The mitochondrial energy transduction system and the aging process

Multivariate meta-analyses of mitochondrial complex I and IV in major depressive disorder, bipolar disorder, schizophrenia, Alzheimer disease, and Parkinson disease

Complex I (NADH dehydrogenase, NDU) and complex IV (cytochrome-c-oxidase, COX) of the mitochondrial electron transport chain have been implicated in the pathophysiology of major psychiatric disorders, such as major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ), as well as in neurodegenerative disorders, such as Alzheimer disease (AD) and Parkinson disease (PD). We conducted meta-analyses comparing complex I and IV in each disorder MDD, BD, SZ, AD, and PD, as well as in normal aging. The electronic databases Pubmed, EMBASE, CENTRAL, and Google Scholar, were searched for studies published between 1980 and 2018. Of 2049 screened studies, 125 articles were eligible for the meta-analyses. Complex I and IV were assessed in peripheral blood, muscle biopsy, or postmortem brain at the level of enzyme activity or subunits. Separate meta-analyses of mood disorder studies, MDD and BD, revealed moderate effect sizes for similar abnormality patterns in the expression of complex I with SZ in frontal cortex, cerebellum and striatum, whereas evidence for complex IV alterations was low. By contrast, the neurodegenerative disorders, AD and PD, showed strong effect sizes for shared deficits in complex I and IV, such as in peripheral blood, frontal cortex, cerebellum, and substantia nigra. Beyond the diseased state, there was an age-related robust decline in both complexes I and IV. In summary, the strongest support for a role for complex I and/or IV deficits, is in the pathophysiology of PD and AD, and evidence is less robust for MDD, BD, or SZ.

Mitochondrial mRNA translation initiation contributes to oxidative metabolism in the myocardia of aged, obese mice

Being both advanced in age and obese each contribute to cardiac hypertrophy in a unique manner. Electron transport complexes I and IV are implicated in deficient electron transport during cardiomyopathies and contain the majority of protein subunits that are transcribed and translated by machinery localized within the mitochondria.

PURPOSE

To assess myocardial mt-mRNA translation factors in relation to mitochondrial content and mtDNA-encoded protein using a mouse model of aged obesity and to test the relationship of mt-mRNA translation initiation factor 2 (mtIF2) to oxidative capacity and the cellular oxidation-reduction (redox) state in cardiomyocytes.

METHODS

Male C56BL/6 J mice fed lean or high fat diet were aged to either ~3 months or ~22 months, the heart was excised and analyzed using immunoblot and qPCR to assess differences in mitochondrial mRNA translation machinery. Using H9c2 cardiomyocytes, mtIF2 was knocked-down and oxidative metabolic characteristics assessed including oxidation/reduction state, bioenergetic flux, and hypoxic resistance was tested.

RESULTS

Aged, obese mouse hearts were ~40% larger than young, lean controls and contained ~50% less mtIF2 protein alongside ~25-50% lower content of Cytb, a protein encoded by mtDNA. Reducing the level of mtIF2 by shRNA is associated with ~15-20% lower content of OXPHOS complex I and IV, ~30% lower optical redox ratio, ~40% oxygen reserve capacity, and ~20% less cell survival following hypoxia.

CONCLUSION

We present evidence of altered mt-mRNA translation during cardiac hypertrophy in aged obesity. We build on these results by demonstrating the necessity of mtIF2 in maintaining oxidative characteristics of cardiac muscle cells.

Effects of apoptosis on liver aging

As an irreversible and perennial process, aging is accompanied by functional and morphological declines in organs. Generally, aging liver exhibits a decline in volume and hepatic blood flow. Even with a preeminent regenerative capacity to restore its functions after liver cell loss, its biosynthesis and metabolism abilities decline, and these are difficult to restore to previous standards. Apoptosis is a programmed death process via intrinsic and extrinsic pathways, in which Bcl-2 family proteins and apoptosis-related genes, such as p21 and p53, are involved. Apoptosis inflicts both favorable and adverse influences on liver aging. Apoptosis eliminates transformed abnormal cells but promotes age-related liver diseases, such as nonalcoholic fatty liver disease, liver fibrosis, cirrhosis, and liver cancer. We summarize the roles of apoptosis in liver aging and age-related liver diseases.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Metabolomics-based identification of metabolic alterations in PARK2

Objective

Parkin is the causative gene for autosomal recessive familial Parkinson's disease (PD), although it remains unclear how parkin dysfunction is involved with the general condition. Recently, serum and/or plasma metabolomics revealed alterations in metabolic pathways that might reflect pathomechanisms of idiopathic PD (iPD). Thus, we hypothesized that serum metabolomics of patients with homozygous or compound heterozygous parkin mutations (namely, PARK2) might reflect metabolic alterations due to parkin dysfunction.

Methods

We enrolled 15 PARK2 patients (52 ± 17.6 years) confirmed with homozygous (seven cases) and compound heterozygous (eight cases) parkin mutations, along with 19 healthy age‐matched controls (51 ± 11.5 years). We analyzed 830 metabolites from participants’ serum using well‐established metabolomics technologies, including ultra‐high performance liquid chromatography/tandem mass spectroscopy.

Results

Based on metabolic profiles, hierarchical matrix analysis can divide samples between control and PARK2 subjects. Profiles from PARK2 patients showed significantly higher levels of fatty acid (FA) metabolites and oxidized lipids, and significantly lower levels of antioxidant, caffeine, and benzoate‐related metabolites.

Interpretation

Metabolomics can identify specific metabolic alterations in PARK2 patients compared with controls. Alterations in FA metabolites suggest a relationship between parkin function and lipid metabolism. The elevation of oxidized lipids in combination with decreasing antioxidants may reflect general hyperoxidative stress. Decreasing benzoate‐related metabolites might be due to the alteration in gut microbiota. Consequently, caffeine and its metabolites may be decreased due to malabsorption. These findings are similar to metabolic alterations in iPD. Thus, serum/plasma metabolomics may reflect the association between parkin dysfunction and parkinsonism.

Quantitative profiling brain proteomes revealed mitochondrial dysfunction in Alzheimer's disease

Mitochondrial dysfunction is a key feature in both aging and neurodegenerative diseases including Alzheimer’s disease (AD), but the molecular signature that distinguishes pathological changes in the AD from healthy aging in the brain mitochondria remain poorly understood. In order to unveil AD specific mitochondrial dysfunctions, this study adopted a discovery-driven approach with isobaric tag for relative and absolute quantitation (iTRAQ) and label-free quantitative proteomics, and profiled the mitochondrial proteomes in human brain tissues of healthy and AD individuals. LC-MS/MS-based iTRAQ quantitative proteomics approach revealed differentially altered mitochondriomes that distinguished the AD’s pathophysiology-induced from aging-associated changes. Our results showed that dysregulated mitochondrial complexes including electron transport chain (ETC) and ATP-synthase are the potential driver for pathology of the AD. The iTRAQ results were cross-validated with independent label-free quantitative proteomics experiments to confirm that the subunit of electron transport chain complex I, particularly NDUFA4 and NDUFA9 were altered in AD patients, suggesting destabilization of the junction between membrane and matrix arms of mitochondrial complex I impacted the mitochondrial functions in the AD. iTRAQ quantitative proteomics of brain mitochondriomes revealed disparity in healthy aging and age-dependent AD.

