Platelet Proteomic Analysis Revealed Differential Pattern of Cytoskeletal- and Immune-Related Proteins at Early Stages of Alzheimer’s Disease

Effects of antidiabetic agents on platelet characteristics with implications in Alzheimer's disease: Mendelian randomization and colocalization study

Background

Observational studies have found a potential link between the use of thiazolidinediones (TZDs) and a lower risk of Alzheimer's disease (AD) development. Platelets were the great source of amyloid-β (Aβ) and involved in the development of AD. This study aimed to assess the correlation between antidiabetic agents and platelet characteristics, hoping to provide a potential mechanism of TZDs neuroprotection in AD.

Method

Drug-targeted Mendelian randomization (MR) was performed to systematically illustrate the long-term effects of antidiabetic agents on platelet characteristics. Four antidiabetic agent targets were considered. Positive control analysis for type 2 diabetes (T2D) was conducted to validate the selection of instrumental variables (IVs). Colocalization analysis was used to further strengthen the robustness of the results.

Result

Positive control analysis showed an association of four antidiabetic agents with lower risk of T2D, which was consistent with their mechanisms of action and previous evidence from clinical trials. Genetically proxied TZDs were associated with lower platelet count (β[IRNT] = -0.410 [95 % CI -0.533 to -0.288], P = 5.32E-11) and a lower plateletcrit (β[IRNT] = -0.344 [95 % CI -0.481 to -0.206], P = 1.04E-6). Colocalization suggested the posterior probability of hypothesis 4 (PPH4) > 0.8, which further strengthened the MR results.

Conclusion

Genetically proxied TZDs were causally associated with lower platelet characteristics, particularly platelet count and plateletcrit, providing insight into the involvement of platelet-related pathways in the neuroprotection of TZDs against AD. Future studies are warranted to reveal the underlying molecular mechanism of TZDs' neuroprotective effects through platelet pathways.

Role of Cytoskeletal Elements in Regulation of Synaptic Functions: Implications Toward Alzheimer's Disease and Phytochemicals-Based Interventions

Alzheimer's disease (AD), a multifactorial disease, is characterized by the accumulation of neurofibrillary tangles (NFTs) and amyloid beta (Aβ) plaques. AD is triggered via several factors like alteration in cytoskeletal proteins, a mutation in presenilin 1 (PSEN1), presenilin 2 (PSEN2), amyloid precursor protein (APP), and post-translational modifications (PTMs) in the cytoskeletal elements. Owing to the major structural and functional role of cytoskeletal elements, like the organization of axon initial segmentation, dendritic spines, synaptic regulation, and delivery of cargo at the synapse; modulation of these elements plays an important role in AD pathogenesis; like Tau is a microtubule-associated protein that stabilizes the microtubules, and it also causes inhibition of nucleo-cytoplasmic transportation by disrupting the integrity of nuclear pore complex. One of the major cytoskeletal elements, actin and its dynamics, regulate the dendritic spine structure and functions; impairments have been documented towards learning and memory defects. The second major constituent of these cytoskeletal elements, microtubules, are necessary for the delivery of the cargo, like ion channels and receptors at the synaptic membranes, whereas actin-binding protein, i.e., Cofilin's activation form rod-like structures, is involved in the formation of paired helical filaments (PHFs) observed in AD. Also, the glial cells rely on their cytoskeleton to maintain synaptic functionality. Thus, making cytoskeletal elements and their regulation in synaptic structure and function as an important aspect to be focused for better management and targeting AD pathology. This review advocates exploring phytochemicals and Ayurvedic plant extracts against AD by elucidating their neuroprotective mechanisms involving cytoskeletal modulation and enhancing synaptic plasticity. However, challenges include their limited bioavailability due to the poor solubility and the limited potential to cross the blood-brain barrier (BBB), emphasizing the need for targeted strategies to improve therapeutic efficacy.

