Recent Developments in Understanding Brain Aging: Implications for Alzheimer's Disease and Vascular Cognitive Impairment

The Glymphatic Response to the Development of Type 2 Diabetes

The glymphatic system has recently been shown to be important in neurological diseases, including diabetes. However, little is known about how the progressive onset of diabetes affects the glymphatic system. The aim of this study is to investigate the glymphatic system response to the progressive onset of diabetes in a rat model of type 2 diabetic mellitus. Male Wistar rats (n = 45) with and without diabetes were evaluated using MRI glymphatic tracer kinetics, functional tests, and brain tissue immunohistochemistry. Our data demonstrated that the contrast agent clearance impairment gradually progressed with the diabetic duration. The MRI data showed that an impairment in contrast clearance occurred prior to the cognitive deficits detected using functional tests and permitted the detection of an early DM stage compared to the immuno-histopathology and cognitive tests. Additionally, the quantitative MRI markers of brain waste clearance demonstrated region-dependent sensitivity in glymphatic impairment. The improved sensitivity of MRI markers in the olfactory bulb and the whole brain at an early DM stage may be attributed to the important role of the olfactory bulb in the parenchymal efflux pathway. MRI can provide sensitive quantitative markers of glymphatic impairment during the progression of DM and can be used as a valuable tool for the early diagnosis of DM with a potential for clinical application.

Deciphering the Mysterious Relationship between the Cross-Pathogenetic Mechanisms of Neurodegenerative and Oncological Diseases

The relationship between oncological pathologies and neurodegenerative disorders is extremely complex and is a topic of concern among a growing number of researchers around the world. In recent years, convincing scientific evidence has accumulated that indicates the contribution of a number of etiological factors and pathophysiological processes to the pathogenesis of these two fundamentally different diseases, thus demonstrating an intriguing relationship between oncology and neurodegeneration. In this review, we establish the general links between three intersecting aspects of oncological pathologies and neurodegenerative disorders, i.e., oxidative stress, epigenetic dysregulation, and metabolic dysfunction, examining each process in detail to establish an unusual epidemiological relationship. We also focus on reviewing the current trends in the research and the clinical application of the most promising chemical structures and therapeutic platforms that have a modulating effect on the above processes. Thus, our comprehensive analysis of the set of molecular determinants that have obvious cross-functional pathways in the pathogenesis of oncological and neurodegenerative diseases can help in the creation of advanced diagnostic tools and in the development of innovative pharmacological strategies.

Effects of electroacupuncture on rats with cognitive impairment: An iTRAQ-based proteomics analysis

OBJECTIVE

The study explores the effects of electroacupuncture (EA) at the governing vessel (GV) on proteomic changes in the hippocampus of rats with cognitive impairment.

METHODS

Healthy male rats were randomly divided into 3 groups: sham, model and EA. Cognitive impairment was induced by left middle cerebral artery occlusion in the model and EA groups. Rats in the EA group were treated with EA at Shenting (GV24) and Baihui (GV20) for 7 d. Neurological deficit was scored using the Longa scale, the learning and memory ability was detected using the Morris water maze (MWM) test, and the proteomic profiling in the hippocampus was analyzed using protein-labeling technology based on the isobaric tag for relative and absolute quantitation (iTRAQ). The Western blot (WB) analysis was used to detect the proteins and validate the results of iTRAQ.

RESULTS

Compared with the model group, the neurological deficit score was significantly reduced, and the escape latency in the MWM test was significantly shortened, while the number of platform crossings increased in the EA group. A total of 2872 proteins were identified by iTRAQ. Differentially expressed proteins (DEPs) were identified between different groups: 92 proteins were upregulated and 103 were downregulated in the model group compared with the sham group, while 142 proteins were upregulated and 126 were downregulated in the EA group compared with the model group. Most of the DEPs were involved in oxidative phosphorylation, glycolipid metabolism and synaptic transmission. Furthermore, we also verified 4 DEPs using WB technology. Although the WB results were not exactly the same as the iTRAQ results, the expression trends of the DEPs were consistent. The upregulation of heat-shock protein β1 (Hspb1) was the highest in the EA group compared to the model group.

CONCLUSION

EA can effect proteomic changes in the hippocampus of rats with cognitive impairment. Hspb1 may be involved in the molecular mechanism by which acupuncture improves cognitive impairment.

Roles and Mechanisms of DNA Methylation in Vascular Aging and Related Diseases

Vascular aging is a pivotal risk factor promoting vascular dysfunction, the development and progression of vascular aging-related diseases. The structure and function of endothelial cells (ECs), vascular smooth muscle cells (VSMCs), fibroblasts, and macrophages are disrupted during the aging process, causing vascular cell senescence as well as vascular dysfunction. DNA methylation, an epigenetic mechanism, involves the alteration of gene transcription without changing the DNA sequence. It is a dynamically reversible process modulated by methyltransferases and demethyltransferases. Emerging evidence reveals that DNA methylation is implicated in the vascular aging process and plays a central role in regulating vascular aging-related diseases. In this review, we seek to clarify the mechanisms of DNA methylation in modulating ECs, VSMCs, fibroblasts, and macrophages functions and primarily focus on the connection between DNA methylation and vascular aging-related diseases. Therefore, we represent many vascular aging-related genes which are modulated by DNA methylation. Besides, we concentrate on the potential clinical application of DNA methylation to serve as a reliable diagnostic tool and DNA methylation-based therapeutic drugs for vascular aging-related diseases.

