X-ray diffraction evidence for myelin disorder in brain from humans with Alzheimer's disease

Wide-angle X-ray diffraction studies revealed that the lipid phase transition temperature of myelin from brain tissue of humans with Alzheimer's disease was about 12 degrees C lower than that of normal age-matched controls, indicating differences in the physical organization of the myelin lipid bilayer. Elevated levels of malondialdehyde and conjugated diene were found in brain tissue from humans with Alzheimer's disease, indicating an increased amount of lipid peroxidation over the controls. An increase in myelin disorder and in lipid peroxidation can both be correlated with aging in human brain, but the changes in myelin from humans with Alzheimer's disease are more pronounced than in normal aging. These changes might represent severe or accelerated aging.     

Acetylcholine and choline levels in post-mortem human brain tissue: Preliminary observations in Alzheimer's disease

Choline and acetylcholine were measured in necropsy brain tissue (temporal cortex and caudate nucleus) obtained from elderly, mentally normal hospital cases and established cases of Alzheimer's disease. ACh levels were as expected, extremely low in all cases; in cases with Alzheimer's disease, the ACh level was lower in the temporal cortex but not changed in the caudate compared with normal cases (matched for ages and post-mortem sampling delays). The level of choline in Alzheimer's disease was not significantly different from the normal in either brain region. The choline levels in the human material were, however, substantially and significantly lower than those obtained from young adult rat cerebral cortex which was cooled after death according to the post-mortem temperature decline in the human cadaver.     

Frontiers of Model Animals for Neuroscience:Two Prosperous Aging Model Animals forPromoting Neuroscience Research

A model animal showing spontaneous onset is a useful tool for investigating the mechanism of disease. Here, I would like to introduce two aging model animals expected to be useful for neuroscience research: the senescence-accelerated mouse (SAM) and the klotho mouse. The SAM was developed as a mouse showing a senescence-related phenotype such as a short lifespan or rapid advancement of senescence. In particular, SAMP8 and SAMP10 show age-related impairment of learning and memory. SAMP8 has spontaneous spongy degeneration in the brain stem and spinal cord with aging, and immunohistochemical studies reveal excess protein expression of amyloid precursor protein and amyloid β in the brain, indicating that SAMP8 is a model for Alzheimer’s disease. SAMP10 also shows age-related impairment of learning and memory, but it does not seem to correspond to Alzheimer’s disease because senile plaques primarily composed of amyloid β or neurofibrillary tangles primarily composed of phosphorylated tau were not observed. However, severe atrophy in the frontal cortex, entorhinal cortex, amygdala, and nucleus accumbens can be seen in this strain in an age-dependent manner, indicating that SAMP10 is a model for normal aging. The klotho mouse shows a phenotype, regulated by only one gene named α-klotho, similar to human progeria. The α-klotho gene is mainly expressed in the kidney and brain, and oxidative stress is involved in the deterioration of cognitive function of the klotho mouse. These animal models are potentially useful for neuroscience research now and in the near future.     

Age-related changes in antioxidant enzymes and lipid peroxidation in brains of control and transgenic mice overexpressing copper-zinc superoxide dismutase.

The aim of our study was first to obtain a comprehensive profile of the brain antioxidant defense potential and peroxidative damage during aging. We investigated copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), seleno-dependent glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R) activities, endogenous and in vitro stimulated lipid peroxidation in 40 brains of control mice divided into 3 age groups: 2 months (young), 12 months (middle-aged) and 28 months (old). We found a positive correlation between age and activities of CuZnSOD (r = 0.47; P < 0.01) and GSH-PX (r = 0.72; P < 0.0001). CuZnSOD and GSH-PX activities are independently regulated during brain aging since temporal changes of these two enzymes do not correlate. No modification in MnSOD activity and basal lipid peroxidation was observed as a function of age. Nevertheless, stimulated lipid peroxidation was significantly higher at 12 months (6.53 +/- 0.71 mumole MDA/g tissue) than at 2 months (5.69 +/- 0.90) and significantly lower at 28 months (5.13 +/- 0.33) than at 12 months. Second, we used genetic manipulations to construct transgenic mice that specifically overexpress CuZnSOD to understand the role of CuZnSOD in neuronal aging. The human CuZnSOD transgene expression was stable during aging. The increased CuZnSOD activity in the brain (1.9-fold) of transgenic mice resulted in an enhanced rate of basal lipid peroxidation and in increased MnSOD activity in the 3 age groups. Other antioxidant enzymes did not exhibit modifications indicating the independence of the regulation between CuZnSOD and glutathione-related enzymes probably due to their different cellular localization in the brain.     

