Heme-Oxygenase I and PCG-1α Regulate Mitochondrial Biogenesis via Microglial Activation of Alpha7 Nicotinic Acetylcholine Receptors Using PNU282987

Regulation of Mitochondrial Biogenesis as a Way for Active Longevity: Interaction Between the Nrf2 and PGC-1α Signaling Pathways

Aging is a general degenerative process related to deterioration of cell functions in the entire organism. Mitochondria, which play a key role in energy homeostasis and metabolism of reactive oxygen species (ROS), require lifetime control and constant renewal. This explains recently peaked interest in the processes of mitochondrial biogenesis and mitophagy. The principal event of mitochondrial metabolism is regulation of mitochondrial DNA (mtDNA) transcription and translation, which is a complex coordinated process that involves at least two systems of transcription factors. It is commonly believed that its major regulatory proteins are PGC-1α and PGC-1β, which act as key factors connecting several regulator cascades involved in the control of mitochondrial metabolism. In recent years, the number of publications on the essential role of Nrf2/ARE signaling in the regulation of mitochondrial biogenesis has grown exponentially. Nrf2 is induced by various xenobiotics and oxidants that oxidize some Nrf2 negative regulators. Thus, ROS, in particular H₂O₂, were found to be strong Nrf2 activators. At present, there are two major concepts of mitochondrial biogenesis. Some authors suggest direct involvement of Nrf2 in the regulation of this process. Others believe that Nrf2 regulates expression of the antioxidant genes, while the major and only regulator of mitochondrial biogenesis is PGC-1α. Several studies have demonstrated the existence of the regulatory loop involving both PGC-1α and Nrf2. In this review, we summarized recent data on the Nrf2 role in mitochondrial biogenesis and its interaction with PGC-1α in the context of extending longevity.

Vagus Nerve Stimulation Attenuates Hepatic Ischemia/Reperfusion Injury via the Nrf2/HO-1 Pathway

It has been demonstrated that vagus nerve stimulation (VNS) plays a protective role in ischemia/reperfusion (I/R) injury of various organs. The present study investigates the protective effect of VNS on hepatic I/R injury and the potential mechanisms. Male Sprague-Dawley rats were randomly allocated into three groups: the sham operation group (Sham; n = 6, sham surgery with sham VNS); the I/R group (n = 6, hepatic I/R surgery with sham VNS); and the VNS group (n = 6, hepatic I/R surgery plus VNS). The I/R model was established by 1 hour of 70% hepatic ischemia. Tissue samples and blood samples were collected after 6 hours of reperfusion. The left cervical vagus nerve was separated and stimulated throughout the whole I/R process. The stimulus intensity was standardized to the voltage level that slowed the sinus rate by 10%. VNS significantly reduced the necrotic area and cell death in I/R tissues. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) were also decreased by VNS. In addition, VNS suppressed inflammation, oxidative stress, and apoptosis in I/R tissues. VNS significantly increased the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) in the liver. These data indicated that VNS may attenuate hepatic I/R injury by inhibiting inflammation, oxidative stress, and apoptosis possibly via the Nrf2/HO-1 pathway.

PGC-1α-Mediated Mitochondrial Biogenesis is Involved in Cannabinoid Receptor 2 Agonist AM1241-Induced Microglial Phenotype Amelioration

Cannabinoid type 2 receptor (CB2R) agonist AM1241 induces anti-inflammation by ameliorating microglial phenotypes, the mechanism, however, is still unknown. Peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) is a transcription protein which can regulate mitochondrial biogenesis, and the aim of this study is to investigate whether PGC-1α is involved in AM1241-induced anti-inflammation in N9 microglial cells. We used 10 ng/ml lipopolysaccharide (LPS) plus 10 U/ml interferon γ (IFNγ) to activate microglia into classic activated phenotype (M1 phenotype), and found that co-administration of 10 µM AM1241 increased the expressions of mitochondria biogenesis-associated proteins, including nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (TFAM) and COX IV, and up-regulated the biomarker levels of microglial M2 phenotype, including arginase 1 (Arg-1) and brain-derived neurotrophic factor (BDNF), and down-regulated biomarker levels of M1 phenotype, including inducible nitric oxide synthase (iNOS) and tumor necrosis factor α (TNF-α), compared to the cells treated with LPS plus IFNγ only (P < 0.05). By using PGC-1α-siRNA, however, we found that down-regulation of PGC-1α significantly reversed the AM1241-induced effects above (P < 0.05). According to the results in this study, we found that PGC-1α may mediate CB2R agonist AM1241-induced anti-inflammation in N9 microglial cells, and the mechanism might be associated with the enhancement of mitochondria biogenesis.

The role of Nrf2 signaling in counteracting neurodegenerative diseases

The transcription factor Nrf2 (nuclear factor-erythroid 2 p45-related factor 2) functions at the interface of cellular redox and intermediary metabolism. Nrf2 target genes encode antioxidant enzymes, and proteins involved in xenobiotic detoxification, repair and removal of damaged proteins and organelles, inflammation, and mitochondrial bioenergetics. The function of Nrf2 is altered in many neurodegenerative disorders, such as Huntington's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and Friedreich's ataxia. Nrf2 activation mitigates multiple pathogenic processes involved in these neurodegenerative disorders through upregulation of antioxidant defenses, inhibition of inflammation, improvement of mitochondrial function, and maintenance of protein homeostasis. Small molecule pharmacological activators of Nrf2 have shown protective effects in numerous animal models of neurodegenerative diseases, and in cultures of human cells expressing mutant proteins. Targeting Nrf2 signaling may provide a therapeutic option to delay onset, slow progression, and ameliorate symptoms of neurodegenerative disorders.

