Longitudinal transcriptomics define the stages of myeloid activation in the living human brain after intracerebral hemorrhage

Opportunities to interrogate the immune responses in the injured tissue of living patients suffering from acute sterile injuries such as stroke and heart attack are limited. We leveraged a clinical trial of minimally invasive neurosurgery for patients with intracerebral hemorrhage (ICH), a severely disabling subtype of stroke, to investigate the dynamics of inflammation at the site of brain injury over time. Longitudinal transcriptional profiling of CD14⁺ monocytes/macrophages and neutrophils from hematomas of patients with ICH revealed that the myeloid response to ICH within the hematoma is distinct from that in the blood and occurs in stages conserved across the patient cohort. Initially, hematoma myeloid cells expressed a robust anabolic proinflammatory profile characterized by activation of hypoxia-inducible factors (HIFs) and expression of genes encoding immune factors and glycolysis. Subsequently, inflammatory gene expression decreased over time, whereas anti-inflammatory circuits were maintained and phagocytic and antioxidative pathways up-regulated. During this transition to immune resolution, glycolysis gene expression and levels of the potent proresolution lipid mediator prostaglandin E₂ remained elevated in the hematoma, and unexpectedly, these elevations correlated with positive patient outcomes. Ex vivo activation of human macrophages by ICH-associated stimuli highlighted an important role for HIFs in production of both inflammatory and anti-inflammatory factors, including PGE₂, which, in turn, augmented VEGF production. Our findings define the time course of myeloid activation in the human brain after ICH, revealing a conserved progression of immune responses from proinflammatory to proresolution states in humans after brain injury and identifying transcriptional programs associated with neurological recovery.

Blood handling and leukocyte isolation methods impact the global transcriptome of immune cells

Background

Transcriptional profiling with ultra-low input methods can yield valuable insights into disease, particularly when applied to the study of immune cells using RNA-sequencing. The advent of these methods has allowed for their use in profiling cells collected in clinical trials and other studies that involve the coordination of human-derived material. To date, few studies have sought to quantify what effects that collection and handling of this material can have on resulting data.

Results

We characterized the global effects of blood handling, methods for leukocyte isolation, and preservation media on low numbers of immune cells isolated from blood. We found overall that storage/shipping temperature of blood prior to leukocyte isolation and sorting led to global changes in both CD8⁺ T cells and monocytes, including alterations in immune-related gene sets. We found that the use of a leukocyte filtration system minimized these alterations and we applied this method to generate high-quality transcriptional data from sorted immune cells isolated from the blood of intracerebral hemorrhage patients and matched healthy controls.

Conclusions

Our data underscore the necessity of processing samples with comparably defined protocols prior to transcriptional profiling and demonstrate that a filtration method can be applied to quickly isolate immune cells of interest while minimizing transcriptional bias.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0268-6) contains supplementary material, which is available to authorized users.

Abstract TP331: Plasma IL-6 Levels are Independently Associated With Functional Outcome and Markers of Secondary Injury in Spontaneous Intracerebral Hemorrhage

Introduction: The impact of the inflammatory response after intracerebral hemorrhage (ICH) has not been well characterized in patients and little is known about the relationship between early markers of inflammation and functional outcome. It is hypothesized that cytokine levels may be associated with three-month functional outcome and radiologic markers of secondary injury.

Methods: Fifty-four patients with spontaneous ICH were prospectively enrolled at Yale-New Haven Hospital. Blood samples were collected at 24 (n=44) and 72 (n = 33) hours post-ICH. Plasma cytokine levels were measured using commercially available multiplex ELISA kits (Millipore). Modified Rankin Scale (mRS) was collected at three months by telephone interview. Associations between cytokines and outcome were assessed using ordinal logistics regression. Linear regression was used to evaluate the association between cytokine levels and markers of secondary injury.

Results: IL-6 was correlated with ICH volume (p = 0.003) and PHE volume (p = 0.009) in univariable analysis. In multivariable analysis, IL-6 was associated with midline shift after adjustment for ICH volume (p=0.027). 24h IL-6 (p < 0.001), IL-10 (p < 0.001), IL-15 (p = 0.001), admission Glasgow Coma Score (GCS), ICH volume, ICH Score, and external ventricular drain (EVD) placement were associated with higher (worse) mRS in univariable ordinal regression. After adjustment for the ICH score, 24h IL-6 (OR 2.00, 95% CI 1.2-3.3, p = 0.003) and IL-15 (OR 2.7, 95% CI 1.4-5.0, p = 0.007) were significantly associated with worse mRS.

