Restoring a balanced pool of host-derived and microbiota-derived ligands of the aryl hydrocarbon receptor is beneficial after stroke

Background

Stroke is a major cause of morbidity and mortality, and its incidence increases with age. While acute therapies for stroke are currently limited to intravenous thrombolytics and endovascular thrombectomy, recent studies have implicated an important role for the gut microbiome in post-stroke neuroinflammation. After stroke, several immuno-regulatory pathways, including the aryl hydrocarbon receptor (AHR) pathway, become activated. AHR is a master regulatory pathway that mediates neuroinflammation. Among various cell types, microglia (MG), as the resident immune cells of the brain, play a vital role in regulating post-stroke neuroinflammation and antigen presentation. Activation of AHR is dependent on a dynamic balance between host-derived and microbiota-derived ligands. While previous studies have shown that activation of MG AHR by host-derived ligands, such as kynurenine, is detrimental after stroke, the effects of post-stroke changes in microbiota-derived ligands of AHR, such as indoles, is unknown. Our study builds on the concept that differential activation of MG AHR by host-derived versus microbiome-derived metabolites affects outcomes after ischemic stroke. We examined the link between stroke-induced dysbiosis and loss of essential microbiota-derived AHR ligands. We hypothesize that restoring the balance between host-derived (kynurenine) and microbiota-derived (indoles) ligands of AHR is beneficial after stroke, offering a new potential avenue for therapeutic intervention in post-stroke neuroinflammation.

Method

We performed immunohistochemical analysis of brain samples from stroke patients to assess MG AHR expression after stroke. We used metabolomics analysis of plasma samples from stroke and non-stroke control patients with matched comorbidities to determine the levels of indole-based AHR ligands after stroke. We performed transient middle cerebral artery occlusion (MCAO) in aged (18 months) wild-type (WT) and germ-free (GF) mice to investigate the effects of post-stroke treatment with microbiota-derived indoles on outcome. To generate our results, we employed a range of methodologies, including flow cytometry, metabolomics, and 16S microbiome sequencing.

Results

We found that MG AHR expression is increased in human brain after stroke and after ex vivo oxygen-glucose deprivation and reperfusion (OGD/R). Microbiota-derived ligands of AHR are decreased in the human plasma at 24 hours after ischemic stroke. Kynurenine and indoles exhibited differential effects on aged WT MG survival after ex vivoOGD/R. We found that specific indole-based ligands of AHR (indole-3-propionic acid and indole-3-aldehyde) were absent in GF mice, thus their production depends on the presence of a functional gut microbiota. Additionally, a time-dependent decrease in the concentration of these indole-based AHR ligands occurred in the brain within the first 24 hours after stroke in aged WT mice. Post-stroke treatment of GF mice with a cocktail of microbiota-derived indole-based ligands of AHR regulated MG-mediated neuroinflammation and molecules involved in antigen presentation (increased CD80, MHC-II, and CD11b). Post-stroke treatment of aged WT mice with microbiota-derived indole-based ligands of AHR reduced both infarct volume and neurological deficits at 24 hours.

Conclusion

Our novel findings provide compelling evidence that the restoration of a well-balanced pool of host-derived kynurenine-based and microbiota-derived indole-based ligands of AHR holds considerable therapeutic potential for the treatment of ischemic stroke.

Estimating Patient Survival and Risk of End-Stage Kidney Disease in Patients With Autosomal Dominant Polycystic Kidney Disease in Iran

INTRODUCTION

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary kidney disease that can affect several organs. The clinical course of the disease varies among patients; some never become symptomatic, and others reach end-stage kidney disease (ESKD) in the 5th decade of their life.

METHODS

This historical cohort study was conducted on ADPKD patients to investigate kidney and patient survival rates and related risk factors in Iran. Survival analysis and risk ratio calculation were performed using the Cox proportional hazards model, Kaplan- Meier method, and log-rank test.

RESULTS

Among the 145 participants, 67 developed ESKD, and 20 died before the end of the study period. Developing chronic kidney disease (CKD) at the age of ≤ 40, baseline serum creatinine level (SCr) of more than 1.5 mg/dL, and cardiovascular disease increased the risk of ESKD by 4, 1.8, and 2.4 times; respectively. Patient survival analysis revealed a fourfold increase in mortality if the glomerular filtration rate (GFR) declined more than 5 cc/min annually and if CKD was diagnosed at the age of ≤ 40. Vascular thrombotic events or ESKD in the course of disease increased the risk of death by approximately 6- and 7-fold, respectively. Kidney survival was 48% by the age of 60 and 28% by the age of 70. Patient survival was 86.05% at the age of 60 and 67.99% at the age of 70. Additionally, men had a significantly better renal function and survival than women.

