High-dosage granulocyte colony stimulating factor treatment alters monocyte trafficking to the brain after experimental stroke

Dual delivery of an NF-κB inhibitor and IL-10 through supramolecular hydrogels polarizes macrophages and promotes cardiac repair after myocardial infarction

The use of anti-inflammatory strategies has the potential to be a definitive treatment for ventricular remodeling post myocardial infarction (MI). The regulation of macrophage phenotypes by anti-inflammatory agents contributes to the alleviation of myocardial fibrosis. However, their poor retention rates severely affect treatment efficacy. Here, we propose a supramolecular compound, NapFFY, to co-assemble with IL-10 and SN50 as a novel anti-inflammatory SN50/IL-10/NapFFY hydrogel with cardioprotective properties. Results from the in vitro and in vivo experiments in murine cell line and rats, respectively, demonstrated that the SN50/IL-10/NapFFY hydrogel exhibits an ideal and sustained release of IL-10 and SN50. Intramyocardial injection of the SN50/IL-10/NapFFY hydrogel in a rat model of MI significantly inhibited the expression of proinflammatory cytokines. It promoted the polarization of M2 macrophages, which reduced cardiomyocyte apoptosis and improved vascularization at the border zones. Specifically, the SN50/IL-10/NapFFY hydrogel significantly improved heart function and ameliorated ventricular remodeling 28 days post MI. We envision that the SN50/IL-10/NapFFY hydrogel could serve as a new anti-inflammatory agent for the clinical treatment of MI in future studies. STATEMENT OF SIGNIFICANCE: Anti-inflammation is an ideal strategy for the treatment of ventricular remodeling post myocardial infarction (MI). SN50 and IL-10 have been shown to have diverse roles in antiinflammatory process, respectively. However, direct intravenous administration or intramyocardial injection of SN50 or IL-10 is not a viable option given its poor half-life in vivo. This study aimed to evaluate the synergistic cardioprotective effects of a supramolecular hydrogel loaded with an NF-κB inhibitor (SN50) and IL-10. Animal experiments showed that the SN50/IL-10/NapFFY hydrogels ameliorated the inflammatory microenvironment, and improved cardiac function to the infarct area in a rat model of MI. We anticipate that SN50/IL10NapFFY hydrogel could be used clinically to treat MI in the near future.

Friends or foes: The mononuclear phagocyte system in ischemic stroke

Ischemic stroke (IS) is a major cause of disability and death in adults, and the immune response plays an indispensable role in its pathological process. After the onset of IS, an inflammatory storm, with the infiltration and mobilization of the mononuclear phagocyte system (MPS), is triggered in the brain. Microglia are rapidly activated in situ, followed by waves of circulating monocytes into the ischemic area. Activated microglia and monocytes/macrophages are mainly distributed in the peri-infarct area. These cells have similar morphology and functions, such as secreting cytokines and phagocytosis. Previously, the presence of the MPS was considered a marker of an exacerbated inflammatory response that contributes to brain damage. However, recent studies have suggested a rather complicated role of the MPS in IS. Here, we reviewed articles focusing on various functions of the MPS among different phases of IS, including recruitment, polarization, phagocytosis, angiogenesis, and interaction with other types of cells. Moreover, due to the characteristics of the MPS, we also noted clinical research addressing alterations in the MPS as potential biomarkers for IS patients for the purposes of predicting prognosis and developing novel therapeutic strategies.

