Sirt3 protects cortical neurons against oxidative stress via regulating mitochondrial Ca2+ and mitochondrial biogenesis

SIRT3 facilitates mitochondrial structural repair and functional recovery in rats after ischemic stroke by promoting OPA1 expression and activity

BACKGROUND

Optical atrophy 1 (OPA1), a protein accountable for mitochondrial fusion, facilitates the restoration of mitochondrial structure and function following cerebral ischemia/reperfusion (I/R) injury. The OPA1-conferred mitochondrial protection involves its expression and activity, which can be improved by SIRT3 in non-cerebral ischemia. Nevertheless, it remains obscure whether SIRT3 enhances the expression and activity of OPA1 after cerebral I/R injury.

METHODS

Mature male Sprague Dawley rats were intracranially injected with adeno-associated viral-Sirtuin-3(AAV-SIRT3) and AAV-sh_OPA1, followed by a 90-min temporary blockage of the middle cerebral artery and subsequent restoration of blood flow. Cultured cortical neurons of rats were transfected with LV-SIRT3 or LV-sh_OPA1 before a 2-h oxygen-glucose deprivation and reoxygenation. The rats and neurons were subsequently treated with a selective OPA1 activity inhibitor (MYLS22). The interaction between SIRT3 and OPA1 was assessed by molecular dynamics simulation technology and co-immunoprecipitation. The expression, function, and specific protective mechanism of SIRT3 were examined by various analyses.

RESULTS

SIRT3 interacted with OPA1 in the rat cerebral cortex before and after cerebral I/R. After cerebral I/R damage, SIRT3 upregulation increased the OPA1 expression, which enhanced deacetylation and OPA1 activity, thus alleviating cerebral infarct volume, neuronal apoptosis, oxidative pressure, and impairment in mitochondrial energy production; SIRT3 upregulation also improved neuromotor performance, repaired mitochondrial ultrastructure and membrane composition, and promoted the mitochondrial biogenesis. These neuroprotective effects were partly reversed by OPA1 expression interference and OPA1 activity inhibitor MYLS22.

CONCLUSION

In rats, SIRT3 enhances the expression and activity of OPA1, facilitating the repair of mitochondrial structure and functional recovery following cerebral I/R injury. These findings highlight that regulating SIRT3 may be a promising therapeutic strategy for ischemic stroke.

Intermittent Metabolic Switching and Vascular Cognitive Impairment

Intermittent fasting (IF), a dietary pattern alternating between eating and fasting periods within a 24-hour cycle, has garnered recognition for its potential to enhance both healthspan and lifespan in animal models and humans. It also shows promise in alleviating age-related diseases, including neurodegeneration. Vascular cognitive impairment (VCI) spans a severity range from mild cognitive deficits to severe cognitive deficits and loss of function in vascular dementia. Chronic cerebral hypoperfusion has emerged as a significant contributor to VCI, instigating vascular pathologies such as microbleeds, blood-brain barrier dysfunction, neuronal loss, and white matter lesions. Preclinical studies in rodents strongly suggest that IF has the potential to attenuate pathological mechanisms, including excitotoxicity, oxidative stress, inflammation, and cell death pathways in VCI models. Hence, this supports evaluating IF in clinical trials for both existing and at-risk VCI patients. This review compiles existing data supporting IF's potential in treating VCI-related vascular and neuronal pathologies, emphasizing the mechanisms by which IF may mitigate these issues. Hence providing a comprehensive overview of the available data supporting IF's potential in treating VCI by emphasizing the underlying mechanisms that make IF a promising intervention for VCI.

Advances in the study of mitophagy in osteoarthritis

Osteoarthritis (OA), characterized by cartilage degeneration, synovial inflammation, and subchondral bone remodeling, is among the most common musculoskeletal disorders globally in people over 60 years of age. The initiation and progression of OA involves the abnormal metabolism of chondrocytes as an important pathogenic process. Cartilage degeneration features mitochondrial dysfunction as one of the important causative factors of abnormal chondrocyte metabolism. Therefore, maintaining mitochondrial homeostasis is an important strategy to mitigate OA. Mitophagy is a vital process for autophagosomes to target, engulf, and remove damaged and dysfunctional mitochondria, thereby maintaining mitochondrial homeostasis. Cumulative studies have revealed a strong association between mitophagy and OA, suggesting that the regulation of mitophagy may be a novel therapeutic direction for OA. By reviewing the literature on mitophagy and OA published in recent years, this paper elaborates the potential mechanism of mitophagy regulating OA, thus providing a theoretical basis for studies related to mitophagy to develop new treatment options for OA.

Mitochondrial sirtuins: Energy dynamics and cancer metabolism

Mitochondria are pivotal for energy regulation and are linked to cancer. Mitochondrial sirtuins, (Sirtuin) SIRT3, SIRT4, and SIRT5, play crucial roles in cancer metabolism. This review explores their impact on cellular processes, with a focus on the NAD+ interplay and the modulation of their enzymatic activities. The varied roles of SIRT3, SIRT4, and SIRT5 in metabolic adaptation and cancer are outlined, emphasizing their tumor suppressor or oncogenic nature. We propose new insights into sirtuin biology, and cancer therapeutics, suggesting an integrated proteomics and metabolomics approach for a comprehensive understanding of mitochondrial sirtuins in cancer.

Sirtuins as Potential Targets for Neuroprotection: Mechanisms of Early Brain Injury Induced by Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a prevalent cerebrovascular disease with significant global mortality and morbidity rates. Despite advancements in pharmacological and surgical approaches, the quality of life for SAH survivors has not shown substantial improvement. Traditionally, vasospasm has been considered a primary contributor to death and disability following SAH, but anti-vasospastic therapies have not demonstrated significant benefits for SAH patients' prognosis. Emerging studies suggest that early brain injury (EBI) may play a crucial role in influencing SAH prognosis. Sirtuins (SIRTs), a group of NAD + -dependent deacylases comprising seven mammalian family members (SIRT1 to SIRT7), have been found to be involved in neural tissue development, plasticity, and aging. They also exhibit vital functions in various central nervous system (CNS) processes, including cognition, pain perception, mood, behavior, sleep, and circadian rhythms. Extensive research has uncovered the multifaceted roles of SIRTs in CNS disorders, offering insights into potential markers for pathological processes and promising therapeutic targets (such as SIRT1 activators and SIRT2 inhibitors). In this article, we provide an overview of recent research progress on the application of SIRTs in subarachnoid hemorrhage and explore their underlying mechanisms of action.

MicroRNA-129-1-3p attenuates autophagy-dependent cell death by targeting MCU in granulosa cells of laying hens under H2O2-induced oxidative stress

The present study aimed to investigate the mechanism of microRNA-129-1-3p (miR-129-1-3p) in regulating hydrogen peroxide (H2O2)-induced autophagic death of chicken granulosa cell by targeting mitochondrial calcium uniporter (MCU). The results indicated that the exposure of hens' ovaries to H2O2 resulted in a significant elevation in reactive oxygen species (ROS) levels, as well as the apoptosis of granulosa cells and follicular atresia. This was accompanied by an upregulation of glucose-regulated protein 75 (GRP75), voltage-dependent anion-selective channel 1 (VDAC1), MCU, mitochondria fission factor (MFF), microtubule-associated protein 1 light chain 3 (LC3) I, and LC3II expression, and a downregulation of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) and mitofusin-2 (MFN2) expression. In hens' granulosa cells, a luciferase reporter assay confirmed that miR-129-1-3p directly regulates MCU. The induction of oxidative stress through H2O2 resulted in the activation of the permeability transition pore, an overload of calcium, depolarization of the mitochondrial membrane potential, dysfunction of mitochondria-associated endoplasmic reticulum membranes (MAMs), and ultimately, autophagic cell death. The overexpression of miR-129-1-3p effectively mitigated these H2O2-induced changes. Furthermore, miR-129-1-3p overexpression in granulosa cells prevented the alterations induced by H2O2 in the expression of key proteins that play crucial roles in maintaining the integrity of MAMs and regulating autophagy, such as GRP75, VDAC1, MFN2, PTEN-induced kinase 1 (Pink1), and parkin RBR E3 ubiquitin-protein ligase (Parkin). Together, these in vitro- and in vivo-based experiments suggest that miR-129-1-3p protects granulosa cells from oxidative stress-induced autophagic cell death by downregulating the MCU-mediated mitochondrial autophagy. miR-129-1-3p/MCU calcium signaling pathway may act as a new target to alleviate follicular atresia caused by oxidative stress in laying hens.

Ursolic acid ameliorates traumatic brain injury in mice by regulating microRNA-141-mediated PDCD4/PI3K/AKT signaling pathway

BACKGROUND

Neuronal apoptosis and inflammation are the key pathogenic features of secondary brain injury, which results in the neurological impairment that traumatic brain injury (TBI) patients experience. Ursolic Acid (UA) has been shown to have neuroprotective properties against brain damage, however, detailed mechanisms have not been fully disclosed. Research on brain-related microRNAs (miRNAs) has opened up new possibilities for the neuroprotective treatment of UA by manipulating miRNAs. The present study was designed to investigate the impact of UA on neuronal apoptosis and the inflammatory response in TBI mice.

METHODS

The mice's neurologic condition was assessed using the modified neurological severity score (mNSS) and the learning and memory abilities were assessed using the Morris water maze (MWM). Cell apoptosis, oxidative stress, and inflammation were utilized to examine the impact of UA on neuronal pathological damage. miR-141-3p was selected to evaluate whether UA influences miRNAs in a way that has neuroprotective benefits.

