The protein level of PGC-1α, a key metabolic regulator, is controlled by NADH-NQO1

Sulforaphane treatment mimics contractile activity-induced mitochondrial adaptations in muscle myotubes

Mitochondria are metabolic hubs that govern skeletal muscle health. Although exercise has been established as a powerful inducer of quality control processes that ultimately enhance mitochondrial function, there are currently limited pharmaceutical interventions available that emulate exercise-induced mitochondrial adaptations. To investigate a novel candidate for this role, we examined sulforaphane (SFN), a naturally occurring compound found in cruciferous vegetables. SFN has been documented as a potent antioxidant inducer through its activation of the nuclear factor erythroid 2-related factor 2 (Nrf-2) antioxidant response pathway. However, its effects on muscle health have been underexplored. To investigate the interplay between chronic exercise and SFN, C2C12 myotubes were electrically stimulated to model chronic contractile activity (CCA) in the presence or absence of SFN. SFN promoted Nrf-2 nuclear translocation, enhanced mitochondrial respiration, and upregulated key antioxidant proteins including catalase and glutathione reductase. These adaptations were accompanied by reductions in cellular and mitochondrial reactive oxygen species (ROS) emission. Signaling toward biogenesis was enhanced, demonstrated by increases in mitochondrial transcription factor A (TFAM), peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α nuclear translocation, PGC-1α promoter activity, mitochondrial content, and organelle branching, suggestive of a larger, more interconnected mitochondrial pool. These mitochondrial adaptations were accompanied by an increase in lysosomal proteins, suggesting coordinated regulation. There was no difference in mitochondrial and antioxidant-related proteins between CCA and non-CCA SFN-treated cells. Our data suggest that SFN activates signaling cascades that are common to those produced by contractile activity, indicating that SFN-centered therapeutic strategies may improve the mitochondrial phenotype in skeletal muscle.NEW & NOTEWORTHY Nrf-2 is a transcription factor that has been implicated in mitigating oxidative stress and regulating mitochondrial homeostasis. However, limited research has demonstrated how Nrf-2-mediated adaptations compare with those produced by exercise. To investigate this, we treated myotubes with Sulforaphane, a well-established Nrf-2 activator, and combined this with stimulation-induced chronic contractile activity to model exercise training. Our work is the first to establish that sulforaphane mimics training-induced mitochondrial adaptations, including enhancements in respiration, biogenesis, and dynamics.

Sulforaphane, Urolithin A, and ZLN005 induce time-dependent alterations in antioxidant capacity, mitophagy, and mitochondrial biogenesis in muscle cells

Efficient signal transduction that mediates mitochondrial turnover is a strong determinant of metabolic health in skeletal muscle. Of these pathways, our focus was aimed towards the enhancement of antioxidant capacity, mitophagy, and mitochondrial biogenesis. While physical activity is an excellent inducer of mitochondrial turnover, its ability to ubiquitously activate and enhance mitochondrial turnover prevents definitive differentiation of the contribution made by each pathway. Therefore, we employed three agents, Sulforaphane (SFN), Urolithin A (UroA), and ZLN005 (ZLN), which are activators of important biological markers involved in antioxidant signaling, mitophagy, and biogenesis, respectively. We investigated the time-dependent changes in proteins related to each mechanism in C2C12 myotubes. SFN treatment resulted in increased nuclear localization of the transcription factor Nuclear factor (erythroid-derived 2)-like 2 (Nrf-2) after 4 ​hour (h), with subsequent 2-fold increases in the antioxidant enzymes Nicotinamide Quinone Oxidoreductase 1 (NQO1) and Heme-Oxygenase-1 (HO-1) by 24 ​h and 48 ​h. Mitochondrial respiration and ATP production were significantly increased by both 24 h and 48 ​h. UroA showed a 2-fold increase in AMP-activated Protein Kinase (AMPK) after 4 ​h, which led to a modest 30% increase in whole cell mitophagy markers p62 and LC3, after 48 ​h. This was accompanied by a reduction in cellular Reactive Oxygen Species (ROS), detected with the CellROX Green reagent. Mitophagy flux measurements showed mitophagy activation as both LC3-II and p62 flux increased with UroA at 24-h and 48-h time points, respectively. Finally, AMPK activation was observed by 4 ​h, in addition to a 2-fold increase in Mitochondrial Transcription Factor A (TFAM) promoter activity by 24 ​h of ZLN treatment following transient transfection of a TFAM promoter-luciferase construct. Mitochondrial respiration and ATP production were enhanced by 24 ​h. Our results suggest that early time points of treatment increase upstream pathway activity, whereas later time points represent the increased phenotypic expression of related downstream markers. Our findings suggest that the spatiotemporal progression of these mechanisms following drug treatment is another important factor to consider when examining subcellular changes towards mitochondrial turnover in muscle.

CYB5R3 overexpression exhibits sexual dimorphism: Mitochondrial and metabolic adaptations in transgenic female mice during calorie restriction

There is a pressing need to develop new strategies for enhancing health in the elderly and preventing the rise in age-related diseases. Calorie restriction without malnutrition (CR) stands among the different antiaging interventions. Lifelong CR leads to increased expression and activity of plasma membrane CYB5R3, and male mice overexpressing CYB5R3 exhibit some beneficial adaptations that are also seen with CR. However, the mechanisms involved in both interventions could be independent since key aspects of energy metabolism and tissue lipid profile do not coincide, and many of the changes induced by CR in mitochondrial abundance and dynamics in the liver and skeletal muscle could be counteracted by CYB5R3 overexpression. In this study, we sought to elucidate the impact of CR on key markers of metabolic status, mitochondrial function, and pro-oxidant/antioxidant balance in transgenic (TG) female mice overexpressing CYB5R3 compared to their WT littermates. In females fed ad libitum, CYB5R3 overexpression decreased fat mass, led to a preferred utilization of fatty acids as an energy source, upregulated key antioxidant enzymes, and boosted respiration both in skeletal muscle and liver mitochondria, supporting that CYB5R3 overexpression is phenotypic closer to CR in females than in males. Whereas some markers of mitochondrial biogenesis and dynamics were found decreased in TG females on CR, as also found for the levels of Estrogen Receptor α, mitochondrial abundance and activity were maintained both in skeletal muscle and in liver. Our results reveal overlapping metabolic adaptations resulting from the overexpression of CYB5R3 and CR in females, but a specific crosstalk occurs when both interventions are combined, differing from the adaptations observed in TG males.

Saikosaponin D potentiates the antineoplastic effects of doxorubicin in drug-resistant breast cancer through perturbing NQO1-mediated intracellular redox balance

BACKGROUND

Drug resistance to doxorubicin (DOX) significantly limits its therapeutic efficacy in breast cancer (BC) patients. Saikosaponin D (SSD), a triterpene saponin derived from the traditional herb Radix Bupleuri, has shown promise as a chemotherapeutic sensitizer in preclinical studies due to its notable antitumor activity. However, the role and mechanism of SSD in DOX-resistant BC cells remain largely unexplored.

PURPOSE

This study aimed to investigate the chemosensitizing effect of SSD on DOX-resistant BC and the underlying molecular mechanisms both in vitro and in vivo.

METHODS

In vitro assays, including cell viability, clone formation, three-dimensional tumor spheroid growth, and apoptosis analysis, were conducted to evaluate the synergistic effect of SSD and DOX on resistant BC cells. Reactive oxygen species (ROS), GSH/GSSG, NADPH/NADP+, and NADH/NAD+ detections were employed to assess the impact of SSD on cellular redox homeostasis. Western blotting, cell cycle distribution assay, and DOX uptake assay were performed to further elucidate the possible antineoplastic mechanism of SSD. Finally, a subcutaneous MCF7/DOX cell xenografted model in nude mice was established to identify the in vivo anticarcinogenic effect of SSD combined with DOX.

RESULTS

SSD significantly inhibited cell viability, proliferation, and clone formation, enhancing DOX's anticancer efficacy in vitro and in vivo. Mechanistically, SSD reduced STAT1, NQO1, and PGC-1α protein levels, leading to cellular redox imbalance, excessive ROS generation, and depletion of GSH, NADPH, and NADH. SSD induced DNA damage by disrupting redox homeostasis, resulting in G0/G1 phase cell cycle arrest. Additionally, SSD increased DOX accumulation in BC cells via inhibiting P-gp protein expression and efflux activity.