Endoplasmic Reticulum Stress Contributes to Mitochondrial Exhaustion of CD8+ T Cells

Tumor antigen-specific T cells rapidly lose energy and effector function in tumors. The cellular mechanisms by which energy loss and inhibition of effector function occur in tumor-infiltrating lymphocytes (TILs) are ill-defined, and methods to identify tumor antigen-specific TILs that experience such stress are unknown. Processes upstream of the mitochondria guide cell-intrinsic energy depletion. We hypothesized that a mechanism of T-cell-intrinsic energy consumption was the process of oxidative protein folding and disulfide bond formation that takes place in the endoplasmic reticulum (ER) guided by protein kinase R-like endoplasmic reticulum kinase (PERK) and downstream PERK axis target ER oxidoreductase 1 (ERO1α). To test this hypothesis, we created TCR transgenic mice with a T-cell-specific PERK gene deletion (OT1 ⁺ Lckcre⁺ PERK ^f/f , PERK KO). We found that PERK KO and T cells that were pharmacologically inhibited by PERK or ERO1α maintained reserve energy and exhibited a protein profile consistent with reduced oxidative stress. These T-cell groups displayed superior tumor control compared with T effectors. We identified a biomarker of ER-induced mitochondrial exhaustion in T cells as mitochondrial reactive oxygen species (mtROS), and found that PD-1⁺ tumor antigen-specific CD8⁺ TILs express mtROS. In vivo treatment with a PERK inhibitor abrogated mtROS in PD-1⁺ CD8⁺ TILs and bolstered CD8⁺ TIL viability. Combination therapy enabled 100% survival and 71% tumor clearance in a sarcoma mouse model. Our data identify the ER as a regulator of T-cell energetics and indicate that ER elements are effective targets to improve cancer immunotherapy.

The Action of Polyphenols in Diabetes Mellitus and Alzheimer's Disease: A Common Agent for Overlapping Pathologies

Diabetes Mellitus (DM) and Alzheimer's disease (AD) are two prevalent diseases in modern societies, which are caused mainly by current lifestyle, aging and genetic alterations. It has already been demonstrated that these two diseases are associated, since individuals suffering from DM are prone to develop AD. Conversely, it is also known that individuals with AD are more susceptible to DM, namely type 2 diabetes (T2DM). Therefore, these two pathologies, although completely different in terms of symptomatology, end up sharing several mechanisms at the molecular level, with the most obvious being the increase of oxidative stress and inflammation. Polyphenols are natural compounds widely spread in fruits and vegetables whose dietary intake has been considered inversely proportional to the incidence of DM and AD. So, it is believed that this group of phytochemicals may have preventive and therapeutic potential, not only by reducing the risk and delaying the development of these pathologies, but also by improving brain's metabolic profile and cognitive function. The aim of this review is to understand the extent to which DM and AD are related pathologies, the degree of similarity and the relationship between them, to detail the molecular mechanisms by which polyphenols may exert a protective effect, such as antioxidant and anti-inflammatory effects, and highlight possible advantages of their use as common preventive and therapeutic alternatives.

Effects of aging on mitochondrial hydrogen peroxide emission and calcium retention capacity in rat heart

Aging is a risk factor for heart disease and heart failure, which result from a progressive impairment of cardiac functions, including stroke volume, cardiac output, blood flow, and oxygen consumption. Age-related cardiac dysfunction is associated with impaired cardiac structures, such as the loss of myocytes, structural remodeling, altered calcium (Ca²⁺) handling, and contractile dysfunction. However, the mechanism by which aging affects mitochondrial function in the heart is poorly understood. The purpose of this study was to determine the effects of aging on mitochondrial function in the rat heart. Male Fischer 344 rats were randomly assigned to very young sedentary (VYS, 1 month), young sedentary (YS, 4 months), middle-aged sedentary (MS, 10 months), and old sedentary (OS, 20 months) groups. mitochondrial complex protein levels and mitochondrial function (e.g., mitochondrial hydrogen peroxide (H₂O₂) emission and Ca²⁺ retention capacity) were analyzed in the left ventricle. Aging was associated with decreased levels of OXPHOS (oxidative phosphorylation) protein expression of complex I to IV in the function of the electron transport chain. Aging increased the mitochondrial H₂O₂ emitting potential in the heart. In contrast, mitochondrial Ca²⁺ retention capacity gradually decreased with age. These data demonstrate that aging impairs mitochondrial function in cardiac muscle, suggesting that mitochondrial dysfunction with aging may be a primary factor for aging-induced cardiac dysfunction in the heart.

Early swelling response to phytohemagglutinin is lower in older toads

The effects of age on performance of life-history traits are diverse, but a common outcome is senescence, an irreversible deterioration of physical and physiological capabilities of older individuals. Immune response is potentially bound to senescence. However, little is known about immune response ageing in amphibians. In this work, we test the hypothesis that amphibian early immune response is reduced in older individuals. To this end, we captured adult natterjack toads (Epidalea calamita) and inoculated them with phytohemagglutinin, an innocuous protein that triggers a skin-swelling immune response whose magnitude is directly proportional to the ability of the individual to mount an immune response. We measured early swelling immune response (corresponding to an innate-response stage) hourly, for six hours, and we calculated the area under the curve (AUC) for each individual's time series, as a measure of immune response magnitude incorporating time. We estimated toad age by means of phalanx skeletochronology. Swelling and AUC decreased with age. Therefore, in accordance with our predictions, early immune response seems subject to senescence in these toads. Reduced ability to get over infections due to senescence of immune respose might be-together with a worse functioning of other organs and systems-among the causes of lower survival of older specimens.

Flavin homeostasis in the mouse retina during aging and degeneration

Involvement of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) in cellular homeostasis has been well established for tissues other than the retina. Here, we present an optimized method to effectively extract and quantify FAD and FMN from a single neural retina and its corresponding retinal pigment epithelium (RPE). Optimizations led to detection efficiency of 0.1 pmol for FAD and FMN while 0.01 pmol for riboflavin. Interestingly, levels of FAD and FMN in the RPE were found to be 1.7- and 12.5-fold higher than their levels in the retina, respectively. Both FAD and FMN levels in the RPE and retina gradually decline with age and preceded the age-dependent drop in the functional competence of the retina as measured by electroretinography. Further, quantifications of retinal levels of FAD and FMN in different mouse models of retinal degeneration revealed differential metabolic requirements of these two factors in relation to the rate and degree of photoreceptor degeneration. We also found twofold reductions in retinal levels of FAD and FMN in two mouse models of diabetic retinopathy. Altogether, our results suggest that retinal levels of FAD and FMN can be used as potential markers to determine state of health of the retina in general and more specifically the photoreceptors.

In vivo X-Nuclear MRS Imaging Methods for Quantitative Assessment of Neuroenergetic Biomarkers in Studying Brain Function and Aging

Brain relies on glucose and oxygen metabolisms to generate biochemical energy in the form of adenosine triphosphate (ATP) for supporting electrophysiological activities and neural signaling under resting or working state. Aging is associated with declined mitochondrial functionality and decreased cerebral energy metabolism, and thus, is a major risk factor in developing neurodegenerative diseases including Alzheimer’s disease (AD). However, there is an unmet need in the development of novel neuroimaging tools and sensitive biomarkers for detecting abnormal energy metabolism and impaired mitochondrial function, especially in an early stage of the neurodegenerative diseases. Recent advancements in developing multimodal high-field in vivo X-nuclear (e.g., ²H, ¹⁷O and ³¹P) MRS imaging techniques have shown promise for quantitative and noninvasive measurement of fundamental cerebral metabolic rates of glucose and oxygen consumption, ATP production as well as nicotinamide adenine dinucleotide (NAD) redox state in preclinical animal and human brains. These metabolic neuroimaging measurements could provide new insights and quantitative bioenergetic markers associated with aging processing and neurodegeneration and can therefore be employed to monitor disease progression and/or determine effectiveness of therapeutic intervention.