The effects of aerobic exercise training on the age-related lipid peroxidation, Schwann cell apoptosis and ultrastructural changes in the sciatic nerve of rats

The potential role of exercise in preventing the age-related spontaneous peripheral neuropathy has not been studied. We examined the effects of long-term aerobic exercise training on lipid peroxidation, Schwann cell (SC) apoptosis and ultrastructural changes in the sciatic nerve of rats during aging. Three groups of 12-week old Wistar rats ran on a treadmill for 6, 9 and 12 months (exercise trained (ET) group, n=10 each) according to an exercise training program targeted at a speed of 22 m/min (at 7 degrees incline), 60 min/day, 6 days/week. Three corresponding groups of untrained rats were used as the controls (sedentary (SED) group). At the end of each period, sciatic nerve biopsies were performed, and processed for biochemical, immunohistochemical and ultrastructural analyses. The results showed that aging was associated with an increased level of nerve malondialdehyde (MDA, marker of lipid peroxidation) and a higher number of SC apoptosis in SED group. The SED group showed irregular nerve fibers with thin myelin sheaths and areas of myelin-axon detachment. However, the ET group had significantly diminished nerve lipid peroxidation and SC apoptosis. In the ET group, nerve fibers had a thick myelin sheath with frequent folding. These findings suggest that aerobic exercise training protects peripheral nerves by attenuating oxidative reactions, and preserving SCs and myelin sheath from pathologic changes, which occur during normal aging.     

Analyzing Gene Expression from Whole Tissue vs. Different Cell Types Reveals the Central Role of Neurons in Predicting Severity of Alzheimer’s Disease

Alterations in gene expression resulting from Alzheimer’s disease have received considerable attention in recent years. Although expression has been investigated separately in whole brain tissue, in astrocytes and in neurons, a rigorous comparative study quantifying the relative utility of these sources in predicting the progression of Alzheimer’s disease has been lacking. Here we analyze gene expression from neurons, astrocytes and whole tissues across different brain regions, and compare their ability to predict Alzheimer’s disease progression by building pertaining classification models based on gene expression sets annotated to different biological processes. Remarkably, we find that predictions based on neuronal gene expression are significantly more accurate than those based on astrocyte or whole tissue expression. The findings explicate the central role of neurons, particularly as compared to glial cells, in the pathogenesis of Alzheimer’s disease, and emphasize the importance of measuring gene expression in the most relevant (pathogenically ‘proximal’) single cell types.     

Disorder in human myelin induced by superoxide radical: an in vitro investigation

Potassium superoxide (KO.2), applied as a source of superoxide radical directly in vitro to white matter from young adult human brain, caused the lipid phase of the myelin to change from a crystalline (ordered) state to a liquid crystalline (disordered) state. The myelin transition temperature decreased from 65 degrees C to 37 degrees C. This alteration was accompanied by a dramatic increase in the levels of lipid peroxidation products--malondialdehyde, a conjugated diene, and ethane. These changes in human myelin, induced by direct application of O2-. radical, simulated myelin deterioration that occurs in the course of natural aging, thus, providing further substantiation for the notion that O2-. might be a major toxic agent associated with the aging process.     

Functions and dysfunctions of nitric oxide in brain

Nitric oxide (NO) works as a retrograde neurotransmitter in synapses, allows the brain blood flow and also has important roles in intracellular signaling in neurons from the regulation of the neuronal metabolic status to the dendritic spine growth. Moreover NO is able to perform post-translational modifications in proteins by the S-nitrosylation of the thiol amino acids, which is a physiological mechanism to regulate protein function. On the other hand, during aging and pathological processes the behavior of NO can turn harmful when reacts with superoxide anion to form peroxynitrite. This gaseous compound can diffuse easily throughout the neuronal membranes damaging lipid, proteins and nucleic acids. In the case of proteins, peroxynitrite reacts mostly with the phenolic ring of the tyrosines forming nitro-tyrosines that affects dramatically to the physiological functions of the proteins. Protein nitrotyrosination is an irreversible process that also yields to the accumulation of the modified proteins contributing to the onset and progression of neurodegenerative processes such as Alzheimer's disease or Parkinson's disease.     

