Compilation of reported protein changes in the brain in Alzheimer's disease
Proteomic studies of human Alzheimer's disease brain tissue have potential to identify protein changes that drive disease, and to identify new drug targets. Here, we analyse 38 published Alzheimer's disease proteomic studies, generating a map of protein changes in human brain tissue across thirteen brain regions, three disease stages (preclinical Alzheimer's disease, mild cognitive impairment, advanced Alzheimer's disease), and proteins enriched in amyloid plaques, neurofibrillary tangles, and cerebral amyloid angiopathy. Our dataset is compiled into a searchable database (NeuroPro). We found 848 proteins were consistently altered in 5 or more studies. Comparison of protein changes in early-stage and advanced Alzheimer's disease revealed proteins associated with synapse, vesicle, and lysosomal pathways show change early in disease, but widespread changes in mitochondrial associated protein expression change are only seen in advanced Alzheimer's disease. Protein changes were similar for brain regions considered vulnerable and regions considered resistant. This resource provides insight into Alzheimer's disease brain protein changes and highlights proteins of interest for further study.
Use of Affinity Purification-Mass Spectrometry to Identify Phosphorylated Tau Interactors in Alzheimer's Disease
Phosphorylated tau is the main protein present in neurofibrillary tangles, the presence of which is a key neuropathological hallmark of Alzheimer's disease (AD). The toxic effects of phosphorylated tau are likely mediated by interacting proteins; however, methods to identify these interacting proteins comprehensively in human brain tissue are limited. Here, we describe a method that enables the efficient identification of hundreds of proteins that interact with phosphorylated tau (pTau), using affinity purification-mass spectrometry (AP-MS) on human, fresh-frozen brain tissue from donors with AD. Tissue is homogenized using a gentle technique that preserves protein-protein interactions, and co-immunoprecipitation of pTau and its interacting proteins is performed using the PHF1 antibody. The resulting protein interactors are then identified using label-free quantitative liquid chromatography-mass spectrometry (LC-MS)/MS. The Significance Analysis of INTeractome (SAINT) algorithm is used to determine which proteins significantly interact with pTau. This approach enables the detection of an abundance of all 6 isoforms of tau, 23 phosphorylated residues on tau, and 125 significant pTau protein interactors, in human AD brain tissue.
The amyloid plaque proteome in early onset Alzheimer's disease and Down syndrome
Amyloid plaques contain many proteins in addition to beta amyloid (AÎ²). Previous studies examining plaque-associated proteins have shown these additional proteins are important; they provide insight into the factors that drive amyloid plaque development and are potential biomarkers or therapeutic targets for Alzheimer's disease (AD). The aim of this study was to comprehensively identify proteins that are enriched in amyloid plaques using unbiased proteomics in two subtypes of early onset AD: sporadic early onset AD (EOAD) and Down Syndrome (DS) with AD. We focused our study on early onset AD as the drivers of the more aggressive pathology development in these cases is unknown and it is unclear whether amyloid-plaque enriched proteins differ between subtypes of early onset AD. Amyloid plaques and neighbouring non-plaque tissue were microdissected from human brain sections using laser capture microdissection and label-free LC-MS was used to quantify the proteins present. 48 proteins were consistently enriched in amyloid plaques in EOAD and DS. Many of these proteins were more significantly enriched in amyloid plaques than AÎ². The most enriched proteins in amyloid plaques in both EOAD and DS were: COL25A1, SMOC1, MDK, NTN1, OLFML3 and HTRA1. Endosomal/lysosomal proteins were particularly highly enriched in amyloid plaques. Fluorescent immunohistochemistry was used to validate the enrichment of four proteins in amyloid plaques (moesin, ezrin, ARL8B and SMOC1) and to compare the amount of total AÎ², AÎ²40, AÎ²42, phosphorylated AÎ², pyroglutamate AÎ² species and oligomeric species in EOAD and DS. These studies showed that phosphorylated AÎ², pyroglutamate AÎ² species and SMOC1 were significantly higher in DS plaques, while oligomers were significantly higher in EOAD. Overall, we observed that amyloid plaques in EOAD and DS largely contained the same proteins, however the amount of enrichment of some proteins was different in EOAD and DS. Our study highlights the significant enrichment of many proteins in amyloid plaques, many of which may be potential therapeutic targets and/or biomarkers for AD.