Type I interferon response-related microglial Mef2c deregulation at the onset of Alzheimer's pathology in 5×FAD mice

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder with multifactorial etiology. The role of microglia in the pathogenesis of AD has been increasingly recognized in recent years; however, the detailed mechanisms shaping microglial phenotypes in AD-relevant pathological settings remain largely unresolved. Myocyte-specific enhancer factor 2C (Mef2C) is a transcription factor with versatile functions. Recent studies have attributed aging-related microglial changes to type I interferon (IFN-I)-associated Mef2C deregulation. In view of the close relationship between brain aging and AD, it is of great interest to determine microglial Mef2C changes in AD-related conditions. In this study, we have found that suppressed Mef2C nuclear translocation was an early and prominent microglial phenotype in a mouse model of brain amyloidosis (5×FAD mice), which exacerbated with age. Echoing the early Mef2C deregulation and its association with microglial activation, transcriptional data showed elicited IFN-I response in microglia from young 5×FAD mice. Amyloid beta 42 (Aβ42) in its oligomeric forms promoted Mef2C deregulation in microglia on acute organotypic brain slices with augmented microglial activation and synapse elimination via microglial phagocytosis. Importantly, these oligomeric Aβ42-mediated microglial changes were substantially attenuated by blocking IFN-I signaling. The simplest interpretation of the results is that Mef2C, concurring with activated IFN-I signaling, constitutes early microglial changes in AD-related conditions. In addition to the potential contribution of Mef2C deregulation to the development of microglial phenotypes in AD, Mef2C suppression in microglia may serve as a potential mechanistic pathway linking brain aging and AD.

Inhibitory Effects of Antipsychotics on the Contractile Response to Acetylcholine in Rat Urinary Bladder Smooth Muscles

The clinical applications of antipsychotics for symptoms unrelated to schizophrenia, such as behavioral and psychological symptoms, in patients with Alzheimer's disease, and the likelihood of doctors prescribing antipsychotics for elderly people are increasing. In elderly people, drug-induced and aging-associated urinary disorders are likely to occur. The most significant factor causing drug-induced urinary disorders is a decrease in urinary bladder smooth muscle (UBSM) contraction induced by the anticholinergic action of therapeutics. However, the anticholinergic action-associated inhibitory effects of antipsychotics on UBSM contraction have not been sufficiently assessed. In this study, we examined 26 clinically available antipsychotics to determine the extent to which they inhibit acetylcholine (ACh)-induced contraction in rat UBSM to predict the drugs that should not be used by elderly people to avoid urinary disorders. Of the 26 antipsychotics, six (chlorpromazine, levomepromazine (phenothiazines), zotepine (a thiepine), olanzapine, quetiapine, clozapine (multi-acting receptor targeted antipsychotics (MARTAs))) competitively inhibited ACh-induced contractions at concentrations corresponding to clinically significant doses. Further, 11 antipsychotics (perphenazine, fluphenazine, prochlorperazine (phenothiazines), haloperidol, bromperidol, timiperone, spiperone (butyrophenones), pimozide (a diphenylbutylpiperidine), perospirone, blonanserin (serotonin-dopamine antagonists; SDAs), and asenapine (a MARTA)) significantly suppressed ACh-induced contraction; however, suppression occurred at concentrations substantially exceeding clinically achievable blood levels. The remaining nine antipsychotics (pipamperone (a butyrophenone), sulpiride, sultopride, tiapride, nemonapride (benzamides), risperidone, paliperidone (SDAs), aripiprazole, and brexpiprazole (dopamine partial agonists)) did not inhibit ACh-induced contractions at concentrations up to 10-5 M. These findings suggest that chlorpromazine, levomepromazine, zotepine, olanzapine, quetiapine, and clozapine should be avoided by elderly people with urinary disorders.

Reduced pericyte and tight junction coverage in old diabetic rats are associated with hyperglycemia-induced cerebrovascular pericyte dysfunction

Diabetes mellitus (DM) is one of the primary pathological factors that contributes to aging-related cognitive impairments, but the underlying mechanisms remain unclear. We recently reported that old DM rats exhibited impaired myogenic responses of the cerebral arteries and arterioles, poor cerebral blood flow autoregulation, enhanced blood-brain barrier (BBB) leakage, and cognitive impairments. These changes were associated with diminished vascular smooth muscle cell contractile capability linked to elevated reactive oxygen species (ROS) and reduced ATP production. In the present study, using a nonobese T2DN DM rat, we isolated parenchymal arterioles (PAs), cultured cerebral microvascular pericytes, and examined whether cerebrovascular pericyte in DM is damaged and whether pericyte dysfunction may play a role in the regulation of cerebral hemodynamics and BBB integrity. We found that ROS and mitochondrial superoxide production were elevated in PAs isolated from old DM rats and in high glucose (HG)-treated α-smooth muscle actin-positive pericytes. HG-treated pericytes displayed decreased contractile capability in association with diminished mitochondrial respiration and ATP production. Additionally, the expression of advanced glycation end products, transforming growth factor-β, vascular endothelial growth factor, and fibronectin were enhanced, but claudin 5 and integrin β1 was reduced in the brain of old DM rats and HG-treated pericytes. Further, endothelial tight junction and pericyte coverage on microvessels were reduced in the cortex of old DM rats. These results demonstrate our previous findings that the impaired cerebral hemodynamics and BBB leakage and cognitive impairments in the same old DM model are associated with hyperglycemia-induced cerebrovascular pericyte dysfunction.NEW & NOTEWORTHY This study demonstrates that the loss of contractile capability in pericytes in diabetes is associated with enhanced ROS and reduced ATP production. Enhanced advanced glycation end products (AGEs) in diabetes accompany with reduced pericyte and endothelial tight junction coverage in the cortical capillaries of old diabetic rats. These results suggest our previous findings that the impaired cerebral hemodynamics, BBB leakage, and cognitive impairments in old DM model are associated with hyperglycemia-induced cerebrovascular pericyte dysfunction.

