Do we age because we have mitochondria?

PKCε activator protects hippocampal microvascular disruption and memory defect in 3×Tg-Alzheimer's disease mice with cerebral microinfarcts

Background

Current evidence suggests that microvessel disease is involved in Alzheimer's disease (AD). Cerebrovascular disease correlates with cardiovascular disease and is complicated in ≈40% of AD patients. The protein kinase C (PKC) ε activator DCPLA can stimulate human antigen (Hu) R that prevents degradation and promotes the translation of mitochondrial Mn-superoxide dismutase (MnSOD) and vascular endothelial growth factor-A (VEGF) mRNAs.

Methods

To induce brain microinfarcts, we injected triple transgenic (3×Tg) and wild-type (WT) control mice with microbeads (20 μm caliber) into common carotid arteries, with or without the DCPLA-ME (methyl-ester) for 2 weeks. After water maze training, mice at 16 months old were examined for confocal immunohistochemistry at a single cell or microvessel level in the hippocampal CA1 area, important for spatial memory storage, and in the dorsal hippocampus by western blots.

Results

In 3×Tg mice without cerebral microinfarcts, an accelerating age-related increase in (mild) oxidative stress and hypoxia inducible factor (HIF)-1α, but a reduction in VEGF, mitochondrial transcription factor A (TFAM), and MnSOD were associated with capillary loss. The change was less pronounced in arterioles. However, in 3×Tg mice with cerebral microinfarcts, increasing arteriolar diameter and their wall cells were related with the strong oxidative DNA damage 8-hydroxy-2'-deoxyguanosine (8-OHdG), apoptosis (cleaved caspase 3), and sustained hypoxia (increased HIF-1α and VEGF/PKCε/extracellular signal regulated kinase or ERK pathway). Microocclusion enhanced the loss of the synaptic marker spinophilin, astrocytic number, and astrocyte-vascular coupling areas and demyelination of axons. DCPLA-ME prevented spatial memory defect; strong oxidative stress-related apoptosis; sustained hypoxia (by reducing HIF-1α and VEGF); and exaggerated cell repair in arteriolar walls, pericapillary space dilation, neuro-glial-vascular disruption, and demyelination.

Conclusion

In conclusion, in 3×Tg mice with cerebral microinfarcts, sustained hypoxia (increased HIF-1α and VEGF signals) is dominant with arteriolar wall thickening, and DCPLA has a protective effect on sustained hypoxia.

Association of Apolipoprotein E4-related Microvascular Disease in the Alzheimer's Disease Hippocampal CA1 Stratum Radiatum

Current data suggest a hypothesis of vascular pathogenesis for the development and progression of Alzheimer's disease (AD). To investigate this, we studied the association of apolipoprotein E4 (APOE4) gene on microvessels in human autopsy-confirmed AD with and without APOE4, compared with age/sex-matched control (AC) hippocampal CA1 stratum radiatum. AD arterioles (without APOE4 gene) had mild oxidative stress and loss of vascular endothelial growth factor (VEGF) and endothelial cell density, reflecting aging progression. In AD + APOE4, an increase in strong oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG), VEGF, and endothelial cell density were associated with increased diameter of arterioles and perivascular space dilation. In cultured human brain microvascular cells (HBMECs), treatment of ApoE4 protein plus amyloid-β (Aβ) oligomers increased superoxide production and the apoptotic marker cleaved caspase 3, sustained hypoxia inducible factor-1α (HIF-1α) stability that was associated with an increase in MnSOD, VEGF, and cell density. This cell over-proliferation was inhibited with the antioxidants N-acetyl cysteine and MnTMPyP, the HIF-1α inhibitor echinomycin, the VEGFR-2 receptor blocker SU1498, the protein kinase C (PKC) ε knock-down (KD) and the extracellular signal-regulated kinase 1/2 (ERK) inhibitor FR180204. The PKCε KD and echinomycin decreased VEGF and/or ERK. In conclusion, AD capillaries and arterioles in hippocampal CA1 stratum radiatum of non-APOE4 carriers are related with aging, while those in APOE4 carriers with AD are related with pathogenesis of cerebrovascular disease.

