Life-long overexpression of S100beta in Down's syndrome: implications for Alzheimer pathogenesis

Chronic overexpression of the neurite growth-promoting factor S100beta has been implicated in the pathogenesis of neuritic plaques in Alzheimer's disease. Such plaques are virtually universal in middle-aged Down's syndrome, making Down's a natural model of Alzheimer's disease. We determined numbers of astrocytes overexpressing S100beta, and of neurons overexpressing beta-amyloid precursor protein (beta-APP), and assayed for neurofibrillary tangles in neocortex of 20 Down's syndrome patients (17 weeks gestation to 68 years). Compared to controls, there were twice as many S100beta-immunoreactive (S100beta+) astrocytes in Down's patients at all ages: fetal, young, and adult (p = 0.01, or better, in each age group). These were activated (i.e., enlarged), and intensely immunoreactive, even in the fetal group. There were no neurofibrillary changes in fetal or young Down's patients. The numbers of S100beta+ astrocytes in young and adult Down's patients correlated with the numbers of neurons overexpressing beta-APP (p < 0.05). Our findings are consistent with the idea that conditions--including Down's syndrome--that promote chronic overexpression of S100beta may confer increased risk for later development of Alzheimer's disease.

Glial-neuronal interactions in Alzheimer's disease: the potential role of a 'cytokine cycle' in disease progression

The role of glial inflammatory processes in Alzheimer's disease has been highlighted by recent epidemiological work establishing head trauma as an important risk factor, and the use of anti-inflammatory agents as an important ameliorating factor, in this disease. This review advances the hypothesis that chronic activation of glial inflammatory processes, arising from genetic or environmental insults to neurons and accompanied by chronic elaboration of neuroactive glia-derived cytokines and other proteins, sets in motion a cytokine cycle of cellular and molecular events with neurodegenerative consequences. In this cycle, interleukin-1 is a key initiating and coordinating agent. Interleukin-1 promotes neuronal synthesis and processing of the beta-amyloid precursor protein, thus favoring continuing deposition of beta-amyloid, and activates astrocytes and promotes astrocytic synthesis and release of a number of inflammatory and neuroactive molecules. One of these, S100beta, is a neurite growth-promoting cytokine that stresses neurons through its trophic actions and fosters neuronal cell dysfunction and death by raising intraneuronal free calcium concentrations. Neuronal injury arising from these cytokine-induced neuronal insults can activate microglia with further overexpression of interleukin-1, thus producing feedback amplification and self-propagation of this cytokine cycle. Additional feedback amplification is provided through other elements of the cycle. Chronic propagation of this cytokine cycle represents a possible mechanism for progression of neurodegenerative changes culminating in Alzheimer's disease.

Nitric oxide synthase in developing retinas and after optic tract section

We compared the pattern of nitric oxide synthase (NOS) immunoreactivity in retinas of rats during normal development and after unilateral transection of the optic tract at postnatal day 7. NOS was first detected in the second postnatal week in the inner nuclear and inner plexiform layers. There was no detectable difference in the overall pattern of immunoreactivity between normal retinas and retinas with severe loss of ganglion cells due to the lesion. We suggest that NOS may have a role in synaptic and vascular development in the inner retina, but is unlikely to play a major role in normal physiological retinal ganglion cell death or axotomy-induced cell death.

A beta 42 is the predominant form of amyloid beta-protein in the brains of short-term survivors of head injury

Fatal head injury results in the formation of diffuse parenchymal deposits of amyloid beta-protein (A beta) in the brains of approximately 30% of individuals. We used carboxyl terminal-specific antisera to examine the exact nature of these deposits in paraffin sections of neocortex from seven head-injured patients. Immunostaining for A beta 42 was observed in all parenchymal deposits whereas staining for A beta 40, the form of the protein which predominates in serum and cerebrospinal fluid, was seen in only a small proportion of deposits. The relative paucity of A beta 40 suggests that post-traumatic deposits do not arise as a result of passive leakage from damaged cerebral blood vessels but are similar to the early A beta 42 parenchymal deposits seen in Down's syndrome and Alzheimer's disease.

Prion protein immunocytochemistry--UK five centre consensus report

Creutzfeldt-Jakob disease (CJD) and other prion diseases are associated with the deposition of insoluble prion protein (PrPCJD) in the central nervous system (CNS). Antibodies raised against PrPCJD also react with its precursor protein, a soluble form of PrP (PrPC), which is widely distributed in the normal CNS. This cross-reactivity has in the past raised doubts as to the specificity and diagnostic reliability of PrP immunolocalization, especially in familial cases which are atypical clinically and which lack characteristic pathology findings. Following an MRC-funded workshop which focused on this problem, a multicentre prospective study was set up to identify a reliable protocol for PrPCJD immunocytochemistry. Five UK centres took part in this study and demonstrated consistent staining of plaques, vacuolar deposits in severe spongiform change, and perineuronal deposits using a variety of antibodies and enhancement procedures. A protocol using formic acid, guanidine thiocyanate, and hydrated autoclaving pre-treatment in conjunction with a monoclonal PrPCJD antibody produced the clearest immunochemical results and is presented as the consensus UK recommendation for PrPCJD immunocytochemical procedures.