Conclusions: Plasma IL-6 is independently associated with 24h midline shift, a measure of global hemispheric swelling, and with functional outcome after spontaneous ICH. These data are consistent with the early robust increase in brain IL-6 in experimental models of ICH. These data warrant further investigation of IL-6 levels as a biomarker for secondary injury and poor outcome in ICH.

Erythrocyte efferocytosis modulates macrophages towards recovery after intracerebral hemorrhage

Macrophages are a source of both proinflammatory and restorative functions in damaged tissue through complex dynamic phenotypic changes. Here, we sought to determine whether monocyte-derived macrophages (MDMs) contribute to recovery after acute sterile brain injury. By profiling the transcriptional dynamics of MDMs in the murine brain after experimental intracerebral hemorrhage (ICH), we found robust phenotypic changes in the infiltrating MDMs over time and demonstrated that MDMs are essential for optimal hematoma clearance and neurological recovery. Next, we identified the mechanism by which the engulfment of erythrocytes with exposed phosphatidylserine directly modulated the phenotype of both murine and human MDMs. In mice, loss of receptor tyrosine kinases AXL and MERTK reduced efferocytosis of eryptotic erythrocytes and hematoma clearance, worsened neurological recovery, exacerbated iron deposition, and decreased alternative activation of macrophages after ICH. Patients with higher circulating soluble AXL had poor 1-year outcomes after ICH onset, suggesting that therapeutically augmenting efferocytosis may improve functional outcomes by both reducing tissue injury and promoting the development of reparative macrophage responses. Thus, our results identify the efferocytosis of eryptotic erythrocytes through AXL/MERTK as a critical mechanism modulating macrophage phenotype and contributing to recovery from ICH.

Abstract WMP105: Human Monocyte Derived Macrophage Phagocytize Eryptotic Erythrocytes in a Phosphotidylserine Dependent Mechanism

Introduction: After intracerebral hemorrhage (ICH), erythrocytes contribute to secondary injury by releasing toxic hemoproteins. Our lab has previously shown that blood derived macrophages play an important role in ICH clearance but mechanisms of phagocytosis by human macrophages are unknown. This study aims to quantify eryptotic (phosphatidylserine (PtdSer)-expressing) red blood cells (RBCs) in an in vivo model of ICH, and to investigate the mechanisms that play a role in autologous eryptotic phagocytosis by human monocyte derived macrophages (huMDMs).

Methods: ICH was induced in mice by autologous blood injection. The mice were sacrificed at 1 day after ICH. The brains were separated into hemispheres and digested into a single cell suspension for analysis by flow cytometry. Cells were stained with antibodies to cell surface markers and annexin V to quantify externalized PtdSer expression. Human monocytes were cultured with M-CSF for 7 days to generate huMDMs. Autologous RBCs were heat shocked (HS) to induce eryptosis. The huMDMs were cocultured with HS RBCs, HS RBCs treated with annexin V, or control RBCs. After 1 hour of coculture, the huMDMs were washed, stained and erythrophagocytosis quantified by microscopy.

Results: The proportion of cells that externalized PtdSer increased by almost 20 fold at day 1 after ICH. Control brains mixed with fresh RBCs and subjected to tissue prep did not show PtdSer expression, ensuring that the PtdSer expression detected was induced in vivo (Fig A). HS RBCs increased PtdSer expression and were efficiently phagocytosed by huMDMs. Treatment of HS RBCs with annexin V to antagonize PtdSer-receptor interactions decreased RBC phagocytosis to levels comparable to control RBCs (Figs B and C).

Conclusions: In vivo after ICH, erythrocytes externalize PtdSer, a cue to be engulfed by macrophages. Human macrophages phagocytose RBCs in a PtdSer-dependent mechanism. These findings highlight potential targets to enhance ICH clearance.

Abstract 213: Hematoma-infiltrating Macrophages Transition From Inflammatory to Reparative Programs in Patients After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) causes rapid recruitment of circulating leukocytes to the injury; however, the roles of these cells in disease progression and repair in the brain are poorly understood. Findings from animal models have failed to translate into effective therapies for ICH, emphasizing the importance of studying the ICH immune response in the patient population. To gain insight into the inflammatory response in patient hematomas, we are utilizing mass cytometry, flow cytometry, and RNA-seq to characterize hematoma-infiltrating leukocytes isolated from ICH patients over a 5 day period, in conjunction with the ongoing MISTIE III trial for surgical evacuation of ICH. We have found that the hematoma immune infiltrate is predominantly composed of neutrophils and macrophages recruited from the circulation, rather than CNS-resident microglia. We have observed that hematoma macrophages have acquired a distinct phenotype differing from phagocyte populations in the peripheral blood, suggesting that their gene expression is controlled by local signals in the hematoma. Preliminary transcriptional analysis of hematoma macrophages 24-50 hours post-ICH has revealed an inflammatory profile characterized by increased expression of antigen presentation, TLR signaling, glycolytic metabolism, and prostaglandin production pathways (Figure 1). Intriguingly, by 100 hours post-ICH, macrophages downregulated these pathways and engaged a wound healing program characterized by TGF-beta signaling, fatty acid metabolism, and collagen deposition (Figure 1). These findings, in agreement with our previous results in animal models of ICH, suggest that recruited macrophages may contribute not only to initial inflammatory damage, but also to clearance of the hematoma and resolution of inflammation, making them potentially ideal targets for therapeutic intervention.

