SIRT1 regulates DNA damage signaling through the PP4 phosphatase complex.

The Sirtuin family of NAD+-dependent enzymes plays an important role in maintaining genome stability upon stress. Several mammalian Sirtuins have been linked directly or indirectly to the regulation of DNA damage during replication through Homologous recombination (HR). The role of one of them, SIRT1, is intriguing as it seems to have a general regulatory role in the DNA damage response (DDR) that has not yet been addressed. SIRT1-deficient cells show impaired DDR reflected in a decrease in repair capacity, increased genome instability and decreased levels of γH2AX. Here we unveil a close functional antagonism between SIRT1 and the PP4 phosphatase multiprotein complex in the regulation of the DDR. Upon DNA damage, SIRT1 interacts specifically with the catalytical subunit PP4c and promotes its inhibition by deacetylating the WH1 domain of the regulatory subunits PP4R3α/ß. This in turn regulates γH2AX and RPA2 phosphorylation, two key events in the signaling of DNA damage and repair by HR. We propose a mechanism whereby during stress, SIRT1 signaling ensures a global control of DNA damage signaling through PP4.

SIRT7 mediates L1 elements transcriptional repression and their association with the nuclear lamina.

Long interspersed elements-1 (LINE-1, L1) are retrotransposons that hold the capacity of self-propagation in the genome with potential mutagenic outcomes. How somatic cells restrict L1 activity and how this process becomes dysfunctional during aging and in cancer cells is poorly understood. L1s are enriched at lamin-associated domains, heterochromatic regions of the nuclear periphery. Whether this association is necessary for their repression has been elusive. Here we show that the sirtuin family member SIRT7 participates in the epigenetic transcriptional repression of L1 genome-wide in both mouse and human cells. SIRT7 depletion leads to increased L1 expression and retrotransposition. Mechanistically, we identify a novel interplay between SIRT7 and Lamin A/C in L1 repression. Our results demonstrate that SIRT7-mediated H3K18 deacetylation regulates L1 expression and promotes L1 association with elements of the nuclear lamina. The failure of such activity might contribute to the observed genome instability and compromised viability in SIRT7 knockout mice. Overall, our results reveal a novel function of SIRT7 on chromatin organization by mediating the anchoring of L1 to the nuclear envelope, and a new functional link of the nuclear lamina with transcriptional repression.

The tumor suppressor SirT2 regulates cell cycle progression and genome stability by modulating the mitotic deposition of H4K20 methylation.

The establishment of the epigenetic mark H4K20me1 (monomethylation of H4K20) by PR-Set7 during G2/M directly impacts S-phase progression and genome stability. However, the mechanisms involved in the regulation of this event are not well understood. Here we show that SirT2 regulates H4K20me1 deposition through the deacetylation of H4K16Ac (acetylation of H4K16) and determines the levels of H4K20me2/3 throughout the cell cycle. SirT2 binds and deacetylates PR-Set7 at K90, modulating its chromatin localization. Consistently, SirT2 depletion significantly reduces PR-Set7 chromatin levels, alters the size and number of PR-Set7 foci, and decreases the overall mitotic deposition of H4K20me1. Upon stress, the interaction between SirT2 and PR-Set7 increases along with the H4K20me1 levels, suggesting a novel mitotic checkpoint mechanism. SirT2 loss in mice induces significant defects associated with defective H4K20me1-3 levels. Accordingly, SirT2-deficient animals exhibit genomic instability and chromosomal aberrations and are prone to tumorigenesis. Our studies suggest that the dynamic cross-talk between the environment and the genome during mitosis determines the fate of the subsequent cell cycle.

SIRT7 promotes chromosome synapsis during prophase I of female meiosis.

