Age-related decline of myelin proteins is highly correlated with activation of astrocytes and microglia in the rat CNS

Is age-related myelinodegenerative change an initial risk factor of neurodegenerative diseases?

Myelination, the continuous ensheathment of neuronal axons, is a lifelong process in the nervous system that is essential for the precise, temporospatial conduction of action potentials between neurons. Myelin also provides intercellular metabolic support to axons. Even minor disruptions in the integrity of myelin can impair neural performance and increase susceptibility to neurological diseases. In fact, myelin degeneration is a well-known neuropathological condition that is associated with normal aging and several neurodegenerative diseases, including multiple sclerosis and Alzheimer's disease. In the central nervous system, compact myelin sheaths are formed by fully mature oligodendrocytes. However, the entire oligodendrocyte lineage is susceptible to changes in the biological microenvironment and other risk factors that arise as the brain ages. In addition to their well-known role in action potential propagation, oligodendrocytes also provide intercellular metabolic support to axons by transferring energy metabolites and delivering exosomes. Therefore, myelin degeneration in the aging central nervous system is a significant contributor to the development of neurodegenerative diseases. Interventions that mitigate age-related myelin degeneration can improve neurological function in aging individuals. In this review, we investigate the changes in myelin that are associated with aging and their underlying mechanisms. We also discuss recent advances in understanding how myelin degeneration in the aging brain contributes to neurodegenerative diseases and explore the factors that can prevent, slow down, or even reverse age-related myelin degeneration. Future research will enhance our understanding of how reducing age-related myelin degeneration can be used as a therapeutic target for delaying or preventing neurodegenerative diseases.

High energy diet-induced prediabetic neuropathic pain is mediated by reduction of SIRT6 negative control of both spinal and peripheral neuroinflammation

Prediabetic neuropathic pain has been classified as peripheral neuropathic pain associated with polyneuropathy caused by impaired glucose tolerance or impaired fasting glucose, which is a preclinical stage and might develop type 2 diabetes mellitus. Our previous research highlighted that prediabetes is accompanied by dramatic bilateral mechanical hyperalgesia following high energy diet (HED) which results in myelin and axonal degenerations along somatosensory system. However, the pathogenic mechanisms underlying prediabetic neuropathic pain remain unclear. The nuclear sirtuin 6 (SIRT6) is a crucial deacetylase in the regulation of multiple cellular biological processes, such as DNA repair, genome stability, inflammation and metabolic homeostasis. In current study, we show that the expressions of SIRT6 were significantly decreased, while its downstream NF-κB and proinflammatory mediator IL-6 and IL-1β were significantly increased in both dorsal root ganglia (DRG) and spinal dorsal horn of rats with prediabetic neuropathic pain induced by HED. Moreover, siRNA-SIRT6 treatment induced a significant reduction in bilateral paw withdrawal mechanical thresholds, indicating that SIRT6 down-regulation contributed to prediabetic neuropathic pain induced by HED. Furthermore, it was also found that SIRT6 reduction induced the activation of HMGB1 via disinhibition of NF-κB in both DRG and spinal dorsal horn of prediabetic rats. In conclusion, prediabetic neuropathic pain is caused by SIRT6 reduction through upregulating HMGB1-RAGE signaling at both peripheral and spinal levels.

Fkbp5 gene deletion: Circadian rhythm profile and brain proteomics in aged mice

FKBP51, also known as FK506-binding protein 51, is a molecular chaperone and scaffolding protein with significant roles in regulating hormone signaling and responding to stress. Genetic variants in FKBP5, which encodes FKBP51, have been implicated in a growing number of neuropsychiatric disorders, which has spurred efforts to target FKBP51 therapeutically. However, the molecular mechanisms and sub-anatomical regions influenced by FKBP51 in these disorders are not fully understood. In this study, we aimed to examine the impact of Fkbp5 ablation using circadian phenotyping and molecular analyses. Our findings revealed that the lack of FKBP51 did not significantly alter circadian rhythms, as detected by wheel-running activity, but did offer protection against stress-mediated disruptions in rhythmicity in a sex-dependent manner. Protein changes in Fkbp5 KO mice, as measured by histology and proteomics, revealed alterations in a brain region- and sex-dependent manner. Notably, regardless of sex, aged Fkbp5 KOs showed elevated MYCBP2, FBXO45, and SPRYD3 levels, which are associated with neuronal-cell adhesion and synaptic integrity. Additionally, pathways such as serotonin receptor signaling and S100 family signaling were differentially regulated in Fkbp5 KO mice. Weighted protein correlation network analysis identified protein networks linked with synaptic transmission and neuroinflammation. The information generated by this work can be used to better understand the molecular changes in the brain during aging and in the absence of Fkbp5, which has implications for the continued development of FKBP51-focused therapeutics for stress-related disorders.

The influence of aging and the microbiome in multiple sclerosis and other neurologic diseases

The human gut microbiome is well-recognized as a key player in maintaining health. However, it is a dynamic entity that changes across the lifespan. How the microbial changes that occur in later decades of life shape host health or impact age-associated inflammatory neurological diseases such as multiple sclerosis (MS) is still unclear. Current understanding of the aging gut microbiome is largely limited to cross-sectional observational studies. Moreover, studies in humans are limited by confounding host-intrinsic and extrinsic factors that are not easily disentangled from aging. This review provides a comprehensive summary of existing literature on the aging gut microbiome and its known relationships with neurological diseases, with a specific focus on MS. We will also discuss preclinical animal models and human studies that shed light on the complex microbiota-host interactions that have the potential to influence disease pathology and progression in aging individuals. Lastly, we propose potential avenues of investigation to deconvolute features of an aging microbiota that contribute to disease, or alternatively promote health in advanced age.