CONCLUSION

We demonstrated for the first time that SSD enhances the sensitivity of chemoresistant BC cells to DOX by disrupting cellular redox homeostasis through inactivation of the STAT1/NQO1/PGC-1α signaling pathway. This study provides evidence for SSD as an adjuvant agent in drug-resistant BC treatment.

Human NQO1 as a Selective Target for Anticancer Therapeutics and Tumor Imaging

Human NAD(P)H-quinone oxidoreductase1 (HNQO1) is a two-electron reductase antioxidant enzyme whose expression is driven by the NRF2 transcription factor highly active in the prooxidant milieu found in human malignancies. The resulting abundance of NQO1 expression (up to 200-fold) in cancers and a barely detectable expression in body tissues makes it a selective marker of neoplasms. NQO1 can catalyze the repeated futile redox cycling of certain natural and synthetic quinones to their hydroxyquinones, consuming NADPH and generating rapid bursts of cytotoxic reactive oxygen species (ROS) and H2O2. A greater level of this quinone bioactivation due to elevated NQO1 content has been recognized as a tumor-specific therapeutic strategy, which, however, has not been clinically exploited. We review here the natural and new quinones activated by NQO1, the catalytic inhibitors, and the ensuing cell death mechanisms. Further, the cancer-selective expression of NQO1 has opened excellent opportunities for distinguishing cancer cells/tissues from their normal counterparts. Given this diagnostic, prognostic, and therapeutic importance, we and others have engineered a large number of specific NQO1 turn-on small molecule probes that remain latent but release intense fluorescence groups at near-infrared and other wavelengths, following enzymatic cleavage in cancer cells and tumor masses. This sensitive visualization/quantitation and powerful imaging technology based on NQO1 expression offers promise for guided cancer surgery, and the reagents suggest a theranostic potential for NQO1-targeted chemotherapy.

The "Sunshine Vitamin" and Its Antioxidant Benefits for Enhancing Muscle Function

Pathological states marked by oxidative stress and systemic inflammation frequently compromise the functional capacity of muscular cells. This progressive decline in muscle mass and tone can significantly hamper the patient's motor abilities, impeding even the most basic physical tasks. Muscle dysfunction can lead to metabolic disorders and severe muscle wasting, which, in turn, can potentially progress to sarcopenia. The functionality of skeletal muscle is profoundly influenced by factors such as environmental, nutritional, physical, and genetic components. A well-balanced diet, rich in proteins and vitamins, alongside an active lifestyle, plays a crucial role in fortifying tissues and mitigating general weakness and pathological conditions. Vitamin D, exerting antioxidant effects, is essential for skeletal muscle. Epidemiological evidence underscores a global prevalence of vitamin D deficiency, which induces oxidative harm, mitochondrial dysfunction, reduced adenosine triphosphate production, and impaired muscle function. This review explores the intricate molecular mechanisms through which vitamin D modulates oxidative stress and its consequent effects on muscle function. The aim is to evaluate if vitamin D supplementation in conditions involving oxidative stress and inflammation could prevent decline and promote or maintain muscle function effectively.

Using network pharmacology and molecular docking to uncover the mechanism by which quercetin alleviates deoxynivalenol-induced porcine intestinal injury

Deoxynivalenol is a widespread feed contaminant that leads to vomit, which results in serious symptom such as increased intestinal permeability and even intestinal mucosal necrosis. Recent studies have reported the role of quercetin in alleviating deoxynivalenol-induced intestinal injury; however, the mechanisms and targets remain unclear. Thus, we aimed to identify the mechanisms of action by using a combination of network pharmacology and molecular docking. We identified 151 quercetin targets, 235 deoxynivalenol targets and 47 porcine intestinal injury targets by searching compound database and PubMed database, among which there were two common targets. The PPI network showed that the key proteins involved are NQO1 and PPAR-γ. The PPI network showed that the key proteins involved were NQO1 and PPARG. GO analysis found that genes were enriched primarily in response to oxidative stress. The PPI network showed that the key proteins involved are NQO1 and PPAR-γ. The genes are enriched primarily in response to oxidative stress. KEGG analysis showed enrichment of the HIF, reactive oxygen species and other signaling pathways. The molecular docking results indicated key binding activity between NQO1-quercetin and PPAR-γ-quercetin. By using network pharmacology, we have revealed the potential molecular mechanisms by which quercetin alleviates deoxynivalenol-induced porcine intestinal injury, which lays the foundation for the development of drugs to treat deoxynivalenol-induced intestinal injury in pigs.

Impact of NQO1 dysregulation in CNS disorders

NAD(P)H Quinone Dehydrogenase 1 (NQO1) plays a pivotal role in the regulation of neuronal function and synaptic plasticity, cellular adaptation to oxidative stress, neuroinflammatory and degenerative processes, and tumorigenesis in the central nervous system (CNS). Impairment of the NQO1 activity in the CNS can result in abnormal neurotransmitter release and clearance, increased oxidative stress, and aggravated cellular injury/death. Furthermore, it can cause disturbances in neural circuit function and synaptic neurotransmission. The abnormalities of NQO1 enzyme activity have been linked to the pathophysiological mechanisms of multiple neurological disorders, including Parkinson's disease, Alzheimer's disease, epilepsy, multiple sclerosis, cerebrovascular disease, traumatic brain injury, and brain malignancy. NQO1 contributes to various dimensions of tumorigenesis and treatment response in various brain tumors. The precise mechanisms through which abnormalities in NQO1 function contribute to these neurological disorders continue to be a subject of ongoing research. Building upon the existing knowledge, the present study reviews current investigations describing the role of NQO1 dysregulations in various neurological disorders. This study emphasizes the potential of NQO1 as a biomarker in diagnostic and prognostic approaches, as well as its suitability as a target for drug development strategies in neurological disorders.

Mass spectrometry-based proteomics approaches to interrogate skeletal muscle adaptations to exercise

Acute exercise and chronic exercise training elicit beneficial whole-body changes in physiology that ultimately depend on profound alterations to the dynamics of tissue-specific proteins. Since the work accomplished during exercise owes predominantly to skeletal muscle, it has received the majority of interest from exercise scientists that attempt to unravel adaptive mechanisms accounting for salutary metabolic effects and performance improvements that arise from training. Contemporary scientists are also beginning to use mass spectrometry-based proteomics, which is emerging as a powerful approach to interrogate the muscle protein signature in a more comprehensive manner. Collectively, these technologies facilitate the analysis of skeletal muscle protein dynamics from several viewpoints, including changes to intracellular proteins (expression proteomics), secreted proteins (secretomics), post-translational modifications as well as fiber-, cell-, and organelle-specific changes. This review aims to highlight recent literature that has leveraged new workflows and advances in mass spectrometry-based proteomics to further our understanding of training-related changes in skeletal muscle. We call attention to untapped areas in skeletal muscle proteomics research relating to exercise training and metabolism, as well as basic points of contention when applying mass spectrometry-based analyses, particularly in the study of human biology. We further encourage researchers to couple the hypothesis-generating and descriptive nature of omics data with functional analyses that propel our understanding of the complex adaptive responses in skeletal muscle that occur with acute and chronic exercise.

Ubiquitin-Dependent and Independent Proteasomal Degradation in Host-Pathogen Interactions

Ubiquitin, a small protein, is well known for tagging target proteins through a cascade of enzymatic reactions that lead to protein degradation. The ubiquitin tag, apart from its signaling role, is paramount in destabilizing the modified protein. Here, we explore the complex role of ubiquitin-mediated protein destabilization in the intricate proteolysis process by the 26S proteasome. In addition, the significance of the so-called ubiquitin-independent pathway and the role of the 20S proteasome are considered. Next, we discuss the ubiquitin-proteasome system's interplay with pathogenic microorganisms and how the microorganisms manipulate this system to establish infection by a range of elaborate pathways to evade or counteract host responses. Finally, we focus on the mechanisms that rely either on (i) hijacking the host and on delivering pathogenic E3 ligases and deubiquitinases that promote the degradation of host proteins, or (ii) counteracting host responses through the stabilization of pathogenic effector proteins.

