20-year Inflation-Adjusted Medicare Reimbursements (Years: 2000-2020) For Common Lumbar and Cervical Degenerative Disc Disease Procedures

OBJECTIVE

Reimbursement trends for common procedures have persistently declined over the past 2 decades. Spinal instrumentational and fusion procedures are increasingly utilized and have increased in clinical complexity, yet longitudinal inflation-adjusted data for Medicare reimbursements of these procedures have not been evaluated.

METHODS

The Centers for Medicare and Medicaid Services (CMS) Physician Fee Schedule Look-Up Tool was used to extract Medicare reimbursements for the 5 most common spinal procedures and associated instrumentations from 2000-2020. Current Procedural Terminology (CPT) codes include 22551, 22600, 22633, 63030, and 63047 as well as instrumentation CPT codes 22840 and 22842-6. The nominal values were adjusted for inflation according to the latest consumer price index (U.S. Bureau of Labor Statistics; reported as 2020 USD) and used to calculate average annual percent changes and compound annual growth rates (CAGRs) in reimbursements.

RESULTS

After inflation adjustment, the physician fee reimbursement decreased by 11.05% ± 8.46% (mean ± s.d., from $2,009.89 in 2011 to $1,787.85 in 2020) for anterior cervical discectomy and fusion (ACDF), 28.38% ± 8.42% (from $1,889.38 in 2000 to $1,353.14 in 2020) for posterior cervical fusion, 7.85% ± 8.20% (from $2,111.20 in 2012 to $1,945.49 in 2020) for transforaminal lumbar interbody fusion (TLIF), 28.17% ± 13.88% (from $1,421.78 in 2000 to $1,021.22 in 2020) for lower back disc surgery, and 31.88% ± 8.22% (from $1,700.38 in 2000 to $1,158.25 in 2020) for lumbar laminectomy. Instrumentation reimbursements showed an average decrease of 33.43% ± 8.4% over this period. Average CAGR was -1.7% ± .41% for procedures and -2.02% ± .14% for instrumentation.

CONCLUSION

Our analysis reveals a persistent decline in reimbursement rates of the most common spine procedures and instrumentation since the year 2000. If unaddressed, this trend can serve as a substantial disincentive for physicians to perform these procedures and can significantly limit access to spinal care at the population level.

Abstract 20: Gut Microbiota-derived Indole Metabolites Influence Outcomes After Neonatal-Hypoxic Ischemic Encephalopathy

Introduction: Neonatal Hypoxic Ischemic Encephalopathy (nHIE) is a leading cause of infant mortality and morbidity worldwide. Males are at greater risk than females, and survivors of nHIE suffer from major disability with limited therapeutic options. Growing clinical and pre-clinical evidence shows neurological injury adversely alters the microbial populations in the gut (dysbiosis) and depletes anti-inflammatory metabolites exclusively made by the gut microbiota. Replacing key microbially-derived beneficial metabolites improves cognitive outcomes in pre-clinical models of adult stroke. However, changes in the gut microbiota and its metabolites after nHIE have not been explored and may lay the foundation for future therapies.

Hypothesis: nHIE leads to gut dysbiosis and reduces microbial-derived metabolites, which worsens neurological outcomes in males and females.

Methods: A modified Rice Vannucci Model on PND9 C57BL/6 mice was used to model nHIE. Fecal, plasma, gut, and brain samples were collected acutely (24hrs) and chronically (7wks) after injury.

Results: We found a significant decrease in 3-indolepropionic acid (p=0.0190, n=4-6), inoxyl-3-sulfate (p=0.0098, n=4-6) and indoxyl acetate (p=0.0096, n=4-6) in the plasma of male mice 24hrs after HIE compared to sham controls, with no significant changes in female plasma. There was a significant increase in indole metabolites in the ischemic hemisphere in both males and females 24hrs after HIE. 7wks after nHIE, there was a significant increase in anxiety-like behavior in males (decrease in % of time immobile during tail suspension=0.018, n=6) and decreased functional ability (nest building score p=0.0147, n=6) in males with HIE compared to sham controls. No significant changes were observed in females. 16S rRNA sequencing data showed dysbiotic microbiota composition after nHIE, consistent with the microbial-metabolite changes found by mass spectroscopy analysis.

Conclusion: nHIE induced brain injury results in gut dysbiosis, with sex-specific alterations in circulating indole metabolites and behavioral deficits. This supports our hypothesis that a sex-specific reduction in bioavailability of microbial-metabolites worsens CNS damage after nHIE.

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 TP170: Heterochronic Parabiosis Lowers Microglia Activation And Myeloid Infiltration In Aged Parabiont

Introduction: Of the 795,000 people who suffer strokes annually, 75% are over the age of 65. Aging is a major risk factor for stroke. The risk of stroke doubles every decade after the age of 55. Aging leads to dramatic changes in peripheral myeloid cells and increases the activation state of microglia in the brain. Although age is an important determinant of stroke susceptibility and outcome, the contribution from the aged immune system remains unclear.

Hypothesis: We hypothesize that aged mice (18-22 mo) parabionts paired with a young parabiont (2-3 mo) would have less microglia activation due to exposure to systemic factors from young mice when compared to aged mice paired with aged mice (18-22 mo).

Methods: Young Pep-boy mice (haplotype CD45.1) were surgically paired with aged mice (haplotype CD45.2) for two months. The brains of these mice were then subjected to flow cytometry analysis. Brain single cell suspensions were isolated and immunophenotyped with a microglia specific panel.