Sirtuins are NAD+-dependent protein deacylases and ADP-ribosyltransferases that are involved in a wide range of cellular processes including genome homeostasis and metabolism. Sirtuins are expressed in human and mouse oocytes yet their role during female gamete development are not fully understood. Here, we investigated the role of a mammalian sirtuin member, SIRT7, in oocytes using a mouse knockout (KO) model. Sirt7 KO females have compromised fecundity characterized by a rapid fertility decline with age, suggesting the existence of a diminished oocyte pool. Accordingly, Sirt7 KO females produced fewer oocytes and ovulated fewer eggs. Because of the documented role of SIRT7 in DNA repair, we investigated whether SIRT7 regulates prophase I when meiotic recombination occurs. Sirt7 KO pachynema-like staged oocytes had approximately twofold increased γH2AX signals associated with regions with unsynapsed chromosomes. Consistent with the presence of asynaptic chromosome regions, Sirt7 KO oocytes had fewer MLH1 foci (~one less), a mark of crossover-mediated repair, than WT oocytes. Moreover, this reduced level of crossing over is consistent with an observed twofold increased incidence of aneuploidy in Metaphase II eggs. In addition, we found that acetylated lysine 18 of histone H3 (H3K18ac), an established SIRT7 substrate, was increased at asynaptic chromosome regions suggesting a functional relationship between this epigenetic mark and chromosome synapsis. Taken together, our findings demonstrate a pivotal role for SIRT7 in oocyte meiosis by promoting chromosome synapsis and have unveiled the importance of SIRT7 as novel regulator of the reproductive lifespan.

SIRT7 promotes genome integrity and modulates non-homologous end joining DNA repair.

Sirtuins, a family of protein deacetylases, promote cellular homeostasis by mediating communication between cells and environment. The enzymatic activity of the mammalian sirtuin SIRT7 targets acetylated lysine in the N-terminal tail of histone H3 (H3K18Ac), thus modulating chromatin structure and transcriptional competency. SIRT7 deletion is associated with reduced lifespan in mice through unknown mechanisms. Here, we show that SirT7-knockout mice suffer from partial embryonic lethality and a progeroid-like phenotype. Consistently, SIRT7-deficient cells display increased replication stress and impaired DNA repair. SIRT7 is recruited in a PARP1-dependent manner to sites of DNA damage, where it modulates H3K18Ac levels. H3K18Ac in turn affects recruitment of the damage response factor 53BP1 to DNA double-strand breaks (DSBs), thereby influencing the efficiency of non-homologous end joining (NHEJ). These results reveal a direct role for SIRT7 in DSB repair and establish a functional link between SIRT7-mediated H3K18 deacetylation and the maintenance of genome integrity.

Stabilization of Suv39H1 by SirT1 is part of oxidative stress response and ensures genome protection.

Sirtuins are NAD-dependent deacetylases that sense oxidative stress conditions and promote a protective cellular response. The Sirtuin SirT1 is involved in facultative heterochromatin formation through an intimate functional relationship with the H3K9me3 methyltransferase Suv39h1, a chromatin organization protein. However, SirT1 also regulates Suv39h1-dependent constitutive heterochromatin (CH) through an unknown mechanism; interestingly, SirT1 does not significantly localize in these regions. Herein, we report that SirT1 controls global levels of Suv39h1 by increasing its half-life through inhibition of Suv39h1 lysine 87 polyubiquitination by the E3-ubiquitin ligase MDM2. This in turn increases Suv39h1 turnover in CH and ensures genome integrity. Stress conditions that lead to SirT1 upregulation, such as calorie restriction, also induce higher levels of Suv39h1 in a SirT1-dependent manner in vivo. These observations reflect a direct link between oxidative stress response and Suv39h1 and support a dynamic view of heterochromatin, in which its structure adapts to cell physiology.

53BP1 ablation rescues genomic instability in mice expressing 'RING-less' BRCA1.