Direct Potential Modulation of Neurogenic Differentiation Markers by Granulocyte-Colony Stimulating Factor (G-CSF) in the Rodent Brain

The hematopoietic granulocyte-colony stimulating growth factor (G-CSF, filgrastim) is an approved drug in hematology and oncology. Filgrastim's potential in neurodegenerative disorders is gaining increasingly more attention, as preclinical and early clinical studies suggest it could be a promising treatment option. G-CSF has had a tremendous record as a safe drug for more than three decades; however, its effects upon the central nervous system (CNS) are still not fully understood. In contrast to conceptual long-term clinical application with lower dosing, our present pilot study intends to give a first insight into the molecular effects of a single subcutaneous (s.c.) high-dose G-CSF application upon different regions of the rodent brain. We analyzed mRNA-and in some instances-protein data of neurogenic and non-neurogenic differentiation markers in different regions of rat brains five days after G-CSF (1.3 mg/kg) or physiological saline. We found a continuous downregulation of several markers in most brain regions. Remarkably, cerebellum and hypothalamus showed an upregulation of different markers. In conclusion, our study reveals minor suppressive or stimulatory effects of a single exceptional high G-CSF dose upon neurogenic and non-neurogenic differentiation markers in relevant brain regions, excluding unregulated responses or unexpected patterns of marker expression.

Inflammatory Responses After Ischemic Stroke

Ischemic stroke generates an immune response that contributes to neuronal loss as well as tissue repair. This is a complex process involving a range of cell types and effector molecules and impacts tissues outside of the CNS. Recent reviews address specific aspects of this response, but several years have passed and important advances have been made since a high-level review has summarized the overall state of the field. The present review examines the initiation of the inflammatory response after ischemic stroke, the complex impacts of leukocytes on patient outcome, and the potential of basic science discoveries to impact the development of therapeutics. The information summarized here is derived from broad PubMed searches and aims to reflect recent research advances in an unbiased manner. We highlight valuable recent discoveries and identify gaps in knowledge that have the potential to advance our understanding of this disease and therapies to improve patient outcomes.

Granulocyte Colony-Stimulating Factor Accelerates the Recovery of Hepatitis B Virus-Related Acute-on-Chronic Liver Failure by Promoting M2-Like Transition of Monocytes

Background and Aim

Acute-on-chronic liver failure (ACLF) has a high mortality rate. The role of granulocyte colony-stimulating factor (G-CSF) in ACLF remains controversial. Monocytes/macrophages are core immune cells, which are involved in the initiation and progression of liver failure; however, the effect of G-CSF on monocytes/macrophages is unclear. The study aimed to verify the clinical efficacy of G-CSF and explore the effect of it on monocytes in hepatitis B virus (HBV)-related ACLF (HBV-ACLF) paitents.

Methods

We performed a large randomized controlled clinical trial for the treatment of HBV-ACLF using G-CSF. A total of 111 patients with HBV-ACLF were prospectively randomized into the G-CSF group (5 μg/kg G-CSF every day for 6 days, then every other day until day 18) or the control group (standard therapy). All participants were followed up for at least 180 days. The relationship between monocyte count and mortality risk was analyzed. The effect of G-CSF on the phenotype and function of monocytes from patients with HBV-ACLF was evaluated using flow cytometry in vivo and in vitro experiments.

Results

The survival probability of the G-CSF group at 180 days was higher than that of the control group (72.2% vs. 53.8%, P = 0.0142). In the G-CSF-treated group, the monocyte counts on days 0 and 7 were independently associated with an evaluated mortality risk in the fully adjusted model (Model 3) [at day 0: hazard ratio (HR) 95% confidence interval (CI): 15.48 (3.60, 66.66), P = 0.0002; at day 7: HR (95% CI): 1.10 (0.50, 2.43), P=0.8080]. Further analysis showed that after treatment with G-CSF in HBV-ACLF patients, the expression of M1-like markers (HLA-DR and CD86) in monocytes decreased (HLA-DR: P = 0.0148; CD86: P = 0.0764). The expression of MerTK (M2-like marker) increased (P = 0.0002). The secretion of TNF-α, IL-6, and IL-10 from monocytes decreased without lipopolysaccharide (LPS) stimulation (TNF-α: P < 0.0001; IL-6: P= 0.0025; IL-10: P = 0.0004) or with LPS stimulation (TNF-α: P = 0.0439; P = 0.0611; IL-10: P = 0.0099). Similar effects were observed in vitro experiments.