Is beta-APP a marker of axonal damage in short-surviving head injury?

beta-Amyloid precursor protein (beta-APP), a normal constituent of neurons which is conveyed by fast axonal transport, has been found to be a useful marker for axonal damage in cases of fatal head injury. Immunocytochemistry for beta-APP is a more sensitive technique for identifying axonal injury than conventional silver impregnation. This study was designed to determine how quickly evidence of axonal damage and bulb formation appears. Using this method a variety of brain areas were studied from 55 patients who died within 24 h of a head injury. Immunocytochemical evidence of axonal injury was first detected after 2 h survival, axonal bulbs were first identified after 3 h survival, and the amount of axonal damage and axonal bulb formation increased the longer the survival time.

Distribution of beta-amyloid precursor and B-cell lymphoma protooncogene proteins in the rat retina after optic nerve transection or vascular lesion

The expression of beta-amyloid precursor protein (APP) and B-cell lymphoma protooncogene protein (Bcl-2) in retinal cells in the rat was studied using immunocytochemistry at different times after intraorbital optic nerve transection or vascular lesion. Three hours to one month after transection of the optic nerve, a significant increase in APP and Bcl-2 immunostaining was observed in retinal Müller glia but not in retinal neurons. In contrast, injury to blood vessels that supply the eye without cutting the optic nerve resulted in a complete loss of APP and Bcl-2 immunostaining in Müller cells and an increase in immunoreactivity in distinct populations of retinal neurons. The overall pattern of APP immunostaining in Müller cells and neurons was essentially the same as that of Bcl-2 under identical experimental conditions. These results suggest that the expression of APP and Bcl-2 in retinal cells is dependent on the nature and severity of injury, and that rapid and common mechanisms are involved in regulating the expression of these molecules.

A quantitative comparison of plaque types in Alzheimer's disease and senile dementia of the Lewy body type

In a previous study we reported no difference in the overall beta-amyloid protein (beta AP) load between Alzheimer's disease (AD) and senile dementia of the Lewy body type (SDLT). However, it is possible that differences in the morphology of beta AP plaque types exist, analogous to the differences in cytoskeletal pathology found in these two disorders. We have carried out a quantitative image analysis of plaque subtypes in the temporal lobe of AD (n = 8), SDLT (n = 9) and control (n = 11) cases. Measurements of beta AP load and plaque density were consistently higher in AD and SDLT than in controls. When AD and SDLT cases were compared no differences were seen in either the density or relative proportions of classic and diffuse plaques. Based on these results we suggest that the variation in the clinical course of these diseases reflects differences in the cytoskeletal pathology, whereas the final stages of profound dementia common to both disorders is associated with the deposition of beta AP.

Altered beta-APP metabolism after head injury and its relationship to the aetiology of Alzheimer's disease

There is increasing evidence of a link between head injury and the subsequent onset of Alzheimer's disease. Deposits of amyloid beta-protein (A beta) are found not only in cases of dementia pugilistica but in some 30% of patients dying after a single episode of severe head injury. Detailed clinicopathological studies have shown that A beta deposition is most likely, but not exclusively, to occur, the older the patient at the time of injury, and if the injury is the result of a fall. Distribution studies have shown that the A beta is widely deposited in the neocortex and there is no apparent association with any of the multiple primary or secondary pathologies of traumatic brain injury. There is an increased expression of beta-APP particularly in the pre-alpha cells of the entorhinal cortex and in areas of axonal damage. Recent molecular genetic studies have shown that there is a strong association between deposits of A beta and the apolipoprotein E genotype of the individual.

Diagnosis and incidence of prion (Creutzfeldt-Jakob) disease: a retrospective archival survey with implications for future research

Reliable identification of Creutzfeldt-Jakob disease (CJD) in the UX has become essential following the suggestion that prion disease in cattle (BSE) might transmit, accidentally, to humans who eat contaminated beef. Recent data suggest that some cases of CJD may be clinically unrecognized; in order to examine this proposal we reviewed all cases of dementia (n = 1000+) collected in the Runwell Hospital Brain Archive between 1964 and 1990. We identified 19 cases of spongiform encephalopathy of which only 11 were diagnosed before death. These 11 individuals had a characteristic clinical history of CJD (relentless mental deterioration, prominent motor signs and death within a year). Their brains showed little or no external abnormality. In contrast, only two of the eight clinically unrecognized cases had characteristic symptoms. The remaining six presented atypically; their illness lasted 3 years or more, motor signs were much less evident, and simple dementia was the most prominent feature. The brains showed moderate or severe cerebral atrophy. Our data indicate that only about 60% of prion disease cases with pathologically typical spongiform encephalopathy were identified clinically during life. This suggests that human prion disease may be more common than previously supposed and that a further review of the epidemiology of the disease is required.

