Heightened inflammasome activation is linked to age-related cognitive impairment in Fischer 344 rats

<p>Abstract</p> <p>Background</p> <p>Members of the mammalian nucleotide binding domain, leucine-rich repeat (LRR)-containing receptor (NLR) family of proteins are key modulators of innate immunity regulating inflammation. Our previous work has shown that among the members of this family, NLRP1/NALP1, present in neurons, plays a crucial role in inflammasome formation and the production of the inflammatory cytokines interleukin (IL) -1β and IL-18 after various types of central nervous system injury.</p> <p>Results</p> <p>We investigated whether age-related cognitive decline may involve a heightened inflammatory response associated with activation of the NLRP1 inflammasome in the hippocampus. Young (3 months) and aged (18 months) male Fischer 344 rats were tested in a spatial acquisition task via Morris water maze. Following behavioral testing, hippocampal lysates were assayed for expression of NLRP1 inflammasome components and inflammatory cytokines. Hippocampal lysates from aged rats showed significantly higher levels of NLRP1 inflammasome constituents, caspase-1, caspase-11, the purinergic receptor P2X7, pannexin-1 and X-linked inhibitor of apoptosis (XIAP) than lysates from younger animals. Following treatment with probenecid, an inhibitor or pannexin-1, aged animals demonstrated reduction in inflammasome activation and improvement in spatial learning performance.</p> <p>Conclusions</p> <p>Our behavioral findings are consistent with increases in IL-1β and IL-18 that have been previously shown to correlate with spatial learning deficits. Probenecid reduced activated caspase-1 and ameliorated spatial learning deficits in aged rats. Thus, aging processes stimulate activation of the NLRP1 inflammasome and secretion of IL-1β and IL-18 that may contribute to age-related cognitive decline in the growing elderly population. Moreover, probenecid may be potentially useful as a therapy to improve cognitive outcomes in the aging population.</p

RIG-I contributes to the innate immune response after cerebral ischemia

BACKGROUND: Focal cerebral ischemia induces an inflammatory response that when exacerbated contributes to deleterious outcomes. The molecular basis regarding the regulation of the innate immune response after focal cerebral ischemia remains poorly understood. METHODS: In this study we examined the expression of retinoic acid-inducible gene (RIG)-like receptor-I (RIG-I) and its involvement in regulating inflammation after ischemia in the brain of rats subjected to middle cerebral artery occlusion (MCAO). In addition, we studied the regulation of RIG-I after oxygen glucose deprivation (OGD) in astrocytes in culture. RESULTS: In this study we show that in the hippocampus of rats, RIG-I and IFN-α are elevated after MCAO. Consistent with these results was an increased in RIG-I and IFN-α after OGD in astrocytes in culture. These data are consistent with immunohistochemical analysis of hippocampal sections, indicating that in GFAP-positive cells there was an increase in RIG-I after MCAO. In addition, in this study we have identified n-propyl gallate as an inhibitor of IFN-α signaling in astrocytes. CONCLUSION: Our findings suggest a role for RIG-I in contributing to the innate immune response after focal cerebral ischemia

Inflammasome signaling proteins as biomarkers of COVID-19

IntroductionOne of the main characteristics of COVID-19 is an exacerbated inflammatory response that results in cardiometabolic complications and dysfunction in the nervous system. Moreover, these complications may extend beyond the period of active SARS-CoV2 infection and even extend over a year. Thus, it is important to better understand the contribution of the inflammatory responses in COVID-19 patients, not just in the acute phase but also after the infection has subsided.MethodsWe measured the protein levels of inflammasome signaling proteins using Simple Plex microfluidics technology in patients with an active SARS-CoV2 infection and in recovered patients to determine their potential use as biomarkers of COVID-19. We carried out statistical analyses to identify which proteins were increased in COVID-19 patients with active infection and in recovered patients. The receiver operating characteristics (ROC) were calculated for each analyte to determine their potential fit as biomarkers.ResultsThe inflammasome proteins caspase-1, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), interleukin (IL)-1β and IL-18 were elevated in the plasma of patients with active infection and remained elevated after the infection was resolved for approximately 2 months after. Levels of caspase-1 and ASC continued to increase long after patients had recovered from the infection. Furthermore, when measuring biomarkers of inflammation during active infection, analyses with area under the curve (AUC) values above 0.75 indicated that caspase-1, ASC, IL-1β and IL-18 are reliable biomarkers of the inflammatory response during active COVID-19 infection. Moreover, when measuring biomarkers of inflammation after recovery from active infection, caspase-1 and ASC presented AUC values above 0.9.DiscussionThese findings indicate that inflammasome signaling proteins can be used to reliably monitor the inflammatory innate immune response in COVID-19 patients

