Role of oxidative stress and caspase 3 in CD47-mediated neuronal cell death

Intravenous Administration of Anti-CD47 Antibody Augments Hematoma Clearance, Mitigates Acute Neuropathology, and Improves Cognitive Function in a Rat Model of Penetrating Traumatic Brain Injury

Traumatic brain injury (TBI)-induced intracerebral hematoma is a major driver of secondary injury pathology such as neuroinflammation, cerebral edema, neurotoxicity, and blood-brain barrier dysfunction, which contribute to neuronal loss, motor deficits, and cognitive impairment. Cluster of differentiation 47 (CD47) is an antiphagocytic cell surface protein inhibiting hematoma clearance. This study was designed to evaluate the safety and efficacy of blockade of CD47 via intravenous (i.v.) administration of anti-CD47 antibodies following penetrating ballistic-like brain injury (PBBI) with significant traumatic intracerebral hemorrhage (tICH). The pharmacokinetic (PK) profile of the anti-CD47 antibody elicited that antibody concentration decayed over 7 days post-administration. Blood tests and necropsy analysis indicated no severe adverse events following treatment. Cerebral hemoglobin levels were significantly increased after injury, however, anti-CD47 antibody administration at 0.1 mg/kg resulted in a significant reduction in cerebral hemoglobin levels at 72 h post-administration, indicating augmentation of hematoma clearance. Immunohistochemistry assessment of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule 1 (IBA1) demonstrated a significant reduction of GFAP levels in the lesion core and peri-lesional area. Based on these analyses, the optimal dose was identified as 0.1 mg/kg. Lesion volume showed a reduction following treatment. Rotarod testing revealed significant motor deficits in all injured groups but no significant therapeutic benefits. Spatial learning performance revealed significant deficits in all injured groups, which were significantly improved by the last testing day. Anti-CD47 antibody treated rats showed significantly improved attention deficits, but not retention scores. These results provide preliminary evidence that blockade of CD47 using i.v. administration of anti-CD47 antibodies may serve as a potential therapeutic for TBI with ICH.

The role of CD47 in non-neoplastic diseases

CD47 is a 50 kDa five-spanning membrane receptor that plays a crucial role in multiple cellular processes, including myeloid cell activation, neutrophils transmigration, vascular remodeling, leukocyte adhesion and trans-endothelial migration. Recent studies have revealed that CD47 is a highly expressed anti-phagocytic signal in several types of cancer, and therefore, blocking of CD47 has shown an effective therapeutic potential in cancer immunotherapy. In addition, CD47 has been found to be involved in a complex interplay with microglia and other types of cells, and increasing evidence indicates that CD47 can be targeted as part of immune modulatory strategies for non-neoplastic diseases as well. In this review, we focus on CD47 and its role in non-neoplastic diseases, including neurological disorders, atherosclerosis and autoimmune diseases. In addition, we discuss the major challenges and potential remedies associated with CD47-SIRPα-based immunotherapies.

CD47 in the Brain and Neurodegeneration: An Update on the Role in Neuroinflammatory Pathways

CD47 is a receptor belonging to the immunoglobulin (Ig) superfamily and broadly expressed on cell membranes. Through interactions with ligands such as SIRPα, TSP-1, integrins, and SH2-domain bearing protein tyrosine phosphatase substrate-1 (SHPS-1), CD47 regulates numerous functions like cell adhesion, proliferation, apoptosis, migration, homeostasis, and the immune system. In this aspect, previous research has shown that CD47 modulates phagocytosis via macrophages, the transmigration of neutrophils, and the activation of T-cells, dendritic cells, and B-cells. Moreover, several studies have reported the increased expression of the CD47 receptor in a variety of diseases, including acute lymphoblastic leukemia (ALL), chronic myeloid leukemia, non-Hodgkin’s lymphoma (NHL), multiple myeloma (MM), bladder cancer, acute myeloid leukemia (AML), Gaucher disease, Multiple Sclerosis and stroke among others. The ubiquitous expression of the CD47 cell receptor on most resident cells of the CNS has previously been established through different methodologies. However, there is little information concerning its precise functions in the development of different neurodegenerative pathologies in the CNS. Consequently, further research pertaining to the specific functions and roles of CD47 and SIRP is required prior to its exploitation as a druggable approach for the targeting of various neurodegenerative diseases that affect the human population. The present review attempts to summarize the role of both CD47 and SIRP and their therapeutic potential in neurodegenerative disorders.

