Age-related proteomic changes in the subventricular zone and their association with neural stem/progenitor cell proliferation

In the mammalian central nervous system, generation of new neurons persists in the subventricular zone (SVZ) throughout life. However, the capacity for neurogenesis in this region declines with aging. Recent studies have examined the degree of these age-related neurogenic declines and the changes of cytoarchitecture of the SVZ with aging. However, little is known about the molecular changes in the SVZ with aging. In this study, we dissected the SVZs from rats aged postnatal day 28, 3 months, and 24 months. The SVZ tissues were processed for 2-D gel electrophoresis to identify protein changes following aging. Protein spots were subsequently subjected to mass spectrometry analysis to compare age-related alterations in the SVZ proteome. We also examined the level of cell proliferation in the SVZ in animals of these three age groups by using bromodeoxyuridine labeling. We found significant age-related changes in the expression of several proteins that play critical roles in the proliferation and survival of neural stem/progenitor cells in the SVZ. Among these proteins, glial fibrillary acidic protein, ubiquitin carboxy terminal hydrolase 1, glutathione S-transferase omega, and preproalbumin were increased with aging, whereas collapsin response-mediated protein 4 (CRMP-4), CRMP-5, and microsomal protease ER60 exhibited declines with aging. We have also observed a significant decline of neural stem/progenitor cell proliferation in the SVZ with aging. These alterations in protein expression in the SVZ with aging likely underlie the diminishing proliferative capacity of stem/progenitor cells in the aging brain.     

大脑老化与神经再生和卒中

大脑老化是神经退行性疾病的主要诱因。而卒中不仅是老年人的神经系统常见疾病,而且也是70岁以上老年人致残和死亡的重要原因,因此,大脑老化与卒中发病息息相关。已经证实,老年卒中患者其缺血性脑组织损伤更加严重、脑梗死面积更大、缺血后的神经功能障碍也更加显著。尽管研究已证实老龄大脑的神经再生减少,但卒中可以诱导神经再生并能有效促进神经功能恢复,这就为神经再生治疗卒中开辟了良好的途径。本文重点就大脑老化及老化后神经再生、缺血性卒中作一简要综述。     

Age-related changes of the adrenal secretory pattern: possible role in pathological brain aging

The biosynthetic dissociation of the adrenocortical secretion occurring with age may have a pathogenetic role in the pathophysiology of brain aging. We studied cortisol and DHEAS secretion in healthy old and young subjects, in senile dementia, in major depression of elderly subjects and in healthy centenarians. A clear age-related decline of DHEAS secretion was well evident in healthy centenarians, and a further decrease in DHEAS concentration was found in old depressed patients and moreover in the demented ones, by comparison with age-matched controls. The circadian profile of serum cortisol was clearly flattened in old subjects, due to the selective increase in the cortisol nocturnal levels, particularly evident in demented subjects; on the other hand, the morning serum cortisol levels were not significantly different among centenarians, young and old controls. The molar ratio between cortisol and DHEAS showed a significant age-related increase; the occurrence of senile dementia and of major depression played an additive role, by comparison to physiological aging. The qualitative and quantitative modifications of the adrenocortical secretion occurring with aging seem mainly dependent on age itself, but the occurrence of pathological conditions may amplify these changes. Since cortisol and DHEAS play opposite effects on the central nervous system, the evaluation of the ratio between cortisol and DHEAS seems to be a good marker of the neuroendocrine features in old subjects.     

Development and aging of noradrenergic cell bodies and axon terminals in the chicken

Tyrosine hydroxylase activity was measured in the region of locus coeruleus, cerebellum, cervical spinal cord, lumbar sympathetic ganglia, and iris throughout most of the life span of the chicken (8 days of incubation to 5 years) to compare developmental trends in tyrosine hydroxylase activity in noradrenergic cell bodies and in axon terminals in both the central and peripheral nervous system. Fluorescence histochemistry and retrograde transport of horseradish peroxidase were used to characterize further the coeruleo-cerebellar projections. Tyrosine hydroxylase activity was detected in the cerebellum as early as 8 days of incubation, which is the earliest stage so far reported. The greatest increase in total tyrosine hydroxylase activity in the region of the locus coeruleus and cerebellum occurred during the embryonic period. There was a more pronounced increase in the cerebellum than in the locus coeruleus region. This is in contrast to the cervical spinal cord where tyrosine hydroxylase activity increased at approximately the same rate during the embryonic and post-hatching periods. Moreover, the cerebellum and cervical spinal cord, two locus coeruleus target sites, displayed different trends in tyrosine hydroxylase activity throughout development and aging. In both structures examined in the peripheral nervous system, the greatest increase in total tyrosine hydroxylase activity occurred during the post-hatching period, with a greater rise in the cell bodies of the lumbar sympathetic ganglia than in the noradrenergic terminals of the iris. In both the central and peripheral nervous system, total tyrosine hydroxylase activity continued to increase in noradrenergic terminals long after hatching reaching the highest levels at 7 months when the chicken is considered fully mature. During aging, 16 months to 5 years, there was a greater decrease in total tyrosine hydroxylase activity in the terminals of noradrenergic neurons than in the cell bodies in both the central and peripheral nervous system, a phenomenon that was more marked in the peripheral nervous system than in the brain.     