Inflammasome Proteins in Serum and Serum-Derived Extracellular Vesicles as Biomarkers of Stroke

The inflammasome is a key contributor to the inflammatory innate immune response after stroke. We have previously shown that inflammasome proteins are released in extracellular vesicles (EV) after brain and spinal cord injury. In addition, we have shown that inflammasome proteins offer great promise as biomarkers of central nervous system (CNS) injury following brain trauma. In the present study, we used a Simple Plex Assay (Protein Simple), a novel multi-analyte automated microfluidic immunoassay platform, to analyze serum and serum-derived EV samples from stroke patients and control subjects for inflammasome protein levels of caspase-1, apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), Interleukins (IL)-1β, and (IL)-18. Receiver operator characteristic (ROC) curves with associated confidence intervals obtained from the analysis of serum samples revealed that the area under the curve (AUC) for ASC was 0.99 with a confidence interval between 0.9914 and 1.004, whereas the AUC for caspase-1, IL-1β, and IL-18 were 0.75, 0.61, and 0.67, respectively. Thus, these data indicate that ASC is a potential biomarker of stroke and highlight the role of the inflammasome in the inflammatory response after brain ischemia

Netosis and Inflammasomes in Large Vessel Occlusion Thrombi

The inflammatory response appears to play a critical role in clotting in which neutrophil extracellular traps (NETs) are the major drivers of thrombosis in acute ischemic stroke (AIS). The inflammasome is an innate immune complex involved in the activation of interleukin (IL)-18 and IL-1β through caspase-1, but whether the inflammasome plays a role in NETosis in AIS remains poorly understood. Here we assessed the levels of inflammasome signaling proteins in NETs and their association with clinical and procedural outcomes of mechanical thrombectomy for AIS. Electron microscopy and immunofluorescence indicate the presence of NETs in thrombi of patients with AIS. Moreover, the inflammasome signaling proteins caspase-1 and apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) were also present in clots associated with the marker of NETosis citrullinated histone H (CitH3). Analysis of protein levels by a simple plex assay show that caspase-1, ASC and interleukin (IL)-1β were significantly elevated in clots when compared to plasma of AIS patients and healthy controls, while IL-18 levels were lower. Moreover, multivariate analyses show that IL-1β levels in clots contribute to the number of passes to achieve complete recanalization, and that ASC, caspase-1 and IL-18 are significant contributors to time to recanalization. Thus, inflammasome proteins are elevated in NETs present in thrombi of patients with AIS that contribute to poor outcomes following stroke.

The Inflammasome in Reproductive Biology: A Promising Target for Novel Therapies

The inflammasome is a key regulator of innate immunity involved in the inflammatory response to infections as well as disease through the activation of caspase-1 and the processing of the inflammatory cytokines interleukin (IL)-1β and IL-18. Even though the inflammasome was first described in the context of infections, most research in recent years has focused on targeting the inflammasome as a therapeutic option in sterile inflammatory events. Recent evidence indicates a clear involvement of the inflammasome in Reproductive Biology such as infertility and preeclampsia. In this mini-review, I summarize the current findings on the inflammasome that have been described in the field of Reproductive Biology and highlight the potential that the inflammasome has as a novel therapeutic option in this field. The topics covered in this review as it pertains to the inflammasome field cover the literature published on male and female infertility, endometriosis, preeclampsia, placental inflammation, and reproductive senescence

Regulation of the NALP1 inflammasome in neurons: A therapeutic target for spinal cord injury