HIV Promotes Neurocognitive Impairment by Damaging the Hippocampal Microvessels

Current evidence suggests that mild cerebrovascular changes could induce neurodegeneration and contribute to HIV-associated neurocognitive disease (HAND) in HIV patients. We investigated both the quantitative and qualitative impact of HIV infection on brain microvessels, especially on hippocampal microvessels, which are crucial for optimal O2 supply, and thus for maintaining memory and cognitive abilities. The results obtained using cultured human brain microvascular endothelial cells (HBMEC) were reproduced using a suitable mouse model and autopsied human HIV hippocampus. In HBMEC, we found significantly higher oxidative stress-dependent apoptotic cell loss following 5 h of treatment of GST-Tat (1 µg/ml) compared to GST (1 µg/ml) control. We noticed complete recovery of HBMEC cells after 24 h of GST-Tat treatment, due to temporal degradation or inactivation of GST-Tat. Interestingly, we found a sustained increase in mitochondrial oxidative DNA damage marker 8-OHdG, as well as an increase in hypoxia-inducible factor hypoxia-inducible factor-1α (HIF-1α). In our mouse studies, upon short-term injection of GST-Tat, we found the loss of small microvessels (mostly capillaries) and vascular endothelial growth factor (VEGF), but not large microvessels (arterioles and venules) in the hippocampus. In addition to capillary loss, in the post-mortem HIV-infected human hippocampus, we observed large microvessels with increased wall cells and perivascular tissue degeneration. Together, our data show a crucial role of Tat in inducing HIF-1α-dependent inhibition of mitochondrial transcriptional factor A (TFAM) and dilated perivascular space. Thus, our results further define the underlying molecular mechanism promoting mild cerebrovascular disease, neuropathy, and HAND pathogenesis in HIV patients.

Hypoxia in Aging and Aging-Related Diseases: Mechanism and Therapeutic Strategies

As the global aging process continues to lengthen, aging-related diseases (e.g., chronic obstructive pulmonary disease (COPD), heart failure) continue to plague the elderly population. Aging is a complex biological process involving multiple tissues and organs and is involved in the development and progression of multiple aging-related diseases. At the same time, some of these aging-related diseases are often accompanied by hypoxia, chronic inflammation, oxidative stress, and the increased secretion of the senescence-associated secretory phenotype (SASP). Hypoxia seems to play an important role in the process of inflammation and aging, but is often neglected in advanced clinical research studies. Therefore, we have attempted to elucidate the role played by different degrees and types of hypoxia in aging and aging-related diseases and their possible pathways, and propose rational treatment options based on such mechanisms for reference.

Dysregulated Purine Metabolism Contributes to Age-Associated Lower Urinary Tract Dysfunctions

Lower urinary tract (LUT) dysfunction is common in the older adult. Aging is associated with a number of both storage and voiding problems which are classified into syndromes with overlapping symptoms. Despite the prevalence and consequences of these syndromes, LUT disorders continue to be undertreated as few therapeutic options exist. Here, we propose that dysregulated metabolism of purine nucleotides results in an accumulation of uro-damaging hypoxanthine (a source of reactive oxygen species or ROS), which provides a mechanism for defects in sensory signaling and contractility, culminating in abnormal urodynamic behavior.

