0127 Brain bacterial peptidoglycan is region-specific and changes after ischemic stroke

Introduction

Sleep disorders and ischemic stroke (IS) are large health burdens. Almost half the USA population reports disturbed sleep and 795,000 Americans suffer a stroke annually. Despite dysregulated sleep being a stroke risk factor that can exacerbate injury and prolong recovery, sleep deprivation immediately preceding experimental stroke is neuroprotective. Bacteria and microbial products associate with (patho-)physiologies, including sleep phenotypes and IS. Peptidoglycans (PGs) are bacterial cell wall components found in diseased and healthy adults, and in developing and sleep-deprived brains. Although they influence atherosclerosis, an IS risk factor, PGs have not been characterized in post-stroke brain.

Methods

Aged (63 weeks) male wildtype mice (n=5) underwent permanent left middle cerebral artery occlusion, a model that mimics atherosclerotic IS, the most common type in humans. Surgeries began at Zeitgeber time (ZT) 12, lasted 30-40 minutes, and were followed by a 2-2.5-hour recovery period before sacrifice at ZT15. Brain stem (BS), somatosensory and prefrontal cortices (Sctx, PFC) were dissected, homogenized in phosphate buffered saline, and centrifuged. A standardized murine peptidoglycan ELISA (MyBioSource) was used for PG/MP quantification in resultant supernates. Brain areas in the left (L) IS, and right (R) control, hemispheres were compared by two-way ANOVA and Tukey’s HSD tests.

Results

Mean PG values are expressed as ng/mg tissue wet weight ± SEM. Post-IS PG in the injured L Sctx (4.28±0.48) was lower (F(2,21)=49.29, p<0.05) than the uninjured R Sctx (5.66±0.29; p=0.048). There were no hemispheric PG differences in either BS or PFC. L hemispheric PG was greater in BS (7.59±0.40) versus Sctx (p=0.0008) and PFC (3.82±0.21, p=0.0002). R hemispheric PG was also greater in BS (8.26±0.53) versus Sctx (p=0.005) and PFC (3.56±0.56, p=0.0006) and in Sctx versus PFC (p=0.02).

Conclusion

This study confirms our parallel study, presented in a separate abstract herein (English et al), that PG regulation is unique within brain areas. Additionally, PG values in uninjured Sctx and in BS were similar between studies. Finally, current results suggest that reduced cerebral blood flow induced by IS reduces PG in the affected brain area. Further, PG may have a role in sleep deprivation-related IS injury and recovery.

Support (If Any)

W.M. Keck Foundation and NIH (NS025378)

0129 Region-Specific Changes in Brain Peptidoglycan Following Sleep Deprivation

Introduction

Bacterial cell wall peptidoglycan (PG) and muramyl peptides (MPs), isolated from mammalian brains and urine following sleep deprivation (SD), promote non-rapid eye movement sleep. These PG/MPs likely originate from the host microbiome and have been quantified in neonatal murine brain. PG/MP amounts and dynamics in healthy, adult murine brain remain unknown.

Methods

Wildtype mice acclimated to standard lab conditions were sacrificed at Zeitgeber time (ZT) 3 or ZT15 with (treatment, N=8), or without (control, N=8) 3h of SD prior to time points. Hypothalamic (HT), somatosensory cortex (Sctx) and brain stem (BS) areas were dissected, homogenized in phosphate buffered saline and centrifuged. PG/MP contents in resultant supernatants were determined using an ELISA (MyBioSource), interpolating sample PG from the standard curve, and expressed as ng peptidoglycan per mg tissue wet weight (ng/mg).

Results

At ZT3 and ZT15, BS PG values were significantly higher than HT or Sctx values, while HT and Sctx values did not differ from each other. At ZT3, mean PG values from control mice were: 3.6 in HT, 3.7 in Sctx, and 8.6 ng/mg in BS. After SD, corresponding values were: 3.0, 4.8 (statistically significant increase, p<0.05), and 7.5 ng/mg. Further, within all 8 individual mice after SD prior to ZT3, PG levels in Sctx were higher than corresponding values in HT (p<0.001).At ZT15, PG control values were: 4.6 in HT, 4.6 in Sctx, and 8.9 ng/mg in BS. After SD, PG level at ZT15 was not significantly changed in any brain area assayed. However, PG values after SD at ZT15 compared to ZT3 SD values were significantly higher for HT and BS (p<0.0005 and p<0.005, respectively). In an independent experiment (see Dykstra-Aiello et. al. this volume) we confirmed PG values at ZT15 in BS were significantly higher than Sctx values.