Functions of Thrombospondin-1 in the Tumor Microenvironment

The identification of thrombospondin-1 as an angiogenesis inhibitor in 1990 prompted interest in its role in cancer biology and potential as a therapeutic target. Decreased thrombospondin-1 mRNA and protein expression are associated with progression in several cancers, while expression by nonmalignant cells in the tumor microenvironment and circulating levels in cancer patients can be elevated. THBS1 is not a tumor suppressor gene, but the regulation of its expression in malignant cells by oncogenes and tumor suppressor genes mediates some of their effects on carcinogenesis, tumor progression, and metastasis. In addition to regulating angiogenesis and perfusion of the tumor vasculature, thrombospondin-1 limits antitumor immunity by CD47-dependent regulation of innate and adaptive immune cells. Conversely, thrombospondin-1 is a component of particles released by immune cells that mediate tumor cell killing. Thrombospondin-1 differentially regulates the sensitivity of malignant and nonmalignant cells to genotoxic stress caused by radiotherapy and chemotherapy. The diverse activities of thrombospondin-1 to regulate autophagy, senescence, stem cell maintenance, extracellular vesicle function, and metabolic responses to ischemic and genotoxic stress are mediated by several cell surface receptors and by regulating the functions of several secreted proteins. This review highlights progress in understanding thrombospondin-1 functions in cancer and the challenges that remain in harnessing its therapeutic potential.

A potential gliovascular mechanism for microglial activation: differential phenotypic switching of microglia by endothelium versus astrocytes

BACKGROUND

Activation of microglia can result in phenotypic and functional diversity. However, the pathways that trigger different states of microglial activation remain to be fully understood. Here, we hypothesized that after injury, astrocytes and endothelium may contribute to a gliovascular switch for microglial activation.

METHODS

Astrocytes or cerebral endothelial cells were subjected to oxygen glucose deprivation, then conditioned media were transferred to microglia. The release of TNFα, IL-1β, IL-10, and IGF-1 was measured using ELISA. Surface markers of CD11b, CD45, CD86, and MHC class II were detected by flow cytometry. mRNA expression of iNOS, CD86, CD206, Arginase1, and transcription factors was measured using real-time PCR. Microglial function including migration and phagocytosis was assessed. Dendritogenesis was determined by counting the number of primary dendrites, secondary dendrites, and dendritic ends in the neurons exposed to either endothelial- or astrocyte-activated microglia.

RESULTS

Exposure to conditioned media from oxygen-glucose-deprived cerebral endothelial cells or oxygen-glucose-deprived astrocytes activated microglia into different forms. The endothelium converted ramified microglia into amoeboid shapes; increased the release of TNFα, IL-1β, and IL-10; decreased IGF-1; upregulated iNOS expression; and inhibited microglial migration and phagocytosis. In contrast, astrocytes increased microglial production of IGF-1, upregulated CD206 expression, and enhanced microglial phagocytosis. These opposing effects of the endothelium versus astrocyte crosstalk partly mirror potentially deleterious versus potentially beneficial microglial phenotypes. Consistent with this idea, endothelial-activated microglia were neurotoxic, whereas astrocyte-activated microglia did not affect neuronal viability but instead promoted neuronal dendritogenesis.

CONCLUSION

These findings provide proof of concept that endothelial cells and astrocytes provide differing signals to microglia that influence their activation states and suggest that a gliovascular switch may be involved in the balance between beneficial versus deleterious microglial properties.

The Roles of Thrombospondins in Hemorrhagic Stroke

Hemorrhagic stroke is a devastating cerebrovascular disease with significant morbidity and mortality worldwide. Thrombospondins (TSPs), as matricellular proteins, belong to the TSP family which is comprised of five members. All TSPs modulate a variety of cellular functions by binding to various receptors. Recently, TSPs gained attention in the area of hemorrhagic stroke, especially TSP-1. TSP-1 participates in angiogenesis, the inflammatory response, apoptosis, and fibrosis after hemorrhagic stroke through binding to various molecules including but not limited to CD36, CD47, and TGF-β. In this review, we will discuss the roles of TSPs in hemorrhagic stroke and focus primarily on TSP-1.

Thrombospondin-1, Free Radicals, and the Coronary Microcirculation: The Aging Conundrum

SIGNIFICANCE

Successful matching of cardiac metabolism to perfusion is accomplished primarily through vasodilation of the coronary resistance arterioles, but the mechanism that achieves this effect changes significantly as aging progresses and involves the contribution of reactive oxygen species (ROS). Recent Advances: A matricellular protein, thrombospondin-1 (Thbs-1), has been shown to be a prolific contributor to the production and modulation of ROS in large conductance vessels and in the peripheral circulation. Recently, the presence of physiologically relevant circulating Thbs-1 levels was proven to also disrupt vasodilation to nitric oxide (NO) in coronary arterioles from aged animals, negatively impacting coronary blood flow reserve.

