Clusterin/Apolipoprotein J immunoreactivity is associated with white matter damage in cerebral small vessel diseases

TMT proteomics analysis of cerebrospinal fluid from patients with cerebral venous sinus thrombosis

CVST is a type of venous stroke that mainly affects young adults with no reliable diagnostic markers and effective treatment strategies for secondary pathologies. However, the underlying pathological molecular mechanisms remain unclear. Here, we systematically analyzed the molecule profiling of the cerebrospinal fluid (CSF) in CVST patients via tandem mass tag (TMT)-based proteomics for the first time, aiming to reveal the pathogenesis and provide evidence for the diagnosis and treatment of CVST. Five CVST patients and five control patients were selected, and CSF samples were analyzed by TMT proteomics. Differentially expressed proteins (DEPs) were acquired and bioinformatics analysis was performed. Besides, parallel reaction monitoring (PRM) was utilized to validate the DEPs. 468 differentially expressed proteins were screened, 185 of which were up-regulated and 283 were down-regulated (fold change >1.2, P < 0.05). Bioinformatics analysis displayed that these proteins were significantly enriched in multiple pathways related to a variety of pathophysiological processes. PRM verification showed that apolipoprotein E, MMP-2, neuroserpin, clusterin, and several other molecules were down-regulated. These identified proteins reveal unique pathophysiological characteristics secondary to CVST. Further characterization of these proteins in future research could enable their application as potential therapeutic targets and biomarkers in CVST therapy. SIGNIFICANCE: Cerebral venous sinus thrombosis (CVST) is an underrated and potentially fatal cause of stroke with a reported mortality of 5-10% worldwide. Currently, in addition to anticoagulant and thrombolytic therapy, effective treatments targeting the injured brain parenchyma after CVST remain limited. Besides, accurate diagnostic markers are still sorely lacking. In the present study, we will detect the alterations of the CSF protein spectrum of CVST patients by TMT technique, screen differentially expressed proteins, analyze the functions of these signals through bioinformatics methods, and finally validate the key molecules through parallel reaction monitoring (PRM) technique. Collectively, the study aimed to offer a reference for the discovery of specific protein/pathway alterations in the CSF of CVST patients and further reveal the underlying pathogenesis, thereby providing evidence for the diagnosis and treatment of CVST.

Extracellular chaperone networks and the export of J-domain proteins

An extracellular network of molecular chaperones protects a diverse array of proteins that reside in or pass through extracellular spaces. Proteins in the extracellular milieu face numerous challenges that can lead to protein misfolding and aggregation. As a checkpoint for proteins that move between cells, extracellular chaperone networks are of growing clinical relevance. J-domain proteins (JDPs) are ubiquitous molecular chaperones that are known for their essential roles in a wide array of fundamental cellular processes through their regulation of heat shock protein 70s. As the largest molecular chaperone family, JDPs have long been recognized for their diverse functions within cells. Some JDPs are elegantly selective for their "client proteins," some do not discriminate among substrates and others act cooperatively on the same target. The realization that JDPs are exported through both classical and unconventional secretory pathways has fueled investigation into the roles that JDPs play in protein quality control and intercellular communication. The proposed functions of exported JDPs are diverse. Studies suggest that export of DnaJB11 enhances extracellular proteostasis, that intercellular movement of DnaJB1 or DnaJB6 enhances the proteostasis capacity in recipient cells, whereas the import of DnaJB8 increases resistance to chemotherapy in recipient cancer cells. In addition, the export of DnaJC5 and concurrent DnaJC5-dependent ejection of dysfunctional and aggregation-prone proteins are implicated in the prevention of neurodegeneration. This review provides a brief overview of the current understanding of the extracellular chaperone networks and outlines the first wave of studies describing the cellular export of JDPs.

The Emerging Roles of Extracellular Chaperones in Complement Regulation

The immune system is essential to protect organisms from internal and external threats. The rapidly acting, non-specific innate immune system includes complement, which initiates an inflammatory cascade and can form pores in the membranes of target cells to induce cell lysis. Regulation of protein homeostasis (proteostasis) is essential for normal cellular and organismal function, and has been implicated in processes controlling immunity and infection. Chaperones are key players in maintaining proteostasis in both the intra- and extracellular environments. Whilst intracellular proteostasis is well-characterised, the role of constitutively secreted extracellular chaperones (ECs) is less well understood. ECs may interact with invading pathogens, and elements of the subsequent immune response, including the complement pathway. Both ECs and complement can influence the progression of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis, as well as other diseases including kidney diseases and diabetes. This review will examine known and recently discovered ECs, and their roles in immunity, with a specific focus on the complement pathway.