RESULTS

The results showed that UA markedly decreased brain edema and neuronal mortality through oxidative stress and neuroinflammation in TBI mice. Using data from the GEO database, we found that miR-141-3p was considerably downregulated in TBI mice and that this downregulation was reversed by UA treatment. Further studies have shown that UA regulates miR-141-3p expression to exhibit its neuroprotective effect in mouse models and cell injury models. Then, miR-141-3p was discovered to directly target PDCD4 in TBI mice and neurons, a well-known PI3K/AKT pathway regulator in the neurons. Most importantly, the upregulation of phosphorylated (p)-AKT and p-PI3K provided the most compelling evidence that UA reactivated the PI3K/AKT pathway in the TBI mouse model, which was through regulating miR-141-3p.

CONCLUSION

Our findings support the notion that UA can improve TBI by modulating miR-141 mediated PDCD4/PI3K/AKT signaling pathway.

Role of Sirtuin 3 in Degenerative Diseases of the Central Nervous System

An NAD⁺-dependent deacetylase called Sirtuin 3 (Sirt3) is involved in the metabolic processes of the mitochondria, including energy generation, the tricarboxylic acid cycle, and oxidative stress. Sirt3 activation can slow down or prevent mitochondrial dysfunction in response to neurodegenerative disorders, demonstrating a strong neuroprotective impact. The mechanism of Sirt3 in neurodegenerative illnesses has been elucidated over time; it is essential for neuron, astrocyte, and microglial function, and its primary regulatory factors include antiapoptosis, oxidative stress, and the maintenance of metabolic homeostasis. Neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS), may benefit from a thorough and in-depth investigation of Sirt3. In this review, we primarily cover Sirt3's role and its regulation in the nerve cells and the connection between Sirt3 and neurodegenerative disorders.

Role of SIRT3 in mitochondrial biology and its therapeutic implications in neurodegenerative disorders

Sirtuin 3 (SIRT3), a mitochondrial deacetylase expressed preferentially in high-metabolic-demand tissues including the brain, requires NAD⁺ as a cofactor for catalytic activity. It regulates various processes such as energy homeostasis, redox balance, mitochondrial quality control, mitochondrial unfolded protein response (UPRmt), biogenesis, dynamics and mitophagy by altering protein acetylation status. Reduced SIRT3 expression or activity causes hyperacetylation of hundreds of mitochondrial proteins, which has been linked with neurological abnormalities, neuro-excitotoxicity and neuronal cell death. A body of evidence has suggested, SIRT3 activation as a potential therapeutic modality for age-related brain abnormalities and neurodegenerative disorders.

Role of Estrogen-Related Receptor γ and PGC-1α/SIRT3 Pathway in Early Brain Injury After Subarachnoid Hemorrhage

Estrogen-related receptors (ERRs) were shown to play an important role in the regulation of free radical-mediated pathology. This study aimed to investigate the neuroprotective effect of ERRγ activation against early brain injury (EBI) after subarachnoid hemorrhage (SAH) and the potential underlying mechanisms. In a rat model of SAH, the time course of ERRs and SIRT3 and the effects of ERRγ activation were investigated. ERRγ agonist DY131, selective inhibitor GSK5182, or SIRT3 selective inhibitor 3-TYP were administered intracerebroventricularly (icv) in the rat model of SAH. The use of 3-TYP was for validating SIRT3 as the downstream signaling of ERRγ activation. Post-SAH assessments included SAH grade, neurological score, Western blot, Nissl staining, and immunofluorescence staining in rats. In an vitro study, the ERRγ agonist DY131 and ERRγ siRNA were administered to primary cortical neurons stimulated by Hb, after which cell viability and neuronal deaths were accessed. Lastly, the brain ERRγ levels and neuronal death were accessed in SAH patients. We found that brain ERRγ expressions were significantly increased, but the expression of SIRT3 dramatically decreased after SAH in rats. In the brains of SAH rats, ERRγ was expressed primarily in neurons, astrocytes, and microglia. The activation of ERRγ with DY131 significantly improved the short-term and long-term neurological deficits, accompanied by reductions in oxidative stress and neuronal apoptosis at 24 h after SAH in rats. DY131 treatment significantly increased the expressions of PGC-1α, SIRT3, and Bcl-2 while downregulating the expressions of 4-HNE and Bax. ERRγ antagonist GSK5182 and SIRT3 inhibitor 3-TYP abolished the neuroprotective effects of ERRγ activation in the SAH rats. An in vitro study showed that Hb stimulation significantly increased intracellular oxidative stress in primary cortical neurons, and DY131 reduced such elevations. Primary cortical neurons transfected with the ERRγ siRNA exhibited notable apoptosis and abolished the protective effect of DY131. The examination of SAH patients' brain samples revealed increases in ERRγ expressions and neuronal apoptosis marker CC3. We concluded that ERRγ activation with DY131 ameliorated oxidative stress and neuronal apoptosis after the experimental SAH. The effects were, at least in part, through the ERRγ/PGC-1α/SIRT3 signaling pathway. ERRγ may serve as a novel therapeutic target to ameliorate EBI after SAH.

Honokiol prevents chronic cerebral hypoperfusion induced astrocyte A1 polarization to alleviate neurotoxicity by targeting SIRT3-STAT3 axis

Alzheimer's Dementia (AD) and Vascular Dementia (VaD) are two main types of dementias for which no specific treatment is available. Chronic Cerebral Hypoperfusion (CCH) is a pathogenesis underlying AD and VaD that promotes neuroinflammatory responses and oxidative stress. Honokiol (HNK) is a natural compound isolated from magnolia leaves that can easily cross blood brain barrier and has anti-inflammatory and antioxidant effects. In the present study, the effects of HNK on astrocyte polarization and neurological damage in in vivo and in vitro models of chronic cerebral hypoperfusion were explored. We found that HNK was able to inhibit the phosphorylation and nuclear translocation of STAT3, A1 polarization, and reduce conditioned medium's neuronal toxicity of astrocyte under chronic hypoxia induced by cobalt chloride; STAT3 phosphorylation inhibitor C188-9 was able to mimic the above effects of HNK, suggesting that HNK may inhibit chronic hypoxia-induced A1 polarization in astrocytes via STAT3. SIRT3 inhibitor 3-TYP reversed, while Sirt3 overexpression mimicked the inhibitory effects of HNK on oxidative stress, STAT3 phosphorylation and nuclear translocation, A1 polarization and neuronal toxicity of astrocyte under chronic hypoxic conditions. For in vivo research, continuous intraperitoneal injection of HNK (1mg/kg) for 21 days ameliorated the decrease in SIRT3 activity and oxidative stress, inhibited astrocytic STAT3 nuclear translocation and A1 polarization, and prevented neuron and synaptic loss in the hippocampal of CCH rats. Besides, HNK application improved the spatial memory impairment of CCH rats, as assessed with Morris Water Maze. In conclusion, these results suggest that the phytochemical HNK can inhibit astrocyte A1 polarization via regulating SIRT3-STAT3 axis, thus improving CCH-induced neurological damage. These results highlight HNK as novel treatment for dementia with underlying vascular mechanisms.

Sirtuin-3: A potential target for treating several types of brain injury

Sirtuin-3 (SIRT3) is responsible for maintaining mitochondrial homeostasis by deacetylating substrates in an NAD+-dependent manner. SIRT3, the primary deacetylase located in the mitochondria, controls cellular energy metabolism and the synthesis of essential biomolecules for cell survival. In recent years, increasing evidence has shown that SIRT3 is involved in several types of acute brain injury. In ischaemic stroke, subarachnoid haemorrhage, traumatic brain injury, and intracerebral haemorrhage, SIRT3 is closely related to mitochondrial homeostasis and with the mechanisms of pathophysiological processes such as neuroinflammation, oxidative stress, autophagy, and programmed cell death. As SIRT3 is the driver and regulator of a variety of pathophysiological processes, its molecular regulation is significant. In this paper, we review the role of SIRT3 in various types of brain injury and summarise SIRT3 molecular regulation. Numerous studies have demonstrated that SIRT3 plays a protective role in various types of brain injury. Here, we present the current research available on SIRT3 as a target for treating ischaemic stroke, subarachnoid haemorrhage, traumatic brain injury, thus highlighting the therapeutic potential of SIRT3 as a potent mediator of catastrophic brain injury. In addition, we have summarised the therapeutic drugs, compounds, natural extracts, peptides, physical stimuli, and other small molecules that may regulate SIRT3 to uncover additional brain-protective mechanisms of SIRT3, conduct further research, and provide more evidence for clinical transformation and drug development.

Stromal Interaction Molecule 1-Mediated Store-Operated Calcium Entry Promotes Autophagy Through AKT/Mammalian Target of Rapamycin Pathway in Hippocampal Neurons After Ischemic Stroke

The pathophysiological process of neuronal injury due to cerebral ischemia is complex among which disturbance of calcium homeostasis and autophagy are two major pathogenesis. However, it remains ambiguous whether the two factors are independent. Stromal interaction molecule 1 (STIM1) is the most important Ca²⁺ sensor mediating the store-operated Ca²⁺ entry (SOCE) through interacting with Orai1 and has recently been proven to participate in autophagy in multiple cells. In this study, we aimed to investigate the potential role of STIM1-induced SOCE on autophagy and whether its regulator function contributes to neuronal injury under hypoxic conditions using in vivo transient middle cerebral artery occlusion (tMCAO) model and in vitro oxygen and glucose deprivation (OGD) primary cultured neuron model respectively. The present data indicated that STIM1 induces autophagic flux impairment in neurons through promoting SOCE and inhibiting AKT/mTOR signaling pathway. Pharmacological inhibition of SOCE or downregulation of STIM1 with siRNA suppressed the autophagic activity in neurons. Moreover, stim1 knockdown attenuated neurological deficits and brain damage after tMCAO, which could be reversed by AKT/mTOR pathway inhibitor AZD5363. Together, the modulation of STIM1 on autophagic activation indicated the potential link between Ca²⁺ homeostasis and autophagy which provided evidence that STIM1 could be a promising therapeutic target for ischemic stroke.

