Monocyte, neutrophil, and whole blood transcriptome dynamics following ischemic stroke

BACKGROUND

After ischemic stroke (IS), peripheral leukocytes infiltrate the damaged region and modulate the response to injury. Peripheral blood cells display distinctive gene expression signatures post-IS and these transcriptional programs reflect changes in immune responses to IS. Dissecting the temporal dynamics of gene expression after IS improves our understanding of immune and clotting responses at the molecular and cellular level that are involved in acute brain injury and may assist with time-targeted, cell-specific therapy.

METHODS

The transcriptomic profiles from peripheral monocytes, neutrophils, and whole blood from 38 ischemic stroke patients and 18 controls were analyzed with RNA-seq as a function of time and etiology after stroke. Differential expression analyses were performed at 0-24 h, 24-48 h, and >48 h following stroke.

RESULTS

Unique patterns of temporal gene expression and pathways were distinguished for monocytes, neutrophils, and whole blood with enrichment of interleukin signaling pathways for different time points and stroke etiologies. Compared to control subjects, gene expression was generally upregulated in neutrophils and generally downregulated in monocytes over all times for cardioembolic, large vessel, and small vessel strokes. Self-organizing maps identified gene clusters with similar trajectories of gene expression over time for different stroke causes and sample types. Weighted Gene Co-expression Network Analyses identified modules of co-expressed genes that significantly varied with time after stroke and included hub genes of immunoglobulin genes in whole blood.

CONCLUSIONS

Altogether, the identified genes and pathways are critical for understanding how the immune and clotting systems change over time after stroke. This study identifies potential time- and cell-specific biomarkers and treatment targets.

Gene expression changes implicate specific peripheral immune responses to Deep and Lobar Intracerebral Hemorrhages in humans

The peripheral immune system response to Intracerebral Hemorrhage (ICH) may differ with ICH in different brain locations. Thus, we investigated peripheral blood mRNA expression of Deep ICH, Lobar ICH, and vascular risk factor-matched control subjects (n = 59). Deep ICH subjects usually had hypertension. Some Lobar ICH subjects had cerebral amyloid angiopathy (CAA). Genes and gene networks in Deep ICH and Lobar ICH were compared to controls. We found 774 differentially expressed genes (DEGs) and 2 co-expressed gene modules associated with Deep ICH, and 441 DEGs and 5 modules associated with Lobar ICH. Pathway enrichment showed some common immune/inflammatory responses between locations including Autophagy, T Cell Receptor, Inflammasome, and Neuroinflammation Signaling. Th2, Interferon, GP6, and BEX2 Signaling were unique to Deep ICH. Necroptosis Signaling, Protein Ubiquitination, Amyloid Processing, and various RNA Processing terms were unique to Lobar ICH. Finding amyloid processing pathways in blood of Lobar ICH patients suggests peripheral immune cells may participate in processes leading to perivascular/vascular amyloid in CAA vessels and/or are involved in its removal. This study identifies distinct peripheral blood transcriptome architectures in Deep and Lobar ICH, emphasizes the need for considering location in ICH studies/clinical trials, and presents potential location-specific treatment targets.

Abstract TMP114: Time-based Dynamic Analyses Of Gene Expression In Monocytes, Neutrophils And Whole Blood Identify Key Hub Genes And Functional Processes Following Acute Ischemic Stroke

Gene expression changes in peripheral blood reflect injury and repair processes occurring post ischemic stroke (IS). Our study explored the dynamic time-dependent expression of key genes involved in the immune response after IS to better understand the biology and to identify specific diagnostic biomarkers. Using RNA-sequencing, we analyzed gene expression profiles of 38 IS patients and 18 controls with at least one vascular risk factor (VRFC) including diabetes and/or hypertension and/or hypercholesterolemia in isolated monocytes, neutrophils and whole blood. We used two approaches: Weighted Gene Co-expression Network Analysis (WGCNA) with respect to time after stroke onset; and differential expression analyses with subject samples split into time points (TPs) from stroke onset (TP0=VRFC; TP1=0-24 h; TP2=24-48 h; and TP3≥48 h). In WGCNA, highly interconnected “hub” genes were identified for modules significant to time (p<0.05). Differentially expressed genes (DEGs) with diagnosisхTP p<0.02 and fold-change>

