Resveratrol stimulates cortisol biosynthesis by activating SIRT-dependent deacetylation of P450scc

The Clock-NAD+ -Sirtuin connection in nonalcoholic fatty liver disease

Nonalcoholic or metabolic associated fatty liver disease (NAFLD/MAFLD) is a hepatic reflection of metabolic derangements characterized by excess fat deposition in the hepatocytes. Identifying metabolic regulatory nodes in fatty liver pathology is essential for effective drug targeting. Fatty liver is often associated with circadian rhythm disturbances accompanied with alterations in physical and feeding activities. In this regard, both sirtuins and clock machinery genes have emerged as critical metabolic regulators in maintaining liver homeostasis. Knockouts of either sirtuins or clock genes result in obesity associated with the fatty liver phenotype. Sirtuins (SIRT1-SIRT7) are a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, protecting cells from metabolic stress by deacetylating vital proteins associated with lipid metabolism. Circadian rhythm is orchestrated by oscillations in expression of master regulators (BMAL1 and CLOCK), which in turn regulate rhythmic expression of clock-controlled genes involved in lipid metabolism. The circadian metabolite, NAD+ , serves as a crucial link connecting clock genes to sirtuin activity. This is because, NAMPT which is a rate limiting enzyme in NAD+ biosynthesis is transcriptionally regulated by the clock genes and NAD+ in turn is a cofactor regulating the deacetylation activity of sirtuins. Intriguingly, on one hand the core circadian clock regulates the sirtuin activity and on the other hand the activated sirtuins regulate the acetylation status of clock proteins thereby affecting their transcriptional functions. Thus, the Clock-NAD+-Sirtuin connection represents a novel "feedback loop" circuit that regulates the metabolic machinery. The current review underpins the importance of NAD+ on the sirtuin and clock connection in preventing fatty liver disorder.

Rationale for Nicotinamide Adenine Dinucleotide (NAD+) Metabolome Disruption as a Pathogenic Mechanism of Post-Acute COVID-19 Syndrome

Many acute COVID-19 convalescents experience a persistent sequelae of infection, called post-acute COVID-19 syndrome (PACS). With incidence ranging between 31% and 69%, PACS is becoming increasingly acknowledged as a new disease state in the context of SARS-CoV-2 infection. As SARS-CoV-2 infection can affect several organ systems to varying degrees and durations, the cellular and molecular abnormalities contributing to PACS pathogenesis remain unclear. Despite our limited understanding of how SARS-CoV-2 infection promotes this persistent disease state, mitochondrial dysfunction has been increasingly recognized as a contributing factor to acute SARS-CoV-2 infection and, more recently, to PACS pathogenesis. The biological mechanisms contributing to this phenomena have not been well established in previous literature; however, in this review, we summarize the evidence that NAD+ metabolome disruption and subsequent mitochondrial dysfunction following SARS-CoV-2 genome integration may contribute to PACS biological pathogenesis. We also briefly examine the coordinated and complex relationship between increased oxidative stress, inflammation, and mitochondrial dysfunction and speculate as to how SARS-CoV-2-mediated NAD+ depletion may be causing these abnormalities in PACS. As such, we present evidence supporting the therapeutic potential of intravenous administration of NAD+ as a novel treatment intervention for PACS symptom management.

Interplay between oxidative stress, SIRT1, reproductive and metabolic functions

Silent information Regulators (SIRT1) gene stimulates antioxidants' expression, repairs cells damaged by oxidative stress (OS), and prevents the cells' dysfunction. In particular, the role of different Sirtuins, particularly SIRT1 in reproduction, has been widely studied over the past decade. Decreased SIRT 1 causes mitochondrial dysfunction by increasing Reactive Oxygen Species (ROS), lipid peroxidation, and DNA damage in both male and female gametes (Sperms and Oocytes), leading to infertility. In the female reproductive system, SIRT1 regulates proliferation and apoptosis in granulosa cells (GCs), and its down-regulation is associated with a reduced ovarian reserve. SIRT1 also modulates the stress response to OS in GCs by targeting a transcription factor vital for ovarian functions and maintenance. ROS-mediated damage to spermatozoa's motility and morphology is responsible for 30-80% of men's infertility cases. High levels of ROS can cause damage to deoxyribo nucleic acid (DNA) in the nucleus and mitochondria, lipid peroxidation, apoptosis, inactivation of enzymes, and oxidation of proteins in spermatozoa. SIRT 1 is a cardioprotective molecule that prevents atherosclerosis by modulating various mechanisms such as endothelial injury due to impaired nitric oxide (NO) production, inflammation, OS, and regulation of autophagy. SIRT 1 is abundantly expressed in tubular cells and podocytes. It is also found to be highly expressed in aquaporin 2 positive cells in the distal nephron suggesting its involvement in sodium and water handling. SIRT1 improves insulin resistance by reducing OS and regulating mitochondrial biogenesis and function. It also decreases adiposity and lipogenesis and increases fatty acid oxidation. So, its involvement in the multiple pathways ensures its unique role in reproductive and metabolic derangement mechanisms.