Abstract TP351: Axl/Mer Receptor Tyrosine Kinase Mediates Erythrophagocytosis-Induced Macrophage Reparative Phenotype and Brain Recovery in Experimental Intracerebral Hemorrhage

Introduction: Local inflammation contributes to both brain injury and recovery after intracerebral hemorrhage (ICH). Our previous studies have shown brain-infiltrating macrophages (BIMs) aggravate early brain injury after ICH; however, BIMs increase scavenger receptor CD36 levels over time, and hematoma clearance is delayed in the absence of BIMs. The mechanism that mediates BIMs phenotypic change in the ICH brain is elusive. In this study, we delineate the dynamic transcriptome profile of BIMs after ICH and test potential mediator that might modulate BIMs polarity in ICH.

Methods: Autologous blood injection ICH model and thrombin-treated bone marrow-derived macrophages (BMDM) were used to mimic ICH in vivo and in vitro . BIMs were isolated by FACS, and the 780 transcriptome of BIMs were determined using NanoString. Flow cytometry and RT-qPCR were performed to detect the frequency of phosphatidylserine-positive (eryptotic) RBCs and to assess BIMs phenotype in the perihematomal tissue. Erythrophagocytosis of eryptotic RBCs was identified by immunofluorescence and microscopy. Neurologic deficit was evaluated by cylinder test. Axl/Mer receptor tyrosine kinase double knockout (AM DKO) mice, AM DKO bone-marrow chimeras, and AM DKO BMDM were used to evaluate the function of Axl/Mer on macrophage phenotype and on brain recovery after ICH.

Results: BIMs highly expressed proinflammatory transcripts such as cd86 , tlr2 , nlrp3 , and tnf at days 1 and 3 post-ICH; these were decreased at days 7 and 10. Transcripts relevant to efferocytosis ( axl ) and lysosome formation ( cd63 ) increased from days 3 to 10 post-ICH. At days 1 and 3, phosphatidylserine levels was increased on RBCs in the ICH brain. Engulfment of eryptotic RBCs reduced proinflammatory phenotype of BMDM. Thrombin-stimulated AM DKO BMDM had reduced erythrophagocytosis ability and increased tnf and il-6 gene expression. AM DKO mice and AM DKO chimeras had low CD36 and high MHC II levels on BIMs and had worse functional outcome after ICH.

Conclusions: BIMs initially express proinflammatory phenotype and then switch to a reparative phenotype after ICH. Axl/Mer is involved in regulation of macrophage polarity through modulating erythrophagocytosis ability and contributes to ICH brain recovery.

TGF-β1 modulates microglial phenotype and promotes recovery after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating form of stroke that results from the rupture of a blood vessel in the brain, leading to a mass of blood within the brain parenchyma. The injury causes a rapid inflammatory reaction that includes activation of the tissue-resident microglia and recruitment of blood-derived macrophages and other leukocytes. In this work, we investigated the specific responses of microglia following ICH with the aim of identifying pathways that may aid in recovery after brain injury. We used longitudinal transcriptional profiling of microglia in a murine model to determine the phenotype of microglia during the acute and resolution phases of ICH in vivo and found increases in TGF-β1 pathway activation during the resolution phase. We then confirmed that TGF-β1 treatment modulated inflammatory profiles of microglia in vitro. Moreover, TGF-β1 treatment following ICH decreased microglial Il6 gene expression in vivo and improved functional outcomes in the murine model. Finally, we observed that patients with early increases in plasma TGF-β1 concentrations had better outcomes 90 days after ICH, confirming the role of TGF-β1 in functional recovery from ICH. Taken together, our data show that TGF-β1 modulates microglia-mediated neuroinflammation after ICH and promotes functional recovery, suggesting that TGF-β1 may be a therapeutic target for acute brain injury.