CD47 antibody blockade suppresses microglia-dependent phagocytosis and monocyte transition to macrophages, impairing recovery in EAE

Gene expression profiles of endothelium, microglia and oligodendrocytes in hippocampus of post-stroke depression rat at single cell resolution

Post-stroke depression (PSD) is a common but severe mental complication after stroke. However, the cellular and molecular understanding of PSD is still yet to be illustrated. In current study, we prepared PSD rat model (MD) via unilateral middle cerebral artery occlusion (MCAO) and chronic stress stimulation (DEPR), and isolated hippocampal tissues for single cell sequencing of 10x Genomics Chromium. First, we determined the presence of the increased cell population of endothelium and microglia and the compromised oligodendrocytes in MD compared to NC, MCAO and DEPR. The enriched functions of highly variable genes (HVGs) of endothelium and microglia suggested a reinforced blood-brain barrier in MD. Next, cell clusters of endothelium, microglia and oligodendrocytes were individually analyzed, and the subtypes with distinct functions were identified. The presence of expression profiles, intercellular communications and signaling pathways of these three cell populations of PSD displayed a similar but more aggressive appearance with DEPR compared to MCAO and NC. Taken together, this study characterized the specific gene profile of endothelium, microglia and oligodendrocytes of hippocampal PSD by single cell sequencing, emphasizing the crosstalk among them to provide theoretical basis for the in-depth mechanism research and drug therapy of PSD.

Beyond cancer: The potential application of CD47-based therapy in non-cancer diseases

CD47 is an immune checkpoint widely regarded as a 'don't eat me' signal. CD47-based anti-cancer therapy has received considerable attention, with a significant number of clinical trials conducted. While anti-cancer therapies based on CD47 remain a focal point of interest among researchers, it is noteworthy that an increasing number of studies have found that CD47-based therapy ameliorated the pathological status of non-cancer diseases. This review aims to provide an overview of the recent progress in comprehending the role of CD47-based therapy in non-cancer diseases, including diseases of the circulatory system, nervous system, digestive system, and so on. Furthermore, we sought to delineate the promising mechanisms of CD47-based therapy in treating non-cancer diseases. Our findings suggest that CD47-based agents may exert their effect by regulating phagocytosis, regulating T cells, dendritic cells, and neutrophils, and regulating the secretion of cytokines and chemokines. Additionally, we put forward the orientation of further research to bring to light the potential of CD47 and its binding partners as a target in non-cancer diseases.

The emerging role of microglia in the development and therapy of multiple sclerosis

Microglia are innate immune cells that maintain homeostasis of the central nervous system (CNS) and affect various neurodegenerative diseases, especially multiple sclerosis (MS). MS is an autoimmune disease of the CNS characterized by persistent inflammation, diffuse axonal damage, and microglia activation. Recent studies have shown that microglia are extremely related to the pathological state of MS and play an important role in the development of MS. This article reviews the multiple roles of microglia in the progression of MS, including the regulatory role of microglia in inflammation, remyelination, oxidative stress, the influence of phagocytosis and antigen-presenting capacity of microglia, and the recent progress by using microglia as a target for MS therapy. Microglia modulation may be a potential way for better MS therapy.

Redefining our vision: an updated guide to the ocular immune system

Balanced immune responses in the eyes are crucial to preserve vision. The ocular immune system has long been considered distinct, owing to the so-called 'immune privilege' of its component tissues. More recently, intravital imaging and transcriptomic techniques have reshaped scientific understanding of the ocular immune landscape, such as revealing the specialization of immune cell populations in the various tissues of the eye. As knowledge of the phenotypes of corneal and retinal immune cells has evolved, links to both the systemic immune system, and the central and peripheral nervous systems, have been identified. Using intravital imaging, T cells have recently been found to reside in, and actively patrol, the healthy human cornea. Disease-associated retinal microglia with links to retinal degeneration have also been identified. This Review provides an updated guide to the ocular immune system, highlighting current knowledge of the immune cells that are present in steady-state and specific diseased ocular tissues, as well as evidence for their relationship to systemic disease. In addition, we discuss emerging intravital imaging techniques that can be used to visualize immune cell morphology and dynamics in living human eyes and how these could be applied to advance understanding of the human immune system.

Phospholipase D Family Member 4 Regulates Microglial Phagocytosis and Remyelination via the AKT Pathway in a Cuprizone-Induced Multiple Sclerosis Mouse Model

AIMS

Remyelination is an endogenous repair process that is often deficient in multiple sclerosis (MS). Stimulation of remyelination is thought to help limit the progression of MS. This study aimed to investigate the expression pattern and function of a microglial phagocytosis-related gene, phospholipase D family member 4 (PLD4), in a cuprizone (CPZ)-induced MS mouse model.