Sex-divergent effects on the NAD+-dependent deacetylase sirtuin signaling across the olfactory-entorhinal-amygdaloid axis in Alzheimer's and Parkinson's diseases

BACKGROUND

Smell impairment is one of the earliest features in Alzheimer's (AD) and Parkinson's diseases (PD). Due to sex differences exist in terms of smell and olfactory structures as well as in the prevalence and manifestation of both neurological syndromes, we have applied olfactory proteomics to favor the discovery of novel sex-biased physio-pathological mechanisms and potential therapeutic targets associated with olfactory dysfunction.

METHODS

SWATH-MS (sequential window acquisition of all theoretical fragment ion spectra mass spectrometry) and bioinformatic workflows were applied in 57 post-mortem olfactory tracts (OT) derived from controls with no known neurological history (n = 6F/11M), AD (n = 4F/13M) and PD (n = 7F/16M) subjects. Complementary molecular analyses by Western-blotting were performed in the olfactory bulb (OB), entorhinal cortex (EC) and amygdala areas.

RESULTS

327 and 151 OT differentially expressed proteins (DEPs) were observed in AD women and AD men, respectively (35 DEPs in common). With respect to PD, 198 DEPs were identified in PD women, whereas 95 DEPs were detected in PD men (20 DEPs in common). This proteome dyshomeostasis induced a disruption in OT protein interaction networks and widespread sex-dependent pathway perturbations in a disease-specific manner, among them Sirtuin (SIRT) signaling. SIRT1, SIRT2, SIRT3 and SIRT5 protein levels unveiled a tangled expression profile across the olfactory-entorhinal-amygdaloid axis, evidencing disease-, sex- and brain structure-dependent changes in olfactory protein acetylation.

CONCLUSIONS

Alteration in the OT proteostasis was more severe in AD than in PD. Moreover, protein expression changes were more abundant in women than men independent of the neurological syndrome. Mechanistically, the tangled SIRT profile observed across the olfactory pathway-associated brain regions in AD and PD indicates differential NAD (+)-dependent deacetylase mechanisms between women and men. All these data shed new light on differential olfactory mechanisms across AD and PD, pointing out that the evaluation of the feasibility of emerging sirtuin-based therapies against neurodegenerative diseases should be considered with caution, including further sex dimension analyses in vivo and in clinical studies.

Sirt3 activates autophagy to prevent DOX-induced senescence by inactivating PI3K/AKT/mTOR pathway in A549 cells

Sirtuin 3 (Sirt3), a mitochondrial deacetylase, regulates mitochondrial redox homeostasis and autophagy and is involved in physiological and pathological processes such as aging, cellular metabolism, and tumorigenesis. We here investigate how Sirt3 regulates doxorubicin (DOX)-induced senescence in lung cancer A549 cells. Sirt3 greatly reduced DOX-induced upregulation of senescence marker proteins p53, p16, p21 and SA-β-Gal activity as well as ROS levels. Notably, Sirt3 reversed DOX-induced autophagic flux blockage, as shown by increased p62 degradation and LC3II/LC3I ratio. Importantly, the autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ) partially abolished the antioxidant stress and antiaging effects of Sirt3, while the autophagy activator rapamycin (Rap) potentiated these effects of Sirt3, demonstrating that autophagy mediates the anti-aging effects of Sirt3. Additionally, Sirt3 inhibited the DOX-induced activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway, which in turn activated autophagy. The PI3K inhibitor LY294002 promoted the antioxidant stress and antiaging effects of Sirt3, while the AKT activator SC-79 reversed these effects of Sirt3. Taken together, Sirt3 counteracts DOX-induced senescence by improving autophagic flux.

SIRT6 is a key regulator of mitochondrial function in the brain

The SIRT6 deacetylase has been implicated in DNA repair, telomere maintenance, glucose and lipid metabolism and, importantly, it has critical roles in the brain ranging from its development to neurodegeneration. Here, we combined transcriptomics and metabolomics approaches to characterize the functions of SIRT6 in mouse brains. Our analysis reveals that SIRT6 is a central regulator of mitochondrial activity in the brain. SIRT6 deficiency in the brain leads to mitochondrial deficiency with a global downregulation of mitochondria-related genes and pronounced changes in metabolite content. We suggest that SIRT6 affects mitochondrial functions through its interaction with the transcription factor YY1 that, together, regulate mitochondrial gene expression. Moreover, SIRT6 target genes include SIRT3 and SIRT4, which are significantly downregulated in SIRT6-deficient brains. Our results demonstrate that the lack of SIRT6 leads to decreased mitochondrial gene expression and metabolomic changes of TCA cycle byproducts, including increased ROS production, reduced mitochondrial number, and impaired membrane potential that can be partially rescued by restoring SIRT3 and SIRT4 levels. Importantly, the changes we observed in SIRT6-deficient brains are also occurring in aging human brains and particularly in patients with Alzheimer's, Parkinson's, Huntington's, and Amyotrophic lateral sclerosis disease. Overall, our results suggest that the reduced levels of SIRT6 in the aging brain and neurodegeneration initiate mitochondrial dysfunction by altering gene expression, ROS production, and mitochondrial decay.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

SIRT3 alleviates mitochondrial dysfunction induced by recurrent low glucose and improves the supportive function of astrocytes to neurons

Hypoglycemia is an independent risk factor of cognitive impairment in patients with diabetes. Our previous study indicated that dysfunction of astrocytic mitochondria induced by recurrent low glucose (RLG) may account for hypoglycemia-associated neuronal injury and cognitive decline. Sirtuin 3 (SIRT3) is a key deacetylase for mitochondrial proteins and has recently been demonstrated to be an important regulator of mitochondrial function. However, whether mitochondrial dysfunction due to hypoglycemia is associated with astrocytic SIRT3 remains unclear, and few studies have focused on the impact of astrocytic SIRT3 on neuronal survival. In the present work, primary mouse cortical astrocytes cultured in normal glucose (5.5 mM) and high glucose (16.5 mM) were treated with five rounds of RLG (0.1 mM). The results showed that RLG suppressed SIRT3 expression in a glucose-dependent manner. High-glucose culture considerably increased the vulnerability of SIRT3 to RLG, leading to disrupted mitochondrial morphology in astrocytes. Overexpression of SIRT3 markedly improved astrocytic mitochondrial function and reduced RLG-induced oxidative stress. Moreover, SIRT3 suppressed a shift towards a neuroinflammatory A1-like reactive phenotype of astrocytes in response to RLG with reduced IL-1β, IL-6, and TNFα levels. Furthermore, it elevated brain-derived neurotrophic factor (BDNF) levels and promoted neurite growth by activating BDNF/TrkB signaling in the co-cultured neurons. The present study reveals the probable crosstalk between neurons and astrocytes after hypoglycemic exposure and provides a potential target in treating hypoglycemia-associated neuronal injury.

The Mfn1-βIIPKC Interaction Regulates Mitochondrial Dysfunction via Sirt3 Following Experimental Subarachnoid Hemorrhage

Neuronal injury following subarachnoid hemorrhage (SAH) has been shown to be associated with mitochondrial dysfunction and oxidative stress. βIIPKC, a subtype of protein kinase C (PKC), accumulates on the mitochondrial outer membrane and phosphorylates mitofusin 1 (Mfn1) at serine 86. Here, we investigated the role of Mfn1-βIIPKC interaction in brain damage and neurological function in both in vivo and in vitro experimental SAH models. The expression of βIIPKC protein and the interaction of Mfn1-βIIPKC were found to be increased after OxyHb treatment in primary cultured cortical neurons and were also observed in the brain following SAH in rats. Treatment with the βIIPKC inhibitor βIIV5-3 or SAMβA, a peptide that selectively antagonizes Mfn1-βIIPKC association, significantly attenuated the OxyHb-induced neuronal injury and apoptosis. These protective effects were accompanied by inhibited mitochondrial dysfunction and preserved mitochondrial biogenesis. The results of western blot showed that βIIV5-3 or SAMβA markedly increased the expression of Sirt3 and enhanced the activities of its downstream mitochondrial antioxidant enzymes in OxyHb-treated neurons. Knockdown of Sirt3 via specific targeted small interfering RNA (siRNA) partially prevented the βIIV5-3- or SAMβA-induced protection and antioxidative effects. In addition, treatment with βIIV5-3 or SAMβA in vivo was found to obviously reduce brain edema, alleviate neuroinflammation, and preserve neurological function after experimental SAH in rats. In congruent with in vitro data, the protection induced by βIIV5-3 or SAMβA was reduced by Sirt3 knockdown in vivo. In summary, our present results showed that blocking Mfn1-βIIPKC interaction protects against brain damage and mitochondrial dysfunction via Sirt3 following experimental SAH.

