Decreased cytochrome c oxidase subunit VIIa in aged rat heart mitochondria: immunocytochemistry

Metabolic Complications in Cardiac Aging

Aging is a process that can be accompanied by molecular and cellular alterations that compromise cardiac function. Although other metabolic disorders with increased prevalence in aged populations, such as diabetes mellitus, dyslipidemia, and hypertension, are associated with cardiovascular complications; aging-related cardiomyopathy has some unique features. Healthy hearts oxidize fatty acids, glucose, lactate, ketone bodies, and amino acids for producing energy. Under physiological conditions, cardiac mitochondria use fatty acids and carbohydrate mainly to generate ATP, 70% of which is derived from fatty acid oxidation (FAO). However, relative contribution of nutrients in ATP synthesis is altered in the aging heart with glucose oxidation increasing at the expense of FAO. Cardiac aging is also associated with impairment of mitochondrial abundance and function, resulting in accumulation of reactive oxygen species (ROS) and activation of oxidant signaling that eventually leads to further mitochondrial damage and aggravation of cardiac function. This review summarizes the main components of pathophysiology of cardiac aging, which pertain to cardiac metabolism, mitochondrial function, and systemic metabolic changes that affect cardiac function.

TDP-43 inhibitory peptide alleviates neurodegeneration and memory loss in an APP transgenic mouse model for Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly, characterized clinically by progressive decline in cognitive function and neuropathologically by the presence of senile plaques and neuronal loss in the brain. While current drugs for AD are always employed as symptomatic therapies with variable benefits, there is no treatment to delay its progression or halt neurodegeneration. TAR DNA-binding protein 43 (TDP-43) proteinopathy has increasingly been implicated as a prominent histopathological feature of AD and related dementias. Our recent studies have implicated mitochondria as critical targets of TDP-43 neurotoxicity. Here, we demonstrate that the suppression of mitochondrial-associated TDP-43 protects against neuronal loss and behavioral deficits in 5XFAD transgenic mice recapitulating AD-related phenotypes. In AD patients and 5XFAD mice, the level of TDP-43 is increased in mitochondria, and TDP-43 highly co-localizes with mitochondria in brain neurons exhibiting TDP-43 proteinopathy. Chronic administration of a TDP-43 mitochondrial localization inhibitory peptide, PM1, significantly alleviates TDP-43 proteinopathy, mitochondrial abnormalities, microgliosis and even neuronal loss without effect on amyloid plaque load in 12-month-old 5XFAD mice well after the onset of symptoms. Additionally, PM1 also improves the cognitive and motor function in 12-month-old 5XFAD mice and completely prevents the onset of mild cognitive impairment in 6-month-old 5XFAD mice. These data indicate that mitochondria-associated TDP-43 is likely involved in AD pathogenesis and that the inhibitor of mitochondria-associated TDP-43 may be a valuable drug to treat underlying AD.

The genetic mechanism of high prolificacy in small tail han sheep by comparative proteomics of ovaries in the follicular and luteal stages

To investigate the genetic mechanism of sheep prolificacy, protein profiling of ovaries in the follicular and luteal phases was conducted. The tandem mass tag technique was used to analyze the proteomes of ovaries from STH sheep that did not have the FecB mutation in the bone morphogenetic protein receptor 1B gene. Parallel Reaction Monitoring (PRM) was operated to validate the target differentially abundant proteins (DAPs). The result showed, a total of 34,037 peptides were found, and 5074 proteins were identified. The screened DAPs strictly related to energy metabolism, hormone synthesis, ovarian function were significantly enriched in oxidative phosphorylation(COX7A, ND5, and UQCR10), ovarian steroidogenesis(StAR and HSD3B), taurine and hypotaurine metabolism(CSAD), glycosaminoglycan biosynthesis-heparin sulfate/heparin(GLCE), necroptosis(H2AX, AIFM1, and FTH1), protein digestion and absorption(COL4A1 and COL4A5) and glycosaminoglycan degradation(HYAL2 and HEXB) pathways. These analyses indicated that the reproductive performance of sheep is regulated through different pathways. In consequence, these findings are an important resource that can be used in future studies of the genetic mechanism of high fecundity traits in sheep, and these DAPs can be further investigated as candidate markers to predict prolificacy of sheep. SIGNIFICANCE: Litter size is an important quantitative trait, but the genetic mechanism of high-prolificacy is still unclear in sheep. Our study identified potential signaling pathways and differentially abundant proteins related to reproductive performance. These findings will facilitate a better revealing the mechanism and provide possible targets for molecular design breeding for the formation of polytocous traits in sheep.

ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington’s disease (HD), a fatal neurodegenerative disease. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in HD. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived cells. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, suggesting that DA1 might be useful for developing HD therapeutics.

Huntington’s disease leads to mitochondrial fragmentation and bioenergetic failure, although how the two events are connected is poorly understood. Here, Zhao et al. identify ATAD3A as a molecular linker and show that a peptide inhibitor of ATAD3A oligomerization suppresses HD phenotypes.

Rejuvenation of Cardiac Tissue Developed from Reprogrammed Aged Somatic Cells

Induced pluripotent stem cells (iPSCs) derived via somatic cell reprogramming have been reported to reset aged somatic cells to a more youthful state, characterized by elongated telomeres, a rearranged mitochondrial network, reduced oxidative stress, and restored pluripotency. However, it is still unclear whether the reprogrammed aged somatic cells can function normally as embryonic stem cells (ESCs) during development and be rejuvenated. In the current study, we applied the aggregation technique to investigate whether iPSCs derived from aged somatic cells could develop normally and be rejuvenated. iPSCs derived from bone marrow myeloid cells of 2-month-old (2 M) and 18-month-old (18 M) C57BL/6-Tg (CAG-EGFP)1Osb/J mice were aggregated with embryos derived from wild-type ICR mice to produce chimeras (referred to as 2 M CA and 18 M CA, respectively). Our observations focused on comparing the ability of the iPSCs derived from 18 M and 2 M bone marrow cells to develop rejuvenated cardiac tissue (the heart is the most vital organ during aging). The results showed an absence of p16 and p53 upregulation, telomere length shortening, and mitochondrial gene expression and deletion in 18 M CA, whereas slight changes in mitochondrial ultrastructure, cytochrome C oxidase activity, ATP production, and reactive oxygen species production were observed in CA cardiac tissues. The data implied that all of the aging characteristics observed in the newborn cardiac tissue of 18 M CA were comparable with those of 2 M CA newborn cardiac tissue. This study provides the first direct evidence of the aging-related characteristics of cardiac tissue developed from aged iPSCs, and our observations demonstrate that partial rejuvenation can be achieved by reprogramming aged somatic cells to a pluripotent state.

Mitochondrial Metabolism in Aging Heart

Altered mitochondrial metabolism is the underlying basis for the increased sensitivity in the aged heart to stress. The aged heart exhibits impaired metabolic flexibility, with a decreased capacity to oxidize fatty acids and enhanced dependence on glucose metabolism. Aging impairs mitochondrial oxidative phosphorylation, with a greater role played by the mitochondria located between the myofibrils, the interfibrillar mitochondria. With aging, there is a decrease in activity of complexes III and IV, which account for the decrease in respiration. Furthermore, aging decreases mitochondrial content among the myofibrils. The end result is that in the interfibrillar area, there is ≈50% decrease in mitochondrial function, affecting all substrates. The defective mitochondria persist in the aged heart, leading to enhanced oxidant production and oxidative injury and the activation of oxidant signaling for cell death. Aging defects in mitochondria represent new therapeutic targets, whether by manipulation of the mitochondrial proteome, modulation of electron transport, activation of biogenesis or mitophagy, or the regulation of mitochondrial fission and fusion. These mechanisms provide new ways to attenuate cardiac disease in elders by preemptive treatment of age-related defects, in contrast to the treatment of disease-induced dysfunction.

In female rat heart mitochondria, oophorectomy results in loss of oxidative phosphorylation

Oophorectomy in adult rats affected cardiac mitochondrial function. Progression of mitochondrial alterations was assessed at one, two and three months after surgery: at one month, very slight changes were observed, which increased at two and three months. Gradual effects included decrease in the rates of oxygen consumption and in respiratory uncoupling in the presence of complex I substrates, as well as compromised Ca²⁺ buffering ability. Malondialdehyde concentration increased, whereas the ROS-detoxifying enzyme Mn²⁺ superoxide dismutase (MnSOD) and aconitase lost activity. In the mitochondrial respiratory chain, the concentration and activity of complex I and complex IV decreased. Among other mitochondrial enzymes and transporters, adenine nucleotide carrier and glutaminase decreased. 2-Oxoglutarate dehydrogenase and pyruvate dehydrogenase also decreased. Data strongly suggest that in the female rat heart, estrogen depletion leads to progressive, severe mitochondrial dysfunction.