Conclusion

Results indicate unique PG regulation by brain area, sleep loss, and time-of-day suggesting physiological roles for brain PG guiding host behaviors such as sleep. Thus, mammalian sleep-wake regulation and its various associated cognitive states, are the product of millions of years of co-evolutionary symbioses between microbes and their hosts.

Support (If Any)

Supported by the W.M. Keck Foundation and NIH (NS025378).

Distinct peripheral blood monocyte and neutrophil transcriptional programs following intracerebral hemorrhage and different etiologies of ischemic stroke

Understanding cell-specific transcriptome responses following intracerebral hemorrhage (ICH) and ischemic stroke (IS) will improve knowledge of the immune response to brain injury. Transcriptomic profiles of 141 samples from 48 subjects with ICH, different IS etiologies, and vascular risk factor controls were characterized using RNA-seq in isolated neutrophils, monocytes and whole blood. In both IS and ICH, monocyte genes were down-regulated, whereas neutrophil gene expression changes were generally up-regulated. The monocyte down-regulated response to ICH included innate, adaptive immune, dendritic, NK cell and atherosclerosis signaling. Neutrophil responses to ICH included tRNA charging, mitochondrial dysfunction, and ER stress pathways. Common monocyte and neutrophil responses to ICH included interferon signaling, neuroinflammation, death receptor signaling, and NFAT pathways. Suppressed monocyte responses to IS included interferon and dendritic cell maturation signaling, phagosome formation, and IL-15 signaling. Activated neutrophil responses to IS included oxidative phosphorylation, mTOR, BMP, growth factor signaling, and calpain proteases-mediated blood-brain barrier (BBB) dysfunction. Common monocyte and neutrophil responses to IS included JAK1, JAK3, STAT3, and thrombopoietin signaling. Cell-type and cause-specific approaches will assist the search for future IS and ICH biomarkers and treatments.

A wake-like state in vitro induced by transmembrane TNF/soluble TNF receptor reverse signaling

Tumor necrosis factor alpha (TNF) has sleep regulatory and brain development roles. TNF promotes sleep in vivo and in vitro while TNF inhibition diminishes sleep. Transmembrane (tm) TNF and the tmTNF receptors (Rs), are cleaved by tumor necrosis factor alpha convertase to produce soluble (s) TNF and sTNFRs. Reverse signaling occurs in cells expressing tmTNF upon sTNFR binding. sTNFR administration in vivo inhibits sleep, thus we hypothesized that a wake-like state in vitro would be induced by sTNFR-tmTNF reverse signaling. Somatosensory cortical neuron/glia co-cultures derived from male and female mice lacking both TNFRs (TNFRKO), or lacking TNF (TNFKO) and wildtype (WT) mice were plated onto six-well multi-electrode arrays. Daily one-hour electrophysiological recordings were taken on culture days 4 through 14. sTNFR1 (0.0, 0.3, 3, 30, 60, and 120 ng/µL) was administered on day 14. A final one-hour recording was taken on day 15. Four measures were characterized that are also used to define sleep in vivo: action potentials (APs), burstiness index (BI), synchronization of electrical activity (SYN), and slow wave power (SWP; 0.25-3.75 Hz). Development rates of these emergent electrophysiological properties increased in cells from mice lacking TNF or both TNFRs compared to cells from WT mice. Decreased SWP, after the three lowest doses (0.3, 3 and 30 ng/µL) of the sTNFR1, indicate a wake-like state in cells from TNFRKO mice. A wake-like state was also induced after 3 ng/µl sTNFR1 treatment in cells from TNFKO mice, which express the TNFR1 ligand, lymphotoxin alpha. Cells from WT mice showed no treatment effects. Results are consistent with prior studies demonstrating involvement of TNF in brain development, TNF reverse signaling, and sleep regulation in vivo. Further, the current demonstration of sTNFR1 induction of a wake-like state in vitro is consistent with the idea that small neuronal/glial circuits manifest sleep- and wake-like states analogous to those occurring in vivo. Finally, that sTNF forward signaling enhances sleep while sTNFR1 reverse signaling enhances a wake-like state is consistent with other sTNF/tmTNF/sTNFR1 brain actions having opposing activities.