Conclusion

G-CSF therapy confers a survival benefit to patients with HBV-ACLF. G-CSF can promote the anti-inflammatory/pro-restorative phenotype (M2-like) transition of monocytes, which may contribute to the recovery of ACLF.

Ultrarapid Inflammation of the Olfactory Bulb After Spinal Cord Injury: Protective Effects of the Granulocyte Colony-Stimulating Factor on Early Neurodegeneration in the Brain

The correlation among olfactory dysfunction, spinal cord injury (SCI), subjective cognitive decline, and neurodegenerative dementia has been established. Impaired olfaction is considered a marker for neurodegeneration. Hence, there is a need to examine if SCI leads to olfactory dysfunction. In this study, the brain tissue of mice with spinal cord hemisection injury was subjected to microarray analysis. The mRNA expression levels of olfactory receptors in the brain began to decline at 8 h post-SCI. SCI promoted neuroinflammation, downregulated the expression of olfactory receptors, decreased the number of neural stem cells (NSCs), and inhibited the production of neurotrophic factors in the olfactory bulbs at 8 h post-SCI. In particular, the SCI group had upregulated mRNA and protein expression levels of glial fibrillary acidic protein (GFAP; a marker of astrocyte reactivation) and pro-inflammatory mediators [IL-1β, IL-6, and Nestin (marker of NSCs)] in the olfactory bulb compared to levels in the sham control group. The mRNA expression levels of olfactory receptors (Olfr1494, Olfr1324, Olfr1241, and Olfr979) and neurotrophic factors [brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), and nerve growth factor (NGF)] were downregulated in the olfactory bulb of the SCI group mice at 8 h post-SCI. The administration of granulocyte colony-stimulating factor (G-CSF) mitigated these SCI-induced pathological changes in the olfactory bulb at 8 h post-SCI. These results indicate that the olfactory bulb is vulnerable to environmental damage even if the lesion is located at sites distant from the brain, such as the spinal cord. Additionally, SCI initiated pathological processes, including inflammatory response, and impaired neurogenesis, at an early stage. The findings of this study will provide a basis for future studies on pathological mechanisms of early neurodegenerative diseases involving the olfactory bulb and enable early clinical drug intervention.

Sphingomyelin Synthase 2 Inhibition Ameliorates Cerebral Ischemic Reperfusion Injury Through Reducing the Recruitment of Toll-Like Receptor 4 to Lipid Rafts

Background

Inflammation is recognized as an important contributor of ischemia/reperfusion (I/R) damage after ischemic stroke. Sphingomyelin synthase 2 (SMS2), the key enzyme for the biosynthesis of sphingomyelin, can function as a critical mediator of inflammation. In the present study, we investigated the role of SMS2 in a mouse model of cerebral I/R.

Methods and Results

Cerebral I/R was induced by 60‐minute transient middle cerebral artery occlusion in SMS2 knockout (SMS2^‐/‐) mice and wild‐type mice. Brain injury was determined by neurological deficits and infarct volume at 24 and 72 hours after transient middle cerebral artery occlusion. Microglia activation and inflammatory factors were detected by immunofluorescence staining, flow cytometry, western blot, and RT‐PCR. SMS2 deficiency significantly improved neurological function and minimized infarct volume at 72 hours after transient middle cerebral artery occlusion. The neuroprotective effects of SMS2 deficiency were associated with (1) suppression of microglia activation through Toll‐like receptor 4/nuclear factor kappa‐light‐chain‐enhancer of activated B cells pathway and (2) downregulation of the level of galactin‐3 and other proinflammatory cytokines. The mechanisms underlying the beneficial effects of SMS2 deficiency may include altering sphingomyelin components in lipid raft fractions, thus impairing the recruitment of Toll‐like receptor 4 to lipid rafts and subsequently reducing Toll‐like receptor 4/myeloid differentiation factor 2 complex formation on the surface of microglia.