MRI Imaging Omics and Risk Factors Analysis of PWMD in Premature Infants Based on Fuzzy Clustering Algorithm

The magnetic resonance imaging (MRI) characteristics of periventricular white matter damage (PWMD) in premature infants using the fuzzy c-means clustering algorithm (FCM) is explored, and the influencing factors are further clarified. A total of 100 premature infants admitted to the neonatal department of our hospital from February 2020 to February 2022 are selected for in-depth investigation. According to the occurrence of PWMD, they are divided into the PWMD group and the simple premature delivery group, with 50 cases in each group. All preterm infants are examined by MRI and the changes in image characteristics and apparent diffusion coefficient (ADC) values are analyzed. Clinical information of the subjects is collected and the influencing factors of PWMD in preterm infants are analyzed by multivariate regression analysis. In the first magnetic resonance imaging (MRI) examination, the cases of punctured, clustered, and linear lesions are 28 cases, 12 cases, and 10 cases, respectively. The experimental results showed that PWMD of preterm infants presented punctate, clustered, and high linear T1 signal MRI manifestations, which caused a downward trend of ADC value, and caused respiratory distress, low birth weight, premature rupture of membranes, respiratory tract infection, and other risk symptoms.

The Dual Roles of Clusterin in Extracellular and Intracellular Proteostasis

Clusterin (CLU) was the first reported secreted mammalian chaperone and impacts on serious diseases associated with inappropriate extracellular protein aggregation. Many studies have described intracellular CLU in locations outside the secretory system and recent work has shown that CLU can be released into the cytosol during cell stress. In this article, we critically evaluate evidence relevant to the proposed origins of cellular CLU found outside the secretory system, and advance the hypothesis that the cytosolic release of CLU induced by stress serves to facilitate the trafficking of misfolded proteins to the proteasome and autophagy for degradation. We also propose future research directions that could help establish CLU as a unique chaperone performing critical and synergic roles in both intracellular and extracellular proteostasis.

Secreted Chaperones in Neurodegeneration

Protein homeostasis, or proteostasis, is a combination of cellular processes that govern protein quality control, namely, protein translation, folding, processing, and degradation. Disruptions in these processes can lead to protein misfolding and aggregation. Proteostatic disruption can lead to cellular changes such as endoplasmic reticulum or oxidative stress; organelle dysfunction; and, if continued, to cell death. A majority of neurodegenerative diseases involve the pathologic aggregation of proteins that subverts normal neuronal function. While prior reviews of neuronal proteostasis in neurodegenerative processes have focused on cytoplasmic chaperones, there is increasing evidence that chaperones secreted both by neurons and other brain cells in the extracellular - including transsynaptic - space play important roles in neuronal proteostasis. In this review, we will introduce various secreted chaperones involved in neurodegeneration. We begin with clusterin and discuss its identification in various protein aggregates, and the use of increased cerebrospinal fluid (CSF) clusterin as a potential biomarker and as a potential therapeutic. Our next secreted chaperone is progranulin; polymorphisms in this gene represent a known genetic risk factor for frontotemporal lobar degeneration, and progranulin overexpression has been found to be effective in reducing Alzheimer's- and Parkinson's-like neurodegenerative phenotypes in mouse models. We move on to BRICHOS domain-containing proteins, a family of proteins containing highly potent anti-amyloidogenic activity; we summarize studies describing the biochemical mechanisms by which recombinant BRICHOS protein might serve as a therapeutic agent. The next section of the review is devoted to the secreted chaperones 7B2 and proSAAS, small neuronal proteins which are packaged together with neuropeptides and released during synaptic activity. Since proteins can be secreted by both classical secretory and non-classical mechanisms, we also review the small heat shock proteins (sHsps) that can be secreted from the cytoplasm to the extracellular environment and provide evidence for their involvement in extracellular proteostasis and neuroprotection. Our goal in this review focusing on extracellular chaperones in neurodegenerative disease is to summarize the most recent literature relating to neurodegeneration for each secreted chaperone; to identify any common mechanisms; and to point out areas of similarity as well as differences between the secreted chaperones identified to date.