Proteomic signature profiling in the cortex of dairy cattle unravels the physiology of brain aging

Introduction

Aging is a physiological process occurring in all living organisms. It is characterized by a progressive deterioration of the physiological and cognitive functions of the organism, accompanied by a gradual impairment of mechanisms involved in the regulation of tissue and organ homeostasis, thus exacerbating the risk of developing pathologies, including cancer and neurodegenerative disorders.

Methods

In the present work, for the first time, the influence of aging has been investigated in the brain cortex of the Podolica cattle breed, through LC-MS/MS-based differential proteomics and the bioinformatic analysis approach (data are available via ProteomeXchange with identifier PXD044108), with the aim of identifying potential aging or longevity markers, also associated with a specific lifestyle.

Results and discussion

We found a significant down-regulation of proteins involved in cellular respiration, dendric spine development, synaptic vesicle transport, and myelination. On the other hand, together with a reduction of the neurofilament light chain, we observed an up-regulation of both GFAP and vimentin in the aged samples. In conclusion, our data pave the way for a better understanding of molecular mechanisms underlying brain aging in grazing cattle, which could allow strategies to be developed that are aimed at improving animal welfare and husbandry practices of dairy cattle from intensive livestock.

Aging compromises oligodendrocyte precursor cell maturation and efficient remyelination in the monkey brain

Age-associated cognitive decline is common among otherwise healthy elderly people, even in the absence of Alzheimer's disease and neuron loss. Instead, white matter loss and myelin damage are strongly associated with cognitive decline. Myelin is subject to lifelong oxidative stress that damages the myelin sheath, which is repaired by cells of the oligodendrocyte lineage. This process is mediated by oligodendrocyte precursor cells (OPCs) that sense the damage and respond by proliferating locally and migrating to the region, where they differentiate into mature myelinating oligodendrocytes. In aging, extensive myelin damage, in combination with inefficient remyelination, leads to chronically damaged myelin and loss of efficient neuronal conduction. This study used the rhesus monkey model of normal aging to examine how myelin regeneration capacity is affected by age. Results show that older subjects have reduced numbers of new BCAS1 + myelinating oligodendrocytes, which are newly formed cells, and that this reduction is associated with poorer cognitive performance. Interestingly, this does not result from limited proliferation of progenitor OPCs. Instead, the transcription factor NKX2.2, which regulates OPCs differentiation, is significantly decreased in aged OPCs. This suggests that these OPCs have a diminished potential for differentiation into mature oligodendrocytes. In addition, mature oligodendrocytes have reduced RNA expression of two essential myelin protein markers, MBP and PLP. These data collectively suggest that in the normal aging brain, there is a reduction in regenerative OPCs as well as myelin production that impairs the capacity for remyelination.

Pharmacologic agents directed at the treatment of pain associated with maladaptive neuronal plasticity

INTRODUCTION

The definition of nociplastic pain in 2016 has changed the way maladaptive chronic pain is viewed in that it may emerge without neural lesions or neural disease. Many endogenous and pharmacologic substances are being investigated for their role in treating the pain associated with neuronal plasticity.

AREAS COVERED

The authors review promising pharmacologic agents for the treatment of pain associated with maladaptive neuronal plasticity. The authors then provide the reader with their expert opinion and provide their perspectives for the future.

EXPERT OPINION

An imbalance between the amplification of ascending pain signals and the poor activation of descending inhibitory signals may be at the root of many chronic pain syndromes. The inhibitory activity of noradrenaline reuptake may play a role in neuropathic and nociplastic analgesia. A better understanding of the brain's pain matrix, its signaling cascades, and the complex bidirectional communication between the immune system and the nervous system may help meet the urgent and unmet medical need for safe, effective chronic pain treatment, particularly for pain with a neuropathic and/or nociplastic component.

Chronic Pain in the Elderly: Mechanisms and Distinctive Features

Background: Chronic pain is a major issue affecting more than 50% of the older population and up to 80% of nursing homes residents. Research on pain in the elderly focuses mainly on the development of clinical tools to assess pain in patients with dementia and cognitive impairment or on the efficacy and tolerability of medications. In this review, we searched for evidence of specific pain mechanisms or modifications in pain signals processing either at the cellular level or in the central nervous system. Methods: Narrative review. Results: Investigation on pain sensitivity led to conflicting results, with some studies indicating a modest decrease in age-related pain sensitivity, while other researchers found a reduced pain threshold for pressure stimuli. Areas of the brain involved in pain perception and analgesia are susceptible to pathological changes such as gliosis and neuronal death and the effectiveness of descending pain inhibitory mechanisms, particularly their endogenous opioid component, also appears to deteriorate with advancing age. Hyperalgesia is more common at older age and recovery from peripheral nerve injury appears to be delayed. In addition, peripheral nociceptors may contribute minimally to pain sensation at either acute or chronic time points in aged populations. Conclusions: Elderly subjects appear to be more susceptible to prolonged pain development, and medications acting on peripheral sensitization are less efficient. Pathologic changes in the central nervous system are responsible for different pain processing and response to treatment. Specific guidelines focusing on specific pathophysiological changes in the elderly are needed to ensure adequate treatment of chronic pain conditions.

Low field magnetic stimulation promotes myelin repair and cognitive recovery in chronic cuprizone mouse model

BACKGROUND

Multiple sclerosis (MS) is an inflammatory demyelinating disease featured with neuroinflammation, demyelination, and the loss of oligodendrocytes. Cognitive impairment and depression are common neuropsychiatric symptoms in MS that are poorly managed with the present interventions.

OBJECTIVE

This study aimed to investigate the effects of low field magnetic stimulation (LFMS), a novel non-invasive neuromodulation technology, on cognitive impairment and depressive symptoms associated with MS using a mouse model of demyelination.