Purine nucleoside phosphorylase inhibition ameliorates age-associated lower urinary tract dysfunctions

In the aging population, lower urinary tract (LUT) dysfunction is common and often leads to storage and voiding difficulties classified into overlapping symptom syndromes. Despite prevalence and consequences of these syndromes, LUT disorders continue to be undertreated simply because there are few therapeutic options. LUT function and structure were assessed in aged (>25 months) male and female Fischer 344 rats randomized to oral treatment with a purine nucleoside phosphorylase (PNPase inhibitor) 8-aminoguanine (8-AG) or vehicle for 6 weeks. The bladders of aged rats exhibited multiple abnormalities: tactile insensitivity, vascular remodeling, reduced collagen-fiber tortuosity, increased bladder stiffness, abnormal smooth muscle morphology, swelling of mitochondria, and increases in urodamaging purine metabolites. Treatment of aged rats with 8-AG restored all evaluated histological, ultrastructural, and physiological abnormalities toward that of a younger state. 8-AG is an effective treatment that ameliorates key age-related structural and physiologic bladder abnormalities. Because PNPase inhibition blocks metabolism of inosine to hypoxanthine and guanosine to guanine, likely uroprotective effects of 8-AG are mediated by increased bladder levels of uroprotective inosine and guanosine and reductions in urodamaging hypoxanthine and xanthine. These findings demonstrate that 8-AG has translational potential for treating age-associated LUT dysfunctions and resultant syndromes in humans.

Cerebral Mitochondrial Function and Cognitive Performance during Aging: A Longitudinal Study in NMRI Mice

Brain aging is one of the major risk factors for the development of several neurodegenerative diseases. Therefore, mitochondrial dysfunction plays an important role in processes of both, brain aging and neurodegeneration. Aged mice including NMRI mice are established model organisms to study physiological and molecular mechanisms of brain aging. However, longitudinal data evaluated in one cohort are rare but are important to understand the aging process of the brain throughout life, especially since pathological changes early in life might pave the way to neurodegeneration in advanced age. To assess the longitudinal course of brain aging, we used a cohort of female NMRI mice and measured brain mitochondrial function, cognitive performance, and molecular markers every 6 months until mice reached the age of 24 months. Furthermore, we measured citrate synthase activity and respiration of isolated brain mitochondria. Mice at the age of three months served as young controls. At six months of age, mitochondria-related genes (complex IV, creb-1, β-AMPK, and Tfam) were significantly elevated. Brain ATP levels were significantly reduced at an age of 18 months while mitochondria respiration was already reduced in middle-aged mice which is in accordance with the monitored impairments in cognitive tests. mRNA expression of genes involved in mitochondrial biogenesis (cAMP response element-binding protein 1 (creb-1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), nuclear respiratory factor-1 (Nrf-1), mitochondrial transcription factor A (Tfam), growth-associated protein 43 (GAP43), and synaptophysin 1 (SYP1)) and the antioxidative defense system (catalase (Cat) and superoxide dismutase 2 (SOD2)) was measured and showed significantly decreased expression patterns in the brain starting at an age of 18 months. BDNF expression reached, a maximum after 6 months. On the basis of longitudinal data, our results demonstrate a close connection between the age-related decline of cognitive performance, energy metabolism, and mitochondrial biogenesis during the physiological brain aging process.

Is there a role for oxidative stress and mitochondrial dysfunction in age-associated bladder disorders?

Millions of individuals worldwide are affected by age-related lower urinary tract symptoms (LUTSs), including impaired detrusor contractility, detrusor overactivity, decreased bladder sensation, as well as increased bladder capacity often resulting in incomplete bladder emptying. Yet, the underlying factors that contribute to these symptoms are not known and there are few therapies to treat these disorders. Because of the complex pathophysiology, a number of animal models have been studied over the years to better understand mechanisms underlying patient symptoms. Such animal models can aid in the investigation of aspects of age-associated LUTSs that cannot be pursued in humans as well as to develop and test potential therapies. In addition, the search for urinary factors that may be a causative agent has resulted in the discovery of a number of potential targets that could serve as predictive biomarkers which can aid in early diagnosis and treatment of these chronic disorders. Recent evidence has supported a role for chronic changes in mitochondrial function and oxidative stress (along with production of reactive oxygen species) and abnormal urodynamic behavior in older patients. This review discusses new insights into how aging alters fundamental cellular processes that impair signaling in the bladder wall, resulting in abnormal voiding function.

