Estifanos Ghebremedhin

Stages in the development of Parkinson’s disease-related pathology

The synucleinopathy, idiopathic Parkinson’s disease, is a multisystem disorder that involves only a few predisposed nerve cell types in specific regions of the human nervous system. The intracerebral formation of abnormal proteinaceous Lewy bodies and Lewy neurites begins at defined induction sites and advances in a topographically predictable sequence. As the disease progresses, components of the autonomic, limbic, and somatomotor systems become particularly badly damaged. During presymptomatic stages 1–2, inclusion body pathology is confined to the medulla oblongata/pontine tegmentum and olfactory bulb/anterior olfactory nucleus. In stages 3–4, the substantia nigra and other nuclear grays of the midbrain and forebrain become the focus of initially slight and, then, severe pathological changes. At this point, most individuals probably cross the threshold to the symptomatic phase of the illness. In the end-stages 5–6, the process enters the mature neocortex, and the disease manifests itself in all of its clinical dimensions.

Stages of the Pathologic Process in Alzheimer Disease: Age Categories From 1 to 100 Years

Two thousand three hundred and thirty two nonselected brains from 1- to 100-year-old individuals were examined using immunocytochemistry (AT8) and Gallyas silver staining for abnormal tau; immunocytochemistry (4G8) and Campbell-Switzer staining were used for the detection of&bgr;-amyloid. A total of 342 cases was negative in the Gallyas stain but when restaged for AT8 only 10 were immunonegative. Fifty-eight cases had subcortical tau predominantly in the locus coeruleus, but there was no abnormal cortical tau (subcortical Stages a-c). Cortical involvement (abnormal tau in neurites) was identified first in the transentorhinal region (Stage 1a, 38 cases). Transentorhinal pyramidal cells displayed pretangle material (Stage 1b, 236 cases). Pretangles gradually became argyrophilic neurofibrillary tangles (NFTs) that progressed in parallel with NFT Stages I to VI. Pretangles restricted to subcortical sites were seen chiefly at younger ages. Of the total cases, 1,031 (44.2%) had &bgr;-amyloid plaques. The first plaques occurred in the neocortex after the onset of tauopathy in the brainstem. Plaques generally developed in the 40s in 4% of all cases, culminating in their tenth decade (75%). &bgr;-amyloid plaques and NFTs were significantly correlated (p < 0.0001). These data suggest that tauopathy associated with sporadic Alzheimer disease may begin earlier than previously thought and possibly in the lower brainstem rather than in the transentorhinal region.

Cerebral amyloid angiopathy and its relationship to Alzheimer’s disease

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of the amyloid β-protein (Aβ) within cerebral vessels. The involvement of different brain areas in CAA follows a hierarchical sequence similar to that of Alzheimer-related senile plaques. Alzheimer’s disease patients frequently exhibit CAA. The expansion of CAA in AD often shows the pattern of full-blown CAA. The deposition of Aβ within capillaries distinguishes two types of CAA. One with capillary Aβ-deposition is characterized by a strong association with the apolipoprotein E (APOE) ε4 allele and by its frequent occurrence in Alzheimer’s disease cases whereas the other one lacking capillary Aβ-deposits is not associated with APOE ε4. Capillary CAA can be seen in every stage of CAA or AD-related Aβ-deposition. AD cases with capillary CAA show more widespread capillary Aβ-deposition than non-demented cases as well as capillary occlusion. In a mouse model of CAA, capillary CAA was associated with capillary occlusion and cerebral blood flow disturbances. Thus, blood flow alterations with subsequent hypoperfusion induced by CAA-related capillary occlusion presumably point to a second mechanism in which Aβ adversely affects the brain in AD in addition to its direct neurotoxic effects.

Parkinson’s disease: the thalamic components of the limbic loop are severely impaired by α-synuclein immunopositive inclusion body pathology

The Parkinsons disease (PD)-related inclusion body pathology comprises Lewy bodies (LBs) as well as Lewy neurites (LNs). The distribution and severity of this pathology were investigated in the thalamus of 12 autopsy cases with clinically diagnosed and neuropathologically confirmed PD. The LBs and LNs were visualized by immunoreactions against the protein alpha-synuclein. In the human thalamus during PD, a specific and highly stereotypical distribution pattern of LBs and LNs evolves. As in cortical and other subcortical regions, the components of human thalamus assigned to the limbic loop bear the brunt of the PD-related pathology. In contrast, the thalamic components integrated into the striatal and cerebellar loops as well as the primary sensory nuclei of the thalamus show at best a mildly developed pathology. Damage to the thalamic components of the limbic loop nuclei may contribute not only to the cognitive, emotional, and autonomic symptoms of PD but to the somatomotor and oculomotor dysfunctions as well.