Conclusions

SMS2 deficiency ameliorated inflammatory injury after cerebral I/R in mice, and SMS2 may be a key modulator of Toll‐like receptor 4/nuclear factor kappa‐light‐chain‐enhancer of activated B cells activation by disturbing the membrane component homeostasis during cerebral I/R.

CX3CR1-CCR2-dependent monocyte-microglial signaling modulates neurovascular leakage and acute injury in a mouse model of childhood stroke

Stroke is among the top 10 causes of death in children. The developmental stage of the brain is central to stroke pathophysiology. The incidence of childhood arterial ischemic stroke (CAIS) is lower than of perinatal arterial ischemic stroke but the rate of recurrence is strikingly high. Vascular inflammation is seen as major contributor to CAIS but the mechanisms that govern structural-functional basis of vascular abnormalities remain poorly understood. To identify the contribution of immune-neurovascular interactions to CAIS, we established stroke model in postnatal day 21 (P21) mice. We demonstrate acute functional deficits and histological injury and chronic MRI-identifiable injury, brain atrophy and marked derangements in the vascular network. In contrast to negligible albumin leakage and neutrophil infiltration following acute perinatal stroke, CAIS leads to significantly increased albumin leakage and neutrophil infiltration in injured regions of wild type mice and mice with functional CX3CR1-CCR2 receptors. In mice with dysfunctional CX3CR1-CCR2 signaling, extravascular albumin leakage is significantly attenuated, infiltration of injurious Ccr2⁺-monocytes essentially aborted, accumulation of Ly6G+ neutrophils reduced and acute injury attenuated. Unique identifiers of microglia and monocytes revealed phenotypic changes in each cell subtype of the monocyte lineage after CAIS. Taken together, CX3CR1-CCR2-dependent microglia-monocyte signaling contributes to cerebrovascular leakage, inflammation and CAIS injury.

Monocyte mobilisation, microbiota & mental illness

The gastrointestinal microbiome has emerged as a key player in regulating brain and behaviour. This has led to the strategy of targeting the gut microbiota to ameliorate disorders of the central nervous system. Understanding the underlying signalling pathways in which the microbiota impacts these disorders is crucial for the development of future therapeutics for improving CNS functionality. One of the major pathways through which the microbiota influences the brain is the immune system, where there is an increasing appreciation for the role of monocyte trafficking in regulating brain homeostasis. In this review, we will shed light on the role of monocyte trafficking as a relay of microbiota signals in conditions where the central nervous system is in disorder, such as stress, peripheral inflammation, ageing, traumatic brain injury, stroke, multiple sclerosis, Alzheimer's disease and Parkinson's disease. We also cover how the gastrointestinal microbiota is implicated in these mental illnesses. In addition, we aim to discuss how the monocyte system can be modulated by the gut microbiota to mitigate disorders of the central nervous system, which will lead to novel microbiota-targeted strategies.

Cell Death Mechanisms in Stroke and Novel Molecular and Cellular Treatment Options

As a result of ischemia or hemorrhage, blood supply to neurons is disrupted which subsequently promotes a cascade of pathophysiological responses resulting in cell loss. Many mechanisms are involved solely or in combination in this disorder including excitotoxicity, mitochondrial death pathways, and the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy and inflammation. Besides neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problem in stroke is the loss of neuronal cells which makes recovery difficult or even not possible in the late states. Acute treatment options that can be applied for stroke are mainly targeting re-establishment of blood flow and hence, their use is limited due to the effective time window of thrombolytic agents. However, if the acute time window is exceeded, neuronal loss starts due to the activation of cell death pathways. This review will explore the most updated cellular death mechanisms leading to neuronal loss in stroke. Ischemic and hemorrhagic stroke as well as subarachnoid hemorrhage will be debated in the light of cell death mechanisms and possible novel molecular and cellular treatment options will be discussed.