Results: Our results show that myeloid infiltration was decreased in the aged parabiont (paired with a young mouse) compared to its naïve counterpart (n=3-6/ grp, p = 0.0036). Microglia activation was assessed utilizing a homeostatic marker, P2RY12, and a microglia specific marker, Tmem119. Interestingly, the expression of Tmem119 on CD45 int CD11b + cells was significantly increased in the aged parabionts compared to aged, naïve mice (n=3-6/ grp, p =0.0006), however, P2RY12 trended upward in the aged parabiont (n=3/6 /grp, p =0.0742). This suggests that the shared circulation created between the heterochronic pair led to a reduction in immune activation in the aged parabiont. Thus, the young parabiont allows the aged parabiont access to rejuvenating factors through the shared flow of blood which reduced neuroinflammation.

Conclusion: Future studies are needed to identify the specific factors contributing to reduced microglial activation and lowered infiltration of peripheral immune cells induced by pairing with young animals. Studies examining the immune response to stroke in young and aged parabionts are needed.

Targeting Hemoglobin to Reduce Delayed Cerebral Ischemia After Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) continues to be a sequela of aneurysmal subarachnoid hemorrhage (aSAH) that carries significant morbidity and mortality. Aside from nimodipine, no therapeutic agents are available to reduce the incidence of DCI. Pathophysiologic mechanisms contributing to DCI are poorly understood, but accumulating evidence over the years implicates several factors. Those have included microvessel vasoconstriction, microthrombosis, oxidative tissue damage, and cortical spreading depolarization as well as large vessel vasospasm. Common to these processes is red blood cell leakage into the cerebrospinal fluids (CSF) and subsequent lysis which releases hemoglobin, a central instigator in these events. This has led to the hypothesis that early blood removal may improve clinical outcome and reduce DCI. This paper will provide a narrative review of the evidence of hemoglobin as an instigator of DCI. It will also elaborate on available human data that discuss blood clearance and CSF drainage as a treatment of DCI. Finally, we will address a recent novel device that is currently being tested, the Neurapheresis CSF Management System™. This is an automated dual-lumen lumbar drainage system that has an option to filter CSF and return it to the patient.

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.

Aging Microbiota-Gut-Brain Axis in Stroke Risk and Outcome

The microbiota-gut-brain-axis (MGBA) is a bidirectional communication network between gut microbes and their host. Many environmental and host-related factors affect the gut microbiota. Dysbiosis is defined as compositional and functional alterations of the gut microbiota that contribute to the pathogenesis, progression and treatment responses to disease. Dysbiosis occurs when perturbations of microbiota composition and function exceed the ability of microbiota and its host to restore a symbiotic state. Dysbiosis leads to dysfunctional signaling of the MGBA, which regulates the development and the function of the host's immune, metabolic, and nervous systems. Dysbiosis-induced dysfunction of the MGBA is seen with aging and stroke, and is linked to the development of common stroke risk factors such as obesity, diabetes, and atherosclerosis. Changes in the gut microbiota are also seen in response to stroke, and may impair recovery after injury. This review will begin with an overview of the tools used to study the MGBA with a discussion on limitations and potential experimental confounders. Relevant MGBA components are introduced and summarized for a better understanding of age-related changes in MGBA signaling and its dysfunction after stroke. We will then focus on the relationship between the MGBA and aging, highlighting that all components of the MGBA undergo age-related alterations that can be influenced by or even driven by the gut microbiota. In the final section, the current clinical and preclinical evidence for the role of MGBA signaling in the development of stroke risk factors such as obesity, diabetes, hypertension, and frailty are summarized, as well as microbiota changes with stroke in experimental and clinical populations. We conclude by describing the current understanding of microbiota-based therapies for stroke including the use of pre-/pro-biotics and supplementations with bacterial metabolites. Ongoing progress in this new frontier of biomedical sciences will lead to an improved understanding of the MGBA's impact on human health and disease.

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 17: Microglial Specific Aryl Hydrocarbon Receptor Activation Via Gut-derived Microbial Indole-metabolites Improves Outcomes After Neonatal-HIE

Introduction: Neonatal Hypoxic Ischemic Encephalopathy (nHIE) is a major cause of mortality and morbidity in infants, occurring in 1.5/1000 live births. Inflammation persists years after injury and detrimentally affects neurocognitive outcomes in children. Recent evidence shows that neuroinflammation and gut injury alters microbial populations in the gut (gut dysbiosis) and reduces the level of bacteria capable of producing beneficial, anti-inflammatory tryptophan (Trp) metabolites. Metabolites are detected by microglia (MG) with the aryl hydrocarbon receptor (AHR). Ligand specific AHR activation can influence MG behavior after CNS injury, potentially modifying recovery. We hypothesize that nHIE leads to chronic gut dysbiosis and reduced microbial-derived Trp metabolites, which exacerbates MG-induced CNS damage. We also hypothesize that Trp-derivatives bind MG AHR to reduce inflammation and improve neurological outcomes in males and females.

Methods: We used a modified Rice Vannucci Model on PND9 C57BL/6J mice to investigate the role of MG AHR as a mediator of gut microbiome-brain communication after nHIE and demonstrated direct microbial metabolite modulation of MG using in vitro cell culture assays.

