Nutrient-dependent regulation of PGC-1alpha's acetylation state and metabolic function through the enzymatic activities of Sirt1/GCN5

Altering heparan sulfate suppresses cell abnormalities and neuron loss in Drosophila presenilin model of Alzheimer Disease

We examined the function of heparan-sulfate-modified proteoglycans (HSPGs) in pathways affecting Alzheimer disease (AD)-related cell pathology in human cell lines and mouse astrocytes. Mechanisms of HSPG influences on presenilin-dependent cell loss were evaluated in Drosophila using knockdown of the presenilin homolog, Psn, together with partial loss-of-function of sulfateless (sfl), a gene specifically affecting HS sulfation. HSPG modulation of autophagy, mitochondrial function, and lipid metabolism were shown to be conserved in human cell lines, Drosophila, and mouse astrocytes. RNA interference (RNAi) of Ndst1 reduced intracellular lipid levels in wild-type mouse astrocytes or those expressing humanized variants of APOE, APOE3, and APOE4. Neuron-directed knockdown of Psn in Drosophila produced apoptosis and cell loss in the brain, phenotypes suppressed by reductions in sfl expression. Abnormalities in mitochondria, liposomes, and autophagosome-derived structures in animals with Psn knockdown were also rescued by reduction of sfl. These findings support the direct involvement of HSPGs in AD pathogenesis.

Exercise ameliorates fine particulate matter-induced metabolic damage through the SIRT1/AMPKα/PGC1-α/NRF1 signaling pathway

Air pollution, particularly fine particulate matter (PM2.5), poses a major threat to human health. Exercise has long been recognized as a beneficial way to maintain physical health. However, there is limited research on whether exercise can mitigate the damage caused by PM2.5 exposure. In this study, the mice were exercised on the IITC treadmill for 1 h per day, then exposed to concentrated PM2.5 for 8 h. After 2, 4 and 6-month exercise and PM2.5 exposure, the glucose tolerance and insulin tolerance were determined. Meanwhile, the corresponding indicators in epididymal white adipose tissue (eWAT), brown adipose tissue (BAT) and skeletal muscle were detected. The results indicated that PM2.5 exposure significantly increased insulin resistance (IR), while exercise effectively attenuated this response. The observations of muscle, BAT and eWAT by transmission electron microscopy (TEM) showed that PM2.5 significantly reduced the number of mitochondria in all of the three tissues mentioned above, and decreased the mitochondrial area in skeletal muscle and BAT. Exercise reversed the changes in mitochondrial area in all of the three tissues, but had no effect on the reduction of mitochondrial number in skeletal muscle. At 2 months, the expressions of Mfn2, Mfn1, OPA1, Drp1 and Fis1 in eWAT of the PM mice showed no significant changes when compared with the corresponding FA mice. However, at 4 months and 6 months, the expression levels of these genes in PM mice were higher than those in the FA mice in skeletal muscle. Exercise intervention significantly reduced the upregulation of these genes induced by PM exposure. The study indicated that PM2.5 may impact mitochondrial biogenesis and dynamics by inhibiting the SIRT1/AMPKα/PGC1-α/NRF1 pathway, which further lead to IR, glucose and lipid disorders. However, exercise might alleviate the damages caused by PM2.5 exposure.

Role of SIRT1 in Potentially Toxic Trace Elements (Lead, Fluoride, Aluminum and Cadmium) Associated Neurodevelopmental Toxicity

The formation of the central nervous system is a meticulously planned and intricate process. Any modification to this process has the potential to disrupt the structure and operation of the brain, which could result in deficiencies in neurological growth. When neurotoxic substances are present during the early stages of development, they can be exceptionally dangerous. Prenatally, the immature brain is extremely vulnerable and is therefore at high risk in pregnant women associated with occupational exposures. Lead, fluoride, aluminum, and cadmium are examples of possibly toxic trace elements that have been identified as an environmental concern in the aetiology of a number of neurological and neurodegenerative illnesses. SIRT1, a member of the sirtuin family has received most attention for its potential neuroprotective properties. SIRT1 is an intriguing therapeutic target since it demonstrates important functions to increase neurogenesis and cellular lifespan by modulating multiple pathways. It promotes axonal extension, neurite growth, and dendritic branching during the development of neurons. Additionally, it contributes to neurogenesis, synaptic plasticity, memory development, and neuroprotection. This review summarizes the possible role of SIRT1 signalling pathway in potentially toxic trace elements -induced neurodevelopmental toxicity, highlighting some molecular pathways such as mitochondrial biogenesis, CREB/BDNF and PGC-1α/NRF1/TFAM.

Heparan sulfate modified proteins affect cellular processes central to neurodegeneration and modulate presenilin function

Mutations in presenilin-1 (PSEN1) are the most common cause of familial, early-onset Alzheimer's disease (AD), typically producing cognitive deficits in the fourth decade. A variant of APOE, APOE3 Christchurch (APOE3ch) , was found associated with protection from both cognitive decline and Tau accumulation in a 70-year-old bearing the disease-causing PSEN1-E280A mutation. The amino acid change in ApoE3ch is within the heparan sulfate (HS) binding domain of APOE, and purified APOEch showed dramatically reduced affinity for heparin, a highly sulfated form of HS. The physiological significance of ApoE3ch is supported by studies of a mouse bearing a knock-in of this human variant and its effects on microglia reactivity and Aβ-induced Tau deposition. The studies reported here examine the function of heparan sulfate-modified proteoglycans (HSPGs) in cellular and molecular pathways affecting AD-related cell pathology in human cell lines and mouse astrocytes. The mechanisms of HSPG influences on presenilin- dependent cell loss and pathology were evaluated in Drosophila using knockdown of the presenilin homolog, Psn , together with partial loss of function of sulfateless (sfl) , a homolog of NDST1 , a gene specifically affecting HS sulfation. HSPG modulation of autophagy, mitochondrial function, and lipid metabolism were shown to be conserved in cultured human cell lines, Drosophila , and mouse astrocytes. RNAi of Ndst1 reduced intracellular lipid levels in wild-type mouse astrocytes or those expressing humanized variants of APOE, APOE3 , and APOE4 . RNA-sequence analysis of human cells deficient in HS synthesis demonstrated effects on the transcriptome governing lipid metabolism, autophagy, and mitochondrial biogenesis and showed significant enrichment in AD susceptibility genes identified by GWAS. Neuron-directed knockdown of Psn in Drosophila produced cell loss in the brain and behavioral phenotypes, both suppressed by simultaneous reductions in sfl mRNA levels. Abnormalities in mitochondria, liposome morphology, and autophagosome-derived structures in animals with Psn knockdown were also rescued by simultaneous reduction of sfl. sfl knockdown reversed Psn- dependent transcript changes in genes affecting lipid transport, metabolism, and monocarboxylate carriers. These findings support the direct involvement of HSPGs in AD pathogenesis.

Cystathionine γ-lyase S-sulfhydrates SIRT1 to attenuate myocardial death in isoprenaline-induced heart failure

OBJECTIVE

Hydrogen sulfide (H₂S), the third gasotransmitter, plays a critical role in protecting against heart failure. Sirtuin-1 (SIRT1) is a highly conserved histone deacetylase that has a protective role in the treatment of heart failure by regulating the deacetylation of some functional proteins. This study investigates the interaction between SIRT1 and H₂S in heart failure and the underlying mechanisms.

METHODS AND RESULTS

Using endogenous H₂S-generating enzyme cystathionine γ-lyase (CSE) knockout mice, we found that CSE deficiency aggravated isoprenaline-induced cardiac injury. Treatment with H₂S attenuated atrial natriuretic peptide level, brain natriuretic peptide level, improved cardiac function. Moreover, H₂S treatment potentiated myocardial SIRT1 expression. Silencing CSE abolished intracellular SIRT1 expression. Furthermore, CSE/ H₂S S-sulfhydrated SIRT1 at its zinc finger domains and augmented its zinc ion binding activity to stabilize the alpha-helix structure.

DISCUSSION

In conclusion, these results uncover that a novel mechanism that CSE/H₂S S-sulfhydrated SIRT1 to prevent heart dysfunction through modulating its activity.