Gender and age modify the association between APOE and AD-related neuropathology

Objective: To assess the impact of apolipoprotein E (APOE) polymorphism on AD-related neurofibrillary tangle (NFT) formation and senile plaques (SP). Methods: A sample of 729 routine autopsy brains (359 men, 370 women; age range, 60 to 99 years) was investigated. All brains were classified neuropathologically according to a procedure permitting differentiation of six NFT stages and three SP stages. APOE genotyping was performed on all cases. Results: The ε4 allele of APOE was associated not only with SP (p < 0.0001) but also with NFT formation (p < 0.0001). The effect of the ε4 allele on NFT formation was noted at ages ≥80 years (p < 0.0001) but not between ages 60 and 79 years (p = 0.12). An association between the ε4 allele and SP for women was found at ages 60 to 79 years (p < 0.0001) but not at ≥80 years of age (p = 0.063). By comparison, men showed an association in both age categories (p = 0.001 and p = 0.001). Conclusion: The results confirm the association between the ε4 allele and both types of AD-related lesions and show that this association is differentially modified by age and gender.

Capillary cerebral amyloid angiopathy identifies a distinct APOE e4-associated subtype of sporadic Alzheimer's disease

The deposition of amyloid β-protein (Aβ) in the vessel wall, i.e., cerebral amyloid angiopathy (CAA), is associated with Alzheimer’s disease (AD). Two types of CAA can be differentiated by the presence or absence of capillary Aβ-deposits. In addition, as in Alzheimer’s disease, risk for capillary CAA is associated with the apolipoprotein E (APOE) ε4-allele. Because these morphological and genetic differences between the two types of AD-related CAA exist, the question arises as to whether there exist further differences between AD cases with and without capillary CAA and, if so, whether capillary CAA can be employed to distinguish and define specific subtypes of AD. To address this question, we studied AD and control cases both with and without capillary CAA to identify the following: (1) distinguishing neuropathological features; (2) alterations in perivascular protein expression; and (3) genotype-specific associations. More widespread Aβ-plaque pathology was observed in AD cases with capillary CAA than in those without. Expression of perivascular excitatory amino acid transporter 2 (EAAT-2/GLT-1) was reduced in cortical astrocytes of AD cases with capillary CAA in contrast to those lacking capillary Aβ-deposition and controls. Genetically, AD cases with capillary CAA were strongly associated with the APOE ε4 allele compared to those lacking capillary CAA and to controls. To further validate the existence of distinct types of AD we analyzed polymorphisms in additional apoE- and cholesterol-related candidate genes. Our results revealed an association between AD cases without capillary CAA (i.e., AD cases with CAA but lacking capillary CAA and AD cases without CAA) and the T-allele of the α2macroglobulin receptor/low-density lipoprotein receptor-related protein-1 (LRP-1) C766T polymorphism as opposed to AD cases with capillary CAA and non-AD controls. Taken together, these results indicate that AD cases with capillary CAA differ significantly from other AD cases both genetically and morphologically, thereby pointing to a specific capillary CAA-related and APOE ε4-associated subtype of AD.

Spinocerebellar Ataxia Type 3 (SCA3): Thalamic Neurodegeneration Occurs Independently from Thalamic Ataxin-3 Immunopositive Neuronal Intranuclear Inclusions

In the last years progress has been made regarding the involvement of the thalamus during the course of the currently known polyglutamine diseases. Although recent studies have shown that the thalamus consistently undergoes neurodegeneration in Huntington’s disease (HD) and spinocerebellar ataxia type 2 (SCA2) it is still unclear whether it is also a consistent target of the pathological process of spinocerebellar ataxia type 3 (SCA3). Accordingly we studied the thalamic pathoanatomy and distribution pattern of ataxin‐3 immunopositive neuronal intranuclear inclusions (NI) in nine clinically diagnosed and genetically confirmed SCA3 patients and carried out a detailed statistical analysis of our findings. During our pathoanatomical study we disclosed (i) a consistent degeneration of the ventral anterior, ventral lateral and reticular thalamic nuclei; (ii) a degeneration of the ventral posterior lateral nucleus and inferior and lateral subnuclei of the pulvinar in the majority of these SCA3 patients; and (iii) a degeneration of the ventral posterior medial and lateral posterior thalamic nuclei, the lateral geniculate body and some of the limbic thalamic nuclei in some of them. Upon immunocytochemical analysis we detected NI in all of the thalamic nuclei of all of our SCA3 patients. According to our statistical analysis (i) thalamic neurodegeneration and the occurrence of ataxin‐3 immunopositive thalamic NI was not associated with the individual length of the CAG‐repeats in the mutated SCA3 allele, the patients age at disease onset and the duration of SCA3 and (ii) thalamic neurodegeneration was not correlated with the occurrence of ataxin‐3 immunopositive thalamic NI. This lack of correlation may suggest that ataxin‐3 immunopositive NI are not immediately decisive for the fate of affected nerve cells but rather represent unspecific and pathognomonic morphological markers of SCA3.