Age‐related neurochemical changes in the rhesus macaque cochlear nucleus

Neurochemical changes in the expression of various proteins within the central auditory system have been associated with natural aging. These changes may compensate in part for the loss of auditory sensitivity arising from two phenomena of the aging auditory system: cochlear histopathologies and increased excitability of central auditory neurons. Recent studies in the macaque monkey have revealed age‐related changes in the density of nicotinamide adenine dinucleotide phosphate (NADPH)‐diaphorase (NADPHd) and parvalbumin (PV)‐positive cells within the inferior colliculus and superior olivary complex. The cochlear nucleus (CN), which is the first central auditory nucleus, remains unstudied. Since the CN participates in the generation of the auditory brainstem response (ABR) and receives direct innervation from the cochlea, it serves as an ideal nucleus to compare the relationship between these neurochemical changes and the physiological and peripheral changes of the aging auditory system. We used stereological sampling to calculate the densities of NADPHd and PV reactive neurons within the three subdivisions of the CN in middle‐aged and aged rhesus macaques. Regression analyses of these values with ABR properties and cochlear histopathologies revealed relationships between these cell types and the changing characteristics of the aging auditory system. Our results indicate that NADPHd expression does change with age in a specific subdivision of the CN, but PV does not. Conversely, PV expression correlated with ABR amplitudes and outer hair cell loss in the cochlea, but NADPHd did not. These results indicate that NADPHd and PV may take part in distinct compensatory efforts of the aging auditory system. J. Comp. Neurol. 522:1527–1541, 2014. © 2013 Wiley Periodicals, Inc.     

Mild cognitive impairment: animal models

Mild cognitive impairment (MCI) is an aspect of cognitive aging that is considered to be a transitional state between normal aging and the dementia into which it may convert. Appropriate animal models are necessary in order to understand the pathogenic mechanisms of MCI and develop drugs for its treatment. In this review, we identify the features that should characterize an animal model of MCI, namely old age, subtle memory impairment, mild neuropathological changes, and changes in the cholinergic system, and the age at which these features can be detected in laboratory animals. These features should occur in aging animals with normal motor activity and feeding behavior. The animal models may be middle-aged rats and mice, rats with brain ischemia, transgenic mice overexpressing amyloid precursor protein and presenilin 1 (tested at an early stage), or aging monkeys. Memory deficits can be detected by selecting appropriately difficult behavioral tasks, and the deficits can be associated with neuropathological alterations. The reviewed literature demonstrates that, under certain conditions, these animal species can be considered to be MCI models, and that cognitive impairment in these models responds to drug treatment.     

Brain and cerebrospinal fluid cholinesterases in Alzheimer's disease, Parkinson's disease and aging. A critical review of clinical and experimental studies

Summary Acetylcholinesterase (AChE), an enzyme responsible for the breakdown of acetylcholine, is found both in cholinergic and non-cholinergic neurons in the central nervous system. In addition to its role in the catabolism of acetylcholine, AChE have other functions in brain, e.g. in the processing of peptides and proteins, and in the modulation of dopaminergic neurons in the brain stem. Several clinical and experimental studies have investigated AChE in brain and cerebrospinal fluid (CSF) in aging and dementia. The results suggest that brain AChE and its molecular forms show interesting changes in dementia and aging. However, CSF-AChE activity is not a very reliable or sensitive marker of the integrity and function of cholinergic neurons in the basal forebrain complex. Additional work is needed to clarify the role of AChE abnormality in the formation of pathology changes in patients with Alzheimer's disease.     