Alternative Splicing of Putative Stroke/Vascular Risk Factor Genes Expressed in Blood Following Ischemic Stroke Is Sexually Dimorphic and Cause-Specific

Genome-wide association studies have identified putative ischemic stroke risk genes, yet, their expression after stroke is unexplored in spite of growing interest in elucidating their specific role and identifying candidate genes for stroke treatment. Thus, we took an exploratory approach to investigate sexual dimorphism, alternative splicing, and etiology in putative risk gene expression in blood following cardioembolic, atherosclerotic large vessel disease and small vessel disease/lacunar causes of ischemic stroke in each sex compared to controls. Whole transcriptome arrays assessed 71 putative stroke/vascular risk factor genes for blood RNA expression at gene-, exon-, and alternative splicing-levels. Male (n = 122) and female (n = 123) stroke and control volunteers from three university medical centers were matched for race, age, vascular risk factors, and blood draw time since stroke onset. Exclusion criteria included: previous stroke, drug abuse, subarachnoid or intracerebral hemorrhage, hemorrhagic transformation, infection, dialysis, cancer, hematological abnormalities, thrombolytics, anticoagulants or immunosuppressants. Significant differential gene expression (fold change > |1.2|, p < 0.05, partial correlation > |0.4|) and alternative splicing (false discovery rate p < 0.3) were assessed. At gene level, few were differentially expressed: ALDH2, ALOX5AP, F13A1, and IMPA2 (males, all stroke); ITGB3 (females, cardioembolic); ADD1 (males, atherosclerotic); F13A1, IMPA2 (males, lacunar); and WNK1 (females, lacunar). GP1BA and ITGA2B were alternatively spliced in both sexes (all patients vs. controls). Six genes in males, five in females, were alternatively spliced in all stroke compared to controls. Alternative splicing and exon-level analyses associated many genes with specific etiology in either sex. Of 71 genes, 70 had differential exon-level expression in stroke patients compared to control subjects. Among stroke patients, 24 genes represented by differentially expressed exons were male-specific, six were common between sexes, and two were female-specific. In lacunar stroke, expression of 19 differentially expressed exons representing six genes (ADD1, NINJ2, PCSK9, PEMT, SMARCA4, WNK1) decreased in males and increased in females. Results demonstrate alternative splicing and sexually dimorphic expression of most putative risk genes in stroke patients' blood. Since expression was also often cause-specific, sex, and etiology are factors to consider in stroke treatment trials and genetic association studies as society trends toward more personalized medicine.

Interleukin-1 receptor accessory proteins are required for normal homeostatic responses to sleep deprivation

Interleukin-1β (IL1) is a sleep regulatory substance. The IL1/IL1 type 1 receptor complex requires a receptor accessory protein (AcP) to signal. There are three isoforms of AcP. In the current experiments, mice lacking a neuron-specific isoform, called AcPb knockout (AcPb KO), or mice lacking AcP + AcPb isoforms (AcP KO) or wild-type (WT) mice were used. Spontaneous sleep and sleep responses to sleep deprivation (SD) between zeitgeber time (ZT) 20-ZT4 and ZT8-ZT16 were characterized. Furthermore, somatosensory cortical protein extracts were examined for phosphorylated (p) proto-oncogene tyrosine-protein kinase sarcoma (Src) and p38MAPK levels at ZT4 and ZT16 and after SD. Spontaneous sleep was similar in the three strains, except rapid eye movement sleep (REMS) duration between ZT12-ZT16 was greater in AcP KO than WT mice. After SD at ZT4, only WT mice had non-REMS (NREMS) rebounds. All mouse strains lacked an NREMS rebound after SD at ZT16. All strains after both SD periods had REMS rebounds. AcPb KO mice, but not AcP KO mice, had greater EEG delta wave (0.5-4 Hz) power during NREMS than WT mice. p-Src was very low at ZT16 but high at ZT4, whereas p-p38MAPK was low at ZT4 and high at ZT16. p-p38MAPK levels were not sensitive to SD. In contrast, p-Src levels were less after SD at the P = 0.08 level of significance in the strains lacking AcPb. We conclude that AcPb is required for NREMS responses to sleep loss, but not for SD-induced EEG delta wave or REMS responses.NEW & NOTEWORTHY Interleukin-1β (IL1), a well-characterized sleep regulatory substance, requires an IL1 receptor accessory protein (AcP); one of its isoforms is neuron-specific (called AcPb). We showed that in mice, AcPb is required for nonrapid eye movement sleep responses following 8 h of sleep loss ending 4 h after daybreak but did not affect rapid eye movement sleep rebound. Sleep loss reduced phosphorylation of proto-oncogene tyrosine-protein kinase sarcoma but not of the less sensitive p38MAPK, downstream IL1 signaling molecules.