Efficacy of Zhuyu Pill Intervention in a Cholestasis Rat Model: Mutual Effects on Fecal Metabolism and Microbial Diversity

Cholestasis is a clinical condition resulting from impaired bile flow. Currently, patients with cholestasis face several barriers in seeking diagnosis and treatment. Zhuyu Pill (ZYP) is an ancient classic formula of the Coptis-Evodia herb couples (CEHC), and has been used for cholestasis treatment in the clinic, however, its underlying biological activity in cholestasis remain to be clarified. In this study, an α-naphthyl-isothiocyanate (ANIT, 50 mg/kg)-induced rat model of cholestasis was treated with ZYP. Serum biochemical indices and histopathological evaluation was performed, together with the metabolomics analyses of feces and 16S rDNA sequencing of the fecal microbiota. We evaluated the anti-cholestatic activity of ZYP and investigated the mechanisms underlying its correlation with fecal microbiota and fecal metabolite regulation. The relationships between biochemical indices and changes in gene expression associated with liver injury, levels fecal metabolites, and composition of fecal microbiota were analyzed. The results showed that both high (1.2 g/kg) and low (0.6 g/kg) doses of ZYP could effectively improve biochemical parameters in the blood of cholestasis-induced rat models; the intervention effect of high dose ZYP was superior to that that of lower dose ZYP. Based on a metabolomics test of fecal samples, significantly altered metabolites in the ANIT and ZYP treatment group were identified. In total, 734 metabolites were differentially expressed, and whose biological functions were mainly associated with amino acid metabolism, steroid hormone biosynthesis, and bile secretion. In addition, sequencing of the 16S rDNA unit in fecal samples revealed that the ZYP could improve the fecal microbiota dysbiosis that ANIT had induced. Therefore, we conclude that ANIT altering of blood biochemical and metabolic profiles and of fecal microbiota could effectively be alleviated with ZYP treatment. This study contributes to the “TCM wisdom” applied in clinical diagnosis and treatment of cholestasis.

SIRTI and cortisol in unexplained infertile females; a cross sectional study, in Karachi Pakistan

OBJECTIVE

To explore a disparity in anti-oxidants (SIRT1) and pro-oxidants (cortisol) levels as a plausible cause of unexplained infertility in females.

METHODOLOGY

It was a cross sectional study in which 342 females with unexplained infertility were recruited from ACIMC outpatient clinic: 135 infertile cases and 207 fertile controls. Biochemical estimation of serum cortisol and SIRT1 was performed using Enzyme Linked Immuno Sorbent Assay. Statistical comparisons were performed using Student-t test and Mann-Whitney U test. Associations between circulating hormone levels and infertility were determined using Spearman's rank correlation. Associations were considered significant where value of p was less than 0.05.

RESULTS

The stress hormones profile of case and control demonstrated that the antioxidant SIRT1 was significantly lower in infertile females when compared with the fertile (p =< 0.001) while (the oxidant) Cortisol showed a contrast of results with higher values of in infertile females when compared with fertile counterparts (p =< 0.01). There was a strong negative association observed between SIRT1 and cortisol serum level (r = 0.244, p < 0.001).

CONCLUSION

Chronic stress causes oxidative stress that is depicted by a decrease in antioxidant levels in infertile females.

