Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions.

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

Age-induced alterations of granulopoiesis generate atypical neutrophils that aggravate stroke pathology.

Aging accounts for increased risk and dismal outcome of ischemic stroke. Here, we investigated the impact of age-related changes in the immune system on stroke. Upon experimental stroke, compared with young mice, aged mice had increased neutrophil clogging of the ischemic brain microcirculation, leading to worse no-reflow and outcomes. Aged mice showed an enhanced granulopoietic response to stroke that led to the accumulation of CD101+CD62Llo mature and CD177hiCD101loCD62Llo and CD177loCD101loCD62Lhi immature atypical neutrophils in the blood, endowed with increased oxidative stress, phagocytosis and procoagulant features. Production of CXCL3 by CD62Llo neutrophils of the aged had a key role in the development and pathogenicity of aging-associated neutrophils. Hematopoietic stem cell rejuvenation reverted aging-associated neutropoiesis and improved stroke outcome. In elderly patients with ischemic stroke, single-cell proteome profile of blood leukocytes identified CD62Llo neutrophil subsets associated with worse reperfusion and outcome. Our results unveil how stroke in aging leads to a dysregulated emergency granulopoiesis impacting neurological outcome.

Harmonization of sensorimotor deficit assessment in a registered multicentre pre-clinical randomized controlled trial using two models of ischemic stroke.

Multicentre preclinical randomized controlled trials (pRCTs) are a valuable tool to improve experimental stroke research, but are challenging and therefore underused. A common challenge regards the standardization of procedures across centres. We here present the harmonization phase for the quantification of sensorimotor deficits by composite neuroscore, which was the primary outcome of two multicentre pRCTs assessing remote ischemic conditioning in rodent models of ischemic stroke. Ischemic stroke was induced by middle cerebral artery occlusion for 30, 45 or 60 min in mice and 50, 75 or 100 min in rats, allowing sufficient variability. Eleven animals per species were video recorded during neurobehavioural tasks and evaluated with neuroscore by eight independent raters, remotely and blindly. We aimed at reaching an intraclass correlation coefficient (ICC) ≥0.60 as satisfactory interrater agreement. After a first remote training we obtained ICC = 0.50 for mice and ICC = 0.49 for rats. Errors were identified in animal handling and test execution. After a second remote training, we reached the target interrater agreement for mice (ICC = 0.64) and rats (ICC = 0.69). In conclusion, a multi-step, online harmonization phase proved to be feasible, easy to implement and highly effective to align each centre's behavioral evaluations before project's interventional phase.

Neutrophils predominate the immune signature of cerebral thrombi in COVID-19 stroke patients.

Coronavirus disease 2019 (COVID-19) is associated with an increased risk of thrombotic events. Ischemic stroke in COVID-19 patients entails high severity and mortality rates. Here we aimed to analyze cerebral thrombi of COVID-19 patients with large vessel occlusion (LVO) acute ischemic stroke to expose molecular evidence for SARS-CoV-2 in the thrombus and to unravel any peculiar immune-thrombotic features. We conducted a systematic pathological analysis of cerebral thrombi retrieved by endovascular thrombectomy in patients with LVO stroke infected with COVID-19 (n = 7 patients) and non-covid LVO controls (n = 23). In thrombi of COVID-19 patients, the SARS-CoV-2 docking receptor ACE2 was mainly expressed in monocytes/macrophages and showed higher expression levels compared to controls. Using polymerase chain reaction and sequencing, we detected SARS-CoV-2 Clade20A, in the thrombus of one COVID-19 patient. Comparing thrombus composition of COVID-19 and control patients, we noted no overt differences in terms of red blood cells, fibrin, neutrophil extracellular traps (NETs), von Willebrand Factor (vWF), platelets and complement complex C5b-9. However, thrombi of COVID-19 patients showed increased neutrophil density (MPO+ cells) and a three-fold higher Neutrophil-to-Lymphocyte Ratio (tNLR). In the ROC analysis both neutrophils and tNLR had a good discriminative ability to differentiate thrombi of COVID-19 patients from controls. In summary, cerebral thrombi of COVID-19 patients can harbor SARS-CoV2 and are characterized by an increased neutrophil number and tNLR and higher ACE2 expression. These findings suggest neutrophils as the possible culprit in COVID-19-related thrombosis.

JAB1 deletion in oligodendrocytes causes senescence-induced inflammation and neurodegeneration in mice.

Oligodendrocytes are the primary target of demyelinating disorders, and progressive neurodegenerative changes may evolve in the CNS. DNA damage and oxidative stress are considered key pathogenic events, but the underlying molecular mechanisms remain unclear. Moreover, animal models do not fully recapitulate human diseases, complicating the path to effective treatments. Here we report that mice with cell-autonomous deletion of the nuclear COP9 signalosome component CSN5 (JAB1) in oligodendrocytes develop DNA damage and defective DNA repair in myelinating glial cells. Interestingly, oligodendrocytes lacking JAB1 expression underwent a senescence-like phenotype that fostered chronic inflammation and oxidative stress. These mutants developed progressive CNS demyelination, microglia inflammation, and neurodegeneration, with severe motor deficits and premature death. Notably, blocking microglia inflammation did not prevent neurodegeneration, whereas the deletion of p21CIP1 but not p16INK4a pathway ameliorated the disease. We suggest that senescence is key to sustaining neurodegeneration in demyelinating disorders and may be considered a potential therapeutic target.