Shedding Light on the Effects of Moderate Acute Exercise on Working Memory Performance in Healthy Older Adults: An fNIRS Study

Numerous studies have reported the beneficial effects of acute exercise on executive functions. Less is known, however, about the effects of exercise on working memory as one subcomponent of executive functions and about its effects on older adults. We investigated the effects of acute moderate-intensity exercise on working memory performance, the respective cortical hemodynamic activation patterns, and the development and persistence of such effects in healthy older adults. Forty-four participants (M: 69.18 years ± 3.92; 21 females) performed a letter 2-back task before and at three time points after (post 15 min, post 30 min, and post 45 min) either listening to an audiobook or exercising (15 min; 50% VO2-peak). Functional near-infrared spectroscopy (fNIRS) was used to assess cortical hemodynamic activation and brain-behavior correlations in the fronto-parietal working memory network. Overall, we found no group differences for working memory performance. However, only within the experimental group, 2-back performance was enhanced 15 min and 45 min post-exercise. Furthermore, 15 min post-exercise frontal activation predicted working memory performance, regardless of group. In sum, our results indicate slight beneficial effects of acute moderate-intensity exercise on working memory performance in healthy older adults. Findings are discussed in light of the cognitive aging process and moderators affecting the exercise-cognition relationship.

Aerobic exercise increases sprouting angiogenesis in the male rat motor cortex

Exercise is beneficial to brain health, and historically, the advantageous effects of exercise on the brain have been attributed to neuronal plasticity. However, it has also become clear that the brain vascular system also exhibits plasticity in response to exercise. This plasticity occurs in areas involved in movement, such as the motor cortex. This experiment aimed to further characterize the effects of exercise on structural vascular plasticity in the male rat motor cortex, by specifically identifying whether features of angiogenesis, the growth of new capillaries, or changes in vessel diameter were present. Male rats in the exercise group engaged in a 5-week bout of voluntary wheel running, while a second group of rats remained sedentary. After the exercise regimen, vascular corrosion casts, resin replicas of the brain vasculature, were made for all animals and imaged using a scanning electron microscope. Results indicate sprouting angiogenesis was the primary form of structural vascular plasticity detected in the motor cortex under these aerobic exercise parameters. Additionally, exercised rats displayed a slight increase in capillary diameter and expanded endothelial cell nuclei diameters in this region.

Nuances in Alzheimer's Genetic Risk Reveal Differential Predictions of Non-demented Memory Aging Trajectories: Selective Patterns by APOE Genotype and Sex

BACKGROUND

Apolipoprotein E (APOE) is a prominent genetic risk factor for Alzheimer's disease (AD) and a frequent target for associations with non-demented and cognitively impaired aging. APOE offers a unique opportunity to evaluate two dichotomous comparisons and selected gradations of APOE risk. Some evidence suggests that APOE effects may differ by sex and emerge especially in interaction with other AD-related biomarkers (e.g., vascular health).

METHODS

Longitudinal trajectories of non-demented adults (n = 632, 67% female, Mage = 68.9) populated a 40-year band of aging. Focusing on memory performance and individualized memory trajectories, a sequence of latent growth models was tested for predictions of (moderation between) APOE and pulse pressure (PP) as stratified by sex. The analyses (1) established robust benchmark PP effects on memory trajectories, (2) compared predictions of alternative dichotomous groupings (ε4- vs ε4+, ε2- vs ε2+), and (3) examined precision-based predictions by disaggregated APOE genotypes.

RESULTS

Healthier (lower) PP was associated with better memory performance and less decline. Therefore, all subsequent analyses were conducted in the interactive context of PP effects and sex stratification. The ε4-based dichotomization produced no differential genetic predictions. The ε2-based analyses showed sex differences, including selective protection for ε2-positive females. Exploratory follow-up disaggregated APOE genotype analyses suggested selective ε2 protection effects for both homozygotic and heterozygotic females.

CONCLUSION

Precision analyses of AD genetic risk will advance the understanding of underlying mechanisms and improve personalized implementation of interventions.

Sleep, brain vascular health and ageing

Sleep maintains the function of the entire body through homeostasis. Chronic sleep deprivation (CSD) is a prime health concern in the modern world. Previous reports have shown that CSD has profound negative effects on brain vasculature at both the cellular and molecular levels, and that this is a major cause of cognitive dysfunction and early vascular ageing. However, correlations among sleep deprivation (SD), brain vascular changes and ageing have barely been looked into. This review attempts to correlate the alterations in the levels of major neurotransmitters (acetylcholine, adrenaline, GABA and glutamate) and signalling molecules (Sirt1, PGC1α, FOXO, P66^shc, PARP1) in SD and changes in brain vasculature, cognitive dysfunction and early ageing. It also aims to connect SD-induced loss in the number of dendritic spines and their effects on alterations in synaptic plasticity, cognitive disabilities and early vascular ageing based on data available in scientific literature. To the best of our knowledge, this is the first article providing a pathophysiological basis to link SD to brain vascular ageing.