DNA hydroxymethylation differences underlie phenotypic divergence of somatic growth in Nile tilapia reared in common garden

Phenotypic plasticity of metabolism and growth are essential for adaptation to new environmental conditions, such as those experienced during domestication. Epigenetic regulation plays a key role in this process but the underlying mechanisms are poorly understood, especially in the case of hydroxymethylation. Using reduced representation 5-hydroxymethylcytosine profiling, we compared the liver hydroxymethylomes in full-sib Nile tilapia with distinct growth rates (3.8-fold difference) and demonstrated that DNA hydroxymethylation is strongly associated with phenotypic divergence of somatic growth during the early stages of domestication. The 2677 differentially hydroxymethylated cytosines between fast- and slow-growing fish were enriched within gene bodies (79%), indicating a pertinent role in transcriptional regulation. Moreover, they were found in genes involved in biological processes related to skeletal system and muscle structure development, and there was a positive association between somatic growth and 5hmC levels in genes coding for growth factors, kinases and receptors linked to myogenesis. Single nucleotide polymorphism analysis revealed no genetic differentiation between fast- and slow-growing fish. In addition to unveiling a new link between DNA hydroxymethylation and epigenetic regulation of growth in fish during the initial stages of domestication, this study suggests that epimarkers may be applied in selective breeding programmes for superior phenotypes.

LDLR heterozygous deletion reduces hamster testicular cholesterol toxicity via AMPK/Sirt1/PGC-1α pathway

Cholesterol is an important part of the human diet. The relationship and molecular mechanisms between intracellular cholesterol and male infertility are unclear. The purpose of this study was to evaluate the role of low-density lipoprotein receptor (LDLR) in male infertility. Both wild-type (WT) and LDLR heterozygous deletion (LDLR+/-) male Golden Syrian hamsters were fed either a high-fat diet (HFD) or a normal diet (ND). Plasma biochemistry, serum hormone, testicular histopathology, mRNA and protein expression of AMPK/Sirt1/PGC-1α in both testicular tissue and isolated Leydig cells (LCs) were measured. Compared with the ND animals, the WT HFD hamsters developed dyslipidemia at three weeks with lipid droplets deposited in LCs, testosterone decreased at four weeks (0.440 ± 0.264 ng/ml vs. 2.367 ± 1.236 ng/ml), the number of the Sertoli cells decreased (21.578 ± 2.934/one tubule vs. 25.733 ± 3.424/one tubule), the seminiferous epithelium became thinner (0.0813 ± 0.01729 mm vs. 0.0944 ± 0.0138 mm), testicular atrophy and AMPK/Sirt1/PGC-1α pathway downregulated at five weeks. All these changes persisted until the end of the study. LDLR+/- alleviated all of the above changes by downregulating the cellular influx of cholesterol induced by HFD except for higher hyperlipidemia. In summary, excessive intracellular cholesterol inactivates AMPK/Sirt1/PGC-1α pathway firstly in LCs and then in both Sertoli and spermatids. Cholesterol toxicity was LDLR dependent.

Targeting mitochondria as a potential therapeutic strategy against chemoresistance in cancer

The importance of mitochondria is not only limited to energy generation but also in several physical and chemical processes critical for cell survival. Mitochondria play an essential role in cellular apoptosis, calcium ion transport and cellular metabolism. Mutation in the nuclear and mitochondrial genes, altered oncogenes/tumor suppressor genes, and deregulated signalling for cell viability are major reasons for cancer progression and chemoresistance. The development of drug resistance in cancer patients is a major challenge in cancer treatment as the resistant cells are often more aggressive. The drug resistant cells of numerous cancer types exhibit the deregulation of mitochondrial function. The increased biogenesis of mitochondria and its dynamic alteration contribute to developing resistance. Further, a small subpopulation of cancer stem cells in the heterogeneous tumor is primarily responsible for chemoresistance and has an attribute of mitochondrial dysfunction. This review highlights the critical role of mitochondrial dysfunction in chemoresistance in cancer cells through the processes of apoptosis, autophagy/mitophagy, and cancer stemness. Mitochondria-targeted therapeutic strategies might help reduce cancer progression and chemoresistance induced by various cancer drugs.

NAD Supplement Alleviates Intestinal Barrier Injury Induced by Ethanol Via Protecting Epithelial Mitochondrial Function

BACKGROUND

The epithelial tight junction is an important intestinal barrier whose disruption can lead to the release of harmful intestinal substances into the circulation and cause damage to systemic injury. The maintenance of intestinal epithelial tight junctions is closely related to energy homeostasis and mitochondrial function. Nicotinamide riboside (NR) is a NAD booster that can enhance mitochondrial biogenesis in liver. However, whether NR can prevent ethanol-induced intestinal barrier dysfunction and the underlying mechanisms remain unclear.

METHODS

We applied the mouse NIAAA model (chronic plus binge ethanol feeding) and Caco-2 cells to explore the effects of NR on ethanol-induced intestinal barrier dysfunction and the underlying mechanisms. NAD homeostasis and mitochondrial function were measured. In addition, knockdown of SirT1 in Caco-2 cells was further applied to explore the role of SirT1 in the protection of NR.

RESULTS

We found that ethanol increased intestinal permeability, increased the release of LPS into the circulation and destroyed the intestinal epithelial barrier structure in mice. NR supplementation attenuated intestinal barrier injury. Both in vivo and in vitro experiments showed that NR attenuated ethanol-induced decreased intestinal tight junction protein expressions and maintained NAD homeostasis. In addition, NR supplementation activated SirT1 activity and increased deacetylation of PGC-1α, and reversed ethanol-induced mitochondrial dysfunction and mitochondrial biogenesis. These effects were diminished with the knockdown of SirT1 in Caco-2 cells.

CONCLUSION

Boosting NAD by NR alleviates ethanol-induced intestinal epithelial barrier damage via protecting mitochondrial function in a SirT1-dependent manner.

Metabokines in the regulation of systemic energy metabolism

Metabolism consists of life-sustaining chemical reactions involving metabolites. Historically, metabolites were defined as the intermediates or end products of metabolism and considered to be passive participants changed by metabolic processes. However, recent research has redefined how we view metabolism. There is emerging evidence of metabolites which function to mediate cellular signalling and interorgan crosstalk, regulating local metabolism and systemic physiology. These bioactive metabolite signals have been termed metabokines. Metabokines regulate diverse energy metabolism pathways across multiple tissues, including fatty acid β-oxidation, mitochondrial oxidative phosphorylation, lipolysis, glycolysis and gluconeogenesis. There is increasing impetus to uncover novel metabokine signalling axes to better understand how these may be perturbed in metabolic diseases and determine their utility as therapeutic targets.

Ovarian aging: mechanisms and intervention strategies

Ovarian reserve is essential for fertility and influences healthy aging in women. Advanced maternal age correlates with the progressive loss of both the quantity and quality of oocytes. The molecular mechanisms and various contributing factors underlying ovarian aging have been uncovered. In this review, we highlight some of critical factors that impact oocyte quantity and quality during aging. Germ cell and follicle reserve at birth determines reproductive lifespan and timing the menopause in female mammals. Accelerated diminishing ovarian reserve leads to premature ovarian aging or insufficiency. Poor oocyte quality with increasing age could result from chromosomal cohesion deterioration and misaligned chromosomes, telomere shortening, DNA damage and associated genetic mutations, oxidative stress, mitochondrial dysfunction and epigenetic alteration. We also discuss the intervention strategies to delay ovarian aging. Both the efficacy of senotherapies by antioxidants against reproductive aging and mitochondrial therapy are discussed. Functional oocytes and ovarioids could be rejuvenated from pluripotent stem cells or somatic cells. We propose directions for future interventions. As couples increasingly begin delaying parenthood in life worldwide, understanding the molecular mechanisms during female reproductive aging and potential intervention strategies could benefit women in making earlier choices about their reproductive health.

Mechanism of Citri Reticulatae Pericarpium as an Anticancer Agent from the Perspective of Flavonoids: A Review

Citri Reticulatae Pericarpium (CRP), also known as “chenpi”, is the most common qi-regulating drug in traditional Chinese medicine. It is often used to treat cough and indigestion, but in recent years, it has been found to have multi-faceted anti-cancer effects. This article reviews the pharmacology of CRP and the mechanism of the action of flavonoids, the key components of CRP, against cancers including breast cancer, lung cancer, prostate cancer, hepatic carcinoma, gastric cancer, colorectal cancer, esophageal cancer, cervical cancer, bladder cancer and other cancers with a high diagnosis rate. Finally, the specific roles of CRP in important phenotypes such as cell proliferation, apoptosis, autophagy and migration–invasion in cancer were analyzed, and the possible prospects and deficiencies of CRP as an anticancer agent were evaluated.