Knockdown of CYP19A1 in Buffalo Follicular Granulosa Cells Results in Increased Progesterone Secretion and Promotes Cell Proliferation

Cytochrome P450 aromatase 19A1 (CYP19A1) is a critical enzyme in estrogen synthesis. However, the effect of CYP19A1 on cell growth and hormone secretion of buffalo follicular granulosa cells (BFGCs) is poorly understood. The objective of this study was to assess the role of CYP19A1 in cell proliferation and hormone secretion of BFGCs by knocking down CYP19A1 mRNA expression. The mRNA expression level of CYP19A1 gene was knocked down in BFGCs using the siCYP19A1-296 fragment with the best interference efficiency of 72.63%, as affirmed by real-time quantitative PCR (qPCR) and cell morphology analysis. The CYP19A1 knockdown promoted the proliferation of BFGCs through upregulating the mRNA expression levels of six proliferation-related genes (CCND1, CCNE1, CCNB1, CDK2, CDKN1A, and CDKN1B). Moreover, CYP19A1 knockdown increased (P < 0.05) the concentrations of progesterone secretion (P4) in BFGCs through increasing the mRNA expression levels of three steroidogenic genes (HSD17B1, HSD17B7, and CYP17A1). Our data further found that the FSH could inhibit the mRNA expression level of CYP19A1 in BFGCs, while LH obtains the opposite effect. These findings showed that the CYP19A1 knockdown had a regulatory role in the hormone secretion and cell proliferation in BFGCs.

Long-term triphenyltin exposure disrupts adrenal function in adult male rats

Triphenyltin is an organotin, which is widely used as a fungicide in agriculture. Here, we reported the effects of triphenyltin on adrenal function in adult male rats. Adult male Sprague Dawley rats were daily gavaged with triphenyltin (0, 0.5, 1, and 2 mg/kg body weight) from postnatal day 56-86. Triphenyltin significantly decreased serum corticosterone levels at 1 and 2 mg/kg without affecting serum levels of aldosterone and adrenocorticotropic hormone. Triphenyltin increased thickness of zona glomerulosa without affecting that of zona fasciculata. Triphenyltin did not affect cell number in zona fasciculata and zona glomerulosa. Triphenyltin down-regulated the expression of Scarb1, Star, Cyp11a1, Hsd3b1, Cyp21, Cyp11b1, and Hsd11b1 at 1 and/or 2 mg/kg while it up-regulated the expression of At1, Nr4a2, and Hsd11b2 at 2 mg/kg. Triphenyltin activated the phosphorylation of AMPKα while suppressed the phosphorylation of AKT1 and SIRT1/PGC-1α in rat adrenals in vivo and H295R cells in vitro. In vitro, triphenyltin also induced ROS production in H295R cells at 100 nM, a concentration at which no apoptosis was induced. In conclusion, triphenyltin disrupts glucocorticoid synthesis in rat adrenal cortex via several mechanisms: 1) lowering AKT1 phosphorylation and SIRT1/PGC-1α levels; 2) activating AMPKα; and 3) possibly inducing ROS production.

ROS-Induced GATA4 and GATA6 Downregulation Inhibits StAR Expression in LPS-Treated Porcine Granulosa-Lutein Cells

LPS is a major endotoxin produced by gram-negative bacteria, and exposure to it commonly occurs in animal husbandry. Previous studies have shown that LPS infection disturbs steroidogenesis, including progesterone production, and subsequently decreases animal reproductive performance. However, little information about the underlying mechanisms is available thus far. In the present study, an in vitro-luteinized porcine granulosa cell model was used to study the underlying molecular mechanisms of LPS treatment. We found that LPS significantly inhibits progesterone production and downregulates the expressions of progesterone synthesis-associated genes (StAR, CYP11A1, and 3β-HSD). Furthermore, the levels of ROS were significantly increased in an LPS dose-dependent manner. Moreover, transcriptional factors GATA4 and GATA6, but not NR5A1, were significantly downregulated. Elimination of LPS-stimulated ROS by melatonin or vitamin C could restore the expressions of GATA4, GATA6, and StAR. In parallel, StAR expression was also inhibited by the knockdown of GATA4 and GATA6. Based on these data, we conclude that LPS impairs StAR expression via the ROS-induced downregulation of GATA4 and GATA6. Collectively, these findings provide new insights into the understanding of reproductive losses in animals suffering from bacterial infection and LPS exposure.