Proteostasis in Cerebral Small Vessel Disease

Maintaining the homeostasis of proteins (proteostasis) by controlling their synthesis, folding and degradation is a central task of cells and tissues. The gradual decline of the capacity of the various proteostasis machineries, frequently in combination with their overload through mutated, aggregation-prone proteins, is increasingly recognized as an important catalyst of age-dependent pathologies in the brain, most prominently neurodegenerative disorders. A dysfunctional proteostasis might also contribute to neurovascular disease as indicated by the occurrence of excessive protein accumulation or massive extracellular matrix expansion within vessel walls in conditions such as cerebral small vessel disease (SVD), a major cause of ischemic stroke, and cerebral amyloid angiopathy. Recent advances in brain vessel isolation techniques and mass spectrometry methodology have facilitated the analysis of cerebrovascular proteomes and fueled efforts to determine the proteomic signatures associated with neurovascular disease. In several studies in humans and mice considerable differences between healthy and diseased vessel proteomes were observed, emphasizing the critical contribution of an impaired proteostasis to disease pathogenesis. These findings highlight the important role of a balanced proteostasis for cerebrovascular health.

Intracellular and secreted forms of clusterin are elevated early in Alzheimer's disease and associate with both Aβ and tau pathology

Clusterin (CLU) is a pleiotropic glycoprotein that exists as a secreted, neuroprotective or intracellular, neurotoxic form, both of which increase in Alzheimer's disease (AD) causing increased Aβ42 deposition. No studies have assessed the association between functionally distinct alloforms of CLU and tau protein or neuronal loss, despite its intracellular toxicity. We confirm previous reports of significant increases in both intracellular CLU and secreted CLU in the brain tissue of individuals with AD (p < 0.01) and show no association with neuronal loss. The increase in CLU alloforms was most closely associated with increases in both insoluble Aβ42 and tau protein (p = 0.001), supporting its role in AD pathogenesis. Further research should investigate whether altering human CLU levels may have viability as a therapeutic option for AD.

CADASIL brain vessels show a HTRA1 loss-of-function profile

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and a phenotypically similar recessive condition (CARASIL) have emerged as important genetic model diseases for studying the molecular pathomechanisms of cerebral small vessel disease (SVD). CADASIL, the most frequent and intensely explored monogenic SVD, is characterized by a severe pathology in the cerebral vasculature including the mutation-induced aggregation of the Notch3 extracellular domain (Notch3ECD) and the formation of protein deposits of insufficiently determined composition in vessel walls. To identify key molecules and pathways involved in this process, we quantitatively determined the brain vessel proteome from CADASIL patient and control autopsy samples (n = 6 for each group), obtaining 95 proteins with significantly increased abundance. Intriguingly, high-temperature requirement protein A1 (HTRA1), the extracellular protease mutated in CARASIL, was found to be strongly enriched (4.9-fold, p = 1.6 × 10-3) and to colocalize with Notch3ECD deposits in patient vessels suggesting a sequestration process. Furthermore, the presence of increased levels of several HTRA1 substrates in the CADASIL proteome was compatible with their reduced degradation as consequence of a loss of HTRA1 activity. Indeed, a comparison with the brain vessel proteome of HTRA1 knockout mice (n = 5) revealed a highly significant overlap of 18 enriched proteins (p = 2.2 × 10-16), primarily representing secreted and extracellular matrix factors. Several of them were shown to be processed by HTRA1 in an in vitro proteolysis assay identifying them as novel substrates. Our study provides evidence for a loss of HTRA1 function as a critical step in the development of CADASIL pathology linking the molecular mechanisms of two distinct SVD forms.

Intraventricular infusion of clusterin ameliorated cognition and pathology in Tg6799 model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is characterized by the deposition of amyloid-β (Aβ) in brain parenchyma and cerebral blood vessels as cerebral amyloid angiopathy (CAA). Clusterin, a chaperon protein associated with Aβ aggregation, toxicity and transport through blood-brain barrier, may play a key role in the development of AD. Recently, clusterin peptide D-[113-122] was shown to mimic clusterin's function and exerted therapeutic effect in atherosclerosis. In this study, we investigated whether this clusterin peptide also affected (Aβ) deposition in AD transgenic mouse.

RESULTS

Using a micropump, synthetic peptide 113-122 of clusterin protein (20 μg/200 μl) was infused into the lateral ventricle of 8-month 5 × FAD transgenic mouse model (Tg6799), for 2 weeks. Water-maze testing showed an improved cognitive function of the Tg6799 mice treated with clusterin. Immunocytochemistry and quantitative analysis revealed that intraventricular (icv) administration of clusterin peptide in Tg6799 mouse reduced Aβ plaques as well the severity of cerebral amyloid angiopathy. Enzyme-linked immunosorbent assay demonstrated a decreased in the soluble levels of Aβ (Aβ40 and Aβ42) in the brain. Western-blot revealed an increased level of LRP-2 after clusterin peptide treatment.

CONCLUSION

These results suggest that icv infusion of clusterin peptide D-[113-122] offers a promising therapeutic approach to reduce Aβ deposition as well as CAA. The LRP2-mediated clearance system might be involved in the mechanism of these effects.