The Potential of the Mediterranean Diet to Improve Mitochondrial Function in Experimental Models of Obesity and Metabolic Syndrome

The abnormal expansion of body fat paves the way for several metabolic abnormalities including overweight, obesity, and diabetes, which ultimately cluster under the umbrella of metabolic syndrome (MetS). Patients with MetS are at an increased risk of cardiovascular disease, morbidity, and mortality. The coexistence of distinct metabolic abnormalities is associated with the release of pro-inflammatory adipocytokines, as components of low-to-medium grade systemic inflammation and increased oxidative stress. Adopting healthy lifestyles, by using appropriate dietary regimens, contributes to the prevention and treatment of MetS. Metabolic abnormalities can influence the function and energetic capacity of mitochondria, as observed in many obesity-related cardio-metabolic disorders. There are preclinical studies both in cellular and animal models, as well as clinical studies, dealing with distinct nutrients of the Mediterranean diet (MD) and dysfunctional mitochondria in obesity and MetS. The term "Mitochondria nutrients" has been adopted in recent years, and it depicts the adequate nutrients to keep proper mitochondrial function. Different experimental models show that components of the MD, including polyphenols, plant-derived compounds, and polyunsaturated fatty acids, can improve mitochondrial metabolism, biogenesis, and antioxidant capacity. Such effects are valuable to counteract the mitochondrial dysfunction associated with obesity-related abnormalities and can represent the beneficial feature of polyphenols-enriched olive oil, vegetables, nuts, fish, and plant-based foods, as the main components of the MD. Thus, developing mitochondria-targeting nutrients and natural agents for MetS treatment and/or prevention is a logical strategy to decrease the burden of disease and medications at a later stage. In this comprehensive review, we discuss the effects of the MD and its bioactive components on improving mitochondrial structure and activity.

PGC-1α-Mediated Mitochondrial Quality Control: Molecular Mechanisms and Implications for Heart Failure

Mitochondria with structural and functional integrity are essential for maintaining mitochondrial function and cardiac homeostasis. It is involved in the pathogenesis of many diseases. Peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α), acted as a transcriptional cofactor, is abundant in the heart, which modulates mitochondrial biogenesis and mitochondrial dynamics and mitophagy to sustain a steady-state of mitochondria. Cumulative evidence suggests that dysregulation of PGC-1α is closely related to the onset and progression of heart failure. PGC-1α deficient-mice can lead to worse cardiac function under pressure overload compared to sham. Here, this review mainly focuses on what is known about its regulation in mitochondrial functions, as well as its crucial role in heart failure.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

Hypoxia: Role of SIRT1 and the protective effect of resveratrol in ovarian function

Background

Ovarian function is closely related to the degree of vascular network development surrounding the ovary. Maternal aging‐related construction defects in this vascular network can cause ovarian hypoxia, which impedes oocyte nutrient supply, leading to physiological changes in the ovaries and oocytes. The anti‐aging gene Sirtuin 1 (SIRT1) senses and adapts to ambient stress and is associated with hypoxic environments and mitochondrial biogenesis.

Methods

The present study is a literature review focusing on investigations involving the changes in SIRT1 and mitochondrial expression during hypoxia and the cytoprotective effects of the SIRT1 activator, resveratrol.

Main findings

Hypoxia suppresses SIRT1 and mitochondrial expression. Resveratrol can reverse the hypoxia‐induced decrease in mitochondrial and SIRT1 activity. Resveratrol suppresses the production of hypoxia‐inducible factor‐1α and vascular endothelial growth factor proteins.

Conclusion

Resveratrol exhibits protective activity against hypoxic stress and may prevent hypoxia‐ or aging‐related mitochondrial dysfunction. Resveratrol treatment may be a potential option for infertility therapy.

Histone Deacetylase Sirtuin 1 Promotes Loss of Primary Cilia in Cholangiocarcinoma

BACKGROUND AND AIMS

Sirtuin 1 (SIRT1) is a complex NAD⁺ -dependent protein deacetylase known to act as a tumor promoter or suppressor in different cancers. Here, we describe a mechanism of SIRT1-induced destabilization of primary cilia in cholangiocarcinoma (CCA).

APPROACH AND RESULTS

A significant overexpression of SIRT1 was detected in human CCA specimens and CCA cells including HuCCT1, KMCH, and WITT1 as compared with normal cholangiocytes (H69 and NHC). Small interfering RNA (siRNA)-mediated knockdown of SIRT1 in HuCCT1 cells induced cilia formation, whereas overexpression of SIRT1 in normal cholangiocytes suppressed ciliary expression. Activity of SIRT1 was regulated by presence of NAD+ in CCA cells. Inhibition of NAD -producing enzyme nicotinamide phosphoribosyl transferase increased ciliary length and frequency in CCA cells and in SIRT1-overexpressed H69 cells. Furthermore, we also noted that SIRT1 induces the proteasomal mediated degradation of ciliary proteins, including α-tubulin, ARL13B, and KIF3A. Moreover, overexpression of SIRT1 in H69 and NHC cells significantly induced cell proliferation and, conversely, SIRT1 inhibition in HuCCT1 and KMCH cells using siRNA or sirtinol reduced cell proliferation. In an orthotopic transplantation rat CCA model, the SIRT1 inhibitor sirtinol reduced tumor size and tumorigenic proteins (glioma-associated oncogene 1, phosphorylated extracellular signal-regulated kinase, and IL-6) expression.

CONCLUSIONS

In conclusion, these results reveal the tumorigenic role of SIRT1 through modulation of primary cilia formation and provide the rationale for developing therapeutic approaches for CCA using SIRT1 as a target.

Relieving Cellular Energy Stress in Aging, Neurodegenerative, and Metabolic Diseases, SIRT1 as a Therapeutic and Promising Node

The intracellular energy state will alter under the influence of physiological or pathological stimuli. In response to this change, cells usually mobilize various molecules and their mechanisms to promote the stability of the intracellular energy status. Mitochondria are the main source of ATP. Previous studies have found that the function of mitochondria is impaired in aging, neurodegenerative diseases, and metabolic diseases, and the damaged mitochondria bring lower ATP production, which further worsens the progression of the disease. Silent information regulator-1 (SIRT1) is a multipotent molecule that participates in the regulation of important biological processes in cells, including cellular metabolism, cell senescence, and inflammation. In this review, we mainly discuss that promoting the expression and activity of SIRT1 contributes to alleviating the energy stress produced by physiological and pathological conditions. The review also discusses the mechanism of precise regulation of SIRT1 expression and activity in various dimensions. Finally, according to the characteristics of this mechanism in promoting the recovery of mitochondrial function, the relationship between current pharmacological preparations and aging, neurodegenerative diseases, metabolic diseases, and other diseases was analyzed.

Activation of cardiac Nmnat/NAD+/SIR2 pathways mediates endurance exercise resistance to lipotoxic cardiomyopathy in aging Drosophila

Endurance exercise is an important way to resist and treat high-fat diet (HFD)-induced lipotoxic cardiomyopathy, but the underlying molecular mechanisms are poorly understood. Here, we used Drosophila to identify whether cardiac Nmnat/NAD+/SIR2 pathway activation mediates endurance exercise-induced resistance to lipotoxic cardiomyopathy. The results showed that endurance exercise activated the cardiac Nmnat/NAD+/SIR2/FOXO pathway and the Nmnat/NAD+/SIR2/PGC-1α pathway, including up-regulating cardiac Nmnat, SIR2, FOXO and PGC-1α expression, superoxide dismutase (SOD) activity and NAD+ levels, and it prevented HFD-induced or cardiac Nmnat knockdown-induced cardiac lipid accumulation, malondialdehyde (MDA) content and fibrillation increase, and fractional shortening decrease. Cardiac Nmnat overexpression also activated heart Nmnat/NAD+/SIR2 pathways and resisted HFD-induced cardiac malfunction, but it could not protect against HFD-induced lifespan reduction and locomotor impairment. Exercise improved lifespan and mobility in cardiac Nmnat knockdown flies. Therefore, the current results confirm that cardiac Nmnat/NAD+/SIR2 pathways are important antagonists of HFD-induced lipotoxic cardiomyopathy. Cardiac Nmnat/NAD+/SIR2 pathway activation is an important underlying molecular mechanism by which endurance exercise and cardiac Nmnat overexpression give protection against lipotoxic cardiomyopathy in Drosophila.