Results: We found an increase in AHR and CD45 expression in MG 24hrs after nHIE (p=0.0169 and p=0.0047 respectively, n=5). RT-qPCR of SIM-A9 MG cells showed that pretreatment with indole-acetic-acid (IAA) followed by LPS injury produced significantly more Il10 than cells pretreated with AHR agonist FICZ, suggesting Trp-derivatives activate an anti-inflammatory response (p=0.013, n=8). IAA mildly reduced Il1β , Il6 , and Tnfα after LPS administration. 16S rRNA sequencing, behavior and metabolomics analysis of acute (24hrs) and chronic (7wks) cohorts showed detriments in behavioral tasks and dysbiotic changes after nHIE.

Conclusion: nHIE results in increased AHR expression in MG, gut dysbiosis, and alterations in microbial-Trp metabolites in males and females. In vitro assays demonstrated that absence of Trp metabolites result in greater inflammatory activity of MG after injury via the AHR pathway, supporting our hypothesis that reduction of microbial-derived Trp metabolites after nHIE worsens MG-induced CNS damage.

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.

Abstract 160: Age-associated CD11b High B Cells Are Recruited To The Brain After Stroke And Regulate Microglial Function

CD11b expression is essential for immunity due to its role in cell motility and phagocytosis. Leukocytes, including monocytes, neutrophils and macrophages, express CD11b. B lymphocytes, which are both adaptive immune cells and antigen presenting cells (APCs), also express CD11b at varying levels. The role of B lymphocytes after stroke is multifaceted, and recent studies have highlighted their deleterious contributions to post-stroke recovery and cognitive decline. CD11b high B cells have not been studied in the context of aging and stroke. We hypothesized that CD11b high B cells increase in the brain after stroke and regulate microglia function. We used a middle cerebral artery occlusion (MCAO) model of stroke in young (2mo) and aged (18mo) WT male mice to investigate the role of CD11b high B cells in post-ischemic immune responses. In the acute phase following stroke, resident immune cells, primarily microglia (MG), are rapidly activated. Thus, we studied the ability of CD11b high B cells to influence MG phenotype in young and aged brain. We found that CD11b high B cells are a heterogeneous subpopulation of B lymphocytes and predominantly found in aged mice (n=4/gp, p=0.0089 ) and after stroke (n=5/gp, p=0.0078 ). This subset is characterized by their higher expression of CD80 and CD73 (n=8/gp, p<0.0001, for both ). The frequency of CD11b high B cells increases in the brain after stroke in both young and aged mice. These cells are capable of changing MG phenotype sorted from either young or aged brain, as assessed by decreased expression of CD45, CD11b, and MHC-II by MG (n=4/gp, p=0.0013, p=0.0033, p=0.0310 , respectively). When co-incubated with ex vivo sorted MG, CD11b high B cells increased phagocytic function MG more than their CD11b low B cell counterparts (n=4/gp, p=0.0486 ). Lastly, the regulatory influence of CD11b high B cells is likely through production of inflammatory cytokines including TNF-α (n=5/gp, p<0.0001 ). As both APCs and adaptive immune cells with memory function, B lymphocytes are uniquely positioned to regulate both acute and chronic phases of the post-stroke immune response, and their influence is subset-specific. Future studies are warranted to better understand the function of these age-associated CD11b high B cells in neuroinflammation.

Abstract WP242: Stabilizing Mast Cell Signaling From The Gut Mitigates Neuroinflammation In The Brain Post Stroke

Background: Clinically, ~65% of stroke patients are left with functional impairments after stroke and 15% die shortly after their stroke. Increasing evidence suggests that peripheral inflammatory responses after stroke play an important role in determining neurological outcome. Mast cells (MCs) are one of the most rapid responders to injury. MCs release histamine (HA), a pro-inflammatory transmitter that enhances inflammation. Gut MCs are a major source of HA.

Hypothesis: We hypothesize that aged animals stroke will lead to robust gut mucosal MC-activation and HA release, with subsequent gut disruption and inflammation. Stabilizing peripheral MCs will decrease peripheral/central inflammation, MC trafficking, and improve stroke outcomes.

Methods: We used a reversible middle cerebral artery occlusion (MCAO) model of ischemic stroke in aged (18mo) wild-type male mice to investigate the MC role in neuroinflammation post-stroke (PS). We stroke the aged animals and treated the animals with 25 mg/kg BW of cromolyn (MC stabilizer), oral gavage. Cromolyn was administered at 3-h, 10-h, 24-h and every other day PS. Positive control group that were stroked but treated only with saline. In total, four groups stroke and sham (surgery control), out of these animals one set received cromolyn and one set received saline. We sacrificed animals at 3-h, 24 –h and 3-days after cromolyn treatment post-stroke.

Results: We found that cromolyn administration significantly reduced MC numbers in the brain at 24-hours (P<0.0051) and 3 days (P<0.0005) PS. In association with that we found behavioral changes with improved motor activity at 3-days post-stroke animals after cromolyn treatment. We also found that gut mast cells are significantly reduced after cromolyn treatment in the 24 hours and 3-days PS groups (P<0.01). Additionally, we found significant decrease in NDS at the 3-days PS animals which was not very prominent at 24-hours (P<0.0125).

Conclusion: Our results show that preventing MC-HA release post-stroke possess clinical value in preventing neuroinflammation PS. Future studies will focus on IgE and FcεR1 due to its cross-linking role in activating MC-HA release.

