into the extracellular environment prior to metastasis. Tetraspanin is a type of 4 times transmembrane proteins. It may be involved in cell motility, adhesion, morphogenesis, as well as cell and vesicular membrane fusion. The exosomal tetraspanin network is a molecular scaffold connecting various proteins for signaling transduction. The complex of tetraspanin-integrin determines the recruiting cancer exosomes to pre-metastatic sites. Tetraspanin is a key element for the target cell selection of exosomes uptake that may lead to the reprogramming of target cells. Reprogrammed target cells assist pre-metastatic niche formation. Previous reviews have described the biogenesis, secretion and intercellular interaction of exosomes in various tumors. However, there is a lack of reviews on the topic of exosomal tetraspanin in the context of cancer. In this review, we will describe the main characteristics of exosomal tetraspanin in cancer cells. We will also discuss how the cancer exosomal tetraspanin alters extracellular environment and regulates cancer metastasis.

Sirt7 promotes adipogenesis in the mouse by inhibiting autocatalytic activation of Sirt1.

Sirtuins (Sirt1-Sirt7) are NAD+-dependent protein deacetylases/ADP ribosyltransferases, which play decisive roles in chromatin silencing, cell cycle regulation, cellular differentiation, and metabolism. Different sirtuins control similar cellular processes, suggesting a coordinated mode of action but information about potential cross-regulatory interactions within the sirtuin family is still limited. Here, we demonstrate that Sirt1 requires autodeacetylation to efficiently deacetylate targets such as p53, H3K9, and H4K16. Sirt7 restricts Sirt1 activity by preventing Sirt1 autodeacetylation causing enhanced Sirt1 activity in Sirt7-/- mice. Increased Sirt1 activity in Sirt7-/- mice blocks PPARγ and adipocyte differentiation, thereby diminishing accumulation of white fat. Thus, reduction of Sirt1 activity restores adipogenesis in Sirt7-/- adipocytes in vitro and in vivo. We disclosed a principle controlling Sirt1 activity and uncovered an unexpected complexity in the crosstalk between two different sirtuins. We propose that antagonistic interactions between Sirt1 and Sirt7 are pivotal in controlling the signaling network required for maintenance of adipose tissue.

Sirt7 stabilizes rDNA heterochromatin through recruitment of DNMT1 and Sirt1.

Maintenance of highly compact heterochromatin at ribosomal DNA (rDNA) segments is essential to prevent homologous recombination between rDNA repeats and for preserving genomic stability and nucleolar architecture. Here, we investigated the role of Sirtuin 7 (Sirt7) in the regulation of rDNA chromatin structure, rDNA repeat stability and nucleolar organization. We found that Sirt7 mediates heterochromatin formation at rRNA genes through recruitment of DNA methyltransferase 1 and another member of the sirtuin family, Sirt1. Lack of Sirt7 leads to nucleolar fragmentation associated with hypomethylation of rDNA and hyperacetylation of histones at rDNA loci resulting in rDNA and genomic instability. Our findings suggest a novel role of Sirt7 in preventing cellular transformation by mediating maintenance of rDNA repeats and nucleolar integrity.

Disruption of spatiotemporal hypoxic signaling causes congenital heart disease in mice.

Congenital heart disease (CHD) represents the most prevalent inborn anomaly. Only a minority of CHD cases are attributed to genetic causes, suggesting a major role of environmental factors. Nonphysiological hypoxia during early pregnancy induces CHD, but the underlying reasons are unknown. Here, we have demonstrated that cells in the mouse heart tube are hypoxic, while cardiac progenitor cells (CPCs) expressing islet 1 (ISL1) in the secondary heart field (SHF) are normoxic. In ISL1+ CPCs, induction of hypoxic responses caused CHD by repressing Isl1 and activating NK2 homeobox 5 (Nkx2.5), resulting in decreased cell proliferation and enhanced cardiomyocyte specification. We found that HIF1α formed a complex with the Notch effector hes family bHLH transcription factor 1 (HES1) and the protein deacetylase sirtuin 1 (SIRT1) at the Isl1 gene. This complex repressed Isl1 in the hypoxic heart tube or following induction of ectopic hypoxic responses. Subsequently, reduced Isl1 expression abrogated ISL1-dependent recruitment of histone deacetylases HDAC1/5, inhibiting Nkx2.5 expression. Inactivation of Sirt1 in ISL1+ CPCs blocked Isl1 suppression via the HIF1α/HES1/SIRT1 complex and prevented CHDs induced by pathological hypoxia. Our results indicate that spatial differences in oxygenation of the developing heart serve as signals to control CPC expansion and cardiac morphogenesis. We propose that physiological hypoxia coordinates homeostasis of CPCs, providing mechanistic explanations for some nongenetic causes of CHD.

Sirt7 Contributes to Myocardial Tissue Repair by Maintaining Transforming Growth Factor-ß Signaling Pathway.