The neuron-specific interleukin-1 receptor accessory protein alters emergent network state properties in Vitro

Small in vitro neuronal/glial networks exhibit sleep-like states. Sleep regulatory substance interleukin-1β (IL1) signals via its type I receptor and a receptor accessory protein (AcP). AcP has a neuron-specific isoform called AcPb. After sleep deprivation, AcPb, but not AcP, upregulates in brain, and mice lacking AcPb lack sleep rebound. Herein we used action potentials (APs), AP burstiness, synchronization of electrical activity (SYN), and delta wave (0.5–3.75 Hz) power to characterize cortical culture network state. Homologous parameters are used in vivo to characterize sleep. Cortical cells from 1–2-day-old pups from AcP knockout (KO, lacking both AcP and AcPb), AcPb KO (lacking only AcPb), and wild type (WT) mice were cultured separately on multi-electrode arrays. Recordings of spontaneous activity were taken each day during days 4–14 in vitro. In addition, cultures were treated with IL1, or in separate experiments, stimulated electrically to determine evoked response potentials (ERPs). In AcP KO cells, the maturation of network properties accelerated compared to those from cells lacking only AcPb. In contrast, the lack of AcPb delayed spontaneous network emergence of sleep-linked properties. The addition of IL1 enhanced delta wave power in WT cells but not in AcP KO or AcPb KO cells. The ontology of electrically-induced ERPs was delayed in AcP KO cells. We conclude IL1 signaling has a critical role in the emergence of sleep-linked network behavior with AcP playing a dominant role in the slowing of development while AcPb enhances development rates of sleep-linked emergent network properties.

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Interleukin-1 receptor accessory protein (AcP) is required for normal development of neuronal/glial network emergent electrophysiological properties.

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The neuron-specific isoform of AcP, AcPb, is required for enhancement of delta wave power by interleukin-1.

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Results provide further support for a) interleukin-1’s involvement in sleep regulation b) that it enhances sleep via AcPb and c) that sleep is a property of mature neuronal/glial networks whether in vitro or in vivo.

Abstract TP274: HMGB1 is Regulated by Microrna in Patients With Ischemic Stroke

Background: High mobility group box 1 (HMGB1) is a strong inducer of inflammatory pathways in ischemic stroke, and a marker of worse neurological outcome at 1 year. As such HMGB1 may contribute to secondary brain injury and decline in ischemic stroke. We sought to understand the regulation of HMGB1 by microRNA in patients with ischemic stroke and the relationship to stroke severity.

Methods: In 106 ischemic stroke patients and 106 vascular risk factor controls levels of HMGB1 were compared in relationship to levels of microRNA. HMGB1 in plasma was measured by ELISA. microRNA isolated from circulating leukocytes were measured by microarray and confirmed by RT-PCR. HMGB1 regulation by identified microRNA were assessed both in-silico and in-vitro by luciferase assay.

Results: HMGB1 is increased in ischemic stroke patients compared to controls (p<0.05) in a manner that is related to severity of stroke. An increase in admission NIHSS is associated with an increase in HMGB1. The increase in HMGB1 corresponded with a decreased in microRNA let7i. Direct regulation of HMGB1 was shown for microRNA let7i. When HMGB1 levels were adjusted for let7i, the association with NIHSS was no longer present.

Conclusions: HMGB1 is increased in patients with stroke and correlates with stroke severity. microRNA regulate HMGB1 in patients with stroke and may be an important mediator of immune activation associated with secondary ischemic brain injury.

Abstract WP424: Let7i Microrna Regulates Immune Response in Patients with Ischemic Stroke

Background and Purpose: The immune system responds rapidly following ischemic brain injury and can contribute to the final extent of brain damage. microRNA are differentially expressed in leukocytes following ischemic stroke and may regulate the immune response to ischemic brain injury. In this study we evaluate microRNA let7i-5p in ischemic stroke and its regulation of leukocytes.

Methods: A total of 212 patients were studied; 106 with acute ischemic stroke and 106 risk factor matched controls. . RNA from circulating leukocytes was isolated from blood collected in PaxGene tubes. Let7i-5p miRNA expression was assessed by Taqman qRT-PCR. Given microRNAs act to destabilize and degrade their target mRNA, mRNA that inversely correlated with let7i were identified. To demonstrate let7i post-transcriptional regulation of target genes, a 3’UTR luciferase assay was performed. Target protein expression was assessed by ELISA.