Redox dyshomeostasis in the experimental chronic hepatic overloads with iron or copper

Male rats of 80-90 g were overloaded with either Fe(II) or Cu(II) for 42 days by high concentrations of FeCl₂ or CuSO₄ in the drinking water. The animals were fed with a commercial rodent diet of 2780 kcal/100 g. Both metal treatments led to a liver redox imbalance and dyshomeostasis with oxidative stress and damage and the concomitant enhancement of oxidative processes as indicated by in vivo surface liver chemiluminescence, the sensitive and organ non-invasive assay for oxidative free radical reactions, and by ex vivo determined processes of phospholipid peroxidation and protein oxidation. In parallel, marked decreases in the antioxidant defense were observed. Liver reduced glutathione (GSH) content and the reduced/oxidized glutathione ratio (GSH/GSSG) were early indicators of oxidative metabolic disturbance upon the metal overloads. Thus, GSH plays a central role in the defense reactions involved in the chronic toxicity of Fe and Cu. Chronic overloads of Fe or Cu in rats afford an experimental animal model of hemochromatosis and of Wilson's disease, respectively. These two animal models could be useful in the study and development of the beneficial effects of pharmacological interventions in the two human diseases.

Ischemia-Reperfusion Injury in Aged Livers-The Energy Metabolism, Inflammatory Response, and Autophagy

Because of the lack of adequate organs, the number of patients with end-stage liver diseases, acute liver failure or hepatic malignancies waiting for liver transplantation is constantly increasing. Accepting aged liver grafts is one of the strategies expanding the donor pool to ease the discrepancy between the growing demand and the limited supply of donor organs. However, recipients of organs from old donors may show an increased posttransplantation morbidity and mortality due to enhanced ischemia-reperfusion injury. Energy metabolism, inflammatory response, and autophagy are 3 critical processes which are involved in the aging progress as well as in hepatic ischemia-reperfusion injury. Compared with young liver grafts, impairment of energy metabolism in aged liver grafts leads to lower adenosine triphosphate production and an enhanced generation of free radicals, both aggravating the inflammatory response. The aggravated inflammatory response determines the extent of hepatic ischemia-reperfusion injury and augments the liver damage. Autophagy protects cells by removal of damaged organelles, including dysfunctional mitochondria, a process impaired in aging and involved in ischemia-reperfusion-related apoptotic cell death. Furthermore, autophagic degradation of cellular compounds relieves intracellular adenosine triphosphate level for the energy depressed cells. Strategies targeting the mechanisms involved in energy metabolism, inflammatory response, and autophagy might be especially useful to prevent the increased risk for ischemia-reperfusion injury in aged livers after major hepatic surgery.

Contribution of the inflammasome to inflammaging

Background

Inflammation is a natural part of the aging process. This process is referred to as inflammaging. Inflammaging has been associated with deleterious outcomes in the aging brain in diseases such as Alzheimer’s disease and Parkinson’s disease. The inflammasome is a multi-protein complex of the innate immune response involved in the activation of caspase-1 and the processing of the inflammatory cytokines interleukin (IL)-1β and IL-18. We have previously shown that the inflammasome plays a role in the aging process in the brain. In this study, we analyzed the brain of young (3 months old) and aged (18 months old) mice for the expression of inflammasome proteins.

Results

Our findings indicate that the inflammasome proteins NLRC4, caspase-1, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and IL-18 are elevated in the cytosol of cortical lysates in aged mice when compared to young. In addition, in the cytosolic fraction of hippocampal lysates in aged mice, we found an increase in NLRC4, caspase-1, caspase-11, ASC and IL-1β. Moreover, we found higher levels of ASC in the mitochondrial fraction of aged mice when compared to young, consistent with higher levels of the substrate of pyroptosis gasdermin-D (GSDM-D) and increased pyroptosome formation (ASC oligomerization). Importantly, in this study we obtained fibroblasts from a subject that donated his cells at three different ages (49, 52 and 64 years old (y/o)) and found that the protein levels of caspase-1 and ASC were higher at 64 than at 52 y/o. In addition, the 52 y/o cells were more susceptible to oxidative stress as determined by lactose dehydrogenase (LDH) release levels. However, this response was ameliorated by inhibition of the inflammasome with Ac-Tyr-Val-Ala-Asp-Chloromethylketone (Ac-YVAD-CMK). In addition, we found that the protein levels of ASC and IL-18 are elevated in the serum of subjects over the age of 45 y/o when compared to younger subjects, and that ASC was higher in Caucasians than Blacks and Hispanics, whereas IL-18 was higher in Caucasians than in blacks, regardless of age.

Conclusions

Taken together, our data indicate that the inflammasome contributes to inflammaging and that the inflammasome-mediated cell death mechanism of pyroptosis contributes to cell demise in the aging brain.

The effects of AICAR and rapamycin on mitochondrial function in immortalized mitochondrial DNA mutator murine embryonic fibroblasts

Mitochondrial DNA mutations accumulate with age and may play a role in stem cell aging as suggested by the premature aging phenotype of mitochondrial DNA polymerase gamma (POLG) exonuclease-deficient mice. Therefore, E1A immortalized murine embryonic fibroblasts (MEFs) from POLG exonuclease-deficient and wild-type (WT) mice were constructed. Surprisingly, when some E1A immortalized MEF lines were cultured in pyruvate-containing media they slowly became addicted to the pyruvate. The POLG exonuclease-deficient MEFs were more sensitive to several mitochondrial inhibitors and showed increased reactive oxygen species (ROS) production under standard conditions. When cultured in pyruvate-containing media, POLG exonuclease-deficient MEFs showed decreased oxygen consumption compared to controls. Increased AMP-activated protein kinase (AMPK) signaling and decreased mammalian target of rapamycin (mTOR) signaling delayed aging and influenced mitochondrial function. Therefore, the effects of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, or rapamycin, an mTOR inhibitor, on measures of mitochondrial function were determined. Rapamycin treatment transiently increased respiration only in WT MEFs and, under most conditions, increased ATP levels. Short term AICAR treatment transiently increased ROS production and, under most conditions, decreased ATP levels. Chronic AICAR treatment decreased respiration and ROS production in WT MEFs. These results demonstrate the context-dependent effects of AICAR and rapamycin on mitochondrial function.

Summary: A novel mitochondrial DNA mutator murine embryonic fibroblast cell line was created and the effects of the anti-aging compounds rapamycin and AICAR on energy metabolism in these cells was determined.

Life History Trade-offs within the Context of Mitochondrial Hormesis

Evolutionary biologists have been interested in the negative interactions among life history traits for nearly a century, but the mechanisms that would create this negative interaction remain poorly understood. One variable that has emerged as a likely link between reproductive effort and longevity is oxidative stress. Specifically, it has been proposed that reproduction generates free radicals that cause oxidative stress and, in turn, oxidative stress damages cellular components and accelerates senescence. We propose that there is limited support for the hypothesis because reactive oxygen species (ROS), the free radicals implicated in oxidative damage, are not consistently harmful. With this review, we define the hormetic response of mitochondria to ROS, termed mitochondrial hormesis, and describe how to test for a mitohormetic response. We interpret existing data using our model and propose that experimental manipulations will further improve our knowledge of this response. Finally, we postulate how the mitohormetic response curve applies to variation in animal performance and longevity.