It takes more than tau to tangle: using proteomics to determine how phosphorylated tau mediates toxicity in neurodegenerative diseases
Proteomics and Transcriptomics of the Hippocampus and Cortex in SUDEP and High-Risk SUDEP Patients
OBJECTIVE:To identify the molecular signaling pathways underlying sudden unexpected death in epilepsy (SUDEP) and high-risk SUDEP compared to epilepsy control patients. METHODS:For proteomics analyses, we evaluated the hippocampus and frontal cortex from microdissected post-mortem brain tissue of 12 SUDEP and 14 non-SUDEP epilepsy patients. For transcriptomics analyses, we evaluated hippocampus and temporal cortex surgical brain tissue from mesial temporal lobe epilepsy (MTLE) patients: 6 low-risk and 8 high-risk SUDEP as determined by a short (< 50 seconds) or prolonged (â‰¥ 50 seconds) postictal generalized EEG suppression (PGES) that may indicate severely depressed brain activity impairing respiration, arousal, and protective reflexes. RESULTS:In autopsy hippocampus and cortex, we observed no proteomic differences between SUDEP and non-SUDEP epilepsy patients, contrasting with our previously reported robust differences between epilepsy and non-epilepsy control patients. Transcriptomics in hippocampus and cortex from surgical epilepsy patients segregated by PGES identified 55 differentially expressed genes (37 protein-coding, 15 lncRNAs, three pending) in hippocampus. CONCLUSION/CONCLUSIONS:The SUDEP proteome and high-risk SUDEP transcriptome were similar to other epilepsy patients in hippocampus and frontal cortex, consistent with diverse epilepsy syndromes and comorbidities associated with SUDEP. Studies with larger cohorts and different epilepsy syndromes, as well as additional anatomic regions may identify molecular mechanisms of SUDEP.
Proteomic differences in the hippocampus and cortex of epilepsy brain tissue
Epilepsy is a common neurological disorder affecting over 70 million people worldwide, with a high rate of pharmaco-resistance, diverse comorbidities including progressive cognitive and behavioural disorders, and increased mortality from direct (e.g. sudden unexpected death in epilepsy, accidents, drowning) or indirect effects of seizures and therapies. Extensive research with animal models and human studies provides limited insights into the mechanisms underlying seizures and epileptogenesis, and these have not translated into significant reductions in pharmaco-resistance, morbidities or mortality. To help define changes in molecular signalling networks associated with seizures in epilepsy with a broad range of aetiologies, we examined the proteome of brain samples from epilepsy and control cases. Label-free quantitative mass spectrometry was performed on the hippocampal cornu ammonis 1-3 region (CA1-3), frontal cortex and dentate gyrus microdissected from epilepsy and control cases (n = 14/group). Epilepsy cases had significant differences in the expression of 777 proteins in the hippocampal CA1 - 3 region, 296 proteins in the frontal cortex and 49 proteins in the dentate gyrus in comparison to control cases. Network analysis showed that proteins involved in protein synthesis, mitochondrial function, G-protein signalling and synaptic plasticity were particularly altered in epilepsy. While protein differences were most pronounced in the hippocampus, similar changes were observed in other brain regions indicating broad proteomic abnormalities in epilepsy. Among the most significantly altered proteins, G-protein subunit beta 1 (GNB1) was one of the most significantly decreased proteins in epilepsy in all regions studied, highlighting the importance of G-protein subunit signalling and G-protein-coupled receptors in epilepsy. Our results provide insights into common molecular mechanisms underlying epilepsy across various aetiologies, which may allow for novel targeted therapeutic strategies.
Phosphorylated tau interactome in the human Alzheimer's disease brain
Accumulation of phosphorylated tau is a key pathological feature of Alzheimer's disease. Phosphorylated tau accumulation causes synaptic impairment, neuronal dysfunction and formation of neurofibrillary tangles. The pathological actions of phosphorylated tau are mediated by surrounding neuronal proteins; however, a comprehensive understanding of the proteins that phosphorylated tau interacts with in Alzheimer's disease is surprisingly limited. Therefore, the aim of this study was to determine the phosphorylated tau interactome. To this end, we used two complementary proteomics approaches: (i) quantitative proteomics was performed on neurofibrillary tangles microdissected from patients with advanced Alzheimer's disease; and (ii) affinity purification-mass spectrometry was used to identify which of these proteins specifically bound to phosphorylated tau. We identified 542 proteins in neurofibrillary tangles. This included the abundant detection of many proteins known to be present in neurofibrillary tangles such as tau, ubiquitin, neurofilament proteins and apolipoprotein E. Affinity purification-mass spectrometry confirmed that 75 proteins present in neurofibrillary tangles interacted with PHF1-immunoreactive phosphorylated tau. Twenty-nine of these proteins have been previously associated with phosphorylated tau, therefore validating our proteomic approach. More importantly, 34 proteins had previously been associated with total tau, but not yet linked directly to phosphorylated tau (e.g. synaptic protein VAMP2, vacuolar-ATPase subunit ATP6V0D1); therefore, we provide new evidence that they directly interact with phosphorylated tau in Alzheimer's disease. In addition, we also identified 12 novel proteins, not previously known to be physiologically or pathologically associated with tau (e.g. RNA binding protein HNRNPA1). Network analysis showed that the phosphorylated tau interactome was enriched in proteins involved in the protein ubiquitination pathway and phagosome maturation. Importantly, we were able to pinpoint specific proteins that phosphorylated tau interacts with in these pathways for the first time, therefore providing novel potential pathogenic mechanisms that can be explored in future studies. Combined, our results reveal new potential drug targets for the treatment of tauopathies and provide insight into how phosphorylated tau mediates its toxicity in Alzheimer's disease.
