Abstract WP254: Inhibition of Calcium/Calmodulin-Dependent Protein Kinase Kinase (CaMKK) Exacerbates Endothelial Cell Impairment After Cerebral Ischemia

CaMKK (α and β) is a major kinase activated by elevated intracellular calcium. We have previously demonstrated CaMKK is neuroprotective in stroke. Pharmacological inhibition of CaMKK exacerbated outcome while overexpression reduced brain injury in mice. Brain microvascular endothelial cells play an essential role in maintaining BBB integrity, disruption of which aggravates ischemic injury. Interestingly, CaMKK activates a key endothelial protectant Sirtuin1 (SIRT1), although this interaction has never been studied in stroke. We hypothesized that CaMKK protects brain endothelial cells (EC) through activation of SIRT1 after ischemia. Oxygen-glucose deprivation (OGD, 18 hours) with reoxygenation (24 hours) was performed in human brain microvascular endothelial cells (HBEC-5i). Cell viability was assessed using a CCK-8 assay. Middle cerebral artery occlusion (MCAO, 90 mins) was used to induce stroke in male mice (20 to 25 g). The CaMKK inhibitor STO-609, SIRT 1 inhibitor EX-527, or CaMKK β siRNA was added to EC before OGD. Data are presented as mean±SEM. STO-609 treatment reduced cell viability (%) after OGD (vehicle 71.45 ± 5.60 vs. STO-609 55.06 ± 5.02, n=4, p<0.05). Knockdown of CaMKK β using siRNA increased cell death following OGD. Mechanistically, inhibition of CaMKK by STO-609 led to significant down-regulation of phosphorated SIRT1 (Ser-27) after OGD. Levels of total SIRT1 were also reduced by STO-609, consistent with the notion that phosphorylation prevents the degradation of this protein. Changes in downstream targets (e.g., eNOS) of SIRT1 were accordingly observed with STO-609 treatment. Further, the effect of STO-609 on cell viability after OGD was absent when SIRT1 was concurrently inhibited by EX-527 (STO-609+EX-527 45.19 ± 2.09 vs. EX-527 44.42 ± 2.89, n=4, p>0.05). Finally, in a MCAO model, intracerebroventricular injection of STO-609 (pre-stroke) significantly worsened BBB integrity (Evans blue assay) after 24-hour reperfusion (MCAO+DMSO 17.83 ± 6.34 versus MCAO+STO-609 55.74 ± 8.88, n=5/6; P <0.05). In conclusion, we demonstrate that CaMKK inhibition reduces EC viability after ischemia via SIRT 1. Our data suggest CaMKK attenuates ischemic brain injury by protecting the microvascular system and preserving BBB integrity.

Ischemic stroke induces gut permeability and enhances bacterial translocation leading to sepsis in aged mice

Aging is an important risk factor for post-stroke infection, which accounts for a large proportion of stroke-associated mortality. Despite this, studies evaluating post-stroke infection rates in aged animal models are limited. In addition, few studies have assessed gut microbes as a potential source of infection following stroke. Therefore we investigated the effects of age and the role of bacterial translocation from the gut in post-stroke infection in young (8-12 weeks) and aged (18-20 months) C57Bl/6 male mice following transient middle cerebral artery occlusion (MCAO) or sham surgery. Gut permeability was examined and peripheral organs were assessed for the presence of gut-derived bacteria following stroke. Furthermore, sickness parameters and components of innate and adaptive immunity were examined. We found that while stroke induced gut permeability and bacterial translocation in both young and aged mice, only young mice were able to resolve infection. Bacterial species seeding peripheral organs also differed between young (Escherichia) and aged (Enterobacter) mice. Consequently, aged mice developed a septic response marked by persistent and exacerbated hypothermia, weight loss, and immune dysfunction compared to young mice following stroke.

Abstract T P80: Inhibition of Ezh2 Leads to Decreased M1 and Enhanced M2 Microglia Phenotypes

Background: Ischemic stroke results in the activation of microglia, which may polarize toward a pro-inflammatory (M1) phenotype or an anti-inflammatory, neuroprotective (M2) phenotype. Thus, simultaneously suppressing the M1 response and promoting the M2 response could be beneficial in the treatment of stroke. Recently, the epigenetic modulator Jmjd3 has been shown to be essential for M2 polarization. However, Jmjd3 is antagonized by Ezh2 which is associated with M1 polarization. Thus, we hypothesized that inhibition of Ezh2 tilts the balance between Jmjd3 and Ezh2, thereby enhancing polarization toward an M2 phenotype and improved outcome in ischemic stroke.

Methods: Mixed glial cultures were isolated from P0.5-P2 C57BL/6J mice and cultured for 14 days before microglial isolation. Microglia were rested for 24 hours before treatment every other day with 6uM GSK343 (Cayman Chemical) or DMSO vehicle control. After 7 days, microglia were stimulated with LPS or IL-4 and RNA was isolated at 4hr and 24hr post-stimulation for qRT-PCR analysis.