Glia Maturation Factor Dependent Inhibition of Mitochondrial PGC-1α Triggers Oxidative Stress-Mediated Apoptosis in N27 Rat Dopaminergic Neuronal Cells

Parkinson's disease (PD) is a progressive neurodegenerative disease affecting over five million individuals worldwide. The exact molecular events underlying PD pathogenesis are still not clearly known. Glia maturation factor (GMF), a neuroinflammatory protein in the brain plays an important role in the pathogenesis of PD. Mitochondrial dysfunctions and oxidative stress trigger apoptosis leading to dopaminergic neuronal degeneration in PD. Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α or PPARGC-α) acts as a transcriptional co-regulator of mitochondrial biogenesis and energy metabolism by controlling oxidative phosphorylation, antioxidant activity, and autophagy. In this study, we found that incubation of immortalized rat dopaminergic (N27) neurons with GMF influences the expression of peroxisome PGC-1α and increases oxidative stress, mitochondrial dysfunction, and apoptotic cell death. We show that incubation with GMF reduces the expression of PGC-1α with concomitant decreases in the mitochondrial complexes. Besides, there is increased oxidative stress and depolarization of mitochondrial membrane potential (MMP) in these cells. Further, GMF reduces tyrosine hydroxylase (TH) expression and shifts Bax/Bcl-2 expression resulting in release of cytochrome-c and increased activations of effector caspase expressions. Transmission electron microscopy analyses revealed alteration in the mitochondrial architecture. Our results show that GMF acts as an important upstream regulator of PGC-1α in promoting dopaminergic neuronal death through its effect on oxidative stress-mediated apoptosis. Our current data suggest that GMF is a critical risk factor for PD and suggest that it could be explored as a potential therapeutic target to inhibit PD progression.

Phenylpropanoids and Alzheimer's disease: A potential therapeutic platform

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by progressive dementia, neuroinflammation and the accumulation of intracellular neurofibrillary tangles and extracellular plaques. The etiology of AD is unclear, but is generally attributed to four leading hypotheses: (i) abnormal folding and aggregation of amyloid-β (Aβ)/tau proteins (ii) activation of the innate immune system, (iii) mitochondrial dysfunction, and (iv) oxidative stress. To date, therapeutic strategies have largely focused on Aβ-centric targets; however, the repeated failure of clinical trials and the continued lack of a disease-modifying therapy demand novel, multifaceted approaches. Natural products are common molecular platforms in drug development; in AD, compounds from the plant phenylpropanoid metabolic pathway have yielded promising associations. Herein, we review developments in the pathogenesis of AD and the metabolism of phenylpropanoids in plants. We further discuss the role of these metabolites as relevant to the four leading mechanisms of AD pathogenesis, and observe multiple protective effects among phenylpropanoids against AD onset and progression.

Superoxide Anion Production and Bioenergetic Profile in Young and Elderly Human Primary Myoblasts

Sarcopenia is the age-related loss of skeletal muscle mass, strength, and function. It is associated with regenerative difficulties by satellite cells, adult muscle stem cells, and alteration of oxidative management, mainly the increase in superoxide anions (O₂^•-). We aimed to investigate the relation between regenerative deficit in elderly and increase in O₂^•- production along with mitochondrial alterations. Myoblasts and myotubes from skeletal muscle of young and elderly healthy subjects (27.8 ± 6 and 72.4 ± 6.5 years old) were measured: (1) superoxide dismutase activity and protein content, (2) mitochondrial O₂^•- production levels, (3) O₂^•- production variability, and (4) mitochondrial bioenergetic profile. Compared to young myoblasts, elderly myoblasts displayed decreased SOD2 protein expression, elevated mitochondrial O₂^•- baseline levels, and decreased oxidative phosphorylation and glycolysis. Additionally, elderly versus young myotubes showed elevated mitochondrial O₂^•- levels when stressed with N-acetyl cysteine or high glucose and higher glycolysis despite showing comparable oxidative phosphorylation levels. Altogether, the elderly may have less metabolic plasticity due to the impaired mitochondrial function caused by O₂^•-. However, the increased energy demand related to the differentiation process appears to activate compensatory mechanisms for the partial mitochondrial dysfunction.

Senescence Induces Dysfunctions in Endothelial Progenitor Cells and Osteoblasts by Interfering Translational Machinery and Bioenergetic Homeostasis

Age-related bone diseases are partly caused by impaired bone integrity, which are closely related to osteoblasts’ activity and angiogenesis. Endothelial progenitor cells (EPCs) are the initiators of angiogenesis and found to have senescent-induced dysfunctions. The aim of this study is to investigate the effects of senescence in EPCs on osteogenesis and angiogenesis. Human primary EPCs and a murine osteoblast cell line (MC3T3-E1) are utilized in this study. The senescence of EPCs are induced by serial passages. When co-cultured with senescent EPCs, the osteoblasts demonstrate weakened alkaline phosphatase (ALP) activity and mineral deposition. On the other hand, osteoblast-induced migration decreases in senescent EPCs. As for the intracellular alterations of senescent EPCs, the activation of Akt/mTOR/p70S6K pathway, MnSOD and catalase are diminished. In contrast, the level of reactive oxygen species are significantly higher in senescent EPCs. Furthermore, senescent EPCs has decreased level intracellular ATP level and coupling efficiency for oxidative phosphorylation while the non-mitochondrial respiration and glycolysis are elevated. The senescence of EPCs impairs the functions of both osteoblasts and EPCs, suggesting EPCs’ role in the pathophysiology of age-related bone diseases. Targeting the alterations found in this study could be potential treatments.

Redox Signaling in Neurotransmission and Cognition During Aging

SIGNIFICANCE

Oxidative stress increases in the brain with aging and neurodegenerative diseases. Previous work emphasized irreversible oxidative damage in relation to cognitive impairment. This research has evolved to consider a continuum of alterations, from redox signaling to oxidative damage, which provides a basis for understanding the onset and progression of cognitive impairment. This review provides an update on research linking redox signaling to altered function of neural circuits involved in information processing and memory. Recent Advances: Starting in middle age, redox signaling triggers changes in nervous system physiology described as senescent physiology. Hippocampal senescent physiology involves decreased cell excitability, altered synaptic plasticity, and decreased synaptic transmission. Recent studies indicate N-methyl-d-aspartate and ryanodine receptors and Ca²⁺ signaling molecules as molecular substrates of redox-mediated senescent physiology.

CRITICAL ISSUES

We review redox homeostasis mechanisms and consider the chemical character of reactive oxygen and nitrogen species and their role in regulating different transmitter systems. In this regard, senescent physiology may represent the co-opting of pathways normally responsible for feedback regulation of synaptic transmission. Furthermore, differences across transmitter systems may underlie differential vulnerability of brain regions and neuronal circuits to aging and disease.

FUTURE DIRECTIONS

It will be important to identify the intrinsic mechanisms for the shift in oxidative/reductive processes. Intrinsic mechanism will depend on the transmitter system, oxidative stressors, and expression/activity of antioxidant enzymes. In addition, it will be important to identify how intrinsic processes interact with other aging factors, including changes in inflammatory or hormonal signals. Antioxid. Redox Signal. 28, 1724-1745.

The Extracts and Major Compounds Derived from Astragali Radix Alter Mitochondrial Bioenergetics in Cultured Cardiomyocytes: Comparison of Various Polar Solvents and Compounds

Astragali Radix (AR) is a widely used "Qi-invigorating" herb in China for its tonic effects in strengthening biological tissues. The extract of AR contains abundant antioxidants, including astragalosides and isoflavonoids. However, very few reports have systematically measured the effects of the major components of AR on cell mitochondrial bioenergetics. Here, a systemic approach employing an extracellular flux analyzer was developed to evaluate mitochondrial respiration in cultured cardiomyocyte cells H9C2. The effects of different polar extractives, as well as of the major compounds of AR, were compared. The contents of astragaloside IV, calycosin, formononetin, and genistein in the AR extracts obtained by using water, 50% ethanol, and 90% ethanol were measured by liquid chromatograph-mass spectrometer (LC⁻MS). The antioxidant activities of the AR extracts, as well as of their major compounds, were determined by measuring the free radical scavenging activity and protective effects in tert-butyl hydroperoxide (tBHP)-treated H9C2 cells. By monitoring the real-time oxygen consumption rate (OCR) in tBHP-treated cardiomyocytes with a Seahorse extracellular flux analyzer, the tonic effects of the AR extracts and of their main compounds on mitochondrial bioenergetics were evaluated. AR water extracts possessed the strongest antioxidant activity and protective effects in cardiomyocytes exposed to oxidative stress. The protection was proposed to be mediated via increasing the spare respiratory capacity and mitochondrial ATP production in the stressed cells. The major compounds of AR, astragaloside IV and genistein, showed opposite effects in regulating mitochondrial bioenergetics. These results demonstrate that highly polar extracts of AR, especially astragaloside-enriched extracts, possess better tonic effects on mitochondrial bioenergetics of cultured cardiomyocytes than extracts with a lower polarity.