Mitochondrial Dysfunction in Cardiovascular Aging

Mitochondria are the prime source of ATP in cardiomyocytes. Impairment of mitochondrial metabolism results in damage to existing proteins and DNA. Such deleterious effects are part and parcel of the aging process, reducing the ability of cardiomyocytes to counter stress, such as myocardial infarction and consequent reperfusion. In such conditions, mitochondria in the heart of aged individuals exhibit decreased oxidative phosphorylation, decreased ATP production, and increased net reactive oxygen species production; all of these effects are independent of the decrease in number of mitochondria that occurs in these situations. Rather than being associated with the mitochondrial population in toto, these defects are almost exclusively confined to those organelles positioned between myofibrils (interfibrillar mitochondria). It is in complex III and IV where these dysfunctional aspects are manifested. In an apparent effort to correct mitochondrial metabolic defects, affected organelles are to some extent eliminated by mitophagy; at the same time, new, unaffected organelles are generated by fission of mitochondria. Because these cardiac health issues are localized to specific mitochondria, these organelles offer potential targets for therapeutic approaches that could favorably affect the aging process in heart.

The inhibition of TDP-43 mitochondrial localization blocks its neuronal toxicity

Genetic mutations in TAR DNA-binding protein 43 (TARDBP, also known as TDP-43) cause amyotrophic lateral sclerosis (ALS), and an increase in the presence of TDP-43 (encoded by TARDBP) in the cytoplasm is a prominent histopathological feature of degenerating neurons in various neurodegenerative diseases. However, the molecular mechanisms by which TDP-43 contributes to ALS pathophysiology remain elusive. Here we have found that TDP-43 accumulates in the mitochondria of neurons in subjects with ALS or frontotemporal dementia (FTD). Disease-associated mutations increase TDP-43 mitochondrial localization. In mitochondria, wild-type (WT) and mutant TDP-43 preferentially bind mitochondria-transcribed messenger RNAs (mRNAs) encoding respiratory complex I subunits ND3 and ND6, impair their expression and specifically cause complex I disassembly. The suppression of TDP-43 mitochondrial localization abolishes WT and mutant TDP-43-induced mitochondrial dysfunction and neuronal loss, and improves phenotypes of transgenic mutant TDP-43 mice. Thus, our studies link TDP-43 toxicity directly to mitochondrial bioenergetics and propose the targeting of TDP-43 mitochondrial localization as a promising therapeutic approach for neurodegeneration.

Parkinson's disease-associated mutant VPS35 causes mitochondrial dysfunction by recycling DLP1 complexes

Mitochondrial dysfunction represents a critical step during the pathogenesis of Parkinson's disease (PD), and increasing evidence suggests abnormal mitochondrial dynamics and quality control as important underlying mechanisms. The VPS35 gene, which encodes a key component of the membrane protein-recycling retromer complex, is the third autosomal-dominant gene associated with PD. However, how VPS35 mutations lead to neurodegeneration remains unclear. Here we demonstrate that PD-associated VPS35 mutations caused mitochondrial fragmentation and cell death in cultured neurons in vitro, in mouse substantia nigra neurons in vivo and in human fibroblasts from an individual with PD who has the VPS35(D620N) mutation. VPS35-induced mitochondrial deficits and neuronal dysfunction could be prevented by inhibition of mitochondrial fission. VPS35 mutants showed increased interaction with dynamin-like protein (DLP) 1, which enhanced turnover of the mitochondrial DLP1 complexes via the mitochondria-derived vesicle-dependent trafficking of the complexes to lysosomes for degradation. Notably, oxidative stress increased the VPS35-DLP1 interaction, which we also found to be increased in the brains of sporadic PD cases. These results revealed a novel cellular mechanism for the involvement of VPS35 in mitochondrial fission, dysregulation of which is probably involved in the pathogenesis of familial, and possibly sporadic, PD.

The subunit composition and function of mammalian cytochrome c oxidase

Cytochrome c oxidase (COX) from mammals and birds is composed of 13 subunits. The three catalytic subunits I-III are encoded by mitochondrial DNA, the ten nuclear-coded subunits (IV, Va, Vb, VIa, VIb, VIc, VIIa, VIIb, VIIc, VIII) by nuclear DNA. The nuclear-coded subunits are essentially involved in the regulation of oxygen consumption and proton translocation by COX, since their removal or modification changes the activity and their mutation causes mitochondrial diseases. Respiration, the basis for ATP synthesis in mitochondria, is differently regulated in organs and species by expression of tissue-, developmental-, and species-specific isoforms for COX subunits IV, VIa, VIb, VIIa, VIIb, and VIII, but the holoenzyme in mammals is always composed of 13 subunits. Various proteins and enzymes were shown, e.g., by co-immunoprecipitation, to bind to specific COX subunits and modify its activity, but these interactions are reversible, in contrast to the tightly bound 13 subunits. In addition, the formation of supercomplexes with other oxidative phosphorylation complexes has been shown to be largely variable. The regulatory complexity of COX is increased by protein phosphorylation. Up to now 18 phosphorylation sites have been identified under in vivo conditions in mammals. However, only for a few phosphorylation sites and four nuclear-coded subunits could a specific function be identified. Research on the signaling pathways leading to specific COX phosphorylations remains a great challenge for understanding the regulation of respiration and ATP synthesis in mammalian organisms. This article reviews the function of the individual COX subunits and their isoforms, as well as proteins and small molecules interacting and regulating the enzyme.