Results: LPS-induced IL6 and IL1B expression was significantly abrogated by 71% and 53%, respectively (p<0.05), at 24hr when Ezh2 was inhibited. Additionally, Ezh2 inhibition both increased baseline expression of M2-associated genes ARG1, CD206, and IRF4 by 196%, 257%, and 395%, respectively (p<0.05), and rescued their expression in the presence of LPS at 24hr (p<0.05) in which they were otherwise significantly down-regulated.

Conclusion: Pharmacological inhibition of Ezh2 limits microglial M1 polarization and enhances M2 polarization.

Abstract W MP88: Worsening Of Stroke Outcome With Age Is Associated With Increased Intestinal Permeability And Peripheral Inflammation

Introduction: Aging remains the biggest risk factor for ischemic stroke. Initial observations into the role of aging on stroke outcome revealed that while aged mice had significantly smaller infarcts compared to young mice, they had greater long-term deficits in behavioral recovery. This study aimed to elucidate the role of systemic factors, such as intestinal stress, underlying the poor outcomes of aging mice after stroke.

Methods: Young (8-12 wks) and aged (18-20 mos) wildtype mice were subjected to 90min of right middle cerebral artery occlusion (MCAO) followed by reperfusion. Intestinal permeability was measured with 4kDa FITC-dextran gavage. Mesenteric lymph node (MLNs) homogenates were plated on blood agar to measure bacterial growth. Bacterial endotoxin was measured using a LAL assay. Flow cytometry was used to assess immune cells. Plasma IL-6 was measured by ELISA.

Results: Baseline gut permeability increased with age as evidenced by increased FITC-dextran extravasation across the intestinal lumina. Bacterial burden in MLNs and serum bacterial endotoxin levels were also elevated with age (p<0.05). These deficits were severely exaggerated by MCAO. A 200-fold increase was observed in the number of colony forming units in the MLNs of aged stroked mice compared to young (p<0.001). MHC II expression was enhanced on dendritic cells in aged MLNs and CD69 expression increased on circulating T-cells (p<0.05). Activated T-cells comprised the majority of infiltrating leukocytes in the ischemic hemisphere at 7 days post-stroke. This delayed recruitment of T-cells was associated with a 50% greater mortality of aged mice compared to young by 7 days. Plasma IL-6, a marker for sepsis, increased similarly at 6hr after MCAO in young and aged mice, but remained elevated in aged mice at 72hrs (p<0.05). Aged mice had lower body temperatures at 72hrs post-stroke (p<0.01).

Conclusion: Our data suggest that the high mortality in aged mice after stroke is secondary to exacerbation of intestinal permeability, increased bacterial translocation, and subsequent induction of sepsis. This data points to gut-targeted interventions as a means to reduce the severity of peripheral inflammation and improve prognosis in aged stroke victims.

Abstract T P225: Loss of Pregnane X Receptor Impairs Stroke Recovery

Introduction: Inflammation plays an important role in exacerbating injury following stroke, but current understanding of the factors regulating this inflammation is incomplete. Pregnane X Receptor (PXR) is a nuclear receptor which binds many xenobiotic targets including many commonly prescribed medications. Recent work has shown that PXR is crucial for maintaining the integrity of the intestinal epithelial barrier as well repressing inflammatory responses mediated by NFκB. Since both these pathways can modify the peripheral immune response, we hypothesized that PXR would play an important role in limiting inflammation following stroke. Using PXR knockout mice, we show that loss of PXR is detrimental for stroke recovery.

Materials & Methods: Male PXR knockout mice and littermate controls underwent sham surgery or 60min middle cerebral artery occlusion (MCAO). Weight loss was monitored post-stroke and mice were sacrificed after 7 days for splenic weights, infarct analysis by cresyl violet staining, and bacterial translocation as assessed by culture of homogenized mesenteric lymph nodes on blood agar plates.

Results: Following MCAO, PXR-/- mice lost significantly more weight than wild type littermate controls (n=6 vs. 4 respectively; p<0.05) and also showed greater splenic atrophy 7 days following MCAO (2.14mg/g body weight vs. 3.40mg/g body weight; p<0.05). However, preliminary studies suggest PXR-/- mice do not have larger infarcts (n=3 vs. 2) and did not exhibit more bacterial translocation 7 days following MCAO (5.4 vs. 7 CFU).

Discussion: PXR is known to negatively regulate NFκB signaling and maintain intestinal barrier integrity. Both of these mechanisms may contribute to delayed recovery following stroke with PXR acting as a master switch. In summary, this early work begins to explore the importance of a xenobiotic sensor, PXR, in stroke recovery.