17β-Estradiol Modulates SIRT1 and Halts Oxidative Stress-Mediated Cognitive Impairment in a Male Aging Mouse Model

Oxidative stress has been considered the main mediator in neurodegenerative disease and in normal aging processes. Several studies have reported that the accumulation of reactive oxygen species (ROS), elevated oxidative stress, and neuroinflammation result in cellular malfunction. These conditions lead to neuronal cell death in aging-related neurodegenerative disorders such as Alzheimer’s disease (AD) and Parkinson’s disease. Chronic administration of d-galactose (d-gal) for a period of 10 weeks causes ROS generation and neuroinflammation, ultimately leading to cognitive impairment. In this study, we evaluated the estrogen receptor α (ERα)/silent mating type information regulation 2 homolog 1 (SIRT1)-dependent antioxidant efficacy of 17β-estradiol against d-gal-induced oxidative damage-mediated cognitive dysfunction in a male mouse model. The results indicate that 17β-estradiol, by stimulating ERα/SIRT1, halts d-gal-induced oxidative stress–mediated JNK/NF-ҡB overexpression, neuroinflammation and neuronal apoptosis. Moreover, 17β-estradiol ameliorated d-gal-induced AD-like pathophysiology, synaptic dysfunction and memory impairment in adult mouse brains. Interestingly, inhibition of SIRT1 with Ex527 (a potent and selective SIRT1 inhibitor) further enhanced d-gal-induced toxicity and abolished the beneficial effect of 17β-estradiol. Most importantly, for the first time, our molecular docking study reveals that 17β-estradiol allosterically increases the expression of SIRT1 and abolishes the inhibitory potential of d-ga. In summary, we can conclude that 17β-estradiol, in an ERα/SIRT1-dependent manner, abrogates d-gal-induced oxidative stress–mediated memory impairment, neuroinflammation, and neurodegeneration in adult mice.

Hypoxia and aging

Eukaryotic cells require sufficient oxygen (O₂) for biological activity and survival. When the oxygen demand exceeds its supply, the oxygen levels in local tissues or the whole body decrease (termed hypoxia), leading to a metabolic crisis, threatening physiological functions and viability. Therefore, eukaryotes have developed an efficient and rapid oxygen sensing system: hypoxia-inducible factors (HIFs). The hypoxic responses are controlled by HIFs, which induce the expression of several adaptive genes to increase the oxygen supply and support anaerobic ATP generation in eukaryotic cells. Hypoxia also contributes to a functional decline during the aging process. In this review, we focus on the molecular mechanisms regulating HIF-1α and aging-associated signaling proteins, such as sirtuins, AMP-activated protein kinase, mechanistic target of rapamycin complex 1, UNC-51-like kinase 1, and nuclear factor κB, and their roles in aging and aging-related diseases. In addition, the effects of prenatal hypoxia and obstructive sleep apnea (OSA)-induced intermittent hypoxia have been reviewed due to their involvement in the progression and severity of many diseases, including cancer and other aging-related diseases. The pathophysiological consequences and clinical manifestations of prenatal hypoxia and OSA-induced chronic intermittent hypoxia are discussed in detail.

The clinical and histopathological features of idiopathic inflammatory myopathies with asymmetric muscle involvement