CONCLUSION

Elevated baseline SCr and cardiovascular disease can increase ESKD risk in ADPKD patients. A rapid decline in GFR, ESKD development, and vascular thrombotic events increase the risk of death, but early CKD can affect both.  DOI: 10.52547/ijkd.7551.

Abstract 40: Gut Dysbiosis Exacerbates Neuroinflammation By Activation Of B Cells In A Mouse Model Of Cerebral Amyloid Angiopathy

Introduction: Cerebral amyloid angiopathy (CAA) is a debilitating disease that leads to intracerebral hemorrhage, white matter disease, and progressive cognitive decline in patients >50 years of age. Studies investigating the neuroimmune landscape in CAA are sparse. Here, we investigate the role of B cells in CAA.

Methods: Pre-symptomatic (2 months) and symptomatic (10-13 months) male Tg-SwDI mice (CAA mice) harboring Swedish, Dutch, and Iowa mutations of human amyloid precursor protein (APP) were used as a mouse model of CAA. Single cells isolated from the brain were analyzed using flow cytometry to characterize neuroinflammation and cognitive impairment was assessed using fear conditioning. Fecal microbiota transplantation (FMT) of the microbiome from pre-symptomatic and symptomatic CAA mice into young wild-type (WT) recipient male mice (2 months) was performed to determine if CAA-induced gut dysbiosis contributes to brain B cell activation.

Results: Cognitive assessment using fear conditioning indicated a significantly lower delta inactive state in symptomatic CAA mice (n=4/grp, * P <0.05) compared to pre-symptomatic CAA mice. Symptomatic CAA mice had a significantly lower relative frequency of microglia (CD45 int CD11b + , n=11-13/grp, ** P <0.01) and significant infiltration of lymphoid (CD45 high CD11b - , n=11-13/grp, *** P <0.001) cells in the brain, as compared to pre-symptomatic CAA mice. Symptomatic CAA mice had significantly higher B cells in the brain (n=10-13/grp, * P <0.05. Further, activated B cells as assessed by the expression level of CD11b showed that CD11b + B cells were significantly higher in the symptomatic CAA brain (n=10-13/grp, * P <0.05). Interestingly, this phenotype was recapitulated in young WT recipients reconstituted with pre-symptomatic CAA and CAA microbiome through FMT. Young WT recipients with CAA biome had significantly higher relative frequency of CD11b + B cells in the brain compared to young recipients with pre-CAA biome (n=7-9/grp, *** P <0.001).

Conclusions: These results suggest that the aberrant activation of B cells in the brain may be influenced by CAA-induced gut dysbiosis. Further investigations upon the functional role of CD11b + B cells in the vascular deposition of Aβ are warranted.

Abstract WMP109: Aged Maternal Biome Impairs Offspring Health

Background: The gut and its microbiome have become highlighted because of their holistic effect on the body in health and disease. The bi-directional communication of the gut-brain axis is highly involved in, among others, the immune response. Additionally, the maternal gut microbiome affects offspring brain, immune system, and gut microbiome formation and development. Therefore, an aged and unhealthy maternal biome that is may increase both stroke risk factors among offspring.

Method: Young female C57B6 mice 3-month (M) of age had their host gut bacteria cleared via antibiotic treatment prior to recolonization via fecal microbiome transplants from 3M control, and 18M reproductively senescent female mice. The subsequent offspring was aged to 18 months, followed by behavioral tests, glucose tolerance, and blood pressure measurement, prior to a transient 90-minute middle cerebral artery occlusion (MCAO).

Results: Compared to control females with 3M biome, females with an aged biome had decreased fecundity from 26.4 days to 54.75 days at the onset of breeding to birth of pups (p=0.0018). There was no change in estrus cycle between the groups. The offspring gut microbiome had been affected in a sex specific manner. Female pups from dysbiotic, aged, biome mothers differed significantly in terms of b-diversity compared to those from control mothers (p=0.009) with pathogenic increases to firmicutes shifting the F:B ratio. There was a less pronounced trend in male offspring (p=0.241). Interestingly, no weight differences were observed in offspring depending on the maternal biome. At 2M of age, a depressive phenotype in tail suspension test was noted for male(p=0.0001) and female (p=0.0059). However, at 6M and older, the depressive phenotype subsided. Male offspring at 18M demonstrated a significant change (p=0.0001) in Glucose tolerance test compared to age matched females.