CRITICAL ISSUES

This review seeks to reconcile how ROS can be successfully utilized as a substrate to mediate vasoreactivity in the coronary microcirculation as "normal" aging progresses, but will also examine how Thbs-1-induced ROS production leads to dysfunctional perfusion and eventual ischemia and why this is more of a concern in advancing age.

FUTURE DIRECTIONS

Current therapies that may effectively disrupt Thbs-1 and its receptor CD47 in the vascular wall and areas for future exploration will be discussed. Antioxid. Redox Signal. 27, 785-801.

Thrombospondin-1 Gene Deficiency Worsens the Neurological Outcomes of Traumatic Brain Injury in Mice

Background: Thrombospondin-1 (TSP-1) is an extracellular matrix protein that plays multiple physiological and pathophysiological roles in the brain. Experimental reports suggest that TSP-1 may have an adverse role in neuronal function recovery under certain injury conditions. However, the roles of TSP-1 in traumatic brain injury (TBI) have not been elucidated. In this study we for the first time investigated the roles of TSP-1 in a controlled cortical impact (CCI) model of TBI in TSP-1 knockout (TSP-1 KO) and wild type (WT) mice. Methods: We examined blood brain-barrier (BBB) damage using at 1 day post-TBI by measuring Evans Blue leakage, and neurological functional recovery at 3 weeks post-TBI by measuring neurological severity score (NSS), wire gripping, corner test and Morris Water Maze (MWM). Mechanistically, we quantified pro-angiogenic biomarkers including cerebral vessel density, vascular endothelial growth factors (VEGF) and angiopoietin-1 (Ang-1) protein expression, synaptic biomarker synaptophysin, and synaptogenesis marker brain-derived neurotrophic factor (BDNF) protein expression in contralateral and ipsilateral (peri-lesion) cortex at 21 days after TBI using immunohistochemistry and Western Blot. Results: TSP-1 is upregulated at early phase of TBI in WT mice. Compared to WT mice, TSP-1 KO (1) significantly worsened TBI-induced BBB leakage at 1 day after TBI; (2) had similar lesion size as WT mice at 3 weeks after TBI; (3) exhibited a significantly worse neurological deficits in motor and cognitive functions; (4) had no significant difference in cerebral vessel density, but significant increase of VEGF and Ang-1 protein expressions in peri-lesion cortex; (5) significantly increased BDNF but not synaptophysin protein level in peri-lesion cortex compared to sham, but both synaptophysin and BDNF expressions were significantly decreased in contralateral cortex compared to WT. Conclusion: Our results suggest that TSP-1 may be beneficial for maintaining BBB integrity in the early phase and functional recovery in late phase after TBI. The molecular mechanisms of TSP-1 in early BBB pathophysiology, and long-term neurological function recovery after TBI need to be further investigated.

Differential subnetwork of chemokines/cytokines in human, mouse, and rat brain cells after oxygen-glucose deprivation

Mice and rats are the most commonly used animals for preclinical stroke studies, but it is unclear whether targets and mechanisms are always the same across different species. Here, we mapped the baseline expression of a chemokine/cytokine subnetwork and compared responses after oxygen-glucose deprivation in primary neurons, astrocytes, and microglia from mouse, rat, and human. Baseline profiles of chemokines (CX3CL1, CXCL12, CCL2, CCL3, and CXCL10) and cytokines (IL-1α, IL-1β, IL-6, IL-10, and TNFα) showed significant differences between human and rodents. The response of chemokines/cytokines to oxygen-glucose deprivation was also significantly different between species. After 4 h oxygen-glucose deprivation and 4 h reoxygenation, human and rat neurons showed similar changes with a downregulation in many chemokines, whereas mouse neurons showed a mixed response with up- and down-regulated genes. For astrocytes, subnetwork response patterns were more similar in rats and mice compared to humans. For microglia, rat cells showed an upregulation in all chemokines/cytokines, mouse cells had many down-regulated genes, and human cells showed a mixed response with up- and down-regulated genes. This study provides proof-of-concept that species differences exist in chemokine/cytokine subnetworks in brain cells that may be relevant to stroke pathophysiology. Further investigation of differential gene pathways across species is warranted.