METHODS

C57BL female mice were fed with a 0.2% cuprizone diet for 12 weeks to induce a chronic demyelinating model followed by 4 weeks of cuprizone withdrawal with either sham or LFMS treatment.

RESULTS

Improved cognition and depression-like behaviour and restored weight gain were observed in mice with LFMS treatment. Immunohistochemical and immunoblotting data showed enhanced myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein expressions (MOG) in the prefrontal cortex of mice with LFMS treatment, supporting that myelin repair was promoted. LFMS also increased the protein expression of mature oligodendrocyte biomarker glutathione-S-transferase (GST-π). In addition, expression of TGF-β and associated receptors were elevated with LFMS treatment, implicating this pathway in the response.

CONCLUSION

Results from the present study revealed LFMS to have neuroprotective effects, suggesting that LFMS has potential therapeutic value for treating cognitive impairment and depression related to demyelination disorders.

Extracellular vesicles derived from bone marrow mesenchymal stem cells enhance myelin maintenance after cortical injury in aged rhesus monkeys

Cortical injury, such as stroke, causes neurotoxic cascades that lead to rapid death and/or damage to neurons and glia. Axonal and myelin damage in particular, are critical factors that lead to neuronal dysfunction and impair recovery of function after injury. These factors can be exacerbated in the aged brain where white matter damage is prevalent. Therapies that can ameliorate myelin damage and promote repair by targeting oligodendroglia, the cells that produce and maintain myelin, may facilitate recovery after injury, especially in the aged brain where these processes are already compromised. We previously reported that a novel therapeutic, Mesenchymal Stem Cell derived extracellular vesicles (MSC-EVs), administered intravenously at both 24 h and 14 days after cortical injury, reduced microgliosis (Go et al. 2019), reduced neuronal pathology (Medalla et al. 2020), and improved motor recovery (Moore et al. 2019) in aged female rhesus monkeys. Here, we evaluated the effect of MSC-EV treatment on changes in oligodendrocyte maturation and associated myelin markers in the sublesional white matter using immunohistochemistry, confocal microscopy, stereology, qRT-PCR, and ELISA. Compared to vehicle control monkeys, EV-treated monkeys showed a reduction in the density of damaged oligodendrocytes. Further, EV-treatment was associated with enhanced myelin maintenance, evidenced by upregulation of myelin-related genes and increases in actively myelinating oligodendrocytes in sublesional white matter. These changes in myelination correlate with the rate of motor recovery, suggesting that improved myelin maintenance facilitates this recovery. Overall, our results suggest that EVs act on oligodendrocytes to support myelination and improves functional recovery after injury in the aged brain. SIGNIFICANCE: We previously reported that EVs facilitate recovery of function after cortical injury in the aged monkey brain, while also reducing neuronal pathology (Medalla et al. 2020) and microgliosis (Go et al. 2019). However, the effect of injury and EVs on oligodendrocytes and myelination has not been characterized in the primate brain (Dewar et al. 1999; Sozmen et al. 2012; Zhang et al. 2013). In the present study, we assessed changes in myelination after cortical injury in aged monkeys. Our results show, for the first time, that MSC-EVs support recovery of function after cortical injury by enhancing myelin maintenance in the aged primate brain.

Towards an understanding of women's brain aging: the immunology of pregnancy and menopause

Women are at significantly greater risk of developing Alzheimer's disease and show higher prevalence of autoimmune conditions relative to men. Women's brain health is historically understudied, and little is therefore known about the mechanisms underlying epidemiological sex differences in neurodegenerative diseases, and how female-specific factors may influence women's brain health across the lifespan. In this review, we summarize recent studies on the immunology of pregnancy and menopause, emphasizing that these major immunoendocrine transition phases may play a critical part in women's brain aging trajectories.

White Matter Alterations in Fmr1 Knockout Mice during Early Postnatal Brain Development

Fragile X syndrome (FXS) is the most commonly inherited form of intellectual disability ascribed to the autism spectrum disorder. Studies with FXS patients have reported altered white matter volume compared to controls. The Fmr1 knockout (KO) mouse, a model for FXS, showed evidence of delayed myelination during postnatal brain development. In this study, we examined several white matter regions in the male Fmr1 KO mouse brain compared to male wild-type (WT) mice at postnatal days (PND) 18, 21, 30, and 60, which coincide with critical stages of myelination and postnatal brain development. White matter volume, T2 relaxation time, and magnetization transfer ratio (MTR) were measured using magnetic resonance imaging and myelin content was determined with histological staining of myelin. Differences in the developmental accumulation of white matter and myelin between Fmr1 KO and WT mice were observed in the corpus callosum, external and internal capsules, cerebral peduncle, and fimbria. Alterations were more predominant in the external and internal capsules and fimbria of Fmr1 KO mice, where the MTR was lower at PND 18, then elevated at PND 30, and again lower at PND 60 compared to the corresponding regions in WT mice. The pattern of changes in MTR were similar to those observed in myelin staining and could be related to the altered protein synthesis that is a hallmark of FXS. While no significant changes in white matter volumes and T2 relaxation time between the Fmr1 KO and WT mice were observed, the altered pattern of myelin staining and MTR, particularly in the external capsule, reflecting the abnormalities associated with myelin content is suggestive of a developmental delay in the white matter of Fmr1 KO mouse brain. These early differences in white matter during critical developmental stages may contribute to altered brain networks in the Fmr1 KO mice.