The platelet transcriptome and proteome in Alzheimer's disease and aging: an exploratory cross-sectional study

Introduction: Alzheimer's disease (AD) and aging are associated with platelet hyperactivity. However, the mechanisms underlying abnormal platelet function in AD and aging are yet poorly understood. Methods: To explore the molecular profile of AD and aged platelets, we investigated platelet activation (i.e., CD62P expression), proteome and transcriptome in AD patients, non-demented elderly, and young individuals as controls. Results: AD, aged and young individuals showed similar levels of platelet activation based on CD62P expression. However, AD and aged individuals had a proteomic signature suggestive of increased platelet activation compared with young controls. Transcriptomic profiling suggested the dysregulation of proteolytic machinery involved in regulating platelet function, particularly the ubiquitin-proteasome system in AD and autophagy in aging. The functional implication of these transcriptomic alterations remains unclear and requires further investigation. Discussion: Our data strengthen the evidence of enhanced platelet activation in aging and provide a first glimpse of the platelet transcriptomic changes occurring in AD.

Platelet-Derived Amyloid-β Protein Precursor as a Biomarker of Alzheimer's Disease

BACKGROUND

Platelet proteins may be associated with Alzheimer's disease (AD) pathology.

OBJECTIVE

To investigate the relationship between platelet proteins and cerebrospinal fluid (CSF) biomarkers of AD and cognition in individuals with memory decline to identify effective screening methods for detecting the early stages of the disease.

METHODS

We classified 68 participants with subjective memory decline according to the ATN framework determined by CSF amyloid-β (A), CSF p-tau (T), and t-tau (N). All participants underwent Mini-Mental State Examination (MMSE) and platelet-related protein content testing.

RESULTS

Eighteen participants had normal AD biomarkers (NCs), 24 subjects had non-AD pathologic changes (non-AD), and 26 subjects fell within the Alzheimer's continuum (AD). The platelet amyloid-β protein precursor (AβPP) ratio in the AD group was significantly lower than in the non-AD and NCs groups, and positively correlated with MMSE scores and CSF amyloid-β42 level, which could affect MMSE scores through CSF amyloid-β42. Levels of platelet phosphorylated-tau 231 and ser396/404 phosphorylated tau were elevated in both AD and non-AD compared to NCs. Additionally, the receiver operating characteristic analysis demonstrated that the platelet AβPP ratio was a sensitive identifier for differentiating the AD from NCs (AUC = 0.846) and non-AD (AUC = 0.768). And ser396/404 phosphorylated tau could distinguish AD from NCs.

CONCLUSION

Our study was the first to find an association between platelet AβPP ratio and CSF biomarkers of AD, which contribute to the understanding of the peripheral changes in AD. These findings may help to discover potential feasible and effective screening tools for AD.

Platelet biomarkers for a descending cognitive function: A proteomic approach

Memory loss is the most common clinical sign in Alzheimer's disease (AD); thus, searching for peripheral biomarkers to predict cognitive decline is promising for early diagnosis of AD. As platelets share similarities to neuron biology, it may serve as a peripheral matrix for biomarkers of neurological disorders. Here, we conducted a comprehensive and in-depth platelet proteomic analysis using TMT-LC-MS/MS in the populations with mild cognitive impairment (MCI, MMSE = 18-23), severe cognitive impairments (AD, MMSE = 2-17), and the age-/sex-matched normal cognition controls (MMSE = 29-30). A total of 360 differential proteins were detected in MCI and AD patients compared with the controls. These differential proteins were involved in multiple KEGG pathways, including AD, AMP-activated protein kinase (AMPK) pathway, telomerase RNA localization, platelet activation, and complement activation. By correlation analysis with MMSE score, three positively correlated pathways and two negatively correlated pathways were identified to be closely related to cognitive decline in MCI and AD patients. Partial least squares discriminant analysis (PLS-DA) showed that changes of nine proteins, including PHB, UQCRH, CD63, GP1BA, FINC, RAP1A, ITPR1/2, and ADAM10 could effectively distinguish the cognitively impaired patients from the controls. Further machine learning analysis revealed that a combination of four decreased platelet proteins, that is, PHB, UQCRH, GP1BA, and FINC, was most promising for predicting cognitive decline in MCI and AD patients. Taken together, our data provide a set of platelet biomarkers for predicting cognitive decline which may be applied for the early screening of AD.