Proteomic Analysis of Mouse Cortex Postsynaptic Density following Neonatal Brain Hypoxia-Ischemia

Proteomics of the synapses and postsynaptic densities (PSDs) have provided a deep understanding of protein composition and signal networks in the adult brain, which underlie neuronal plasticity and neurodegenerative or psychiatric disorders. However, there is a paucity of knowledge about the architecture and organization of PSDs in the immature brain, and how it is modified by brain injury in an early developing stage. Mass spectrometry (MS)-based proteomic analysis was performed on PSDs prepared from cortices of postnatal day 9 naïve mice or pups which had suffered hypoxic-ischemic (HI) brain injury. 512 proteins of different functional groups were identified from PSDs collected 1 h after HI injury, among which 60 have not been reported previously. Seven newly identified proteins involved in neural development were highlighted. HI injury increased the yield of PSDs at early time points upon reperfusion, and multiple proteins were recruited into PSDs following the insult. Quantitative analysis was performed using spectral counting, and proteins whose relative expression was more than 50% up- or downregulated compared to the sham animals 1 h after HI insult were reported. Validation with Western blotting demonstrated changes in expression and phosphorylation of the N-methyl-D-aspartate receptor, activation of a series of postsynaptic protein kinases and dysregulation of scaffold and adaptor proteins in response to neonatal HI insult. This work, along with other recent studies of synaptic protein profiling in the immature brain, builds a foundation for future investigation on the molecular mechanisms underlying developing plasticity. Furthermore, it provides insights into the biochemical changes of PSDs following early brain hypoxia-ischemia, which is helpful for understanding not only the injury mechanisms, but also the process of repair or replenishment of neuronal circuits during recovery from brain damage.

CD47 deficiency improves neurological outcomes of traumatic brain injury in mice

CD47 is a receptor for signal-regulatory protein alpha (SIRPα) in self-recognition by the innate immune system, and a receptor of thrombospondin-1 (TSP-1) contributing to vascular impairment in response to stress. However, the roles of CD47 in traumatic brain injury (TBI) have not been investigated. In this study we aimed to test our hypothesis that CD47 mediates early neutrophil brain infiltration and late brain vascular remodeling after TBI. Mice were subjected to TBI using a controlled cortical impact (CCI) device. We examined early phase neutrophil infiltration, and late phase brain vessel density, pro-angiogenic markers VEGF and Ang-1 protein expression, neurological function deficits and lesion volumes for up to three weeks after TBI. Our results show that mice deficient in CD47 (CD47 Knockout) had significantly less brain neutrophil infiltration at 24h, upregulated VEGF expression in peri-lesion cortex at 7 and 14days, and increased blood vessel density at 21days after TBI, compared to wild type (WT) mice. CD47 knockout also significantly decreased sensorimotor function deficits and reduced brain lesion volume at 21days after TBI. We conclude that CD47 may play pathological roles in brain neutrophil infiltration, progression of brain tissue damage, impairment of cerebrovascular remodeling and functional recovery after TBI.

Thrombospondin 1 protects pancreatic β-cells from lipotoxicity via the PERK-NRF2 pathway

The failure of β-cells has a central role in the pathogenesis of type 2 diabetes, and the identification of novel approaches to improve functional β-cell mass is essential to prevent/revert the disease. Here we show a critical novel role for thrombospondin 1 (THBS1) in β-cell survival during lipotoxic stress in rat, mouse and human models. THBS1 acts from within the endoplasmic reticulum to activate PERK and NRF2 and induce a protective antioxidant defense response against palmitate. Prolonged palmitate exposure causes THBS1 degradation, oxidative stress, activation of JNK and upregulation of PUMA, culminating in β-cell death. These findings shed light on the mechanisms leading to β-cell failure during metabolic stress and point to THBS1 as an interesting therapeutic target to prevent oxidative stress in type 2 diabetes.

CD47 signaling pathways controlling cellular differentiation and responses to stress

CD47 is a widely expressed integral membrane protein that serves as the counter-receptor for the inhibitory phagocyte receptor signal-regulatory protein-α (SIRPα) and as a signaling receptor for the secreted matricellular protein thrombospondin-1. Recent studies employing mice and somatic cells lacking CD47 have revealed important pathophysiological functions of CD47 in cardiovascular homeostasis, immune regulation, resistance of cells and tissues to stress and chronic diseases of aging including cancer. With the emergence of experimental therapeutics targeting CD47, a more thorough understanding of CD47 signal transduction is essential. CD47 lacks a substantial cytoplasmic signaling domain, but several cytoplasmic binding partners have been identified, and lateral interactions of CD47 with other membrane receptors play important roles in mediating signaling resulting from the binding of thrombospondin-1. This review addresses recent advances in identifying the lateral binding partners, signal transduction pathways and downstream transcription networks regulated through CD47 in specific cell lineages. Major pathways regulated by CD47 signaling include calcium homeostasis, cyclic nucleotide signaling, nitric oxide and hydrogen sulfide biosynthesis and signaling and stem cell transcription factors. These pathways and other undefined proximal mediators of CD47 signaling regulate cell death and protective autophagy responses, mitochondrial biogenesis, cell adhesion and motility and stem cell self-renewal. Although thrombospondin-1 is the best characterized agonist of CD47, the potential roles of other members of the thrombospondin family, SIRPα and SIRPγ binding and homotypic CD47 interactions as agonists or antagonists of signaling through CD47 should also be considered.