Directed Network Motifs in Alzheimer’s Disease and Mild Cognitive Impairment

Directed network motifs are the building blocks of complex networks, such as human brain networks, and capture deep connectivity information that is not contained in standard network measures. In this paper we present the first application of directed network motifs in vivo to human brain networks, utilizing recently developed directed progression networks which are built upon rates of cortical thickness changes between brain regions. This is in contrast to previous studies which have relied on simulations and in vitro analysis of non-human brains. We show that frequencies of specific directed network motifs can be used to distinguish between patients with Alzheimer’s disease (AD) and normal control (NC) subjects. Especially interesting from a clinical standpoint, these motif frequencies can also distinguish between subjects with mild cognitive impairment who remained stable over three years (MCI) and those who converted to AD (CONV). Furthermore, we find that the entropy of the distribution of directed network motifs increased from MCI to CONV to AD, implying that the distribution of pathology is more structured in MCI but becomes less so as it progresses to CONV and further to AD. Thus, directed network motifs frequencies and distributional properties provide new insights into the progression of Alzheimer’s disease as well as new imaging markers for distinguishing between normal controls, stable mild cognitive impairment, MCI converters and Alzheimer’s disease.     

Alzheimer's disease and Down's syndrome: Sharing of a unique cerebrovascular amyloid fibril protein

The cerebrovascular amyloid protein from a case of adult Down's syndrome was isolated and purified. Amino acid sequence analysis showed it to be homologous to that of the β protein of Alzheimer's disease. This is the first chemical evidence of a relationship between Down's syndrome and Alzheimer's disease. It suggests that Down's syndrome may be a predictable model for Alzheimer's disease. Assuming the β protein is a human gene product, it also suggests that the genetic defect in Alzheimer's disease is localized on chromosome 21.     

Myelin Membranes Isolated from Rats Intracranially Injected with apoTransferrin Are More Susceptible to in Vitro Peroxidation

Purified myelin obtained from 17 day old rats intracranially injected with aTf at 3 days of age was submitted to in vitro peroxidation using Fe + ascorbic acid (FeA) or Cu + H₂O₂ (CuH), to investigate the susceptibility of this membrane to in vitro metal catalyzed peroxidation. There was an increase in thiobarbituric acid-reactive-substances (TBARS) (60%) and in protein-associated carbonyls (PAC) (20%) in the myelin from aTf injected rats in comparison to myelin from controls, indicating a higher susceptibility to peroxidation. Desferoxamine (DFX) injected simultaneously with aTf did not change the response of myelin to aTf. CNS myelin is highly vulnerable to oxidative stress, and its susceptibility to peroxidation increases in myelin isolated from aTf injected rats. This increased liability to peroxidation as well as the previously reported aTf-dependent increment in certain myelin proteins and lipids and in the expression of specific myelin mRNAS, does not appear to be due to an increased amount of iron bound to the injected aTf. The changes in composition that we have previously reported could result in an abnormal myelin, allowing the peroxidative system to act upon the membrane more easily than in normal circumstances.     

AT1 Receptor Blocker Candesartan-induced Attenuation of Brain Injury of Rats Subjected to Chronic Cerebral Hypoperfusion

One of common pathophysiological states associated with central nervous system is chronic cerebral hypoperfusion (CH) that frequently occurs in conditions such as vascular dementia and Alzheimer’s disease. Long term blockage of angiotensin II type 1 (AT₁) receptor provides protection from ischemia induced injury of brain as well as reduction of cerebrovascular inflammation. Examining effect of the blockage on reduced glutathione (GSH), ascorbic acid (AA), and lipid peroxidation were of purpose in the present study. Modeling CH, rats were subjected to permanent occlusion of common carotid arteries bilaterally. AT₁ receptor antagonist, candesartan, was given daily for 14 days after surgery. CH caused a significant increase in lipid peroxidation and decrease in GSH content of cerebral hippocampal tissue with no change in AA level. Candesartan (0.5 mg/kg, oral) not only reduced lipid peroxidation but also restored GSH significantly besides elevating AA and improving histopathological alterations. In conclusion, long term AT₁ receptor blockage may be considered as novel therapeutic approach for protection from damage associated with CH. Underlying mechanism(s) may in part be related to suppressing oxidative stress and preserving brain antioxidant capacity.     

