Traumatic brain injury is a common and serious neurodegenerative condition that lacks a pharmaceutical intervention to improve long-term outcome. Hyperphosphorylated tau is implicated in some of the consequences of traumatic brain injury and is a potential pharmacological target. Protein phosphatase 2A is a heterotrimeric protein that regulates key signalling pathways, and protein phosphatase 2A heterotrimers consisting of the PR55 B-subunit represent the major tau phosphatase in the brain. Here we investigated whether traumatic brain injury in rats and humans would induce changes in protein phosphatase 2A and phosphorylated tau, and whether treatment with sodium selenate-a potent PR55 activator-would reduce phosphorylated tau and improve traumatic brain injury outcomes in rats. Ninety young adult male Long-Evans rats were administered either a fluid percussion injury or sham-injury. A proportion of rats were killed at 2, 24, and 72 h post-injury to assess acute changes in protein phosphatase 2A and tau. Other rats were given either sodium selenate or saline-vehicle treatment that was continuously administered via subcutaneous osmotic pump for 12 weeks. Serial magnetic resonance imaging was acquired prior to, and at 1, 4, and 12 weeks post-injury to assess evolving structural brain damage and axonal injury. Behavioural impairments were assessed at 12 weeks post-injury. The results showed that traumatic brain injury in rats acutely reduced PR55 expression and protein phosphatase 2A activity, and increased the expression of phosphorylated tau and the ratio of phosphorylated tau to total tau. Similar findings were seen in post-mortem brain samples from acute human traumatic brain injury patients, although many did not reach statistical significance. Continuous sodium selenate treatment for 12 weeks after sham or fluid percussion injury in rats increased protein phosphatase 2A activity and PR55 expression, and reduced the ratio of phosphorylated tau to total tau, attenuated brain damage, and improved behavioural outcomes in rats given a fluid percussion injury. Notably, total tau levels were decreased in rats 12 weeks after fluid percussion injury, and several other factors, including the use of anaesthetic, the length of recovery time, and that some brain injury and behavioural dysfunction still occurred in rats treated with sodium selenate must be considered in the interpretation of this study. However, taken together these data suggest protein phosphatase 2A and hyperphosphorylated tau may be involved in the neurodegenerative cascade of traumatic brain injury, and support the potential use of sodium selenate as a novel traumatic brain injury therapy.

Highlights d Granzyme B + CD8 + T cells accumulate in the brain after traumatic brain injury (TBI) d Brain CD8 + T cells contribute to chronic motor deficits and myelin pathology d Deficiency/depletion of CD8 + T cells promotes neurological recovery following TBI d B cells and autoreactive antibodies appear to play a regulatory role in TBI

Tranexamic acid (TXA) is an antifibrinolytic agent that blocks plasmin formation. Because plasmin is known to promote inflammatory and immunosuppressive responses, we explored the possibility that plasmin-mediated immunosuppression in patients undergoing cardiac surgery can be directly reversed by TXA and decrease postoperative infection rates. The modulatory effect of TXA on inflammatory cytokine levels and on innate immune cell activation were evaluated with multiplex enzyme-linked immunosorbent assay and flow cytometry, respectively. Postoperative infection rates were determined in patients undergoing cardiac surgery and randomized to TXA (ACTRN12605000557639; http://www.anzca.edu.au). We demonstrate that TXA-mediated plasmin blockade modulates the immune system and reduces surgery-induced immunosuppression in patients following cardiac surgery. TXA enhanced the expression of immune-activating markers while reducing the expression of immunosuppressive markers on multiple myeloid and lymphoid cell populations in peripheral blood. TXA administration significantly reduced postoperative infection rates, despite the fact that patients were being administered prophylactic antibiotics. This effect was independent of the effect of TXA at reducing blood loss. TXA was also shown to exert an immune-modulatory effect in healthy volunteers, further supporting the fibrin-independent effect of TXA on immune function and indicating that baseline plasmin levels contribute to the regulation of the immune system in the absence of any comorbidity or surgical trauma. Finally, the capacity of TXA to reduce infection rates, modulate the innate immune cell profile, and generate an antifibrinolytic effect overall was markedly reduced in patients with diabetes, demonstrating for the first time that the diabetic condition renders patients partially refractory to TXA.

Type-1 interferons (IFNs) are pleiotropic cytokines that signal through the type-1 IFN receptor (IFNAR1). Recent literature has implicated the type-1 IFNs in disorders of the CNS. In this study, we have investigated the role of type-1 IFNs in neuroinflammation following traumatic brain injury (TBI). Using a controlled cortical impact model, TBI was induced in 8- to 10-week-old male C57BL/6J WT and IFNAR1−/− mice and brains were excised to study infarct volume, inflammatory mediator release via quantitative PCR analysis and immune cell profile via immunohistochemistry. IFNAR1−/− mice displayed smaller infarcts compared with WT mice after TBI. IFNAR1−/− mice exhibited an altered anti-inflammatory environment compared with WT mice, with significantly reduced levels of the proinflammatory mediators TNFα, IL-1β and IL-6, an up-regulation of the anti-inflammatory mediator IL-10 and an increased activation of resident and peripheral immune cells after TBI. WT mice injected intravenously with an anti-IFNAR1 blocking monoclonal antibody (MAR1) 1 h before, 30 min after or 30 min and 2 d after TBI displayed significantly improved histological and behavioral outcome. Bone marrow chimeras demonstrated that the hematopoietic cells are a peripheral source of type-1 IFNs that drives neuroinflammation and a worsened TBI outcome. Type-1 IFN mRNA levels were confirmed to be significantly altered in human postmortem TBI brains. Together, these data demonstrate that type-1 IFN signaling is a critical pathway in the progression of neuroinflammation and presents a viable therapeutic target for the treatment of TBI.