Functions and transcriptional regulation of thrombospondins and their interrelationship with fibroblast growth factor-2 in bovine luteal cells

Previously, we showed luteal stage-specific regulation of angiogenesis-modulating factors by prostaglandin F2 alpha (PGF2alpha). Fibroblast growth factor 2 (FGF2) and thrombospondins (THBSs) exhibited the most divergent profile of induction by PGF2alpha. We therefore examined the transcriptional regulation and roles of THBSs in luteal cells and studied their interaction with FGF2. THBSs and their receptors exhibited cell-specific expression: THBS1 was the predominant form in luteal endothelial cells (LEC), whereas luteinized granulosa cells (LGC) expressed mostly THBS2. CD36 was confined to LGC, but CD47 did not exhibit preferential expression between LEC and LGC. THBS1 and THBS2 were both stimulated in vitro by PGF2a and its analog in LGC. In contrast, luteinizing signals (LH and insulin) decreased the expression of THBS1, THBS2, and CD36. Importantly, LH increased FGF2 expression, suggesting that THBSs and FGF2 are conversely regulated. We found that FGF2 inhibited THBS1 and vice versa, and that THBS1 treatment decreased FGF2 expression, suggesting reciprocal inhibition. In agreement, ablation of THBS1 by specific small interference RNAs elevated FGF2 levels. THBS1 reduced LEC numbers and promoted apoptosis by activation of caspase-3. In contrast, FGF2 reduced basal and THBS1-induced caspase-3 levels. Consistent with these findings, small interference RNA silencing of THBS1 in luteal cells reduced the levels of active caspase-3 and improved the survival of cells when challenged with staurosporine. Taken together, these studies suggest that THBSs are suppressed during luteinization but are induced by PGF2alpha in luteolysis. THBS1 has antiangiogenic, proapoptotic properties; these, together with its ability to inhibit FGF2 expression and activity, can promote luteolysis.

Brain CD47 expression in a swine model of intracerebral hemorrhage

CD47 contributes to neuronal death, inflammation and angiogenesis after brain ischemia. The role of CD47 in intracerebral hemorrhage (ICH) has not been investigated and the current study examined brain CD47 expression in a pig ICH model. Pigs received a blood injection or needle insertion into the right frontal lobe and were euthanized at different times to examine CD47 expression. Pigs were also treated with an iron chelator, deferoxamine, (50mg/kg, i.m.) or vehicle and killed at day-3 to examine the effects on CD47. ICH resulted in upregulation of brain CD47 in both white and gray matter by both immunohistochemistry and Western blot. A time-course showed ICH-induced CD47 upregulation from 4h to day-14, with a peak at day-3. CD47 positive cells were neurons, microglia/macrophage and oliogodendrocytes. Brain CD47 levels were lower in the ipsilateral white and gray matter in pigs which had deferoxamine treatment. In conclusion, CD47 expression was increased in the perihematomal white and gray matter after ICH. Deferoxamine and iron may modulate CD47 expression.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

Cardiovascular homeostasis and health is maintained through the balanced interactions of cardiac generated blood flow and cross-talk between the cellular components that comprise blood vessels. Central to this cross-talk is endothelial generated nitric oxide (NO) that stimulates relaxation of the contractile vascular smooth muscle (VSMC) layer of blood vessels. In cardiovascular disease this balanced interaction is disrupted and NO signaling is lost. Work over the last several years indicates that regulation of NO is much more complex than previously believed. It is now apparent that the secreted protein thrombospondin-1 (TSP1), that is upregulated in cardiovascular disease and animal models of the same, on activating cell surface receptor CD47, redundantly inhibits NO production and NO signaling. This inhibitory event has implications for baseline and disease-related responses mediated by NO. Further work has identified that TSP1-CD47 signaling stimulates enzymatic reactive oxygen species (ROS) production to further limit blood flow and promote vascular disease. Herein consideration is given to the most recent discoveries in this regard which identify the TSP1-CD47 axis as a major proximate governor of cardiovascular health.