The Essential Role of SIRT1 in Hypothalamic-Pituitary Axis

The endocrine system plays an essential role in the physiological adaptation to malnutrition. The adaptive response of various hormones directs the energy utilization toward the survival functions and away from growth and reproduction. Particularly, the hypothalamic pituitary axis plays an integral and a central role in the regulation of endocrine organs. Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase that is activated in response to calorie restriction (CR). SIRT1 is involved in cellular processes via the deacetylation of histone as well as various transcription factors and signal transduction molecules and thereby modulates the endocrine/metabolic functions. There is much evidence to demonstrate clearly that SIRT1 in the hypothalamus, pituitary gland, and other target organs modifies the synthesis, secretion, and activities of hormones and in turn induces the adaptive responses. In this review, we discussed the role of SIRT1 in the hypothalamic pituitary axis and its pathophysiological significance.

Resveratrol inhibits androgen production of human adrenocortical H295R cells by lowering CYP17 and CYP21 expression and activities

Resveratrol, a natural compound found in grapes, became very popular for its suggested protective effects against aging. It was reported to have similar positive effects on the human metabolism as caloric restriction. Recently, positive effects of resveratrol on steroid biosynthesis in cell systems and in humans suffering from polycystic ovary syndrome have also been reported, but the exact mechanism of this action remains unknown. Sirtuins seem targeted by resveratrol to mediate its action on energy homeostasis. In this study, we investigated the mechanisms of action of resveratrol on steroidogenesis in human adrenal H295R cells. Resveratrol was found to inhibit protein expression and enzyme activities of CYP17 and CYP21. It did not alter CYP17 and CYP21 mRNA expression, nor protein degradation. Only SIRT3 mRNA expression was found to be altered by resveratrol, but SIRT1, 3 and 5 overexpression did not result in a change in the steroid profile of H295R cells, indicating that resveratrol may not engage sirtuins to modulate steroid production. Previous studies showed that starvation leads to a hyperandrogenic steroid profile in H295R cells through inhibition of PKB/Akt signaling, and that resveratrol inhibits steroidogenesis of rat ovarian theca cells via the PKB/Akt pathway. Therefore, the effect of resveratrol on PKB/Akt signaling was tested in H295R cells and was found to be decreased under starvation growth conditions, but not under normal growth conditions. Overall, these properties of action together with recent clinical findings make resveratrol a candidate for the treatment of hyperandrogenic disorders such as PCOS.

Mechanisms and Dynamics of Protein Acetylation in Mitochondria

Reversible protein acetylation is a major regulatory mechanism for controlling protein function. Through genetic manipulations, dietary perturbations, and new proteomic technologies, the diverse functions of protein acetylation are coming into focus. Protein acetylation in mitochondria has taken center stage, revealing that 63% of mitochondrially localized proteins contain lysine acetylation sites. We summarize the field and discuss salient topics that cover spurious versus targeted acetylation, the role of SIRT3 deacetylation, nonenzymatic acetylation, and molecular models for regulatory acetylations that display high and low stoichiometry.

Resveratrol Ameliorates the Anxiety- and Depression-Like Behavior of Subclinical Hypothyroidism Rat: Possible Involvement of the HPT Axis, HPA Axis, and Wnt/β-Catenin Pathway

Metabolic disease subclinical hypothyroidism (SCH) is closely associated with depression-like behavior both in human and animal studies, and our previous studies have identified the antidepressant effect of resveratrol (RES) in stressed rat model. The aim of this study was to investigate whether RES would manifest an antidepressant effect in SCH rat model and explore the possible mechanism. A SCH rat model was induced by hemi-thyroid electrocauterization, after which the model rats in the RES and LT4 groups received a daily intragastric injection of RES at the dose of 15 mg/kg or LT4 at the dose of 60 μg/kg for 16 days. The rats' plasma concentrations of thyroid hormones were measured. Behavioral performance and hypothalamic-pituitary-adrenal (HPA) activity were evaluated. The protein expression levels of the Wnt/β-catenin in the hippocampus were detected by western blot. The results showed that RES treatment downregulated the elevated plasma thyroid-stimulating hormone concentration and the hypothalamic mRNA expression of thyrotropin-releasing hormone in the SCH rats. RES-treated rats showed increased rearing frequency and distance in the open-field test, increased sucrose preference in the sucrose preference test, and decreased immobility in the forced swimming test compared with SCH rats. The ratio of the adrenal gland weight to body weight, the plasma corticosterone levels, and the hypothalamic corticotrophin-releasing hormone mRNA expression were reduced in the RES-treated rats. Moreover, RES treatment upregulated the relative ratio of phosphorylated-GSK3β (p-GSK3β)/GSK3β and protein levels of p-GSK3β, cyclin D1, and c-myc, while downregulating the relative ratio of phosphorylated-β-catenin (p-β-catenin)/β-catenin and expression of GSK3β in the hippocampus. These findings suggest that RES exerts anxiolytic- and antidepressant-like effect in SCH rats by downregulating hyperactivity of the HPA axis and regulating both the HPT axis and the Wnt/β-catenin pathway.