Effects of anticonvulsant drugs on life span

Aging is characterized by widespread degenerative changes in tissue morphology and function and an increase in the incidence of human diseases such as cancer, stroke, and Alzheimer disease. Findings from recent genetic studies suggest that molecular mechanisms that influence life span are evolutionarily conserved, and interventions that extend the life span of model organisms such as worms and flies are likely to have similar effects on vertebrates such as humans. However, little progress has been made in identifying drugs that delay aging. We identified 3 pharmacologic compounds, ethosuximide, trimethadione, and 3,3-diethyl-2-pyrrolidinone, that extend lifespan and delay age-related degenerative changes in the nematode worm Caenorhabditis elegans. All 3 compounds are anticonvulsants that modulate neural activity in vertebrates, and ethosuximide and trimethadione are used to treat absence seizures in humans. We discuss existing evidence that these drugs might also delay vertebrate aging and suggest experiments that could test this hypothesis. Genetic and cell ablation studies conducted with model organisms have demonstrated connections between the nervous system and aging. Our studies provide additional support for the hypothesis that neural activity plays a role in lifespan determination, since ethosuximide and trimethadione regulated neuromuscular activity in nematodes. Our findings suggest that the lifespan extending activity of these compounds is related to the anticonvulsant activity, implicating neural activity in the regulation of aging. We also discuss models that explain how the nervous system influences lifespan.     

New insights into brain BDNF function in normal aging and Alzheimer disease

The decline observed during aging involves multiple factors that influence several systems. It is the case for learning and memory processes which are severely reduced with aging. It is admitted that these cognitive effects result from impaired neuronal plasticity, which is altered in normal aging but mainly in Alzheimer disease. Neurotrophins and their receptors, notably BDNF, are expressed in brain areas exhibiting a high degree of plasticity (i.e. the hippocampus, cerebral cortex) and are considered as genuine molecular mediators of functional and morphological synaptic plasticity. Modification of BDNF and/or the expression of its receptors (TrkB.FL, TrkB.T1 and TrkB.T2) have been described during normal aging and Alzheimer disease. Interestingly, recent findings show that some physiologic or pathologic age-associated changes in the central nervous system could be offset by administration of exogenous BDNF and/or by stimulating its receptor expression. These molecules may thus represent a physiological reserve which could determine physiological or pathological aging. These data suggest that boosting the expression or activity of these endogenous protective systems may be a promising therapeutic alternative to enhance healthy aging.     

Gray matter alterations in early aging: A diffusion magnetic resonance imaging study

Many studies have observed altered neurofunctional and structural organization in the aging brain. These observations from functional neuroimaging studies show a shift in brain activity from the posterior to the anterior regions with aging (PASA model), as well as a decrease in cortical thickness, which is more pronounced in the frontal lobe followed by the parietal, occipital, and temporal lobes (retrogenesis model). However, very little work has been done using diffusion MRI (dMRI) with respect to examining the structural tissue alterations underlying these neurofunctional changes in the gray matter. Thus, for the first time, we propose to examine gray matter changes using diffusion MRI in the context of aging. In this work, we propose a novel dMRI based measure of gray matter “heterogeneity” that elucidates these functional and structural models (PASA and retrogenesis) of aging from the viewpoint of diffusion MRI. In a cohort of 85 subjects (all males, ages 15–55 years), we show very high correlation between age and “heterogeneity” (a measure of structural layout of tissue in a region‐of‐interest) in specific brain regions. We examine gray matter alterations by grouping brain regions into anatomical lobes as well as functional zones. Our findings from dMRI data connects the functional and structural domains and confirms the “retrogenesis” hypothesis of gray matter alterations while lending support to the neurofunctional PASA model of aging in addition to showing the preservation of paralimbic areas during healthy aging. Hum Brain Mapp 35:3841–3856, 2014. © 2013 Wiley Periodicals, Inc.     

Distribution and levels of insulin-like growth factor I mRNA across the life span in the Brown Norway×Fischer 344 rat brain

Previous studies have reported changes in insulin-like growth factor I (IGF-I) mRNA expression during early postnatal development of the rat brain. Although changes in IGF-I gene expression have been documented in a wide range of central nervous system structures during early development and investigated in the hippocampus during aging, no study has compared changes in IGF-I gene expression in different brain regions across the life span. The present study assessed the distribution of IGF-I gene expression using in situ hybridization in rats aged 2–30 months. Dot blots were used as a quantitative assessment of cortical IGF-I mRNA. Results indicate that both the distribution and levels of brain IGF-I mRNA do not change significantly between 2 and 30 months of age in the rat. However, in spite of relatively constant levels of mRNA, other studies from our laboratory have demonstrated that cortical IGF-I protein levels decrease 36.6% between 11 and 32 months of age, suggesting that IGF-I function is decreased with increasing age.     