Cell death following spinal cord injury (SCI) involves an inflammatory response that activates interleukin-1beta (IL-1beta). In the peripheral immune response, the inflammasome activates caspase-1 to process proinflammatory cytokines, but the regulation of inflammation in the nervous system is poorly understood. In this study, the cellular distribution, levels and protein association of inflammasome proteins were investigated in spinal cords of female Fischer (180-200g) rats subjected to moderated cervical (C5) injury and naive controls. Coimmunoprecipitation experiments revealed that Apoptosis-associated Speck-like protein containing a CARD (ASC) associates with caspase-1, -11, NAcht Leucine-Rich-Repeat Protein 1 (NALP1) and the inhibitor of apoptosis, XIAP, forming the NALP1 inflammasome. SCI resulted in increased levels of caspase-1, -11 and ASC, but levels of NALP1 were not significantly altered. After SCI, the composition of the inflammasome changed with increased association of caspase-1, -11 and NALP1 with ASC and cleavage of XIAP. Immunohistochemistry and confocal microscopy revealed that spinal cord neurons express NALP1 inflammasome proteins. Traumatized spinal cords showed alterations in the cellular distribution of these proteins. Therapeutic neutralization of ASC inhibited inflammasome activation, reduced caspase-1 activation, XIAP cleavage, and interleukin processing, resulting in significant tissue sparing and functional improvement. This thesis describes the first in vivo identification of the inflammasome. Furthermore, this work demonstrates that the NALP1 inflammasome is present and is activated in neurons after trauma to the spinal cord. Thus, the NALP1 inflammasome constitutes an important arm of the inflammatory response following SCI that can be used as a therapeutic target after trauma to the spinal cord

Inflammasome Proteins as Inflammatory Biomarkers of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) can result in severe vision loss and blurriness in the older population. The early and intermediate stages of AMD typically start without noticeable symptoms and can only be detected with a comprehensive eye exam. Because of the quiet onset of the disease, it is necessary to identify potential biomarkers to aid in the diagnosis, staging, and association with disease onset. Inflammasome signaling proteins are prominent biomarkers in the central nervous system, and the inflammasome has been shown to play a role in the innate inflammatory response in aging and AMD. Serum from healthy controls and AMD patients were analyzed for the protein levels of Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), interleukin (IL)-18 and C-reactive protein (CRP) to determine cutoff points, positive and negative predictive values, and receiver operator characteristic curves, as well as univariate and multivariate linear and logistic regression models. ASC, IL-18, and CRP were elevated in the serum of AMD patients when compared to healthy controls. The area under the curve (AUC) for ASC was 0.98 with a cutoff point of 365.6 pg/mL, whereas IL-18 had an AUC of 0.73 and a cutoff point of 242.4 pg/mL, and the AUC for CRP was 0.67 with a cutoff point of 8,684,152 pg/mL. Levels of IL-18 had a statistically significant linear correlation with that of ASC with an adjusted of 0.1906, indicating that 19% of IL-18 could be explained by ASC protein levels in serum. Moreover, a logistic regression model for the diagnosis of AMD consists of ASC and having a diagnosis of hypertension, indicating that these two factors (elevated levels of ASC and a diagnosis of hypertension [HTN]) are associated with the diagnosis of AMD. ASC, IL-18, and CRP are elevated in patients with AMD, and the protein levels of IL-18 are partially the result of ASC protein expression. Moreover, elevated protein levels of ASC in serum and a diagnosis of HTN increase the odds of patients having a diagnosis of AMD. Biomarkers of AMD may be used to monitor disease risk, response to treatment and disease progression

Sex Differences in the Inflammatory Profile in the Brain of Young and Aged Mice

Neurodegenerative diseases are a leading cause of death worldwide with no cures identified. Thus, there is a critical need for preventative measures and treatments as the number of patients is expected to increase. Many neurodegenerative diseases have sex-biased prevalence, indicating a need to examine sex differences when investigating prevention and treatment strategies. Inflammation is a key contributor to many neurodegenerative diseases and is a promising target for prevention since inflammation increases with age, which is known as inflammaging. Here, we analyzed the protein expression levels of cytokines, chemokines, and inflammasome signaling proteins in the cortex of young and aged male and female mice. Our results show an increase in caspase-1, interleukin (IL)-1β, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and ASC specks in females compared to males. Additionally, there was an increase in IL-1α, VEGF-A, CCL3, CXCL1, CCL4, CCL17, and CCL22 in aging females and an increase in IL-8, IL-17a, IL-7, LT-α, and CCL22 in aging males. IL-12/IL-23p40, CCL13, and IL-10 were increased in females compared to males but not with age. These results indicate that there are sex differences in cortical inflammaging and provide potential targets to attenuate inflammation to prevent the development of neurodegenerative disease