What does complement do in Alzheimer's disease? Old molecules with new insights

Increasing evidence suggests that inflammatory and immune components in brain are important in Alzheimer's disease (AD) and anti-inflammatory and immunotherapeutic approaches may be amenable to AD treatment. It is known that complement activation occurs in the brain of patients with AD, and contributes to a local inflammatory state development which is correlated with cognitive impairment. In addition to the complement's critical role in the innate immune system recognizing and killing, or targeting for destruction, complement proteins can also interact with cell surface receptors to promote a local inflammatory response and contributes to the protection and healing of the host. On the other hand, complement activation also causes inflammation and cell damage as an essential immune function to eliminate cell debris and potentially toxic protein aggregates. It is the balance of these seemingly competing events that influences the ultimate state of neuronal function. Our mini review will be focusing on the unique molecular interactions happening in the AD development, the functional outcomes of those interactions, as well as the contribution of each element to AD.

Thrombospondin-1 regulates blood flow via CD47 receptor-mediated activation of NADPH oxidase 1

OBJECTIVE

Although the matricellular protein thrombospondin-1 (TSP1) is highly expressed in the vessel wall in response to injury, its pathophysiological role in the development of vascular disease is poorly understood. This study was designed to test the hypothesis that TSP1 stimulates reactive oxygen species production in vascular smooth muscle cells and induces vascular dysfunction by promoting oxidative stress.

METHODS AND RESULTS

Nanomolar concentrations of TSP1 found in human vascular disease robustly stimulated superoxide (O(2)(•-)) levels in vascular smooth muscle cells at both cellular and tissue level as measured by cytochrome c and electron paramagnetic resonance. A peptide mimicking the C terminus of TSP1 known to specifically bind CD47 recapitulated this response. Transcriptional knockdown of CD47 and a monoclonal inhibitory CD47 antibody abrogated TSP1-triggered O(2)(•-) in vitro and ex vivo. TSP1 treatment of vascular smooth muscle cells activated phospholipase C and protein kinase C, resulting in phosphorylation of the NADPH oxidase organizer subunit p47(phox) and subsequent Nox1 activation, leading to impairment of arterial vasodilatation ex vivo. Further, we observed that blockade of CD47 and NADPH oxidase 1 gene silencing in vivo in rats improves TSP1-induced impairment of tissue blood flow after ischemia reperfusion.

CONCLUSIONS

Our data suggest a highly regulated process of reactive oxygen species stimulation and blood flow regulation promoted through a direct TSP1/CD47-mediated activation of Nox1. This is the first report, to our knowledge, of a matricellular protein acting as a ligand for NADPH oxidase activation and through specific engagement of integrin-associated protein CD47.

Activated CD47 regulates multiple vascular and stress responses: implications for acute kidney injury and its management

Ischemia-reperfusion injury (IRI) remains a significant source of early and delayed renal transplant failure. Therapeutic interventions have yet to resolve this ongoing clinical challenge although the reasons for this remain unclear. The cell surface receptor CD47 is widely expressed on vascular cells and in tissues. It has one known soluble ligand, the stress-released matricellular protein thrombospondin-1 (TSP1). The TSP1-CD47 ligand receptor axis controls a number of important cellular processes, inhibiting survival factors such as nitric oxide, cGMP, cAMP, and VEGF, while activating injurious pathways such as production of reactive oxygen species. A role of CD47 in renal IRI was recently revealed by the finding that the TSP1-CD47 axis is induced in renal tubular epithelial cells (RTEC) under hypoxia and following IRI. The absence of CD47 in knockout mice increases survival, mitigates RTEC damage, and prevents subsequent kidney failure. Conversely, therapeutic blockade of TSP1-CD47 signaling provides these same advantages to wild-type animals. Together, these findings suggest an important role for CD47 in renal IRI as a proximate promoter of injury and as a novel therapeutic target.

Effects of heat shock protein 72 (Hsp72) on evolution of astrocyte activation following stroke in the mouse

Astrocyte activation is a hallmark of the response to brain ischemia consisting of changes in gene expression and morphology. Heat shock protein 72 (Hsp72) protects from cerebral ischemia, and although several protective mechanisms have been investigated, effects on astrocyte activation have not been studied. To identify potential mechanisms of protection, microarray analysis was used to assess gene expression in the ischemic hemispheres of wild-type (WT) and Hsp72-overexpressing (Hsp72Tg) mice 24 h after middle cerebral artery occlusion or sham surgery. After stroke both genotypes exhibited changes in genes related to apoptosis, inflammation, and stress, with more downregulated genes in Hsp72Tg and more inflammation-related genes increased in WT mice. Genes indicative of astrocyte activation were also upregulated in both genotypes. To measure the extent and time course of astrocyte activation after stroke, detailed histological and morphological analyses were performed in the cortical penumbra. We observed a marked and persistent increase in glial fibrillary acidic protein (GFAP) and a transient increase in vimentin. No change in overall astrocyte number was observed based on glutamine synthetase immunoreactivity. Hsp72Tg and WT mice were compared for density of astrocytes expressing activation markers and astrocytic morphology. In animals with comparable infarct size, overexpression of Hsp72 reduced the density of GFAP- and vimentin-expressing cells, and decreased astrocyte morphological complexity 72 h following stroke. However, by 30 days astrocyte activation was similar between genotypes. These data indicate that early modulation of astrocyte activation provides an additional novel mechanism associated with Hsp72 overexpression in the setting of ischemia.