Effects of aging on the myelination of the optic nerve in rats

Aim of the study: Cognitive decline due to aging is most probably the result of changes in the white matter in the central nervous system (CNS) and/or demyelination.

Material and methods: We used electron microscopic analysis of the morphological changes in aging rats’ optic nerves as an easily accessible part of the CNS.

Results: Several age changes were observed in aging rats (36?months) vs. young adult rats (6?months), namely degeneration of axons, decreased packing density and morphological alterations of myelination, including the ballooning of some myelin sheaths, separation of myelin lamellae and degenerative changes in the oligodendrocytes population.

Conclusion: Cognitive decline related to aging may occur in part due to the disturbed myelination of axons in CNS white matter.     

Increased hypoxia-inducible factor 1alpha expression in rat brain tissues in response to aging

The present study observed changes in rat neural cells at various ages (3, 18, 24, and 30 months). With age, neural cells became large and were sparsely arranged, and the number of Nissl bodies decreased. In addition, hypoxia-inducible factor 1α expression increased with increasing age in hippocampal CA1 and CA3 regions, motor cortex, and the first subfolium, especially from 3 to 18 months. In the open-field test, grid crossing decreased with increasing age, especially from 18 months. The number of rearings reached a peak in the 18 months group, and then subsequently decreased. The results suggested that hypoxia-inducible factor 1α played an important role in the nervous system aging process.     

Contribution of neuroinflammation and immunity to brain aging and the mitigating effects of physical and cognitive interventions

It is widely accepted that the brain and the immune system continuously interact during normal as well as pathological functioning. Human aging is commonly accompanied by low-grade inflammation in both the immune and central nervous systems, thought to contribute to many age-related diseases. This review of the current literature focuses first on the normal neuroimmune interactions occurring in the brain, which promote learning, memory and neuroplasticity. Further, we discuss the protective and dynamic role of barriers to neuroimmune interactions, which have become clearer with the recent discovery of the meningeal lymphatic system. Next, we consider age-related changes of the immune system and possible deleterious influences of immunosenescence and low-grade inflammation (inflammaging) on neurodegenerative processes in the normally aging brain. We survey the major immunomodulators and neuroregulators in the aging brain and their highly tuned dynamic and reciprocal interactions. Finally, we consider our current understanding of how physical activity, as well as a combination of physical and cognitive interventions, may mediate anti-inflammatory effects and thus positively impact brain aging.     

Overexpression of p53 but not Rb in the cytoplasm of neurons and small vessels in an autopsy of a patient with Cockayne syndrome

Cockayne syndrome presents senescence‐like changes starting in early infancy; however, the mechanism of premature aging remains unclear. In an autopsy of a 23‐year‐old woman with Cockayne syndrome, we evaluated the correlation between Cockayne pathology and the expression patterns of the senescence‐associated proteins p53 and Rb. Neuropathological findings in this case revealed basal ganglia calcification, tigroid leukodystrophy, bizarre reactive astrocytes, severe cerebellar atrophy with loss of Purkinje cells, and arteriolar/neuronal calcifications in the hypothalamus. Multiple arteriolar calcifications and sclerotic changes were seen in the central nervous system and kidney, but the endothelium of the aorta and coronary arteries remained intact appropriately for the individual's age without any finding of arteriosclerosis. Overexpression of p53 protein was confirmed in the cytoplasm of neurons in the basal ganglia, thalamus, hypothalamus, hippocampus and cerebellum, of arteriolar endothelial cells of the cerebrum and renal glomerular capillaries, and of cutaneous epithelial cells. The distribution of p53 overexpression was coincident with that of pathological alteration, such as neuronal loss, calcification and atrophy. High expression of p53 was localized in the cytoplasm, not in the nucleus. In contrast to p53, Rb was not expressed in any senescence lesion. In terms of senescence, distinct differences are found among organs in a patient with Cockayne syndrome. This segmental progeria differs from natural aging, and implicates p53 overexpression in the etiology of CS.     

Psychopathological syndromes of neurological diseases in the elderly

Vascular and degenerative diseases of the central nervous system are one of the most common health problems in the elderly. Cognitive dysfunction, mood disorders and behavioural changes as well as psychotic symptoms constitute an invariable part of the clinical manifestation of these diseases. Psychopathological syndromes influence management decisions, commonly being a reason for patients' institutionalization; they are also a cause of suffering of patients and their caregivers and relatives. Relevant diagnosis of psychological symptoms is crucial in establishing adequate therapy, which improves quality of life of patients and their caregivers. The paper provides an overview of the psychopathological presentation of the most common central nervous system diseases in the elderly.     