Methylmercury (MeHg) transcriptionally regulates NAD(P)H:quinone oxidoreductase 1 (NQO1) in Hepa-1c1c7 cells

The detoxification of quinones through NAD(P)H:quinone oxidoreductase (NQO1) is a crucial mechanism to maintain cellular homeostasis. The exposure to heavy metals, specifically methylmercury (MeHg), induces several antioxidant enzymes, including NQO1. The nuclear factor erythroid 2-related factor-2 (NRF2) is known to regulate the expression of Nqo1 gene and also the aryl hydrocarbon receptor (AHR) is another Nqo1 gene regulator. This co-regulation prompted us to investigate which transcription factor (NRF2 or AHR) orchestrates the regulation of NQO1 expression upon MeHg exposure. Therefore, we investigated how MeHg can modulate the level of NQO1 expression by exposing Hepa-1c1c7 cells to several concentrations of MeHg with and without the addition of NQO1 inducers, DL-sulforaphane (SUL) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We found that the mRNA expression of Nqo1 is up-regulated by MeHg in time- as well as dose-dependent fashions. Additionally, MeHg increased the NQO1 at all expression levels with and without the presence of its inducers, SUL or TCDD. Furthermore, the MeHg-mediated increase of NQO1 expression was in parallel with a concurrent increase in the nuclear localization of NRF2 protein, but not that of AHR. Mechanistically, the antioxidant response element-driven reporter gene activity was induced by 215% upon MeHg exposure. Also, transfecting Hepa-1c1c7 with Nrf2 siRNA reduced the MeHg-induced NQO1 protein expression by 60%. In conclusion, our findings provide evidence supporting the hypothesis that MeHg upregulates the Nqo1 gene through a transcriptional mechanism at least in part via a NRF2-dependent mechanism.

The master energy homeostasis regulator PGC-1α exhibits an mRNA nuclear export function

PGC-1α plays a central role in maintaining mitochondrial and energy metabolism homeostasis, linking external stimuli to transcriptional co-activation of genes involved in adaptive and age-related pathways. The carboxyl-terminus encodes a serine/arginine-rich (RS) region and an RNA recognition motif, however the RNA-processing function(s) were poorly investigated over the past 20 years. Here, we show that the RS domain of human PGC-1α directly interacts with RNA and the nuclear RNA export receptor NXF1. Inducible depletion of PGC-1α and expression of RNAi-resistant RS-deleted PGC-1α further demonstrate that its RNA/NXF1-binding activity is required for the nuclear export of some canonical mitochondrial-related mRNAs and mitochondrial homeostasis. Genome-wide investigations reveal that the nuclear export function is not strictly linked to promoter-binding, identifying in turn novel regulatory targets of PGC-1α in non-homologous end-joining and nucleocytoplasmic transport. These findings provide new directions to further elucidate the roles of PGC-1α in gene expression, metabolic disorders, aging and neurodegeneration.

Engineered allele substitution at PPARGC1A rs8192678 alters human white adipocyte differentiation, lipogenesis, and PGC-1α content and turnover

AIMS/HYPOTHESIS

PPARGC1A encodes peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), a central regulator of energy metabolism and mitochondrial function. A common polymorphism in PPARGC1A (rs8192678, C/T, Gly482Ser) has been associated with obesity and related metabolic disorders, but no published functional studies have investigated direct allele-specific effects in adipocyte biology. We examined whether rs8192678 is a causal variant and reveal its biological function in human white adipose cells.

METHODS

We used CRISPR-Cas9 genome editing to perform an allelic switch (C-to-T or T-to-C) at rs8192678 in an isogenic human pre-adipocyte white adipose tissue (hWAs) cell line. Allele-edited single-cell clones were expanded and screened to obtain homozygous T/T (Ser482Ser), C/C (Gly482Gly) and heterozygous C/T (Gly482Ser) isogenic cell populations, followed by functional studies of the allele-dependent effects on white adipocyte differentiation and mitochondrial function.

RESULTS

After differentiation, the C/C adipocytes were visibly less BODIPY-positive than T/T and C/T adipocytes, and had significantly lower triacylglycerol content. The C allele presented a dose-dependent lowering effect on lipogenesis, as well as lower expression of genes critical for adipogenesis, lipid catabolism, lipogenesis and lipolysis. Moreover, C/C adipocytes had decreased oxygen consumption rate (OCR) at basal and maximal respiration, and lower ATP-linked OCR. We determined that these effects were a consequence of a C-allele-driven dysregulation of PGC-1α protein content, turnover rate and transcriptional coactivator activity.

CONCLUSIONS/INTERPRETATION

Our data show allele-specific causal effects of the rs8192678 variant on adipogenic differentiation. The C allele confers lower levels of PPARGC1A mRNA and PGC-1α protein, as well as disrupted dynamics of PGC-1α turnover and activity, with downstream effects on cellular differentiation and mitochondrial function. Our study provides the first experimentally deduced insights on the effects of rs8192678 on adipocyte phenotype.

Metabolic Changes in Cardiac Aging

Cardiac aging is a natural process accompanied by cardiomyocyte hypertrophy and dysfunction. These changes can lead to adverse organ remodeling and ultimately lead to the development of heart failure. The study of cardiac aging is helpful to explore the mechanism of senescence and is of great significance for preventing cardiac aging. Cardiac aging is accompanied by changes in various metabolic functions. In this process, due to the change of metabolic substrates and enzyme activities, oxidative stress response increases, and reactive oxygen species (ROS) increases, accompanied by mitochondrial dysfunction and gene expression changes, so related protein metabolism also changes. Hormone metabolism and autophagy are also involved in the process of cardiac aging. Based on these findings, changes in diet, caloric restriction, improvement of mitochondrial function and promotion of autophagy have been proven to have positive effects in delaying cardiac aging. This article reviews the metabolic changes involved in the process of cardiac aging from different aspects, and briefly reviews the measures to improve cardiac aging.

Arginine Methylation of the PGC-1α C-Terminus Is Temperature-Dependent

We set out to determine whether the C-terminus (amino acids 481-798) of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α, UniProt Q9UBK2), a regulatory metabolic protein involved in mitochondrial biogenesis, and respiration, is an arginine methyltransferase substrate. Arginine methylation by protein arginine methyltransferases (PRMTs) alters protein function and thus contributes to various cellular processes. In addition to confirming methylation of the C-terminus by PRMT1 as described in the literature, we have identified methylation by another member of the PRMT family, PRMT7. We performed in vitro methylation reactions using recombinant mammalian PRMT7 and PRMT1 at 37, 30, 21, 18, and 4 °C. Various fragments of PGC-1α corresponding to the C-terminus were used as substrates, and the methylation reactions were analyzed by fluorography and mass spectrometry to determine the extent of methylation throughout the substrates, the location of the methylated PGC-1α arginine residues, and finally, whether temperature affects the deposition of methyl groups. We also employed two prediction programs, PRmePRed and MePred-RF, to search for putative methyltransferase sites. Methylation reactions show that arginine residues R548 and R753 in PGC-1α are methylated at or below 30 °C by PRMT7, while methylation by PRMT1 was detected at these same residues at 30 °C. Computational approaches yielded additional putative methylarginine sites, indicating that since PGC-1α is an intrinsically disordered protein, additional methylated arginine residues have yet to be experimentally verified. We conclude that temperature affects the extent of arginine methylation, with more methylation by PRMT7 occurring below physiological temperature, uncovering an additional control point for PGC-1α.

Parkin regulates adiposity by coordinating mitophagy with mitochondrial biogenesis in white adipocytes

Parkin, an E3 ubiquitin ligase, plays an essential role in mitochondrial quality control. However, the mechanisms by which Parkin connects mitochondrial homeostasis with cellular metabolism in adipose tissue remain unclear. Here, we demonstrate that Park2 gene (encodes Parkin) deletion specifically from adipose tissue protects mice against high-fat diet and aging-induced obesity. Despite a mild reduction in mitophagy, mitochondrial DNA content and mitochondrial function are increased in Park2 deficient white adipocytes. Moreover, Park2 gene deletion elevates mitochondrial biogenesis by increasing Pgc1α protein stability through mitochondrial superoxide-activated NAD(P)H quinone dehydrogenase 1 (Nqo1). Both in vitro and in vivo studies show that Nqo1 overexpression elevates Pgc1α protein level and mitochondrial DNA content and enhances mitochondrial activity in mouse and human adipocytes. Taken together, our findings indicate that Parkin regulates mitochondrial homeostasis by balancing mitophagy and Pgc1α-mediated mitochondrial biogenesis in white adipocytes, suggesting a potential therapeutic target in adipocytes to combat obesity and obesity-associated disorders.

