Amyloid-beta (25-35) peptide induces the release of pro-matrix metalloprotease 9 (pro-MMP-9) from human neutrophils

Soluble Biomarkers of Cerebrovascular Pathologies

Vascular contributions to cognitive impairment and dementia (VCID) is an all-encompassing term that describes cognitive impairment due to cerebrovascular origins. With the advancement of imaging and pathological studies, we now understand that VCID is often comorbid with Alzheimer disease. While researchers in the Alzheimer disease field have been working for years to establish and test blood-based biomarkers for Alzheimer disease diagnosis, prognosis, clinical therapy discovery, and early detection, blood-based biomarkers for VCID are in their infancy and also face challenges. VCID is heterogeneous, comprising many different pathological entities (ischemic, or hemorrhagic), and spatial and temporal differences (acute or chronic). This review highlights pathways that are aiding the search for sensitive and specific blood-based cerebrovascular dysfunction markers, describes promising candidates, and explains ongoing initiatives to discover blood-based VCID biomarkers.

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.

Role of the Extracellular Traps in Central Nervous System

It has been reported that several immune cells can release chromatin and granular proteins into extracellular space in response to the stimulation, forming extracellular traps (ETs). The cells involved in the extracellular trap formation are recognized including neutropils, macrophages, basophils, eosinophils, and mast cells. With the development of research related to central nervous system, the role of ETs has been valued in neuroinflammation, blood–brain barrier, and other fields. Meanwhile, it has been found that microglial cells as the resident immune cells of the central nervous system can also release ETs, updating the original understanding. This review aims to clarify the role of the ETs in the central nervous system, especially in neuroinflammation and blood–brain barrier.

The Role of Neutrophil Extracellular Traps in Central Nervous System Diseases and Prospects for Clinical Application

Neutrophil extracellular traps (NETs) are complexes of decondensed DNA fibers and antimicrobial peptides that are released by neutrophils and play important roles in many noninfectious diseases, such as cystic fibrosis, systemic lupus erythematosus, diabetes, and cancer. Recently, the formation of NETs has been detected in many central nervous system diseases and is thought to play different roles in the occurrence and development of these diseases. Researchers have detected NETs in acute ischemic stroke thrombi, and these NETs are thought to promote coagulation and thrombosis. NETs in ischemic brain parenchyma were identified as the cause of secondary nerve damage. High levels of NETs were also detected in grade IV glioma tissues, where NETs were involved in the proliferation and invasion of glioma cells by activating a signaling pathway. Extracellular web-like structures have also recently been observed in mice with traumatic brain injury (TBI), and it was hypothesized that NETs contribute to the development of edema after TBI. This article reviews the effect of NETs on multiple diseases that affect the CNS and explores their clinical application prospects.

Fibrillar amyloid peptides promote platelet aggregation through the coordinated action of ITAM- and ROS-dependent pathways

BACKGROUND

Amyloid peptides Aβ40 and Aβ42, whose deposition in brain correlates with Alzheimer disease, are also present in platelets and have prothrombotic activities.

OBJECTIVE

In this study, we analyze the ability of Aβ peptides to form fibrils and to induce platelet activation and aggregation.

METHODS

Aβ40, Aβ42, and their scrambled peptides were diluted in phosphate buffered saline and fibrillogenesis was investigated by ThioflavinT and Congo Red. Aggregation, protein phosphorylation, and reactive oxygen species (ROS) production were analyzed.

RESULTS

Aβ40 and Aβ42, but not scrambled peptides, were able to form fibrils when diluted in phosphate buffered saline. Fibrillogenesis of Aβ42 was very rapid, whereas fibril formation by Aβ40 was completed only after 48 hours of incubation. Fibrillar Aβ40 and Aβ42 promoted dose-dependent aggregation of washed platelets in the presence of extracellular CaCl2 . Cleavage of GPIbα by mocarhagin or blockade of the ITAM-containing FcγRIIA prevented platelet aggregation induced by fibrillary Aβ40 and Aβ42. Fibrillar Aβ peptides stimulated the phosphorylation of FcγRIIA, resulting in the downstream stimulation of PLC, protein kinase C, and phosphoinositide 3-kinases, whose activity was necessary for full aggregation of platelets. Fibrillar Aβ peptides also induced ROS generation, and NOX inhibitors, as well as ROS scavengers, prevented platelet aggregation. However, Aβ peptide-induced ROS production did not require binding to GPIbα or activation of FcγRIIA, but was initiated by CD36, which provided an important contribution to full platelet aggregation.

CONCLUSION

These results suggest that fibrillar amyloid Aβ40 and Aβ42 induce platelet aggregation through the recruitment of GPIb-IX-V and CD36, which requires the convergence of ITAM- and ROS-dependent pathways.

The proline-rich tyrosine kinase Pyk2 modulates integrin-mediated neutrophil adhesion and reactive oxygen species generation