Molecular changes associated with spinal cord aging

Age-related muscle weakness and loss of muscle mass (sarcopenia) is a universal problem in the elderly. Our previous studies indicate that alpha motor neurons (α-MNs) play a critical role in this process. The goal of the current study is to uncover changes in the aging spinal cord that contribute to loss of innervation and the downstream degenerative processes that occur in skeletal muscle. The number of α-MNs is decreased in the spinal cord of wildtype mice during aging, beginning in middle age and reaching a 41% loss by 27 months of age. There is evidence for age-related loss of myelin and mild inflammation, including astrocyte and microglia activation and an increase in levels of sICAM-1. We identified changes in metabolites consistent with compromised neuronal viability, such as reduced levels of N-acetyl-aspartate. Cleaved caspase-3 is more abundant in spinal cord from old mice, suggesting that apoptosis contributes to neuronal loss. RNA-seq analysis revealed changes in the expression of a number of genes in spinal cord from old mice, in particular genes encoding extracellular matrix components (ECM) and a 172-fold increase in MMP-12 expression. Furthermore, blood-spinal cord barrier (BSCB) permeability is increased in old mice, which may contribute to alterations in spinal cord homeostasis and exacerbate neuronal distress. Together, these data show for the first time that the spinal cord undergoes significant changes during aging, including progressive α-MNs loss that is associated with low-grade inflammation, apoptosis, changes in ECM, myelination, and vascular permeability.

FTY720-Mitoxy reduces synucleinopathy and neuroinflammation, restores behavior and mitochondria function, and increases GDNF expression in Multiple System Atrophy mouse models

Multiple system atrophy (MSA) is a fatal disorder with no effective treatment. MSA pathology is characterized by α-synuclein (aSyn) accumulation in oligodendrocytes, the myelinating glial cells of the central nervous system (CNS). aSyn accumulation in oligodendrocytes forms the pathognomonic glial cytoplasmic inclusions (GCIs) of MSA. MSA aSyn pathology is also associated with motor and autonomic dysfunction, including an impaired ability to sweat. MSA patients have abnormal CNS expression of glial-cell-line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF). Our prior studies using the parent compound FTY720, a food and drug administration (FDA) approved immunosuppressive for multiple sclerosis, reveal that FTY720 protects parkinsonian mice by increasing BDNF. Our FTY720-derivative, FTY720-Mitoxy, is known to increase expression of oligodendrocyte BDNF, GDNF, and nerve growth factor (NGF) but does not reduce levels of circulating lymphocytes as it is not phosphorylated so cannot modulate sphingosine 1 phosphate receptors (S1PRs). To preclinically assess FTY720-Mitoxy for MSA, we used mice expressing human aSyn in oligodendrocytes under a 2,' 3'-cyclic nucleotide 3'-phosphodiesterase (CNP) promoter. CNP-aSyn transgenic (Tg) mice develop motor dysfunction between 7 and 9 mo, and progressive GCI pathology. Using liquid chromatography-mass spectrometry (LC-MS/MS) and enzymatic assays, we confirmed that FTY720-Mitoxy was stable and active. Vehicle or FTY720-Mitoxy (1.1 mg/kg/day) was delivered to wild type (WT) or Tg littermates from 8.5-11.5 mo by osmotic pump. We behaviorally assessed their movement by rotarod and sweat production by starch‑iodine test. Postmortem tissues were evaluated by qPCR for BDNF, GDNF, NGF and GDNF-receptor RET mRNA and for aSyn, BDNF, GDNF, and Iba1 protein by immunoblot. MicroRNAs (miRNAs) were also assessed by qPCR. FTY720-Mitoxy normalized movement, sweat function and soleus muscle mass in 11.5 mo Tg MSA mice. FTY720-Mitoxy also increased levels of brain GDNF and reduced brain miR-96-5p, a miRNA that acts to decrease GDNF expression. Moreover, FTY720-Mitoxy blocked aSyn pathology measured by sequential protein extraction and immunoblot, and microglial activation assessed by immunohistochemistry and immunoblot. In the 3-nitropropionic acid (3NP) toxin model of MSA, FTY720-Mitoxy protected movement and mitochondria in WT and CNP-aSyn Tg littermates. Our data confirm potent in vivo protection by FTY720-Mitoxy, supporting its further evaluation as a potential therapy for MSA and related synucleinopathies.

FTY720 Improves Behavior, Increases Brain Derived Neurotrophic Factor Levels and Reduces α-Synuclein Pathology in Parkinsonian GM2+/- Mice

Parkinson's disease (PD) is a progressive aging disorder that affects millions worldwide, thus, disease-modifying-therapies are urgently needed. PD pathology includes α-synuclein (aSyn) accumulation as synucleinopathy. Loss of GM1 gangliosides occurs in PD brain, which is modeled in GM2 synthase transgenic mice. GM2+/- mice have low, not absent GM1 and develop age-onset motor deficits, making them an excellent PD drug testing model. FTY720 (fingolimod) reduces synucleinopathy in A53T aSyn mice and motor dysfunction in 6-OHDA and rotenone PD models, but no one has tested FTY720 in mice that develop age-onset PD-like motor problems. We confirmed that GM2+/-mice had equivalent rotarod, hindlimb reflexes, and adhesive removal functions at 9 mo. From 11 mo, GM2+/- mice received oral FTY720 or vehicle 3x/week to 16 mo. As bladder problems occur in PD, we also assessed GM2+/- bladder function. This allowed us to demonstrate improved motor and bladder function in GM2+/- mice treated with FTY720. By immunoblot, FTY720 reduced levels of proNGF, a biomarker of bladder dysfunction. In humans with PD, arm swing becomes abnormal, and brachial plexus modulates arm swing. Ultrastructure of brachial plexus in wild type and GM2 transgenic mice confirmed abnormal myelination and axons in GM2 transgenics. FTY720 treated GM2+/- brachial plexus sustained myelin associated protein levels and reduced aggregated aSyn and PSer129 aSyn levels. FTY720 increases brain derived neurotrophic factor (BDNF) and we noted increased BDNF in GM2+/- brachial plexus and cerebellum, which contribute to rotarod performance. These findings provide further support for testing low dose FTY720 in patients with PD.

