Douglas G. Walker

Inflammation and Alzheimer’s disease

Inflammation clearly occurs in pathologically vulnerable regions of the Alzheimers disease (AD) brain, and it does so with the full complexity of local peripheral inflammatory responses. In the periphery, degenerating tissue and the deposition of highly insoluble abnormal materials are classical stimulants of inflammation. Likewise, in the AD brain damaged neurons and neurites and highly insoluble amyloid beta peptide deposits and neurofibrillary tangles provide obvious stimuli for inflammation. Because these stimuli are discrete, microlocalized, and present from early preclinical to terminal stages of AD, local upregulation of complement, cytokines, acute phase reactants, and other inflammatory mediators is also discrete, microlocalized, and chronic. Cumulated over many years, direct and bystander damage from AD inflammatory mechanisms is likely to significantly exacerbate the very pathogenic processes that gave rise to it. Thus, animal models and clinical studies, although still in their infancy, strongly suggest that AD inflammation significantly contributes to AD pathogenesis. By better understanding AD inflammatory and immunoregulatory processes, it should be possible to develop anti-inflammatory approaches that may not cure AD but will likely help slow the progression or delay the onset of this devastating disorder.

Multi-organ distribution of phosphorylated α-synuclein histopathology in subjects with Lewy body disorders

A sensitive immunohistochemical method for phosphorylated α-synuclein was used to stain sets of sections of spinal cord and tissue from 41 different sites in the bodies of 92 subjects, including 23 normal elderly, 7 with incidental Lewy body disease (ILBD), 17 with Parkinson’s disease (PD), 9 with dementia with Lewy bodies (DLB), 19 with Alzheimer’s disease with Lewy bodies (ADLB) and 17 with Alzheimer’s disease with no Lewy bodies (ADNLB). The relative densities and frequencies of occurrence of phosphorylated α-synuclein histopathology (PASH) were tabulated and correlated with diagnostic category. The greatest densities and frequencies of PASH occurred in the spinal cord, followed by the paraspinal sympathetic ganglia, the vagus nerve, the gastrointestinal tract and endocrine organs. The frequency of PASH within other organs and tissue types was much lower. Spinal cord and peripheral PASH was most common in subjects with PD and DLB, where it appears likely that it is universally widespread. Subjects with ILBD had lesser densities of PASH within all regions, but had frequent involvement of the spinal cord and paraspinal sympathetic ganglia, with less-frequent involvement of end-organs. Subjects with ADLB had infrequent involvement of the spinal cord and paraspinal sympathetic ganglia with rare involvement of end-organs. Within the gastrointestinal tract, there was a rostrocaudal gradient of decreasing PASH frequency and density, with the lower esophagus and submandibular gland having the greatest involvement and the colon and rectum the lowest.

Inflammation and Alzheimer's disease pathogenesis

Appreciation of the role that inflammatory mediators play in Alzheimers disease (AD) pathogenesis continues to be hampered by two related misconceptions. The first is that to be pathogenically significant a neurodegenerative mechanism must be primary. The second is that inflammation merely occurs to clear the detritis of already existent pathology. The present review addresses these issues by showing that 1) inflammatory molecules and mechanisms are uniquely present or significantly elevated in the AD brain, 2) inflammation may be a necessary component of AD pathogenesis, 3) inflammation may be sufficient to cause AD neurodegeneration, and 4) retrospective and direct clinical trials suggest a therapeutic benefit of conventional antiinflammatory medications in slowing the progress or even delaying the onset of AD.