Conclusion: The maternal microbiome has a significant impact on offspring biome composition and health. Mice from mothers with aged microbiome exhibited early life depressive phenotypes, slower glucose metabolism, and a pathogenic gut microbiome composition. Therefore, maternal gut has transgenerational health effects which may be exacerbating stroke risk and potentially outcome.

CD11bhigh B Cells Increase after Stroke and Regulate Microglia

Recent studies have highlighted the deleterious contributions of B cells to post-stroke recovery and cognitive decline. Different B cell subsets have been proposed on the basis of expression levels of transcription factors (e.g., T-bet) as well as specific surface proteins. CD11b (α-chain of integrin) is expressed by several immune cell types and is involved in regulation of cell motility, phagocytosis, and other essential functions of host immunity. Although B cells express CD11b, the CD11b^high subset of B cells has not been well characterized, especially in immune dysregulation seen with aging and after stroke. Here, we investigate the role of CD11b^high B cells in immune responses after stroke in young and aged mice. We evaluated the ability of CD11b^high B cells to influence pro- and anti-inflammatory phenotypes of young and aged microglia (MG). We hypothesized that CD11b^high B cells accumulate in the brain and contribute to neuroinflammation in aging and after stroke. We found that CD11b^high B cells are a heterogeneous subpopulation of B cells predominantly present in naive aged mice. Their frequency increases in the brain after stroke in young and aged mice. Importantly, CD11b^high B cells regulate MG phenotype and increase MG phagocytosis in both ex vivo and in vivo settings, likely by production of regulatory cytokines (e.g., TNF-α). As both APCs and adaptive immune cells with long-term memory function, B cells are uniquely positioned to regulate acute and chronic phases of the post-stroke immune response, and their influence is subset specific.

Fixed drug eruption after the Sinopharm COVID‐19 vaccine

After coronavirus disease 2019 (COVID‐19) became widespread around the world, several vaccines have been developed with variable efficacy and potency and based on different platforms to control the pandemic. One of these vaccines is Sinopharm (BBIBP‐CorV), which is an inactivated virus that was released by Sinopharm's Beijing institute in the summer of 2020. The most commonly reported side effects of the Sinopharm vaccine have included pain at the injection site, muscle pain, headache and fatigue. Dermatological reactions are also reported as less common and were mainly local injection site reactions. Fixed drug eruption (FDE) is a rare and unusual adverse effect and accounts for less than 1% of all severe acute respiratory syndrome coronavirus 2 vaccine‐related cutaneous manifestations. FDE has not been reported following the COVID‐19 inactivated vaccine. Here, we describe a rare case of FDE following the administration of the first shot of the Sinopharm vaccine.

Abstract 83: Stroke-induced Gut Microbiota Dysbiosis Regulates Microfold Cells In Peyer’s Patches

Microfold or membranous cells (M cells) are specialized antigen sampling cells residing in the epithelium of Peyer’s patches (PPs), the gut-associated lymphoid tissue in the small intestine. M cells are in continuous crosstalk with luminal microbes and host immune cells. The detrimental shift of the microbiota seen with aging and after stroke contribute to bacterial antigen translocation. This axis has emerged as an epicenter for post-stroke immune dysfunction and systemic infection. The role of M cells in the PPs as an initiation site for host mucosal immunity after stroke is undefined.

Hypothesis: Stroke-induced gut dysbiosis and M cell ablation leads to impaired antigen sampling mechanisms and clearance of translocating bacteria in PPs after stroke. We used a 60-minute reversible middle cerebral artery occlusion model in young (8-10 wks) C57BL/6 male mice to investigate how brain ischemia affects M cells in the PPs. We performed microbiota transplants from the cecal contents of stroke mice to naïve age-matched recipients via oral gavage for three consecutive days before tissue harvest on day four. We determined that stroke-induced changes in gut microbiota alone can cause M cell dysfunction. We found that both the number of PPs and M cells decrease 24 hours after stroke (n=8/gp, p=0.0104 and p=0.0054, respectively). Our imaging studies revealed disruption of tissue architecture and reduction in size of PPs after stroke. Microbiota transplant from stroke mice cecum to naïve recipients showed a similar effect on the number of PPs and M cells (n=10/gp, p=0.0568 and p=0.0299 ). The decrease in the number of M cells after microbiota transplantation was associated with immune dysregulation in the PPs, such as a reduction in the number of regulatory T cells (n=5/gp, p=0.0084 ). This is the first study that specifically examined M cells in a mouse model of stroke. Our results show that 1) stroke reduces the number of PPs and M cells and 2) stroke-induced gut dysbiosis can independently reduce the number of PPs and likely M cells and may regulate gut-originated immune responses after stroke. Future studies are needed to understand the effects of stroke-induced dysbiosis on M cell-mediated antigen processing in the gut and their immunoregulatory functions.

