Background: Increasing evidence shows a link between the central nervous system and the immune system in mediating damage, as well as regeneration and repair, following stroke, though most studies focus on T-cell-mediated pathology. While previous work links the B-cell secretion of IL-10 with acute neuroprotection following experimental stroke (PMID: 24374817), the role of B cells in long-term functional recovery is unknown. Hypothesis: The purpose of this study was to assess the protective role of B-cells in improving post-stroke motor function in B-cell deficient mice. Materials and Methods: Adult male transgenic mice expressing human CD20+ (hCD20+) or wild-type (WT) littermate controls (PMID: 17709552) were trained on rotorod for a 2 week duration. Following training, all mice were administered Rituximab (50g ip; PMID: 21359213) daily for 3 days and weekly thereafter. Stroke was induced by a 60-min transient middle cerebral artery occlusion (tMCAo). Post-stroke functional recovery was evaluated 2, 4, 7 and 14 days post-tMCAo. Lymphocytes were isolated from spleen 2 weeks post-tMCAo, stained with antibodies, profiled on a FACS Canto flow cytometer, and analyzed with FlowJo. Results: WT mice recovered to near pre-stroke rotorod performance by 4 days post-tMCAo. In contrast, hCD20+ mice exhibited deficits through 7 days (p<0.05). We confirmed that Rituximab depleted CD20+ B-cells (p<0.05) in the spleen of hCD20+ mice. This post-stroke B-cell depletion reduced CD45+ (p<0.0001) populations, as well as pro-inflammatory CD11b+ macrophage populations (p<0.01). Overall, B-cell depletion increased splenic T-cell percent representation (p<0.001), while decreasing monocyte (p<0.0005) and macrophage (p<0.0001) representation. Conclusions: B-cell depletion in hCD20+ mice prolonged motor deficits in rotorod performance beyond WT mice. B-cell depletion also enhanced a post-stroke immunosuppression of splenic immune cell populations. These data suggest a potential role for B-cells as a therapeutic tool to enhance functional recovery, and counter potentially detrimental post-stroke immunosuppression that contributes to comorbidity during recovery.
Individuals with amnestic mild cognitive impairment (aMCI) experience cognitive declines in learning and memory greater than expected for normal aging, and are at a high risk of dementia. We previously reported that sedentary aMCI patients exhibited neuroinflammation that correlated with brain amyloid beta (Aβ) burden, as determined by 18F-florbetapir positron emission tomography (PET). These aMCI patients enrolled in a one-year randomized control trial (AETMCI, NCT01146717) to test the beneficial effects of 12 months of moderate-to-high intensity aerobic exercise training (AET) or stretching/toning (ST) control intervention on neurocognitive function. A subset of aMCI participants had PET imaging, cognitive testing, and immunophenotyping of cerebrospinal fluid (CSF) and peripheral blood after AET or ST interventions. As adaptive immune responses were similar between AET and ST groups, we combined AET/ST into a general 'physical activity' (PA) group and compared Aβ burden, cognitive function, and adaptive immune cell subsets to sedentary lifestyle before intervention. We found that PAinduced immunomodulation of CD4+ and CD8+ T cells in CSF correlated with changes in Aβ burden in brain regions associated with executive function. Furthermore, after PA, cognitive scores on tests of memory, processing speed, attention, verbal fluency, and executive function were associated with increased percent representation of circulating naïve B + T cells. We review the literature on aMCI-related cognition and immune changes as they relate to exercise, and highlight how our preliminary data suggest a complex interplay between the adaptive immune system, physical activity, cognition, and Aβ burden in aMCI.
The discovery of meningeal lymphatic vessels (LVs) has sparked interest in identifying their role in diseases of the central nervous system. Similar to peripheral LVs, meningeal LVs depend on vascular endothelial growth factor receptor-3 (VEGFR3) signaling for development. Here we characterize the effect of stroke on meningeal LVs, and the impact of meningeal lymphatic hypoplasia on post-stroke outcomes. We show that photothrombosis (PT), but not transient middle cerebral artery occlusion (tMCAo), induces meningeal lymphangiogenesis in young male C57Bl/J6 mice. We also show that Vegfr3 wt/mut mice develop significantly fewer meningeal LVs than Vegfr3 wt/wt mice. Again, meningeal lymphangiogenesis occurs in the alymphatic zone lateral to the sagittal sinus only after PT-induced stroke in Vegfr3 wt/wt mice. Interestingly, Vegfr3 wt/mut mice develop larger stroke volumes than Vegfr3 wt/wt mice after tMCAo, but not after PT. Our results reveal differences between PT and tMCAo models of stroke and underscore the need to consider method of stroke induction when investigating the role of meningeal lymphatics. Taken together, our data indicate that ischemic injury can induce the growth of meningeal LVs and that the absence of these LVs can impact post-stroke outcomes.
Stroke and Alzheimer's disease, two diseases that disproportionately affect the aging population, share a subset of pathological findings and risk factors. The primary genetic risk factor after age for late-onset Alzheimer's disease, ApoE4, has also been shown to increase stroke risk and the incidence of post-stroke dementia. One mechanism by which ApoE4 contributes to disease is by inducing in neurons a resistance to Reelin, a neuromodulator that enhances synaptic function. Previous studies in Reelin knockout mice suggest a role for Reelin in protection against stroke; however, these studies were limited by the developmental requirement for Reelin in neuronal migration. To address the question of the effect of Reelin loss on stroke susceptibility in an architecturally normal brain, we utilized a novel mouse with induced genetic reduction of Reelin. We found that after transient middle cerebral artery occlusion, mice with complete adult loss of Reelin exhibited a similar level of functional deficit and extent of infarct as control mice. Together, these results suggest that physiological Reelin does not play a strong role in protection against stroke pathology.
Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition.
Abstract Background Vascular contributions to cognitive impairment and dementia (VCID) and Alzheimer’s disease (AD) are the two most common forms of dementia, with overlapping risk factors including cardiovascular risk factors such as hypertension and dyslipidemia. The etiology of both VCID and AD shows sex‐based differences, as well as sex‐based differences in cardiovascular risk factors. However, how sex differences influence AD and angiogenic biomarkers in older adults who have high cardiovascular risk factors is not known. Method AD and angiogenic biomarkers for VCID were measured from the plasma of a subgroup (n=96) of participants from the ‘risk reduction for Alzheimer’s disease’ (rrAD) two‐year clinical trial (NCT02913664; completed Jan. 2022; n=513 total participants). rrAD participants had a family history of dementia or subjective memory complaints, hypertension, and dyslipidemia. The subgroup in the study included 31 males and 65 females (aged: 71‐85). Baseline values for AD biomarkers: Total tau, pTau181, Aβ40, and Aβ42, angiogenic biomarkers: Tie‐2, VEGF‐A, VEGF‐C, VEGFR1, and VCID biomarkers: bFGF, VEGF‐D, PlGF were analyzed using Meso Scale Discovery (MSD). Nonparametric analysis evaluated the sex differences in biomarkers, linear regression evaluated the relationship between AD biomarkers and angiogenic biomarkers in both sexes. Result We found sex‐based differences in AD biomarkers such that females had a higher expression in Total tau and Total tau/Aβ42 (p=0.0021, p=0.0003, respectively) while pTau181 was higher in males (p=0.0216). pTau181/ Aβ42 and Aβ42/40 ratios showed no sex differences, nor did baseline angiogenic biomarkers. There was, however, a selective sex difference in the association between angiogenic and AD biomarkers. In females, Total tau is associated with VEGF‐D (R 2 = 0.0746, p=0.0277), and Tau/Aβ42 is associated with VEGF‐A and VEGFR‐1(R 2 = 0.0747, p=0.0275; R 2 = 0.0973, p=0.0114, respectively). In males, pTau181 and pTau181/Aβ42 are associated with VEGF‐D (R 2 = 0.2637, p=0.0031; R 2 = 0.1799, p=0.0174, respectively), Aβ42/Aβ40 is associated with VEGF‐C (R 2 = 0.1491, p=0.0319), and Tau/Aβ42 is associated with bFGF (R 2 = 0.1458, p=0.0340). Conclusion There is a selective sex‐based difference in plasma AD biomarkers and their association with angiogenic biomarkers in this preliminary cohort of older adults with high risks of developing Alzheimer’s disease and related dementias.
Abstract Impairment of vascular pathways of cerebral β-amyloid (Aβ) elimination contributes to Alzheimer disease (AD). Vascular damage is commonly associated with diabetes. Here we show in human tissues and AD-model rats that bloodborne islet amyloid polypeptide (amylin) secreted from the pancreas perturbs cerebral Aβ clearance. Blood amylin concentrations are higher in AD than in cognitively unaffected persons. Amyloid-forming amylin accumulates in circulating monocytes and co-deposits with Aβ within the brain microvasculature, possibly involving inflammation. In rats, pancreatic expression of amyloid-forming human amylin indeed induces cerebrovascular inflammation and amylin-Aβ co-deposits. LRP1-mediated Aβ transport across the blood-brain barrier and Aβ clearance through interstitial fluid drainage along vascular walls are impaired, as indicated by Aβ deposition in perivascular spaces. At the molecular level, cerebrovascular amylin deposits alter immune and hypoxia-related brain gene expression. These converging data from humans and laboratory animals suggest that altering bloodborne amylin could potentially reduce cerebrovascular amylin deposits and Aβ pathology.
Stroke affects millions of people worldwide every year. Despite this prevalence, mechanisms of long-term injury and repair within the ischemic brain are still understudied. Sterile inflammation occurs in the injured brain after stroke, with damaged tissue exposing central nervous system (CNS)-derived antigen that could initiate potential autoimmune responses. We used a standard immunology-based recall response assay for murine immune cells, isolated from the cervical lymph nodes and spleen after transient stroke, to determine if stroke induces autoreactivity to CNS target antigens. Our assays included novel neuronal peptides, in addition to myelin-, nuclear-, glial-, and endothelial-derived peptides. Autoimmune responses to an antigen were considered positive based on proliferation and activation over non-stimulated conditions. Stroke induced a significant increase in autoreactive CD4+ and CD8+ T cells, as well as autoreactive CD19+ B cells, as early as 4 days after stroke onset. Mice with large infarct volumes exhibited early T and B cell autoreactivity to NR2A, an NMDA receptor subunit, in cells isolated from lymph nodes but not spleen. Mice with small infarct volumes exhibited high autoreactivity to MAP2, a dendritic cytoskeletal protein, as well as myelin-derived peptides. This autoimmunity was maintained through 10 days post-stroke in both lymph nodes and spleen for all lymphocyte subsets. Sham surgery also induced early autoreactive B cell responses to MAP2 and myelin. Based on these observations, we hypothesize that stroke induces a secondary, complex, and dynamic autoimmune response to neuronal antigens with the potential to potentiate, or perhaps even ameliorate, long-term neuroinflammation.