Redox state and the sirtuin deacetylases are major factors that regulate the acetylation status of the stress protein NQO1

The stress induced protein NQO1 can participate in a wide range of biological pathways which are dependent upon the interaction of NQO1 with protein targets. Many of the protein-protein interactions involving NQO1 have been shown to be regulated by the pyridine nucleotide redox balance. NQO1 can modify its conformation as a result of redox changes in pyridine nucleotides and sites on the C-terminal and helix seven regions of NQO1 have been identified as potential areas that may be involved in redox-dependent protein-protein interactions. Since post-translational modifications can modify the functionality of proteins, we examined whether redox-dependent conformational changes induced in NQO1 would alter lysine acetylation. Recombinant NQO1 was incubated with and without NADH then acetylated non-enzymatically by acetic anhydride or S-acetylglutathione (Ac-GSH). NQO1 acetylation was determined by immunoblot and site-specific lysine acetylation was quantified by mass spectrometry (MS). NQO1 was readily acetylated by acetic anhydride and Ac-GSH. Interestingly, despite a large number of lysine residues (9%) in NQO1 only a small subset of lysines were acetylated and the majority of these were located in or near the functional C-terminal or helix seven regions. Reduction of NQO1 by NADH prior to acetylation resulted in almost complete protection of NQO1 from lysine acetylation as confirmed by immunoblot analysis and MS. Lysines located within the redox-active C-terminus and helix seven regions were readily acetylated when NQO1 was in an oxidized conformation but were protected from acetylation when NQO1 was in the reduced conformation. To investigate regulatory mechanisms of enzymatic deacetylation, NQO1 was acetylated by Ac-GSH then exposed to purified sirtuins (SIRT 1-3) or histone deacetylase 6 (HDAC6). NQO1 could be deacetylated by all sirtuin isoforms and quantitative MS analysis performed using SIRT2 revealed very robust deacetylation of NQO1, specifically at K262 and K271 in the C-terminal region. No deacetylation of NQO1 by HDAC6 was detected. These data demonstrate that the same subset of key lysine residues in the C-terminal and helix seven regions of NQO1 undergo redox dependent acetylation and are regulated by sirtuin-mediated deacetylation.

Targeting HIF-1α Function in Cancer through the Chaperone Action of NQO1: Implications of Genetic Diversity of NQO1

HIF-1α is a master regulator of oxygen homeostasis involved in different stages of cancer development. Thus, HIF-1α inhibition represents an interesting target for anti-cancer therapy. It was recently shown that the HIF-1α interaction with NQO1 inhibits proteasomal degradation of the former, thus suggesting that targeting the stability and/or function of NQO1 could lead to the destabilization of HIF-1α as a therapeutic approach. Since the molecular interactions of NQO1 with HIF-1α are beginning to be unraveled, in this review we discuss: (1) Structure–function relationships of HIF-1α; (2) our current knowledge on the intracellular functions and stability of NQO1; (3) the pharmacological modulation of NQO1 by small ligands regarding function and stability; (4) the potential effects of genetic variability of NQO1 in HIF-1α levels and function; (5) the molecular determinants of NQO1 as a chaperone of many different proteins including cancer-associated factors such as HIF-1α, p53 and p73α. This knowledge is then further discussed in the context of potentially targeting the intracellular stability of HIF-1α by acting on its chaperone, NQO1. This could result in novel anti-cancer therapies, always considering that the substantial genetic variability in NQO1 would likely result in different phenotypic responses among individuals.

Review on NAD(P)H dehydrogenase quinone 1 (NQO1) pathway

NQO1 is an enzyme present in humans which is encoded by NQO1 gene. It is a protective antioxidant agent, versatile cytoprotective agent and regulates the oxidative stresses of chromatin binding proteins for DNA damage in cancer cells. The oxidization of cellular pyridine nucleotides causes structural alterations to NQO1 and changes in its capacity to binding of proteins. A strategy based on NQO1 to have protective effect against cancer was developed by organic components to enhance NQO1 expression. The quinone derivative compounds like mitomycin C, RH1, E09 (Apaziquone) and β-lapachone causes cell death by NQO1 reduction of two electrons. It was also known to be overexpressed in various tumor cells of breast, lung, cervix, pancreas and colon when it was compared with normal cells in humans. The mechanism of NQO1 by the reduction of FAD by NADPH to form FADH2 is by two ways to inhibit cancer cell development such as suppression of carcinogenic metabolic activation and prevention of carcinogen formation. The NQO1 exhibit suppression of chemical-mediated carcinogenesis by various properties of NQO1 which includes, detoxification of quinone scavenger of superoxide anion radical, antioxidant enzyme, protein stabilizer. This review outlines the NQO1 structure, mechanism of action to inhibit the cancer cell, functions of NQO1 against oxidative stress, drugs acting on NQO1 pathways, clinical significance.

Butyrate Ameliorates Mitochondrial Respiratory Capacity of The Motor-Neuron-like Cell Line NSC34-G93A, a Cellular Model for ALS

Mitochondrial defects in motor neurons are pathological hallmarks of ALS, a neuromuscular disease with no effective treatment. Studies have shown that butyrate, a natural gut-bacteria product, alleviates the disease progression of ALS mice overexpressing a human ALS-associated mutation, hSOD1^G93A. In the current study, we examined the potential molecular mechanisms underlying the effect of butyrate on mitochondrial function in cultured motor-neuron-like NSC34 with overexpression of hSOD1^G93A (NSC34-G93A). The live cell confocal imaging study demonstrated that 1mM butyrate in the culture medium improved the mitochondrial network with reduced fragmentation in NSC34-G93A cells. Seahorse analysis revealed that NSC34-G93A cells treated with butyrate showed an increase of ~5-fold in mitochondrial Spare Respiratory Capacity with elevated Maximal Respiration. The time-dependent changes in the mRNA level of PGC1α, a master regulator of mitochondrial biogenesis, revealed a burst induction with an early increase (~5-fold) at 4 h, a peak at 24 h (~19-fold), and maintenance at 48 h (8-fold) post-treatment. In line with the transcriptional induction of PGC1α, both the mRNA and protein levels of the key molecules (MTCO1, MTCO2, and COX4) related to the mitochondrial electron transport chain were increased following the butyrate treatment. Our data indicate that activation of the PGC1α signaling axis could be one of the molecular mechanisms underlying the beneficial effects of butyrate treatment in improving mitochondrial bioenergetics in NSC34-G93A cells.

Roles of NAD(P)H:quinone Oxidoreductase 1 in Diverse Diseases

NAD(P)H:quinone oxidoreductase (NQO) is an antioxidant flavoprotein that catalyzes the reduction of highly reactive quinone metabolites by employing NAD(P)H as an electron donor. There are two NQO enzymes—NQO1 and NQO2—in mammalian systems. In particular, NQO1 exerts many biological activities, including antioxidant activities, anti-inflammatory effects, and interactions with tumor suppressors. Moreover, several recent studies have revealed the promising roles of NQO1 in protecting against cardiovascular damage and related diseases, such as dyslipidemia, atherosclerosis, insulin resistance, and metabolic syndrome. In this review, we discuss recent developments in the molecular regulation and biochemical properties of NQO1, and describe the potential beneficial roles of NQO1 in diseases associated with oxidative stress.

NQO1 Binds and Supports SIRT1 Function

Silent information regulator 2-related enzyme 1 (SIRT1) is an NAD⁺-dependent class III deacetylase and a key component of the cellular metabolic sensing pathway. The requirement of NAD⁺ for SIRT1 activity led us to assume that NQO1, an NADH oxidoreductase producing NAD⁺, regulates SIRT1 activity. We show here that SIRT1 is capable of increasing NQO1 (NAD(P)H Dehydrogenase Quinone 1) transcription and protein levels. NQO1 physically interacts with SIRT1 but not with an enzymatically dead SIRT1 H363Y mutant. The interaction of NQO1 with SIRT1 is markedly increased under mitochondrial inhibition. Interestingly, under this condition the nuclear pool of NQO1 is elevated. Depletion of NQO1 compromises the role of SIRT1 in inducing transcription of several target genes and eliminates the protective role of SIRT1 following mitochondrial inhibition. Our results suggest that SIRT1 and NQO1 form a regulatory loop where SIRT1 regulates NQO1 expression and NQO1 binds and mediates the protective role of SIRT1 during mitochondrial stress. The interplay between an NADH oxidoreductase enzyme and an NAD⁺ dependent deacetylase may act as a rheostat in sensing mitochondrial stress.

