The Evolving Concept of Neuro-Thromboinflammation for Neurodegenerative Disorders and Neurotrauma: A Rationale for PAR1-Targeting Therapies.

Interest in the role of coagulation and fibrinolysis in the nervous system was active in several laboratories dating back before cloning of the functional thrombin receptor in 1991. As one of those, our attention was initially on thrombin and plasminogen activators in synapse formation and elimination in the neuromuscular system, with orientation towards diseases such as amyotrophic lateral sclerosis (ALS) and how clotting and fibrinolytic pathways fit into its pathogenesis. This perspective is on neuro-thromboinflammation, emphasizing this emerging concept from studies and reports over more than three decades.

Thrombin and the in Neurotrauma, ALS, and Other Neurodegenerative Disorders.

This review details our current understanding of thrombin signaling in neurodegeneration, with a focus on amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease) as well as future directions to be pursued. The key factors are multifunctional and involved in regulatory pathways, namely innate immune and the coagulation cascade activation, that are essential for normal nervous system function and health. These two major host defense systems have a long history in evolution and include elements and regulators of the coagulation pathway that have significant impacts on both the peripheral and central nervous system in health and disease.

Proximate Mediators of Microvascular Dysfunction at the Blood-Brain Barrier: Neuroinflammatory Pathways to Neurodegeneration.

Current projections are that by 2050 the numbers of people aged 65 and older with (AD) in the US may increase threefold while is projected to double every 20 years reaching ~115 million by 2050. AD is clinically characterized by progressive dementia and neuropathologically by neuronal and synapse loss, accumulation of amyloid plaques, and neurofibrillary tangles (NFTs) in specific brain regions. The preclinical or presymptomatic stage of AD-related brain changes may begin over 20 years before symptoms occur, .

HMGB1 and thrombin mediate the blood-brain barrier dysfunction acting as biomarkers of neuroinflammation and progression to neurodegeneration in Alzheimer's disease.

Background: The blood-brain barrier (BBB) dysfunction represents an early feature of Alzheimer's disease (AD) that precedes the hallmarks of amyloid beta (amyloid β) plaque deposition and neuronal neurofibrillary tangle (NFT) formation. A damaged BBB correlates directly with neuroinflammation involving microglial activation and reactive astrogliosis, which is associated with increased expression and/or release of high-mobility group box protein 1 (HMGB1) and thrombin. However, the link between the presence of these molecules, BBB damage, and progression to neurodegeneration in AD is still elusive.

Membrane lipid peroxidation in neurodegeneration: Role of thrombin and proteinase-activated receptor-1.

Thrombin and membrane lipid peroxidation (MLP) have been implicated in various central nervous system (CNS) disorders from CNS trauma to stroke, Alzheimer's (AD) and Parkinson's (PD) diseases. Because thrombin also induces MLP in platelets and its involvement in neurodegenerative diseases we hypothesized that its deleterious effects might, in part, involve formation of MLP in neuronal cells. We previously showed that thrombin induced caspase-3 mediated apoptosis in motor neurons, via a proteinase-activated receptor (PAR1).

Mitochondrial lysates induce inflammation and Alzheimer's disease-relevant changes in microglial and neuronal cells.

Neuroinflammation occurs in Alzheimer's disease (AD). While AD genetic studies implicate inflammation-relevant genes and fibrillar amyloid-β protein promotes inflammation, our understanding of AD neuroinflammation nevertheless remains incomplete. In this study we hypothesized damage-associated molecular pattern (DAMP) molecules arising from mitochondria, intracellular organelles that resemble bacteria, could contribute to AD neuroinflammation.

Bioenergetic dysfunction and inflammation in Alzheimer's disease: a possible connection.

Inflammation is observed in Alzheimer's disease (AD) subject brains. Inflammation-relevant genes are increasingly implicated in AD genetic studies, and inflammatory cytokines to some extent even function as peripheral biomarkers. What underlies AD inflammation is unclear, but no "foreign" agent has been implicated.

Designing drugs that encourage spinal cord injury healing.

Introduction: Spinal cord injury (SCI) occurs within seconds, but host responses may take years. Although life expectancy has increased, half of the survivors end up as paraplegics, with many indeed as quadriplegics. Host responses may have multiple effects ranging from inhibiting inflammation to preventing repair and regeneration.

Novel mutation in VCP gene causes atypical amyotrophic lateral sclerosis.