Cerebral thrombi of cardioembolic etiology have an increased content of neutrophil extracellular traps.

BACKGROUND: Inflammation is emerging as an essential trigger for thrombosis. In the interplay between innate immunity and coagulation cascade, neutrophils and neutrophil extracellular traps (NETs) can promote thrombus formation and stabilization. In ischemic stroke, it is uncertain whether the involvement of the inflammatory component may differ in thrombi of diverse etiology. We here aimed to evaluate the presence of neutrophils and NETs in cerebral thrombi of diverse etiology retrieved by endovascular thrombectomy (EVT). METHODS: We performed a systematic histological analysis on 80 human cerebral thrombi retrieved through EVT in acute ischemic stroke patients. Thrombus composition was investigated in terms of neutrophils (MPO+ cells) and NET content (citH3+ area), employing specific immunostainings. NET plasma content was determined and compared to NET density in the thrombus. RESULTS: Neutrophils and NETs were heterogeneously represented within all cerebral thrombi. Thrombi of diverse etiology did not display a statistically significant difference in the number of neutrophils (p = 0.51). However, NET content was significantly increased in cardioembolic compared to large artery atherosclerosis thrombi (p = 0.04), and the association between NET content and stroke etiology remained significant after adjusted analysis (beta coefficient = -6.19, 95%CI = -11.69 to -1.34, p = 0.01). Moreover, NET content in the thrombus was found to correlate with NET content in the plasma (p ≤ 0.001, r = 0.62). CONCLUSION: Our study highlights how the analysis of the immune component within the cerebral thrombus, and specifically the NET burden, might provide additional insight for differentiating stroke from diverse etiologies.

Multicentre translational Trial of Remote Ischaemic Conditioning in Acute Ischaemic Stroke (TRICS): protocol of multicentre, parallel group, randomised, preclinical trial in female and male rat and mouse from the Italian Stroke Organization (ISO) Basic Science network.

INTRODUCTION: Multicentre preclinical randomised controlled trials (pRCT) are emerging as a necessary step to confirm efficacy and improve translation into the clinic. The aim of this project is to perform two multicentre pRCTs (one in rats and one in mice) to investigate the efficacy of remote ischaemic conditioning (RIC) in an experimental model of severe ischaemic stroke. METHODS AND ANALYSIS: Seven research laboratories within the Italian Stroke Organization (ISO) Basic Science network will participate in the study. Transient endovascular occlusion of the proximal right middle cerebral artery will be performed in two species (rats and mice) and in both sexes. Animals will be randomised to receive RIC by transient surgical occlusion of the right femoral artery, or sham surgery, after reperfusion. Blinded outcome assessment will be performed for dichotomised functional neuroscore (primary endpoint) and infarct volume (secondary endpoint) at 48 hours. A sample size of 80 animals per species will yield 82% power to detect a significant difference of 30% in the primary outcome in both pRCTs. Analyses will be performed in a blind status and according to an intention-to-treat paradigm. The results of this study will provide robust, translationally oriented, high-quality evidence on the efficacy of RIC in multiple species of rodents with large ischaemic stroke. ETHICS AND DISSEMINATION: This is approved by the Animal Welfare Regulatory Body of the University of Milano Bicocca, under project license from the Italian Ministry of Health. Trial results will be subject to publication according to the definition of the outcome presented in this protocol. TRIAL REGISTRATION NUMBER: PCTE0000177.

Insights from thrombi retrieved in stroke due to large vessel occlusion.

The recent advances of endovascular procedures to treat stroke due to large cerebral vessel occlusion have made it possible to analyze the retrieved thrombus material. Analysis of cerebral thrombi is emerging as a relevant opportunity to complement the diagnostic workup of etiology, to develop new lytic approaches and to optimize the acute treatment of stroke due to large vessel occlusion. Nonetheless, retrieved thrombi are frequently discarded since their informative potential is often neglected and standards are missing. This review provides an overview of the current knowledge and expanding research relating to thrombus composition analysis in large vessel occlusions. We first discuss the heterogeneity of thrombogenic factors that underlie the thrombotic formation in stroke and its implications to identify stroke etiology and thrombus age. Further, we show that understanding structural characteristics of thrombus is pivotal for the development of new-targeted lytic therapies as well as to improve, through thrombus modeling, the development of thrombectomy devices. Finally, we discuss the on-going attempts to identify a signature of thrombus composition indirectly through imaging and peripheral blood biomarkers, which might in future assist treatment decision-making as well as secondary prevention. Thrombus analysis might contribute to the advancement and optimization of personalized stroke treatments.