STAT1 potentiates oxidative stress revealing a targetable vulnerability that increases phenformin efficacy in breast cancer

Bioenergetic perturbations driving neoplastic growth increase the production of reactive oxygen species (ROS), requiring a compensatory increase in ROS scavengers to limit oxidative stress. Intervention strategies that simultaneously induce energetic and oxidative stress therefore have therapeutic potential. Phenformin is a mitochondrial complex I inhibitor that induces bioenergetic stress. We now demonstrate that inflammatory mediators, including IFNγ and polyIC, potentiate the cytotoxicity of phenformin by inducing a parallel increase in oxidative stress through STAT1-dependent mechanisms. Indeed, STAT1 signaling downregulates NQO1, a key ROS scavenger, in many breast cancer models. Moreover, genetic ablation or pharmacological inhibition of NQO1 using β-lapachone (an NQO1 bioactivatable drug) increases oxidative stress to selectively sensitize breast cancer models, including patient derived xenografts of HER2+ and triple negative disease, to the tumoricidal effects of phenformin. We provide evidence that therapies targeting ROS scavengers increase the anti-neoplastic efficacy of mitochondrial complex I inhibitors in breast cancer.

Complex I inhibition induces oxidative stress leading to cancer cell cytotoxicity. Here, the authors show, in breast cancer models, that inflammatory mediators can potentiate complex I inhibitor phenformin cytotoxicity through STAT1-mediated downregulation of the reactive oxygen species scavenger NQO1.

The diverse functionality of NQO1 and its roles in redox control

In this review, we summarize the multiple functions of NQO1, its established roles in redox processes and potential roles in redox control that are currently emerging. NQO1 has attracted interest due to its roles in cell defense and marked inducibility during cellular stress. Exogenous substrates for NQO1 include many xenobiotic quinones. Since NQO1 is highly expressed in many solid tumors, including via upregulation of Nrf2, the design of compounds activated by NQO1 and NQO1-targeted drug delivery have been active areas of research. Endogenous substrates have also been proposed and of relevance to redox stress are ubiquinone and vitamin E quinone, components of the plasma membrane redox system. Established roles for NQO1 include a superoxide reductase activity, NAD+ generation, interaction with proteins and their stabilization against proteasomal degradation, binding and regulation of mRNA translation and binding to microtubules including the mitotic spindles. We also summarize potential roles for NQO1 in regulation of glucose and insulin metabolism with relevance to diabetes and the metabolic syndrome, in Alzheimer's disease and in aging. The conformation and molecular interactions of NQO1 can be modulated by changes in the pyridine nucleotide redox balance suggesting that NQO1 may function as a redox-dependent molecular switch.

Role of PGC-1α in the Mitochondrial NAD+ Pool in Metabolic Diseases

Mitochondria play vital roles, including ATP generation, regulation of cellular metabolism, and cell survival. Mitochondria contain the majority of cellular nicotinamide adenine dinucleotide (NAD⁺), which an essential cofactor that regulates metabolic function. A decrease in both mitochondria biogenesis and NAD⁺ is a characteristic of metabolic diseases, and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) orchestrates mitochondrial biogenesis and is involved in mitochondrial NAD⁺ pool. Here we discuss how PGC-1α is involved in the NAD⁺ synthesis pathway and metabolism, as well as the strategy for increasing the NAD⁺ pool in the metabolic disease state.

The MicroRNA miR-696 is regulated by SNARK and reduces mitochondrial activity in mouse skeletal muscle through Pgc1α inhibition

OBJECTIVE

MicroRNAs (miRNA) are known to regulate the expression of genes involved in several physiological processes including metabolism, mitochondrial biogenesis, proliferation, differentiation, and cell death.

METHODS

Using "in silico" analyses, we identified 219 unique miRNAs that potentially bind to the 3'UTR region of a critical mitochondrial regulator, the peroxisome proliferator-activated receptor gamma coactivator (PGC) 1 alpha (Pgc1α). Of the 219 candidate miRNAs, miR-696 had one of the highest interactions at the 3'UTR of Pgc1α, suggesting that miR-696 may be involved in the regulation of Pgc1α.

RESULTS

Consistent with this hypothesis, we found that miR-696 was highly expressed in the skeletal muscle of STZ-induced diabetic mice and chronic high-fat-fed mice. C2C12 muscle cells exposed to palmitic acid also exhibited a higher expression of miR-696. This increased expression corresponded with a reduced expression of oxidative metabolism genes and reduced mitochondrial respiration. Importantly, reducing miR-696 reversed decreases in mitochondrial activity in response to palmitic acid. Using C2C12 cells treated with the AMP-activated protein kinase (AMPK) activator AICAR and skeletal muscle from AMPKα2 dominant-negative (DN) mice, we found that the signaling mechanism regulating miR-696 did not involve AMPK. In contrast, overexpression of SNF1-AMPK-related kinase (SNARK) in C2C12 cells increased miR-696 transcription while knockdown of SNARK significantly decreased miR-696. Moreover, muscle-specific transgenic mice overexpressing SNARK exhibited a lower expression of Pgc1α, elevated levels of miR-696, and reduced amounts of spontaneous activity.

CONCLUSIONS

Our findings demonstrate that metabolic stress increases miR-696 expression in skeletal muscle cells, which in turn inhibits Pgc1α, reducing mitochondrial function. SNARK plays a role in this process as a metabolic stress signaling molecule inducing the expression of miR-696.

The Nrf2 pathway in psychiatric disorders: pathophysiological role and potential targeting

Introduction: All psychiatric disorders exhibit excitotoxicity, mitochondrial dysfunction, inflammation, oxidative stress, and neural damage as their common characteristic. The endogenous nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway is implicated in the defense mechanism against oxidative stress and has a significant role in psychiatric disorders.Areas covered: We explore the role of Nrf2 pathway and its modulators in psychiatric disorders. The literature was searched utilizing various databases such as Embase, Medline, Web of Science, Pub-Med, and Google Scholar from 2010 to 2020. The search included research articles, clinical reports, systematic reviews, and meta-analyses.Expert opinion: Environmental factors and genetic predisposition can be a trigger for the development of psychiatric disorders. Nrf2 downregulates certain inflammatory pathways and upregulates various antioxidant enzymes to maintain a balance. However, its intricate balance with NF-Kβ (Nuclear factor kappa light chain enhancer of activated B cells) and its crosstalk with the transcription factor Nrf2 is critical in severe oxidative stress. Several Nrf2 modulators are now in clinical trials and can help reduce oxidative stress and neuroinflammation. There are immense potential opportunities for these modulators to become a novel therapeutic option.

The Oral Administration of Sanguisorba officinalis Extract Improves Physical Performance through LDHA Modulation

Muscle fatigue is induced by an acute or chronic physical performance inability after excessive physical activity often associated with lactate accumulation, the end-product of glycolysis. In this study, the water-extracted roots of Sanguisorba officinalis L., a herbal medicine traditionally used for inflammation and diarrhea, reduced the activities of lactate dehydrogenase A (LDHA) in in vitro enzyme assay myoblast C2C12 cells and murine muscle tissue. Physical performance measured by a treadmill test was improved in the S. officinalis-administrated group. The analysis of mouse serum and tissues showed significant changes in lactate levels. Among the proteins related to energy metabolism-related physical performance, phosphorylated-AMP-activated protein kinase alpha (AMPKα) and peroxisome proliferator-activated receptor-coactivator-1 alpha (PGC-1α) levels were enhanced, whereas the amount of LDHA was suppressed. Therefore, S. officinalis might be a candidate for improving physical performance via inhibiting LDHA and glycolysis.

Insulin-stimulated endoproteolytic TUG cleavage links energy expenditure with glucose uptake

TUG tethering proteins bind and sequester GLUT4 glucose transporters intracellularly, and insulin stimulates TUG cleavage to translocate GLUT4 to the cell surface and increase glucose uptake. This effect of insulin is independent of phosphatidylinositol 3-kinase, and its physiological relevance remains uncertain. Here we show that this TUG cleavage pathway regulates both insulin-stimulated glucose uptake in muscle and organism-level energy expenditure. Using mice with muscle-specific Tug (Aspscr1)-knockout and muscle-specific constitutive TUG cleavage, we show that, after GLUT4 release, the TUG C-terminal cleavage product enters the nucleus, binds peroxisome proliferator-activated receptor (PPAR)γ and its coactivator PGC-1α and regulates gene expression to promote lipid oxidation and thermogenesis. This pathway acts in muscle and adipose cells to upregulate sarcolipin and uncoupling protein 1 (UCP1), respectively. The PPARγ2 Pro12Ala polymorphism, which reduces diabetes risk, enhances TUG binding. The ATE1 arginyltransferase, which mediates a specific protein degradation pathway and controls thermogenesis, regulates the stability of the TUG product. We conclude that insulin-stimulated TUG cleavage coordinates whole-body energy expenditure with glucose uptake, that this mechanism might contribute to the thermic effect of food and that its attenuation could promote obesity.