Early Onset of Sex-Dependent Mitochondrial Deficits in the Cortex of 3xTg Alzheimer's Mice

Alzheimer’s disease (AD) is a major public health concern worldwide. Advanced age and female sex are two of the most prominent risk factors for AD. AD is characterized by progressive neuronal loss, especially in the cortex and hippocampus, and mitochondrial dysfunction has been proposed to be an early event in the onset and progression of the disease. Our results showed early perturbations in mitochondrial function in 3xTg mouse brain, with the cortex being more susceptible to mitochondrial changes than the hippocampus. In the cortex of 3xTg females, decreased coupled and uncoupled respiration were evident early (at 2 months of age), while in males it appeared later at 6 months of age. We observed increased coupled respiration in the hippocampus of 2-month-old 3xTg females, but no changes were detected later in life. Changes in mitochondrial dynamics were indicated by decreased mitofusin (Mfn2) and increased dynamin related protein 1 (Drp1) (only in females) in the hippocampus and cortex of 3xTg mice. Our findings highlight the importance of controlling and accounting for sex, brain region, and age in studies examining brain bioenergetics using this common AD model in order to more accurately evaluate potential therapies and improve the sex-specific translatability of preclinical findings.

Age- and sex-dependent changes in levels of circulating brain-enriched microRNAs during normal aging

Aging is a major risk factor for many common and life-threatening pathologies. The development of reliable biomarkers of aging should lead to a better understanding of aging-associated processes and facilitate the development of therapeutic regimens that delay aging. Levels of 38 brain-enriched microRNAs (miRNA) circulating in plasma were measured by quantitative RT-PCR in two age groups: 26-35 and 56-65 years old. An miRNA-pair approach was used for data normalization and determination of effective miRNA biomarker ratios. Nineteen miRNAs, comprising miRNA pairs and pair combinations (classifiers) that effectively differentiated the age and sex (individual pairs: 74-95% and 68-95%, respectively; classifiers: up to 100% accuracy) groups, were selected for further analysis of plasma samples from 5 donor age groups: 26-35, 36-45, 46-55, 56-65 and 66-75 years old. Dynamic changes in the plasma concentrations of certain miRNAs occurred at different ages in females and males, with peaks in the 46-55-year-old and 56-65-year-old groups, respectively. This finding suggests that the changes in miRNA levels can reflect centrally regulated processes, including changes in hormone levels during menopause. Certain miRNAs and miRNA pairs correlated with age in the sex-stratified groups at different ages and should be investigated further as potentially promising biomarkers of brain aging.

Stromal Cell-Derived Factor 1 Protects Brain Vascular Endothelial Cells from Radiation-Induced Brain Damage

Stromal cell-derived factor 1 (SDF-1) and its main receptor, CXC chemokine receptor 4 (CXCR4), play a critical role in endothelial cell function regulation during cardiogenesis, angiogenesis, and reendothelialization after injury. The expression of CXCR4 and SDF-1 in brain endothelial cells decreases due to ionizing radiation treatment and aging. SDF-1 protein treatment in the senescent and radiation-damaged cells reduced several senescence phenotypes, such as decreased cell proliferation, upregulated p53 and p21 expression, and increased senescence-associated beta-galactosidase (SA-β-gal) activity, through CXCR4-dependent signaling. By inhibiting extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription protein 3 (STAT3), we confirmed that activation of both is important in recovery by SDF-1-related mechanisms. A CXCR4 agonist, ATI2341, protected brain endothelial cells from radiation-induced damage. In irradiation-damaged tissue, ATI2341 treatment inhibited cell death in the villi of the small intestine and decreased SA-β-gal activity in arterial tissue. An ischemic injury experiment revealed no decrease in blood flow by irradiation in ATI2341-administrated mice. ATI2341 treatment specifically affected CXCR4 action in mouse brain vessels and partially restored normal cognitive ability in irradiated mice. These results demonstrate that SDF-1 and ATI2341 may offer potential therapeutic approaches to recover tissues damaged during chemotherapy or radiotherapy, particularly by protecting vascular endothelial cells.

The extracellular matrix of the blood-brain barrier: structural and functional roles in health, aging, and Alzheimer's disease

There is increasing interest in defining the location, content, and role of extracellular matrix (ECM) components in brain structure and function during development, aging, injury, and neurodegeneration. Studies in vivo confirm brain ECM has a dynamic composition with constitutive and induced alterations that impact subsequent cell-cell and cell-matrix interactions. Moreover, it is clear that for any given ECM component, the brain region, and cell type within that location, determines the direction, magnitude, and composition of those changes. This review will examine the ECM at the neurovascular unit (NVU) and the blood-brain barrier (BBB) within the NVU. The discussion will begin at the glycocalyx ECM on the luminal surface of the vasculature, and progress to the abluminal side with a focus on changes in basement membrane ECM during aging and neurodegeneration.

Imaging the aged brain: pertinence and methods

The global population is ageing at an accelerating speed. The ability to perform working memory tasks together with rapid processing becomes increasingly difficult with increases in age. With increasing national average life spans and a rise in the prevalence of age-related disease, it is pertinent to discuss the unique perspectives that can be gained from imaging the aged brain. Differences in structure, function, blood flow, and neurovascular coupling are present in both healthy aged brains and in diseased brains and have not yet been explored to their full depth in contemporary imaging studies. Imaging methods ranging from optical imaging to magnetic resonance imaging (MRI) to newer technologies such as photoacoustic tomography each offer unique advantages and challenges in imaging the aged brain. This paper will summarize first the importance and challenges of imaging the aged brain and then offer analysis of potential imaging modalities and their representative applications. The potential breakthroughs in brain imaging are also envisioned.