Abstract WP133: Sex Differences In The Human Intracerebral Hemorrhage Peripheral Blood Transcriptome Implicate Differential Immune And Inflammatory Responses

Sex differences in immune and inflammatory pathways have been shown in health and disease. However, little research has been done on sex differences following human Intracerebral Hemorrhage (ICH). We sought to unveil transcriptome differences in blood between Male (M) and Female (F) ICH responses. We evaluated 33 ICH patients and 33 vascular risk factor matched controls (VRFC), 9F and 24M each. Peripheral blood expression of 21,175 genes was analyzed at the co-expression network level with WGCNA - separate F (F-ICH and F-VRFC) and M (M-ICH and M-VRFC) networks generated; and per gene level (ANCOVA: Age, Time, and Sex*Dx (Diagnosis)). Five F (F-6, F-20, F-21, F-19, F-5) and 2 M (M-32, M-26) WGCNA modules were significant to Dx (p < 0.05) (Fig 1A). 105 genes were significant for the direct comparison (F-ICH vs M-ICH p < 0.05, |FC| > 1.2; Sex*Dx FDR < 0.2), which separated Sex*Dx groups (Fig 1B). 1,425 genes were differentially expressed in F-ICH (F-ICH vs F-VRFC p < 0.05, |FC| > 1.2; Sex*Dx FDR < 0.2) and 421 in M-ICH (M-ICH vs M-VRFC p < 0.05, |FC| > 1.2; Sex*Dx FDR < 0.2) (Fig 1C). F-ICH response was enriched in Monocyte and T Cell Specific genes and M-ICH in B Cell and Erythroblast specific genes; both were enriched in Neutrophil specific genes (Fig 1A). Overall, F modules and gene lists were significantly enriched in 236 GO terms (FDR < 0.1) and M modules in 55; 20 were common (Fig 1D). The ICH response unique to F-ICH included Inflammatory Response, T Cell Activation, Autophagy, Apoptotic Process, and RNA Splicing. M-ICH unique included B Cell Receptor Signaling, Immunoglobulin Receptor Binding, Antigen Binding, Complement Activation, and Receptor Mediated Endocytosis. Common responses included Innate Immune Response, Blood Coagulation, and Fc-ã Receptor Signaling Involved in Phagocytosis (Fig 1E). We found sex differences in ICH transcriptome responses in human peripheral blood. These implicate specific cell types in each sex that could represent novel sex-specific treatment targets.

Bacterial lipopolysaccharide is associated with stroke

We aimed to determine if plasma levels of bacterial lipopolysaccharide (LPS) and lipoteichoic acid (LTA) are associated with different causes of stroke and correlate with C-reactive protein (CRP), LPS-binding protein (LBP), and the NIH stroke scale (NIHSS). Ischemic stroke (cardioembolic (CE), large artery atherosclerosis (LAA), small vessel occlusion (SVO)), intracerebral hemorrhage (ICH), transient ischemic attack (TIA) and control subjects were compared (n = 205). Plasma LPS, LTA, CRP, and LBP levels were quantified by ELISA. LPS and CRP levels were elevated in ischemic strokes (CE, LAA, SVO) and ICH compared to controls. LBP levels were elevated in ischemic strokes (CE, LAA) and ICH. LTA levels were increased in SVO stroke compared to TIA but not controls. LPS levels correlated with CRP and LBP levels in stroke and TIA. LPS, LBP and CRP levels positively correlated with the NIHSS and WBC count but negatively correlated with total cholesterol. Plasma LPS and LBP associate with major causes of ischemic stroke and with ICH, whereas LPS/LBP do not associate with TIAs. LTA only associated with SVO stroke. LPS positively correlated with CRP, LBP, and WBC but negatively correlated with cholesterol. Higher LPS levels were associated with worse stroke outcomes.