Bacterial Amyloid Curli Associated Gut Epithelial Neuroendocrine Activation Predominantly Observed in Alzheimer's Disease Mice with Central Amyloid-β Pathology

BACKGROUND

Substantial evidence from recent research suggests an influential and underappreciated force in Alzheimer's disease (AD) pathogenesis: the pathological signals originate from outside the brain. Pathogenic bacteria produce amyloid-like proteins "curli" that form biofilms and show functional similarities to human amyloid-β (Aβ). These proteins may contribute to neurological disease progression via signaling cascade from the gut to the brain.

OBJECTIVE

We propose that curli causes neuroendocrine activation from the gut to brain that promotes central Aβ pathology.

METHODS

PGP9.5 and TLR2 levels in response to curli in the lumen of Tg2576 AD mice were analyzed by immunohistochemical and qRT-PCR analysis. Western blot and human 3D in vitro enteroids culture systems were also used. 16S rRNA gene sequencing was used to investigate bacterial dysbiosis.

RESULTS

We found significant increase in bacterial-amyloid curli with elevated TLR2 at the mRNA level in the pre- and symptomatic Tg-AD gut compared to littermate WT controls. This data associates with increased gram-positive bacterial colonization in the ileum of the symptomatic AD mice. We found fundamental evidence for vagus nerve activation in response to bacterial curli. Neuroendocrine marker PGP9.5 was significantly elevated in the gut epithelium of symptomatic AD mice, and this was colocalized with increased TLR2 expression. Enteroids, 3D-human ileal mini-gut monolayer in vitro model system also revealed increase levels of TLR2 upon stimulation with purified bacterial curli fibrils.

CONCLUSION

These findings reveal the importance of pathological changes within the gut-vagus-brain signaling in response to luminal bacterial amyloid that might play a vital role in central Aβ pathogenesis seen in the AD brain.

Neuronal CD200 Signaling Is Protective in the Acute Phase of Ischemic Stroke

BACKGROUND AND PURPOSE

CD200 (cluster of differentiation 200), a highly glycosylated protein primarily expressed on neurons in the central nervous system, binds with its receptor CD200R to form an endogenous inhibitory signal against immune responses. However, little is known about the effect of neuronal CD200 signaling in cerebral ischemia. The aim of this study was to investigate how neuronal CD200 signaling impacts poststroke inflammation and the ischemic injury.

METHODS

CD200 tma1^lf/fl:Thy1CreER mice were treated with tamoxifen to induce conditional gene knockout (ICKO) of neuronal CD200. The mice were subjected to a 60-minute transient middle cerebral artery occlusion. Stroke outcomes, apoptotic cell death, immune cell infiltration, microglia activation, and other inflammatory profiles were evaluated at 3 and 7 days after stroke.

RESULTS

Infarct volumes were significantly larger, and behavioral deficits more severe in ICKO versus control mice at 3 days after middle cerebral artery occlusion. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed a significant increase in apoptotic neuronal death in CD200 ICKO mice. An enhancement in lymphocytic infiltration and microglial proinflammatory responses were revealed by flow cytometry at 3 and 7 days after stroke in ICKO mice, accompanied by an increased microglial phagocytosis activity. Plasma proinflammatory cytokine (TNFα [tumor necrosis factor alpha] and IL [interleukin]-1β) levels significantly increased at 3 days, and IL-1β/IL-6 levels increased at 7 days in ICKO versus control animals. ICKO led to significantly lower baseline level of CD200 both in brain and plasma.

CONCLUSIONS

Neuronal CD200 inhibits proinflammatory responses and is protective against stroke injury.

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.

Peripherally-sourced myeloid antigen presenting cells increase with advanced aging

Aging is associated with dysfunction of the gut microbiota-immune-brain axis, a major regulatory axis in both brain health and in central nervous system (CNS) diseases. Antigen presenting cells (APCs) play a major role in sensing changes in the gut microbiota and regulation of innate and adaptive immune responses. APCs have also been implicated in various chronic inflammatory conditions, including age-related neurodegenerative diseases. The increase in chronic low-level inflammation seen with aging has also been linked to behavioral decline. Despite their acknowledged importance along the gut microbiota-immune-brain axis, there is limited evidence on how APCs change with aging. In this study, we examined age-related changes in myeloid APCs in the gut, spleen, and brain as well as changes in the gut microbiota and behavioral phenotype in mice ranging in age from 2 months up to 32 months of both sexes. Our data show that the number of peripherally-sourced myeloid APCs significantly increases with advanced aging in the brain. In addition, our data showed that age-related changes in APCs are subset-specific in the gut and sexually dimorphic in the spleen. Our work highlights the importance of studying myeloid APCs in an age-, tissue-, and sex-specific manner.

Regulation of autophagy by DNA G-quadruplexes

Guanine-rich DNA strands can form secondary structures known as G-quadruplexes (G4-DNA or G4s). G4-DNA is important for the regulation of replication and transcription. We recently showed that the expression of Atg7, a gene that is critical for macroautophagy/autophagy, is controlled by G4-DNA in neurons. We demonstrated that the transcription factor SUB1/PC4 and the G4-DNA-specific antibody HF2 bind to a putative G4-DNA motif located in the Atg7 gene. Stabilizing G4-DNA with the G4-ligand pyridostatin (PDS) downregulates Atg7 expression in neurons. Here, we further investigated how G4-DNA in the Atg7 gene is stabilized by PDS. We show that PDS can form 1:1 and 2:1 complexes with the Atg7's G4. We also demonstrate that PDS downregulates the ATG7 protein and the expression of Atg7 in astrocytes as well as in neurons. Together with our previous findings, these data establish a novel G4-DNA-associated mechanism of autophagy regulation at a transcriptional level in neurons and astrocytes.