Beta-blockers and salbutamol limited emotional memory disturbance and damage induced by orchiectomy in the rat hippocampus

AIM

To evaluate the therapeutic potential of ligands of beta-adrenoceptors in cognitive disorders. Testosterone and adrenergic pathways are involved in hippocampal and emotional memory. Moreover, is strongly suggested that androgen diminishing in aging is involved in cognitive deficit, as well as beta-adrenoceptors, particularly beta2-adrenoceptor, participate in the adrenergic modulation of memory. In this regard, some animal models of memory disruption have shown improved performance after beta-drug administration.

MATERIAL AND METHODS

In this work, we evaluated the effects of agonists (isoproterenol and salbutamol) and antagonists (propranolol and carvedilol) on beta-adrenoceptors in orchiectomized rats, as well as their effects in the performance on avoidance task and damage in hippocampal neurons by immunohistochemistry assays.

KEY FINDINGS

Surprisingly, we found that both antagonists and salbutamol (but not isoproterenol) modulate the effects of hormone deprivation, improving memory and decreasing neuronal death and amyloid-beta related changes in some regions (particularly CA1-3 and dentate gyrus) of rat hippocampus.

SIGNIFICANCE

Two β-antagonists and one β2-agonist modulated the effects of hormone deprivation on memory and damage in brain. The mechanisms of signaling of these drugs for beneficial effects remain unclear, even if used β-ARs ligands share a weak activity on β-arrestin/ERK-pathway activation which can be involved in these effects as we proposed in this manuscript. Our observations could be useful for understanding effects suggested of adrenergic drugs to modulate emotional memory. But also, our results could be related to other pathologies involving neuronal death and Aβ accumulation.

Dysregulation of the SNARE-binding protein Munc18-1 impairs BDNF secretion and synaptic neurotransmission: a novel interventional target to protect the aging brain

Brain-derived neurotrophic factor (BDNF) has a central role in maintaining and strengthening neuronal connections and to stimulate neurogenesis in the adult brain. Decreased levels of BDNF in the aging brain are thought to usher cognitive impairment. BDNF is stored in dense core vesicles and released through exocytosis from the neurites. The exact mechanism for the regulation of BDNF secretion is not well understood. Munc18-1 (STXBP1) was found to be essential for the exocytosis of synaptic vesicles, but its involvement in BDNF secretion is not known. Interestingly, neurons lacking munc18-1 undergo severe degeneration in knock-out mice. Here, we report the effects of BDNF treatment on the presynaptic terminal using munc18-1-deficient neurons. Reduced expression of munc18-1 in heterozygous (+/-) neurons diminishes synaptic transmitter release, as tested here on individual synaptic connections with FM1-43 fluorescence imaging. Transduction of cultured neurons with BDNF markedly increased BDNF secretion in wild-type but was less effective in munc18-1 +/- cells. In turn, BDNF enhanced synaptic functions and restored the severe synaptic dysfunction induced by munc18-1 deficiency. The role of munc18-1 in the synaptic effect of BDNF is highlighted by the finding that BDNF upregulated the expression of munc18-1 in neurons, consistent with enhanced synaptic functions. Accordingly, this is the first evidence showing the functional effect of BDNF in munc18-1 deficient synapses and about the direct role of munc18-1 in the regulation of BDNF secretion. We propose a molecular model of BDNF secretion and discuss its potential as therapeutic target to prevent cognitive decline in the elderly.

Icariin Delays Brain Aging in Senescence-Accelerated Mouse Prone 8 (SAMP8) Model via Inhibiting Autophagy

Icariin (ICA), a major flavonoid extracted from the Chinese tonic herb Epimedium, exerts beneficial effects in a variety of age-dependent diseases, such as Alzheimer's disease (AD). However, the antiaging mechanisms remain unclear. The senescence-accelerated mouse-prone 8 (SAMP8) model has been used to study age-related neurodegenerative changes associated with aging and the pathogenesis of AD. Hence, the current study was designed to examine the effect of ICA on age-related cognitive decline in SAMP8 mice and explore the role of autophagy in the ICA-mediated neuroprotection. SAMP8 mice were administered with ICA starting at 5 months of age, and the treatment lasted for 3 consecutive months. Morris water maze was used to evaluate cognitive function. The senescence-associated β-galactosidase staining was used to determine the number of senescence cells. The neuronal morphologic changes were examined via Nissl staining. The hippocampal neuronal ultrastructure was examined by transmission electron microscopy. The expression of autophagy protein was examined by Western blot. ICA-treated SAMP8 mice exhibited a robust improvement in spatial learning and memory function. Meanwhile, ICA reduced the number of senescence cells in the brains of SAMP8 mice, inhibited neuronal loss, and reversed neuronal structural changes in the hippocampi of SAMP8 mice. Moreover, ICA treatment also decreased the formation of autophagosomes in the hippocampus of SAMP8 mice, and reduced the expression of autophagy-related proteins LC3-II and p62. These results demonstrate that ICA possesses the ability to delay brain aging in SAMP8 mice, and the mechanisms are possibly mediated through the regulation of autophagy.