Coincident enrichment of phosphorylated IκBα, activated IKK, and phosphorylated p65 in the axon initial segment of neurons

Phosphorylation of the inhibitory protein IκBα by the activated IκB kinase (IKK) is a crucial step in the activation of the transcription factor NF-κB. In neurons of the mammalian central nervous system, constitutive activation of NF-κB has been previously documented. The cellular compartments involved in this activation have not yet been fully identified. Here we document a striking enrichment of several molecules involved in NF-κB activation in the axon initial segment (AIS) of neurons: Phosphorylated-IκBα (pIκBα), activated IKK, and p65 phosphorylated at serine 536 were found to be enriched in the AIS in vivo as well as in vitro. Both, pIκBα and activated IKK, were associated with cytoskeletal components of the AIS. Activated IKK was associated with the membrane cytoskeleton, whereas pIκBα was sequestered to microtubules of the AIS. Colchicine-induced depolymerization of microtubules resulted in the loss of pIκBα in the AIS, demonstrating that the integrity of the axonal cytoskeleton is essential for the clustering of this NF-κB pathway component. These data provide the first evidence for a compartmentalized clustering of NF-κB pathway components in the AIS and implicate this neuronal compartment in the activation of NF-κB.

The impact of argyrophilic grain disease on the development of dementia and its relationship to concurrent Alzheimer's disease-related pathology

Argyrophilic grain disease (AGD) constitutes a neurodegenerative disorder that occurs in the brains of the elderly and affects 5% of all patients with dementia. τ protein‐containing lesions known as argyrophilic grains and located predominantly in limbic regions of the brain characterize this disease. Dementia is encountered in only a subset of cases that display the morphological pattern of AGD. The aim of this study is to determine the role of concurrent Alzheimers disease (AD)‐related pathology for the development of dementia in AGD patients. A total of 204 post‐mortem brains from 30 demented and 49 nondemented AGD patients, 39 AD patients, and from 86 nondemented controls without AGD were staged for AD‐related neurofibrillary tangles (NFTs) as well as amyloid β‐protein (Aβ) deposition. To identify differences in AD‐related pathology between demented and nondemented AGD cases, and to differentiate the pattern of AD‐related changes in demented and nondemented AGD cases from that seen in AD and nondemented controls, we  statistically  compared  the  stages of Aβ and NFT distribution among these groups. Using a logistic regression model, we showed that AGD has a significant effect on the development of dementia beyond that attributable to AD‐related pathology (P < 0.005). Demented AGD cases showed lower stages of AD‐related pathology than did pure AD cases but higher stages than nondemented AGD patients. AGD associated dementia was seen in the presence of NFT (Braak)‐stages II–IV and Aβ‐phases 2–3, whereas those stages were not associated with dementia in the absence of AGD. In conclusion, AGD is a clinically relevant neurodegenerative entity that significantly contributes to the development of dementia by lowering the threshold for cognitive deficits in the presence of moderate amounts of AD‐related pathology.

Cerebral small vessel disease-induced Apolipoprotein E leakage is associated with Alzheimer disease and the accumulation of amyloid [beta]-protein in perivascular astrocytes

Apolipoprotein E (apoE) plays a role in the pathogenesis of Alzheimer disease (AD). It is involved in the receptor-mediated cellular clearance of the amyloid &bgr;-protein (A&bgr;) and in the perivascular drainage of the extracellular fluid. Microvascular changes are also associated with AD and have been discussed as a possible reason for altered perivascular drainage. To further clarify the role of apoE in the perivascular and vascular pathology in AD patients, we studied its occurrence and distribution in the perivascular space, the perivascular neuropil, and in the vessel wall of AD and control cases with and without small vessel disease (SVD). Apolipoprotein E was found in the perivascular space and in the neuropil around arteries of the basal ganglia from control and AD cases disclosing no major differences. Western blot analysis of basal ganglia tissue also revealed no significant differences pertaining to the amount of full-length and C-terminal truncated apoE in AD cases compared with controls. In contrast, A&bgr; occurred in apoE-positive perivascular astrocytes in AD cases but not in controls. In blood vessels, apoE and immunoglobulin G were detected within the SVD-altered vessel wall. The severity of SVD was associated with the occurrence of apoE in the vessel wall and with that of A&bgr; in perivascular astrocytes. These results point to an important role of apoE in the perivascular clearance of A&bgr; in the human brain. The occurrence of apoE and immunoglobulin G in SVD lesions and in the perivascular space suggests that the presence of SVD results in plasma-protein leakage into the brain. It is therefore tempting to speculate that apoE represents a pathogenetic link between SVD and AD.