Results: Let7i was decreased in patients with acute ischemic stroke (fold change -1.70, p<0.00001). A modest inverse correlation between let7i and NIH Stroke Scale at admission (r= -0.32, p=0.02), infarct volume (r= -0.21, p=0.04) and plasma MMP9 (r= -0.46, p=0.01) was identified. The decrease in let7i was associated with increased expression of several of its messenger RNA targets including CD86, CXCL8 and HMGB1. In vitro studies confirm let7i post-transcriptional regulation of target genes CD86, CXCL8 and HMGB1. Functional analysis predicted let7i regulates pathways involved in leukocyte activation, recruitment, and proliferation including canonical pathways CD86 signaling in T helper cells, HMGB1 signaling, and CXCL8 signaling.

Conclusions: Let7i is decreased in circulating leukocytes of patients with acute ischemic stroke. Mechanisms by which let7i regulates inflammatory response post-stroke include targeting CD86, CXCL8 and HMGB1.

Altered Expression of Long Noncoding RNAs in Blood After Ischemic Stroke and Proximity to Putative Stroke Risk Loci

BACKGROUND AND PURPOSE

Although peripheral blood mRNA and micro-RNA change after ischemic stroke, any role for long noncoding RNA (lncRNA), which comprise most of the genome and have been implicated in various diseases, is unknown. Thus, we hypothesized that lncRNA expression also changes after stroke.

METHODS

lncRNA expression was assessed in 266 whole-blood RNA samples drawn once per individual from patients with ischemic stroke and matched with vascular risk factor controls. Differential lncRNA expression was assessed by ANCOVA (P<0.005; fold change>|1.2|), principal components analysis, and hierarchical clustering on a derivation set (n=176) and confirmed on a validation set (n=90). Poststroke temporal lncRNA expression changes were assessed using ANCOVA with confounding factor correction (P<0.005; partial correlation with time since event >|0.4|). Because sexual dimorphism exists in stroke, analyses were performed for each sex separately.

RESULTS

A total of 299 lncRNAs were differentially expressed between stroke and control males, whereas 97 lncRNAs were differentially expressed between stroke and control females. Significant changes of lncRNA expression with time after stroke were detected for 49 lncRNAs in men and 31 lncRNAs in women. Some differentially expressed lncRNAs mapped close to genomic locations of previously identified putative stroke-risk genes, including lipoprotein, lipoprotein(a)-like 2, ABO (transferase A, α1-3-N-acetylgalactosaminyltransferase; transferase B, α1-3-galactosyltransferase) blood group, prostaglandin 12 synthase, and α-adducins.

CONCLUSIONS

This study provides evidence of altered and sexually dimorphic lncRNA expression in peripheral blood of patients with stroke compared with that of controls and suggests that lncRNAs have potential for stroke biomarker development. Some regulated lncRNA could regulate some previously identified putative stroke-risk genes.

Leukocyte response is regulated by microRNA let7i in patients with acute ischemic stroke

OBJECTIVE

To evaluate microRNA let7i in ischemic stroke and its regulation of leukocytes.

METHODS

A total of 212 patients were studied: 106 with acute ischemic stroke and 106 controls matched for risk factors. RNA from circulating leukocytes was isolated from blood collected in PAXgene tubes. Let7i microRNA expression was assessed using TaqMan quantitative reverse transcription PCR. To assess let7i regulation of gene expression in stroke, messenger RNA (mRNA) from leukocytes was measured by whole-genome Human Transcriptome Array Affymetrix microarray. Given microRNAs act to destabilize and degrade their target mRNA, mRNAs that inversely correlated with let7i were identified. To demonstrate let7i posttranscriptional regulation of target genes, a 3' untranslated region luciferase assay was performed. Target protein expression was assessed using ELISA.

RESULTS

Let7i was decreased in patients with acute ischemic stroke (fold change -1.70, p < 0.00001). A modest inverse correlation between let7i and NIH Stroke Scale score at admission (r = -0.32, p = 0.02), infarct volume (r = -0.21, p = 0.04), and plasma MMP9 (r = -0.46, p = 0.01) was identified. The decrease in let7i was associated with increased expression of several of its mRNA targets, including CD86, CXCL8, and HMGB1. In vitro studies confirm let7i posttranscriptional regulation of target genes CD86, CXCL8, and HMGB1. Functional analysis predicted let7i regulates pathways involved in leukocyte activation, recruitment, and proliferation including canonical pathways of CD86 signaling in T helper cells, HMGB1 signaling, and CXCL8 signaling.