Platelet Amyloid-β Protein Precursor (AβPP) Ratio and Phosphorylated Tau as Promising Indicators for Early Alzheimer's Disease

To identify whether platelet amyloid-β protein precursor (AβPP) ratio, phosphorylated-tau (P-tau) 231, P-tau181, and serine 396 and 404 (Ser396/404) phosphorylated tau are potential peripheral indicators for early Alzheimer's disease (AD). Forty-three amnesic mild cognitive impairment (aMCI) patients and 45 normal controls were recruited. Peripheral venous blood was drawn and platelets were collected and evaluated for potential indicators by Western blot analysis. Subsequent meta-analysis was completed on these selected indicators. In platelets of aMCI patients, the AβPP ratio level was significantly lower and levels of P-tau231 and Ser396/404 phosphorylated tau were significantly higher. Moreover, in aMCI patients, a negative correlation was observed between platelet P-tau231 level and the Trail Making Tests A score, and it was found that higher platelet P-tau231 levels significantly associated with a worse performance of information processing speed. Furthermore, values of the area under the curve of platelet P-tau231 and Ser396/404 phosphorylated tau were 0.624 and 0.657, respectively. Finally, a meta-analysis indicated platelet AβPP ratio level was significantly lower in MCI cohorts. In conclusion, platelets of aMCI subjects showed a lower AβPP ratio and higher levels of P-tau231 and Ser396/404 phosphorylated tau when compared to normal controls, which may be critical in identifying early AD.

The canine activated platelet secretome (CAPS): A translational model of thrombin-evoked platelet activation response

BACKGROUND

Domestic dogs represent a translational animal model to study naturally occurring human disease. Proteomics has emerged as a promising tool for characterizing human platelet pathophysiology; thus a detailed characterization of the core canine activated platelet secretome (CAPS) will enhance utilization of the canine model. The objectives of this study were development of a robust, high throughput, label-free approach for proteomic identification and quantification of the canine platelet (i) thrombin releasate proteins, and (ii) the protein subgroup that constitutes CAPS.

METHODS

Platelets were isolated from 10 healthy dogs and stimulated with 50 nmol/L of γ-thrombin or saline. Proteins were in-solution trypsin-digested and analyzed by nano-liquid chromatography-tandem spectrometry. Core releasate proteins were defined as those present in 10 of 10 dogs, and CAPS defined as releasate proteins with a significantly higher abundance in stimulated versus saline controls (corrected P < .05).

RESULTS

A total of 2865 proteins were identified; 1126 releasate proteins were present in all dogs, 650 were defined as CAPS. Among the differences from human platelets were a canine lack of platelet factor 4 and vascular endothelial growth factor C, and a 10- to 20-fold lower concentration of proteins such as haptoglobin, alpha-2 macroglobulin, von Willebrand factor, and amyloid-beta A4. Twenty-eight CAPS proteins, including cytokines, adhesion molecules, granule proteins, and calcium regulatory proteins have not previously been attributed to human platelets.

CONCLUSIONS

CAPS proteins represent a robust characterization of a large animal platelet secretome and a novel tool to model platelet physiology, pathophysiology, and to identify translational biomarkers of platelet-mediated disease.

Alzheimer's disease and type 2 diabetes mellitus: A systematic review of proteomic studies

Similar to dementia, the risk for developing type 2 diabetes mellitus (T2DM) increases with age, and T2DM also increases the risk for dementia, particularly Alzheimer's disease (AD). Although T2DM is primarily a peripheral disorder and AD is a central nervous system disease, both share some common features as they are chronic and complex diseases, and both show involvement of oxidative stress and inflammation in their progression. These characteristics suggest that T2DM may be associated with AD, which gave rise to a new term, type 3 diabetes (T3DM). In this study, we searched for matching peripheral proteomic biomarkers of AD and T2DM based in a systematic review of the available literature. We identified 17 common biomarkers that were differentially expressed in both patients with AD or T2DM when compared with healthy controls. These biomarkers could provide a useful workflow for screening T2DM patients at risk to develop AD.

Exploratory study of association between blood immune markers and cognitive symptom severity in major depressive disorder: Stratification by body mass index status

BACKGROUND

A subset of patients with Major Depressive Disorder (MDD) have shown differences relative to healthy controls in blood inflammatory and immune markers. Meanwhile, MDD and comorbid obesity appear to present with distinct biological and symptom characteristics, categorised as "atypical" or "immunometabolic" depression, although the relevant underlying biological mechanisms are still uncertain. Therefore, this exploratory study aimed to better characterise the relationship between peripheral blood immune markers and symptoms of MDD, as well as the extent to which body mass index (BMI) may alter this relationship.