The objective is to determine the frequency of idiopathic inflammatory myopathies (IIMs) with asymmetric muscle involvement (IIMs-A) as initial manifestations in total IIMs and to compare the demographic, clinical, histopathological and radiological characteristics of IIMs-A with classical IIMs (IIMs-C). We retrospectively reviewed the clinical, laboratory, muscle images, histopathological features and treatment response of patients at the Qilu hospital who were diagnosed as IIMs from April 2005 to August 2017. We found among 134 IIMs patients, 13(9.2%) patients with IIMs-A were identified, of which 7 patients were diagnosed as dermatomyositis (DM), 2 as polymyositis (PM), 4 as immune-mediated necrotizing myopathy (IMNM) using the European Neuromuscular Centre (ENMC) criteria. The mean age of our group was 59.1 years old. The duration from the initial symptoms to the first examination was less than 12 months in 12 patients (92.3%). 46.2% patients accompanied with weakness of distal limbs and bulbar symptoms. Finger flexion involvement was found in 5 patients (38.5%). There was no patient that finger flexion was weaker than shoulder abduction. The creatine kinase (CK) level in the serum ranged from 41 IU/L to 9125 IU/L (average: 3192.7 ± 2769.9 IU/L). Serum positive anti-mitochondrial antibodies (AMAs) were found in four patients (30.8%). Endomysial fibrosis and inflammatory cell infiltration were detected in 92.3%, 84.6% patients respectively. Mitochondrial abnormalities in histopathological finding of muscle biopsy were seen in 100% cases. The major histocompatibility complex class I (MHC-I) (84.6%) and class II (MHC-II) (92.3%) expressed on muscle biopsies from almost all cases of our patients. MAC antibody, however, was detected in only 20-40% patients. Eight patients (61.5%) had favorable outcomes. The conclusion was that IIMs-A presented mainly in DM, generally with mitochondrial abnormality and highly positive AMAs. The relationship between the presence of AMAs and the asymmetric muscle involvement in DM needs to be further clarified. We should also consider the diagnosis of IIMs when the patient has features of positive AMAs and asymmetric muscle involvement.

MKK3 mediates inflammatory response through modulation of mitochondrial function

Mitochondria are increasingly recognized as drivers of inflammatory responses. MAP kinase kinase 3 (MKK3), a dual-specificity protein kinase, is activated in inflammation and in turn activates p38 MAP kinase signaling. Here we show that MKK3 influences mitochondrial function and acts as a critical mediator of inflammation. MKK3-deficient (MKK3(-/-)) mice and bone marrow-derived macrophages (BMDMs) secreted smaller amounts of cytokines than wild type (WT) after lipopolysaccharide (LPS) exposure. There was improved mitochondrial function, as measured by basal oxygen consumption rate, mitochondrial membrane potential, and ATP production, in MKK3(-/-) BMDMs. After LPS exposure, MKK3(-/-) BMDMs did not show a significant increase in cellular reactive oxygen species production or in mitochondrial superoxide compared to WT. Activation of two important inflammatory mediators, i.e., the nuclear translocation of NF-κB and caspase-1 activity (a key component of the inflammasome), was lower in MKK3(-/-) BMDMs. p38 and JNK activation was lower in MKK3(-/-) BMDMs compared to WT after exposure to LPS. Knockdown of MKK3 by siRNA in wild-type BMDMs improved mitochondrial membrane potential, reduced LPS-induced caspase-1 activation, and attenuated cytokine secretion. Our studies establish MKK3 as a regulator of mitochondrial function and inflammatory responses to LPS and suggest that MKK3 may be a therapeutic target in inflammatory disorders such as sepsis.

Parental age affects somatic mutation rates in the progeny of flowering plants

In humans, it is well known that the parental reproductive age has a strong influence on mutations transmitted to their progeny. Meiotic nondisjunction is known to increase in older mothers, and base substitutions tend to go up with paternal reproductive age. Hence, it is clear that the germinal mutation rates are a function of both maternal and paternal ages in humans. In contrast, it is unknown whether the parental reproductive age has an effect on somatic mutation rates in the progeny, because these are rare and difficult to detect. To address this question, we took advantage of the plant model system Arabidopsis (Arabidopsis thaliana), where mutation detector lines allow for an easy quantitation of somatic mutations, to test the effect of parental age on somatic mutation rates in the progeny. Although we found no significant effect of parental age on base substitutions, we found that frameshift mutations and transposition events increased in the progeny of older parents, an effect that is stronger through the maternal line. In contrast, intrachromosomal recombination events in the progeny decrease with the age of the parents in a parent-of-origin-dependent manner. Our results clearly show that parental reproductive age affects somatic mutation rates in the progeny and, thus, that some form of age-dependent information, which affects the frequency of double-strand breaks and possibly other processes involved in maintaining genome integrity, is transmitted through the gametes.