A novel histochemistry assay to assess and quantify focal cytochrome c oxidase deficiency

Defects in the respiratory chain, interfering with energy production in the cell, are major underlying causes of mitochondrial diseases. In spite of this, the surprising variety of clinical symptoms, disparity between ages of onset, as well as the involvement of mitochondrial impairment in ageing and age‐related diseases continue to challenge our understanding of the pathogenic processes. This complexity can be in part attributed to the unique metabolic needs of organs or of various cell types. In this view, it remains essential to investigate mitochondrial dysfunction at the cellular level. For this purpose, we developed a novel enzyme histochemical method that enables precise quantification in fresh‐frozen tissues using competing redox reactions which ultimately lead to the reduction of tetrazolium salts and formazan deposition in cytochrome c oxidase‐deficient mitochondria. We demonstrate that the loss of oxidative activity is detected at very low levels – this achievement is unequalled by previous techniques and opens up new opportunities for the study of early disease processes or comparative investigations. Moreover, human biopsy samples of mitochondrial disease patients of diverse genotypic origins were used and the successful detection of COX‐deficient cells suggests a broad application for this new method. Lastly, the assay can be adapted to a wide range of tissues in the mouse and extends to other animal models, which we show here with the fruit fly, Drosophila melanogaster. Overall, the new assay provides the means to quantify and map, on a cell‐by‐cell basis, the full extent of COX deficiency in tissues, thereby expending new possibilities for future investigation. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Mitochondrial cAMP-PKA signaling: What do we really know?

Mitochondria are key organelles for cellular homeostasis. They generate the most part of ATP that is used by cells through oxidative phosphorylation. They also produce reactive oxygen species, neurotransmitters and other signaling molecules. They are important for calcium homeostasis and apoptosis. Considering the role of this organelle, it is not surprising that most mitochondrial dysfunctions are linked to the development of pathologies. Various mechanisms adjust mitochondrial activity according to physiological needs. The cAMP-PKA signaling emerged in recent years as a direct and powerful mean to regulate mitochondrial functions. Multiple evidence demonstrates that such pathway can be triggered from cytosol or directly within mitochondria. Notably, specific anchor proteins target PKA to mitochondria whereas enzymes necessary for generation and degradation of cAMP are found directly in these organelles. Mitochondrial PKA targets proteins localized in different compartments of mitochondria, and related to various functions. Alterations of mitochondrial cAMP-PKA signaling affect the development of several physiopathological conditions, including neurodegenerative diseases. It is however difficult to discriminate between the effects of cAMP-PKA signaling triggered from cytosol or directly in mitochondria. The specific roles of PKA localized in different mitochondrial compartments are also not completely understood. The aim of this work is to review the role of cAMP-PKA signaling in mitochondrial (patho)physiology.

Zmynd17 controls muscle mitochondrial quality and whole-body metabolism

Muscle mitochondria are crucial for systemic metabolic function, yet their regulation remains unclear. The zinc finger MYND domain-containing protein 17 (Zmynd17) was recently identified as a muscle-specific gene in mammals. Here, we investigated the role of Zmynd17 in mice. We found Zmynd17 predominantly expressed in skeletal muscle, especially in fast glycolytic muscle. Genetic Zmynd17 inactivation led to morphologic and functional abnormalities in muscle mitochondria, resulting in decreased respiratory function. Metabolic stress induced by a high-fat diet upregulated Zmynd17 expression and further exacerbated muscle mitochondrial morphology in Zmynd17-deficient mice. Strikingly, Zmynd17 deficiency significantly aggravated metabolic stress-induced hepatic steatosis, glucose intolerance, and insulin resistance. Furthermore, middle-aged mice lacking Zmynd17 exhibited impaired aerobic exercise performance, glucose intolerance, and insulin resistance. Thus, our results indicate that Zmynd17 is a metabolic stress-inducible factor that maintains muscle mitochondrial integrity, with its deficiency profoundly affecting whole-body glucose metabolism.-Fujita, R., Yoshioka, K., Seko, D., Suematsu, T., Mitsuhashi, S., Senoo, N., Miura, S., Nishino, I., Ono, Y. Zmynd17 controls muscle mitochondrial quality and whole-body metabolism.

Nicotine Modulates Mitochondrial Dynamics in Hippocampal Neurons

Mitochondria are widely recognized as fundamental organelles for cellular physiology and constitute the main energy source for different cellular processes. The location, morphology, and interactions of mitochondria with other organelles, such as the endoplasmic reticulum (ER), have emerged as critical events capable of determining cellular fate. Mitochondria-related functions have proven particularly relevant in neurons; mitochondria are necessary for proper neuronal morphogenesis and the highly energy-demanding synaptic transmission process. Mitochondrial health depends on balanced fusion-fission events, termed mitochondrial dynamics, to repair damaged organelles and/or improve the quality of mitochondrial function, ATP production, calcium homeostasis, and apoptosis, which represent some mitochondrial functions closely related to mitochondrial dynamics. Several neurodegenerative disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases, have been correlated with severe mitochondrial dysfunction. In this regard, nicotine, which has been associated with relevant neuroprotective effects mainly through activation of the nicotinic acetylcholine receptor (nAChR), exerts its effects at least in part by acting directly on mitochondrial physiology and morphology. Additionally, a recent description of mitochondrial nAChR localization suggests a nicotine-dependent mitochondrial function. In the present work, we evaluated in cultured hipocampal neurons the effects of nicotine on mitochondrial dynamics by assessing mitochondrial morphology, membrane potential, as well as interactions between mitochondria, cytoskeleton and IP₃R, levels of the cofactor PGC-1α, and fission-fusion-related proteins. Our results suggest that nicotine modulates mitochondrial dynamics and influences mitochondrial association from microtubules, increasing IP₃ receptor clustering showing modulation between mitochondria-ER communications, together with the increase of mitochondrial biogenesis.

Mitochondria-Accessing Ratiometric Fluorescent Probe for Imaging Endogenous Superoxide Anion in Live Cells and Daphnia magna

Superoxide anion (O₂^•-), as the precursor of other reactive oxygen species (ROS), is significantly important in the maintenance of redox homeostasis and various cellular signaling pathways. Here we present a ratiometric mitochondria-accessing fluorescent probe (NA-T) based on nucleophilic substitution mechanism for real-time measuring O₂^•-. By regulating the intramolecular charge of 1,8-naphthalimide, a ratiometric response model was obtained, which evinced 18-fold enhancement of fluorescence ratio ( I_540 nm/ I_475 nm) in the presence of O₂^•- over other ROS with rapid response (132 s), high sensitivity (DL = 0.370 μM) and selectivity. Confocal fluorescence images demonstrated that the probe could well permeate through plasma membrane for visualizing endogenous O₂^•- changes in mitochondria of living cells and in inflammatory Daphnia magna, indicating NA-T a potential tool for the diagnosis and research of corresponding diseases.