Quantification of beta APP immunoreactive pre-alpha cells in the entorhinal cortex using image analysis

The neuropathological diagnosis of Alzheimer's disease requires an assessment of the quantity of pathology present. Advances in molecular biology have highlighted the role of beta-amyloid precursor protein (beta APP) in the pathogenesis of the disease. This protein is found in neurons and other cells and many neuropathological studies would benefit from a method which generates reliable data on the numbers of cells containing significant amounts of the protein. Classically, generation of such data would have involved laborious manual counting. This particular approach carries low levels of inter- and intra-rater reliability and is much dependent on the skill and experience of the operator. We have used immunocytochemistry to specifically define a single cell population, pre-alpha cells, containing beta APP, and have developed a computerized cell counting programme that can reliably quantify these cells in human post-mortem brain samples. We have obtained a high level of accuracy (> 95%) and efficiency in identifying and quantifying target cells and have demonstrated that our protocol can be used effectively by both novice and expert. This method could be easily configured to provide quantitative data for a wide range of immunocytochemically defined cell populations.

Distribution of beta-amyloid protein in the brain following severe head injury

Deposits of beta-amyloid protein (beta AP) can be found in the brains of 30% of fatally head-injured patients; they have been found in children and after survival times of only 4 h. The principal aims of this study were to map the distribution of beta AP in 14 patients aged 65 years or less in whom it was known that the protein had been deposited, and to correlate its distribution with the pathologies of traumatic brain injury. The results show that beta AP is widely distributed, and that there is no correlation between its presence and cerebral contusions, intracranial haematoma, axonal injury, ischaemic brain damage, brain swelling or the pathology of raised intracranial pressure. These findings suggest that the deposition of beta AP is a consequence of the acute phase response of nerve cells to stress in susceptible individuals. Further studies will be required to establish the possible relationship between the deposition of beta AP following head injury and the molecular neuropathology of Alzheimer's disease.

Axonal injury: a universal consequence of fatal closed head injury?

beta-Amyloid precursor protein immunostaining has recently been shown to be a reliable method for detecting the damage to axons associated with fatal head injury. In an attempt to compare the efficacy of this technique with conventional histological detection of axonal damage, we have reanalysed sections from a large well-characterised series of head-injured and control patients. The results indicate that the frequency of axonal injury has been vastly underestimated using conventional silver techniques, and that axonal injury may in fact be an almost universal consequence of fatal head injury.

Increased numbers of beta APP-immunoreactive neurones in the entorhinal cortex after head injury

In a previous publication we hypothesized that Alzheimer's disease (AD) can be induced by the age-related increase in expression of beta-amyloid precursor protein (beta APP) in the medial temporal lobe. Head injury has also been identified as a risk factor for AD and as such, similarities should exist between the pathology found after head injury and the earliest stages of pathology in AD. In this study, we have quantified the number of beta APP-immunoreactive neurones in the medial temporal cortex (pre-alpha cells, layer II) of 13 head injured and 17 control patients. Significantly more beta APP immunoreactive neurones were observed in head injury cases (mean 18.4 per cluster) compared with controls (mean 13.4 per cluster, p < 0.05). These data provide a mechanism to explain how an environmental event such as head injury can generate the same molecular pathology (increased neuronal beta APP) as is found in the earliest stages of AD.

Microglial interleukin-1 alpha expression in human head injury: correlations with neuronal and neuritic beta-amyloid precursor protein expression

Activated microglia containing IL-1 alpha-immunoreactive (IL-1 alpha +) product were increased 3-fold in number in the acute phase following head injury, a risk factor for later development of Alzheimer's disease, and this increase was correlated with a 7-fold increase in the number of neurons with elevated beta-amyloid precursor protein (beta-APP) levels (R = 0.78; P < 0.05). Furthermore, clusters of beta-APP+ dystrophic neurites present in these patients were invariably associated with activated IL-1 alpha + microglia. These findings suggest that early overexpression of IL-1 alpha and beta-APP is a priming event for later neuropathological changes evident at end stages of Alzheimer's disease.