Dexamethasone suppresses neurosteroid biosynthesis via downregulation of steroidogenic enzyme gene expression in human glioma GI-1 cells

Emerging evidence indicates that stress hormone glucocorticoids (GC) are an important modulator of brain development and function. To investigate whether GCs modulate neurosteroid biosynthesis in neural cells, we studied the effects of GCs on steroidogenic gene expression in human glioma GI-1 cells. The GC dexamethasone (Dex) reduced steroidogenic acute regulatory protein (StAR), CYP11A1 and 3β-hydroxysteroid dehydrogenase gene expression in a dose- and GC receptor-dependent manner. In addition to its effects on steroidogenic gene expression, Dex also reduced de novo synthesis of progesterone (PROG). Furthermore, Dex inhibited all-trans retinoic acid (ATRA) and vitamin D3-induced steroidogenic gene expression and PROG production. This suggests that GC regulates steroidogenic gene expression in neural cells via cross-talk with the two fat-soluble vitamins, A and D. The relationship between the effects of GCs on neurosteroid biosynthesis and on cognitive behaviors and hippocampal neural activity is also discussed herein.

Cellular consequences of oxidative stress in riboflavin responsive multiple acyl-CoA dehydrogenation deficiency patient fibroblasts

Mitochondrial dysfunction and oxidative stress are central to the molecular pathology of many human diseases. Riboflavin responsive multiple acyl-CoA dehydrogenation deficiency (RR-MADD) is in most cases caused by variations in the gene coding for electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). Currently, patients with RR-MADD are treated with high doses of riboflavin resulting in improvements of the clinical and biochemical profiles. However, in our recent studies of RR-MADD, we have shown that riboflavin treatment cannot fully correct the molecular defect in patient cells producing increased reactive oxygen species (ROS). In the current study, we aim to elucidate the cellular consequences of increased ROS by studying the cellular ROS adaption systems including antioxidant system, mitochondrial dynamics and metabolic reprogramming. We have included fibroblasts from six unrelated RR-MADD patients and two control fibroblasts cultivated under supplemented and depleted riboflavin conditions and with coenzyme Q10 (CoQ10) treatment. We demonstrated inhibition of mitochondrial fusion with increased fractionation and mitophagy in the patient fibroblasts. Furthermore, we indicated a shift in the energy metabolism by decreased protein levels of SIRT3 and decreased expression of fatty acid β-oxidation enzymes in the patient fibroblasts. Finally, we showed that CoQ10 treatment has a positive effect on the mitochondrial dynamic in the patient fibroblasts, indicated by increased mitochondrial fusion marker and reduced mitophagy. In conclusion, our results indicate that RR-MADD patient fibroblasts suffer from a general mitochondria dysfunction, probably initiated as a rescue mechanism for the patient cells to escape apoptosis as a result of the oxidative stress.

Forever young: SIRT3 a shield against mitochondrial meltdown, aging, and neurodegeneration

Caloric restriction (CR), fasting, and exercise have long been recognized for their neuroprotective and lifespan-extending properties; however, the underlying mechanisms of these phenomena remain elusive. Such extraordinary benefits might be linked to the activation of sirtuins. In mammals, the sirtuin family has seven members (SIRT1–7), which diverge in tissue distribution, subcellular localization, enzymatic activity, and targets. SIRT1, SIRT2, and SIRT3 have deacetylase activity. Their dependence on NAD⁺ directly links their activity to the metabolic status of the cell. High NAD⁺ levels convey neuroprotective effects, possibly via activation of sirtuin family members. Mitochondrial sirtuin 3 (SIRT3) has received much attention for its role in metabolism and aging. Specific small nucleotide polymorphisms in Sirt3 are linked to increased human lifespan. SIRT3 mediates the adaptation of increased energy demand during CR, fasting, and exercise to increased production of energy equivalents. SIRT3 deacetylates and activates mitochondrial enzymes involved in fatty acid β-oxidation, amino acid metabolism, the electron transport chain, and antioxidant defenses. As a result, the mitochondrial energy metabolism increases. In addition, SIRT3 prevents apoptosis by lowering reactive oxygen species and inhibiting components of the mitochondrial permeability transition pore. Mitochondrial deficits associated with aging and neurodegeneration might therefore be slowed or even prevented by SIRT3 activation. In addition, upregulating SIRT3 activity by dietary supplementation of sirtuin activating compounds might promote the beneficial effects of this enzyme. The goal of this review is to summarize emerging data supporting a neuroprotective action of SIRT3 against Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis.