Age-dependent involvement of gut mast cells and histamine in post-stroke inflammation

BACKGROUND

Risk of stroke-related morbidity and mortality increases significantly with age. Aging is associated with chronic, low-grade inflammation, which is thought to contribute to the poorer outcomes after stroke seen in the elderly. Histamine (HA) is a major molecular mediator of inflammation, and mast cells residing in the gut are a primary source of histamine.

METHODS

Stroke was induced in male C57BL/6 J mice at 3 months (young) and 20 months (aged) of age. Role of histamine after stroke was examined using young (Yg) and aged (Ag) mice; mice underwent MCAO surgery and were euthanized at 6 h, 24 h, and 7 days post-ischemia; sham mice received the same surgery but no MCAO. In this work, we evaluated whether worsened outcomes after experimental stroke in aged mice were associated with age-related changes in mast cells, histamine levels, and histamine receptor expression in the gut, brain, and plasma.

RESULTS

We found increased numbers of mast cells in the gut and the brain with aging. Using the middle cerebral artery occlusion (MCAO) model of ischemic stroke, we demonstrate that stroke leads to increased numbers of gut mast cells and gut histamine receptor expression levels. These gut-centric changes are associated with elevated levels of HA and other pro-inflammatory cytokines including IL-6, G-CSF, TNF-α, and IFN-γ in the peripheral circulation. Our data also shows that post-stroke gut inflammation led to a significant reduction of mucin-producing goblet cells and a loss of gut barrier integrity. Lastly, gut inflammation after stroke is associated with changes in the composition of the gut microbiota as early as 24-h post-stroke.

CONCLUSION

An important theme emerging from our results is that acute inflammatory events following ischemic insults in the brain persist longer in the aged mice when compared to younger animals. Taken together, our findings implicate mast cell activation and histamine signaling as a part of peripheral inflammatory response after ischemic stroke, which are profound in aged animals. Interfering with histamine signaling orally might provide translational value to improve stroke outcome.

Gut Microbiota-Derived Short-Chain Fatty Acids Promote Poststroke Recovery in Aged Mice

RATIONALE

The elderly experience profound systemic responses after stroke, which contribute to higher mortality and more severe long-term disability. Recent studies have revealed that stroke outcomes can be influenced by the composition of gut microbiome. However, the potential benefits of manipulating the gut microbiome after injury is unknown.

OBJECTIVE

To determine if restoring youthful gut microbiota after stroke aids in recovery in aged subjects, we altered the gut microbiome through young fecal transplant gavage in aged mice after experimental stroke. Further, the effect of direct enrichment of selective bacteria producing short-chain fatty acids (SCFAs) was tested as a more targeted and refined microbiome therapy.

METHODS AND RESULTS

Aged male mice (18-20 months) were subjected to ischemic stroke by middle cerebral artery occlusion. We performed fecal transplant gavage 3 days after middle cerebral artery occlusion using young donor biome (2-3 months) or aged biome (18-20 months). At day 14 after stroke, aged stroke mice receiving young fecal transplant gavage had less behavioral impairment, and reduced brain and gut inflammation. Based on data from microbial sequencing and metabolomics analysis demonstrating that young fecal transplants contained much higher SCFA levels and related bacterial strains, we selected 4 SCFA-producers (Bifidobacterium longum, Clostridium symbiosum, Faecalibacterium prausnitzii, and Lactobacillus fermentum) for transplantation. These SCFA-producers alleviated poststroke neurological deficits and inflammation, and elevated gut, brain and plasma SCFA concentrations in aged stroke mice.

CONCLUSIONS

This is the first study suggesting that the poor stroke recovery in aged mice can be reversed via poststroke bacteriotherapy following the replenishment of youthful gut microbiome via modulation of immunologic, microbial, and metabolomic profiles in the host.

Dysregulated Gut Homeostasis Observed Prior to the Accumulation of the Brain Amyloid-β in Tg2576 Mice

Amyloid plaques in Alzheimer's disease (AD) are associated with inflammation. Recent studies demonstrated the involvement of the gut in cerebral amyloid-beta (Aβ) pathogenesis; however, the mechanisms are still not well understood. We hypothesize that the gut bears the Aβ burden prior to brain, highlighting gut-brain axis (GBA) interaction in neurodegenerative disorders. We used pre-symptomatic (6-months) and symptomatic (15-months) Tg2576 mouse model of AD compared to their age-matched littermate WT control. We identified that dysfunction of intestinal epithelial barrier (IEB), dysregulation of absorption, and vascular Aβ deposition in the IEB occur before cerebral Aβ aggregation is detectible. These changes in the GBA were associated with elevated inflammatory plasma cytokines including IL-9, VEGF and IP-10. In association with reduced cerebral myelin tight junction proteins, we identified reduced levels of systemic vitamin B12 and decrease cubilin, an intestinal B12 transporter, after the development of cerebral Aβ pathology. Lastly, we report Aβ deposition in the intestinal autopsy from AD patients with confirmed cerebral Aβ pathology that is not present in intestine from non-AD controls. Our data provide evidence that gut dysfunction occurs in AD and may contribute to its etiology. Future therapeutic strategies to reverse AD pathology may involve the early manipulation of gut physiology and its microbiota.