Role of NAD+ and FAD in Ischemic Stroke Pathophysiology: An Epigenetic Nexus and Expanding Therapeutic Repertoire

The redox coenzymes viz., oxidized β-nicotinamide adenine dinucleotide (NAD⁺) and flavin adenine dinucleotide (FAD) by way of generation of optimal reducing power and cellular energy currency (ATP), control a staggering array of metabolic reactions. The prominent cellular contenders for NAD⁺ utilization, inter alia, are sirtuins (SIRTs) and poly(ADP-ribose) polymerase (PARP-1), which have been significantly implicated in ischemic stroke (IS) pathogenesis. NAD⁺ and FAD are also two crucial epigenetic enzyme-required metabolites mediating histone deacetylation and poly(ADP-ribosyl)ation through SIRTs and PARP-1 respectively, and demethylation through FAD-mediated lysine specific demethylase activity. These enzymes and post-translational modifications impinge on the components of neurovascular unit, primarily neurons, and elicit diverse functional upshots in an ischemic brain. These could be circumstantially linked with attendant cognitive deficits and behavioral outcomes in post-stroke epoch. Parsing out the contribution of NAD⁺/FAD-synthesizing and utilizing enzymes towards epigenetic remodeling in IS setting, together with their cognitive and behavioral associations, combined with possible therapeutic implications will form the crux of this review.

Mitochondrial brain proteome acetylation levels and behavioural responsiveness to amphetamine are altered in mice lacking Sirt3

Post-translational modification of mitochondrial proteins represents one mechanism by which the functional activity of mitochondria can be regulated. In the brain, these modifications can influence the functional properties of different neural circuitries. Given that the sirtuin family member Sirt3 represents the primary protein deacetylase enzyme in mitochondria, we tested whether brain mitochondrial proteome acetylation would increase in male or female mice lacking Sirt3. Our results confirm that whole brain mitochondrial proteome acetylation levels are indeed elevated in both sexes of Sirt3-KO mice relative to controls. Consistently, we found the mitochondria of mouse embryonic fibroblast (MEF) cells derived from Sirt3-KO mice were smaller in size, and fewer in number than in wild-type MEFs, and that mitochondrial free calcium levels were elevated within the mitochondria of these cells. As protein acetylation can influence mitochondrial function, and changes in mitochondrial function have been linked to alterations in neural circuit function regulating motor activity and anxiety-like behavior, we tested whether Sirt3-deficient mice would display sensitized responsiveness to the stimulant amphetamine. Both male and female Sirt3-KO mice displayed hyper-locomotion and attenuated anxiety-like behavior in response to a dose of amphetamine that was insufficient to promote any behavioural responses in wild-type mice. Collectively, these results confirm that Sirt3 regulates mitochondrial proteome acetylation levels in brain tissue, and that the absence of Sirt3 increases the sensitivity of neural systems to amphetamine-induced behavioural responses.

MicroRNA-668-3p regulates oxidative stress and cell damage induced by Aβ1-42 by targeting the OXR1/p53-p21 axis

Background

Alzheimer’s disease (AD) is the most common type of dementia in old age and has become a serious social and medical problem threatening human health. We aimed to explore the mechanisms underlying AD development by screening for microRNAs (miRNAs) that affect AD progression and examining their role in AD development.

Methods

Hematoxylin-eosin (HE) staining, immunohistochemistry, and immunofluorescence (IF) were used to analyze the characteristics of the hippocampus, neuron cell separation, and related protein expression in mice. We used Gene Expression Omnibus (GEO) data analysis to screen miRNAs and mRNAs that affect AD progression, and quantitative reverse transcription polymerase chain reaction (RT-qPCR) and western blot analysis to determine changes in miRNA and mRNA levels before and after amyloid β (Aβ)1-42 induction. In addition, we used luciferase analysis to examine miRNA and mRNA binding and the effect of miRNA/mRNA interaction on neuronal cell proliferation. Apoptosis and reactive oxygen species (ROS) levels were examined using Cell Counting Kit-8 analysis and flow cytometry (FCM), respectively. The enzyme-linked immunosorbent assay was used to analyze changes in neuronal cell-secreted oxidative stress-related protein levels through miRNA/mRNA interaction.

Results

Oxidative stress levels were significantly increased in the AD mouse model. GEO data analysis revealed 67 dysregulated miRNAs, and miR-668-3p was identified as a potential therapeutic target for AD. We found that the AD and Aβ1-42-induced models showed an increase in miR-668-3p and a decrease in oxidation resistance 1 (OXR1) expression. The luciferase analysis results revealed that miR-668-3p may play a role in AD development by targeting OXR1 and promoting intracellular oxidative stress by activating p53-p21 signaling. The final rescue experiment also confirmed that Aβ1-42-induction decreased cell proliferation, increased apoptosis, increased cell cycle arrest, and promoted oxidative stress. Tenovin-1 (TEN) enhanced the effect of Aβ1-42, and the miR-668-3p inhibitor partially alleviated it, although the effect of the miR-668-3p inhibitor was weakened by TEN.

Conclusions

MiR-668-3p negatively regulated OXR1 expression by targeting OXR1, affecting p53-p21 protein signaling, and regulating cell damage and oxidative stress induced by Aβ1-42. Therefore, miR-668-3p may be a potential therapeutic target for AD.

Effects of fluoride exposure on mitochondrial function: Energy metabolism, dynamics, biogenesis and mitophagy

Fluoride is ubiquitous in the environment. Furthermore, drinking water represents the main source of exposure to fluoride for humans. Interestingly, low fluoride concentrations have beneficial effects on bone and teeth development; however, chronic fluoride exposure has harmful effects on human health. Besides, preclinical studies associate fluoride toxicity with oxidative stress, inflammation, and apoptosis. On the other hand, it is well-known that mitochondria play a key role in reactive oxygen species production. By contrast, fluoride's effect on processes such as mitochondrial dynamics, biogenesis and mitophagy are little known. These processes modulate the size, content, and distribution of mitochondria and their depuration help to counter the reactive oxygen species production and cytochrome c release, thereby allowing cell survival. However, a maladaptive response could enhance fluoride-induced toxicity. The present review gives a brief account of fluoride-induced mitochondrial alterations on soft and hard tissues, including liver, reproductive organs, heart, brain, lung, kidney, bone, and tooth.

Intermittent hypoxia promotes the recovery of motor function in rats with cerebral ischemia by regulating mitochondrial function

Hypoxia preconditioning is neuroprotective, but the therapeutic effects of intermittent hypoxia were not fully considered. The present study investigated the neuroprotective effect and mechanism of intermittent hypoxia on motor function after cerebral ischemia and explored alternative clinical treatment options. In total, 36 8-week-old male Sprague-Dawley rats were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO) and then randomly divided into a sham-operated group (SHAM), tMCAO-sedentary group (SED), and tMCAO-intermittent hypoxia group (IH). The intervention was performed 1 week after tMCAO and lasted 4 weeks. Rats in the IH group were placed in an animal hypoxic chamber (altitude 5000 m and oxygen concentration of 13%) for 4 h/day and 7 days/week, and rats in the SED group were placed in a normoxic environment for 4 weeks. Body weights, neurological deficit scores, cerebral infarction volume ratios, gait analyses, mitochondrial structure, adenosine triphosphate (ATP) content and AMO-activated protein kinase (AMPK), peroxisome proliferator-activated receptor γ co-activator-1α (PGC-1α), and silencing regulatory protein 3 (Sirt3) expression in the peri-ischemic region brain tissues were detected during the intervention. Compared with the SED group, the body weight of the IH group gradually recovered, and the neurological deficit scores were significantly reduced (P < 0.05). The gait analysis results showed that the pressure of the affected paw and the maximum content area, swing speed, stride length, and other parameters were significantly restored (P < 0.05). The cerebral infarction volume ratio was significantly reduced (P < 0.01). Mitochondrial morphological structure damage in the peri-ischemic region brain tissues recovered, the number was significantly increased (P < 0.05), and the expression of AMPK, PGC-1α, and Sirt3 proteins (P < 0.05), and ATP content were significantly increased (P < 0.05). Intermittent hypoxia may activate the AMPK-PGC-1α-Sirt3 signaling pathway, promote mitochondrial biogenesis, repair mitochondrial ultrastructural damage, and improve mitochondrial function to reduce brain damage and promote motor function recovery in rats with cerebral ischemia.

Sirtuins and cognition: implications for learning and memory in neurological disorders

Sirtuins are an evolutionarily conserved family of regulatory proteins that function in an NAD+ -dependent manner. The mammalian family of sirtuins is composed of seven histone deacetylase and ADP-ribosyltransferase proteins (SIRT1-SIRT7) that are found throughout the different cellular compartments of the cell. Sirtuins in the brain have received considerable attention in cognition due to their role in a plethora of metabolic and age-related diseases and their ability to induce neuroprotection. More recently, sirtuins have been shown to play a role in normal physiological cognitive function, and aberrant sirtuin function is seen in pathological cellular states. Sirtuins are believed to play a role in cognition through enhancing synaptic plasticity, influencing epigenetic regulation, and playing key roles in molecular pathways involved with oxidative stress affecting mitochondrial function. This review aims to discuss recent advances in the understanding of the role of mammalian sirtuins in cognitive function and the therapeutic potential of targeting sirtuins to ameliorate cognitive deficits in neurological disorders.