Caloric restriction and redox homeostasis in various regions of aging male rat brain: Is caloric restriction still worth trying even after early-adulthood?: Redox homeostasis and caloric restriction in brain

Despite recent studies have shown that caloric restriction (CR) could improve some functional loss associated with brain aging, the biochemical effects of CR on brain aging are still not well understood on a quantifiable biochemical basis, including whether CR could be protective when started around middle adulthood, when age-related neurodegenerative diseases are thought to set in. Therefore, in the light of more than ever aging societies and increasing neurodegenerative diseases, we aimed to test the biochemical effects of CR on redox homeostasis in different parts of male Sprague-Dawley rat brain by using the biomarkers we consistently validated in our previous work (TOS, PCO, AOPP, AGEs, sRAGE, P-SH, LHPs, 4-HNE, TAS, Cu, Zn-SOD). Our results indicate that oxidative stress biomarkers are lower in CR group, implying a more favorable redox status that has been previously shown to be correlated with better neural function. PRACTICAL APPLICATIONS: We report that the beneficial effects of caloric restriction (CR) on various brain tissues result in significant improvements in biochemical markers, even though CR is not started in early adulthood. Hence, our select age group provides a sound redox status-related neurochemical understanding for many recent CR studies, where a functional loss was detected at this age.

Phenolic Compounds Characteristic of the Mediterranean Diet in Mitigating Microglia-Mediated Neuroinflammation

Neuroinflammation is a pathological feature of quite a number of Central Nervous System diseases such as Alzheimer and Parkinson's disease among others. The hallmark of brain neuroinflammation is the activation of microglia, which are the immune resident cells in the brain and represents the first line of defense when injury or disease occur. Microglial activated cells can adopt different phenotypes to carry out its diverse functions. Thus, the shift into pro-inflammatory/neurotoxic or anti-inflammatory/neuroprotective phenotypes, depending of the brain environment, has totally changed the understanding of microglia in neurodegenerative disease. For this reason, novel therapeutic strategies which aim to modify the microglia polarization are being developed. Additionally, the understanding of how nutrition may influence the prevention and/or treatment of neurodegenerative diseases has grown greatly in recent years. The protective role of Mediterranean diet (MD) in preventing neurodegenerative diseases has been reported in a number of studies. The Mediterranean dietary pattern includes as distinctive features the moderate intake of red wine and extra virgin olive oil, both of them rich in polyphenolic compounds, such as resveratrol, oleuropein and hydroxytyrosol and their derivatives, which have demonstrated anti-inflammatory effects on microglia on in vitro studies. This review summarizes our understanding of the role of dietary phenolic compounds characteristic of the MD in mitigating microglia-mediated neuroinflammation, including explanation regarding their bioavailability, metabolism and blood-brain barrier.

The Effects of Normal Aging on Regional Accumulation of Hyaluronan and Chondroitin Sulfate Proteoglycans in the Mouse Brain

The brain changes in volume and composition with normal aging. Cellular components of the brain are supported by an extracellular matrix (ECM) comprised largely of hyaluronan (HA) and HA-associated members of the lectican family of chondroitin sulfate proteoglycans (CSPGs). We examined regional differences in microvascular density, neuronal and glial markers, and accumulation of HA and CSPGs in mouse brains during normal aging. The cortex, hippocampus, dentate gyrus, and cerebellum of young (4 months), middle-aged (14 months), and aged (24-26 months) brains were analyzed. Microvascular density decreased in cerebral cortex and cerebellum with age. There were no detectable differences in neuronal density. There was an increase in astrocytes in the hippocampus with aging. HA accumulation was higher in aged brain relative to young brain in the cerebral cortex and cerebellum, but not in other regions examined. In contrast, CSPGs did not change with aging in any of the brain regions examined. HA and CSPGs colocalized with a subset of neuronal cell bodies and astrocytes, and at the microvasculature. Differences in accumulation of ECM in the aging brain, in the setting of decreased microvascular density and/or increased glial activation, might contribute to age-related regional differences in vulnerability to injury and ischemia.

NKCC1 Inhibition Attenuates Chronic Cerebral Hypoperfusion-Induced White Matter Lesions by Enhancing Progenitor Cells of Oligodendrocyte Proliferation

Cerebral white matter is vulnerable to ischemic condition. However, no effective treatment to alleviate or restore the myelin damage caused by chronic cerebral hypoperfusion has been found. Na⁺-K⁺-Cl^- cotransporter 1 (NKCC1), a Na⁺-K⁺-Cl^- cotransporter widely expressed in the central nervous system (CNS), involves in regulation of cell swelling, EAA release, cell apoptosis, and proliferation. Nevertheless, the role of NKCC1 in chronic hypoperfusion-induced white matter lesions (WMLs) has not been explored. Here, mice subjected to bilateral common carotid artery stenosis (BCAS) were used as model of chronic cerebral hypoperfusion; density of progenitor cells of oligodendrocyte (OPCs), oligodendrocytes (OLs), astrocytes, and microglia was assessed by immunofluorescent staining and Western blot analysis; working memory was examined by eight-arm radial maze test; expression of MAPK signaling pathway was determined by Western blot analysis. After BCAS, white matter integrity disruption and working memory impairment were observed. NKCC1 inhibition by bumetanide administration enhanced OPC proliferation, attenuated chronic hypoperfusion-induced white matter damage, and promoted recovery of neurological function. However, NKCC1 inhibition caused no significant change in the densities of GFAP- and Iba-1-positive cells in the corpus callosum. Bumetanide administration significantly increased the expression of p-ERK and decreased the expression of p-JNK and p-p38 in comparison to vehicle-BCAS groups. In conclusion, NKCC1 inhibition might significantly ameliorate chronic cerebral hypoperfusion-induced WMLs and cognitive impairment by enhancing progenitor cells of oligodendrocyte proliferation, and this protective function of bumetanide might be mediated by modulation of the MAPK signaling pathway.

