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Background

Olfactory impairment (OI) is an early symptom of neurodegenerative diseases (ND) and COVID-19 infection. Proteinopathies associated with ND include amyloid-β (Aβ), hyperphosphorylated τ (HPτ), α-synuclein (α-syn), and Tar DNA binding protein 43 (TDP43). It is unclear whether COVID-19 infection influences the listed proteinopathies in the olfactory bulb and tract (OB/OT) aggravating the OI.

Objective

To study proteinopathies associated with ND in the brain and OB/OT in 32 subjects with COVID-19 infection and 10 age- and gender-matched controls.

Methods

Postmortem brain tissue was assessed for various proteinopathies and the OB/OT for proteinopathies, inflammatory markers and a marker for severe acute respiratory syndrome coronavirus 2 spike protein.

Results

Twenty percent of control and 16% of COVID-19 subjects lacked proteinopathies in their OB/OT. HPτ was detected in OB/OT in 80% of controls and 81% of COVID-19 subjects, Aβ in 30% of controls and 16% of COVID-19 subjects. All controls lacked TDP43 in OB/OT, 40% displayed TDP43 in their brain. TDP43 was seen in the OB/OT in 38% of COVID-19 subjects, of whom 42% lacked TDP43 in the brain. Sixty percent of controls displayed α-syn in OB/OT and the brain, whereas 34% of COVID-19 subjects displayed α-syn in the OB/OT, of whom 36% lacked it in the brain.

Conclusions

All proteinopathies associated with ND were detected in OB/OT in COVID-19 patients whereas TDP43 was lacking in controls. Our results suggest that there might be an association between COVID-19 and TDP43 and α-syn in the OB/OT, which may explain the chronic OI.

Neuropathological assessment was conducted on 1630 subjects, representing 5% of all the deceased that had been sent to the morgue of Uppsala University Hospital during a 15-year-long period. Among the 1630 subjects, 1610 were ≥ 41 years of age (range 41 to 102 years). Overall, hyperphosphorylated (HP) τ was observed in the brains of 98% of the 1610 subjects, and amyloid β-protein (Aβ) in the brains of 64%. The most common alteration observed was Alzheimer disease neuropathologic change (ADNC) (56%), followed by primary age-related tauopathy (PART) in 26% of the subjects. In 16% of the subjects, HPτ was limited to the locus coeruleus. In 14 subjects (<1%), no altered proteins were observed. In 3 subjects, only Aβ was observed, and in 17, HPτ was observed in a distribution other than that seen in ADNC/PART. The transactive DNA-binding protein 43 (TDP43) associated with limbic-predominant age-related TDP encephalopathy (LATE) was observed in 565 (35%) subjects and α-synuclein (αS) pathology, i.e., Lewy body disease (LBD) or multi system atrophy (MSA) was observed in the brains of 21% of the subjects. A total of 39% of subjects with ADNC, 59% of subjects with PART, and 81% of subjects with HPτ limited to the locus coeruleus lacked concomitant pathologies, i.e., LATE-NC or LBD-NC. Of the 293 (18% of the 1610 subjects) subjects with dementia, 81% exhibited a high or intermediate level of ADNC. In 84% of all individuals with dementia, various degrees of concomitant alterations were observed; i.e., MIXED-NC was a common cause of dementia. A high or intermediate level of PART was observed in 10 subjects with dementia (3%), i.e., tangle-predominant dementia. No subjects exhibited only vascular NC (VNC), but in 17 subjects, severe VNC might have contributed to cognitive decline. Age-related tau astrogliopathy (ARTAG) was observed in 37% of the 1610 subjects and in 53% of those with dementia.