The GCN5: its biological functions and therapeutic potentials

General control non-depressible 5 (GCN5) or lysine acetyltransferase 2A (KAT2A) is one of the most highly studied histone acetyltransferases. It acts as both histone acetyltransferase (HAT) and lysine acetyltransferase (KAT). As an HAT it plays a pivotal role in the epigenetic landscape and chromatin modification. Besides, GCN5 regulates a wide range of biological events such as gene regulation, cellular proliferation, metabolism and inflammation. Imbalance in the GCN5 activity has been reported in many disorders such as cancer, metabolic disorders, autoimmune disorders and neurological disorders. Therefore, unravelling the role of GCN5 in different diseases progression is a prerequisite for both understanding and developing novel therapeutic agents of these diseases. In this review, we have discussed the structural features, the biological function of GCN5 and the mechanical link with the diseases associated with its imbalance. Moreover, the present GCN5 modulators and their limitations will be presented in a medicinal chemistry perspective.

Glucagon's Metabolic Action in Health and Disease

Discovered almost simultaneously with insulin, glucagon is a pleiotropic hormone with metabolic action that goes far beyond its classical role to increase blood glucose. Albeit best known for its ability to directly act on the liver to increase de novo glucose production and to inhibit glycogen breakdown, glucagon lowers body weight by decreasing food intake and by increasing metabolic rate. Glucagon further promotes lipolysis and lipid oxidation and has positive chronotropic and inotropic effects in the heart. Interestingly, recent decades have witnessed a remarkable renaissance of glucagon's biology with the acknowledgment that glucagon has pharmacological value beyond its classical use as rescue medication to treat severe hypoglycemia. In this article, we summarize the multifaceted nature of glucagon with a special focus on its hepatic action and discuss the pharmacological potential of either agonizing or antagonizing the glucagon receptor for health and disease. © 2021 American Physiological Society. Compr Physiol 11:1759-1783, 2021.

Caffeine protects against stress-induced murine depression through activation of PPARγC1α-mediated restoration of the kynurenine pathway in the skeletal muscle

Exercise prevents depression through peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α)-mediated activation of a particular branch of the kynurenine pathway. From kynurenine (KYN), two independent metabolic pathways produce neurofunctionally different metabolites, mainly in somatic organs: neurotoxic intermediate metabolites via main pathway and neuroprotective end product, kynurenic acid (KYNA) via the branch. Elevated levels of KYN have been found in patients with depression. Herein, we investigated whether and how caffeine prevents depression, focusing on the kynurenine pathway. Mice exposed to chronic mild stress (CMS) exhibited depressive-like behaviours with an increase and decrease in plasma levels of pro-neurotoxic KYN and neuroprotective KYNA, respectively. However, caffeine rescued CMS-exposed mice from depressive-like behaviours and restored the plasma levels of KYN and KYNA. Concomitantly, caffeine induced a key enzyme converting KYN into KYNA, namely kynurenine aminotransferase-1 (KAT1), in murine skeletal muscle. Upon caffeine stimulation murine myotubes exhibited KAT1 induction and its upstream PGC-1α sustainment. Furthermore, a proteasome inhibitor, but not translational inhibitor, impeded caffeine sustainment of PGC-1α, suggesting that caffeine induced KAT1 by inhibiting proteasomal degradation of PGC-1α. Thus, caffeine protection against CMS-induced depression may be associated with sustainment of PGC-1α levels and the resultant KAT1 induction in skeletal muscle, and thereby consumption of pro-neurotoxic KYN.

Vitamin K2 Alleviates Insulin Resistance in Skeletal Muscle by Improving Mitochondrial Function Via SIRT1 Signaling

Aims: High-fat diet (HFD)-induced insulin resistance (IR) impairs skeletal muscle mitochondrial biogenesis and functions, adversely affecting human health and lifespan. Vitamin K2 (VK2) has a beneficial role in improving insulin sensitivity and glucose metabolism. However, the underlying molecular mechanisms of VK2 on insulin sensitivity have not been well established. We investigated VK2's modulation of mitochondrial function to protect against IR in mice and cell models. Results: VK2 supplementation could effectively ameliorate the development of IR by improving mitochondrial function in both HFD-fed mice and palmitate acid-exposed cells. We revealed for the first time that HFD-caused mitochondrial dysfunction could be reversed by VK2 treatment. VK2 enhanced the mitochondrial function by improving mitochondrial respiratory capacity, increasing mitochondrial biogenesis and the enzymatic activities of mitochondrial complexes through SIRT1 signaling. The benefits of VK2 were abrogated in C₂C₁₂ transfected with SIRT1 siRNA but not in C₂C₁₂ transfected with AMPK siRNA. VK2 and SRT1720, a specific agonist of SIRT1, had the same effect on improving mitochondrial function via SIRT1 signaling. Thus, SIRT1 is required for VK2 improvement in skeletal muscle. Further, the beneficial effects of both VK2 and geranylgeraniol contribute to inhibited IR in skeletal muscle via SIRT1. Innovation and Conclusion: These studies demonstrated a previously undiscovered mechanism by which VK2 alleviates IR in skeletal muscle by improving mitochondrial function via SIRT1. Naturally occurring VK2 prevents IR by improving mitochondrial function through SIRT1 signaling. These results could provide a foundation to identify new VK2-based preventive and therapeutic strategies for IR.

Mitochondrial dysfunction in nonalcoholic fatty liver disease and alcohol related liver disease

Fatty liver disease constitutes a spectrum of liver diseases which begin with simple steatosis and may progress to advance stages of steatohepatitis, cirrhosis, and hepatocellular carcinoma (HCC). The two main etiologies are-alcohol related fatty liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD). NAFLD is a global health epidemic strongly associated with modern dietary habits and life-style. It is the second most common cause of chronic liver disease in the US after chronic hepatitis C virus (HCV) infection. Approximately 100 million people are affected with this condition in the US alone. Excessive intakes of calories, saturated fat and refined carbohydrates, and sedentary life style have led to explosion of this health epidemic in developing nations as well. ALD is the third most common cause of chronic liver disease in the US. Even though the predominant trigger for onset of steatosis is different in these two conditions, they share common themes in progression from steatosis to the advance stages. Oxidative stress (OS) is considered a very significant contributor to hepatocyte injury in these conditions. Mitochondrial dysfunction contributes to this OS. Role of mitochondrial dysfunction in pathogenesis of fatty liver diseases is emerging but far from completely understood. A better understanding is essential for more effective preventive and therapeutic interventions. Here, we discuss the pathogenesis and therapeutic approaches of NAFLD and ALD from a mitochondrial perspective.

Ketogenesis and SIRT1 as a tool in managing obesity

Obesity is a serious chronic disease and a public health concern in both developing and developed countries. Managing obesity has been a great challenge for both health care professionals and patients alike. Among the various diet programs aimed at promoting weight loss, the ketogenic diet, a diet high in fat and low in carbohydrates, has been at the forefront recently and its mechanism in weight loss is much debated. Activation of Sirtuin 1 or SIRT1 is able to circumvent various diseases, including metabolic syndrome and obesity and is thought to be a potentially reliable treatment target for both of them. Augmentation of SIRT1 may be carried out using dietary means such as nicotinamide adenine dinucleotide (NAD) supplementation and/or ketogenic diet. Although ketogenic diet may augment SIRT1 activation in people affected by obesity, recent studies have indicated that the relationship between SIRT1 and ketogenesis is unpredictable. The exact circumstances and mechanisms of SIRT1, NAD and ketogenesis in the clinical setting as an intervention tool in managing obesity remained uncertain. Although several recent literatures have documented significant weight-loss following ketogenic diet interventions, there were limitations with regards to duration of trial, choice and the number of trial subjects. Studies investigating the safety of ketogenic diet in the long term, beyond 46 weeks and related mechanism and pathways are still lacking and the sustainability of this diet remains to be determined. This review explores the recent progress on ketogenic diet and its relationships with SIRT1 as a tool in managing obesity and relevant clinical implications.