Regional elevations in microglial activation and cerebral glucose utilization in frontal white matter tracts of rhesus monkeys following prolonged cocaine self-administration

It has been shown that exposure to cocaine can result in neuroinflammatory responses. Microglia, the resident CNS immune cells, undergo a transition to an activated state when challenged. In rodents, and possibly humans, cocaine exposure activates microglia. The goal of this study was to assess the extent and magnitude of microglial activation in rhesus monkeys with an extensive history of cocaine self-administration. Male rhesus monkeys (N = 4/group) were trained to respond on a fixed-interval 3-min schedule of food or 0.3 mg/kg/injection cocaine presentation (30 reinforcers/session) for 300 sessions. At the end of the final session, monkeys were administered 2-[¹⁴C]deoxyglucose intravenously and 45 min later euthanized. Brain sections were used for autoradiographic assessments of glucose utilization and for microglia activation with [³H]PK11195, a marker for the microglial 18-kDa translocator protein. There were no group differences in gray matter [³H]PK11195 binding, while binding was significantly greater in cocaine self-administration animals as compared to food controls in 8 of the 11 white matter tracts measured at the striatal level. Binding did not differ from control at other levels. There were also significant increases in white matter local cerebral glucose utilization at the striatal level, which were positively correlated with [³H]PK11195 binding. The present findings demonstrate an elevation in [³H]PK11195 binding in forebrain white matter tracts of nonhuman primates with a prolonged history of cocaine self-administration. These elevations were also associated with greater cerebral metabolic rates. These data suggest that white matter deficits may contribute to behavioral, motivational, and cognitive impairments observed in cocaine abusers.

Inflammation: Bridging Age, Menopause and APOEε4 Genotype to Alzheimer's Disease

Neuro-inflammatory processes that contribute to development of Alzheimer’s are evident early in the latent prodromal phase and worsen during the course of the disease. Despite substantial mechanistic and clinical evidence of inflammation, therapeutic approaches targeting inflammation have failed to alter the course of the disease. Disparate results from epidemiological and clinical trials targeting inflammation, highlight the complexity of the inflammatory process. Herein we review the dynamics of the inflammatory process across aging, midlife endocrine transitions, and the APOEε4 genotype and their contribution to progression of Alzheimer’s disease (AD). We discuss the chronic inflammatory processes that are activated during midlife chronological and endocrine aging, which ultimately limit the clearance capacity of microglia and lead to immune senescence. Aging, menopause, and APOEε4 combine the three hits of a compromised bioenergetic system of menopause with the chronic low grade innate inflammation of aging with the APOEε4 dyslipidemia and adaptive immune response. The inflammatory immune response is the unifying factor that bridges across each of the risk factors for AD. Immune system regulators that are specific to stage of disease and inflammatory phenotype would provide a therapeutic strategy to disconnect the bridge that drives disease. Outcomes of this analysis provide plausible mechanisms underlying failed clinical trials of anti-inflammatory agents in Alzheimer’s patients. Further, they highlight the need for stratifying AD clinical trial cohorts based on inflammatory phenotype. Combination therapies that include targeted use of anti-inflammatory agent’s specific to the immune phenotype are considered.

Long-term effects of curcumin in the non-human primate brain

Curcumin has recently been shown to be a potential treatment for slowing or ameloriating cognitive decline during aging in our nonhuman primate model of normal aging. In these same monkeys, we studied for the first time the neurological impacts of long-term curcumin treatments using longitudinal magnetic resonance imaging (MRI). Sixteen rhesus monkeys received curcumin or a vehicle control for 14-18 months. We applied a combination of structural and diffusion MRI to determine whether the curcumin resulted in structural or functional changes in focal regions of the brain. The longitudinal imaging revealed decreased microscale diffusivity (mD) measurements mainly in the hippocampus and basal forebrain structures of curcumin treated animals. Changes in generalized fractional anisotropy (GFA) and grey matter density (GMd) measurements indicated an increased grey matter density in cortical ROIs with improved white matter integrity in limbic, cerebellar, and brain stem regions. These findings suggest that noticeable changes in the neuronal environment could be induced from long-term curcumin treatments. Results may provide a neurological basis on the recent findings demonstrating improved spatial working memory and motor function in nonhuman primates.

Glial cell line-derived neurotrophic factor (GDNF) attenuates the peripheral neuromuscular dysfunction without inhibiting the activation of spinal microglia/monocyte

Background

Peripheral neuromuscular dysfunctions were found in elderly individuals, and spinal microglia/monocyte plays an important role on this process. This study aims to test whether the glial cell line-derived neurotrophic factor (GDNF) could attenuate age-related neuromuscular dysfunction by inhibiting the activation of spinal microglia/monocyte.

Methods

Male Sprague-Dawley rats were divided into an adult group and an aged group. The aged rats were intrathecally injected with normal saline (NS) and GDNF. All the rats were harvested 5 days after each injection. The muscular function was tested by compound muscle action potential, and the activation of microglia/monocyte was detected by immunofluorescence staining; cytokines were assayed by enzyme-linked immunosorbent assay; the expression level of GDNF and its known receptor GFR-α in the spinal cord, the expression level of neuregulin-1 (NRG-1) in the sciatic nerve, and the expression level of γ- and α7- ε-nicotinic acetylcholine receptors in the tibialis anterior muscle were measured by western blotting.

Results

The activated microglia/monocyte was found in the aged rats compared to the adult rats. The aged rats showed a significant neuromuscular dysfunction and cytokine release as well as increased expression of γ- and α7-nAChR. The protein expression of GDNF, GFR-α, and NRG-1 in the aged rats were significantly lower than that in the adult rats. However, the exogenous injection of GDNF could alleviate the neuromuscular dysfunction but not inhibit the activation of spinal microglia/monocyte. Furthermore, the levels of GFR-α and NRG-1 also increased after GDNF treatment.