Inflammatory repertoire of Alzheimer's disease and nondemented elderly microglia in vitro

We have previously developed and characterized isolated microglia and astrocyte cultures from rapid (<4 h) brain autopsies of Alzheimers disease (AD) and nondemented elderly control (ND) patients. In the present study, we evaluate the inflammatory repertoire of AD and ND microglia cultured from white matter (corpus callosum) and gray matter (superior frontal gyrus) with respect to three major proinflammatory cytokines, three chemokines, a classical pathway complement component, a scavenger cell growth factor, and a reactive nitrogen intermediate. Significant, dose‐dependent increases in the production of pro‐interleukin‐1β (pro‐IL‐1β), interleukin‐6 (IL‐6), tumor necrosis factor‐α (TNF‐α), monocyte chemoattractant protein‐1 (MCP‐1), macrophage inflammatory peptide‐1α (MIP‐1α), IL‐8, and macrophage colony‐stimulating factor (M‐CSF) were observed after exposure to pre‐aggregated amyloid β peptide (1–42) (Aβ1–42). Across constitutive and Aβ‐stimulated conditions, secretion of complement component C1q, a reactive nitrogen intermediate, and M‐CSF was significantly higher in AD compared with ND microglia. Taken together with previous in situ hybridization findings, these results demonstrate unequivocally that elderly human microglia provide a brain endogenous source for a wide range of inflammatory mediators. GLIA 35:72–79, 2001.

Unified Staging System for Lewy Body Disorders: Correlation with Nigrostriatal Degeneration, Cognitive Impairment and Motor Dysfunction

The two current major staging systems in use for Lewy body disorders fail to classify up to 50% of subjects. Both systems do not allow for large numbers of subjects who have Lewy-type α-synucleinopathy (LTS) confined to the olfactory bulb or who pass through a limbic-predominant pathway that at least initially bypasses the brainstem. The results of the current study, based on examination of a standard set of ten brain regions from 417 subjects stained immunohistochemically for α-synuclein, suggest a new staging system that, in this study, allows for the classification of all subjects with Lewy body disorders. The autopsied subjects included elderly subjects with Parkinson’s disease, dementia with Lewy bodies, incidental Lewy body disease and Alzheimer’s disease with Lewy bodies, as well as comparison groups without Lewy bodies. All subjects were classifiable into one of the following stages: I. Olfactory Bulb Only; IIa Brainstem Predominant; IIb Limbic Predominant; III Brainstem and Limbic; IV Neocortical. Progression of subjects through these stages was accompanied by a generally stepwise worsening in terms of striatal tyrosine hydroxylase concentration, substantia nigra pigmented neuron loss score, Mini Mental State Examination score and score on the Unified Parkinson’s Disease Rating Scale Part 3. Additionally, there were significant correlations between these measures and LTS density scores. It is suggested that the proposed staging system would improve on its predecessors by allowing classification of a much greater proportion of cases.

RAGE potentiates Aβ‐induced perturbation of neuronal function in transgenic mice

Receptor for Advanced Glycation Endproducts (RAGE), a multiligand receptor in the immunoglobulin superfamily, functions as a signal‐transducing cell surface acceptor for amyloid‐beta peptide (Aβ). In view of increased neuronal expression of RAGE in Alzheimers disease, a murine model was developed to assess the impact of RAGE in an Aβ‐rich environment, employing transgenics (Tgs) with targeted neuronal overexpression of RAGE and mutant amyloid precursor protein (APP). Double Tgs (mutant APP (mAPP)/RAGE) displayed early abnormalities in spatial learning/memory, accompanied by altered activation of markers of synaptic plasticity and exaggerated neuropathologic findings, before such changes were found in mAPP mice. In contrast, Tg mice bearing a dominant‐negative RAGE construct targeted to neurons crossed with mAPP animals displayed preservation of spatial learning/memory and diminished neuropathologic changes. These data indicate that RAGE is a cofactor for Aβ‐induced neuronal perturbation in a model of Alzheimers‐type pathology, and suggest its potential as a therapeutic target to ameliorate cellular dysfunction.

Molecular and Cellular Characterization of the Membrane Attack Complex, C5b-9, in Alzheimer’s Disease

The membrane attack complex, C5b-9, is of considerable importance in many inflammatory reactions. It is the terminal, cytolytic component of both classical and alternative pathway activation, and its presence presupposes other potentially destructive complement constituents, including anaphylotoxins and opsonins. We have characterized C5b-9 and its C9 constituent in the Alzheimers disease (AD) and nondemented elderly (ND) brain using immunohistochemistry at the light and electron microscopic levels, Western blot analysis, and the reverse transcriptase polymerase chain reaction. We have also conducted in vitro ELISA assays of amyloid beta-peptide-stimulated SC5b-9 production. C5b-9 is abundantly present in Alzheimers disease cortex, associated with neurofibrillary tangle containing neurons, dystrophic neurites within neuritic plaques, and neuropil threads, but is weakly detected, if at all, in nondemented elderly cortex under the same conditions. Staining of Alzheimers disease sections is abolished both by deletion of primary antibody or preabsorption with purified SC5b-9.