A redox-mediated conformational change in NQO1 controls binding to microtubules and α-tubulin acetylation

The localization of NQO1 near acetylated microtubules has led to the hypothesis that NQO1 may work in concert with the NAD⁺-dependent deacetylase SIRT2 to regulate acetyl α-tubulin (K⁴⁰) levels on microtubules. NQO1 catalyzes the oxidation of NADH to NAD⁺ and may supplement levels of NAD⁺ near microtubules to aid SIRT2 deacetylase activity. While HDAC6 has been shown to regulate the majority of microtubule acetylation at K⁴⁰, SIRT2 is also known to modulate microtubule acetylation (K⁴⁰) in the perinuclear region. In this study we examined the potential roles NQO1 may play in modulating acetyl α-tubulin levels. Knock-out or knock-down of NQO1 or SIRT2 did not change the levels of acetyl α-tubulin in 16HBE human bronchial epithelial cells and 3T3-L1 fibroblasts; however, treatment with a mechanism-based inhibitor of NQO1 (MI2321) led to a short-lived temporal increase in acetyl α-tubulin levels in both cell lines without impacting the intracellular pools of NADH or NAD⁺. Inactivation of NQO1 by MI2321 resulted in lower levels of NQO1 immunostaining on microtubules, consistent with redox-dependent changes in NQO1 conformation as evidenced by the use of redox-specific, anti-NQO1 antibodies in immunoprecipitation studies. Given the highly dynamic nature of acetylation-deacetylation reactions at α-tubulin K⁴⁰ and the crowded protein environment surrounding this site, disruption in the binding of NQO1 to microtubules may temporally disturb the physical interactions of enzymes responsible for maintaining the microtubule acetylome.

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NQO1which produces NAD and Sirt2 which uses NAD are located in the perinuclear region.

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Depleting cellular NAD⁺ led to increased levels of acetyl α-tubulin.

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Knockout or knockdown of NQO1 did not change perinuclear acetyl α-tubulin levels.

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Pharmacological inhibition of NQO1 by MI2321 increased α-tubulin acetylation.

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Redox changes in NQO1 conformation and binding modulate microtubule acetyltubulin.

NQO1 promotes an aggressive phenotype in hepatocellular carcinoma via amplifying ERK-NRF2 signaling

Patients with hepatocellular carcinoma (HCC) are usually diagnosed at the later stages and have poor survival outcomes. New molecules are urgently needed for the prognostic predication and individual treatment. Our study showed that high levels of NQO1 expression frequently exist in HCC with an obvious cancer‐specific pattern. Patients with NQO1‐high tumors are significantly associated with poor survival outcomes and serve as independent predictors. Functional experiments showed that NQO1 promotes the growth and aggressiveness of HCC in both in vitro and in vivo models, and the underlying mechanism involved NQO1‐derived amplification of ERK/p38‐NRF2 signaling. Combined block of ERK and NRF2 signaling generated stronger growth inhibition compared with any single block, especially for HCC with high‐NQO1. Therefore, NQO1 is a potential biomarker for HCC early diagnosis and prognosis prediction, and also attractive for cancer‐specific targets for HCC treatment.

Degradation of Intrinsically Disordered Proteins by the NADH 26S Proteasome

The 26S proteasome is the endpoint of the ubiquitin- and ATP-dependent degradation pathway. Over the years, ATP was regarded as completely essential for 26S proteasome function due to its role in ubiquitin-signaling, substrate unfolding and ensuring its structural integrity. We have previously reported that physiological concentrations of NADH are efficient in replacing ATP to maintain the integrity of an enzymatically functional 26S PC. However, the substrate specificity of the NADH-stabilized 26S proteasome complex (26S PC) was never assessed. Here, we show that the binding of NADH to the 26S PC inhibits the ATP-dependent and ubiquitin-independent degradation of the structured ODC enzyme. Moreover, the NADH-stabilized 26S PC is efficient in degrading intrinsically disordered protein (IDP) substrates that might not require ATP-dependent unfolding, such as p27, Tau, c-Fos and more. In some cases, NADH-26S proteasomes were more efficient in processing IDPs than the ATP-26S PC. These results indicate that in vitro, physiological concentrations of NADH can alter the processivity of ATP-dependent 26S PC substrates such as ODC and, more importantly, the NADH-stabilized 26S PCs promote the efficient degradation of many IDPs. Thus, ATP-independent, NADH-dependent 26S proteasome activity exemplifies a new principle of how mitochondria might directly regulate 26S proteasome substrate specificity.

NQO1 protects obese mice through improvements in glucose and lipid metabolism

Chronic nutrient excess leads to metabolic disorders and insulin resistance. Activation of stress-responsive pathways via Nrf2 activation contributes to energy metabolism regulation. Here, inducible activation of Nrf2 in mice and transgenesis of the Nrf2 target, NQO1, conferred protection from diet-induced metabolic defects through preservation of glucose homeostasis, insulin sensitivity, and lipid handling with improved physiological outcomes. NQO1-RNA interaction mediated the association with and inhibition of the translational machinery in skeletal muscle of NQO1 transgenic mice. NQO1-Tg mice on high-fat diet had lower adipose tissue macrophages and enhanced expression of lipogenic enzymes coincident with reduction in circulating and hepatic lipids. Metabolomics data revealed a systemic metabolic signature of improved glucose handling, cellular redox, and NAD+ metabolism while label-free quantitative mass spectrometry in skeletal muscle uncovered a distinct diet- and genotype-dependent acetylation pattern of SIRT3 targets across the core of intermediary metabolism. Thus, under nutritional excess, NQO1 transgenesis preserves healthful benefits.

Activation of TNFR1 and TLR4 following oxygen glucose deprivation promotes mitochondrial fission in C6 astroglial cells

Astrocytes have emerged as active players in the innate immune response triggered by various types of insults. Recent literature suggests that mitochondria are key participants in innate immunity. The present study investigates the role of ischemia-induced innate immune response on p65/PGC-1α mediated mitochondrial dynamics in C6 astroglial cells. OGD conditions induced astroglial differentiation in C6 cells and increased the expression of hypoxia markers; HIF-1α, HO-1 and Cox4i2. OGD conditions resulted in induction of innate immune response in terms of expression of TNFR1 and TLR4 along with increase in IL-6 and TNF-α levels. OGD conditions resulted in decreased expression of I-κB with a concomitant increase in phos-p65 levels. The expression of PGC-1α, a key regulator of mitochondrial biogenesis, was also increased. Immunochemical staining suggested that phos-p65 and PGC-1α was co-localized. Studies on mitochondrial fusion (Mfn-1) and fission (DRP1) markers revealed shift toward fission. In addition, mitochondrial membrane potential decreased with increased DNA degradation and apoptosis confirming mitochondrial fission under OGD conditions. However, inhibition of phos-p65 by MG132 reduced the co-localization of phos-p65/ PGC-1α and significantly increased the Mfn-1 expression. The findings demonstrate the involvement of TNFR1 and TLR4 mediated immune response followed by interaction between phos-p65 and PGC-1α in promoting fission in C6 cells under hypoxic condition.

Insights into the Conserved Regulatory Mechanisms of Human and Yeast Aging

Aging represents a significant biological process having strong associations with cancer, diabetes, and neurodegenerative and cardiovascular disorders, which leads to progressive loss of cellular functions and viability. Astonishingly, age-related disorders share several genetic and molecular mechanisms with the normal aging process. Over the last three decades, budding yeast Saccharomyces cerevisiae has emerged as a powerful yet simple model organism for aging research. Genetic approaches using yeast RLS have led to the identification of hundreds of genes impacting lifespan in higher eukaryotes. Numerous interventions to extend yeast lifespan showed an analogous outcome in multi-cellular eukaryotes like fruit flies, nematodes, rodents, and humans. We collected and analyzed a multitude of observations from published literature and provide the contribution of yeast in the understanding of aging hallmarks most applicable to humans. Here, we discuss key pathways and molecular mechanisms that underpin the evolutionarily conserved aging process and summarize the current understanding and clinical applicability of its trajectories. Gathering critical information on aging biology would pave the way for future investigation targeted at the discovery of aging interventions.