Mitochondrial dysfunction: cause and consequence of Alzheimer's disease

The etiology of common, nonfamiliar late-onset Alzheimer's disease (LOAD) is only partly understood and seems to be extremely complex including many genetic and environmental factors. The most important environmental risk factor to develop LOAD is aging itself. Aging and LOAD are considered to be strongly linked to mitochondrial dysfunction and enhanced oxidative stress. In this review, we focus on the interaction between mitochondrial dysfunction in aging especially on defects of the respiratory chain of the oxidative phosphorylation system resulting in enhanced oxidative stress and the interplay between aging-associated mitochondrial defects and LOAD-associated mitochondrial failure. The deleterious effects of the two hallmarks of LOAD, amyloid beta, and hyperphosphorylated tau, on mitochondrial function, movement, and morphology are described as well as the toxic effects of the most relevant genetic risk factor of LOAD, the apolipoprotein E4 allele. Finally, the review provides an overview about drugs and nutritional ingredients which improve mitochondrial function or/and act as antioxidants and discusses their potential role in the treatment of LOAD.

Mitochondrial dynamics in aging and disease

Mitochondria are self-replicating organelles but nevertheless strongly depend on supply coded in nuclear genes. They serve many physiological demands in living cells. Supply of the cytoplasm with ATP and engagement in Ca(2+) regulation belong to the main functions of mitochondria. In large eukaryotic cells, in particular in neurons, with their long dendrites and axons, mitochondria have to move to the sites of their action. This trafficking involves several motor molecules and mechanisms to sense the sites of requirements of mitochondria. With aging and as a consequence of some diseases, mitochondrial components may be rendered dysfunctional, and mtDNA mutations arise during the course of replication and by the action of reactive oxygen species. Mutants in motor molecules engaged in trafficking and in the machinery of fusion and fission are causing severe deficiencies on the cellular level; they support neurodegeneration and, thus, cause many diseases. Frequent fusion and fission events mediate the elimination of impaired parts from mitochondria which finally will be degraded by autophagosomes. Extensive fusion provides a basis for functional complementation. Mobility of proteins and small molecules within the mitochondria is necessary to reach the functional goals of fusion and fission, although cristae and a large fraction of proteins of the respiratory complexes proved to be stable for hours after fusion and perform slow exchange of material.

Systems Biology Profiling of AMD on the Basis of Gene Expression

Genetic pathways underlying the initiation and progression of age-related macular degeneration (AMD) have not been yet sufficiently revealed, and the correlations of AMD's genotypes, phenotypes, and disease spectrum are still awaiting resolution. We are tackling both problems with systems biology phylogenetic parsimony analysis. Gene expression data (GSE29801: NCBI, Geo) of macular and extramacular specimens of the retinas and retinal pigment epithelium (RPE) choroid complexes representing dry AMD without geographic atrophy (GA), choroidal neovascularization (CNV), GA, as well as pre-AMD and subclinical pre-AMD were polarized against their respective normal specimens and then processed through the parsimony program MIX to produce phylogenetic cladograms. Gene lists from cladograms' nodes were processed in Genomatix GePS to reveal the affected signaling pathway networks. Cladograms exposed a highly heterogeneous transcriptomic profiles within all the conventional phenotypes. Moreover, clades and nodal synapomorphies did not support the classical AMD phenotypes as valid transcriptomal genotypes. Gene lists defined by cladogram nodes showed that the AMD-related deregulations occurring in the neural retina were different from those in RPE-choroidal tissue. Our analysis suggests a more complex transcriptional profile of the phenotypes than expected. Evaluation of the disease in much earlier stages is needed to elucidate the initial events of AMD.