Increased Degradation Rates in the Components of the Mitochondrial Oxidative Phosphorylation Chain in the Cerebellum of Old Mice

Brain structures differ in the magnitude of age-related neuron loss with the cerebellum being more affected. An underlying cause could be an age-related decline in mitochondrial bioenergetics. Successful aging of mitochondria reflects a balanced turnover of proteins involved in mitochondrial biogenesis and mitophagy. Thus, an imbalance in mitochondrial turnover can contribute to the diminution of cellular function seen during aging. Mitochondrial biogenesis and mitophagy are mediated by a set of proteins including MFN1, MFN2, OPA1, DRP1, FIS1 as well as DMN1l and DNM1, all of which are required for mitochondrial fission. Using N15 labeling, we report that the turnover rates for DMN1l and FIS1 go in opposite directions in the cerebellum of 22-month-old C57BL6j mice as compared to 3-month-old mice. Previous studies have reported decreased turnover rates for the mitochondrial respiratory complexes of aged rodents. In contrast, we found increased turnover rates for mitochondrial proteins of the oxidative phosphorylation chain in the aged mice as compared to young mice. Furthermore, the turnover rate of the components that are most affected by aging –complex III components (ubiquinol cytochrome C oxidoreductase) and complex IV components (cytochrome C oxidase)– was significantly increased in the senescent cerebellum. However, the turnover rates of proteins involved in mitophagy (i.e., the proteasomal and lysosomal degradation of damaged mitochondria) were not significantly altered with age. Overall, our results suggest that an age-related imbalance in the turnover rates of proteins involved in mitochondrial biogenesis and mitophagy (DMN1l, FIS1) in conjunction with an age-related imbalance in the turnover rates of proteins of the complexes III and IV of the electron transfer chain, might impair cerebellar mitochondrial bioenergetics in old mice.

Proteome changes in the aging Drosophila melanogaster head

A combination of liquid chromatography, ion mobility spectrometry, mass spectrometry, and database searching techniques were used to characterize the proteomes of four biological replicates of adult Drosophila melanogaster heads at seven time points across their lifespans. Based on the detection of tryptic peptides, the identities of 1281 proteins were determined. An estimate of the abundance of each protein, based on the three most intense peptide ions, shows that the quantified species vary in concentration over a factor of ~103. Compared to initial studies in the field of Drosophila proteomics, our current results show an eight-fold higher temporal protein coverage with increased quantitative accuracy. Across the lifespan, we observe a range of trends in the abundance of different proteins, including: an increase in abundance of proteins involved in oxidative phosphorylation, and the tricarboxylic acid cycle; a decrease in proteasomal proteins, as well as ribosomal proteins; and, many types of proteins, which remain relatively unchanged. For younger flies, proteomes are relatively similar within their age group. For older flies, proteome similarity decreases within their age group. These combined results illustrate a correlation between increasing age and decreasing proteostasis.

Centella asiatica - Phytochemistry and mechanisms of neuroprotection and cognitive enhancement

This review describes in detail the phytochemistry and neurological effects of the medicinal herb Centella asiatica (L.) Urban. C. asiatica is a small perennial plant that grows in moist, tropical and sub-tropical regions throughout the world. Phytochemicals identified from C. asiatica to date include isoprenoids (sesquiterpenes, plant sterols, pentacyclic triterpenoids and saponins) and phenylpropanoid derivatives (eugenol derivatives, caffeoylquinic acids, and flavonoids). Contemporary methods for fingerprinting and characterization of compounds in C. asiatica extracts include liquid chromatography and/or ion mobility spectrometry in conjunction with high-resolution mass spectrometry. Multiple studies in rodent models, and a limited number of human studies support C. asiatica's traditional reputation as a cognitive enhancer, as well as its anxiolytic and anticonvulsant effects. Neuroprotective effects of C.asiatica are seen in several in vitro models, for example against beta amyloid toxicity, and appear to be associated with increased mitochondrial activity, improved antioxidant status, and/or inhibition of the pro-inflammatory enzyme, phospholipase A2. Neurotropic effects of C. asiatica include increased dendritic arborization and synaptogenesis, and may be due to modulations of signal transduction pathways such as ERK1/2 and Akt. Many of these neurotropic and neuroprotective properties of C.asiatica have been associated with the triterpene compounds asiatic acid, asiaticoside and madecassoside. More recently, caffeoylquinic acids are emerging as a second important group of active compounds in C. asiatica, with the potential of enhancing the Nrf2-antioxidant response pathway. The absorption, distribution, metabolism and excretion of the triterpenes, caffeoylquinic acids and flavonoids found in C. asiatica have been studied in humans and animal models, and the compounds or their metabolites found in the brain. This review highlights the remarkable potential for C. asiatica extracts and derivatives to be used in the treatment of neurological conditions, and considers the further research needed to actualize this possibility.

Homocysteine, Infections, Polyamines, Oxidative Metabolism, and the Pathogenesis of Dementia and Atherosclerosis

Hyperhomocysteinemia is a risk factor for development of dementia and Alzheimer's disease (AD), and low blood levels of folate and cobalamin are associated with hyperhomocysteinemia and AD. In elderly subjects with cognitive decline, supplementation with folate, cobalamin, and pyridoxal demonstrated reduction of cerebral atrophy in gray matter regions vulnerable to the AD process. Multiple pathogenic microbes are implicated as pathogenic factors in AD and atherosclerosis, and the deposition of amyloid-β (Aβ), phosphorylation of tau protein, neuronal injury, and apoptosis in AD are secondary to microbial infection. Glucose utilization and blood flow are reduced in AD, and these changes are accompanied by downregulation of glucose transport, Na, K-ATPase, oxidative phosphorylation, and energy consumption. Thioretinaco ozonide, the complex formed from thioretinamide, cobalamin, ozone, and oxygen is proposed to constitute the active site of oxidative phosphorylation, catalyzing synthesis of adenosine triphosphate (ATP) from nicotinamide adenine dinucleotide (NAD+) and phosphate. Pathogenic microbes cause synthesis of polyamines in host cells by increasing the transfer of aminopropyl groups from adenosyl methionine to putrescine, resulting in depletion of intracellular adenosyl methionine concentrations in host cells. Depletion of adenosyl methionine causes dysregulation of methionine metabolism, hyperhomocysteinemia, reduced biosynthesis of thioretinamide and thioretinaco ozonide, decreased oxidative phosphorylation, decreased production of nitric oxide and peroxynitrite, and impaired host response to infectious microbes, contributing to the pathogenesis of dementia and atherosclerosis.

The risks of sarcopenia, falls and fractures in patients with type 2 diabetes mellitus

Fracture risk in patients with type 2 diabetes mellitus (T2DM) is increased, and the mechanism is multifactorial. Recent research on T2DM-induced bone fragility shows that bone mineral density (BMD) is often normal or even slightly elevated. However, bone turnover may be decreased and bone material and microstructural properties are altered, especially when microvascular complications are present. Besides bone fragility, extra-skeletal factors leading to an increased propensity to experience falls may also contribute to the increased fracture risk in T2DM, such as peripheral neuropathy, retinopathy and diabetes medication (e.g. insulin use). One of the probable additional contributing factors to the increased fall and fracture risks in T2DM is sarcopenia, the age-related decline in skeletal muscle mass, quality and function. Although the association between sarcopenia, fall risk, and fracture risk has been studied in the general population, few studies have examined the association between T2DM and muscle tissue and the risks of falls and fractures. This narrative review provides an overview of the literature regarding the multifactorial mechanisms leading to increased fracture risk in patients with T2DM, with a focus on sarcopenia and falls.