Abstract 165: Age-specific Effects Of Maternal Gut Biome Influence Sex Dependent Changes In Offspring Weight, Behavior, And Depression

Background: The gut-brain axis has recently become key in understanding stroke pathogenesis. The bidirectional communication between the gut and the brain are highly involved in the immune response to stroke. The effect of the aged biome, naturally occurring dysbiosis through the process of inflammaging, may have significant impact on offspring in terms of stroke risk factors.

Method: Young (3-month) female wildtype C57B/6 mice were subjected to antibiotic treatment to clear their native gut biome and were then treated with fecal microbiome transplants from 3-month (M) control, 14M menopausal, and 18M reproductively senescent female mice, and were bred in our facility. Subsequent pups obtained were aged to 9 months followed by a battery of behavioral tests (novel object recognition (NORT), Y-maze, tail suspension, and open field test) and body weight measurements. Feces was collected periodically for 16s rRNA sequencing analysis.

Results: Aged biome affected the female fecundity significantly (p=0.028, n=7/12) and the pup biome showed a significant sex specific difference in composition through 16s sequencing (p=0.009, n=7). Female pup from 14- or 18M biome mothers had consistently higher body weight from 21 days to 9 months of age compared to controls (p=0.183, n=6/9/13). Male pups from 18M biome dams showed significantly low body weight 2 months post birth (p=0.048, n= 7/10). Mothers that received 14M biome had overweight male offspring at 9 months of age (p=0.017. Cognitive assessment through NORT showed that female pups from mothers colonized with 14M biome had a significantly lower discrimination index compared to controls (p=0.045, n=6/9). Only male pups from 14M biome mothers showed a deficit in spatial cognition (p=0.018). Both males and females exhibited an early depressive phenotype compared to controls at 2 months of age (p=0.028), with female pups also exhibiting this phenotype at 9 months (p=0.018).

Conclusion: Age of the maternal biome has a significant effect on its offspring’s health, specifically body weight, cognition, and depressive phenotype in a sex and time dependent manner. These effects correlate positively with stroke risk factors highlighting the importance of the microbiome as an epigenetic regulator of offspring health.

Abstract 161: Aberrant B Cell Responses Promote Neuroinflammation In Mice With Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is a small vessel disease, characterized by amyloid beta deposition in the cerebral vasculature. CAA increases the incidence of hemorrhagic stroke and dementia in the elderly. Evidence has revealed that aging alone induces disruption in B cell differentiation and immunosenescence by promoting the presence of age-associated B cells (ABCs) characterized by an upregulation of CD11b high . However, little is known on how these ABCs influence the neuroimmune landscape of vascular dementia, an immune-mediated age-associated disease.

Hypothesis: CAA induces the differentiation of B cells in the brain resulting in neuroinflammation characterized by an exacerbated presence of microglia and lymphocytic infiltration. Pre-symptomatic (2mo) and symptomatic (18mo) Tg-SwDI (harboring Swedish, Dutch, and Iowa) mutations of human amyloid precursor protein male mice were used as a model of CAA. Through flow cytometry, we investigated the role of CD11b high B cells in promoting neuroinflammation in CAA. Age-matched C57BL/6 wild-type (WT) male mice were included to determine CAA-specific effects.

Results: A remarkably heterogeneous CD19 + B cell population was identified in symptomatic CAA mice. Interestingly, CD19 + CD11b high B cells were significantly increased in the symptomatic CAA brain (n=4-6/gp, P =<0.0001) as compared to pre-symptomatic and age-matched WT mice. Protein expression of CD73, CD80, and CD138 was assessed to determine memory formation, antibody production, and inflammatory properties of these CD19 + CD11b high B cells. Notably, CD19 + CD11b high B cells from CAA symptomatic mice had significantly lower expression of CD73 (n=4-6/gp, P =0.0004), CD80 (n=4-6/gp, P =0.0007), and CD138 (n=4-6/gp, P =0.0154) compared with those CD19 + CD11b high B cells from age-matched WT brain. Finally, CAA mice had significantly higher microglial counts (n=4-6/gp, P =0.0013) and lymphocytic infiltration (n=4-6/gp, P =0.0071) in the brain as compared to pre-symptomatic and WT aged mice. Here, we highlight the diversity of B cells in age-associated vascular dementia. Our data give us further perception into the influence of humoral immunity mediated by ABCs and their immune crosstalk in CAA.