It has been suggested that alcohol consumption protects against Parkinson's disease (PD). Here we assessed postmortem tissue samples from the brains and livers of 100 subjects with ages at death ranging from 51 to 93. Twenty percent of these subjects were demented. We used standardized assessment strategies to assess both the brain and liver pathologies (LP). Our cohort included subjects with none, mild, moderate, and severe LP caused by alcohol consumption. We noted a significant negative correlation of categorical data between liver steatosis and alpha-synuclein (alpha S) in the brain and a significant negative correlation between the extent of liver steatosis and fibrosis and the extent of alpha S in the brain. There was a significant negative association between the observation of Alzheimer's type II astrocytes and alpha S pathology in the brain. No association was noted between LP and hyperphosphorylated tau (HP tau). No significant correlation could be seen between the extent of LP and the extent of HP tau, amyloid beta protein (A beta) or transactive DNA binding protein 43 (TDP43) in the brain. There were significant correlations observed between the extent of HP tau, A beta, alpha S, and TDP43 in the brain and between liver steatosis, inflammation, and fibrosis. Subjects with severe LP displayed a higher frequency of Alzheimer's type II astrocytes compared to those with no, or mild, LP. The assessed protein alterations were not more prevalent or severe in subjects with Alzheimer's type II astrocytes in the brain. In all cases, dementia was attributed to a combination of altered proteins, i.e., mixed dementia and dementia was observed in 30% of those with mild LP when compared with 13% of those with severe LP. In summary, our results are in line with the outcome obtained by the two recent meta-analyses suggesting that subjects with a history of alcohol consumption seldom develop an alpha-synucleinopathy.

Background: Amyloid-beta (A beta) is one of the hallmark lesions of Alzheimer's disease (AD). During the disease process, A beta undergoes biochemical changes, producing toxic beta variants, proposed to be detected within the neurons. Idiopathic normal pressure hydrocephalus (iNPH) causes cognitive impairment, gait, and urinary symptoms in elderly, that can be reversed by a ventriculo-peritoneal shunt. Majority of iNPH subjects display different A beta variants in their brain biopsies, obtained during shunting. Objective: To study the cellular compartmentalization of different A beta variants in brain biopsies from iNPH subjects. Methods: We studied the cellular localization of different proteoforms of A beta using antibodies towards different amino acid sequences or post-translational modifications of A beta, including clones 4G8, 6F/3D, unmodified- (7H3D6), pyroglutamylated-(N3pE), phosphorylated-(1E4E11) A beta and A beta protein precursor (A beta PP), in brain biopsies from 3 iNPH subjects, using immunohistochemistry and light microscopy (LM), light microscopy on semi-thin sections (LMst), and electron microscopy (EM). Results: In LM all A beta variants were detected. In LMst and EM, the A beta 4G8, 6F/3D, and the pyroglutamylated A beta were detected. The A beta PP was visualized by all methods. The A beta labelling was located extracellularly with no specific signal within the intracellular compartment, whereas the A beta PP was seen both intra- and extracellularly. Conclusions: TheA beta markers displayed extracellular localization when visualized by three assessment techniques, reflecting the pathological extracellular accumulation of A beta in the human brain. No intracellular A beta pathology was seen. A beta PP was visualized in intra- and extracellularly, which corresponds to the localization of the protein in the membranes of cells and organelles.

The objective of this study was to assess who is merited an autopsy in Sweden. Data from the Swedish cause of death (COD) registry over a period of 20 years was retrieved and analysed. A multinominal logistic regression analysis was performed to identify the variables that were most strongly associated with the performance of a clinical or forensic autopsy (CA/FA). A definite COD, i.e. a COD based on autopsy findings, was registered in 12.6% of all deceased during the investigated period. In the remaining cases, the COD was presumed by the clinicians. Being male, born in the Nordic region, dying in a private residence, and unnatural death were most strongly associated with the performance of CA/FA. In contrast, being female, dying from dementia, dying at a nursing home, being born outside of Europe, or living in a small city or rural area seldom led to the performance of CA/FA.

The above is certainly surprising as an autopsy provides an opportunity to investigate the cause of death, validate clinical diagnoses, detect unexpected aberrations, audit health care, and provide feedback to clinicians to facilitate their continuing education.

The hallmark alteration in alpha-synucleinopathies, alpha-synuclein, is observed not only in the brain but also in the peripheral tissues, particularly in the intestine. This suggests that endoscopic biopsies performed for colon cancer screening could facilitate the assessment of alpha-synuclein in the gastrointestinal (GI) tract. Using immunohistochemistry for alpha-synuclein, we assessed whether GI biopsies could be used to confirm an ongoing alpha-synucleinopathy. Seventy-four subjects with cerebral alpha-synucleinopathy in various Braak stages with concomitant GI biopsies were available for study. In 81% of the subjects, alpha-synuclein was seen in the mucosal/submucosal GI biopsies. Two subjects with severe cerebral alpha-synucleinopathy and a long delay between biopsy and death displayed no alpha-synuclein pathology in the gut, and 11 subjects with sparse cerebral alpha-synucleinopathy displayed GI alpha-synuclein up to 36 years prior to death. The finding that there was no GI alpha-synuclein in 19% of the subjects with cerebral alpha-synucleinopathy, and alpha-synuclein was observed in the gut of 11 subjects (15%) with sparse cerebral alpha-synucleinopathy even many years prior to death is unexpected and jeopardizes the use of assessment of alpha-synuclein in the peripheral tissue for confirmation of an ongoing cerebral alpha-synucleinopathy.