Conclusion

The GDNF could attenuate the age-related peripheral neuromuscular dysfunction without inhibiting the activation of microglia/monocyte in the spinal cord.

An Inflammation-Centric View of Neurological Disease: Beyond the Neuron

Inflammation is a complex biological response fundamental to how the body deals with injury and infection to eliminate the initial cause of cell injury and effect repair. Unlike a normally beneficial acute inflammatory response, chronic inflammation can lead to tissue damage and ultimately its destruction, and often results from an inappropriate immune response. Inflammation in the nervous system (“neuroinflammation”), especially when prolonged, can be particularly injurious. While inflammation per se may not cause disease, it contributes importantly to disease pathogenesis across both the peripheral (neuropathic pain, fibromyalgia) and central [e.g., Alzheimer disease, Parkinson disease, multiple sclerosis, motor neuron disease, ischemia and traumatic brain injury, depression, and autism spectrum disorder] nervous systems. The existence of extensive lines of communication between the nervous system and immune system represents a fundamental principle underlying neuroinflammation. Immune cell-derived inflammatory molecules are critical for regulation of host responses to inflammation. Although these mediators can originate from various non-neuronal cells, important sources in the above neuropathologies appear to be microglia and mast cells, together with astrocytes and possibly also oligodendrocytes. Understanding neuroinflammation also requires an appreciation that non-neuronal cell—cell interactions, between both glia and mast cells and glia themselves, are an integral part of the inflammation process. Within this context the mast cell occupies a key niche in orchestrating the inflammatory process, from initiation to prolongation. This review will describe the current state of knowledge concerning the biology of neuroinflammation, emphasizing mast cell-glia and glia-glia interactions, then conclude with a consideration of how a cell's endogenous mechanisms might be leveraged to provide a therapeutic strategy to target neuroinflammation.

Oral curcumin supplementation improves fine motor function in the middle-aged rhesus monkey

Aged individuals experience decreased fine motor function of the hand and digits, which could result, in part, from the chronic, systemic state of inflammation that occurs with aging. Recent research for treating age-related inflammation has focused on the effects of nutraceuticals that have anti-inflammatory properties. One particular dietary polyphenol, curcumin, the principal curcuminoid of the spice turmeric, has been shown to have significant anti-inflammatory effects and there is mounting evidence that curcumin may serve to reduce systemic inflammation. Therefore, it could be useful for alleviating age-related impairments in fine motor function. To test this hypothesis we assessed the efficacy of a dietary intervention with a commercially available optimized curcumin to ameliorate or delay the effects of aging on fine motor function of the hand of rhesus monkeys. We administered oral daily doses of curcumin or a control vehicle to 11 monkeys over a 14- to 18-month period in which they completed two rounds of fine motor function testing. The monkeys receiving curcumin were significantly faster at retrieving a food reward by round 2 of testing than monkeys receiving a control vehicle. Further, the monkeys receiving curcumin demonstrated a greater degree of improvement in performance on our fine motor task by round 2 of testing than monkeys receiving a control vehicle. These findings reveal that fine motor function of the hand and digits is improved in middle-aged monkeys receiving chronic daily administration of curcumin.

Aminooxyacetic acid improves learning and memory in a rat model of chronic alcoholism

Chronic alcoholism seriously damages the central nervous system and leads to impaired learning and memory. Cell damage in chronic alcoholism is strongly associated with elevated levels of hydrogen sulfide (H₂S) and calcium ion overload. Aminooxyacetic acid is a cystathionine-β-synthase activity inhibitor that can reduce H₂S formation in the brain. This study sought to observe the effect of aminooxyacetic acid on learning and memory in a chronic alcoholism rat model. Rats were randomly divided into three groups. Rats in the control group were given pure water for 28 days. Rats in the model group were given 6% alcohol for 28 days to establish an alcoholism rat model. Rats in the aminooxyacetic acid remedy group were also given 6% alcohol for 28 days and were also intraperitoneally injected daily with aminooxyacetic acid (5 mg/kg) from day 15 to day 28. Learning and memory was tested using the Morris water maze test. The ultrastructure of mitochondria in the hippocampus was observed by electron microscopy. H₂S levels in the hippocampus were measured indirectly by spectrophotometry, and ATPase activity was measured using a commercial kit. The expression of myelin basic protein was determined by immunohistochemistry and western blotting. Compared with the control group, latency and swimming distance were prolonged in the navigation test on days 2, 3, and 4 in the model group. In the spatial probe test on day 5, the number of platform crosses was reduced in the model group. Cristae cracks, swelling or deformation of mitochondria appeared in the hippocampus, the hippocampal H₂S level was increased, the mitochondrial ATPase activity was decreased, and the expression of myelin basic protein in the hippocampus was down-regulated in the model group compared with the control group. All the above indexes were ameliorated in the aminooxyacetic acid remedy group compared with the model group. These findings indicate that aminooxyacetic acid can improve learning and memory in a chronic alcoholism rat model, which may be associated with reduction of hippocampal H₂S level and mitochondrial ATPase activity, and up-regulation of myelin basic protein levels in the hippocampus.