Senile dementia and Alzheimer's disease: A current view

Senile dementia, of which the most common cause is known as Alzheimer's disease, is a neurological disorder characterized clinically by memory and learning deficits. The disease may be shown to have a prevalence rate in the United States of greater than three per 1000 of the general population, and it may be shown that at any one time 600,000 individuals are affected by advanced stages of this disease. The disease, unique to man, is relentlessly progressive and refractory to treatment. In most cases, it is unrelated to cerebral vascular insufficiency, it is however associated with well defined morphological and biochemical changes at the cellular level. These include altered dendritic morphology, intracellular changes such as granulovacuolar and neurofibrillary degeneration, and extracellular deposits termed neuritic plaques. Moreover, a selective dysfunction in central cholinergic mechanisms has been demonstrated. Recent results from this laboratory have indicated that significant changes in chromatin conformation may be demonstrated to occur in this disease. Specifically, a significant “heterochromatization” was found to occur in chromatin from brains of patients who had died with this disease, suggesting that a major alteration in chromatin structure may be related to the etiology of this condition. In addition, an accumulation of the environmental agent aluminum upon brain cell chromatin has been implicated to contribute to the pathophysiology of Alzheimer's disease. During the past few years it has become possible to model several of the morphological markers of this disease in the laboratory. Specifically, the paired helical filament, representing a major intracellular marker can now be induced in cultured neurons and a filamentous hyperplasia similar to neurofibrillary degeneration, but not identical in morphology, may be induced in experimental animals and in neurons in vitro by trace amounts of aluminum. The understanding of Alzheimer's disease is in its infancy, however, the availability of model systems now permits extensive investigations into the nature and mechanisms of the agents responsible for the changes observed.     

Cerebral Apolipoprotein-D Is Hypoglycosylated Compared to Peripheral Tissues and Is Variably Expressed in Mouse and Human Brain Regions

Recent studies have shown that cerebral apoD levels increase with age and in Alzheimer’s disease (AD). In addition, loss of cerebral apoD in the mouse increases sensitivity to lipid peroxidation and accelerates AD pathology. Very little data are available, however, regarding the expression of apoD protein levels in different brain regions. This is important as both brain lipid peroxidation and neurodegeneration occur in a region-specific manner. Here we addressed this using western blotting of seven different regions (olfactory bulb, hippocampus, frontal cortex, striatum, cerebellum, thalamus and brain stem) of the mouse brain. Our data indicate that compared to most brain regions, the hippocampus is deficient in apoD. In comparison to other major organs and tissues (liver, spleen, kidney, adrenal gland, heart and skeletal muscle), brain apoD was approximately 10-fold higher (corrected for total protein levels). Our analysis also revealed that brain apoD was present at a lower apparent molecular weight than tissue and plasma apoD. Utilising peptide N-glycosidase-F and neuraminidase to remove N-glycans and sialic acids, respectively, we found that N-glycan composition (but not sialylation alone) were responsible for this reduction in molecular weight. We extended the studies to an analysis of human brain regions (hippocampus, frontal cortex, temporal cortex and cerebellum) where we found that the hippocampus had the lowest levels of apoD. We also confirmed that human brain apoD was present at a lower molecular weight than in plasma. In conclusion, we demonstrate apoD protein levels are variable across different brain regions, that apoD levels are much higher in the brain compared to other tissues and organs, and that cerebral apoD has a lower molecular weight than peripheral apoD; a phenomenon that is due to the N-glycan content of the protein.     

Male Microchimerism in the Human Female Brain

In humans, naturally acquired microchimerism has been observed in many tissues and organs. Fetal microchimerism, however, has not been investigated in the human brain. Microchimerism of fetal as well as maternal origin has recently been reported in the mouse brain. In this study, we quantified male DNA in the human female brain as a marker for microchimerism of fetal origin (i.e. acquisition of male DNA by a woman while bearing a male fetus). Targeting the Y-chromosome-specific DYS14 gene, we performed real-time quantitative PCR in autopsied brain from women without clinical or pathologic evidence of neurologic disease (n = 26), or women who had Alzheimer’s disease (n = 33). We report that 63% of the females (37 of 59) tested harbored male microchimerism in the brain. Male microchimerism was present in multiple brain regions. Results also suggested lower prevalence (p = 0.03) and concentration (p = 0.06) of male microchimerism in the brains of women with Alzheimer’s disease than the brains of women without neurologic disease. In conclusion, male microchimerism is frequent and widely distributed in the human female brain.     

Neuroanatomical Correlates of Recognizing Face Expressions in Mild Stages of Alzheimer’s Disease