Targeting Nrf2 to Suppress Ferroptosis and Mitochondrial Dysfunction in Neurodegeneration

Ferroptosis is a newly described form of regulated cell death, distinct from apoptosis, necroptosis and other forms of cell death. Ferroptosis is induced by disruption of glutathione synthesis or inhibition of glutathione peroxidase 4, exacerbated by iron, and prevented by radical scavengers such as ferrostatin-1, liproxstatin-1, and endogenous vitamin E. Ferroptosis terminates with mitochondrial dysfunction and toxic lipid peroxidation. Although conclusive identification of ferroptosis in vivo is challenging, several salient and very well established features of neurodegenerative diseases are consistent with ferroptosis, including lipid peroxidation, mitochondrial disruption and iron dysregulation. Accordingly, interest in the role of ferroptosis in neurodegeneration is escalating and specific evidence is rapidly emerging. One aspect that has thus far received little attention is the antioxidant transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). This transcription factor regulates hundreds of genes, of which many are either directly or indirectly involved in modulating ferroptosis, including metabolism of glutathione, iron and lipids, and mitochondrial function. This potentially positions Nrf2 as a key deterministic component modulating the onset and outcomes of ferroptotic stress. The minimal direct evidence currently available is consistent with this and indicates that Nrf2 may be critical for protection against ferroptosis. In contrast, abundant evidence demonstrates that enhancing Nrf2 signaling is potently neuroprotective in models of neurodegeneration, although the exact mechanism by which this is achieved is unclear. Further studies are required to determine to extent to which the neuroprotective effects of Nrf2 activation involve the prevention of ferroptosis.

Flutamide Induces Hepatic Cell Death and Mitochondrial Dysfunction via Inhibition of Nrf2-Mediated Heme Oxygenase-1

Flutamide is a widely used nonsteroidal antiandrogen for prostate cancer therapy, but its clinical application is restricted by the concurrent liver injury. Increasing evidence suggests that flutamide-induced liver injury is associated with oxidative stress, though the precise mechanism is poorly understood. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master transcription factor regulating endogenous antioxidants including heme oxygenase-1 (HO-1). This study was designed to delineate the role of Nrf2/HO-1 in flutamide-induced hepatic cell injury. Our results showed that flutamide concentration dependently induced cytotoxicity, hydrogen peroxide accumulation, and mitochondrial dysfunction as indicated by mitochondrial membrane potential loss and ATP depletion. The protein expression of Nrf2 and HO-1 was induced by flutamide at 12.5 μM but was downregulated by higher concentrations of flutamide. Silencing either Nrf2 or HO-1 was found to aggravate flutamide-induced hydrogen peroxide accumulation and mitochondrial dysfunction as well as inhibition of the Nrf2 pathway. Moreover, preinduction of HO-1 by Copp significantly attenuated flutamide-induced oxidative stress and mitochondrial dysfunction, while inhibition of HO-1 by Snpp aggravated these deleterious effects. These findings suggest that flutamide-induced hepatic cell death and mitochondrial dysfunction is assoicated with inhibition of Nrf2-mediated HO-1. Pharmacologic intervention of Nrf2/HO-1 may provide a promising therapeutic approach in flutamide-induced liver injury.

PGC-1α sparks the fire of neuroprotection against neurodegenerative disorders

Recently, growing evidence has demonstrated that peroxisome proliferator activated receptor γ (PPARγ) coactivator-1α (PGC-1α) is a superior transcriptional regulator that acts via controlling the expression of anti-oxidant enzymes and uncoupling proteins and inducing mitochondrial biogenesis, which plays a beneficial part in the central nervous system (CNS). Given the significance of PGC-1α, we summarize the current literature on the molecular mechanisms and roles of PGC-1α in the CNS. Thus, in this review, we first briefly introduce the basic characteristics regarding PGC-1α. We then depict some of its important cerebral functions and discuss upstream modulators, partners, and downstream effectors of the PGC-1α signaling pathway. Finally, we highlight recent progress in research on the involvement of PGC-1α in certain major neurodegenerative disorders (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Collectively, the data presented here may be useful for supporting the future potential of PGC-1α as a therapeutic target.

β-Guanidinopropionic Acid Stimulates Brain Mitochondria Biogenesis and Alters Cognitive Behavior in Nondiseased Mid-Age Mice

β-guanidinopropionic acid (β-GPA) has been used as a nutritional supplement for increasing physical strength and endurance with positive and predictable results. In muscles, it works as a nonadaptive stimulator of mitochondria biogenesis; it also increases lipid metabolism. There are data indicating that β-GPA can be also neuroprotective, but its mechanisms of action in the brain are less understood. We studied the effects of β-GPA on animal behavior and mitochondrial biogenesis in the cortex and midbrain of mid-age healthy mice. We found that even short-term 3-week-long β-GPA treatment increased the mitochondrial DNA (mtDNA) copy number in the cortex and ventral midbrain, as well as the expression of several key antioxidant and metabolic enzymes—indicators of mitochondria proliferation and the activation of Nrf2/ARE signaling cascade. At the same time, β-GPA downregulated the expression of the β-oxidation genes. Administration of β-GPA in mice for 3 weeks improved the animals’ physical strength and endurance health, ie, increased their physical strength and endurance and alleviated anxiety. Thus, β-GPA might be considered an adaptogene affecting both the muscle and brain metabolism in mammals.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.