Small-molecule G-quadruplex stabilizers reveal a novel pathway of autophagy regulation in neurons

Guanine-rich DNA sequences can fold into four-stranded G-quadruplex (G4-DNA) structures. G4-DNA regulates replication and transcription, at least in cancer cells. Here, we demonstrate that, in neurons, pharmacologically stabilizing G4-DNA with G4 ligands strongly downregulates the Atg7 gene. Atg7 is a critical gene for the initiation of autophagy that exhibits decreased transcription with aging. Using an in vitro assay, we show that a putative G-quadruplex-forming sequence (PQFS) in the first intron of the Atg7 gene folds into a G4. An antibody specific to G4-DNA and the G4-DNA-binding protein PC4 bind to the Atg7 PQFS. Mice treated with a G4 stabilizer develop memory deficits. Brain samples from aged mice contain G4-DNA structures that are absent in brain samples from young mice. Overexpressing the G4-DNA helicase Pif1 in neurons exposed to the G4 stabilizer improves phenotypes associated with G4-DNA stabilization. Our findings indicate that G4-DNA is a novel pathway for regulating autophagy in neurons.

Abstract WP144: Cerebral Amyloid Angiopathy Pathology Worsens Stroke Outcome and Has a Detrimental Effect on the Gut Microbiome in Mice

Background: Cerebral amyloid angiopathy (CAA) is associated with both ischemic and hemorrhagic stroke, is a known cause of vascular cognitive impairment (VCI), and predicts worsened outcome after stroke. A growing body of literature has highlighted the importance of the gut microbiome in stroke outcome and neurodegenerative diseases such as Alzheimerz’s. However, little is known about how changes in the microbiome can affect CAA progression. The gut-brain axis is highly involved in the systemic inflammatory response following stroke. Furthermore, the gut is a primary source of bacterial translocation resulting in cerebral inflammation which further may contribute to vascular pathology. Therefore, the cross talk between CAA, stroke, and gut function could be key in our understanding and treatment of stroke in patients with CAA.

Methods: Symptomatic male Tg-SwDI (4 mths old) and C57BL/6 wild type (WT) mice underwent a 60 minute transient MCAO. Stroke was confirmed with cresyl violet staining and presence of amyloid β (Aβ) plaques were demonstrated with thioflavin. Post-stroke motor function was assessed at day 4 with open field-testing and results were compared to pre-stroke baseline and WT values and cognitive assessment was performed with the Y-maze test. Furthermore, PCR was used to identify the presence of Firmicutes and Bacteroidetes ratio (F:B) in both brain tissue and gut content.

Results: We demonstrate a significant decrease in the total distance traveled in both open field and cognitive Y-maze (p<0.05 and p<0.01 respectively) at baseline of Tg-SwDI mice. This was associated with the presence of Aβ plaque in the brain. PCR did not reveal any conclusive evidence for bacterial translocation in the brain at day 4. However, there was a pathogenic shift in the gut F:B ratio following stroke in Tg-SwDI mice compared to sham Tg-SwDI or sham WT controls and this will be confirmed by 16S rRNA gene sequencing.

Conclusion: Symptomatic CAA mice exhibit decreased motor and cognitive function compared to WT controls. Furthermore, 16S sequencing was performed to look at the bacterial translocation in detail from the gut to the brain. This is the first study to link CAA, stroke, and the gut brain axis, that may be crucial in understanding the complexity of stroke pathology.

Abstract TP108: Dendritic Cells Mediate the Detrimental Effects of Age-related Gut Dysbiosis After Stroke

Aging is a non-modifiable risk factor for stroke. Aging is accompanied by chronic low-grade inflammation and gut dysbiosis (a pathological imbalance of microbial organisms in the gut). Age-related gut dysbiosis exacerbates stroke outcomes and can be reversed by manipulation of the gut microbiota (GM) via fecal microbiota transplants (FMTs) from young animals, or “rejuvenation.” But, the mechanisms that mediate these effects are poorly understood. Dendritic cells (DCs) are potent antigen presenting cells and uniquely equipped to mediate the effects of dysbiosis. DCs constantly sample their environment to regulate the inflammatory response to antigens and tissue injury. In this study we investigated the role of intestinal DCs in mediating the detrimental effects of dysbiosis on stroke outcomes. We hypothesize that age-related dysbiosis exacerbates stroke outcomes by inducing an inflammatory and migratory phenotype in intestinal DCs. We studied four cohorts of C57Bl6 mice consisting of (1) naïve young (4mo), (2) naïve aged (22-26mo), (3) middle-aged (14mo) with FMT from aged donors, and (4) naïve young with 60-min middle cerebral artery occlusion (MCAO). Phenotyping of DCs by flow cytometry was performed.

Results: In our MCAO cohort, we found a significant increase in activated DCs in the gut (1.4% vs. 7.6%, p = 0.051) but a decrease in frequency of activated DCs in the brain (8.4% vs. 3.9%, p = 0.042). In our FMT cohort, frequency of intestinal DCs was altered in a subset-specific manner after FMT from aged donors. Specifically, our data showed that the MHC-II expression by DC subsets with a migratory phenotype (CD11b + DCs) and resident DCs (CD103 + DCs) were significantly increased when middle-aged mice received FMT from aged donors (p < 0.05). In our naïve cohorts, we found a significant decrease of MHC-II surface expression in brain DCs (p = 0.044) and a significant increase in splenic DCs (p = 0.049) with aging.