Transcriptome-wide analysis of PGC-1α-binding RNAs identifies genes linked to glucagon metabolic action

The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a transcriptional coactivator that controls expression of metabolic/energetic genes, programming cellular responses to nutrient and environmental adaptations such as fasting, cold, or exercise. Unlike other coactivators, PGC-1α contains protein domains involved in RNA regulation such as serine/arginine (SR) and RNA recognition motifs (RRMs). However, the RNA targets of PGC-1α and how they pertain to metabolism are unknown. To address this, we performed enhanced ultraviolet (UV) cross-linking and immunoprecipitation followed by sequencing (eCLIP-seq) in primary hepatocytes induced with glucagon. A large fraction of RNAs bound to PGC-1α were intronic sequences of genes involved in transcriptional, signaling, or metabolic function linked to glucagon and fasting responses, but were not the canonical direct transcriptional PGC-1α targets such as OXPHOS or gluconeogenic genes. Among the top-scoring RNA sequences bound to PGC-1α were Foxo1, Camk1δ, Per1, Klf15, Pln4, Cluh, Trpc5, Gfra1, and Slc25a25 PGC-1α depletion decreased a fraction of these glucagon-induced messenger RNA (mRNA) transcript levels. Importantly, knockdown of several of these genes affected glucagon-dependent glucose production, a PGC-1α-regulated metabolic pathway. These studies show that PGC-1α binds to intronic RNA sequences, some of them controlling transcript levels associated with glucagon action.

GDF15: A Hormone Conveying Somatic Distress to the Brain

GDF15 has recently gained scientific and translational prominence with the discovery that its receptor is a GFRAL-RET heterodimer of which GFRAL is expressed solely in the hindbrain. Activation of this receptor results in reduced food intake and loss of body weight and is perceived and recalled by animals as aversive. This information encourages a revised interpretation of the large body of previous research on the protein. GDF15 can be secreted by a wide variety of cell types in response to a broad range of stressors. We propose that central sensing of GDF15 via GFRAL-RET activation results in behaviors that facilitate the reduction of exposure to a noxious stimulus. The human trophoblast appears to have hijacked this signal, producing large amounts of GDF15 from early pregnancy. We speculate that this encourages avoidance of potential teratogens in pregnancy. Circulating GDF15 levels are elevated in a range of human disease states, including various forms of cachexia, and GDF15-GFRAL antagonism is emerging as a therapeutic strategy for anorexia/cachexia syndromes. Metformin elevates circulating GDF15 chronically in humans and the weight loss caused by this drug appears to be dependent on the rise in GDF15. This supports the concept that chronic activation of the GDF15-GFRAL axis has efficacy as an antiobesity agent. In this review, we examine the science of GDF15 since its identification in 1997 with our interpretation of this body of work now being assisted by a clear understanding of its highly selective central site of action.

Targeting Multiple Mitochondrial Processes by a Metabolic Modulator Prevents Sarcopenia and Cognitive Decline in SAMP8 Mice

The age-dependent declines of skeletal muscle and cognitive functions often coexist in elderly subjects. The underlying pathophysiological mechanisms share common features of mitochondrial dysfunction, which plays a central role in the development of overt sarcopenia and/or dementia. Dietary supplementation with formulations of essential and branched-chain amino acids (EAA-BCAA) is a promising preventive strategy because it can preserve mitochondrial biogenesis and function. The senescence-accelerated mouse prone 8 (SAMP8) is considered an accurate model of age-related muscular and cognitive alterations. Hence, we aimed to investigate the progression of mitochondrial dysfunctions during muscular and cognitive aging of SAMP8 mice and to study the effects of a novel EAA-BCAA-based metabolic modulator on these changes. We evaluated body condition, motor endurance, and working memory of SAMP8 mice at 5, 9, 12, and 15 months of age. Parallel changes in protein levels of mitochondrial respiratory chain subunits, regulators of mitochondrial biogenesis and dynamics, and the antioxidant response, as well as respiratory complex activities, were measured in the quadriceps femoris and the hippocampus. The same variables were assessed in 12-month-old SAMP8 mice that had received dietary supplementation with the novel EAA-BCAA formulation, containing tricarboxylic acid cycle intermediates and co-factors (PD-0E7, 1.5 mg/kg/body weight/day in drinking water) for 3 months. Contrary to untreated mice, which had a significant molecular and phenotypic impairment, PD-0E7-treated mice showed preserved healthy body condition, muscle weight to body weight ratio, motor endurance, and working memory at 12 months of age. The PD-0E7 mixture increased the protein levels and the enzymatic activities of mitochondrial complex I, II, and IV and the expression of proliferator-activated receptor γ coactivator-1α, optic atrophy protein 1, and nuclear factor, erythroid 2 like 2 in muscles and hippocampi. The mitochondrial amyloid-β-degrading pitrilysin metallopeptidase 1 was upregulated, while amyloid precursor protein was reduced in the hippocampi of PD-0E7 treated mice. In conclusion, we show that a dietary supplement tailored to boost mitochondrial respiration preserves skeletal muscle and hippocampal mitochondrial quality control and health. When administered at the early onset of age-related physical and cognitive decline, this novel metabolic inducer counteracts the deleterious effects of precocious aging in both domains.

Molecular characterization, tissue expression and polymorphisms of buffalo PPARGC1A gene

PPARGC1A exerts important functions in activating many nuclear receptors and transcription factors that are related to energy balance. Previous studies have shown that PPARGC1A gene is associated with lactation traits of dairy cattle. However, the functional role of the buffalo PPARGC1A gene is still unknown. In this work, the complete coding sequence (CDS) of buffalo PPARGC1A was isolated and characterized for swamp and river buffalo. The CDS length of PPARGC1A for both types of buffalo was the same, which was composed of 2394 nucleotides and encoded a peptide composed of 797 amino acid residues. This protein belonged to a hydrophilic protein and contained one RRM_PPARGC1A domain (AA 674–764) without a signal peptide or a transmembrane domain. The differential expressions of this gene in 10 buffalo tissues in lactation and non-lactation displayed that the PPARGC1A was highly expressed in the muscle, heart, liver, brain and kidney of both non-lactating and lactating periods, but its expression was significantly different in the muscle, heart, liver, small intestine, mammary gland, rumen, spleen and lung between the two periods. Eight single nucleotide polymorphisms (SNPs) were found in buffalo, in which the c.778C>T, c.1257G>A and c.1311G>A were shared by two types of buffalo with similar allele frequencies, while the c.419C>T, c.759A>G, c.920C>A, c.926G>A and c.1509A>T were only observed in river buffalo. The SNP419, SNP920 and SNP926 were non-synonymous, which led to the amino acid changes of p.Ser140Phe, p.Pro307His and p.Arg309Lys. Seven nucleotide differential sites were identified in the PPARGC1A gene between buffalo and other Bovidae species. Phylogenetic analysis indicated that buffaloes were independently clustered into one branch, but they were closely related to the species of the Bos genus. The results indicate that buffalo PPARGC1A is an inducible transcriptional coactivator involved in regulating carbohydrate and fat metabolism. It can exert a functional role in a variety of buffalo tissues and may participate in milk fat synthesis and development in the mammary gland.

Non-histone protein acetylation by the evolutionarily conserved GCN5 and PCAF acetyltransferases

GCN5, conserved from yeast to humans, and the vertebrate specific PCAF, are lysine acetyltransferase enzymes found in large protein complexes. Both enzymes have well documented roles in the histone acetylation and the concomitant regulation of transcription. However, these enzymes also acetylate non-histone substrates to impact diverse aspects of cell physiology. Here, I review our current understanding of non-histone acetylation by GCN5 and PCAF across eukaryotes, from target identification to molecular mechanism and regulation. I focus mainly on budding yeast, where Gcn5 was first discovered, and mammalian systems, where the bulk of non-histone substrates have been characterized. I end the review by defining critical caveats and open questions that apply to all models.