Age‑dependent alteration in the expression of oligodendrocyte‑specific protein in the gerbil hippocampus

Oligodendrocytes are myelin-forming cells in the central nervous system. Research into the effects of aging on oligodendrocyte protein expression remains limited. The present study aimed to determine the alterations in oligodendrocyte-specific protein (OSP) expression in the gerbil hippocampus at 1, 2, 3, 4, 6 and 24 months of age with western blot and immunohistochemistry analyses. OSP expression levels in the hippocampus were highest at 6 months of age. OSP immunoreactivity was identified in numerous cell bodies at 1 month, although the number of OSP immunoreactive cells was different according to hippocampal subregion. The number of OSP immunoreactive cells significantly decreased at 2 months and, thereafter, numbers decreased gradually. The detection of OSP immunoreactive fibers was negligible in all layers in the hippocampal subregions until 4 months. OSP immunoreactive fibers were abundant at 6 and 24 months, although the fiber distribution patterns in the CA1-3 areas and dentate gyrus were different. The results demonstrated that OSP expression in the gerbil hippocampus was age-dependent. The detection of OSP immunoreactive cell bodies and fibers was significantly different according to the layers of hippocampal subregions, indicating that myelination may be continuously altered in the hippocampus during normal aging.

Protective effect of epigenetic silencing of CyclinD1 against spinal cord injury using bone marrow-derived mesenchymal stem cells in rats

This study focuses on the protective effect of epigenetic silencing of CyclinD1 against spinal cord injury (SCI) using bone marrow-derived mesenchymal stem cells (BMSCs) in rats. Eighty-eight adult female Wistar rats were randomly assigned into the sham group, the control group, the si-CyclinD1 + BMSCs group and the BMSCs group. CyclinD1 protein and mRNA expressions after siRNA transfection were detected by Western blotting and qRT-PCR. The siRNA-CyclinD1 BMSCs were transplanted into rats in the si-CyclinD1 + BMSCs group using stereotaxic method 6 hr after SCI. Hindlimb locomotor performance was determined using inclined plane test and Basso-Beattie-Bresnahan (BBB) locomotor rating scale. Expressions of glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) were detected by immunohistochemistry. Inclined plane and BBB scores in the control, si-CyclinD1 + BMSCs, and BMSCs groups were significantly lower than the sham group, but these scores were evidently decreased in the control group and increased in the si-CyclinD1 + BMSCs group compared with the BMSCs group. The repair degree of spinal cord tissues of rats in the si-CyclinD1 + BMSCs group was obvious than the BMSCs group. GFAP and NGF protein expressions were markedly decreased in the control, si-CyclinD1 + BMSCs and BMSCs groups when compared with the sham group. GFAP- and NGF-positive cells were significantly increased in the si-CyclinD1 + BMSCs group while decreased in the control group. Our study provides evidence that epigenetic silencing of CyclinD1 using BMSCs might accelerate the repair of SCI in rats.

Chronic curcumin treatment improves spatial working memory but not recognition memory in middle-aged rhesus monkeys

Studies of both humans and non-human primates have demonstrated that aging is typically characterized by a decline in cognition that can occur as early as the fifth decade of life. Age-related changes in working memory are particularly evident and mediated, in part, by the prefrontal cortex, an area known to evidence age-related changes in myelin that is attributed to inflammation. In recent years, several nutraceuticals, including curcumin, by virtue of their anti-inflammatory and antioxidant effects, have received considerable attention as potential treatments for age-related cognitive decline and inflammation. Accordingly, we assessed for the first time in a non-human primate model of normal aging the efficacy of dietary intervention using the natural phenol curcumin to ameliorate the effects of aging on spatial working and recognition memory. Results revealed that monkeys receiving daily administration of curcumin over 14-18 months demonstrated a greater improvement in performance on repeated administration of a task of spatial working memory compared to monkeys that received a control substance.

Age-dependent differences in myelin basic protein expression in the hippocampus of young, adult and aged gerbils

Myelin degeneration is one of the characteristics of aging and degenerative diseases. This study investigated age-related alterations in expression of myelin basic protein (MBP) in the hippocampal subregions (dentate gyrus, CA2/3 and CA1 areas) of gerbils of various ages; young (1 month), adult (6 months) and aged (24 months), using western blot and immunohistochemistry. Western blot results showed tendencies of age-related reductions of MBP levels. MBP immunoreactivity was significantly decreased with age in synaptic sites of trisynaptic loops, perforant paths, mossy fibers, and Schaffer collaterals. In particular, MBP immunoreactive fibers in the dentate molecular cell layer (perforant path) was significantly reduced in adult and aged subjects. In addition, MBP immunoreactive mossy fibers in the dentate polymorphic layer and in the CA3 striatum radiatum was significantly decreased in the aged group. Furthermore, we observed similar age-related alterations in the CA1 stratum radiatum (Schaffer collaterals). However, the density of MBP immunoreactive fibers in the dentate granular cell layer and CA stratum pyramidale was decreased with aging. These findings indicate that expression of MBP is age-dependent and tissue specific according to hippocampal layers.

Neonatal Lipopolysaccharide Infection Causes Demyelination and Behavioral Deficits in Adult and Senile Rat Brain

BACKGROUND

Neonatal bacterial infections have been reported to cause white matter loss, although studies concerning the influence of infection on the expression of myelin and aging are still in their emerging state.

PURPOSE

The present study aimed to investigate the effects of perinatal lipopolysaccharide (LPS) exposure on the myelination at different age points using histochemical and immunocytochemical techniques and the relative motor coordination.

METHODS

A rat bacterial infection model was established by exposing the neonatal rats with LPS (0.3 mg/kg body weight, i.p., on postnatal day (PND) 3 followed by a booster at PND 5) and its impact was studied on the myelination and motor coordination in young, adult, and senile rats.

RESULTS

The results obtained suggest that the administration of LPS induces demyelination, predominantly in cortex and corpus callosum. Low expression level of myelin oligodendrocyte glycoprotein (MOG) was observed at all time points, with prominence at 12, 18, and 24 months of age. In addition, reduced staining with luxol fast blue stain was also recorded in the experimentals. With the increasing demyelination and declining motor ability, LPS exposure also seemed to accelerate normal aging symptoms.