Mitochonic Acid-5 Inhibits Reactive Oxygen Species Production and Improves Human Chondrocyte Survival by Upregulating SIRT3-Mediated, Parkin-dependent Mitophagy

Mitochondrial dysfunction is related to the pathogenesis of osteoarthritis (OA); however, there are no effective drugs to treat OA for maintaining mitochondrial homeostasis. Studies have shown that mitochonic acid-5 (MA-5) has a protective effect against mitochondrial damage and plays a role in mitophagy. However, it is not clear whether MA-5 has a beneficial effect on inflammatory articular cartilage. Here, human OA cartilage was obtained from patients undergoing total joint replacement. Interleukin-1β (IL-1β) was used to stimulate chondrocytes and induce inflammatory injury. Cell Counting Kit-8, TUNEL, and flow cytometry assays were used to assess apoptosis. Gene expression was examined using quantitative reverse transcription-polymerase chain reaction. Mitochondrial function was evaluated using immunoblotting, mitochondrial membrane potential assay, JC-1 staining, and immunofluorescence analysis. Mitophagy was detected using immunoblotting and immunofluorescence. 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP), a specific inhibitor of Sirtuin 3 (SIRT3), was used to block the SIRT3/Parkin pathway. Mitophagy in the cartilage sections was evaluated via immunohistochemistry. IL-1β was found to induce chondrocyte apoptosis by inhibiting SIRT3 expression and mitophagy. In addition, inflammatory damage reduced the mitochondrial membrane potential and promoted the production of intracellular reactive oxygen species (ROS), leading to increased mitochondrial division, mitochondrial fusion inhibition, and the consequent mitochondrial damage. In contrast, the MA-5 treatment inhibited excessive ROS production by upregulating mitophagy, maintaining the mitochondrial membrane potential, and reducing mitochondrial apoptosis. After chemically blocking SIRT3 with 3-TYP, Parkin-related mitophagy was also inhibited, an effect that was prevented by pretreatment of the chondrocytes with MA-5, thereby suggesting that SIRT3 is upstream of Parkin. Overall, MA-5 was found to enhance the activity of SIRT3, promote Parkin-dependent mitophagy, eliminate depolarized/damaged mitochondria in chondrocytes, and protect cartilage cells. In conclusion, MA-5 inhibits IL-1β-induced oxidative stress and protects chondrocytes by upregulating the SIRT3/Parkin-related autophagy signaling pathway.

Mitochondrial Transplantation Attenuates Neural Damage and Improves Locomotor Function After Traumatic Spinal Cord Injury in Rats

Mitochondrial dysfunction is a hallmark of secondary neuroinflammatory responses and neuronal death in spinal cord injury (SCI). Even though mitochondria-based therapy is an attractive therapeutic option for SCI, the efficacy of transplantation of allogeneic mitochondria in the treatment of SCI remains unclear. Herein, we determined the therapeutic effects of mitochondrial transplantation in the traumatic SCI rats. Compressive SCI was induced by applying an aneurysm clip on the T10 spinal cord of rats. A 100-μg bolus of soleus-derived allogeneic mitochondria labeled with fluorescent tracker was transplanted into the injured spinal cords. The results showed that the transplanted mitochondria were detectable in the injured spinal cord up to 28 days after treatment. The rats which received mitochondrial transplantation exhibited better recovery of locomotor and sensory functions than those who did not. Both the expression of dynamin-related protein 1 and severity of demyelination in the injured cord were reduced in the mitochondrial transplanted groups. Mitochondrial transplantation also alleviated SCI-induced cellular apoptosis and inflammation responses. These findings suggest that transplantation of allogeneic mitochondria at the early stage of SCI reduces mitochondrial fragmentation, neuroapoptosis, neuroinflammation, and generation of oxidative stress, thus leading to improved functional recovery following traumatic SCI.

Targeting the multifaceted roles of mitochondria in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a severe, life-threatening subtype of stoke that constitutes a crucial health and socioeconomic problem worldwide. However, the current clinical treatment can only reduce the mortality of patients to a certain extent, but cannot ameliorate neurological dysfunction and has a high recurrence rate. Increasing evidence has demonstrated that mitochondrial dysfunction occurs in the early stages of brain injury and participates in all stages of secondary brain injury (SBI) after ICH. As the energy source of cells, various pathobiological processes that lead to SBI closely interact with the mitochondria, such as oxidative stress, calcium overload, and neuronal injury. In this review, we discussed the structure and function of mitochondria and the abnormal morphological changes after ICH. In addition, we discussed recent research on the involvement of mitochondrial dynamics in the pathological process of SBI after ICH and introduced the pathological variations and related molecular mechanisms of mitochondrial dysfunction in the occurrence of brain injury. Finally, we summarized the latest progress in mitochondrion-targeted agents for ICH, which provides a direction for the development of emerging therapeutic strategies targeting the mitochondria after ICH.

Tricyclodecan-9-yl-Xanthogenate (D609): Mechanism of Action and Pharmacological Applications

Tricyclodecan-9-yl xanthogenate (D609) is a synthetic tricyclic compound possessing a xanthate group. This xanthogenate compound is known for its diverse pharmacological properties. Over the last three decades, many studies have reported the biological activities of D609, including antioxidant, antiapoptotic, anticholinergic, anti-tumor, anti-inflammatory, anti-viral, anti-proliferative, and neuroprotective activities. Its mechanism of action is extensively attributed to its ability to cause the competitive inhibition of phosphatidylcholine (PC)-specific phospholipase C (PC-PLC) and sphingomyelin synthase (SMS). The inhibition of PCPLC or SMS affects secondary messengers with a lipidic nature, i.e., 1,2-diacylglycerol (DAG) and ceramide. Various in vitro/in vivo studies suggest that PCPLC and SMS inhibition regulate the cell cycle, block cellular proliferation, and induce differentiation. D609 acts as a pro-inflammatory cytokine antagonist and diminishes Aβ-stimulated toxicity. PCPLC enzymatic activity essentially requires Zn²⁺, and D609 might act as a potential chelator of Zn²⁺, thereby blocking PCPLC enzymatic activity. D609 also demonstrates promising results in reducing atherosclerotic plaque formation, post-stroke cerebral infarction, and cancer progression. The present compilation provides a comprehensive mechanistic insight into D609, including its chemistry, mechanism of action, and regulation of various pharmacological activities.

Overexpression of NMNAT3 improves mitochondrial function and enhances anti-oxidative stress of bone marrow mesenchymal stem cells via the NAD+-Sirt3 pathway

Oxidative stress damage is a common problem in bone marrow mesenchymal stem cell (BMSC) transplantation. Under stress conditions, the mitochondrial function of BMSCs is disrupted, which accelerates senescence and apoptosis of BMSCs, ultimately leading to poor efficacy. Therefore, improving mitochondrial function and enhancing the anti-oxidative stress capacity of BMSCs may be an effective way of improving the survival rate and curative effect of BMSCs. In this study, we have confirmed that overexpression of nicotinamide mononucleotide adenylyl transferase 3 (NMNAT3) improves mitochondrial function and resistance to stress-induced apoptosis in BMSCs. We further revealed the mechanism of NMNAT3-mediated resistance to stress-induced apoptosis in BMSCs. We increased the level of nicotinamide adenine dinucleotide (NAD+) by overexpressing NMNAT3 in BMSCs and found that it could significantly increase the activity of silent mating type information regulation 2 homolog 3 (Sirt3) and significantly decrease the acetylation levels of Sirt3-dependent deacetylation-related proteins isocitrate dehydrogenase 2 (Idh2) and Forkhead-box protein O3a (FOXO3a). These findings show that NMNAT3 may increase the activity of Sirt3 by increasing NAD+ levels. Our results confirm that the NMNAT3-NAD+-Sirt3 axis is a potential mechanism for improving mitochondrial function and enhancing anti-oxidative stress of BMSCs. In this study, we take advantage of the role of NMNAT3 in inhibiting stress-induced apoptosis of BMSCs and provide new methods and ideas for breaking through the bottleneck of transplantation efficacy of BMSCs in the clinic.

Mitochondrial sirtuins, metabolism, and aging

Maintaining metabolic homeostasis is essential for cellular and organismal health throughout life. Of the multiple signaling pathways that regulate metabolism, such as PI3K/AKT, mTOR, AMPK, and sirtuins, mammalian sirtuins also play unique roles in aging. By understanding how sirtuins regulate metabolic processes, we can start to understand how they slow down or accelerate biological aging. Here, we review the biology of SIRT3, SIRT4, and SIRT5, known as the mitochondrial sirtuins due to their localization in the mitochondrial matrix. First, we will focus on canonical pathways that regulate metabolism more broadly and how these are integrated with aging regulation. Then, we will summarize the current knowledge about functional differences between SIRT3, SIRT4, and SIRT5 in metabolic control and integration in signaling networks. Finally, we will discuss how mitochondrial sirtuins regulate processes associated with aging and oxidative stress, calorie restriction and disease.

7,8-Dihydroxyflavone improves neuropathological changes in the brain of Tg26 mice, a model for HIV-associated neurocognitive disorder

The combined antiretroviral therapy era has significantly increased the lifespan of people with HIV (PWH), turning a fatal disease to a chronic one. However, this lower but persistent level of HIV infection increases the susceptibility of HIV-associated neurocognitive disorder (HAND). Therefore, research is currently seeking improved treatment for this complication of HIV. In PWH, low levels of brain derived neurotrophic factor (BDNF) has been associated with worse neurocognitive impairment. Hence, BDNF administration has been gaining relevance as a possible adjunct therapy for HAND. However, systemic administration of BDNF is impractical because of poor pharmacological profile. Therefore, we investigated the neuroprotective effects of BDNF-mimicking 7,8 dihydroxyflavone (DHF), a bioactive high-affinity TrkB agonist, in the memory-involved hippocampus and brain cortex of Tg26 mice, a murine model for HAND. In these brain regions, we observed astrogliosis, increased expression of chemokine HIV-1 coreceptors CXCR4 and CCR5, neuroinflammation, and mitochondrial damage. Hippocampi and cortices of DHF treated mice exhibited a reversal of these pathological changes, suggesting the therapeutic potential of DHF in HAND. Moreover, our data indicates that DHF increases the phosphorylation of TrkB, providing new insights about the role of the TrkB-Akt-NFkB signaling pathway in mediating these pathological hallmarks. These findings guide future research as DHF shows promise as a TrkB agonist treatment for HAND patients in adjunction to the current antiviral therapies.