Recent progress in translational research on neurovascular and neurodegenerative disorders

The already established and widely used intravenous application of recombinant tissue plasminogen activator as a re-opening strategy for acute vessel occlusion in ischemic stroke was recently added by mechanical thrombectomy, representing a fundamental progress in evidence-based medicine to improve the patient’s outcome. This has been paralleled by a swift increase in our understanding of pathomechanisms underlying many neurovascular diseases and most prevalent forms of dementia. Taken together, these current advances offer the potential to overcome almost two decades of marginally successful translational research on stroke and dementia, thereby spurring the entire field of translational neuroscience. Moreover, they may also pave the way for the renaissance of classical neuroprotective paradigms.

This review reports and summarizes some of the most interesting and promising recent achievements in neurovascular and dementia research. It highlights sessions from the 9th International Symposium on Neuroprotection and Neurorepair that have been discussed from April 19th to 22nd in Leipzig, Germany. To acknowledge the emerging culture of interdisciplinary collaboration and research, special emphasis is given on translational stories ranging from fundamental research on neurode- and -regeneration to late stage translational or early stage clinical investigations.

Polyphenols journey through blood-brain barrier towards neuronal protection

Age-related complications such as neurodegenerative disorders are increasing and remain cureless. The possibility of altering the progression or the development of these multifactorial diseases through diet is an emerging and attractive approach with increasing experimental support. We examined the potential of known bioavailable phenolic sulfates, arising from colonic metabolism of berries, to influence hallmarks of neurodegenerative processes. In silico predictions and in vitro transport studies across blood-brain barrier (BBB) endothelial cells, at circulating concentrations, provided evidence for differential transport, likely related to chemical structure. Moreover, endothelial metabolism of these phenolic sulfates produced a plethora of novel chemical entities with further potential bioactivies. Pre-conditioning with phenolic sulfates improved cellular responses to oxidative, excitotoxicity and inflammatory injuries and this attenuation of neuroinflammation was achieved via modulation of NF-κB pathway. Our results support the hypothesis that these small molecules, derived from dietary (poly)phenols may cross the BBB, reach brain cells, modulate microglia-mediated inflammation and exert neuroprotective effects, with potential for alleviation of neurodegenerative diseases.

Internet Searches and Their Relationship to Cognitive Function in Older Adults: Cross-Sectional Analysis

BACKGROUND

Alzheimer disease (AD) is a very challenging experience for all those affected. Unfortunately, detection of Alzheimer disease in its early stages when clinical treatments may be most effective is challenging, as the clinical evaluations are time-consuming and costly. Recent studies have demonstrated a close relationship between cognitive function and everyday behavior, an avenue of research that holds great promise for the early detection of cognitive decline. One area of behavior that changes with cognitive decline is language use. Multiple groups have demonstrated a close relationship between cognitive function and vocabulary size, verbal fluency, and semantic ability, using conventional in-person cognitive testing. An alternative to this approach which is inherently ecologically valid may be to take advantage of automated computer monitoring software to continually capture and analyze language use while on the computer.

OBJECTIVE

The aim of this study was to understand the relationship between Internet searches as a measure of language and cognitive function in older adults. We hypothesize that individuals with poorer cognitive function will search using fewer unique terms, employ shorter words, and use less obscure words in their searches.

METHODS

Computer monitoring software (WorkTime, Nestersoft Inc) was used to continuously track the terms people entered while conducting searches in Google, Yahoo, Bing, and Ask.com. For all searches, punctuation, accents, and non-ASCII characters were removed, and the resulting search terms were spell-checked before any analysis. Cognitive function was evaluated as a z-normalized summary score capturing five unique cognitive domains. Linear regression was used to determine the relationship between cognitive function and Internet searches by controlling for variables such as age, sex, and education.

RESULTS

Over a 6-month monitoring period, 42 participants (mean age 81 years [SD 10.5], 83% [35/42] female) conducted 2915 searches using these top search engines. Participants averaged 3.08 words per search (SD 1.6) and 5.77 letters per word (SD 2.2). Individuals with higher cognitive function used more unique terms per search (beta=.39, P=.002) and employed less common terms in their searches (beta=1.39, P=.02). Cognitive function was not significantly associated with the length of the words used in the searches.

CONCLUSIONS

These results suggest that early decline in cognitive function may be detected from the terms people search for when they use the Internet. By continuously tracking basic aspects of Internet search terms, it may be possible to detect cognitive decline earlier than currently possible, thereby enabling proactive treatment and intervention.