Benefits of Caloric Restriction in Longevity and Chemical-Induced Tumorigenesis Are Transmitted Independent of NQO1

Caloric restriction (CR) is the most potent nonpharmacological intervention known to both protect against carcinogenesis and delay aging in laboratory animals. There is a growing number of anticarcinogens and CR mimetics that activate NAD(P)H:quinone oxidoreductase 1 (NQO1). We have previously shown that NQO1, an antioxidant enzyme that acts as an energy sensor through modulation of intracellular redox and metabolic state, is upregulated by CR. Here, we used NQO1-knockout (KO) mice to investigate the role of NQO1 in both the aging process and tumor susceptibility, specifically in the context of CR. We found that NQO1 is not essential for the beneficial effects of CR on glucose homeostasis, physical performance, metabolic flexibility, life-span extension, and (unlike our previously observation with Nrf2) chemical-induced tumorigenesis.

Essential role of the PGC-1α/PPARβ axis in Ucp3 gene induction

KEY POINTS

We report that the peroxisome proliferator-activated receptor (PPAR)γ coactivator 1-α (PGC-1α)/PPARβ axis is a crucial mediator of uncoupling protein 3 (UCP3) expression in skeletal muscle cells via the transactivativation of a distal PPAR response element at the Ucp3 gene promoter. This mechanism is activated during the myogenic process and by high concentrations of fatty acids independent of PGC-1α protein levels. Ucp3 is essential for PGC-1α-induced oxidative capacity and the adaptive mitochondrial response to fatty acid exposure. These findings provide further evidence for the broad spectrum of the coactivator action in mitochondrial homeostasis, positioning the PGC-1ɑ/PPARβ axis as an essential component of the molecular regulation of Ucp3 gene in skeletal muscle cells.

ABSTRACT

Uncoupling protein 3 (UCP3) has an essential role in fatty acid metabolism and mitochondrial redox regulation in skeletal muscle. However, the molecular mechanisms involved in the expression of Ucp3 are poorly known. In the present study, we show that the peroxisome proliferator-activated receptor (PPAR)γ coactivator 1-α (PGC-1α)/PPARβ axis is a crucial mediator of Ucp3 expression in skeletal muscle cells. In silico analysis of the UCP3 promoter and quantitative chromatin immunoprecipitation experiments revealed that the induction of the UCP3 transcript is mediated by the transactivation of a distal PPAR response element at the Ucp3 gene promoter by the coactivator PGC-1α. This mechanism is activated during myogenesis and during metabolic stress induced by fatty acids independent of PGC-1α protein levels. We also provide evidence that Ucp3 is essential for PGC-1α-induced oxidative capacity. Taken together, our results highlight PGC-1ɑ/PPARβ as an essential component of the molecular regulation of Ucp3 gene in skeletal muscle cells.

[Ubiquitin-independent protein degradation in proteasomes]

Proteasomes are large supramolecular protein complexes present in all prokaryotic and eukaryotic cells, where they perform targeted degradation of intracellular proteins. Until recently, it was generally accepted that prior proteolytic degradation in proteasomes the proteins had to be targeted by ubiquitination: the ATP-dependent addition of (typically four sequential) residues of the low-molecular ubiquitin protein, involving the ubiquitin-activating enzyme, ubiquitin-conjugating enzyme and ubiquitin ligase. The cytoplasm and nucleoplasm proteins labeled in this way are then digested in 26S proteasomes. However, in recent years it has become increasingly clear that using this route the cell eliminates only a part of unwanted proteins. Many proteins can be cleaved by the 20S proteasome in an ATP-independent manner and without previous ubiquitination. Ubiquitin-independent protein degradation in proteasomes is a relatively new area of studies of the role of the ubiquitin-proteasome system. However, recent data obtained in this direction already correct existing concepts about proteasomal degradation of proteins and its regulation. Ubiquitin-independent proteasome degradation needs the main structural precondition in proteins: the presence of unstructured regions in the amino acid sequences that provide interaction with the proteasome. Taking into consideration that in humans almost half of all genes encode proteins that contain a certain proportion of intrinsically disordered regions, it appears that the list of proteins undergoing ubiquitin-independent degradation will demonstrate further increase. Since 26S of proteasomes account for only 30% of the total proteasome content in mammalian cells, most of the proteasomes exist in the form of 20S complexes. The latter suggests that ubiquitin-independent proteolysis performed by the 20S proteasome is a natural process of removing damaged proteins from the cell and maintaining a constant level of intrinsically disordered proteins. In this case, the functional overload of proteasomes in aging and/or other types of pathological processes, if it is not accompanied by triggering more radical mechanisms for the elimination of damaged proteins, organelles and whole cells, has the most serious consequences for the whole organism.

Mitochondrial regulator PGC-1a-Modulating the modulator

Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1a) is a central regulator of metabolism that is poised at the intersection of myriad intracellular signaling pathways. In this brief update, we discuss regulation of PGC-1a at multiple levels, including transcriptional, post-transcriptional, and post-translational modifications. We discuss recently identified small molecule effectors of PGC-1a that offer translational potential and promise new insight into PGC-1a biology. We highlight novel mechanistic insights relating to PGC-1a's interactions with RNA to enhance transcription and potentially influence transcript processing. Finally, we place these exciting new data in the context of aging biology, offering PGC-1a as a candidate target with terrific potential in anti-aging interventions.

Proteasomal Degradation Machinery: Favorite Target of HIV-1 Proteins

Proteasomal degradation pathways play a central role in regulating a variety of protein functions by controlling not only their turnover but also the physiological behavior of the cell. This makes it an attractive target for the pathogens, especially viruses which rely on the host cellular machinery for their propagation and pathogenesis. Viruses have evolutionarily developed various strategies to manipulate the host proteasomal machinery thereby creating a cellular environment favorable for their own survival and replication. Human immunodeficiency virus-1 (HIV-1) is one of the most dreadful viruses which has rapidly spread throughout the world and caused high mortality due to its high evolution rate. Here, we review the various mechanisms adopted by HIV-1 to exploit the cellular proteasomal machinery in order to escape the host restriction factors and components of host immune system for supporting its own multiplication, and successfully created an infection.

Peroxisome proliferator-activated receptor γ coactivator family members competitively regulate hepatitis b virus biosynthesis

Transcriptional coactivators represent critical components of the transcriptional pre-initiation complex and are required for efficient gene activation. Members of the peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1) family differentially regulate hepatitis b virus (HBV) biosynthesis. Whereas PGC1α has been shown to be a potent activator of HBV biosynthesis, PGC1β only very poorly activates HBV RNA and DNA synthesis in human hepatoma (HepG2) and embryonic kidney (HEK293T) cells. Furthermore, PGC1β inhibits PGC1α-mediated HBV biosynthesis. These observations suggest that a potential competition between human hepatoma (HepG2) and embryonic kidney (HEK293T) cells PGC1α and PGC1β for common transcription factor target(s) may regulate HBV transcription and replication in a context and signal transduction pathway dependent manner.

NQO1 induction mediated by photodynamic therapy synergizes with β-Lapachone-halogenated derivative against melanoma

The elevated expression of NQO1 in many human solid tumors along with its ability to activate quinone-based anticancer agents makes it an excellent target for enzyme-directed drug development. NQO1 plays an important role in melanogenesis and given its correlation with a poor patient outcome we propose this enzyme as an intriguing target for molecular-based therapeutic regimen against melanoma. Unfortunately, the natural product β-Lapachone (β-Lap), whose antitumor activity is based on NQO1, reported dose-limiting toxicity which hampered its pre-clinical and clinical use. Therefore, new effective and safe therapeutic NQO1-bioactivatable agents for melanoma treatment are desirable. Regarding NQO1, we demonstrated that halogenated β-Lap derivative named PFB is an excellent substrate and effective tumor-selective anticancer compound. In addition, PFB resulted more attractive than the parent β-Lap for treating metastatic-derived melanoma cells. In this context, it would be interesting to design strategies to induce NQO1 activity in cancer cells as a promising combinatorial approach with bioreductive drugs. In this sense, we had reported that photodynamic therapy (PDT) significantly upregulated NQO1 expression. Based on this event, here we demonstrated that the cytotoxic regimen consisting of PFB plus PDT improved synergistic therapeutic combination on melanoma cells. In conclusion, our contribution provides a strong rationale for using therapies that associate photo- and chemotherapy to effectively treat melanoma with modular NQO1 status.