Abstract P787: Sexually Dimorphic Gene Expression Molecular Correlates of Improvement in Human Ischemic Stroke

Objective: Ischemic stroke (IS) is sexually dimorphic for risk factors, age, heritability, causes, treatment, and outcome. We identified transcriptional correlates with 90-day outcome that differed between male and female IS subjects.

Methods: RNA from 72 samples from 2 peripheral blood draws (at ≤3 and 24h post IS onset) was analyzed on Affymetrix U133 Plus 2 microarrays. These represented samples from 36 CLEAR trial IS patients treated with tPA with or without eptifibatide after the first blood sample within 3 hours of stroke onset. Changes in gene expression levels (deltaGE) between 3h and 24h were calculated and the association with percent NIH Stroke Scale (NIHSS) improvement from 3h to 90 days (% Improvement) examined. We used mixed-effects linear regression, including Treatment, Age, Sex, Vascular Risk Factors, 3h NIHSS, % Improvement, and a Sex * % Improvement interaction. Sex differences in association of gene expression with % Improvement were determined by examining the Sex * % Improvement interaction term, p<0.005 was considered statistically significant.

Results: 577 genes correlated differently with % Improvement in IS males and females. These included matrix metalloproteinases (MMPs), which play a major role in BBB dysfunction and outcomes post IS. MMP11 , MMP14 and MM17 correlated with % Improvement in opposite direction in males and females. Inflammatory genes like IL-27 , implicated in infarct volume and stroke outcome, and ABC transporters ( ABCC9 ) also had opposite correlation with % Improvement in males and females. Calmodulin 1 ( CAML1 ) was also sexually dimorphic, and a SNP in CALM1 has been implicated in IS risk and blood coagulation in female IS patients. EIF2 signaling, a major protein synthesis pathway was activated in males (adj. p = 1e-8), while suppressed in females (adj. p value = 1e-9). Protein synthesis and associated unfolded protein response cascade have previously been implicated in stroke outcome.

Conclusions: The identified sexually dimorphic gene expression associated with 90-day improvement might relate to sex differences in blood immune and clotting pathways. The findings expand our understanding of the genomic underpinnings associated with stroke outcome and may serve as potential sex-specific treatment targets.

Abstract P744: Gene Transcript Clusters Distinguish Time-Dependent Expression Patterns in Monocytes, Neutrophils and Whole Blood After Ischemic Stroke Injury

Introduction: After ischemic stroke (IS), peripheral leukocytes infiltrate the damaged region and modulate the response to injury. We previously showed that peripheral blood cells display different gene expression profiles after IS and these transcriptional programs reflect the changes in immune processes in response to IS. Dissecting the temporal dynamics of gene expression after IS improves our understanding of the changes of molecular and cellular pathways involved in acute brain injury.

Methods: We analyzed the transcriptomic profiles of 33 IS patients in isolated monocytes, neutrophils and whole blood. RNA-sequencing was performed on all the stroke samples as well as 12 controls with vascular risk factors (diabetes and/or hypertension and/or hypercholesterolemia). To identify differentially expressed genes, subjects were split into time points (TPs) from stroke onset (TP1= 0-24 h; TP2= 24-48 h; and TP3= > 48 h), and controls were assigned TP0. A linear regression model including time and the interaction of diagnosis x TP with cutoff of p<0.02 and fold-change>|1.2| was used. Time dependent changes were analyzed using artificial neural networks to identify clusters of genes that behave in a similar way across TPs.

Results: Unique patterns of temporal expression were distinguished for the three sample types. These include genes not expressed in TP0 that peak only within the first 24 h, others that peak or decrease in TP2 and TP3, and more complex patterns. Genes that peak at TP1 in monocytes and neutrophils are related to cell adhesion and leukocyte differentiation/migration, respectively. Early peaks in whole blood occur in genes related to transcriptional regulation. In monocytes, interleukin pathways are enriched across all TPs, whereas there is a trend of suppression after 24 h in neutrophils. The inflammasome pathway is enriched in the earlier TPs in neutrophils, while not enriched in monocytes until over 48 hours.

Conclusion: Our analyses on gene expression dynamics and cluster patterns allow identification of key genes and pathways at different time points following ischemic injury that are valuable as IS biomarkers and may be possible treatment targets.