Effect of Multi-walled Carbon Nanotubes on Metabolism and Morphology of Filamentous Green Microalgae

Multi-walled carbon nanotubes (MWCNTs) have potential applications in the industrial, agricultural, pharmaceutical, medical, and environmental remediation fields. However, many uncertainties exist regarding the environmental implications of engineered nanomaterials. This study examined the effect of the MWCNTs on metabolic status and morphology of filamentous green microalgae Klebsormidium flaccidum. Appropriate concentrations of MWCNT (1, 50, and 100 μg mL^-1) were added to a microalgal culture in the exponential growth phase and incubated for 24, 48, 72, and 96 h. Exposure to MWCNT led to reductions in algal growth after 48 h and decreased on cell viability for all experimental endpoints except for 1 µg mL^-1 at 24 h and 100 µg mL^-1 after 72 h. At 100 µg mL^-1, MWCNTs induced reactive oxygen species (ROS) production and had an effect on intracellular adenosine triphosphate (ATP) content depending on concentration and time. No photosynthetic activity variation was observed. Observations by scanning transmission electron microscopy showed cell damage. In conclusion, we have demonstrated that exposure to MWCNTs affects cell metabolism and microalgal cell morphology. To our best knowledge, this is the first case in which MWCNTs exhibit adverse effects on filamentous green microalgae K. flaccidum. These results contribute to elucidate the mechanism of MWCNT nanotoxicity in the bioindicator organism of terrestrial and freshwater habitats.

Mitochondrial bioenergetics decay in aging: beneficial effect of melatonin

Aging is a biological process characterized by progressive decline in physiological functions, increased oxidative stress, reduced capacity to respond to stresses, and increased risk of contracting age-associated disorders. Mitochondria are referred to as the powerhouse of the cell through their role in the oxidative phosphorylation to generate ATP. These organelles contribute to the aging process, mainly through impairment of electron transport chain activity, opening of the mitochondrial permeability transition pore and increased oxidative stress. These events lead to damage to proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid of the inner mitochondrial membrane, plays a pivotal role in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis and in mitochondrial membrane stability and dynamics. Cardiolipin alterations are associated with mitochondrial bienergetics decline in multiple tissues in a variety of physiopathological conditions, as well as in the aging process. Melatonin, the major product of the pineal gland, is considered an effective protector of mitochondrial bioenergetic function. Melatonin preserves mitochondrial function by preventing cardiolipin oxidation and this may explain, at least in part, the protective role of this compound in mitochondrial physiopathology and aging. Here, mechanisms through which melatonin exerts its protective role against mitochondrial dysfunction associated with aging and age-associated disorders are discussed.

Mechanisms driving the ageing heart

Cardiovascular disease (CVD) is the leading cause of death globally. One of the main risk factors for CVD is age, however the biological processes that occur in the heart during ageing are poorly understood. It is therefore important to understand the fundamental mechanisms driving heart ageing to enable the development of preventions and treatments targeting these processes. Cellular senescence is often described as the irreversible cell-cycle arrest which occurs in somatic cells. Emerging evidence suggests that cellular senescence plays a key role in heart ageing, however the cell-types involved and the underlying mechanisms are not yet elucidated. In this review we discuss the current understanding of how mechanisms known to contribute to senescence impact on heart ageing and CVD. Finally, we evaluate recent data suggesting that targeting senescent cells may be a viable therapy to counteract the ageing of the heart.

Hyperhomocysteinemia, Suppressed Immunity, and Altered Oxidative Metabolism Caused by Pathogenic Microbes in Atherosclerosis and Dementia

Many pathogenic microorganisms have been demonstrated in atherosclerotic plaques and in cerebral plaques in dementia. Hyperhomocysteinemia, which is a risk factor for atherosclerosis and dementia, is caused by dysregulation of methionine metabolism secondary to deficiency of the allosteric regulator, adenosyl methionine. Deficiency of adenosyl methionine results from increased polyamine biosynthesis by infected host cells, causing increased activity of ornithine decarboxylase, decreased nitric oxide and peroxynitrate formation and impaired immune reactions. The down-regulation of oxidative phosphorylation that is observed in aging and dementia is attributed to deficiency of thioretinaco ozonide oxygen complexed with nicotinamide adenine dinucleotide and phosphate, which catalyzes oxidative phosphorylation. Adenosyl methionine biosynthesis is dependent upon thioretinaco ozonide and adenosine triphosphate (ATP), and the deficiency of adenosyl methionine and impaired immune function in aging are attributed to depletion of thioretinaco ozonide from mitochondrial membranes. Allyl sulfides and furanonaphthoquinones protect against oxidative stress and apoptosis by increasing the endogenous production of hydrogen sulfide and by inhibiting electron transfer to the active site of oxidative phosphorylation. Diallyl trisulfide and napabucasin inhibit the signaling by the signal transducer and activator of transcription 3 (Stat3), potentially enhancing immune function by effects on T helper lymphocytes and promotion of apoptosis. Homocysteine promotes endothelial dysfunction and apoptosis by the unfolded protein response and endoplasmic reticulum stress through activation of the N-methyl D-aspartate (NMDA) receptor, causing oxidative stress, calcium influx, apoptosis and endothelial dysfunction. The prevention of atherosclerosis and dementia may be accomplished by a proposed nutritional metabolic homocysteine-lowering protocol which enhances immunity and corrects the altered oxidative metabolism in atherosclerosis and dementia.

Pathophysiology of mitochondrial lipid oxidation: Role of 4-hydroxynonenal (4-HNE) and other bioactive lipids in mitochondria

Mitochondrial lipids are essential for maintaining the integrity of mitochondrial membranes and the proper functions of mitochondria. As the "powerhouse" of a cell, mitochondria are also the major cellular source of reactive oxygen species (ROS). Oxidative stress occurs when the antioxidant system is overwhelmed by overproduction of ROS. Polyunsaturated fatty acids in mitochondrial membranes are primary targets for ROS attack, which may lead to lipid peroxidation (LPO) and generation of reactive lipids, such as 4-hydroxynonenal. When mitochondrial lipids are oxidized, the integrity and function of mitochondria may be compromised and this may eventually lead to mitochondrial dysfunction, which has been associated with many human diseases including cancer, cardiovascular diseases, diabetes, and neurodegenerative diseases. How mitochondrial lipids are oxidized and the underlying molecular mechanisms and pathophysiological consequences associated with mitochondrial LPO remain poorly defined. Oxidation of the mitochondria-specific phospholipid cardiolipin and generation of bioactive lipids through mitochondrial LPO has been increasingly recognized as an important event orchestrating apoptosis, metabolic reprogramming of energy production, mitophagy, and immune responses. In this review, we focus on the current understanding of how mitochondrial LPO and generation of bioactive lipid mediators in mitochondria are involved in the modulation of mitochondrial functions in the context of relevant human diseases associated with oxidative stress.

PGC-1α in aging and lifelong exercise training-mediated regulation of UPR in mouse liver

Aging is associated with changes in several metabolic pathways affecting liver function including the adaptive unfolded protein response (UPR). On the other hand, exercise training has been shown to exert beneficial effects on metabolism in the liver and exercise training has been reported to affect hepatic UPR. PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in skeletal muscle and liver. Therefore, the aim of the present study was to examine the impact of PGC-1α in aging and lifelong exercise training-induced hepatic UPR in mice. Liver was obtained from young (3months old), aged (15months old) and lifelong exercise trained aged wild-type (WT) and whole-body PGC-1α knockout (KO) mice. Hepatic BiP, IRE1α and cleaved ATF6 protein content increased, whereas PERK protein content was reduced with aging indicating both increased and decreased capacity of specific UPR pathways and increased activity of the ATF6 pathway in the liver with aging. Lifelong exercise training prevented the age-associated change in BiP and IRE1α protein, but not cleaved ATF6 protein and resulted in further decreased PERK protein. Taken together, the present study provides evidence that the capacity and activity of the three UPR pathways are differentially regulated in the liver with aging and lifelong exercise training. In addition, PGC-1α does not seem to regulate the activity of hepatic UPR in response to exercise training, but to influence the capacity of the liver to induce UPR in a pathway specific manner.