Early Alzheimer’s disease can involve social disinvestment, possibly as a consequence of impairment of nonverbal communication skills. This study explores whether patients with Alzheimer’s disease at the mild cognitive impairment or mild dementia stage have impaired recognition of emotions in facial expressions, and describes neuroanatomical correlates of emotion processing impairment. As part of the ongoing PACO study (personality, Alzheimer’s disease and behaviour), 39 patients with Alzheimer’s disease at the mild cognitive impairment or mild dementia stage and 39 matched controls completed tests involving discrimination of four basic emotions—happiness, fear, anger, and disgust—on photographs of faces. In patients, automatic volumetry of 83 brain regions was performed on structural magnetic resonance images using MAPER (multi-atlas propagation with enhanced registration). From the literature, we identified for each of the four basic emotions one brain region thought to be primarily associated with the function of recognizing that emotion. We hypothesized that the volume of each of these regions would be correlated with subjects’ performance in recognizing the associated emotion. Patients showed deficits of basic emotion recognition, and these impairments were correlated with the volumes of the expected regions of interest. Unexpectedly, most of these correlations were negative: better emotional facial recognition was associated with lower brain volume. In particular, recognition of fear was negatively correlated with the volume of amygdala, disgust with pallidum, and happiness with fusiform gyrus. Recognition impairment in mild stages of Alzheimer’s disease for a given emotion was thus associated with less visible atrophy of functionally responsible brain structures within the patient group. Possible explanations for this counterintuitive result include neuroinflammation, regional β-amyloid deposition, or transient overcompensation during early stages of Alzheimer’s disease.     

Neuroinflammation and Memory: The Role of Prostaglandins

Neuroinflammation is a complex response to brain injury involving the activation of glia, release of inflammatory mediators within the brain, and recruitment of peripheral immune cells. Interestingly, memory deficits have been observed following many inflammatory states including infection, traumatic brain injury (TBI), normal aging, and Alzheimer’s disease (AD). Prostaglandins (PGs), a class of lipid mediators which can have inflammatory actions, are upregulated by these inflammatory challenges and can impair memory. In this paper, we critically review the success of nonsteroidal anti-inflammatory drugs, which prevent the formation of PGs, in preventing neuroinflammation-induced memory deficits following lipopolysaccharide injection, TBI, aging, and experimental models of AD in rodents and propose a mechanism by which PGs could disrupt memory formation.     

The Response of Cerebral Cortex to Haemorrhagic Damage: Experimental Evidence from a Penetrating Injury Model

Understanding the response of the brain to haemorrhagic damage is important in haemorrhagic stroke and increasingly in the understanding the cerebral degeneration and dementia that follow head trauma and head-impact sports. In addition, there is growing evidence that haemorrhage from small cerebral vessels is important in the pathogenesis of age-related dementia (Alzheimer’s disease). In a penetration injury model of rat cerebral cortex, we have examined the neuropathology induced by a needlestick injury, with emphasis on features prominent in the ageing and dementing human brain, particularly plaque-like depositions and the expression of related proteins. Needlestick lesions were made in neo- and hippocampal cortex in Sprague Dawley rats aged 3–5 months. Brains were examined after 1–30 d survival, for haemorrhage, for the expression of hyperphosphorylated tau, Aβ, amyloid precursor protein (APP), for gliosis and for neuronal death. Temporal cortex from humans diagnosed with Alzheimer’s disease was examined with the same techniques. Needlestick injury induced long-lasting changes–haem deposition, cell death, plaque-like deposits and glial invasion–along the needle track. Around the track, the lesion induced more transient changes, particularly upregulation of Aβ, APP and hyperphosporylated tau in neurons and astrocytes. Reactions were similar in hippocampus and neocortex, except that neuronal death was more widespread in the hippocampus. In summary, experimental haemorrhagic injury to rat cerebral cortex induced both permanent and transient changes. The more permanent changes reproduced features of human senile plaques, including the formation of extracellular deposits in which haem and Aβ-related proteins co-localised, neuronal loss and gliosis. The transient changes, observed in tissue around the direct lesion, included the upregulation of Aβ, APP and hyperphosphorylated tau, not associated with cell death. The findings support the possibility that haemorrhagic damage to the brain can lead to plaque-like pathology.     

The Role of Citrullinated Proteins Suggests a Novel Mechanism in the Pathogenesis of Multiple Sclerosis

The pathogenesis of MS is unknown. In our studies, we have demonstrated an important role for citrullinated myelin basic protein (MBP). The accompanying loss of positive charge compromises the ability of MBP to interact with the lipid bilayer. The conversion of arginine to citrulline in brain is carried out by an enzyme peptidyl arginine deiminase (PAD) 2. The amount of PAD 2 in brain was increased in MS normal-appearing white matter. The mechanism responsible for this increase involved hypomethylation of the promoter region in the PAD 2 gene in MS, but no change (compared to normal) was found in thymus tissue DNA from the same MS patients. In addition, no change was observed in other neurological diseases, including Alzheimer’s, Parkinson’s, and Huntington’s. We propose that citrullinated MBP, resulting from elevated levels of PAD 2 represents an important biochemical pathway in the pathogenesis of MS. Special issue dedicated to Anthony Campagnoni.