Proinsulin protects against age-related cognitive loss through anti-inflammatory convergent pathways

Brain inflammaging is increasingly considered as contributing to age-related cognitive loss and neurodegeneration. Despite intensive research in multiple models, no clinically effective pharmacological treatment has been found yet. Here, in the mouse model of brain senescence SAMP8, we tested the effects of proinsulin, a promising neuroprotective agent that was previously proven to be effective in mouse models of retinal neurodegeneration. Proinsulin is the precursor of the hormone insulin but also upholds developmental physiological effects, particularly as a survival factor for neural cells. Adeno-associated viral vectors of serotype 1 bearing the human proinsulin gene were administered intramuscularly to obtain a sustained release of proinsulin into the blood stream, which was able to reach the target area of the hippocampus. SAMP8 mice and the control strain SAMR1 were treated at 1 month of age. At 6 months, behavioral testing exhibited cognitive loss in SAMP8 mice treated with the null vector. Remarkably, the cognitive performance achieved in spatial and recognition tasks by SAMP8 mice treated with proinsulin was similar to that of SAMR1 mice. In the hippocampus, proinsulin induced the activation of neuroprotective pathways and the downstream signaling cascade, leading to the decrease of neuroinflammatory markers. Furthermore, the decrease of astrocyte reactivity was a central effect, as demonstrated in the connectome network of changes induced by proinsulin. Therefore, the neuroprotective effects of human proinsulin unveil a new pharmacological potential therapy in the fight against cognitive loss in the elderly.

Microvasculature of the Mouse Cerebral Cortex Exhibits Increased Accumulation and Synthesis of Hyaluronan With Aging

The microvasculature of the aged brain is less dense and more vulnerable to dysfunction than that of the young brain. Brain microvasculature is supported by its surrounding extracellular matrix, which is comprised largely of hyaluronan (HA). HA is continually degraded into lower molecular weight forms that induce neuroinflammation. We examined HA associated with microvessels (MV) of the cerebral cortex of young (4 months), middle-aged (14 months), and aged (24-26 months) mice. We confirmed that the density of cortical MV decreased with age. Perivascular HA levels increased with age, but there was no age-associated change in HA molecular weight profile. MV isolated from aged cortex had more HA than MV from young cortex. Examination of mechanisms that might account for elevated HA levels with aging showed increased HA synthase 2 (HAS2) mRNA and protein in aged MV relative to young MV. In contrast, mRNAs for HA-degrading hyaluronidases or hyaladherins that mitigate HA degradation showed no changes with age. Corresponding to increased HAS2, aged MV synthesized significantly more HA (of all molecular weight classes) in vitro than young MV. We propose that increased HA synthesis and accumulation in brain MV contributes to neuroinflammation and reduced MV density and function in aging.

Amyloid β Protein Aggravates Neuronal Senescence and Cognitive Deficits in 5XFAD Mouse Model of Alzheimer's Disease

BACKGROUND

Amyloid β (Aβ) has been established as a key factor for the pathological changes in the brains of patients with Alzheimer's disease (AD), and cellular senescence is closely associated with aging and cognitive impairment. However, it remains blurred whether, in the AD brains, Aβ accelerates the neuronal senescence and whether this senescence, in turn, impairs the cognitive function. This study aimed to explore the expression of senescence-associated genes in the hippocampal tissue from young to aged 5XFAD mice and their age-matched wild type (WT) mice to determine whether senescent neurons are present in the transgenic AD mouse model.

METHODS

The 5XFAD mice and age-matched wild type mice, both raised from 1 to 18 months, were enrolled in the study. The senescence-associated genes in the hippocampus were analyzed and differentially expressed genes (DEGs) were screened by quantitative real-time polymerase chain reaction. Cognitive performance of the mice was evaluated by Y-maze and Morris water maze tests. Oligomeric Aβ (oAβ) (1-42) was applied to culture primary neurons to simulate the in vivo manifestation. Aging-related proteins were detected by Western blotting analysis and immunofluorescence.

RESULTS

In 5XFAD mice, of all the DEGs, the senescence-associated marker p16 was most significantly increased, even at the early age. It was mainly localized in neurons, with a marginal expression in astrocytes (labeled as glutamine synthetase), nil expression in activated microglia (labeled as Iba1), and negatively correlated with the spatial cognitive impairments of 5XFAD mice. oAβ (1-42) induced the production of senescence-related protein p16, but not p53 in vitro, which was in line with the in vivo manifestation.

CONCLUSIONS

oAβ-accelerated neuronal senescence may be associated with the cognitive impairment in 5XFAD mice. Senescence-associated marker p16 can serve as an indicator to estimate the cognitive prognosis for AD population.

Cognitive Difficulty Intensifies Age-related Changes in Anterior Frontal Hemodynamics: Novel Evidence from Near-infrared Spectroscopy

Alongside age-related brain deterioration, cognitive functioning declines, particularly for more demanding tasks. Past research indicates that, to offset this decline, older adults exhibit hemodynamic changes consistent with recruitment of more anterior brain regions. However, the nature of the hemodynamic changes remains unclear. To address this knowledge gap, we used near-infrared spectroscopy in 36 young adults (aged 18-30 years) and 36 older adults (aged 60-72 years) to assess anterior frontal hemodynamic responses to engagement in three cognitive tasks of increasing difficulty. Behavioral results for all three tasks confirmed aging deficits (evidenced by slower reaction times and reduced accuracy rates) that progressively increased with task difficulty. Hemodynamic results showed opposing effects in young versus older adults, with oxygenated and total hemoglobin decreasing in young but increasing in older adults, particularly during the harder tasks. Also, tissue oxygenation increased only in older adults during the harder tasks. Among the older adults only, anterior frontal hemodynamic changes correlated with better cognitive performance, indicating that they were compensatory in nature. These findings provide novel evidence of age-related anterior frontal hemodynamic changes that intensify with cognitive demands and compensate for performance deficits.