Enhanced tissue plasminogen activator synthesis by the sympathetic neurons that innervate aging vessels

We investigated the source of the increased release of tissue plasminogen activator (t-PA) into the circulation that occurs during natural aging. Both the basal release and the acute stress-associated release induced by sympathetic stimulations are greater in older subjects. It is widely assumed that the source of these increases is vascular endothelium. However, the sympathetic neurons that densely innervate resistance vessel walls were recently shown to synthesize and transport active t-PA to axon terminals in vascular smooth muscle, suggesting an alternative source. These fine t-PA-bearing axons lie in the seldom-studied deep adventitia of vessel walls, where they are less visible than endothelium in tissue sections. Using Northern blot analysis, we observed that t-PAmRNA synthesis is increased 54% in the ganglion parent neuron cell bodies that innervate aged vessels. The t-PA release from isolated, aged ganglia in cultures was twofold greater than that from younger controls. In addition, aged whole-artery explants showed a 20% greater basal and a 50% greater acute release of stored t-PA in vitro. In vivo levels of active t-PA were 33% greater in the blood and 40% greater in the aqueous humor. These results are consistent with an increased infusion of the active t-PA protease from sympathetic axon terminals into the vessel wall extracellular matrix and the blood during natural aging, in addition to the basal endothelial release. We suggest that the cumulative impact of an accelerated plasmin production and matrix degradation within vessel walls, especially during repetitive stress, may play an unrecognized role in the pathogenesis of vascular aging. The possibility that increased sympathetic nervous system plasminogenesis influences the aging process in nonvascular tissues also deserves further investigation.     

Expression of NCAM mRNA and polypeptides in aging rat brain

In aging brain, degenerative as well as compensatory regenerative processes are believed to occur. The neural cell adhesion molecule NCAM is involved in developmental and regenerative processes in the brain. However, the role of NCAM in aging brain has not been characterized. In this study, the expression of NCAM mRNAs and polypeptides was investigated in aging rat brain. The 7.4 and 6.7 kb NCAM mRNAs were selectively downregulated during postnatal development, and the 5.2 and 2.9 kb NCAM mRNAs were upregulated. However, from postnatal day 40 to old age no change in NCAM mRNA classes was observed. The fraction of NCAM mRNA containing the VASE exon increased postnatally but remained stable during adult life. VASE, which is believed to modulate the binding capacity, seemed to be relatively more abundant in the 7.4 and 6.7 kb NCAM mRNAs, encoding transmembrane NCAM forms, than in the 5.2 and 2.9 kb NCAM mRNAs, coding for glycosyl phosphatidylinositol (GPI) linked NCAM. Conversely, insertion of exons a and AAG between exons 12 and 13, a region containing two fibronectin type III repeats, seemed to be more pronounced in 5.2 and 2.9 kb NCAM mRNAs than in the 7.4 and 6.7 kb mRNAs. During postnatal development an increase in the fraction of 6.7 kb NCAM mRNA containing the exons a and AAG was observed. However, during aging the fraction of NCAM mRNAs containing this exon combination seemed constant. At the protein level, NCAM-A was downregulated both during development and aging. No changes were observed during aging in the composition of soluble NCAM forms in the brain, cerebrospinal fluid or blood plasma. The amount of NCAM in rat brain decreased during postnatal development, but remained at a constant level from postnatal day 40 to old age.To conclude, several changes in NCAM expression occur during early postnatal development emphasizing the important role of this molecule in the morphogenetic processes. During aging, a significant selective downregulation of NCAM-A was observed indicating that in general only minor regenerative processes occur in the brain.     

Septo-hippocampal neurons: altered properties in the aged rat

The septo-hippocampal pathway is one of the best characterized cholinergic pathways of the mammalian central nervous system. It is very likely that this pathway is involved in the pathophysiology of dementia of the Alzheimer's type and perhaps of normal aging also. The properties of the septo-hippocampal neurons identified by their antidromic response to the electrical stimulation of the fimbria-fornix were altered in aged (27 months) rats as compared to young (2-3 months) controls: their pattern of spontaneous activity (including the frequency of occurrence of a rhythmically bursting activity) and their axonal conduction velocity were altered. The intensity of these changes was dependent on the presence of pituitary tumor which developed spontaneously in about 1/3 of the animals. These results provide direct evidence of the involvement of septo-hippocampal neurons in the aging process.