Melatonin reshapes the mitochondrial network and promotes intercellular mitochondrial transfer via tunneling nanotubes after ischemic-like injury in hippocampal HT22 cells

Mitochondrial dysfunction is considered one of the hallmarks of ischemia/reperfusion injury. Mitochondria are plastic organelles that undergo continuous biogenesis, fusion, and fission. They can be transferred between cells through tunneling nanotubes (TNTs), dynamic structures that allow the exchange of proteins, soluble molecules, and organelles. Maintaining mitochondrial dynamics is crucial to cell function and survival. The present study aimed to assess the effects of melatonin on mitochondrial dynamics, TNT formation, and mitochondria transfer in HT22 cells exposed to oxygen/glucose deprivation followed by reoxygenation (OGD/R). The results showed that melatonin treatment during the reoxygenation phase reduced mitochondrial reactive oxygen species (ROS) production, improved cell viability, and increased the expression of PGC1α and SIRT3. Melatonin also preserved the expression of the membrane translocase proteins TOM20 and TIM23, and of the matrix protein HSP60, which are involved in mitochondrial biogenesis. Moreover, it promoted mitochondrial fusion and enhanced the expression of MFN2 and OPA1. Remarkably, melatonin also fostered mitochondrial transfer between injured HT22 cells through TNT connections. These results provide new insights into the effect of melatonin on mitochondrial network reshaping and cell survival. Fostering TNTs formation represents a novel mechanism mediating the protective effect of melatonin in ischemia/reperfusion injury.

Inhibition of miR-134-5p protects against kainic acid-induced excitotoxicity through Sirt3-mediated preservation of mitochondrial function

Epilepsy is a neurological disorder which is characterized by brain hyper-excitability and manifests as seizure. Due to its complicated pathogenesis, treatment for epilepsy still remains a huge challenge for neurology in the whole world. MciroRNA-134 (miR-134) is one kind of miRNAs which was firstly found abundant in synapses. In this study, we tried to unveil the role of inhibiting MciroRNA-134-5p (miR-134-5p) in excitotoxicity induced by kainic acid (KA) in the hippocampal neurons (HT22) cells. The results showed that treatment of KA increased the expression of miR-134-5p significantly and caused marked neuron excitotoxicity, evidenced by risen cell death rate, higher LDH release and aggravated cell viability. After suppressing miR-134-5p expression via transfecting HT22 cells with miR-134-5p antisense (Anti-134), cell viability was promoted obviously, along with decreased LDH release and cell death rate. In addition, KA-induced lipid peroxidation, cytochrome c release and mitochondrial ROS generation were also attenuated by Anti-134. The level of Sirtuin 3 (Sirt3) and its downstream antioxidant enzymes, such as mitochondrial superoxide dismutase 2 (SOD2), isocitrate dehydrogenase 2 (IDH2) and glutathione peroxidase (GSH-Px), were significantly higher in Anti-134 group compared with the control and scramble group. After inhibiting Sirt3 expression with SiRNA targeting Sirt3 (Si-Sirt3) and 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP), the positive role of Anti-134 was apparently reversed. In conclusion, this research highly suggests that inhibition of miR-134-5p could protect neurons from KA-induced excitotoxicity through Sirt3-mediated preservation of mitochondrial function.

Melatonin protects against focal cerebral ischemia-reperfusion injury in diabetic mice by ameliorating mitochondrial impairments: involvement of the Akt-SIRT3-SOD2 signaling pathway

Diabetic patients are more vulnerable to cerebral ischemia-reperfusion (CIR) injury and have a worse prognosis and higher mortality after ischemic stroke than non-diabetic counterparts. Melatonin can exert neuroprotective effects against CIR injury in nondiabetic animal models. However, its effects on diabetic CIR injury and the underlying mechanisms remain unclarified. Herein, we found that melatonin administration improved neurological deficit, cerebral infarct volume, brain edema, and cell viability, reduced mitochondrial swelling, reactive oxygen species generation, and cytoplasmic cytochrome C release, and increased mitochondrial antioxidant enzymes activities, adenosine triphosphate production, and mitochondrial membrane potential in both streptozotocin-induced diabetic mice and high glucose-treated HT22 cells. Importantly, melatonin also activated protein kinase B (Akt) and sirtuin 3 (SIRT3)/superoxide dismutase 2 (SOD2) signaling and upregulated mitochondrial biogenesis-related transcription factors. However, these effects were largely attenuated by LY294002 (a specific Akt signaling blocker) administration. Additionally, 3-TYP (a selective SIRT3 inhibitor) and SIRT3 siRNA inhibited the above protective effects of melatonin as well as the upregulation of SIRT3 and the decrease of SOD2 acetylation but did not affect the p-Akt/Akt ratio. Overall, we demonstrate that melatonin can alleviate CIR injury in diabetic mice by activating Akt-SIRT3-SOD2 signaling and subsequently improving mitochondrial damage.

SIRT3 ameliorates osteoarthritis via regulating chondrocyte autophagy and apoptosis through the PI3K/Akt/mTOR pathway

Osteoarthritis (OA) is the most common form of joint disease. The aim of this study was to explore the functions of SIRT3 on OA pathophysiology and the mechanism involved. Rat chondrocytes and destabilized medial meniscus (DMM) rat OA model were used as in vitro and in vivo models. In addition, lentivirus and plasmid were used to overexpress SIRT3, while siRNA was applied to establish SIRT3 knockdown. IL-1β induced inflammation, apoptosis, mitochondrial dysfunction, and chondrocyte degeneration were inhibited by SIRT3 overexpression, which were enhanced in SIRT3-knockdown rat chondrocytes. Furthermore, overexpression of SIRT3 could restore IL-1β-induced autophagy inhibition. We also found that IL-1β-induced PI3K/Akt/mTOR signaling pathway activation was inhibited by SIRT3 overexpression, which was enhanced by SIRT3 knockdown. Last, intra-articular SIRT3 overexpression alleviated the severity of OA-induced rat joint damage. Our results demonstrated that SIRT3 is an important protective agent against OA pathophysiology via inhibiting PI3K/Akt/mTOR signaling.

Sirtuin-3 activation by honokiol restores mitochondrial dysfunction in the hippocampus of the hepatic encephalopathy rat model of ammonia neurotoxicity

The neurotoxic level of ammonia in the brain during liver cirrhosis causes a nervous system disorder, hepatic encephalopathy (HE), by affecting mitochondrial functions. Sirtuin-3 (SIRT3) is emerging as a master regulator of mitochondrial integrity, which is currently being focused as a pathogenic hotspot for HE. This article describes SIRT3 level versus mitochondrial dysfunction markers in the hippocampus of the control, the moderate-grade hepatic encephalopathy (MoHE), developed in thioacetamide-induced (100 mg/kg bw ip for 10 days) liver cirrhotic rats, and the MoHE rats treated with an SIRT3 activator, honokiol (HKL; 10 mg/kg bw ip), for 7 days from 8th day of the thioacetamide schedule. As compared with the control group rats, hippocampus mitochondria of MoHE rats showed a significant decline in SIRT3 expression and its activity with concordant enhancement of ROS and declined membrane permeability transition and organelle viability scores. This was consistent with the declined mitochondrial thiol level and thiol-regenerating enzyme, isocitrate dehydrogenase 2. Also, significantly declined activities of electron transport chain complexes I, III, IV, and Q₁₀ , decreased NAD⁺ /NADH and ATP/AMP ratios, and enhanced number of the shrunken mitochondria were recorded in the hippocampus of those MoHE rats. However, all these mitochondrial aberrations were observed to regain their normal profiles/levels, concordant to the enhanced SIRT3 expression and its activity due to treatment with HKL. The findings suggest a role of SIRT3 in mitochondrial structure-function derangements associated with MoHE pathogenesis and SIRT3 activation by HKL as a relevant strategy to protect mitochondrial integrity during ammonia neurotoxicity.

The AMPAR antagonist perampanel protects the neurovascular unit against traumatic injury via regulating Sirt3

Introduction

Perampanel is a highly selective and noncompetitive α‐amino‐3 ‐hydroxy‐5‐methyl‐4‐isoxazole propionate receptor (AMPAR) antagonist, which has been used as an orally administered antiepileptic drug in more than 55 countries. Recently, perampanel was shown to exert neuroprotective effects in hemorrhagic and ischemic stroke models via regulating blood–brain barrier (BBB) function.

Aim

Here, the protective effects of perampanel were investigated in an in vitro neurovascular unit (NVU) system established using a triple cell co‐culture model (neurons, astrocytes, and brain microvascular endothelial cells) and in an in vivo traumatic brain injury (TBI) model.