Physiological and structural differences in spatially distinct subpopulations of cardiac mitochondria: influence of cardiac pathologies

Cardiac tissue contains discrete pools of mitochondria that are characterized by their subcellular spatial arrangement. Subsarcolemmal mitochondria (SSM) exist below the cell membrane, interfibrillar mitochondria (IFM) reside in rows between the myofibrils, and perinuclear mitochondria are situated at the nuclear poles. Microstructural imaging of heart tissue coupled with the development of differential isolation techniques designed to sequentially separate spatially distinct mitochondrial subpopulations have revealed differences in morphological features including shape, absolute size, and internal cristae arrangement. These findings have been complemented by functional studies indicating differences in biochemical parameters and, potentially, functional roles for the ATP generated, based upon subcellular location. Consequently, mitochondrial subpopulations appear to be influenced differently during cardiac pathologies including ischemia/reperfusion, heart failure, aging, exercise, and diabetes mellitus. These influences may be the result of specific structural and functional disparities between mitochondrial subpopulations such that the stress elicited by a given cardiac insult differentially impacts subcellular locales and the mitochondria contained within. The goal of this review is to highlight some of the inherent structural and functional differences that exist between spatially distinct cardiac mitochondrial subpopulations as well as provide an overview of the differential impact of various cardiac pathologies on spatially distinct mitochondrial subpopulations. As an outcome, we will instill a basis for incorporating subcellular spatial location when evaluating the impact of cardiac pathologies on the mitochondrion. Incorporation of subcellular spatial location may offer the greatest potential for delineating the influence of cardiac pathology on this critical organelle.

P23H opsin knock-in mice reveal a novel step in retinal rod disc morphogenesis

Retinal rod photoreceptor cells have double membrane discs located in their outer segments (ROS) that are continuously formed proximally from connecting cilia (CC) and phagocytized distally by the retinal pigmented epithelium. The major component of these rod discs, the light-sensitive visual pigment rhodopsin (Rho), consists of an opsin protein linked to 11-cis-retinal. The P23H mutation of rod opsin (P23H opsin) is the most common cause of human blinding autosomal dominant retinitis pigmentosa (adRP). A mouse model of adRP with this mutation (Rho(P23H/+)) shows low levels of P23H opsin protein, partial misalignment of discs and progressive retinal degeneration. However, the impact of mutant P23H opsin on the formation of abnormal discs is unclear and it is still unknown whether this mutant pigment can mediate phototransduction. Using transretinal ERG recordings, we demonstrate that P23H mutant Rho can trigger phototransduction but Rho(P23H/P23H) rods are ∼17 000-fold less sensitive to light than Rho(+/+) rods and produce abnormally fast photo-responses. By analyzing homozygous Rho(P23H/P23H) knock-in mice, we show that P23H opsin is transported to ciliary protrusions where it forms sagittally elongated discs. Transmission electron microscopy of postnatal day (PND) 14 Rho(P23H/+) mouse retina revealed disordered sagittally oriented discs before the onset of retinal degeneration. Surprisingly, we also observed smaller, immature sagittally oriented discs in PND14 Rho(+/)(-) and Rho(+/+) mice that were not seen in older animals. These findings provide fundamental insights into the pathogenesis of the P23H mutant opsin and reveal a novel early sagittally aligned disc formation step in normal ROS disc expansion.

Can proteomics yield insight into aging aorta?

The aging aorta exhibits structural and physiological changes that are reflected in the proteome of its component cells types. The advance in proteomic technologies has made it possible to analyze the quantity of proteins associated with the natural history of aortic aging. These alterations reflect the molecular and cellular mechanisms of aging and could provide an opportunity to predict vascular health. This paper focuses on whether discoveries stemming from the application of proteomic approaches of the intact aging aorta or vascular smooth muscle cells can provide useful insights. Although there have been limited studies to date, a number of interesting proteins have been identified that are closely associated with aging in the rat aorta. Such proteins, including milk fat globule-EGF factor 8, matrix metalloproteinase type-2, and vitronectin, could be used as indicators of vascular health, or even explored as therapeutic targets for aging-related vascular diseases.