BRCA1 mutations strongly predispose affected individuals to breast and ovarian cancer, but the mechanism by which BRCA1 acts as a tumor suppressor is not fully understood. Homozygous deletion of exon 2 of the mouse Brca1 gene normally causes embryonic lethality, but we show that exon 2-deleted alleles of Brca1 are expressed as a mutant isoform that lacks the N-terminal RING domain. This "RING-less" BRCA1 protein is stable and efficiently recruited to the sites of DNA damage. Surprisingly, robust RAD51 foci form in cells expressing RING-less BRCA1 in response to DNA damage, but the cells nonetheless display the substantial genomic instability. Genomic instability can be rescued by the deletion of Trp53bp1, which encodes the DNA damage response factor 53BP1, and mice expressing RING-less BRCA1 do not show an increased susceptibility to tumors in the absence of 53BP1. Genomic instability in cells expressing RING-less BRCA1 correlates with the loss of BARD1 and a defect in restart of replication forks after hydroxyurea treatment, suggesting a role of BRCA1-BARD1 in genomic integrity that is independent of RAD51 loading.

SIRT1 regulates the histone methyl-transferase SUV39H1 during heterochromatin formation.

In contrast to stably repressive, constitutive heterochromatin and stably active, euchromatin, facultative heterochromatin has the capacity to alternate between repressive and activated states of transcription. As such, it is an instructive source to understand the molecular basis for changes in chromatin structure that correlate with transcriptional status. Sirtuin 1 (SIRT1) and suppressor of variegation 3-9 homologue 1 (SUV39H1) are amongst the enzymes responsible for chromatin modulations associated with facultative heterochromatin formation. SUV39H1 is the principal enzyme responsible for the accumulation of histone H3 containing a tri-methyl group at its lysine 9 position (H3K9me3) in regions of heterochromatin. SIRT1 is an NAD+-dependent deacetylase that targets histone H4 at lysine 16 (refs 3 and 4), and through an unknown mechanism facilitates increased levels of H3K9me3 (ref. 3). Here we show that the mammalian histone methyltransferase SUV39H1 is itself targeted by the histone deacetylase SIRT1 and that SUV39H1 activity is regulated by acetylation at lysine residue 266 in its catalytic SET domain. SIRT1 interacts directly with, recruits and deacetylates SUV39H1, and these activities independently contribute to elevated levels of SUV39H1 activity resulting in increased levels of the H3K9me3 modification. Loss of SIRT1 greatly affects SUV39H1-dependent H3K9me3 and impairs localization of heterochromatin protein 1. These findings demonstrate a functional link between the heterochromatin-related histone methyltransferase SUV39H1 and the histone deacetylase SIRT1.

SIRT7 and p53 interaction in embryonic development and tumorigenesis.

p53 is a hallmark tumor suppressor due in part to its role in cell cycle progression, DNA damage repair, and cellular apoptosis; its protein activity interrelates with the Sirtuin family of proteins, major regulators of the cellular response to metabolic, oxidative, and genotoxic stress. In the recent years, mammalian Sirtuin 7 (SIRT7) has emerged as a pivotal regulator of p53, fine-tuning its activity in a context dependent manner. SIRT7 is frequently overexpressed in human cancer, yet its precise role in tumorigenesis and whether it involves p53 regulation is insufficiently understood. Depletion of SIRT7 in mice results in impaired embryo development and premature aging. While p53 activity has been suggested to contribute to tissue specific dysfunction in adult Sirt7 -/- mice, whether this also applies during development is currently unknown. By generating SIRT7 and p53 double-knockout mice, here we show that the demise of SIRT7-deficient embryos is not the result of p53 activity. Notably, although SIRT7 is commonly considered an oncogene, SIRT7 haploinsufficiency increases tumorigenesis in p53 knockout mice. Remarkably, in specific human tumors harboring p53 mutation, we identified that SIRT7 low expression correlates with poor patient prognosis. Transcriptomic analysis unveils a previously unrecognized interplay between SIRT7 and p53 in epithelial-to-mesenchymal transition (EMT) and extracellular matrix regulation with major implications for our understanding of embryonic development and tumor progression.

Patterns of substance use in adolescents attending a mental health department.