Neutrophils are first responders in infection and inflammation. They are able to roll, adhere and transmigrate through the endothelium to reach the site of infection, where they fight pathogens through secretion of granule contents, production of reactive oxygen species, extrusion of neutrophil extracellular traps, and phagocytosis. In this study we explored the role of the non-receptor focal adhesion kinase Pyk2 in neutrophil adhesion and activation. Using a specific Pyk2 pharmacological inhibitor, PF-4594755, as well as Pyk2-deficient murine neutrophils, we found that Pyk2 is activated upon integrin αMβ2-mediated neutrophil adhesion to fibrinogen. This process is triggered by Src family kinases-mediated phosphorylation and supported by Pyk2 autophosphorylation on Y402. In neutrophil adherent to fibrinogen, Pyk2 activates PI3K-dependent pathways promoting the phosphorylation of Akt and of its downstream effector GSK3. Pyk2 also dynamically regulates MAP kinases in fibrinogen-adherent neutrophils, as it stimulates p38MAPK but negatively regulates ERK1/2. Pharmacological inhibition of Pyk2 significantly prevented adhesion of human neutrophils to fibrinogen, and neutrophils from Pyk2-knockout mice showed a reduced ability to adhere compared to wildtype cells. Accordingly, neutrophil adhesion to fibrinogen was reduced upon inhibition of p38MAPK but potentiated by ERK1/2 inhibition. Neutrophil adherent to fibrinogen, but not to polylysine, were able to produce ROS upon lipopolysaccharide challenge and ROS production was completely suppressed upon inhibition of Pyk2. By contrast PMA-induced ROS production by neutrophil adherent to either fibrinogen or polylysine was independent from Pyk2. Altogether these results demonstrate that Pyk2 is an important effector in the coordinated puzzle regulating neutrophil adhesion and activation.

Metalloproteinases and their tissue inhibitors in Alzheimer's disease and other neurodegenerative disorders

As life expectancy increases worldwide, age-related neurodegenerative diseases will increase in parallel. The lack of effective treatment strategies may soon lead to an unprecedented health, social and economic crisis. Any attempt to halt the progression of these diseases requires a thorough knowledge of the pathophysiological mechanisms involved to facilitate the identification of new targets and the application of innovative therapeutic strategies. The metzincin superfamily of metalloproteinases includes matrix metalloproteinases (MMP), a disintegrin and metalloproteinase (ADAM) and ADAM with thrombospondin motifs (ADAMTS). These multigenic and multifunctional proteinase families regulate the functions of an increasing number of signalling and scaffolding molecules involved in neuroinflammation, blood-brain barrier disruption, protein misfolding, synaptic dysfunction or neuronal death. Metalloproteinases and their physiological inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), are therefore, at the crossroads of molecular and cellular mechanisms that support neurodegenerative processes, and emerge as potential new therapeutic targets. We provide an overview of current knowledge on the role and regulation of metalloproteinases and TIMPs in four major neurodegenerative diseases: Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease.

Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an in vitro model of CNS tuberculosis

Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB.

A roadmap for investigating the role of the prion protein in depression associated with neurodegenerative disease

The physiological properties of the native, endogenous prion protein (PrP(C)) is a matter of concern, due to its pleiotropic functions and links to neurodegenerative disorders and cancer. In line with our hypothesis that the basic function of PrP(C) is to serve as a cell surface scaffold for the assembly of signaling modules, multiple interactions have been identified of PrP(C) with signaling molecules, including neurotransmitter receptors. We recently reported evidence that PrP(C) may modulate monoaminergic neurotransmission, as well as depressive-like behavior in mice. Here, we discuss how those results, together with a number of other studies, including our previous demonstration that both inflammatory and behavioral stress modulate PrP(C) content in neutrophils, suggest a distributed role of PrP(C) in clinical depression and inflammation associated with neurodegenerative diseases. An overarching understanding of the multiple interventions of PrP(C) upon physiological events may both shed light on the pathogenesis of, as well as help the identification of novel therapeutic targets for clinical depression, Prion and Alzheimer's Diseases.

NETosis in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Its neuropathological features include amyloid-β (Aβ) accumulation, the formation of neurofibrillary tangles, and the loss of neurons and synapses. Neuroinflammation is a well-established feature of AD pathogenesis, and a better understanding of its mechanisms could facilitate the development of new therapeutic approaches. Recent studies in transgenic mouse models of AD have shown that neutrophils adhere to blood vessels and migrate inside the parenchyma. Moreover, studies in human AD subjects have also shown that neutrophils adhere and spread inside brain vessels and invade the parenchyma, suggesting these cells play a role in AD pathogenesis. Indeed, neutrophil depletion and the therapeutic inhibition of neutrophil trafficking, achieved by blocking LFA-1 integrin in AD mouse models, significantly reduced memory loss and the neuropathological features of AD. We observed that neutrophils release neutrophil extracellular traps (NETs) inside blood vessels and in the parenchyma of AD mice, potentially harming the blood–brain barrier and neural cells. Furthermore, confocal microscopy confirmed the presence of NETs inside the cortical vessels and parenchyma of subjects with AD, providing more evidence that neutrophils and NETs play a role in AD-related tissue destruction. The discovery of NETs inside the AD brain suggests that these formations may exacerbate neuro-inflammatory processes, promoting vascular and parenchymal damage during AD. The inhibition of NET formation has achieved therapeutic benefits in several models of chronic inflammatory diseases, including autoimmune diseases affecting the brain. Therefore, the targeting of NETs may delay AD pathogenesis and offer a novel approach for the treatment of this increasingly prevalent disease.

Matrix Metalloproteinase in Blood-Brain Barrier Breakdown in Dementia

The neurovascular unit, which consists of astrocytic end-feet, neurons, pericytes, and endothelial cells, plays a key role in maintaining brain homeostasis by forming the blood-brain barrier and carefully controlling local cerebral blood flow. When the blood-brain barrier is disrupted, blood components can leak into the brain, damage the surrounding tissue and lead to cognitive impairment. This disruption in the blood-brain barrier and subsequent impairment in cognition are common after stroke and during cerebral amyloid angiopathy and Alzheimer's disease. Matrix metalloproteinases are proteases that degrade the extracellular matrix as well as tight junctions between endothelial cells and have been implicated in blood-brain barrier breakdown in neurodegenerative diseases. This review will focus on the roles of MMP2 and MMP9 in dementia, primarily post-stroke events that lead to dementia, cerebral amyloid angiopathy, and Alzheimer's disease.