Results

Neurons in the NVU system exhibit a more mature morphological phenotype compared with neurons cultured alone, and the co‐culture system mimicked an impermeable barrier in vitro. Perampanel protects the NVU system against traumatic and excitotoxic injury, as evidenced by reduced lactate dehydrogenase (LDH) release and apoptotic rate. Treatment with perampanel attenuated lipid peroxidation and expression of inflammatory cytokines. In addition, perampanel increased Sirt3 protein expression, enhanced the activities of mitochondrial enzyme IDH2 and SOD2, and preserved BBB function in vitro. Knockdown of Sirt3 using specific siRNA (Si‐Sirt3) partially reserved the effects of perampanel on neuronal injury and BBB function. Treatment with perampanel in vivo attenuated brain edema, preserved neurological function, inhibited apoptosis and microglia activation after TBI. Furthermore, perampanel increased the expression of Sirt3 and preserved BBB function after TBI. The effect of perampanel on BBB function and brain edema was abolished by knockdown of Sirt3 in vivo.

Conclusion

Our results indicate that the noncompetitive AMPAR antagonist perampanel protects the NVU system and reduces brain damage after TBI via activating the Sirt3 cascades.

Tau Oligomers Neurotoxicity

Although the mechanisms of toxic activity of tau are not fully recognized, it is supposed that the tau toxicity is related rather not to insoluble tau aggregates but to its intermediate forms. It seems that neurofibrillar tangles (NFTs) themselves, despite being composed of toxic tau, are probably neither necessary nor sufficient for tau-induced neuronal dysfunction and toxicity. Tau oligomers (TauOs) formed during the early stages of tau aggregation are the pathological forms that play a key role in eliciting the loss of neurons and behavioral impairments in several neurodegenerative disorders called tauopathies. They can be found in tauopathic diseases, the most common of which is Alzheimer's disease (AD). Evidence of co-occurrence of b-amyloid, α-synuclein, and tau into their most toxic forms, i.e., oligomers, suggests that these species interact and influence each other's aggregation in several tauopathies. The mechanism responsible for oligomeric tau neurotoxicity is a subject of intensive investigation. In this review, we summarize the most recent literature on the damaging effect of TauOs on the stability of the genome and the function of the nucleus, energy production and mitochondrial function, cell signaling and synaptic plasticity, the microtubule assembly, neuronal cytoskeleton and axonal transport, and the effectiveness of the protein degradation system.

Role of Sirtuins in Modulating Neurodegeneration of the Enteric Nervous System and Central Nervous System

Neurodegeneration of the central and enteric nervous systems is a common feature of aging and aging-related diseases, and is accelerated in individuals with metabolic dysfunction including obesity and diabetes. The molecular mechanisms of neurodegeneration in both the CNS and ENS are overlapping. Sirtuins are an important family of histone deacetylases that are important for genome stability, cellular response to stress, and nutrient and hormone sensing. They are activated by calorie restriction (CR) and by the coenzyme, nicotinamide adenine dinucleotide (NAD+). Sirtuins, specifically the nuclear SIRT1 and mitochondrial SIRT3, have been shown to have predominantly neuroprotective roles in the CNS while the cytoplasmic sirtuin, SIRT2 is largely associated with neurodegeneration. A systematic study of sirtuins in the ENS and their effect on enteric neuronal growth and survival has not been conducted. Recent studies, however, also link sirtuins with important hormones such as leptin, ghrelin, melatonin, and serotonin which influence many important processes including satiety, mood, circadian rhythm, and gut homeostasis. In this review, we address emerging roles of sirtuins in modulating the metabolic challenges from aging, obesity, and diabetes that lead to neurodegeneration in the ENS and CNS. We also highlight a novel role for sirtuins along the microbiota-gut-brain axis in modulating neurodegeneration.

Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.

Oxidative Stress, Neuroinflammation and Mitochondria in the Pathophysiology of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron (MN) disease. Its primary cause remains elusive, although a combination of different causal factors cannot be ruled out. There is no cure, and prognosis is poor. Most patients with ALS die due to disease-related complications, such as respiratory failure, within three years of diagnosis. While the underlying mechanisms are unclear, different cell types (microglia, astrocytes, macrophages and T cell subsets) appear to play key roles in the pathophysiology of the disease. Neuroinflammation and oxidative stress pave the way leading to neurodegeneration and MN death. ALS-associated mitochondrial dysfunction occurs at different levels, and these organelles are involved in the mechanism of MN death. Molecular and cellular interactions are presented here as a sequential cascade of events. Based on our present knowledge, the discussion leads to the idea that feasible therapeutic strategies should focus in interfering with the pathophysiology of the disease at different steps.

Roles of Mitochondrial Sirtuins in Mitochondrial Function, Redox Homeostasis, Insulin Resistance and Type 2 Diabetes

Mitochondria are the metabolic hubs that process a number of reactions including tricarboxylic acid cycle, β-oxidation of fatty acids and part of the urea cycle and pyrimidine nucleotide biosynthesis. Mitochondrial dysfunction impairs redox homeostasis and metabolic adaptation, leading to aging and metabolic disorders like insulin resistance and type 2 diabetes. SIRT3, SIRT4 and SIRT5 belong to the sirtuin family proteins and are located at mitochondria and also known as mitochondrial sirtuins. They catalyze NAD⁺-dependent deacylation (deacetylation, demalonylation and desuccinylation) and ADP-ribosylation and modulate the function of mitochondrial targets to regulate the metabolic status in mammalian cells. Emerging evidence has revealed that mitochondrial sirtuins coordinate the regulation of gene expression and activities of a wide spectrum of enzymes to orchestrate oxidative metabolism and stress responses. Mitochondrial sirtuins act in synergistic or antagonistic manners to promote respiratory function, antioxidant defense, insulin response and adipogenesis to protect individuals from aging and aging-related metabolic abnormalities. In this review, we focus on the molecular mechanisms by which mitochondrial sirtuins regulate oxidative metabolism and antioxidant defense and discuss the roles of their deficiency in the impairment of mitochondrial function and pathogenesis of insulin resistance and type 2 diabetes.

Inhibition of the Peroxisome Proliferator-Activated Receptor gamma Coactivator 1-alpha (PGC-1α)/Sirtuin 3 (SIRT3) Pathway Aggravates Oxidative Stress After Experimental Subarachnoid Hemorrhage

Background

Emerging evidence shows that Sirtuin 3 (SIRT3) can exert an antioxidative effect in various neurodegenerative diseases, but whether and how SIRT3 modulates neuronal death after subarachnoid hemorrhage (SAH) remains to be elucidated.

Materia/Methods

Experimental SAH was induced in adult mice by prechiasmatic cistern injection and primary neurons by OxyHb incubation. The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and SIRT3 protein levels were examined at different time points after SAH induction. The PGC-1α protein gene knockdown in vivo and in vitro was achieved by transfection of lentivirus (LV) vectors expressing shPGC-1α or negative control (NC). Western blot, oxidative stress index, histopathology, neurological function, and cell viability analysis was performed.

Results

Results showed that the PGC-1α/SIRT3 pathway was remarkably activated in vivo and in vitro after SAH. LV-shPGC-1α treatment significantly inhibited the activation of this pathway after SAH, accompanied by deteriorated neurologic function, aggravated oxidative stress, increased neuronal apoptosis, and enhanced cytotoxicity compared with the mice or primary neurons treated with LV-NC only.

Conclusions

The present results highlight the detrimental PGC-1α/SIRT3 pathway, involving regulation of the endogenous antioxidant activity against neuronal damage, which may provide a potential therapeutic target in SAH.

α-Cyperone Attenuates H2O2-Induced Oxidative Stress and Apoptosis in SH-SY5Y Cells via Activation of Nrf2

α-Cyperone, extracted from Cyperus rotundus, has been reported to inhibit microglia-mediated neuroinflammation. Oxidative stress and apoptosis play crucial roles in the course of Parkinson’s disease (PD). PD is a common neurodegenerative disease characterized by selective death of dopaminergic neurons. This study was designed to investigate the neuroprotective effects of α-cyperone against hydrogen peroxide (H₂O₂)-induced oxidative stress and apoptosis in dopaminergic neuronal SH-SY5Y cells. Neurotoxicity was assessed by MTT assay and the measurement of lactic dehydrogenase (LDH) release. The level of reactive oxygen species (ROS) was measured by dichlorodihydrofluorescin diacetate (DCFH-DA) staining. The apoptosis of SH-SY5Y cells was evaluated by annexin-V-FITC staining. The translocation of NF-E2-related factor 2 (Nrf2) was determined by western blot and immunofluorescence staining. Western blot analysis was conducted to determine the expression level of cleaved-caspase-3, the pro-apoptotic factor Bax, and the anti-apoptotic factor, Bcl-2. The results showed that α-cyperone substantially decreased H₂O₂-induced death, release of LDH, and the production of ROS in SH-SY5Y cells. In addition, we found that α-cyperone attenuated H₂O₂-induced cellular apoptosis. Moreover, α-cyperone remarkably reduced the expression of cleaved-caspase-3 and Bax, and upregulated Bcl-2. Furthermore, α-cyperone enhanced the nuclear translocation of Nrf2. Pretreatment with brusatol (BT, an Nrf2 inhibitor) attenuated α-cyperone-mediated suppression of ROS, cleaved-caspase-3, and Bax, as well as α-cyperone-induced Bcl-2 upregulation in H₂O₂-treated SH-SY5Y cells. α-cyperone neuroprotection required Nrf2 activation. In conclusion, α-cyperone attenuated H₂O₂-induced oxidative stress and apoptosis in SH-SY5Y cells via the activation of Nrf2, suggesting the potential of this compound in the prevention and treatment of PD.