Sirtuins, brain and cognition: A review of resveratrol effects

Sirtuins (SIRTs) are a protein family with high preservation degree among evolutionary scale. SIRTs are histone deacetylases regulatory enzymes of genetic material deeply involved in numerous physiological tasks including metabolism, brain function and aging. Mammals sirtuins comprise seven enzymatic components (SIRT1–SIRT7). The highest studied sirtuin is SIRT1, which plays an essential position in the prevention and evolution of neuro-disorders. Resveratrol (3,5,4-trihydroxystylbene) (RSV) is a polyphenol, which belongs to a family compounds identified as stilbenes, predominantly concentrated in grapes and red wine. RSV is the must studied Sirtuin activator and is used as food supplementary compound. Resveratrol exhibits strong antioxidant activity, reducing free radicals, diminishing quinone-reductase-2 activity and exerting positive regulation of several endogenous enzymes. Resveratrol is also able to inhibit pro-inflammatory factors, reducing the stimulation of the nuclear factor kB (NF-kB) and the release of endogenous cytokines. Resveratrol treatment can modulate multiple signaling pathway effectors related to programmed cell death, cell survival, and synaptic plasticity. In this context, the present review looks over news and the role of Sirtuins activation and resveratrol effects on modulating target genes, cognition and neurodegenerative disorders.

Phosphodiesterase Inhibitors for Alzheimer's Disease: A Systematic Review of Clinical Trials and Epidemiology with a Mechanistic Rationale

BACKGROUND

Preclinical studies, clinical trials, and reviews suggest increasing 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) with phosphodiesterase inhibitors is disease-modifying in Alzheimer's disease (AD). cAMP/protein kinase A (PKA) and cGMP/protein kinase G (PKG) signaling are disrupted in AD. cAMP/PKA and cGMP/PKG activate cAMP response element binding protein (CREB). CREB binds mitochondrial and nuclear DNA, inducing synaptogenesis, memory, and neuronal survival gene (e.g., brain-derived neurotrophic factor) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). cAMP/PKA and cGMP/PKG activate Sirtuin-1, which activates PGC1α. PGC1α induces mitochondrial biogenesis and antioxidant genes (e.g.,Nrf2) and represses BACE1. cAMP and cGMP inhibit BACE1-inducing NFκB and tau-phosphorylating GSK3β.

OBJECTIVE AND METHODS

We review efficacy-testing clinical trials, epidemiology, and meta-analyses to critically investigate whether phosphodiesteraseinhibitors prevent or treat AD.

RESULTS

Caffeine and cilostazol may lower AD risk. Denbufylline and sildenafil clinical trials are promising but preliminary and inconclusive. PF-04447943 and BI 409,306 are ineffective. Vinpocetine, cilostazol, and nicergoline trials are mixed. Deprenyl/selegiline trials show only short-term benefits. Broad-spectrum phosphodiesterase inhibitor propentofylline has been shown in five phase III trials to improve cognition, dementia severity, activities of daily living, and global assessment in mild-to-moderate AD patients on multiple scales, including the ADAS-Cogand the CIBIC-Plus in an 18-month phase III clinical trial. However, two books claimed based on a MedScape article an 18-month phase III trial failed, so propentofylline was discontinued. Now, propentofylline is used to treat canine cognitive dysfunction, which, like AD, involves age-associated wild-type Aβ deposition.

CONCLUSION

Phosphodiesterase inhibitors may prevent and treat AD.

Nicotinamide Mononucleotide Administration Prevents Experimental Diabetes-Induced Cognitive Impairment and Loss of Hippocampal Neurons

Diabetes predisposes to cognitive decline leading to dementia and is associated with decreased brain NAD⁺ levels. This has triggered an intense interest in boosting nicotinamide adenine dinucleotide (NAD⁺) levels to prevent dementia. We tested if the administration of the precursor of NAD⁺, nicotinamide mononucleotide (NMN), can prevent diabetes-induced memory deficits. Diabetes was induced in Sprague-Dawley rats by the administration of streptozotocin (STZ). After 3 months of diabetes, hippocampal NAD⁺ levels were decreased (p = 0.011). In vivo localized high-resolution proton magnetic resonance spectroscopy (MRS) of the hippocampus showed an increase in the levels of glucose (p < 0.001), glutamate (p < 0.001), gamma aminobutyric acid (p = 0.018), myo-inositol (p = 0.018), and taurine (p < 0.001) and decreased levels of N-acetyl aspartate (p = 0.002) and glutathione (p < 0.001). There was a significant decrease in hippocampal CA1 neuronal volume (p < 0.001) and neuronal number (p < 0.001) in the Diabetic rats. Diabetic rats showed hippocampal related memory deficits. Intraperitoneal NMN (100 mg/kg) was given after induction and confirmation of diabetes and was provided on alternate days for 3 months. NMN increased brain NAD⁺ levels, normalized the levels of glutamate, taurine, N-acetyl aspartate (NAA), and glutathione. NMN-treatment prevented the loss of CA1 neurons and rescued the memory deficits despite having no significant effect on hyperglycemic or lipidemic control. In hippocampal protein extracts from Diabetic rats, SIRT1 and PGC-1α protein levels were decreased, and acetylation of proteins increased. NMN treatment prevented the diabetes-induced decrease in both SIRT1 and PGC-1α and promoted deacetylation of proteins. Our results indicate that NMN increased brain NAD⁺, activated the SIRT1 pathway, preserved mitochondrial oxidative phosphorylation (OXPHOS) function, prevented neuronal loss, and preserved cognition in Diabetic rats.

Sildenafil for the Treatment of Alzheimer's Disease: A Systematic Review

Nitric oxide/cyclic guanosine monophosphate (cGMP) signaling is compromised in Alzheimer’s disease (AD), and phosphodiesterase 5 (PDE5), which degrades cGMP, is upregulated. Sildenafil inhibits PDE5 and increases cGMP levels. Integrating previous findings, we determine that most doses of sildenafil (especially low doses) likely activate peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) via protein kinase G-mediated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) phosphorylation and/or Sirtuin-1 activation and PGC1α deacetylation. Via PGC1α signaling, low-dose sildenafil likely suppresses β-secretase 1 expression and amyloid-β (Aβ) generation, upregulates antioxidant enzymes, and induces mitochondrial biogenesis. Plus, sildenafil should increase brain perfusion, insulin sensitivity, long-term potentiation, and neurogenesis while suppressing neural apoptosis and inflammation. A systematic review of sildenafil in AD was undertaken. In vitro, sildenafil protected neural mitochondria from Aβ and advanced glycation end products. In transgenic AD mice, sildenafil was found to rescue deficits in CREB phosphorylation and memory, upregulate brain-derived neurotrophic factor, reduce reactive astrocytes and microglia, decrease interleukin-1β, interleukin-6, and tumor necrosis factor-α, decrease neural apoptosis, increase neurogenesis, and reduce tau hyperphosphorylation. All studies that tested Aβ levels reported significant improvements except the two that used the highest dosage, consistent with the dose-limiting effect of cGMP-induced phosphodiesterase 2 (PDE2) activation and cAMP depletion on PGC1α signaling. In AD patients, a single dose of sildenafil decreased spontaneous neural activity, increased cerebral blood flow, and increased the cerebral metabolic rate of oxygen. A randomized control trial of sildenafil (ideally with a PDE2 inhibitor) in AD patients is warranted.

Silent Mating-Type Information Regulation 2 Homolog 1 Attenuates the Neurotoxicity Associated with Alzheimer Disease via a Mechanism Which May Involve Regulation of Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-α

To investigate the neuroprotective role of silent mating-type information regulation 2 homolog 1 (SIRT1) in Alzheimer disease (AD), brain tissues from patients with AD and APP/PS1 mice as well as primary rat neurons exposed to oligomers of amyloid-β peptide were examined. The animals were treated with resveratrol (RSV) or suramin for 2 months. Cell cultures were treated with RSV, suramin, and the peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) stimulator ZLN005. Cells were transiently transfected with PGC-1α silencing RNA. The level of SIRT1 in brain tissues from patients with AD and APP/PS1 mice, including nuclear and mitochondrial proteins, as well as in primary neurons exposed to oligomers of amyloid-β peptide, was decreased. Overexpression of APP/PS1 impaired learning and memory of mice; produced more senile plaques, disrupted membranes, and resulted in broken or absent cristae of mitochondria in the brain; decreased levels of A disintegrin and metallopeptidase domain 10, beta-secretase 2, 8-oxoguanine DNA glycosylase-1, PGC-1α, and NAD+; and increased levels of beta-secretase 1 and apoptosis. Interestingly, these changes were attenuated significantly by RSV treatment but enhanced by suramin administration. By activating PGC-1α but inhibiting SIRT1, apoptotic cell death was significantly decreased; however, by activating SIRT1 but inhibiting PGC-1α with small interfering PGC-1α, these levels remained unchanged. These findings indicate that SIRT1 may protect against AD-associated neurotoxicity, which might involve PGC-1α regulation.