CONCLUSION

There is a direct correlation of myelin damage and poor motor coordination with age. This would provide a better incite to understand inflammation-associated demyelinating changes in age-associated neurodegenerative disorders. Since, no long-term studies on behavioral impairments caused by LPS-induced demyelination in the central nervous system has been reported so far, this work would help in the better understanding of the long-term pathological effects of bacterial-induced demyelination.

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions.

The involvement of homocysteine in stress-induced Aβ precursor protein misprocessing and related cognitive decline in rats

Chronic stress is a risk factor in the development of cognitive decline and even Alzheimer's disease (AD), although its underlying mechanism is not fully understood. Our previous data demonstrated that the level of homocysteine (Hcy) was significantly elevated in the plasma of stressed animals, which suggests the possibility that Hcy is a link between stress and cognitive decline. To test this hypothesis, we compared the cognitive function, plasma concentrations of Hcy, and the brain beta-amyloid (Aβ) level between rats with or without chronic unexpected mild stress (CUMS). A lower performance by rats in behavioral tests indicated that a significant cognitive decline was induced by CUMS. Stress also disturbed the normal processing of Aβ precursor protein (APP) and resulted in the accumulation of Aβ in the brains of rats, which showed a positive correlation with the hyperhomocysteinemia (HHcy) that appeared in stressed rats. Hcy-targeting intervention experiments were used to verify further the involvement of Hcy in stress-induced APP misprocessing and related cognitive decline. The results showed that diet-induced HHcy could mimic the cognitive impairment and APP misprocessing in the same manner as CUMS, while Hcy reduction by means of vitamin B complex supplements and betaine could alleviate the cognitive deficits and dysregulation of Aβ metabolism in CUMS rats. Taken together, the novel evidence from our present study suggests that Hcy is likely to be involved in chronic stress-evoked APP misprocessing and related cognitive deficits. Our results also suggested the possibility of Hcy as a target for therapy and the potential value of vitamin B and betaine intake in the prevention of stress-induced cognitive decline.

Perturbed cholesterol homeostasis in aging spinal cord

The spinal cord is vital for the processing of sensorimotor information and for its propagation to and from both the brain and the periphery. Spinal cord function is affected by aging, however, the mechanisms involved are not well-understood. To characterize molecular mechanisms of spinal cord aging, microarray analyses of gene expression were performed on cervical spinal cords of aging rats. Of the metabolic and signaling pathways affected, cholesterol-associated pathways were the most comprehensively altered, including significant downregulation of cholesterol synthesis-related genes and upregulation of cholesterol transport and metabolism genes. Paradoxically, a significant increase in total cholesterol content was observed-likely associated with cholesterol ester accumulation. To investigate potential mechanisms for the perturbed cholesterol homeostasis, we quantified the expression of myelin and neuroinflammation-associated genes and proteins. Although there was minimal change in myelin-related expression, there was an increase in phagocytic microglial and astrogliosis markers, particularly in the white matter. Together, these results suggest that perturbed cholesterol homeostasis, possibly as a result of increased inflammatory activation in spinal cord white matter, may contribute to impaired spinal cord function with aging.

Dissecting the Contribution of Vascular Alterations and Aging to Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that afflicts as many as 45 % of individuals who survive past the age of 85. AD has been associated with neurovascular dysfunction and brain accumulation of amyloid-β peptide, as well as tau phosphorylation and neurodegeneration, but the pathogenesis of the disease is still somewhat unclear. According to the amyloid cascade hypothesis of AD, accumulation of amyloid-β peptide (Aβ) aggregates initiates a sequence of events leading to neuronal injury and loss, and dementia. Alternatively, the vascular hypothesis of AD incorporates the vascular contribution to the disease, stating that a primary insult to brain microcirculation (e.g., stroke) not only contributes to amyloidopathy but initiates a non-amyloidogenic pathway of vascular-mediated neuronal dysfunction and injury, which involves blood-brain barrier compromise, with increased permeability of blood vessels, leakage of blood-borne components into the brain, and, consequently, neurotoxicity. Vascular dysfunction also includes a diminished brain capillary flow, causing multiple focal ischemic or hypoxic microinjuries, diminished amyloid-β clearance, and formation of neurotoxic oligomers, which lead to neuronal dysfunction. Here we present and discuss relevant findings on the contribution of vascular alterations during aging to AD, with the hope that a better understanding of the players in the "orchestra" of neurodegeneration will be useful in developing therapies to modulate the "symphony".

Gene profiling in the dynamic regulation of the lifespan of the myelin sheath structure in the optic nerve of rats

Aging of the nervous system leads to impairments in cognition and motor skills, and is a major risk factor for several neurological disorders. Recently, numerous nerve function deficits that appear with aging have been found to be a consequence of myelin abnormalities; however, the genetic mechanism of the age‑related alterations in the myelin sheath has not yet been fully elucidated. In the present study, the morphology of the myelin sheath in the optic nerve of rats was analyzed at 10 time‑points throughout life. Marked alterations in the myelin sheath were observed in aging and aged optic nerves, and these became progressively more severe with time. To determine the biological processes affected by aging in the myelin sheath, the age‑related profiling of the myelin sheath in rat optic nerves was established using microarray hybridization at 10 time‑points throughout life, between birth and senescence. From the results, 3,826 transcripts associated with the age‑related alterations in the myelin sheath of the optic nerve were identified. It was found that the biological processes most significantly altered by aging were lipid metabolism, the immune response and transmitter transport. This suggests that the downregulation of lipid synthesis genes and the upregulation of immune and neurotransmitter transport genes in aging may be the genetic basis for the age‑related alterations observed in the myelin sheath.