The role of amyloid beta clearance in cerebral amyloid angiopathy: more potential therapeutic targets

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of amyloid β-protein (Aβ) in the leptomeningeal and cortical blood vessels, which is an age-dependent risk factor for intracerebral hemorrhage (ICH), ischemic stroke and contributes to cerebrovascular dysfunction leading to cognitive impairment. However clinical prevention and treatment of the disease is very difficult because of its occult onset and severity of the symptoms. In recent years, many anti-amyloid β immunotherapies have not demonstrated clinical efficacy in subjects with Alzheimer’s disease (AD), and the failure may be due to the deposition of Aβ in the cerebrovascular export pathway resulting in further damage to blood vessels and aggravating CAA. So decreased clearance of Aβ in blood vessels plays a crucial role in the development of CAA and AD, and identification of the molecular pathways involved will provide new targets for treatment. In this review, we mainly describe the mechanisms of Aβ clearance through vessels, especially in terms of some proteins and receptors involved in this process.

Serum amyloid P component: A novel potential player in vessel degeneration in CADASIL

In cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), granular osmiophilic material (GOM) may play some roles in inducing cerebrovascular events. To elucidate the pathogenesis of CADASIL, we used laser microdissection and liquid chromatography-tandem mass spectrometry to analyze cerebrovascular lesions of patients with CADASIL for GOM. The analyses detected serum amyloid P component (SAP), annexin A2, and periostin as the proteins with the largest increase in the samples, which also demonstrated NOTCH3. For the three proteins, anti-human SAP antibody had the strongest reaction in the lesions where the anti-human NOTCH3 antibody showed positive staining. Moreover, immunofluorescence staining with the two antibodies clearly showed co-localization of SAP and NOTCH3. mRNA analyses indicated no positive SAP expression in the brain materials, which suggested that the source of SAP found in the GOM was only the liver. A solid phase enzyme-linked immunosorbent assay confirmed the binding of SAP with NOTCH3. Serum SAP concentrations were neither up-regulated nor down-regulated in CADASIL patients, when compared with those in control subjects. SAP may play an important role in GOM formation although precise mechanisms remain to be elucidated.

Systems proteomic analysis reveals that clusterin and tissue inhibitor of metalloproteinases 3 increase in leptomeningeal arteries affected by cerebral amyloid angiopathy

Aims

Amyloid beta (Aβ) accumulation in the walls of leptomeningeal arteries as cerebral amyloid angiopathy (CAA) is a major feature of Alzheimer's disease. In this study, we used global quantitative proteomic analysis to examine the hypothesis that the leptomeningeal arteries derived from patients with CAA have a distinct endophenotypic profile compared to those from young and elderly controls.

Methods

Freshly dissected leptomeningeal arteries from the Newcastle Brain Tissue Resource and Edinburgh Sudden Death Brain Bank from seven elderly (82.9 ± 7.5 years) females with severe capillary and arterial CAA, as well as seven elderly (88.3 ± 8.6 years) and five young (45.4 ± 3.9 years) females without CAA were used in this study. Arteries from four patients with CAA, two young and two elderly controls were individually analysed using quantitative proteomics. Key proteomic findings were then validated using immunohistochemistry.

Results

Bioinformatics interpretation of the results showed a significant enrichment of the immune response/classical complement and extracellular matrix remodelling pathways (P < 0.05) in arteries affected by CAA vs. those from young and elderly controls. Clusterin (apolipoprotein J) and tissue inhibitor of metalloproteinases‐3 (TIMP3), validated using immunohistochemistry, were shown to co‐localize with Aβ and to be up‐regulated in leptomeningeal arteries from CAA patients compared to young and elderly controls.

Conclusions

Global proteomic profiling of brain leptomeningeal arteries revealed that clusterin and TIMP3 increase in leptomeningeal arteries affected by CAA. We propose that clusterin and TIMP3 could facilitate perivascular clearance and may serve as novel candidate therapeutic targets for CAA.