Epigenetic Control of Mitochondrial Function in the Vasculature

The molecular signatures of epigenetic regulation and chromatin architecture are emerging as pivotal regulators of mitochondrial function. Recent studies unveiled a complex intersection among environmental factors, epigenetic signals, and mitochondrial metabolism, ultimately leading to alterations of vascular phenotype and increased cardiovascular risk. Changing environmental conditions over the lifetime induce covalent and post-translational chemical modification of the chromatin template which sensitize the genome to establish new transcriptional programs and, hence, diverse functional states. On the other hand, metabolic alterations occurring in mitochondria affect the availability of substrates for chromatin-modifying enzymes, thus leading to maladaptive epigenetic signatures altering chromatin accessibility and gene transcription. Indeed, several components of the epigenetic machinery require intermediates of cellular metabolism (ATP, AcCoA, NADH, α-ketoglutarate) for enzymatic function. In the present review, we describe the emerging role of epigenetic modifications as fine tuners of gene transcription in mitochondrial dysfunction and vascular disease. Specifically, the following aspects are described in detail: (i) mitochondria and vascular function, (ii) mitochondrial ROS, (iii) epigenetic regulation of mitochondrial function; (iv) the role of mitochondrial metabolites as key effectors for chromatin-modifying enzymes; (v) epigenetic therapies. Understanding epigenetic routes may pave the way for new approaches to develop personalized therapies to prevent mitochondrial insufficiency and its complications.

Acetylation of PGC1α by Histone Deacetylase 1 Downregulation Is Implicated in Radiation-Induced Senescence of Brain Endothelial Cells

Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) is a potent transcription factor for mitochondrial function, lipid metabolism, and detoxification in a variety of tissues. PGC1α also promotes brain cell proliferation and memory. However, how PGC1α is involved in aging is not well known. In brain endothelial cells, we found that PGC1α knockdown accelerated DNA damage-induced senescence, evidenced by an increase in senescence-associated β-galactosidase-positive cells and a decrease in cell proliferation and adenosine triphosphate production. PGC1α knockdown delayed DNA damage repair mechanisms compared with the wild-type condition as shown by γ-H2AX foci staining assay. Overexpression of PGC1α reduced senescence-associated β-galactosidase-positive cells and increased the proliferation of senescent cells. Although PGC1α protein levels were not decreased, PGC1 acetylation was increased by ionizing radiation treatment and aging. Histone deacetylase 1 (HDAC1) expression was decreased by ionizing radiation treatment and aging, and downregulation of HDAC1 induced acetylation of PGC1α. HDAC1 knockdown affected sirtuin 1 expression and decreased its deacetylation of PGC1α. In the mouse brain cortex, acetylation of PGC1α was increased by ionizing radiation treatment. These results suggest that acetylation of PGC1α is induced by DNA damage agents such as ionizing radiation, which deregulates mitochondrial mechanisms and metabolism, resulting in acceleration of radiation-induced senescence. Therefore, acetylation of PGC1α may be a cause of brain disorders and has the potential to serve as a therapeutic target for radiation-induced senescence after radiation cancer therapy.

Combined overexpression of SIRT1 and knockout of GCN5 in adult skeletal muscle does not affect glucose homeostasis or exercise performance in mice

Sirtuin 1 (SIRT1) and general control of amino acid synthesis 5 (GCN5) regulate mitochondrial biogenesis via opposing modulation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) acetylation status and activity. However, the combined contribution of SIRT1 and GCN5 to skeletal muscle metabolism and endurance performance in vivo is unknown. In this study, we investigated the impact of combined skeletal muscle-specific overexpression of SIRT1 and deletion of GCN5 on glucose homeostasis, skeletal muscle mitochondrial biogenesis and function, and metabolic adaptation to endurance exercise training in mice. We generated mice with combined and tamoxifen-inducible skeletal muscle-specific overexpression of SIRT1 and knockout of GCN5 (dTG) and floxed [wild type (WT)] littermates using a Cre-LoxP approach. All mice were treated with tamoxifen at 5-6 wk of age, and 4-7 wk later glucose homeostasis, skeletal muscle contractile function, mitochondrial function, and the effects of 14 days of voluntary wheel running on expression of metabolic proteins and exercise capacity were assessed. There was no difference in oral glucose tolerance, skeletal muscle contractile function, mitochondrial abundance, or maximal respiratory capacity between dTG and WT mice. Additionally, there were no genotype differences in exercise performance and markers of mitochondrial biogenesis after 14 days of voluntary wheel running. These results demonstrate that combined overexpression of SIRT1 and loss of GCN5 in vivo does not promote metabolic remodeling in skeletal muscle of sedentary or exercise-trained mice.

WITHDRAWN: Demethylation of Di-Methylation of Lysine 4 on Histone 3 Is Inhibited by General Control Nondepressible 5-Induced Acetylation of Lysine-Specific Demethylase 1

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Sirt1 regulates the expression of critical metabolic genes in chicken hepatocytes

Context Studies in mammals show that SIRT1 plays an important role in many biological processes including liver metabolism through histone and non-histone deacetylation. Little is known about the function of Sirt1 in the chicken. Aims The current study investigated the expression pattern of Sirt1 mRNA in the chicken and its functions in the chicken liver. Methods In this work, we used real-time quantitative polymerase chain reaction to quantify the expression levels of Sirt1 mRNA in major chicken organs and tissue types, siRNA to knock down Sirt1 expression in primary chicken hepatocytes, RNA sequencing to identify gene-expression changes induced by Sirt1 knockdown, and analysed the function of the differentially expressed genes (DEGs) through gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes ontology analysis. Key results In total, 86 DEGs were found between Sirt1 knockdown and control chicken hepatocytes, of which 63 genes were downregulated and 23 genes were upregulated by Sirt1 knockdown. The Kyoto Encyclopedia of Genes and Genomes analysis showed that 24 DEGs were involved in metabolism. Seven DEGs were involved in carbohydrate and lipid metabolism. Conclusions The present study showed that Sirt1 regulates the expression of genes involved in carbohydrate and lipid metabolism and many other biological processes in the chicken liver. Implications The results of the present study imply that Sirt1 has various functions in the chicken liver and that Sirt1 plays a potentially important role in hepatic carbohydrate and lipid metabolism in the chicken.

Overexpression of Sirtuin 1 protein in neurons prevents and reverses experimental diabetic neuropathy

In diabetic neuropathy, there is activation of axonal and sensory neuronal degeneration pathways leading to distal axonopathy. The nicotinamide-adenine dinucleotide (NAD+)-dependent deacetylase enzyme, Sirtuin 1 (SIRT1), can prevent activation of these pathways and promote axonal regeneration. In this study, we tested whether increased expression of SIRT1 protein in sensory neurons prevents and reverses experimental diabetic neuropathy induced by a high fat diet (HFD). We generated a transgenic mouse that is inducible and overexpresses SIRT1 protein in neurons (nSIRT1OE Tg). Higher levels of SIRT1 protein were localized to cortical and hippocampal neuronal nuclei in the brain and in nuclei and cytoplasm of small to medium sized neurons in dorsal root ganglia. Wild-type and nSIRT1OE Tg mice were fed with either control diet (6.2% fat) or a HFD (36% fat) for 2 months. HFD-fed wild-type mice developed neuropathy as determined by abnormal motor and sensory nerve conduction velocity, mechanical allodynia, and loss of intraepidermal nerve fibres. In contrast, nSIRT1OE prevented a HFD-induced neuropathy despite the animals remaining hyperglycaemic. To test if nSIRT1OE would reverse HFD-induced neuropathy, nSIRT1OE was activated after mice developed peripheral neuropathy on a HFD. Two months after nSIRT1OE, we observed reversal of neuropathy and an increase in intraepidermal nerve fibre. Cultured adult dorsal root ganglion neurons from nSIRT1OE mice, maintained at high (30 mM) total glucose, showed higher basal and maximal respiratory capacity when compared to adult dorsal root ganglion neurons from wild-type mice. In dorsal root ganglion protein extracts from nSIRT1OE mice, the NAD+-consuming enzyme PARP1 was deactivated and the major deacetylated protein was identified to be an E3 protein ligase, NEDD4-1, a protein required for axonal growth, regeneration and proteostasis in neurodegenerative diseases. Our results indicate that nSIRT1OE prevents and reverses neuropathy. Increased mitochondrial respiratory capacity and NEDD4 activation was associated with increased axonal growth driven by neuronal overexpression of SIRT1. Therapies that regulate NAD+ and thereby target sirtuins may be beneficial in human diabetic sensory polyneuropathy.