The distribution of nitric oxide synthase immunoreactivity in the human brain

Nitric oxide is a free radical which is produced in the brain and is thought to be the first of a new class of neural messenger molecules. It is postulated to act by inducing an increase in cyclic guanosine monophosphate levels in target cells. The neuronal isoform of nitric oxide synthase, the enzyme responsible for the calcium-dependent synthesis of nitric oxide from L-arginine, has been purified from brain homogenate. Using a specific polyclonal antibody, we have localized brain nitric oxide synthase to the cytosol of discrete neuronal subpopulations and glial elements. These include non-pyramidal cells in the cerebral cortex, pyramidal and non-pyramidal cells of the hippocampus, aspiny neurons of the corpus striatum, basket, Purkinje and granule cells in the cerebellum and neurons of various brain stem nuclei. The localization of nitric oxide-producing neurons in morphologically different and neurochemically diverse cell types suggests a widespread neuromodulatory role for nitric oxide in the central nervous system of man.

Beta amyloid protein deposition in the brain after severe head injury: implications for the pathogenesis of Alzheimer's disease

In a recent preliminary study it was reported that a severe head injury resulted in the deposition of beta amyloid protein (beta AP) in the cortical ribbon of 30% of patients who survived for less than two weeks. Multiple cortical areas have now been examined from 152 patients (age range 8 weeks-81 years) after a severe head injury with a survival time of between four hours and 2.5 years. This series was compared with a group of 44 neurologically normal controls (age range 51 to 80 years). Immunostaining with an antibody to beta AP confirmed the original findings that 30% of cases of head injury have beta AP deposits in one or more cortical areas. Increasing age seemed to accentuate the extent of beta AP deposition and potential correlations with other pathological changes associated with head injury were also investigated. In addition, beta amyloid precursor protein (beta APP) immunoreactivity was increased in the perikarya of neurons in the vicinity of beta AP deposits. The data from this study support proposals that increased expression of beta APP is part of an acute phase response to neuronal injury in the human brain, that extensive overexpression of beta APP can lead to deposition of beta AP and the initiation of an Alzheimer disease-type process within days, and that head injury may be an important aetiological factor in Alzheimer's disease.

Markers of axonal injury in post mortem human brain

beta-Amyloid precursor protein (beta APP) can be detected immunocytochemically at sites of axonal injury in the brain, and has recently been found to be a useful marker for injured axons in patients who survived for only 3 h after head trauma. It is transported by fast axonal transport and is thought to accumulate in detectable levels where the cytoskeleton breaks down. If this theory is correct, other substances should accumulate here in the same way, so we have used antibodies to other neuronal proteins to compare their efficacy as markers of axonal injury. SNAP-25, chromogranin A and cathepsin D also marked injured axons at all survival times studied (2.5 h-2 weeks), although they were not as sensitive or specific as beta APP. Immunolabelling for the 68-kDa neurofilament subunit (NF68) was present in most uninjured axons, and allowed axonal swellings to be seen in some cases. Synaptophysin, GAP-43, ubiquitin or tau did not label any normal or injured axons in this study. We, therefore, suggest that beta APP should be the immunocytochemical marker of choice for the detection of injured axons. This study also showed that microwave antigen retrieval significantly enhances the immunoreactivity of SNAP-25, chromogranin A, synaptophysin, GAP-43, ubiquitin and tau, in addition to that of beta APP, in formalin-fixed, paraffin-embedded tissue, and reveals NF68 antigenicity where it was not previously detectable.

Beta-amyloid precursor protein (beta APP) as a marker for axonal injury after head injury

It has been demonstrated recently that beta-amyloid protein (beta AP), generally associated with the plaques of Alzheimer's disease, can also be found in the brains of survivors of head injury. In this study the distribution of the beta AP precursor protein (beta APP) was examined immunohistochemically to determine if it is colocalized with beta AP in such cases. beta APP immunoreactivity was observed in neuronal perikarya in the neocortex and in dystrophic neurites surrounding beta AP immunoreactive plaques i.e. in a distribution similar to that seen in Alzheimer's disease. In addition, beta APP immunoreactivity was noted within white matter tracts where it marked damaged axons. However, no colocalisation of beta APP with beta AP was observed in any white matter region. These results indicate that processing of beta APP to produce beta AP occurs in the synaptic terminal field of axons and illustrate the utility of beta APP immunoreactivity as a general marker for axonal injury.

Differential pattern of beta-amyloid protein deposition within cortical sulci and gyri in Alzheimer's disease

We have quantified the pattern of beta-amyloid protein (beta AP) deposition in the sulci and gyri of the frontal cortex in Alzheimer's disease. The distribution pattern in the frontal cortex gyri is unequivocally different from the pattern found in the frontal sulci. These findings, in conjunction with our previous studies, reflect a differential vulnerability between the sulci and the gyri with respect to Alzheimer's disease pathology, sulci being affected to a greater extent. It is probable that the different patterns of deposition relate to the underlying cytoarchitecture of the cortex.