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Traumatic Brain Injury (TBI) is a major cause of death and disability in the US and a recognized risk factor for the development of Alzheimer's disease (AD). The relationship between these conditions is not completely understood, but the conditions may share additive or synergistic pathological hallmarks that may serve as novel therapeutic targets. Heightened inflammasome signaling plays a critical role in the pathogenesis of central nervous system injury (CNS) and the release of apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) speck from neurons and activated microglia contribute significantly to TBI and AD pathology. This study investigated whether inflammasome signaling after TBI was augmented in AD and whether this signaling pathway impacted biochemical and neuropathological outcomes and overall cognitive function. Five-month-old, 3xTg mice and respective wild type controls were randomized and underwent moderate controlled cortical impact (CCI) injury or served as sham/uninjured controls. Animals were sacrificed at 1 hour, 1 day, or 1 week after TBI to assess acute pathology or at 12 weeks after assessing cognitive function. The ipsilateral cerebral cortex was processed for inflammasome protein expression by immunoblotting. Mice were evaluated for behavior by open field (3 days), novel object recognition (2 weeks), and Morris water maze (6 weeks) testing after TBI. There was a statistically significant increase in the expression of inflammasome signaling proteins Caspase-1, Caspase-8, ASC, and interleukin (IL)-1β after TBI in both wild type and 3xTg animals. At 1-day post injury, significant increases in ASC and IL-1β protein expression were measured in AD TBI mice compared to WT TBI. Behavioral testing showed that injured AD mice had altered cognitive function when compared to injured WT mice. Elevated Aβ was seen in the ipsilateral cortex and hippocampus of sham and injured AD when compared to respective groups at 12 weeks post injury. Moreover, treatment of injured AD mice with IC100, an anti-ASC monoclonal antibody, inhibited the inflammasome, as evidenced by IL-1β reduction in the injured cortex at 1-week post injury. These findings show that the inflammasome response is heightened in mice genetically predisposed to AD and suggests that AD may exacerbate TBI pathology. Thus, dampening inflammasome signaling may offer a novel approach for the treatment of AD and TBI. [ABSTRACT FROM AUTHOR]

Traumatic brain injury (TBI) and Alzheimer's disease (AD) represent 2 of the largest sources of death and disability in the United States. Recent studies have identified TBI as a potential risk factor for AD development, and numerous reports have shown that TBI is linked with AD associated protein expression during the acute phase of injury, suggesting an interplay between the 2 pathologies. The inflammasome is a multi-protein complex that plays a role in both TBI and AD pathologies, and is characterized by inflammatory cytokine release and pyroptotic cell death. Products of inflammasome signaling pathways activate microglia and astrocytes, which attempt to resolve pathological inflammation caused by inflammatory cytokine release and phagocytosis of cellular debris. Although the initial phase of the inflammatory response in the nervous system is beneficial, recent evidence has emerged that the heightened inflammatory response after trauma is self-perpetuating and results in additional damage in the central nervous system. Inflammasome-induced cytokines and inflammasome signaling proteins released from activated microglia interact with AD associated proteins and exacerbate AD pathological progression and cellular damage. Additionally, multiple genetic mutations associated with AD development alter microglia inflammatory activity, increasing and perpetuating inflammatory cell damage. In this review, we discuss the pathologies of TBI and AD and how they are impacted by and potentially interact through inflammasome activity and signaling proteins. We discuss current clinical trials that target the inflammasome to reduce heightened inflammation associated with these disorders. [ABSTRACT FROM AUTHOR]

Inflammasomes are multiprotein complexes of the innate immune response that recognize a diverse range of intracellular sensors of infection or cell damage and recruit the adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) into an inflammasome signaling complex. The recruitment, polymerization and cross-linking of ASC is upstream of caspase-1 activation and interleukin-1β release. Here we provide evidence that IC 100, a humanized IgG4κ monoclonal antibody against ASC, is internalized into the cell and localizes with endosomes, while another part is recycled and redistributed out of the cell. IC 100 binds intracellular ASC and blocks interleukin-1β release in a human whole blood cell inflammasome assay. In vitro studies demonstrate that IC 100 interferes with ASC polymerization and assembly of ASC specks. In vivo bioluminescence imaging showed that IC 100 has broad tissue distribution, crosses the blood brain barrier, and readily penetrates the brain and spinal cord parenchyma. Confocal microscopy of fluorescent-labeled IC 100 revealed that IC 100 is rapidly taken up by macrophages via a mechanism utilizing the Fc region of IC 100. Coimmunoprecipitation experiments and confocal immunohistochemistry showed that IC 100 binds to ASC and to the atypical antibody receptor Tripartite motif-containing protein-21 (TRIM21). In A549 WT and TRIM21 KO cells treated with either IC 100 or IgG4κ isotype control, the levels of intracellular IC 100 were higher than in the IgG4κ-treated controls at 2 hours, 1 day and 3 days after administration, indicating that IC 100 escapes degradation by the proteasome. Lastly, electron microscopy studies demonstrate that IC 100 binds to ASC filaments and alters the architecture of ASC filaments. Thus, IC 100 readily penetrates a variety of cell types, and it binds to intracellular ASC, but it is not degraded by the TRIM21 antibody-dependent intracellular neutralization pathway. [ABSTRACT FROM AUTHOR]