This study aimed to describe patterns of substance use in adolescents initiating mental health treatment and analyse factors associated with a high-risk pattern of substance use differentially by gender. Two hundred and thirty-seven 12- to 17-year-old new patients in an urban public mental health service were prospectively recruited and evaluated using semi-structured interviews and standardized questionnaires to obtain socio-demographic, psychopathological, family, school and substance use data. The most prevalent primary diagnoses among males were attention deficit disorder and conduct disorder, while among females they were eating disorders, affective and conduct disorders. Substance use disorder was diagnosed as follows: cannabis in 10.1% of the sample, alcohol in 3.4% and other drugs in 0.4%. A pattern of substance use with high risk of developing problems (at least regular use of alcohol or occasional use of cannabis or other illegal drugs) was found in 48.9% of the sample. After adjusting for age in the multivariate logistic regression, this pattern of risky use of drugs was found to be associated with Youth Self-Report scales of thought problems, delinquent and aggressive behaviour, in both genders. Altered family structure, having had to repeat a school grade and Youth Self-Report attention problems were only significantly associated with risky drug consumption in females. The high prevalence of risky and problematic substance use in adolescents entering mental health treatment warrants early systematic screening and specific preventive and therapeutic interventions, addressing mental health psychoeducation and motivation to avoid drugs, as well as differential associated risk factors for males and females.

Depletion of DSS1 protein disables homologous recombinational repair in human cells.

DSS1 is a small, highly acidic protein widely conserved among eukaryotes as a component of the 19S proteasome and implicated in ubiquitin-mediated proteolysis. The BRCA2 tumor suppressor protein functions in homologous recombinational repair (HRR) of DNA double-strand breaks, and does so in part through the actions of a carboxy-proximal region that binds DNA and several other proteins, including DSS1. In the unicellular eukaryote Ustilago maydis, Dss1 interacts with Brh2, a BRCA2-like protein, and regulates its function in mediating HRR. We used RNA interference to deplete DSS1 in human cells, and assayed the effects on double-strand break repair by homologous recombination. Partial depletion of DSS1 protein in human cells reduced the efficiency of HRR to small fractions of normal levels. Residual HRR activity correlated roughly with the residual level of DSS1 expression. The results imply that mammalian DSS1 makes a critical contribution to the function of BRCA2 in mediating HRR, and hence to genomic stability. Activity of the ubiquitin-proteasome system can influence HRR. However, treatment with proteasome inhibitors only partially reproduced the effects of DSS1 depletion on HRR, suggesting that the function of DSS1 in HRR involves more than proteolysis per se.

Prevalence and factors related to substance use among adolescents with eating disorders.

OBJECTIVE: Very few studies have assessed substance use in clinical samples of adolescents with eating disorders (ED). This paper reports the prevalence of regular or risky substance use (RRSU) and substance use disorder (SUD) in adolescents with ED. METHODS: The Teen-Addiction Severity Index (T-ASI), the Youth Self-Report (YSR) scale and substance use questionnaires were administered to 95 adolescent patients aged 12-17 years who fulfilled the DSM-IV-TR diagnostic criteria for anorexia nervosa, bulimia nervosa and ED not otherwise specified. All patients were consecutively attended at an Eating Disorders Unit. RESULTS: 14.7% presented SUD related to tobacco, 3.2% to cannabis, 1.1% to alcohol, and 1.1% to other substances. Patients with RRSU-SUD of any substance except tobacco were 34.7%. Patients with RRSU-SUD failed more subjects, repeated more school years and had higher scores on T-ASI scales of problems at school, family function and social relationships, and on YSR scales of delinquent behavior and externalizing problems. CONCLUSIONS: Substance use problems in ED adolescents are frequent and formal screening of them as well as a specific therapeutic approach are necessary.

Brief intervention in substance-use among adolescent psychiatric patients: a randomized controlled trial.