Microarray-based gene expression analysis of an animal model for closed head injury

OBJECTIVE

Traumatic brain injury (TBI) is a major cause of death and disability in both children and the elderly. Mortality from TBI is said account for 1-2% of all deaths. One-third to one-half of all traumatic deaths is due to head injury. Of those who survive, the majority is left with significant disabilities, including 3% who remain in a vegetative state and only approximately 30% who make a good recovery. Microarray studies and other genomic techniques facilitate the discovery of new targets for the treatment of diseases, which aids in drug development, immunotherapeutics and gene therapy. Gene expression profiling or microarray analysis enables the measurement of thousands of genes in a single RNA sample.

METHODS

In this study, adult Wistar-albino rats underwent TBI using a trauma device. Brain tissues and blood samples were taken for gene expression at 1, 12 and 48 h post-trauma and were then analysed via microarray. Total RNA was isolated using an RNeasy Mini Kit (QIAGEN-Sample & Assay Technologies, Hilden, Germany) and tested using a 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA). Overall changes in gene expression were evaluated using Agilent Whole Rat Genome 4 × 44 K oligonucleotide arrays and analysed with GeneSpring (GeneSpring 6.1, Silicon Genetics, Redwood City, CA) software. Only genes with a signal-to-noise ratio of above 2 in the experiments were included in the statistical analysis.

RESULTS

ANOVA (p<0.05) was performed to identify differentially expressed probe sets. Additional filtering (minimum 2-fold change) was applied to extract the most differentially expressed genes based on the study groups (Control vs. 1st hour, Control vs. 12th hour, Control vs. 48th hour). Differentially expressed genes were detected via microarray analysis. A gene interaction-based network investigation of the genes that were identified via traditional microarray data analysis describes a significantly relevant gene network that includes the C1ql2, Cbnl, Sdc1, Bdnf, MMP9, and Cd47 genes, which were differentially expressed compared with the controls.

CONCLUSIONS

In this study, we will review the current understanding of the genetic susceptibility of TBI with microarrays. Our results highlight the importance of genes that control the response of the brain to injury as well as the suitability of microarrays for identifying specific targets for further study.

SHPS-1 deficiency induces robust neuroprotection against experimental stroke by attenuating oxidative stress

Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1), also known as Signal-regulatory protein alpha (SIRPα) or SIRPA is a transmembrane protein that is predominantly expressed in neurons, dendritic cells, and macrophages. This study was conducted to investigate the role of SHPS-1 in the oxidative stress and brain damage induced by acute focal cerebral ischemia. Wild-type (WT) and SHPS-1 mutant (MT) mice were subjected to middle cerebral artery occlusion (60 min) followed by reperfusion. SHPS-1 MT mice had significantly reduced infarct volumes and improved neurological function after brain ischemia. In addition, neural injury and oxidative stress were inhibited in SHPS-1 MT mice. The mRNA and protein levels of the antioxidant genes nuclear factor-E2-related factor 2 (Nrf2) and heme oxygenase 1 were up-regulated in SHPS-1 MT mice. The SHPS-1 mutation suppressed the phosphorylation of SHP-1 and SHP-2 and increased the phosphorylation of Akt and GSK3β. These results provide the first demonstration that SHPS-1 plays an important role in the oxidative stress and brain injury induced by acute cerebral ischemia. The activation of Akt signaling and the up-regulation of Nrf2 and heme oxygenase 1 likely account for the protective effects that were observed in the SHPS-1 MT mice.

Therapeutic Targeting of CD47 to Modulate Tissue Responses to Ischemia and Radiation