Conclusion: Our findings show that frequency and maturity state of DCs significantly differ with aging in a tissue- specific manner and can be influenced by manipulation of the gut microbiota. Our data also support the notion that intestinal DCs are involved in mediating the detrimental effects of age-related gut dysbiosis on stroke outcomes.

Abstract WP136: Peripheral Activation of Gut-Immune-Brain Axis in Cerebral Amyloid Angiopathy

Cerebral Amyloid Angiopathy (CAA) is an emerging cause of vascular cognitive impairment in the elderly. CAA is characterized by amyloid-β (Aβ) deposition in the central nervous system (CNS) vasculature and is associated with increased neuroinflammation. Aging is risk factor for CAA and is accompanied by low-grade inflammation and gut dysbiosis (a pathological imbalance of microbial organisms in the gut). Activation of peripheral immunity by a dysfunctional gut-immune axis may contribute to CAA progression. We hypothesize that CAA-induced gut dysbiosis leads to activation of a peripheral immune response which can accelerate CAA progression. We used the Tg-SwDI mouse (harboring Swedish, Dutch, and Iowa mutations of human amyloid precursor protein (APP), “CAA mice”) model that develops cerebral Aβ deposits and cognitive deficits around 3-4 months. We used 2mo mice as pre-onset and 10mo mice as post-onset groups.

Results: Our preliminary fecal 16S rRNA sequencing data showed higher microbiome alpha- (or “within-sample”) diversity in CAA mice (n=207, Inverse-Simpson diversity score, p=0.036). Upon visualization of beta- (or “between samples”) diversity in CAA and WT animals, with weighted-UniFrac-distances by principal coordinate analysis (PCoA), we found a notable clustering by strain (34.6% and 26.4% PCoA axes, p=0.001). Immunophenotyping of liver showed significant decrease in the B:T cell ratios when comparing the pre- to post-onset CAA mice (0.53 vs. 0.19, p = 0.005). Additionally, we observed a significant increase in the relative frequency of MHC-II (high) non-myeloid cells, when comparing the pre- to post-onset CAA (11.5% vs. 41.8%, p = 0.027).

Conclusion: Our findings suggest that gut dysbiosis occur early in CAA pathogenesis and may be responsible for ongoing increased peripheral and CNS inflammation. This work is significant if follow-up studies confirm that manipulation of the gut microbiota can modulate the peripheral immune response to reduce neuroinflammation in CAA and improve CAA-associated cognitive phenotype.

CBMT-40. THE RELATIONSHIP BETWEEN GLIOMA AND THE GUT-BRAIN AXIS

Recent studies demonstrate the potential role of the microbiome in immune-oncology, revealing specific microbial taxa can augment the effects of various therapeutic modalities against tumors. Gut dysbiosis, a disequilibrium in the host’s bacterial ecosystem, can potentially lead to overrepresentation of some bacteria and favor chronic inflammation and immunosuppression. However, the effects of microbial dysbiosis on non-gastrointestinal cancers in particular gliomas are unknown. Here, we explored the effects of glioma and Temozolomide (TMZ) on the fecal microbiome (FM) in mice (n=24) and FM and metabolome in humans (n=40). Aged C57/B6 mice were implanted with Gl261 tumor cells or vehicle and were assigned to one of the following treatment (oral) groups: vehicle, 5mg/kg TMZ or 25mg/kg TMZ beginning 14 days after surgery for 3-weeks following a 5 day on/2 day off treatment. Fecal samples were collected prior to surgery, at treatment initiation and weekly thereafter until sacrifice and sequenced for 16s RNA. Fecal samples were collected from humans with newly diagnosed glioma before resection, chemoradiation, and after chemoradiation (16s RNA, metabolomic, neurotransmitter analysis). In mice, FM beta diversity was significantly altered with glioma (p=0.003) while the alpha diversity remained unchanged. At a genus and family level analysis the relative abundance of Bacteroides (p=0.01) and Bacteroidaceae (p=0.02) was increased. Beta diversity of mice receiving 5mg/kg TMZ changed from baseline (p=0.02). Collectively, this suggests that glioma alters the FM, to what consequence remains to be explored. Alpha (Observed OTUs, p=0.029) and beta diversity (p=0.034) differences in mice correlated with survival (< 25 - >25 days). In humans, norepinephrine and 5-hydroxyindoleacetic acid were significantly lower in glioma patients at diagnosis compared to controls. Our findings demonstrate for the first time the relationship between glioma and the gut-brain axis. Understanding alterations in the FM in glioma patients may allow novel interventions and should be further investigated.