Objective of the study is to assess the efficacy of a brief motivational enhancement intervention in adolescents referred to psychiatric treatment who reported substance-use. In a sample of adolescents (n = 237) consecutively admitted to a psychiatry department, 143 were identified as users. Subjects were randomly allocated to one of two groups: an experimental group that received a brief intervention aimed at increasing their awareness of the risks of substance-use, or a control group. All subjects received standard treatment according to the primary diagnosis. Structured questionnaires assessing knowledge, problems, perception of risks and intention of use of psychoactive substances were administered upon admission and 1 month later. Fifty-nine subjects entered the experimental group and 44 the control group. No significant differences between the two groups were identified in socio-demographic features or substance-use. Non-parametric analyses showed a significant increase across time in overall knowledge about drugs and perception of risk in the experimental group (P < 0.05). A significant increase in overall knowledge in the experimental group compared to controls was found (P < 0.05). No differences were observed for other variables such as intention of use or perception of risk. Brief intervention in adolescents entering psychiatric treatment led to a significant change in overall knowledge about psychoactive substances but not in other variables related to use. Our results point to the need of more intensive interventions.

SirT7 auto-ADP-ribosylation regulates glucose starvation response through mH2A1.

Sirtuins are key players of metabolic stress response. Originally described as deacetylases, some sirtuins also exhibit poorly understood mono-adenosine 5'-diphosphate (ADP)-ribosyltransferase (mADPRT) activity. We report that the deacetylase SirT7 is a dual sirtuin, as it also features auto-mADPRT activity. SirT7 mADPRT occurs at a previously undefined active site, and its abrogation alters SirT7 chromatin distribution. We identify an epigenetic pathway by which ADP-ribosyl-SirT7 is recognized by the ADP-ribose reader mH2A1.1 under glucose starvation, inducing SirT7 relocalization to intergenic regions. SirT7 promotes mH2A1 enrichment in a subset of nearby genes, many of them involved in second messenger signaling, resulting in their specific up- or down-regulation. The expression profile of these genes under calorie restriction is consistently abrogated in SirT7-deficient mice, resulting in impaired activation of autophagy. Our work provides a novel perspective on sirtuin duality and suggests a role for SirT7/mH2A1.1 axis in glucose homeostasis and aging.

Antipsychotic-induced weight gain and birth weight in psychosis: A fetal programming model.

Antipsychotic induced weight gain is a frequent reason for treatment discontinuation in psychosis, subsequently increasing the risk of relapse and negatively affecting patient well-being. The metabolic effect of weight gain and the subsequent risk of obesity constitute a major medical problem on the long term. Despite its consequences, to date few risk factors have been identified (age, gender, body mass index at baseline), with some authors suggesting the implication of early life stressful events, such as perinatal conditions. We aim to describe if a surrogate marker of intrauterine environment (birth weight) might predict weight gain in a cohort of 23 antipsychotic naïve patients at the onset of the psychotic disease evaluated during 16 weeks with olanzapine treatment and in another cohort of 24 psychosis-resistant patients initiating clozapine assessed for 18 weeks. Two independent linear mixed model analyses were performed in each cohort of patients, with prospective weight gain as the dependent variable, age, gender, body mass index, duration of treatment and time as independent variables. Only in naïve patients, weight gain due to antipsychotics was significantly associated with birth weight, while male gender and body mass index at baseline were associated in both cohorts of patients. Treatment-resistant psychotic patients under clozapine were older, had previous antipsychotic treatment and more years of disease, confounders that might have influence a non significant association. Our results suggest that early environmental events might be playing a role in weight evolution in naïve patients treated with antipsychotics.

Food craving and consumption evolution in patients starting treatment with clozapine.