CD47 is a widely expressed cell surface receptor that serves as a counter-receptor for signal regulatory protein-α and as a receptor for the secreted matricellular protein thrombospondin-1. Thrombospondin-1 signaling through CD47 regulates cellular signaling pathways that control cell survival, growth, motility, mitochondrial biogenesis, arterial vasoactive responses to physiologic vasodilators and blood flow, and responsiveness to growth factors. Studies employing mice lacking either thrombospondin-1 or CD47 have revealed an important role for this receptor-ligand interaction in tissue responses to injury and stress. These null mice show enhanced recovery from soft tissue fixed ischemic injuries, ischemia reperfusion injuries, and radiation injuries. These studies have led to development of antisense strategies to locally or globally suppress CD47 gene expression. A translation-blocking CD47 morpholino improves tissue survival in skin flap and hindlimb fixed ischemia models, full thickness skin grafts, and a liver ischemia/reperfusion model of organ transplantation in mice. Furthermore, the benefits of morpholino treatment extend to aged mice and mice with dysregulated fat metabolism that characteristically exhibit impaired recovery from ischemic injuries. Activity of the morpholino was also demonstrated for treatment of ischemic injury in miniature pigs. Treatment with the CD47 morpholino protects mice from major effects of ionizing radiation including alopecia, deterioration of muscle function, soft tissue and cutaneous fibrosis, and loss of hematopoietic stem cells in bone marrow. Remarkably, the same treatment does not protect tumors but instead enhances their ablation by irradiation. We discuss prospects for further development of CD47 antisense therapeutics for clinical applications including reconstructive surgery, organ transplantation, angioplasty, and cancer.

Induction of vascular endothelial growth factor and matrix metalloproteinase-9 via CD47 signaling in neurovascular cells

Neurovascular injury comprises a wide spectrum of pathophysiology that underlies the progression of brain injury after cerebral ischemia. Recently, it has been shown that activation of the integrin-associated protein CD47 mediates the development of blood-brain barrier injury and edema after cerebral ischemia. However, the mechanisms that mediate these complex neurovascular effects of CD47 remain to be elucidated. Here, we compare the effects of CD47 signaling in brain endothelial cells, astrocytes, and pericytes. Exposure to 4N1 K, a specific CD47-activating peptide derived from the major CD47 ligand thrombospondin-1, upregulated two major neurovascular mediators, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9), in brain endothelial cells and astrocytes. No changes were detected in pericytes. These findings may provide a potential mechanism for CD47-induced changes in blood-brain barrier homeostasis, and further suggest that CD47 may be a relevant neurovascular target in stroke.

Neurovascular effects of CD47 signaling: promotion of cell death, inflammation, and suppression of angiogenesis in brain endothelial cells in vitro

The concept of the neurovascular unit emphasizes that common signals and substrates underlie the physiology and pathophysiology of neuronal and endothelial compartments in brain. Recent data suggest that activation of the integrin-associated protein CD47 promotes neuronal cell death. Is it possible that CD47 may also negatively affect cerebral endothelial cells? Exposure of wild-type primary mouse cerebral endothelial cells to the CD47 ligand thrombospondin 1 (TSP-1) induced an increasing amount of cell death, whereas cytotoxicity was significantly decreased in cerebral endothelial cells derived from CD47 knockout mice. The specific CD47-activating peptide, 4N1K, similarly induced cell death in human brain microvascular endothelial cells. Promotion of inflammation was also involved because lower TSP-1 was able to up-regulate the adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Finally, CD47 signaling may suppress angiogenesis because 4N1K significantly inhibited endothelial cell migration and tube formation in vitro. We conclude that CD47 signaling can negatively affect the viability and function of cerebral endothelial cells, further supporting the notion that CD47 may be a potential neurovascular target for stroke and brain injury.

CD47 gene knockout protects against transient focal cerebral ischemia in mice

CD47 is a cell surface glycoprotein that helps mediate neutrophil transmigration across blood vessels. The present study was performed to determine whether absence of the CD47 gene decreases focal ischemic brain damage. Mice were subjected to 90 min middle cerebral artery occlusion. CD47 knockout mice were compared against matching wildtype mice. CD47 expression was checked by Western blotting. Infarct volume and ischemic brain swelling were quantified with cresyl violet-stained brain sections at 24 and 72 h after ischemia. The tight junction protein claudin-5 was detected by imunohistochemistry. Two surrogate markers of neuroinflammation, brain levels of matrix metalloproteinase-9 (MMP-9) and infiltration of neutrophils, were assessed by immunohistochemistry. Western blots confirmed that CD47 was absent in knockout brains. Ischemia did not appear to upregulate total brain levels of CD47 in WT mice. In CD47 knockout mice, infarct volumes were reduced at 24 and 72 h after ischemia, and hemispheric swelling was decreased at 72 h. Loss of claudin-5 was observed in ischemic WT brain. This effect was ameliorated in CD47 knockout brains. Extravasation of neutrophils into the brain parenchyma was significantly reduced in CD47 knockout mice compared to wildtype mice. MMP-9 appeared to be upregulated in microvessels within ischemic brain. MMP-9 levels were markedly lower in CD47 knockout brains compared to wildtype brains. We conclude that CD47 is broadly involved in neuroinflammation, and this integrin-associated-protein plays a role in promoting MMP-9 upregulaton, neutrophil extravasation, brain swelling and progression of acute ischemic brain injury.