Sustained in vivo blockade of α₁-adrenergic receptors prevented some of stress-triggered effects on steroidogenic machinery in Leydig cells

This study was designed to systematically analyze and evaluate the effects of in vivo blockade of α₁-adrenergic receptors (α₁-ADRs) on the stress-induced disturbance of steroidogenic machinery in Leydig cells. Parameters followed 1) steroidogenic enzymes/proteins, transcription factors, and cAMP/testosterone production; 2) the main hallmarks of stress (epinephrine, glucocorticoids); and 3) transcription profiles of ADRs and oxidases with high affinity to inactivate glucocorticoids. Results showed that sustained blockade of α₁-ADRs prevented stress-induced 1) decrease of the transcripts/proteins for main steroidogenic CYPs (CYP11A1, CYP17A1); 2) decrease of Scarb1 and Hsd3b1 transcripts; 3) decrease of transcript for Nur77, one of the main activator of the steroidogenic expression; and 4) increase of Dax1 and Arr19, the main steroidogenic repressors in Leydig cells. In the same cells, the expression of steroidogenic stimulatory factor Creb1, StAR, and androgen receptor increased. In this signaling scenario, stress-induced stimulation of Adra1a/Adra1b/Adrbk1 and Hsd11b2 (the unidirectional oxidase with high affinity to inactivate glucocorticoids) was not changed. Blockade additionally stimulated stress-increased transcription of the most abundantly expressed ADRs Adra1d/Adrb1/Adrb2 in Leydig cells. In the same cells, stress-decreased testosterone production, the main marker of Leydig cells functionality, was completely prevented, while reduction of cAMP, the main regulator of androgenesis, was partially prevented. Accordingly, the presented data provide a new molecular/transcriptional base for "fight/adaptation" of steroidogenic cells and new molecular insights into the role of α₁-ADRs in stress-impaired Leydig cell steroidogenesis. The results are important in term of wide use of α₁-ADR selective antagonists, alone/in combination, to treat high blood pressure, nightmares associated with posttraumatic stress disorder, and disrupted sexual health.

Seven sirtuins for seven deadly diseases of aging

Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.

Dioxin exposure reduces the steroidogenic capacity of mouse antral follicles mainly at the level of HSD17B1 without altering atresia

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent ovarian toxicant. Previously, we demonstrated that in vitro TCDD (1nM) exposure decreases production/secretion of the sex steroid hormones progesterone (P4), androstenedione (A4), testosterone (T), and 17β-estradiol (E2) in mouse antral follicles. The purpose of this study was to determine the mechanism by which TCDD inhibits steroidogenesis. Specifically, we examined the effects of TCDD on the steroidogenic enzymes, atresia, and the aryl hydrocarbon receptor (AHR) protein. TCDD exposure for 48h increased levels of A4, without changing HSD3B1 protein, HSD17B1 protein, estrone (E1), T or E2 levels. Further, TCDD did not alter atresia ratings compared to vehicle at 48h. TCDD, however, did down regulate the AHR protein at 48h. TCDD exposure for 96h decreased transcript levels for Cyp11a1, Cyp17a1, Hsd17b1, and Cyp19a1, but increased Hsd3b1 transcript. TCDD exposure particularly lowered both Hsd17b1 transcript and HSD17B1 protein. However, TCDD exposure did not affect levels of E1 in the media nor atresia ratings at 96h. TCDD, however, decreased levels of the proapoptotic factor Bax. Collectively, these data suggest that TCDD exposure causes a major block in the steroidogenic enzyme conversion of A4 to T and E1 to E2 and that it regulates apoptotic pathways, favoring survival over death in antral follicles. Finally, the down-regulation of the AHR protein in TCDD exposed follicles persisted at 96h, indicating that the activation and proteasomal degradation of this receptor likely plays a central role in the impaired steroidogenic capacity and altered apoptotic pathway of exposed antral follicles.