Objective: To identify the genetic variant that causes autosomal dominantly inherited motor neuron disease in a 4-generation Israeli-Arab family using genetic linkage and whole exome sequencing.

Methods: Genetic linkage analysis was performed in this family using Illumina single nucleotide polymorphism chips. Whole exome sequencing was then undertaken on DNA samples from 2 affected family members using an Illumina 2000 HiSeq platform in pursuit of potentially pathogenic genetic variants that comigrate with the disease in this pedigree.

Soluble thrombomodulin levels in plasma of multiple sclerosis patients and their implication.

Thrombomodulin (TM) on the cell-surface of cerebrovascular endothelial cells (CECs) is released into blood upon CEC damage. TM promotes activation of protein C (APC), an anticoagulant, anti-inflammatory, neuroprotective molecule that protects CECs and impedes inflammatory cell migration across the blood-brain barrier (BBB). Multiple sclerosis (MS) is associated with CEC damage and BBB dysfunction.

Neuroprotective effects of caspase-3 inhibition on functional recovery and tissue sparing after acute spinal cord injury.

Study Design: We used gene microarrays and found that caspase-related death genes were upregulated. We tested caspase inhibition and evaluated its effect on the spinal cord after traumatic injury.

Objective: The logical extension of previous studies was to determine whether downstream CASP genes might also be involved and whether inhibition might prevent injury-induced cell death.

Longitudinal magnetic resonance imaging of spinal cord injury in mouse: changes in signal patterns associated with the inflammatory response.

Contusion-type spinal cord injury (SCI) in mice was followed longitudinally using in vivo magnetic resonance (MR) imaging along with neurobehavioral tests performed on postinjury Days 1, 7, 14 and 28. Magnetic resonance images were acquired from seven injured wild-type mice using a 9.4-T scanner and presented in sagittal and axial views to reflect the current state of the injured cord neuropathology on each day.

GRK5 deficiency leads to early Alzheimer-like pathology and working memory impairment.

G-protein coupled receptor kinase-5 (GRK5) deficiency has been linked to early Alzheimer's disease in humans and mouse models of the disease. To determine potential roles of GRK5 in the disease pathogenesis, the GRK5 knockout mouse was evaluated at pathological and behavioral levels. We found that these mice displayed an age-dependent increase in hippocampal axonal defects characterized by clusters of axonal swellings that accumulated abnormal amounts of molecular motor proteins, microtubule-associated proteins, intracellular beta-amyloid, and subcellular organelles.

Minocycline neuroprotects, reduces microgliosis, and inhibits caspase protease expression early after spinal cord injury.

Minocycline, a clinically used tetracycline for over 40 years, crosses the blood-brain barrier and prevents caspase up-regulation. It reduces apoptosis in mouse models of Huntington's disease and familial amyotrophic lateral sclerosis (ALS) and is in clinical trial for sporadic ALS. Because apoptosis also occurs after brain and spinal cord (SCI) injury, its prevention may be useful in improving recovery.

Magnetic resonance imaging of mouse spinal cord.

The feasibility of performing high-resolution in vivo MRI on mouse spinal cord (SC) at 9.4 T magnetic field strength is demonstrated. The MR properties of the cord tissue were measured and the characteristics of water diffusion in the SC were quantified.

Tissue transglutaminase during mouse central nervous system development: lack of alternative RNA processing and implications for its role(s) in murine models of neurotrauma and neurodegeneration.

Tissue transglutaminase (tTG) is a member of a multigene family principally involved in catalyzing the formation of protein cross-links. Unlike other members of the transglutaminase family, tTG is multifunctional since it also serves as a guanosine triphosphate (GTP) binding protein (Galpha(h)) and participates in cell adhesion. Different isoforms of tTG can be produced by proteolysis or alternative splicing.

Neuroprotective effects of recombinant thrombomodulin in controlled contusion spinal cord injury implicates thrombin signaling.

Although the central nervous system (CNS) of mammals has had poor prospects for regeneration, recent studies suggest this might improve from blocking "secondary cell loss" or apoptosis. In this regard, intravenous activated protein C (aPC) improved neurologic outcomes in a rat compression spinal cord injury (SCI) model. Protein C activation occurs when the serine protease thrombin binds to the cell surface proteoglycan thrombomodulin (TM) forming a complex that halts coagulation.