BACKGROUND: Antipsychotic-induced weight gain has been especially related to clozapine and olanzapine. Underlying mechanisms in relation to food preferences with an increased food craving and consumption of specific nutrients have not been extensively studied in patients with serious mental illness (SMI). We aim to describe specific food preferences (craving) and subsequent food consumption in SMI patients starting clozapine, as well as their possible relation to weight and body mass index (BMI). METHODS: An observational prospective follow-up study (18 weeks) was conducted in a cohort of 34 SMI patients who started clozapine due to resistant-psychotic symptoms. Anthropometric measures, Food Craving Inventory (FCI), and a food consumption frequency questionnaire were evaluated at baseline, weeks 8 and 18 of treatment. Statistical analysis included generalized estimating equations models with adjustment for potential confounding factors. RESULTS: No longitudinal changes over time were found across the different food craving scores after 18 weeks of treatment. However, adjusted models according to BMI status showed that the normal weight (NW) group presented an increased score for the "complex carbohydrates/proteins" food cravings (- 0.67; 95% CI [- 1.15, - 0.19]; P = 0.010), while baseline scores for "fast-food fats" cravings were significantly higher in the overweight/obese (OWO) group in comparison with NW patients (NW, 2.05; 95% CI [1.60, 2.49]; OWO, 2.81, 95% CI [2.37, 3.25]; P = 0.016). When considering if food craving could predict weight gain, only increments in "fast-food fats" cravings were associated (ß = - 5.35 ± 1.67; 95% CI [- 8.64, - 2.06]; P = 0.001). CONCLUSIONS: No longitudinal differences were found for any of the food craving scores evaluated; however, in the NW group, food craving for "complex carbohydrates/proteins" changed. Thus, changes in "fast-food fats" cravings predicted weight increase in this sample. Interventions targeting food preferences may help to mitigate weight gain in patients starting treatment with clozapine.

Clinical and research utility of Spanish Teen-Addiction Severity Index (T-ASI).

This paper aims to test the clinical and research utility of a Spanish version of the Teen-Addiction Severity Index (T-ASI) in adolescents with psychiatric disorders attending a treatment programme. Eighty adolescents, 12 to 17 years old (Mean=14.5; SD=1.48) were evaluated with a research battery including the T-ASI to obtain data on socio-demographics, psychopathology, drug use, family environment and school achievement. The Substance Use scale of the T-ASI correlated significantly (Rho=0.90, p

Predictive study of academic stress with the irritable bowel syndrome in medicine students at a public university in Mexico.

BACKGROUND: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder associated with stress, which may appear by an educational context, given that students are exposed to demands in the academic environment during their education process that may lead to developing diseases. This study reports on the relationship between the IBS and academic stress and compares results of men and women. METHODS: A random survey was made of 561 medicine students at a public university in Mexico. The ROMA III criteria were used for the IBS and the Academic Stress Inventory for academic stress. A multiple regression analysis was made. RESULTS: The results showed that students with academic overload and lack of time are at risk for developing the IBS. CONCLUSIONS: Therefore, the recommendation is to implement educational programs aiming at self-care as well as gaining knowledge about academic stress-related factors and the physical responses that may result in repercussions with serious consequences for student life such as pain, disease and dropping out of school.

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.

Sirtuins and DNA damage repair: SIRT7 comes to play.

Aging is characterized by a cumulative loss of genome integrity, which involves chromatin reorganization, transcriptional dysregulation and the accumulation of DNA damage. Sirtuins participate in the protection against these aging processes by promoting genome homeostasis in response to cellular stress. We recently reported that SirT7-/- mice suffer from partial embryonic lethality and a progeroid like phenotype. At the cellular level, SIRT7 depletion results in the impaired repair of DNA double-strand breaks (DSBs), one the most dangerous DNA lesions, leading to genome instability. SIRT7 is recruited to DSBs, where it specifically deacetylates histone H3 at lysine 18 and affects the focal accumulation of the DNA damage response factor 53BP1, thus influencing the efficiency of repair. Here, we integrate our findings with the current knowledge on the mode of action of other sirtuin family members in DNA repair. We emphasize their capacity to regulate chromatin structure as a response to DNA damage within the constraints imposed by cellular status.