Distribution of clusterin in Alzheimer brain tissue

The immunohistochemical distribution of clusterin (SP40,40, SGP-2) was determined in Alzheimer disease (AD) and normal human brain tissue and compared with the distributions of vitronectin, protectin and the complement membrane attack complex (MAC). Antibodies to all four proteins showed staining of dystrophic neurites and neuropil threads in AD tissue, and residual serum in normal tissue, but only antibodies to clusterin and vitronectin strongly stained amyloid deposits in senile plaques. The clusterin antibody also showed punctate staining of some normal appearing AD pyramidal neurons, and very scattered staining of intracellular neurofibrillary tangles. Clusterin, vitronectin and protectin are all believed to inhibit membrane insertion by the MAC, and these data are consistent with upregulation of all three proteins in response to MAC formation in AD, and with a neuronal origin of clusterin.

The Sun Health Research Institute Brain Donation Program: description and experience, 1987-2007.

The Brain Donation Program at Sun Health Research Institute has been in continual operation since 1987, with over 1000 brains banked. The population studied primarily resides in the retirement communities of northwest metropolitan Phoenix, Arizona. The Institute is affiliated with Sun Health, a nonprofit community-owned and operated health care provider. Subjects are enrolled prospectively to allow standardized clinical assessments during life. Funding comes primarily from competitive grants. The Program has made short postmortem brain retrieval a priority, with a 2.75-h median postmortem interval for the entire collection. This maximizes the utility of the resource for molecular studies; frozen tissue from approximately 82% of all cases is suitable for RNA studies. Studies performed in-house have shown that, even with very short postmortem intervals, increasing delays in brain retrieval adversely affect RNA integrity and that cerebrospinal fluid pH increases with postmortem interval but does not predict tissue viability.

RAGE-dependent signaling in microglia contributes to neuroinflammation, Aβ accumulation, and impaired learning/memory in a mouse model of Alzheimer’s disease

Microglia are critical for amyloid‐β peptide (Aβ)‐mediated neuronal perturbation relevant to Alzheimers disease (AD) pathogenesis. We demonstrate that overexpression of receptor for advanced glycation end products (RAGE) in imbroglio exaggerates neuroinflammation, as evidenced by increased proinflammatory mediator production, Aβ accumulation, impaired learning/memory, and neurotoxicity in an Aβ‐rich environment. Transgenic (Tg) mice expressing human mutant APP (mAPP) in neurons and RAGE in microglia displayed enhanced IL‐1β and TNF‐α production, increased infiltration of microglia and astrocytes, accumulation of Aβ, reduced acetylcholine esterase (AChE) activity, and accelerated deterioration of spatial learning/memory. Notably, introduction of a signal transduction‐defective mutant RAGE (DN‐RAGE) to microglia attenuates deterioration induced by Aβ. These findings indicate that RAGE signaling in microglia contributes to the pathogenesis of an inflammatory response that ultimately impairs neuronal function and directly affects amyloid accumulation. We conclude that blockade of microglial RAGE may have a beneficial effect on Aβ‐mediated neuronal perturbation relevant to AD pathogenesis.—Fang, F., Lue, L.‐F., Yan, S., Xu, H., Luddy, J. S., Chen, D., Walker, D. G., Stern, D. M., Yan, S., Schmidt, A. M., Chen, J. X., Yan, S. S. RAGE‐dependent signaling in microglia contributes to neuroinflammation, Aβ accumulation, and impaired learning/memory in a mouse model of Alzheimers disease. FASEB J. 24, 1043–1055 (2010). www.fasebj.org