How Epigenetic Modifications Drive the Expression and Mediate the Action of PGC-1α in the Regulation of Metabolism

Epigenetic changes are a hallmark of short- and long-term transcriptional regulation, and hence instrumental in the control of cellular identity and plasticity. Epigenetic mechanisms leading to changes in chromatin structure, accessibility for recruitment of transcriptional complexes, and interaction of enhancers and promoters all contribute to acute and chronic adaptations of cells, tissues and organs to internal and external perturbations. Similarly, the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is activated by stimuli that alter the cellular energetic demand, and subsequently controls complex transcriptional networks responsible for cellular plasticity. It thus is of no surprise that PGC-1α is under the control of epigenetic mechanisms, and constitutes a mediator of epigenetic changes in various tissues and contexts. In this review, we summarize the current knowledge of the link between epigenetics and PGC-1α in health and disease.

Natural constituents from food sources: potential therapeutic agents against muscle wasting

Skeletal muscle wasting is highly correlated with not only reduced quality of life but also higher morbidity and mortality. Although an increasing number of patients are suffering from various kinds of muscle atrophy and weakness, there is still no effective therapy available, and skeletal muscle is considered as an under-medicated organ. Food provided not only essential macronutrients but also functional substances involved in the modulation of the physiological systems of our body. Natural constituents from commonly consumed dietary plants, either extracts or compounds, have attracted more and more attention to be developed as agents for preventing and treating muscle wasting due to their safety and effectiveness, as well as structural diversity. This review provides an overview of the mechanistic aspects of muscle wasting, and summarizes the extracts and compounds from food sources as potential therapeutic agents against muscle wasting.

Sustained ER stress promotes hyperglycemia by increasing glucagon action through the deubiquitinating enzyme USP14

Endoplasmic reticulum (ER) stress plays an important role in metabolic diseases like obesity and type 2 diabetes mellitus (T2DM), although the underlying mechanisms and regulatory pathways remain to be elucidated. Here, we induced chronic low-grade ER stress in lean mice to levels similar to those in high-fat diet (HFD)-fed obese mice and found that it promoted hyperglycemia due to enhanced hepatic gluconeogenesis. Mechanistically, sustained ER stress up-regulated the deubiquitinating enzyme ubiquitin-specific peptidase 14 (USP14), which increased the stability and levels of 3',5'-cyclic monophosphate-responsive element binding (CREB) protein (CBP) to enhance glucagon action and hepatic gluconeogenesis. Exogenous overexpression of USP14 in the liver significantly increased hepatic glucose output. Consistent with this, liver-specific knockdown of USP14 abrogated the effects of ER stress on glucose metabolism, and also improved hyperglycemia and glucose intolerance in obese mice. In conclusion, our findings show a mechanism underlying ER stress-induced disruption of glucose homeostasis, and present USP14 as a potential therapeutic target against T2DM.

Poly(ADP-ribose) polymerase-1 inhibits mitochondrial respiration by suppressing PGC-1α activity in neurons

Poly(ADP-ribose) polymerase-1 (PARP1) is a ubiquitous nuclear enzyme that regulates DNA repair and genomic stability. In oxidative genotoxic conditions, PARP1 activity is enhanced significantly, leading to excessive depletion of nicotinamide adenine dinucleotide (NAD⁺) and mitochondrial dysfunction. We hypothesized that PARP1-induced NAD⁺ depletion inhibits NAD⁺-dependent sirtuin deacetylase activity, thereby interfering with the mitochondrial regulator, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). The DNA alkylator, N'-Nitro-N-nitroso-N-methylguanidine (MNNG), induced NAD⁺ depletion, inhibited sirtuin deacetylase activity and enhanced acetylation of PGC-1α. This was associated with reduced interaction between PGC-1α and nuclear respiratory factor 1 (NRF-1), which is a nuclear transcription factor that drives mitochondrial replication by regulating mitochondrial transcription factor A (TFAM). MNNG also reduced binding of NRF-1 to the tfam upstream promoter region and reduced TFAM mRNA, mitochondrial DNA copy number and respiratory function. MNNG effects were mitigated by PARP1 inhibition and genetic loss of function, by enhancing intracellular NAD⁺ levels, and with sirtuin (SIRT1) gain of function, supporting a mechanism dependent on PARP1 activity, NAD⁺-depletion and SIRT1 inhibition. This and other work from our group supports a destructive sequelae of events related to PARP1-induced sirtuin inhibition and sirtuin-mediated regulation of transcription.

Glucagon-Induced Acetylation of Energy-Sensing Factors in Control of Hepatic Metabolism

The liver is the central organ of glycolipid metabolism, which regulates the metabolism of lipids and glucose to maintain energy homeostasis upon alterations of physiological conditions. Researchers formerly focused on the phosphorylation of glucagon in controlling liver metabolism. Noteworthily, emerging evidence has shown glucagon could additionally induce acetylation to control hepatic metabolism in response to different physiological states. Through inducing acetylation of complex metabolic networks, glucagon interacts extensively with various energy-sensing factors in shifting from glucose metabolism to lipid metabolism during prolonged fasting. In addition, glucagon-induced acetylation of different energy-sensing factors is involved in the advancement of nonalcoholic fatty liver disease (NAFLD) to liver cancer. Here, we summarize the latest findings on glucagon to control hepatic metabolism by inducing acetylation of energy-sensing factors. Finally, we summarize and discuss the potential impact of glucagon on the treatment of liver diseases.

Identification of Compounds That Inhibit Estrogen-Related Receptor Alpha Signaling Using High-Throughput Screening Assays

The nuclear receptor, estrogen-related receptor alpha (ERRα; NR3B1), plays a pivotal role in energy homeostasis. Its expression fluctuates with the demands of energy production in various tissues. When paired with the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), the PGC/ERR pathway regulates a host of genes that participate in metabolic signaling networks and in mitochondrial oxidative respiration. Unregulated overexpression of ERRα is found in many cancer cells, implicating a role in cancer progression and other metabolism-related diseases. Using high throughput screening assays, we screened the Tox21 10K compound library in stably transfected HEK293 cells containing either the ERRα-reporter or the reporter plus PGC-1α expression plasmid. We identified two groups of antagonists that were potent inhibitors of ERRα activity and/or the PGC/ERR pathway: nine antineoplastic agents and thirteen pesticides. Results were confirmed using gene expression studies. These findings suggest a novel mechanism of action on bioenergetics for five of the nine antineoplastic drugs. Nine of the thirteen pesticides, which have not been investigated previously for ERRα disrupting activity, were classified as such. In conclusion, we demonstrated that high-throughput screening assays can be used to reveal new biological properties of therapeutic and environmental chemicals, broadening our understanding of their modes of action.

Interconnection between Metabolism and Cell Cycle in Cancer

Cell cycle progression and division is regulated by checkpoint controls and sequential activation of cyclin-dependent kinases (CDKs). Understanding of how these events occur in synchrony with metabolic changes could have important therapeutic implications. For biosynthesis, cancer cells enhance glucose and glutamine consumption. Inactivation of pyruvate kinase M2 (PKM2) promotes transcription in G1 phase. Glutamine metabolism supports DNA replication in S phase and lipid synthesis in G2 phase. A boost in glycolysis and oxidative metabolism can temporarily furnish more ATP when necessary (G1/S transition, segregation of chromosomes). Recent studies have shown that a few metabolic enzymes [PKM2, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB3), GAPDH] also periodically translocate to the nucleus and oversee cell cycle regulators or oncogene expression (c-Myc). Targeting these metabolic enzymes could increase the response to CDK inhibitors (CKIs).