Hippocampal tau oligomerization early in tau pathology coincides with a transient alteration of mitochondrial homeostasis and DNA repair in a mouse model of tauopathy

Insoluble intracellular aggregation of tau proteins into filaments and neurodegeneration are histopathological hallmarks of Alzheimer disease (AD) and other tauopathies. Recently, prefibrillar, soluble, oligomeric tau intermediates have emerged as relevant pathological tau species; however, the molecular mechanisms of neuronal responses to tau oligomers are not fully understood. Here, we show that hippocampal neurons in six-month-old transgenic mouse model of tauopathy, THY-Tau22, are enriched with oligomeric tau, contain elongated mitochondria, and display cellular stress, but no overt cytotoxicity compared to the control mice. The levels of several key mitochondrial proteins were markedly different between the THY-Tau22 and control mice hippocampi including the mitochondrial SIRT3, PINK1, ANT1 and the fission protein DRP1. DNA base excision repair (BER) is the primary defense system against oxidative DNA damage and it was elevated in six-month-old transgenic mice. DNA polymerase β, the key BER DNA polymerase, was enriched in the cytoplasm of hippocampal neurons in six-month-old transgenic mice and localized with and within mitochondria. Polβ also co-localized with mitochondria in human AD brains in neurons containing oligomeric tau. Most of these altered mitochondrial and DNA repair events were specific to the transgenic mice at 6 months of age and were not different from control mice at 12 months of age when tau pathology reaches its maximum and oligomeric forms of tau are no longer detectable. In summary, our data suggests that we have identified key cellular stress responses at early stages of tau pathology to preserve neuronal integrity and to promote survival. To our knowledge, this work provides the first description of multiple stress responses involving mitochondrial homeostasis and BER early during the progression of tau pathology, and represents an important advance in the etiopathogenesis of tauopathies.

Alpha-synuclein-induced mitochondrial dysfunction is mediated via a sirtuin 3-dependent pathway

BACKGROUND

Misfolding and aggregation of the presynaptic protein alpha-synuclein (αsyn) is a hallmark of Parkinson's disease (PD) and related synucleinopathies. Although predominantly localized in the cytosol, a body of evidence has shown that αsyn localizes to mitochondria and contributes to the disruption of key mitochondrial processes. Mitochondrial dysfunction is central to the progression of PD and mutations in mitochondrial-associated proteins are found in familial cases of PD. The sirtuins are highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent enzymes that play a broad role in cellular metabolism and aging. Interestingly, mitochondrial sirtuin 3 (SIRT3) plays a major role in maintaining mitochondrial function and preventing oxidative stress, and is downregulated in aging and age-associated diseases such as neurodegenerative disorders. Herein, we hypothesize that αsyn is associated with decreased SIRT3 levels contributing to impaired mitochondrial dynamics and biogenesis in PD.

METHODS

The level of mitochondrial SIRT3 was assessed in cells expressing oligomeric αsyn within the cytosolic and mitochondrial-enriched fractions. Mitochondrial integrity, respiration, and health were examined using several markers of mitochondrial dynamics and stress response and by measuring the rate of oxygen consumption (OCR). Our findings were validated in a rodent model of PD as well as in human post-mortem Lewy body disease (LBD) brain tissue.

RESULTS

Here, we demonstrate that αsyn associates with mitochondria and induces a decrease in mitochondrial SIRT3 levels and mitochondrial biogenesis. We show that SIRT3 downregulation is accompanied by decreased phosphorylation of AMPK and cAMP-response element binding protein (CREB), as well as increased phosphorylation of dynamin-related protein 1 (DRP1), indicative of impaired mitochondrial dynamics. OCR was significantly decreased suggesting a mitochondria respiratory deficit. Interestingly treatment with AMPK agonist 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) restores SIRT3 expression, improves mitochondrial function, and decreases αsyn oligomer formation in a SIRT3-dependent manner.

CONCLUSIONS

Together, our findings suggest that pharmacologically increasing SIRT3 levels can counteract αsyn-induced mitochondrial dysfunction by reducing αsyn oligomers and normalizing mitochondrial bioenergetics. These data support a protective role for SIRT3 in PD-associated pathways and contribute significant mechanistic insight into the interplay of SIRT3 and αsyn.

SIRT3, PP2A and TTP protein stability in the presence of TNF-α on vincristine-induced apoptosis of leukaemia cells

The contribution of vincristine (VCR)-induced microtubule destabilization to evoke apoptosis in cancer cells remains to be resolved. Thus, we investigated the cytotoxic mechanism of VCR on U937 and HL-60 human leukaemia cell lines. We discovered that VCR treatment resulted in the up-regulation of TNF-α expression and activation of the death receptor pathway, which evoked apoptosis of U937 cells. Moreover, VCR induced microtubule destabilization and mitotic arrest. VCR treatment down-regulated SIRT3, and such down-regulation caused mitochondrial ROS to initiate phosphorylation of p38 MAPK. p38 MAPK suppressed MID1-modulated degradation of the protein phosphatase 2A (PP2A) catalytic subunit. The SIRT3-ROS-p38 MAPK-PP2A axis inhibited tristetraprolin (TTP)-controlled TNF-α mRNA degradation, consequently, up-regulating TNF-α expression. Restoration of SIRT3 and TTP expression, or inhibition of the ROS-p38 MAPK axis increased the survival of VCR-treated cells and repressed TNF-α up-regulation. In contrast to suppression of the ROS-p38 MAPK axis, overexpression of SIRT3 modestly inhibited the effect of VCR on microtubule destabilization and mitotic arrest in U937 cells. Apoptosis of HL-60 cells, similarly, went through the same pathway. Collectively, our data indicate that the SIRT3-ROS-p38 MAPK-PP2A-TTP axis modulates TNF-α expression, which triggers apoptosis of VCR-treated U937 and HL-60 cells. We also demonstrate that the apoptotic signalling is not affected by VCR-elicited microtubule destabilization.

Metformin Protects against Oxidative Stress Injury Induced by Ischemia/Reperfusion via Regulation of the lncRNA-H19/miR-148a-3p/Rock2 Axis

Previous studies have shown that metformin not only is a hypoglycemic agent but also has neuroprotective effects. However, the mechanism of action of metformin in ischemic stroke is unclear. Oxidative stress is an important factor in the pathogenesis of cerebral ischemia-reperfusion injury. It has been reported that metformin is associated with stroke risk in the clinical population. This study is aimed at investigating the effect and mechanism of metformin in an experimental model of oxidative stress induced by ischemia/reperfusion (I/R) in vivo and oxygen glucose deprivation/reperfusion (OGD/R) in vitro. Metformin (100, 200, and 300 mg/kg) was administered intraperitoneally immediately after induction of cerebral ischemia. The indicators of oxidative stress selected were antioxidant enzyme activities of catalase, malondialdehyde (MDA), nitric oxide (NO), superoxide dismutase (SOD), and glutathione peroxidation enzyme (GSHPx). First, we demonstrated that metformin can significantly alleviate acute and chronic cerebral I/R injury and it has a strong regulatory effect on stroke-induced oxidative stress. It can reduce the elevated activities of MDA and NO and increase the levels of GSHPx and SOD in the cerebrum of mice and N2a cells exposed to I/R. Furthermore, real-time PCR and western blot were used to detect the expression of long noncoding RNA H19 (lncRNA-H19), microRNA-148a-3p (miR-148a-3p), and Rho-associated protein kinase 2 (Rock2). The direct interaction of lncRNA-H19, miR-148a-3p, and Rock2 was tested using a dual luciferase reporter assay. lncRNA-H19 altered OGD/R-induced oxidative stress by modulating miR-148a-3p to increase Rock2 expression. The expression of lncRNA-H19 and Rock2 could be downregulated with metformin in vivo and in vitro. In conclusion, our study confirmed that metformin exerts neuroprotective effects by regulating ischemic stroke-induced oxidative stress injury via the lncRNA-H19/miR-148a-3p/Rock2 axis. These results provide new evidence that metformin may represent a potential treatment for stroke-related brain injury.

Drugs used in the treatment of bipolar disorder and their effects on cholesterol biosynthesis - A possible therapeutic mechanism

Objectives: To understand the therapeutic mechanisms of bipolar disorder (BD) drugs at molecular and cellular levels.Methods: Next generation sequencing was used to determine the transcriptional effects of a combination of four commonly prescribed BD drugs (lithium, valproate, lamotrigine and quetiapine) or vehicle (0.2% DMSO) in NT2-N (human neuronal) cells and rats. Differential expression of genes and pathway analysis were performed using edgeR in R and Gene Set Enrichment Analysis software respectively. Free cholesterol levels and neurite outgrowth were quantified in NT2-N cells following combination and individual BD drug treatments.Results: Pathway analysis showed up-regulation of many elements of the cholesterol biosynthesis pathway in NT2-N cells and oxidative phosphorylation in rat brains. Intracellular cholesterol transport genes were upregulated (NPC1, NPC2 and APOE), while the cholesterol efflux gene (ABCA1) was downregulated. BD drug combination tended to increase intracellular cholesterol levels and neurite outgrowth, but these effects were not seen for the drugs when used individually.Conclusions: These data suggest that BD drug combination is increasing cholesterol biosynthesis and the newly synthesised cholesterol is being utilised within the cells, possibly for synthesis of new membranes to facilitate neurite outgrowth. This mechanism possibly underpins clinical efficacy in individuals with BD treated with polypharmacy.