PGC-1α as a Biomarker of Physical Activity-Protective Effect on Colorectal Cancer

Colorectal cancer is a significant public health concern. As a multistage and multifactorial disease, environmental and genetic factors interact at each stage of the process, and an individual's lifestyle also plays a relevant role. We set out to review the scientific evidence to study the need to investigate the role of the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) gene as a biomarker of the physical activity's (PA) effect on colorectal cancer. PA is a protective factor against colorectal cancer and usually increases the expression of PGC-1α This gene has pleiotropic roles and is the main regulator of mitochondrial functions. The development of colorectal cancer has been associated with mitochondrial dysfunction; in addition, alterations in this organelle are associated with colorectal cancer risk factors, such as obesity, decreased muscle mass, and the aging process. These are affected by PA acting, among other aspects, on insulin sensitivity and oxygen reactive species/redox balance. Therefore, this gene demands special attention in the understanding of its operation in the consensual protective effect of PA in colorectal cancer. A significant amount of indirect evidence points to PGC-1α as a potential biomarker in the PA-protective effect on colorectal cancer. The article focuses on the possible involvement of PGC-1α in the protective role that physical activity has on colorectal cancer. This is an important topic both in relation to advances in prevention of the development of this widespread disease and in its therapeutic treatment. We hope to generate an initial hypothesis for future studies associated with physical activity-related mechanisms that may be involved in the development or prevention of colorectal cancer. PGC-1α is highlighted because it is the main regulator of mitochondrial functions. This organelle, on one hand, is positively stimulated by physical activity; on the other hand, its dysfunction or reduction increases the probability of developing colorectal cancer. Therefore, we consider the compilation of existing information about the possible ways to understand the mechanisms of this gene to be highly relevant. This study is based on evidence of PGC-1α and physical activity, on PGC-1α and colorectal cancer, on colorectal cancer and physical activity/inactivity, and the absence of studies that have sought to relate all of these variables. Cancer Prev Res; 11(9); 523-34. ©2018 AACR.

Effects of long-term sucrose overfeeding on rat brown adipose tissue: a structural and immunohistochemical study

The aim of this study was to determine the effects of long-term sucrose overfeeding on functional capacity and ultrastructural characteristics of the rat brown adipose tissue (BAT). For the study, 16 male Wistar rats, chow-fed and kept under standard laboratory conditions, were divided into 2 equal groups. The rats from a control group drank tap water, whereas those from a sucrose overfed group were allowed to drink 10% sucrose solution for 21 days. Structural changes of BAT were analysed at the level of light and electron microscopy on routinely prepared tissue sections or using immunohistochemical staining, in combination with stereological methods. Obtained results have shown that the significantly increased energy intake in sucrose overfed rats did not result in a higher gain of body mass compared with controls. The light microscopy analysis revealed that the BAT acquired the appearance of a thermogenically active tissue, with intensified vascularisation, reduced size of brown adipocytes and increased multilocularity. At the ultrastructural level, mitochondria of brown adipocytes became more abundant, enlarged and contained more cristae in comparison to control animals. The immunoexpression of uncoupling protein 1 (UCP1) and noradrenaline, as markers of BAT thermogenic status, was increased, whereas the pattern of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) was slightly modified. Taken together, the results of this investigation indicated that BAT possesses the ability to increase thermogenic capacity/activity in response to high energy intake and to prevent body mass gain. These findings are particularly relevant in view of recent reports on the existence of functional BAT in adult humans and its potential use to combat obesity.

Deciphering the Dichotomous Effects of PGC-1α on Tumorigenesis and Metastasis

Metabolic reprogramming confers cancer cells the ability to grow and survive under nutrient-depleted or stressful microenvironments. The amplification of oncogenes, the loss of tumor suppressors, as well as context- and lineage-specific determinants can converge and profoundly affect the metabolic status of cancer cells. Cumulating evidences suggest that highly glycolytic cells under the influence of oncogenes such as BRAF, or evolving in hypoxic microenvironments, will promote metastasis through modulation of multiple steps of tumorigenesis such as the epithelial-to-mesenchymal transition (EMT). On the contrary, increased reliance on mitochondrial respiration is associated with hyperplasic rather than metastatic disease. The PGC-1α transcriptional coactivator, a master regulator of mitochondrial biogenesis, has recently been shown to exert antimetastatic effects in cancer, notably through inhibition of EMT. Besides, PGC-1α has the opposite role in specific cancer subtypes, in which it appears to provide growth advantages. Thus, the regulation and role of PGC-1α in cancer is not univocal, and its use as a prognostic marker appears limited given its highly dynamic nature and its multifaceted regulation by transcriptional and posttranslational mechanisms. Herein, we expose key oncogenic and lineage-specific modules that finely regulate PGC-1α to promote or dampen the metastatic process. We propose a unifying model based on the systematic analysis of its controversial implication in cancer from cell proliferation to EMT and metastasis. This short review will provide a good understanding of current challenges associated with the study of PGC-1α.

Protective effect of Potentilla anserina polysaccharide on cadmium-induced nephrotoxicity in vitro and in vivo

The aim of this research was to investigate the antioxidant and anti-apoptotic activities of Potentilla anserina polysaccharide (PAP) on kidney damage induced by cadmium (Cd) in vitro and in vivo. PAP has been suggested to have anti-oxidation, anti-apoptosis, immunoregulation, antimicrobial, antitussive, and expectorant abilities. In this study, PAP was extracted and the major components of PAP were analyzed. It was shown that PAP pretreatment remarkably improved redox homeostasis, both in human embryonic kidney 293 (HEK293) cells and in BALB/c mice. Administration of PAP attenuated the mitochondrial dysfunction, degeneration, and fibrosis of kidney induced by Cd. Furthermore, PAP exhibited anti-apoptotic activity, which involved regulating both the mitochondria-mediated intrinsic apoptotic pathway and the death receptor-initiated extrinsic pathway. These results suggest that PAP is a potential therapeutic agent for Cd-induced nephrotoxicity.

SIRT3 deficiency exacerbates p53/Parkin‑mediated mitophagy inhibition and promotes mitochondrial dysfunction: Implication for aged hearts

Mitochondrial dynamics have critical roles in aging, and their impairment represents a prominent risk factor for myocardial dysfunction. Mitochondrial deacetylase sirtuin (SIRT)3 contributes greatly to the prevention of redox stress and cell aging. The present study explored the role of SIRT3 on myocardium aging. Western blot analysis demonstrated that SIRT3 expression levels were significantly lower in the myocardia of aged mice compared with young mice. Immunoprecipitation and western blot assays indicated that the activity of mitochondrial manganese superoxide dismutase (MnSOD) and peroxisome proliferator‑activated receptor γ coactivator (PGC)‑1α was reduced in the aged heart. To further explore the association between SIRT3 and myocardial senescence, SIRT3 heart‑specific knockout (SIRT3-/-) mice were used in the present study. The results revealed that obvious features of aging were present in the myocardium of SIRT3-/- mice, including mitochondrial protein dysfunction, enhanced oxidative stress, and energy metabolism dysfunction. SIRT3 deficiency impaired Parkin‑mediated mitophagy by increasing p53‑Parkin binding and blocking the mitochondrial translocation of Parkin in cardiomyocytes. Injection of autophagy agonist CCCP significantly increased the mitochondrial Parkin level in young wild‑type hearts but not in aged hearts; the effect was less pronounced in SIRT3-/- hearts. These data suggest that CCCP‑induced Parkin translocation was reduced in aged and SIRT3-/- hearts. CCCP‑induced mitochondrial clearance, which could be rescued by autophagy antagonist bafilomycin‑A1, was markedly weakened in aged and SIRT3-/- hearts vs. young hearts. SIRT3 deficiency exacerbated p53/Parkin‑mediated mitophagy inhibition and disrupted mitochondrial homeostasis, suggesting that loss of SIRT3 may increase the susceptibility of aged hearts to cardiac dysfunction. Therapeutic activation of SIRT3 and improved mitochondrial function may ameliorate the symptoms of cardiac aging.