CONCLUSIONS

Let7i is decreased in circulating leukocytes of patients with acute ischemic stroke. Mechanisms by which let7i regulates inflammatory response post stroke include targeting CD86, CXCL8, and HMGB1.

Elevating microRNA-122 in blood improves outcomes after temporary middle cerebral artery occlusion in rats

Because our recent studies have demonstrated that miR-122 decreased in whole blood of patients and in whole blood of rats following ischemic stroke, we tested whether elevating blood miR-122 would improve stroke outcomes in rats. Young adult rats were subjected to a temporary middle cerebral artery occlusion (MCAO) or sham operation. A polyethylene glycol-liposome-based transfection system was used to administer a miR-122 mimic after MCAO. Neurological deficits, brain infarction, brain vessel integrity, adhesion molecule expression and expression of miR-122 target and indirect-target genes were examined in blood at 24 h after MCAO with or without miR-122 treatment. miR-122 decreased in blood after MCAO, whereas miR-122 mimic elevated miR-122 in blood 24 h after MCAO. Intravenous but not intracerebroventricular injection of miR-122 mimic decreased neurological deficits and brain infarction, attenuated ICAM-1 expression, and maintained vessel integrity after MCAO. The miR-122 mimic also down-regulated direct target genes (e.g. Vcam1, Nos2, Pla2g2a) and indirect target genes (e.g. Alox5, Itga2b, Timp3, Il1b, Il2, Mmp8) in blood after MCAO which are predicted to affect cell adhesion, diapedesis, leukocyte extravasation, eicosanoid and atherosclerosis signaling. The data show that elevating miR-122 improves stroke outcomes and we postulate this occurs via downregulating miR-122 target genes in blood leukocytes.

Intracerebral Hemorrhage and Ischemic Stroke of Different Etiologies Have Distinct Alternatively Spliced mRNA Profiles in the Blood: a Pilot RNA-seq Study

Whole transcriptome studies have used 3′-biased expression microarrays to study genes regulated in the blood of stroke patients. However, alternatively spliced messenger RNA isoforms have not been investigated for ischemic stroke or intracerebral hemorrhage (ICH) in animals or humans. Alternative splicing is the mechanism whereby different combinations of exons of a single gene produce distinct mRNA and protein isoforms. Here, we used RNA sequencing (RNA-seq) to determine if alternative splicing differs for ICH and cardioembolic, large vessel and lacunar causes of ischemic stroke compared to controls. RNA libraries from 20 whole blood samples were sequenced to 200 M 2 × 100 bp reads using Illumina sequencing-by-synthesis technology. Differential alternative splicing was assessed using one-way analysis of variance (ANOVA), and differential exon usage was calculated. Four hundred twelve genes displayed differential alternative splicing among the groups (false discovery rate, FDR; p < 0.05). They were involved in cellular immune response, cell death, and cell survival pathways. Distinct expression signatures based on usage of 308 exons (292 genes) differentiated the groups (p < 0.0005; fold change >|1.2|). This pilot study demonstrates that alternatively spliced genes from whole blood differ in ICH compared to ischemic stroke and differ between different ischemic stroke etiologies. These results require validation in a separate cohort.

Abstract W P93: MiR-122 Improves Stroke Outcomes after Middle Cerebral Artery Occlusion in Rats

MicroRNA (miRNA) are recently discovered small (~22 nucleotides), non-coding RNA that regulate translation of messenger RNA (mRNA) to protein. Though there are only hundreds of miRNAs, each of them can potentially regulate hundreds of target genes, via base-pairing with complementary sequences in mRNA. This provides one approach that targets a single miRNA to have effects on multiple genes.

Our previous genomic studies have demonstrated that miR-122 decreased significantly in blood of experimental strokes produced by middle cerebral artery (MCA) occlusion in rats as well as in blood of patients with ischemic strokes. Therefore, we hypothesized that elevating blood miR-122 has the potential for treating stroke. Using the newly developed in vivo polyethylene glycol-liposome based miRNA transfection system and rat suture MCAO occlusion model, we show that injection of chemically modified mimic miR-122 (600ug/rat, i.v.) through tail vein immediately after MCAO occlusion significantly decreases the neurological impairment and significantly attenuates brain infarct volumes. Ongoing studies are identifying the target genes that are associated with the neuroprotective effects of miR-122 following stroke.

Acknowledgements: This study was supported by NIH grant R01NS066845 (FRS). There were no conflicts of interest.