Abstract WP240: Beneficial Gut Microbiome-Derived Ligands Can Outcompete Detrimental Brain-Derived Ligands Of Aryl Hydrocarbon Receptor After Stroke

Microbiome-derived ligands of the aryl hydrocarbon receptor (AHR) including tryptophan-derived indole acetic acid (IAA) have anti-inflammatory effects in some tissues. However, their effect on neuroinflammation after stroke is unknown. Brain-derived ligands of AHR (e.g. kynurenine) increase post-ischemia and are detrimental. Consistently, pharmacological inhibition of AHR after stroke reduces deleterious effects of kynurenine-mediated activation of AHR and improves outcome. However, whether IAA-mediated activation of AHR is detrimental or beneficial after stroke is unknown. We hypothesized that post-stroke treatment with IAA will reduce neuroinflammation and improve outcomes via beneficial activation of microglial (MG) AHR. We used a reversible middle cerebral artery occlusion (MCAO) model in aged (18mo) WT male mice to investigate temporal changes in biome-derived (IAA) versus host-derived (kynurenine) AHR ligands. Using metabolomics analysis, we determined that plasma levels of IAA can be restored in naïve aged mice by oral probiotics administration of AHR ligand producers. We found that brain kynurenine increases but plasma IAA decreases as early as 3 hours after MCAO in aged mice (n=4/gp, p=0.0029 ) while brain IAA levels remain unchanged. Our 16S rRNA-sequencing shows that aging leads to reduction in AHR ligand-producers (e.g. Bifidobacterium [B] and Lactobacillus [L] ). Oral gavage with AHR ligand-producing BBL-probiotic cocktail restored the age-related decline in plasma IAA both acutely (24 hours post-treatment) and chronically (weekly for 6 weeks, n=8/gp, p=0.0086 and p=0.0073 , respectively). Further, the increase in plasma levels of IAA after probiotic bacteriotherapy with AHR ligand producers was associated with modulation of AHR activity in the brain (decreased AHR expression in MG, n=8/gp, p=0.0119 ) and reduced MG activation ( p=0.0069 ). Our results show that IAA modulates MG-mediated neuroinflammation after stroke. We plan to utilize post-stroke treatment with IAA in aged WT mice and in inducible knock-out mice with microglial Ahr deletion to further validate our hypothesis. Future studies are needed to focus on the regulatory function of other biome-derived AHR ligands in post-stroke neuroinflammation.

Potential caveats of putative microglia-specific markers for assessment of age-related cerebrovascular neuroinflammation

BACKGROUND

The ability to distinguish resident microglia from infiltrating myeloid cells by flow cytometry-based surface phenotyping is an important technique for examining age-related neuroinflammation. The most commonly used surface markers for the identification of microglia include CD45 (low-intermediate expression), CD11b, Tmem119, and P2RY12.

METHODS

In this study, we examined changes in expression levels of these putative microglia markers in in vivo animal models of stroke, cerebral amyloid angiopathy (CAA), and aging as well as in an ex vivo LPS-induced inflammation model.

RESULTS

We demonstrate that Tmem119 and P2RY12 expression is evident within both CD45^int and CD45^high myeloid populations in models of stroke, CAA, and aging. Interestingly, LPS stimulation of FACS-sorted adult microglia suggested that these brain-resident myeloid cells can upregulate CD45 and downregulate Tmem119 and P2RY12, making them indistinguishable from peripherally derived myeloid populations. Importantly, our findings show that these changes in the molecular signatures of microglia can occur without a contribution from the other brain-resident or peripherally sourced immune cells.

CONCLUSION

We recommend future studies approach microglia identification by flow cytometry with caution, particularly in the absence of the use of a combination of markers validated for the specific neuroinflammation model of interest. The subpopulation of resident microglia residing within the "infiltrating myeloid" population, albeit small, may be functionally important in maintaining immune vigilance in the brain thus should not be overlooked in neuroimmunological studies.