Abnormality of G-protein-coupled receptor kinases at prodromal and early stages of Alzheimer's disease: an association with early beta-amyloid accumulation.

Overwhelming evidence indicates that the effects of beta-amyloid (Abeta) are dose dependent both in vitro and in vivo, which implies that Abeta is not directly detrimental to brain cells until it reaches a threshold concentration. In an effort to understand early Alzheimer's disease (AD) pathogenesis, this study focused on the effects of subthreshold soluble Abeta and the underlying molecular mechanisms in murine microglial cells and an AD transgenic mouse model. We found that there were two phases of dose-dependent Abeta effects on microglial cells: at the threshold of 5 microm and above, Abeta directly induced tumor necrosis factor-alpha (TNF-alpha) release, and at subthreshold doses, Abeta indirectly potentiated TNF-alpha release induced by certain G-protein-coupled receptor (GPCR) activators.

Prospects for the pharmacotherapy of amyotrophic lateral sclerosis : old strategies and new paradigms for the third millennium.

Biomedical researchers interested in amyotrophic lateral sclerosis (ALS) must invoke newly developing technologies if we are to discover pharmaceutical treatments that will help a significant population of patients with the disease. The focus of ALS research over the last 10 years has been on reactive oxygen species (ROS) and glutamate excitotoxicity, resulting in several clinical trials and the launch of the only drug currently available for the treatment of ALS, riluzole. Unfortunately, the therapeutic benefits have been minimal, at best, and the prognosis for patients with ALS has not improved beyond very modest retardation of the disease course.

Rapid tau aggregation and delayed hippocampal neuronal death induced by persistent thrombin signaling.

Tau hyperphosphorylation, leading to self-aggregation, is widely held to underlie the neurofibrillary degeneration found in Alzheimer's disease (AD) and other tauopathies. However, it is unclear exactly what environmental factors may trigger this pathogenetic tau hyperphosphorylation. From several perspectives, the coagulation serine protease, thrombin, has been implicated in AD and activates several different protein kinase pathways but has not previously been shown how it may contribute to AD pathogenesis.

Persistent protease-activated receptor 4 signaling mediates thrombin-induced microglial activation.

We have previously reported that thrombin, the ultimate serine protease in the coagulation cascades, is a proinflammatory agent that causes proliferation and activation of brain microglial cells. However, participation of its principal receptor, the protease-activated receptor 1 (PAR1) appears to be limited to promoting microglial proliferation and not induction of inflammatory mediators. In the present study, we now report that thrombin action in promoting inflammatory mediators from brain microglia is mediated through another thrombin receptor, PAR4.

Injury-induced "switch" from GTP-regulated to novel GTP-independent isoform of tissue transglutaminase in the rat spinal cord.

We recently found that alternative transcripts of tissue transglutaminase (tTG or TG2) were present in hippocampal brain regions of Alzheimer's disease (AD), but not in control, non-demented, age-matched brains. Since antecedent non-severe trauma has been implicated in AD and other neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), we were interested in whether alternative transcripts might be detected in a model of neurotrauma, controlled-contusion spinal cord injury (SCI) in the rat. Implicated in diverse roles from growth and differentiation to apoptotic cell death, only bifunctional tTG, of the nine member TG family, has dual catalytic activities: guanine trinucleotide (GTP) hydrolyzing activity (GTPase), as well as protein cross-linking.

Participation of protease-activated receptor-1 in thrombin-induced microglial activation.

Activation of microglia, the resident macrophages in the CNS, plays a significant role in neuronal death or degeneration in a broad spectrum of CNS disorders. Recent studies indicate that nanomolar concentrations of the serine protease, thrombin, can activate microglia in culture. However, in contrast to other neural cells responsive to thrombin, the participation of novel protease-activated receptors (PARs), such as the prototypic thrombin receptor PAR1, in thrombin-induced microglial activation was cast in doubt.

Protein crosslinking, tissue transglutaminase, alternative splicing and neurodegeneration.

Increasing interest and awareness of protein aggregation as being implicated in neurodegenerative processes has developed in recent years. One novel mechanism for this may be transglutaminase (TGase)-mediated protein crosslinking, that is involved in a variety of natural processes ranging from the stabilization of fibrin clots to production of the epidermal cell envelope and the fluid barrier of the skin. TGases are also implicated in both function and dysfunction of the central (CNS) and peripheral (PNS) nervous systems.