APOE-amyloid interaction: Therapeutic targets
Alzheimer's disease (AD) is a devastating neurodegenerative disorder that is growing in prevalence globally. It is the only major cause of death without any effective pharmacological means to treat or slow progression. Inheritance of the Îµ4 allele of the Apolipoprotein (APO) E gene is the strongest genetic risk factor for late-onset AD. The interaction between APOE and amyloid Î² (AÎ²) plays a key role in AD pathogenesis. The APOE-AÎ² interaction regulates AÎ² aggregation and clearance and therefore directly influences the development of amyloid plaques, congophilic amyloid angiopathy and subsequent tau related pathology. Relatively few AD therapeutic approaches have directly targeted the APOE-AÎ² interaction thus far. Here we review the critical role of APOE in the pathogenesis of AD and some of the most promising therapeutic approaches that focus on the APOE-AÎ² interaction.
Using Proteomics to Understand Alzheimer's Disease Pathogenesis
Brisbane (AU) : Codon Publications, 2019
Secernin-1 is a novel phosphorylated tau binding protein that accumulates in Alzheimer's disease and not in other tauopathies
We recently identified Secernin-1 (SCRN1) as a novel amyloid plaque associated protein using localized proteomics. Immunohistochemistry studies confirmed that SCRN1 was present in plaque-associated dystrophic neurites and also revealed distinct and abundant co-localization with neurofibrillary tangles (NFTs). Little is known about the physiological function of SCRN1 and its role in Alzheimer's disease (AD) and other neurodegenerative diseases has not been studied. Therefore, we performed a comprehensive study of SCRN1 distribution in neurodegenerative diseases. Immunohistochemistry was used to map SCRN1 accumulation throughout the progression of AD in a cohort of 58 patients with a range of NFT pathology (Abundant NFT, nâ€‰=â€‰21; Moderate NFT, nâ€‰=â€‰22; Low/No NFT, nâ€‰=â€‰15), who were clinically diagnosed as having AD, mild cognitive impairment or normal cognition. SCRN1 accumulation was also examined in two cases with both Frontotemporal Lobar Degeneration (FTLD)-Tau and AD-related neuropathology, cases of Down Syndrome (DS) with AD (nâ€‰=â€‰5), one case of hereditary cerebral hemorrhage with amyloidosis - Dutch type (HCHWA-D) and other non-AD tauopathies including: primary age-related tauopathy (PART, [nâ€‰=â€‰5]), Corticobasal Degeneration (CBD, [nâ€‰=â€‰5]), Progressive Supranuclear Palsy (PSP, [nâ€‰=â€‰5]) and Pick's disease (PiD, [nâ€‰=â€‰4]). Immunohistochemistry showed that SCRN1 was a neuronal protein that abundantly accumulated in NFTs and plaque-associated dystrophic neurites throughout the progression of AD. Quantification of SCRN1 immunohistochemistry confirmed that SCRN1 preferentially accumulated in NFTs in comparison to surrounding non-tangle containing neurons at both early and late stages of AD. Similar results were observed in DS with AD and PART. However, SCRN1 did not co-localize with phosphorylated tau inclusions in CBD, PSP or PiD. Co-immunoprecipitation revealed that SCRN1 interacted with phosphorylated tau in human AD brain tissue. Together, these results suggest that SCRN1 is uniquely associated with tau pathology in AD, DS and PART. As such, SCRN1 has potential as a novel therapeutic target and could serve as a useful biomarker to distinguish AD from other tauopathies.