BACKGROUND: Sirt7, 1 of the 7 members of the mammalian sirtuin family, promotes oncogenic transformation. Tumor growth and metastasis require fibrotic and angiogenic responses. Here, we investigated the role of Sirt7 in cardiovascular tissue repair process. METHODS AND RESULTS: In wild-type mice, Sirt7 expression increased in response to acute cardiovascular injury, including myocardial infarction and hind-limb ischemia, particularly at the active wound healing site. Compared with wild-type mice, homozygous Sirt7-deficient (Sirt7(-/-)) mice showed susceptibility to cardiac rupture after myocardial infarction, delayed blood flow recovery after hind-limb ischemia, and impaired wound healing after skin injury. Histological analysis showed reduced fibrosis, fibroblast differentiation, and inflammatory cell infiltration in the border zone of infarction in Sirt7(-/-) mice. In vitro, Sirt7(-/-) mouse-derived or Sirt7 siRNA-treated cardiac fibroblasts showed reduced transforming growth factor-ß signal activation and low expression levels of fibrosis-related genes compared with wild-type mice-derived or control siRNA-treated cells. These changes were accompanied by reduction in transforming growth factor receptor I protein. Loss of Sirt7 activated autophagy in cardiac fibroblasts. Transforming growth factor-ß receptor I downregulation induced by loss of Sirt7 was blocked by autophagy inhibitor, and interaction of Sirt7 with protein interacting with protein kinase-Cα was involved in this process. CONCLUSION: Sirt7 maintains transforming growth factor receptor I by modulating autophagy and is involved in the tissue repair process.

Dissection of metabolic pathways in the Db/Db mouse model by integrative proteome and acetylome analysis.

Insulin resistance is often associated with excessive caloric intake and metabolic syndrome (MS) favours the development of Diabetes Mellitus Type II (T2DM). T2DM is a chronic disease with severe long-term consequences, such as dyslipidemia, retinopathy, kidney failure, and cardiovascular diseases. Although studied extensively, several aspects of T2DM remain poorly understood. Liver is the leading organ in the maintenance of metabolic fitness serving as the first relay station for processing dietary information in a direct response to nutritional input and changes in insulin and other endocrine signals. Evidence from several murine models suggests a unique function of the liver in the development of MS and T2DM. Here, we utilised Db/Db mice to understand the impact of T2DM on the proteome of liver cells. Global analysis of the liver proteome using a SILAC approach identified 407 significantly regulated proteins under diabetic conditions out of 8500 identified liver proteins. Furthermore, we mapped 1604 different acetylation sites in liver proteins. After normalization of the protein level, we identified 34 regulated acetyl lysine residues on 21 individual proteins, which were significantly altered in Db/Db compared to wild-type livers. We reason that the dataset provides a versatile resource for functional studies aiming to understand consequences of changes in protein abundances and acetylation in livers of diabetic animals.

SIRT7 controls hepatic lipid metabolism by regulating the ubiquitin-proteasome pathway.

Sirtuins (SIRT1-7) have attracted considerable attention as regulators of metabolism over the past decade. However, the physiological functions and molecular mechanisms of SIRT7 are poorly understood. Here we demonstrate that Sirt7 knockout mice were resistant to high-fat diet-induced fatty liver, obesity, and glucose intolerance, and that hepatic triglyceride accumulation was also attenuated in liver-specific Sirt7 knockout mice. Hepatic SIRT7 positively regulated the protein level of TR4/TAK1, a nuclear receptor involved in lipid metabolism, and as a consequence activated TR4 target genes to increase fatty acid uptake and triglyceride synthesis/storage. Biochemical studies revealed that the DDB1-CUL4-associated factor 1 (DCAF1)/damage-specific DNA binding protein 1 (DDB1)/cullin 4B (CUL4B) E3 ubiquitin ligase complex interacted with TR4, leading to its degradation, while binding of SIRT7 to the DCAF1/DDB1/CUL4B complex inhibited the degradation of TR4. In conclusion, we propose that hepatic SIRT7 controls lipid metabolism in liver by regulating the ubiquitin-proteasome pathway.

The sirtuin SIRT6 regulates stress granule formation in C. elegans and mammals.

SIRT6 is a NAD(+)-dependent deacetylase that modulates chromatin structure and safeguards genomic stability. Until now, SIRT6 has been assigned to the nucleus and only nuclear targets of SIRT6 are known. Here, we demonstrate that in response to stress, C. elegans SIR-2.4 and its mammalian orthologue SIRT6 localize to cytoplasmic stress granules, interact with various stress granule components and induce their assembly. Loss of SIRT6 or inhibition of its catalytic activity in mouse embryonic fibroblasts impairs stress granule formation and delays disassembly during recovery, whereas deficiency of SIR-2.4 diminishes maintenance of P granules and decreases survival of C. elegans under stress conditions. Our findings uncover a novel, evolutionary conserved function of SIRT6 in the maintenance of stress granules in response to stress.