METHODS

Linear regression analyses were performed between selected baseline characteristics including clinical scales and blood inflammatory markers in participants with MDD (n = 119) enrolled in the PREDDICT randomised controlled trial (RCT), using age, sex and BMI as covariates, and then stratified by BMI status. Specifically, the Montgomery-Åsberg Depression Rating Scale (MADRS) for symptom severity, Clinical Global Impression scale (CGI) for functional impairment, Oxford Depression Questionnaire (ODQ) for emotional blunting, and THINC integrated tool (THINC-it) for cognitive function were considered as clinical measures.

RESULTS

There was a significant association between basophil count and THINC-it Codebreaker mean response time (associated with complex attention, perceptual motor, executive function, and learning and memory abilities) in overweight individuals and with THINC-it Trails total response time (associated with executive function ability) in moderately obese individuals, when controlling for age, sex, and years of education. No correlation was found between any tested blood markers and MADRS, CGI or ODQ clinical measures, regardless of BMI.

DISCUSSION

Although the present study is exploratory, the results suggest that targeting of the immune system and of metabolic parameters might confer benefits, specifically in patients with high BMI and experiencing cognitive impairment associated with MDD.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR), ACTRN12617000527369p. Registered on 11 April 2017.

Platelets in Healthy and Disease States: From Biomarkers Discovery to Drug Targets Identification by Proteomics

Platelets are a heterogeneous small anucleate blood cell population with a central role both in physiological haemostasis and in pathological states, spanning from thrombosis to inflammation, and cancer. Recent advances in proteomic studies provided additional important information concerning the platelet biology and the response of platelets to several pathophysiological pathways. Platelets circulate systemically and can be easily isolated from human samples, making proteomic application very interesting for characterizing the complexity of platelet functions in health and disease as well as for identifying and quantifying potential platelet proteins as biomarkers and novel antiplatelet therapeutic targets. To date, the highly dynamic protein content of platelets has been studied in resting and activated platelets, and several subproteomes have been characterized including platelet-derived microparticles, platelet granules, platelet releasates, platelet membrane proteins, and specific platelet post-translational modifications. In this review, a critical overview is provided on principal platelet proteomic studies focused on platelet biology from signaling to granules content, platelet proteome changes in several diseases, and the impact of drugs on platelet functions. Moreover, recent advances in quantitative platelet proteomics are discussed, emphasizing the importance of targeted quantification methods for more precise, robust and accurate quantification of selected proteins, which might be used as biomarkers for disease diagnosis, prognosis and therapy, and their strong clinical impact in the near future.

Proteomic profiling of the thrombin-activated canine platelet secretome (CAPS)

Domestic dogs share the same environment as humans, and they represent a valuable animal model to study naturally-occurring human disease. Platelet proteomics holds promise for the discovery of biomarkers that capture the contribution of platelets to the pathophysiology of many disease states, however, canine platelet proteomic studies are lacking. Our study objectives were to establish a protocol for proteomic identification and quantification of the thrombin-activated canine platelet secretome (CAPS), and to compare the CAPS proteins to human and murine platelet proteomic data. Washed platelets were isolated from healthy dogs, and stimulated with saline (control) or gamma-thrombin (releasate). Proteins were separated by SDS-page, trypsin-digested and analyzed by liquid chromatography and tandem mass spectrometry (MS). CAPS proteins were defined as those with a MS1-abundance ratio of two or more for releasate vs. unstimulated saline control. A total of 1,918 proteins were identified, with 908 proteins common to all dogs and 693 characterized as CAPS proteins. CAPS proteins were similar to human and murine platelet secretomes and were highly represented in hemostatic pathways. Differences unique to CAPS included replacement of platelet factor 4 with other cleavage products of platelet basic protein (e.g. interleukin-8), novel proteins (e.g. C-C motif chemokine 14), and proteins in relatively high (e.g. protease nexin-1) or low (e.g. von Willebrand factor) abundance. This study establishes the first in-depth platelet releasate proteome from healthy dogs with a reference database of 693 CAPS proteins. Similarities between CAPS and the human secretome confirm the utility of dogs as translational models of human disease, but we also identify differences unique to canine platelets. Our findings provide a resource for further investigations into disease-related CAPS profiles, and for comparative pathway analyses of platelet activation among species.