Plasmin is the effector protease of the fibrinolytic system, well known for its involvement in fibrin degradation and clot removal. However, plasmin is also recognized as a potent modulator of immunological processes by directly interacting with various cell types including leukocytes (monocytes, macrophages, and dendritic cells) and cells of the vasculature (endothelial cells, smooth muscle cells) as well as soluble factors of the immune system and components of the extracellular matrix. In fact, the removal of misfolded proteins and maintenance of tissue homeostasis seem to be major physiological functions of plasmin. However, a large body of evidence also suggests that excessive plasmin generation frequently contributes to the pathophysiology of acute and chronic inflammatory processes. Hence, one question arising from the broadening effects of plasmin in physiology is whether antifibrinolytic drugs (i.e., tranexamic acid, epsilon aminocaproic acid, or aprotinin) that target plasmin either directly or indirectly and which are commonly used to prevent or treat bleeding might have unintended consequences on the immune response or on other nonfibrinolytic processes in vivo.

The neurovascular unit provides a dynamic interface between the circulation and central nervous system. Disruption of neurovascular integrity occurs in numerous brain pathologies including neurotrauma and ischaemic stroke. Tissue plasminogen activator is a serine protease that converts plasminogen to plasmin, a protease that dissolves blood clots. Besides its role in fibrinolysis, tissue plasminogen activator is abundantly expressed in the brain where it mediates extracellular proteolysis. However, proteolytically active tissue plasminogen activator also promotes neurovascular disruption after ischaemic stroke; the molecular mechanisms of this process are still unclear. Tissue plasminogen activator is naturally inhibited by serine protease inhibitors (serpins): plasminogen activator inhibitor-1, neuroserpin or protease nexin-1 that results in the formation of serpin:protease complexes. Proteases and serpin:protease complexes are cleared through high-affinity binding to low-density lipoprotein receptors, but their binding to these receptors can also transmit extracellular signals across the plasma membrane. The matrix metalloproteinases are the second major proteolytic system in the mammalian brain, and like tissue plasminogen activators are pivotal to neurological function but can also degrade structures of the neurovascular unit after injury. Herein, we show that tissue plasminogen activator potentiates neurovascular damage in a dose-dependent manner in a mouse model of neurotrauma. Surprisingly, inhibition of activity following administration of plasminogen activator inhibitor-1 significantly increased cerebrovascular permeability. This led to our finding that formation of complexes between tissue plasminogen activator and plasminogen activator inhibitor-1 in the brain parenchyma facilitates post-traumatic cerebrovascular damage. We demonstrate that following trauma, the complex binds to low-density lipoprotein receptors, triggering the induction of matrix metalloproteinase-3. Accordingly, pharmacological inhibition of matrix metalloproteinase-3 attenuates neurovascular permeability and improves neurological function in injured mice. Our results are clinically relevant, because concentrations of tissue plasminogen activator: plasminogen activator inhibitor-1 complex and matrix metalloproteinase-3 are significantly elevated in cerebrospinal fluid of trauma patients and correlate with neurological outcome. In a separate study, we found that matrix metalloproteinase-3 and albumin, a marker of cerebrovascular damage, were significantly increased in brain tissue of patients with neurotrauma. Perturbation of neurovascular homeostasis causing oedema, inflammation and cell death is an important cause of acute and long-term neurological dysfunction after trauma. A role for the tissue plasminogen activator-matrix metalloproteinase axis in promoting neurovascular disruption after neurotrauma has not been described thus far. Targeting tissue plasminogen activator: plasminogen activator inhibitor-1 complex signalling or dow...

BackgroundLysophosphatidic acid (LPA) is a bioactive phospholipid with a potentially causative role in neurotrauma. Blocking LPA signaling with the LPA-directed monoclonal antibody B3/Lpathomab is neuroprotective in the mouse spinal cord following injury.FindingsHere we investigated the use of this agent in treatment of secondary brain damage consequent to traumatic brain injury (TBI). LPA was elevated in cerebrospinal fluid (CSF) of patients with TBI compared to controls. LPA levels were also elevated in a mouse controlled cortical impact (CCI) model of TBI and B3 significantly reduced lesion volume by both histological and MRI assessments. Diminished tissue damage coincided with lower brain IL-6 levels and improvement in functional outcomes.ConclusionsThis study presents a novel therapeutic approach for the treatment of TBI by blocking extracellular LPA signaling to minimize secondary brain damage and neurological dysfunction.

Cellular injury causes a myriad of processes that affect proteostasis. We describe nucleocytoplasmic coagulation (NCC), an intracellular disulfide-dependent protein crosslinking event occurring upon late-stage cell death that orchestrates the proteolytic removal of misfolded proteins. In vitro and in vivo models of neuronal injury show that NCC involves conversion of soluble intracellular proteins, including tubulin, into insoluble oligomers. These oligomers, also seen in human brain tissue following neurotrauma, act as a cofactor and substrate for the plasminogen-activating system. In plasminogen(-/-) mice, levels of misfolded β-tubulin were elevated and its clearance delayed following neurotrauma, demonstrating a requirement for plasminogen in the removal of NCC constituents. While additional in vivo studies will further dissect this phenomenon, our study clearly shows that NCC, a process analogous to the formation of thrombi, generates an aggregated protein scaffold that limits release of cellular components and recruits clearance mechanisms to the site of injury.