Headbobber: a combined morphogenetic and cochleosaccular mouse model to study 10qter deletions in human deafness.

The recessive mouse mutant headbobber (hb) displays the characteristic behavioural traits associated with vestibular defects including headbobbing, circling and deafness. This mutation was caused by the insertion of a transgene into distal chromosome 7 affecting expression of native genes. We show that the inner ear of hb/hb mutants lacks semicircular canals and cristae, and the saccule and utricle are fused together in a single utriculosaccular sac. Moreover, we detect severe abnormalities of the cochlear sensory hair cells, the stria vascularis looks severely disorganised, Reissner's membrane is collapsed and no endocochlear potential is detected. Myo7a and Kcnj10 expression analysis show a lack of the melanocyte-like intermediate cells in hb/hb stria vascularis, which can explain the absence of endocochlear potential. We use Trp2 as a marker of melanoblasts migrating from the neural crest at E12.5 and show that they do not interdigitate into the developing strial epithelium, associated with abnormal persistence of the basal lamina in the hb/hb cochlea. We perform array CGH, deep sequencing as well as an extensive expression analysis of candidate genes in the headbobber region of hb/hb and littermate controls, and conclude that the headbobber phenotype is caused by: 1) effect of a 648 kb deletion on distal Chr7, resulting in the loss of three protein coding genes (Gpr26, Cpmx2 and Chst15) with expression in the inner ear but unknown function; and 2) indirect, long range effect of the deletion on the expression of neighboring genes on Chr7, associated with downregulation of Hmx3, Hmx2 and Nkx1.2 homeobox transcription factors. Interestingly, deletions of the orthologous region in humans, affecting the same genes, have been reported in nineteen patients with common features including sensorineural hearing loss and vestibular problems. Therefore, we propose that headbobber is a useful model to gain insight into the mechanisms underlying deafness in human 10qter deletion syndrome.

Different extent of cardiac malfunction and resistance to oxidative stress in heterozygous and homozygous manganese-dependent superoxide dismutase-mutant mice.

AIMS: The mitochondrially expressed manganese-dependent superoxide dismutase (MnSOD, SOD2) is an essential antioxidative enzyme that is necessary for normal heart function. In this study, we investigated the heart function of mice that were exposed to increased oxidative stress for time periods of up to 6 months due to decreased MnSOD activity caused by heterozygous deletion of the MnSOD gene. METHODS AND RESULTS: We generated a mouse strain in which the gene encoding MnSOD was exchanged against a cassette containing the SOD cDNA under the control of the tetracycline response element. After breeding with mice carrying the tetracycline receptor, compound mice express MnSOD depending on the presence of tetracycline. Without tetracycline receptor the MnSOD gene is fully inactivated, and animals show an MnSOD-deficient phenotype. Using echocardiographic recordings, we found an impairment of left ventricular functions: MnSOD+/- mice displayed a decrease in fraction shortening and ejection fraction and an increase in left ventricular internal diameter in systole. Furthermore, MnSOD+/- mice developed heart hypertrophy with accompanying fibrosis and necrosis revealed by immunhistochemical analysis. Although we did not find an increase in apoptosis in MnSOD+/- hearts under normal conditions, we observed an increase of the number of apoptotic cells and vascular senescence after treatment with doxorubicin. CONCLUSION: Our study demonstrates that lifelong reduction of MnSOD activity has a negative effect on normal heart function. This animal model presents a valuable tool to investigate the mechanism of heart pathology reported in patients bearing different polymorphic variants of the MnSOD gene and to develop new therapeutic strategies through manipulation of the antioxidative defence system.

Sirt7 increases stress resistance of cardiomyocytes and prevents apoptosis and inflammatory cardiomyopathy in mice.

Sirt7 is a member of the mammalian sirtuin family consisting of 7 genes, Sirt1 to Sirt7, which all share a homology to the founding family member, the yeast Sir2 gene. Most sirtuins are supposed to act as histone/protein deacetylases, which use oxidized NAD in a sirtuin-specific, 2-step deacetylation reaction. To begin to decipher the biological role of Sirt7, we inactivated the Sirt7 gene in mice. Sirt7-deficient animals undergo a reduction in mean and maximum lifespans and develop heart hypertrophy and inflammatory cardiomyopathy. Sirt7 mutant hearts are also characterized by an extensive fibrosis, which leads to a 3-fold increase in collagen III accumulation. We found that Sirt7 interacts with p53 and efficiently deacetylates p53 in vitro, which corresponds to hyperacetylation of p53 in vivo and an increased rate of apoptosis in the myocardium of mutant mice. Sirt7-deficient primary cardiomyocytes show a approximately 200% increase in basal apoptosis and a significantly diminished resistance to oxidative and genotoxic stress suggesting a critical role of Sirt7 in the regulation of stress responses and cell death in the heart. We propose that enhanced activation of p53 by lack of Sirt7-mediated deacetylation contributes to the heart phenotype of Sirt7 mutant mice.