Innate immunity is part of the early response of the body to deal with tissue damage and infections. Because of the early nature of the innate immune inflammatory response, this inflammatory reaction represents an attractive option as a therapeutic target. The inflammasome is a component of the innate immune response involved in the activation of caspase 1 and the processing of pro-interleukin 1β. In this article, we discuss the therapeutic potential of the inflammasome after central nervous system (CNS) injury and stroke, as well as the basic knowledge we have gained so far regarding inflammasome activation in the CNS. In addition, we discuss some of the therapies available or under investigation for the treatment of brain injury, spinal cord injury, and stroke. [ABSTRACT FROM AUTHOR]

Abstract: Pannexin1 (Panx1) originally was discovered as a gap junction related protein. However, rather than forming the cell-to-cell channels of gap junctions, Panx1 forms a mechanosensitive and highly ATP permeable channel in the cell membrane allowing the exchange of molecules between the cytoplasm and the extracellular space. The list of arguments for Panx1 representing the major ATP release channel includes: (1) Panx1 is expressed in (all?) cells releasing ATP in a non-vesicular fashion, such as erythrocytes; (2) in cells with polar release of ATP, Panx1 is expressed at the ATP release site, such as the apical membrane in airway epithelial cells; (3) the pharmacology of Panx1 channels matches that of ATP release; (4) mutation of Panx1 in strategic positions in the protein modifies ATP release; and (5) knockdown or knockout of Panx1 attenuates or abolishes ATP release. Panx1, in association with the purinergic receptor P2X7, is involved in the innate immune response and in apoptotic/pyroptotic cell death. Inflammatory processes are responsible for amplification of the primary lesion in CNS trauma and stroke. Panx1, as an early signal event and as a signal amplifier in these processes, is an obvious target for the prevention of secondary cell death due to inflammasome activity. Since Panx1 inhibitors such as probenecid are already clinically tested in different settings they should be considered for therapy in stroke and CNS trauma. [Copyright &y& Elsevier]

N-Methyl-D-aspartate (NMDA)-gated ion channels are known to play a critical role in motoneuron depolarization, but the molecular mechanisms modulating NMDA activation in the spinal cord are not well understood. This study demonstrates that activated 5HT2C receptors enhance NMDA depolarizations recorded electrophysiologically from motoneurons. Pharmacological studies indicate involvement of Src tyrosine kinase mediates 5HT2C facilitation of NMDA. RT-PCR analysis revealed edited forms of 5HT2C were present in mammalian spinal cord, indicating the availability of G-protein-independent isoforms. Spinal cord neurons treated with the 5HT2C agonist MK 212 showed increased SrcTyr-416 phosphorylation in a dose-dependent manner thus verifying that Src is activated after treatment. In addition, 5HT2C antagonists and tyrosine kinase inhibitors blocked 5HT2C-mediated SrcTyr-416 phosphorylation and also enhanced NMDA-induced motoneuron depolarization. Co-immunoprecipitation of synaptosomal fractions showed that GluN2A, 5HT2C receptors, and Src tyrosine kinase form protein associations in synaptosomes. Moreover, immunohistochemical analysis demonstrated GluN2A and 5HT2C receptors co-localize on the processes of spinal neurons. These findings reveal that a distinct multiprotein complex links 5-hydroxytryptamine-activated intracellular signaling events with NMDA-mediated functional activity. [ABSTRACT FROM AUTHOR]

Invasive neuroprosthetics rely on microelectrodes (MEs) to record or stimulate the activity of large neuron assemblies. However, MEs are subjected to tissue reactivity in the central nervous system (CNS) due to the foreign body response (FBR) that contribute to chronic neuroinflammation and ultimately result in ME failure. An endogenous, acute set of mechanisms responsible for the recognition and targeting of foreign objects, called the innate immune response, immediately follows the ME implant-induced trauma. Inflammasomes are multiprotein structures that play a critical role in the initiation of an innate immune response following CNS injuries. The activation of inflammasomes facilitates a range of innate immune response cascades and results in neuroinflammation and programmed cell death. Despite our current understanding of inflammasomes, their roles in the context of neural device implantation remain unknown. In this study, we implanted a non-functional Utah electrode array (UEA) into the rat somatosensory cortex and studied the inflammasome signaling and the corresponding downstream effects on inflammatory cytokine expression and the inflammasome-mediated cell death mechanism of pyroptosis. Our results not only demonstrate the continuous activation of inflammasomes and their contribution to neuroinflammation at the electrode-tissue interface but also reveal the therapeutic potential of targeting inflammasomes to attenuate the FBR in invasive neuroprosthetics. [ABSTRACT FROM AUTHOR]