Clusterin levels are increased in Alzheimer's disease and influence the regional distribution of Aβ

Clusterin, also known as apoJ, is a lipoprotein abundantly expressed within the CNS. It regulates Aβ fibril formation and toxicity and facilitates amyloid-β (Aβ) transport across the blood-brain barrier. Genome-wide association studies have shown variations in the clusterin gene (CLU) to influence the risk of developing sporadic Alzheimer's disease (AD). To explore whether clusterin modulates the regional deposition of Aβ, we measured levels of soluble (NP40-extracted) and insoluble (guanidine-HCl-extracted) clusterin, Aβ40 and Aβ42 by sandwich ELISA in brain regions with a predilection for amyloid pathology-mid-frontal cortex (MF), cingulate cortex (CC), parahippocampal cortex (PH), and regions with little or no pathology-thalamus (TH) and white matter (WM). Clusterin level was highest in regions with plaque pathology (MF, CC, PH and PC), approximately mirroring the regional distribution of Aβ. It was significantly higher in AD than controls, and correlated positively with Aβ42 and insoluble Aβ40. Soluble clusterin level rose significantly with severity of cerebral amyloid angiopathy, and in MF and PC regions was highest in APOE ɛ4 homozygotes. In the TH and WM (areas with little amyloid pathology) clusterin was unaltered in AD and did not correlate with Aβ level. There was a significant positive correlation between the concentration of clusterin and the regional levels of insoluble Aβ42; however, the molar ratio of clusterin : Aβ42 declined with insoluble Aβ42 level in a region-dependent manner, being lowest in regions with predilection for Aβ plaque pathology. Under physiological conditions, clusterin reduces aggregation and promotes clearance of Aβ. Our findings indicate that in AD, clusterin increases, particularly in regions with most abundant Aβ, but because the increase does not match the rising level of Aβ42, the molar ratio of clusterin : Aβ42 in those regions falls, probably contributing to Aβ deposition within the tissue.

Clusterin expression is upregulated following acute head injury and localizes to astrocytes in old head injury

There is mounting evidence linking traumatic brain injury (TBI) to neurodegeneration. Clusterin (apolipoprotein J or ApoJ) is a complement inhibitor that appears to have a neuroprotective effect in response to tissue damage and has been reported to be upregulated in Alzheimer's disease. Here we investigated the time course and cellular expression pattern of clusterin in human TBI. Tissue from 32 patients with TBI of varying survival times (from under 30 min to 10 months) was examined using immunohistochemistry for clusterin alongside other markers of neurodegeneration and neuroinflammation. TBI cases were compared to ischemic brain damage, Alzheimer's disease and controls. Double immunofluorescence was carried out in order to examine cellular expression. Clusterin was initially expressed in an axonal location less than 30 min following TBI and increased in intensity and the frequency of deposits with increasing survival time up to 24 h, after which it appeared to reduce in intensity but was still evident several weeks after injury. Clusterin was first evident in astrocytes after 45 min, being increasingly seen up to 48 h but remaining intense in TBI cases with long survival times. Our results suggest clusterin plays a role in modulating the inflammatory response of acute and chronic TBI and that it is a useful marker for TBI, particularly in cases with short survival times. Its prominent accumulation in astrocytes, alongside a mounting inflammatory response and activation of microglial cells supports a potential role in the neurodegenerative changes that occur as a result of TBI.

ApoA1, ApoJ and ApoE Plasma Levels and Genotype Frequencies in Cerebral Amyloid Angiopathy

The involvement of apolipoproteins, such as the ApoE4 isoform, in Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) highlights the fact that certain lipid carriers may participate in soluble β-amyloid (Aβ) transport. Our general aim was to characterize the soluble levels of the apolipoproteins apoE, apoA1 and apoJ/clusterin and their genotype status in patients with CAA. We analyzed the genotypes frequency of APOA1 (rs5069, rs670), CLU (rs11136000, rs1532278, rs7012010, rs9331888) and APOE (rs429358, rs7412) in a cohort of patients with CAA-associated intracerebral hemorrhage (ICH) (n = 59) and compared the results with those from hypertension-associated ICH (n = 42), AD patients (n = 73) and controls (n = 88). In a subgroup of patients, we also determined the plasma concentrations of apoE, apoA1 and apoJ/clusterin. We found increased plasma apoJ/clusterin levels in CAA patients compared to AD patients or controls after adjusting for sex and age (CAA vs. controls, p = 0.033; CAA vs. AD, p = 0.013). ApoA1 levels were not altered between groups, although a strong correlation was observed between plasma Aβ(1-40) and apoA1 among CAA patients (r = 0.583, p = 0.007). Regarding plasma apoE concentration, a robust association between circulating levels and genotype status was confirmed (p < 0.001). Whereas the APOE4 frequency was higher in AD (p < 0.001) and CAA (p = 0.013), the APOA1 and CLU genotypes were not different among groups. In the CAA cohort, the risk-linked CLU variant (C) rs11136000 was associated with white matter hyperintensities (p = 0.045) and the presence of lobar microbleeds (p = 0.023) on MRI. In summary, our findings suggest that apoA1 may act as a physiological transporter of Aβ(1-40) and that apoJ/clusterin appears to be a chaperone related to distinctive lesions in CAA brains.