Family history and TOMM40 '523 interactive associations with memory in middle-aged and Alzheimer's disease cohorts

INTRODUCTION

Family history (FH) of Alzheimer's disease (AD) affects mitochondrial function and may modulate effects of translocase of the outer mitochondrial membrane 40 kDa (TOMM40) rs10524523 ('523) poly-T length on memory decline.

METHODS

For 912 nonapolipoprotein ε4 middle-aged adults and 365 aged adults across the AD spectrum, linear mixed models gauged FH and TOMM40 '523 interactions on memory and global cognition between baseline and up to 10 years later. A cerebrospinal fluid mitochondrial function biomarker was also assessed.

RESULTS

For FH negative participants, gene-dose preservation of memory and global cognition was seen for "very long" versus "short" carriers. For FH positive, an opposite gene-dose decline was seen for very long versus short carriers. Maternal FH was a stronger predictor in aged, but not middle-aged, participants. Similar gene-dose effects were seen for the mitochondrial biomarker aspartate aminotransferase.

DISCUSSION

These results may clarify conflicting findings on TOMM40 poly-T length and AD-related decline.

Effect of acute and long-term administration of gold nanoparticles on biochemical parameters in rat brain

The present study investigated stress oxidative parameters and activities of enzymes of the energy metabolism in various brain structures. Rats were subjected to acute and long-term administration of gold nanoparticles (GNPs) with mean diameters of 10nm and 30nm. Adult (60days old) male Wistar rats received a single intraperitoneal injection (acute administration; 70μg·kg^-1) or repeated injections once daily for 28days (long-term administration; 70μg·kg^-1) of saline solution or GNPs (10nm or 30nm). Twenty-four hours after administration of the final dose, the animals were killed and the cerebral structures were isolated for enzyme analysis. In this study, we observed that the thiobarbituric acid-reactive species and carbonyl protein levels were decreased after acute administration of GNPs, whereas the superoxide dismutase activity was increased after acute and long-term of GNPs. The catalase activity was affected by the administration of GNPs. Furthermore, we have not found change in the citrate synthase activity. The succinate dehydrogenase, malate dehydrogenase, complexes I, II, II-III and IV, and creatine kinase activities were altered. These results indicate that inhibition energy metabolism can be caused by oxidative stress.

Molecular Pathogenesis of Alzheimer's Disease: An Update

Dementia is a chronic or progressive syndrome, characterized by impaired cognitive capacity beyond what could be considered a consequence of normal aging. It affects the memory, thinking process, orientation, comprehension, calculation, learning ability, language, and judgment; although awareness is usually unaffected. Alzheimer's disease (AD) is the most common form of dementia; symptoms include memory loss, difficulty solving problems, disorientation in time and space, among others. The disease was first described in 1906 at a conference in Tubingen, Germany by Alois Alzheimer. One hundred and ten years since its first documentation, many aspects of the pathophysiology of AD have been discovered and understood, however gaps of knowledge continue to exist. This literature review summarizes the main underlying neurobiological mechanisms in AD, including the theory with emphasis on amyloid peptide, cholinergic hypothesis, glutamatergic neurotransmission, the role of tau protein, and the involvement of oxidative stress and calcium.

Skeletal muscle insulin resistance: role of mitochondria and other ROS sources

At present, obesity is one of the most important public health problems in the world because it causes several diseases and reduces life expectancy. Although it is well known that insulin resistance plays a pivotal role in the development of type 2 diabetes mellitus (the more frequent disease in obese people) the link between obesity and insulin resistance is yet a matter of debate. One of the most deleterious effects of obesity is the deposition of lipids in non-adipose tissues when the capacity of adipose tissue is overwhelmed. During the last decade, reduced mitochondrial function has been considered as an important contributor to 'toxic' lipid metabolite accumulation and consequent insulin resistance. More recent reports suggest that mitochondrial dysfunction is not an early event in the development of insulin resistance, but rather a complication of the hyperlipidemia-induced reactive oxygen species (ROS) production in skeletal muscle, which might promote mitochondrial alterations, lipid accumulation and inhibition of insulin action. Here, we review the literature dealing with the mitochondria-centered mechanisms proposed to explain the onset of obesity-linked IR in skeletal muscle. We conclude that the different pathways leading to insulin resistance may act synergistically because ROS production by mitochondria and other sources can result in mitochondrial dysfunction, which in turn can further increase ROS production leading to the establishment of a harmful positive feedback loop.

Propofol protects against oxidative-stress-induced COS-7 cell apoptosis by inducing autophagy

Background

In oxidative stress, reactive oxygen species (ROS) production contributes to cellular dysfunction and initiates the apoptotic cascade. Autophagy is considered the mechanism that decreases ROS concentration and oxidative damage. Propofol shows antioxidant properties, but the mechanisms underlying the effect of propofol preconditioning (PPC) on oxidative injury remain unclear. Therefore, we investigated whether PPC protects against cell damage from hydrogen peroxide (H₂O₂)-induced oxidative stress and influences cellular autophagy.

Method

COS-7 cells were randomly divided into the following groups: control, cells were incubated in normoxia (5% CO₂, 21% O₂, and 74% N₂) for 24 h without propofol; H₂O₂, cells were exposed to H₂O₂ (400 µM) for 2 h; PPC + H₂O₂, cells pretreated with propofol were exposed to H₂O₂; and 3-methyladenine (3-MA) + PPC + H₂O₂, cells pretreated with 3-MA (1 mM) for 1 h and propofol were exposed to H₂O₂. Cell viability was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide thiazolyl blue (MTT) reduction. Apoptosis was determined using Hoechst 33342 staining and fluorescence microscopy. The relationship between PPC and autophagy was detected using western blot analysis.

Results

Cell viability decreased more significantly in the H₂O₂ group than in the control group, but it was improved by PPC (100 µM). Pretreatment with propofol effectively decreased H₂O₂-induced COS-7 cell apoptosis. However, pretreatment with 3-MA inhibited the protective effect of propofol during apoptosis. Western blot analysis showed that the level of autophagy-related proteins was higher in the PPC + H₂O₂ group than that in the H₂O₂ group.

Conclusion

PPC has a protective effect on H₂O₂-induced COS-7 cell apoptosis, which is mediated by autophagy activation.

Changes in the mitochondrial function and in the efficiency of energy transfer pathways during cardiomyocyte aging

The role of mitochondria in alterations that take place in the muscle cell during healthy aging is a matter of debate during recent years. Most of the studies in bioenergetics have a focus on the model of isolated mitochondria, while changes in the crosstalk between working myofibrils and mitochondria in senescent cardiomyocytes have been less studied. The aim of our research was to investigate the modifications in the highly regulated ATP production and energy transfer systems in heart cells in old rat cardiomyocytes. The results of our work demonstrated alterations in the diffusion restrictions of energy metabolites, manifested by changes in the apparent Michaelis-Menten constant of mitochondria to exogenous ADP. The creatine kinase (CK) phosphotransfer pathway efficiency declines significantly in senescence. The ability of creatine to stimulate OXPHOS as well as to increase the affinity of mitochondria for ADP is falling and the most critical decline is already in the 1-year group (middle-age model in rats). Also, a moderate decrease in the adenylate kinase phosphotransfer system was detected. The importance of glycolysis increases in senescence, while the hexokinase activity does not change during healthy aging. The main result of our study is that the decline in the heart muscle performance is not caused by the changes in the respiratory chain complexes activity but mainly by the decrease in the energy transfer efficiency, especially by the CK pathway.