Alpha-synuclein (alpha-syn) aggregation is the hallmark pathological lesion in brains of patients with Parkinson's disease (PD) and related neurological disorders characterized as synucleinopathies. Accumulating evidence now indicates that alpha-syn deposition is also present within the gut and other peripheral organs outside the central nervous system (CNS). In the current study, we demonstrate for the first time that alpha-syn pathology also accumulates within the liver, the main organ responsible for substance clearance and detoxification. We further demonstrate that cultured human hepatocytes readily internalize oligomeric alpha-syn assemblies mediated, at least in part, by the gap junction protein connexin-32 (Cx32). Moreover, we identified a time-dependent accumulation of alpha-syn within the liver of three different transgenic (tg) mouse models expressing human alpha-syn under CNS-specific promoters, despite the lack of alpha-syn mRNA expression within the liver. Such a brain-to-liver transmission route could be further corroborated by detection of alpha-syn pathology within the liver of wild type mice one month after a single striatal alpha-syn injection. In contrast to the synucleinopathy models, aged mice modeling AD rarely show any amyloid-beta (Ass) deposition within the liver. In human post-mortem liver tissue, we identified cases with neuropathologically confirmed alpha-syn pathology containing alpha-syn within hepatocellular structures to a higher degree (75%) than control subjects without alpha-syn accumulation in the brain (57%). Our results reveal that alpha-syn accumulates within the liver and may be derived from the brain or other peripheral sources. Collectively, our findings indicate that the liver may play a role in the clearance and detoxification of pathological proteins in PD and related synucleinopathies.

Background: Stepwise occurrence of biochemically modified amyloid-beta (A beta) in the brain of subjects with Alzheimer's disease (AD) has been suggested to be of significance for cognitive impairment. Our previous reports have shown that A beta is observed in 63% of all subjects with idiopathic normal pressure hydrocephalus (iNPH) suggesting that the majority of iNPH subjects with A beta are indeed also suffering from AD.

Objective: We assessed the occurrence of biochemically modified A beta variants, in vivo, in subjects with iNPH and in a cohort of postmortem brain samples from patients with dementia.

Methods: We assessed A beta proteins in 127 diagnostic brain biopsies obtained from subjects with iNPH and in a cohort of subjects with dementia by means of immunohistochemistry.

Results: The pyroglutamylated A beta (pyA beta) precedes the aggregation of phosphorylated A beta (pA beta) during the AD neuropatho-logical change progression; moreover, these modified variants of A beta correlate with hyperphosphorylated tau in the frontal cortical area of human brain. Our results confirm the existence of the suggested biochemical stages of A beta aggregation that might be of significance for neurodegeneration leading to cognitive impairment.

Conclusion: The observation that both pyA beta and pA beta are seen in vivo in iNPH subjects is intriguing. It has been reported that most of the iNPH subjects with A beta in the brain biopsy indeed develop AD with time. Based on our current and previous results, it is clinically merited to obtain a diagnostic biopsy from a subject with iNPH. When A beta is observed in the biopsy, the biochemical characterization is of interest.

Point mutations in the amyloid precursor protein gene (APP) cause familial Alzheimer's disease (AD) by increasing generation or altering conformation of amyloid beta (A beta). Here, we describe the Uppsala APP mutation (Delta 690-695), the first reported deletion causing autosomal dominant AD. Affected individuals have an age at symptom onset in their early forties and suffer from a rapidly progressing disease course. Symptoms and biomarkers are typical of AD, with the exception of normal cerebrospinal fluid (CSF) A beta 42 and only slightly pathological amyloid-positron emission tomography signals. Mass spectrometry and Western blot analyses of patient CSF and media from experimental cell cultures indicate that the Uppsala APP mutation alters APP processing by increasing beta-secretase cleavage and affecting alpha-secretase cleavage. Furthermore, in vitro aggregation studies and analyses of patient brain tissue samples indicate that the longer form of mutated A beta, A beta Upp1-42(Delta 19-24), accelerates the formation of fibrils with unique polymorphs and their deposition into amyloid plaques in the affected brain.