Sex as a biological variable in the pathology and pharmacology of neurodegenerative and neurovascular diseases

The incidence of dementia, most commonly caused by cerebrovascular and neurodegenerative diseases, continues to grow as our population ages. Alzheimer disease (AD) and vascular cognitive impairment (VCI) are responsible for more than 80% of all cases of dementia. There are few effective, long-term treatments for AD and VCI-related conditions (e.g., stroke and cerebral amyloid angiopathy (CAA)). This review focuses on AD (as the most common "neurodegenerative" cause of dementia), CAA (as an "emerging" cause of dementia), and stroke (as the most common cause of "vascular" dementia). We will discuss the available literature on the pharmacological therapies that demonstrate sex differences, which refer to any combination of structural, chromosomal, gonadal, or hormonal differences between males and females. We will emphasize the importance of considering sex as a biological variable in the design of preclinical and clinical studies that investigate underlying pathologies or response to pharmacological interventions in dementia. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Abstract WP140: The Effect of Age-related Gut Dysbiosis on Microglial Function in Cerebral Amyloid Angiopathy

The role of “gut-immune-brain axis” across our lifespan is well recognized as a biologic variable. As our populations age, so does the prevalence of age-related illnesses including stroke and its sequelae. We examined how manipulating the microbiome alters the natural history of cerebral amyloid angiopathy (CAA), a major cause of recurring brain hemorrhages, stroke, and cognitive decline. Microglial phenotype changes with aging and deficits in microglial phagocytosis lead to increased amyloid burden in animal models of Alzheimer’s but it is not known if this occurs in CAA. We hypothesize that age-related dysbiosis accelerates initiation and progression of CAA and this effect is mediated by failure of microglial amyloid phagocytosis (MAP). We have investigated the effects of dysbiosis on MAP and cognitive decline in wild-type (WT) and Tg2576 transgenic mice. Gut microbiomes were altered in pre- and post-symptomatic transgenic mice via fecal microbiota transfer (FMT) from young and aged WT mice. Cognitive decline and microglial phenotype were assessed using behavioral tests and flow cytometry. Function of microglia using in vitro primary and ex vivo sorted cultures from CAA mice were also examined. Our preliminary data shows: 1) An increased Firmicutes:Bacteroidetes ratio, indicative of an aging microbiome, occurred in young recipients given aged donor FMT; conversely, the ratio decreased in aged mice given young biome(P<0.001, n=14); 2) Microglial phagocytosis was impaired in aged WT microglia (n=7/gp, P<0.01); and 3) Motor strength in both young and aged WT mice after FMT (n=17/gp) were dependent on the age of the donor microbiome rather than the age of the host (P<0.001). Our studies demonstrate an important role for the gut microbiome in modulating CAA pathogenesis and progression in the brain. Thus, manipulation of the gut microbiota could be an effective therapy to delay the onset and/or slow the progression of disease in CAA patients.

Sex differences in neuroinflammation and neuroprotection in ischemic stroke

Stroke is not only a leading cause of mortality and morbidity worldwide it also disproportionally affects women. There are currently over 500,000 more women stroke survivors in the US than men, and elderly women bear the brunt of stroke-related disability. Stroke has dropped to the fifth leading cause of death in men, but remains the third in women. This review discusses sex differences in common stroke risk factors, the efficacy of stroke prevention therapies, acute treatment responses, and post-stroke recovery in clinical populations. Women have an increased lifetime risk of stroke compared to men, largely due to a steep increase in stroke incidence in older postmenopausal women, yet most basic science studies continue to only evaluate young male animals. Women also have an increased lifetime prevalence of many common stroke risk factors, including hypertension and atrial fibrillation, as well as abdominal obesity and metabolic syndrome. None of these age-related risk factors have been well modeled in the laboratory. Evidence from the bench has implicated genetic and epigenetic factors, differential activation of cell-death programs, cell-cell signaling pathways, and systemic immune responses as contributors to sex differences in ischemic stroke. The most recent basic scientific findings have been summarized in this review, with an emphasis on factors that differ between males and females that are pertinent to stroke outcomes. Identification and understanding of the underlying biological factors that contribute to sex differences will be critical to the development of translational targets to improve the treatment of women after stroke. © 2016 Wiley Periodicals, Inc.

Abstract 46: The Influence of Age and Stroke on Gut Inflammation and Microbiota

Introduction: Earlier work by our laboratory and other groups has identified that aging leads to changes in both the immune system and the microbiome. The elderly have high mortality and more disability after a stroke, a finding that is recapitulated in murine model. Recently, pro-inflammatory γδ T cells have received increasing attention as a major contributor to gut immune responses. These cells may be a link in the bidirectional communication between the microbiome and the central nervous system. We hypothesize that fecal transplant of aged biome into young animals will enhance inflammation, γδ T cell numbers, and worsen functional recovery after stroke in young mice.

Methods: Young C57BL/6 male mice, were randomized and subjected to sham surgery/right middle cerebral artery occlusion (MCAO-60min) followed by reperfusion. All mice received streptomycin treatment at 24h and 48h after MCAO. Subsequently, mice were gavaged with biome from either young or aged animals at 72 and 96 h post-stroke. Behavioral and functional outcomes were evaluated. Animals were sacrificed 15 days after stroke. Brain atrophy was quantified, and Flow Cytometry (FACS) and immunohistochemistry was performed on gut tissue and spleen to determine if stroke or the aged biome influence γδ T cells.

Results: Young mice transplanted with aged biome take a longer time to regain their pre-stroke body weight. These mice have higher post-stroke hyperactivity compared with mice treated with young biome, as measured by average velocity (p<.006) and total distance traveled (p<.006) in the Open Field. Young mice given aged biome had poorer grip strength, as well as a depressive phenotype, when compared with mice transplanted with young biome. FACS analysis shows higher levels of γδ T cell in the gut with stroke and with fecal transplant of aged biome (sham vs. stroke p=0.0443; young vs. aged biome p=0.0199).

Conclusion: Collectively our findings suggests that the gut microbiome plays an important role in post-stroke recovery. Understanding the underlying mechanisms may identify novel therapeutic targets for the treatment of stroke patients.