Abstract: Bone morphogenetic protein 7 (BMP7) has been shown to ameliorate reduced dendritic growth induced by glutamate excitotoxicity in neuronal tissue cultures and/or provide an enhancement of functional recovery in central nervous system (CNS) injury. BMP7 expression is modulated by spinal cord injury (SCI), but the molecular mechanisms involved in neuroprotection have not been clearly defined. Here, we show that BMP7 treatment of rats subjected to mild cervical SCI significantly increased the pro-survival mitogen-activated protein kinase-38 (MAPK-38) pathway and levels of N-methyl-d-aspartate receptor 1 (NMDAR-1) resulting in a significant increase in neuronal sparing in the ventral horn of the spinal cord. Moreover, BMP7 was neuroprotective against glutamate-mediated excitotoxicity in cultured cortical neurons. These studies show that BMP7 administration may be used as a therapeutic strategy to reduce the damaging excitotoxic effects following SCI. [Copyright &y& Elsevier]

Abstract: Sex influences histological and behavioral outcomes following traumatic brain injury (TBI), but the underlying sex-dependent pathomechanisms regulating outcome measures remain poorly defined. Here, we investigated the TBI-induced regulation of the X-linked inhibitor of apoptosis protein (XIAP) that, in addition to suppressing cell death by inhibition of caspases, is involved in signaling cascades, including immune regulation and cell migration. Since estrogen has been shown to have anti-apoptotic properties, we specifically examined sex differences and the influence of estrogen on XIAP processing after TBI. Sprague–Dawley male (TBI-M), female (TBI-F), ovariectomized female (TBI-OVX) and ovariectomized females supplemented with estrogen (TBI-OVX+EST) were subjected to moderate (1.7–2.2atm) fluid percussion (FP) injury. Animals were sacrificed 24h after FP injury; cortical tissue (ipsilateral and contralateral) was dissected and analyzed for XIAP processing by immunoblot analysis (n =6–7/group) or confocal microscopy (n =2–3/group). Significant differences in XIAP cleavage products in the ipsilateral cortex were found between groups (p <0.03). Post hoc analysis showed an increase in XIAP processing in both TBI-F and TBI-OVX+EST compared to TBI-M and TBI-OVX (p <0.05), indicating that more XIAP is cleaved following injury in intact females and TBI-OVX+EST than in TBI-M and TBI-OVX groups. Co-localization of XIAP within neurons also demonstrated sex-dependent changes. Based on these data, it appears that the processing of XIAP after injury is different between males and females and may be influenced by exogenous estrogen treatment. [Copyright &y& Elsevier]

The inflammasome is a multiprotein complex involved in innate immunity. Activation of the inflammasome causes the processing and release of the cytokines interleukins 1β and 18. In primary macrophages, potassium ion flux and the membrane channel pannexin 1 have been suggested to play roles in inflammasome activation. However, the molecular mechanism(s) governing inflammasome signaling remains poorly defined, and it is undetermined whether these mechanisms apply to the central nervous system. Here we show that high extracellular potassium opens pannexin channels leading to caspase1 activation in primary neurons and astrocytes. The effect of K[sup+] on pannexin 1 channels was independent of membrane potential, suggesting that stimulation of inflammasome signaling was mediated by an allosteric effect. The activation of the inflammasome by K[sup+] was inhibited by the pannexin 1 channel blocker probenecid, supporting a role of pannexin 1 in inflammasome activation. Co-immunoprecipitation of neuronal lysates indicates that pannexin 1 associates with components of the multiprotein inflammasome complex, including the P2X7 receptor and caspase-1. Moreover antibody neutralization of the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) blocked ATP-induced cell death in oocytes coexpressing P2X7 receptor and pannexin 1. Thus, in contrast to macrophages and monocytes in which low intracellular K[sup+] has been suggested to trigger inflammasome activation, in neural cells, high extracellular K[sup+] activates caspase-1 probably through pannexin 1. [ABSTRACT FROM AUTHOR]

Objective: To study the mechanism leading to elevated semen cytokines in men with spinal cord injury (SCI) and to understand if inflammasome pathways are involved in this process. To investigate inflammasome components and end-product cytokines in semen of SCI and control subjects. Design: Prospective study. Setting: Major university medical center. Patient(s): Men with and without SCI (n = 28 per group). Intervention(s): None. Main Outcome Measure(s): Seminal plasma concentrations of caspase-1, interleukin (IL) 1β, and IL-18 were quantified by ELISA. Caspase-1 in sperm fractions and apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) in seminal plasma and sperm fractions were identified by Western blot. Localization of proteins in sperm was accomplished by immunocytochemistry. Result(s): ASC, caspase-1, IL-1β, and IL-18 concentrations were elevated in the seminal plasma of SCI subjects compared with control subjects. ASC and caspase-1 were elevated in sperm cells of SCI subjects. Immunocytochemistry revealed that ASC was located in the acrosome, equatorial segment, and midpiece, and caspase-1 in the midpiece. Conclusion(s): This study provides the first evidence of ASC in human semen and demonstrates the involvement of inflammasome proteins in semen of men with SCI. These findings suggest an immunologic basis for abnormal semen quality in men with SCI. [ABSTRACT FROM AUTHOR]