METHODS

The extent of remyelination was assessed using LFB staining. Myelin phagocytosis assay was used to investigate the effect of Pld4 on microglial phagocytic activity.

RESULTS

Pld4 was upregulated in the corpus callosum during demyelination and remyelination. AAV9-mediated Pld4 deficiency impaired remyelination and reduced the number of Olig2-positive cells. In the corpus callosum of Pld4-deficient mice, the microglial phagocytosis marker MAC2 was reduced, accompanied by inhibition of TrkA/AKT signaling. Similarly, the phagocytosis assay showed that Pld4 knockdown significantly inhibited myelin debris phagocytosis by BV2 cells. The AKT activator SC79 reversed the Pld4 deficiency-induced inhibition of microglial phagocytic activity and rescued the impaired remyelination in Pld4-deficient mice.

CONCLUSION

PLD4 is upregulated in CPZ-induced MS and modulates microglial phagocytosis and remyelination via the AKT pathway. Our findings provide experimental evidence for a better understanding of the molecular mechanism of MS.

Cell autonomous functions of CD47 in regulating cellular plasticity and metabolic plasticity

CD47 is a ubiquitously expressed cell surface receptor, which is widely known for preventing macrophage-mediated phagocytosis by interacting with signal regulatory protein α (SIRPα) on the surface of macrophages. In addition to its role in phagocytosis, emerging studies have reported numerous noncanonical functions of CD47 that include regulation of various cellular processes such as proliferation, migration, apoptosis, differentiation, stress responses, and metabolism. Despite lacking an extensive cytoplasmic signaling domain, CD47 binds to several cytoplasmic proteins, particularly upon engaging with its secreted matricellular ligand, thrombospondin 1. Indeed, the regulatory functions of CD47 are greatly influenced by its interacting partners. These interactions are often cell- and context-specific, adding a further level of complexity. This review addresses the downstream cell-intrinsic signaling pathways regulated by CD47 in various cell types and environments. Some of the key pathways modulated by this receptor include the PI3K/AKT, MAPK/ERK, and nitric oxide signaling pathways, as well as those implicated in glucose, lipid, and mitochondrial metabolism. These pathways play vital roles in maintaining tissue homeostasis, highlighting the importance of understanding the phagocytosis-independent functions of CD47. Given that CD47 expression is dysregulated in a variety of cancers, improving our understanding of the cell-intrinsic signals regulated by this molecule will help advance the development of CD47-targeted therapies.

Cortical CD200-CD200R and CD47-SIRPα expression is associated with multiple sclerosis pathology

Control of microglia activity through CD200-CD200R and CD47-SIRPα interactions has been implicated in brain homeostasis. Here, we assessed CD200, CD47, CD200R and SIRPα expression with qPCR and immunohistochemistry in multiple sclerosis (MS) normal-appearing cortical grey matter (NAGM), normal-appearing white matter (NAWM), cortical grey matter (GM) lesions and perilesional GM, and compared this to control GM and white matter (WM), to investigate possible altered control of microglia in MS. In MS NAGM, CD200 expression is lower compared with control GM, specifically in cortical layers 1 and 2, and CD200 expression in NAGM negatively correlates with the cortical lesion rate. Interestingly, NAGM and NAWM CD200 expression is positively correlated, and NAGM CD200 expression negatively correlates with the proportion of active and mixed WM lesions. In GM lesions, CD200 and CD47 expressions are lower compared with NAGM and perilesional GM. CD200R expression is lower in MS NAGM, whereas SIRPα was increased in and around GM lesions. Taken together, our data indicate that CD200 and CD47 play a role in GM MS lesion formation and progression, respectively, and that targeting CD200 pathways may offer therapeutic avenues to mitigate MS pathology in both WM and GM.

The aging mouse CNS is protected by an autophagy-dependent microglia population promoted by IL-34

Microglia harness an unutilized health-promoting potential in age-related neurodegenerative and neuroinflammatory diseases, conditions like progressive multiple sclerosis (MS). Our research unveils an microglia population emerging in the cortical brain regions of aging mice, marked by ERK1/2, Akt, and AMPK phosphorylation patterns and a transcriptome indicative of activated autophagy - a process critical for cellular adaptability. By deleting the core autophagy gene Ulk1 in microglia, we reduce this population in the central nervous system of aged mice. Notably, this population is found dependent on IL-34, rather than CSF1, although both are ligands for CSF1R. When aging mice are exposed to autoimmune neuroinflammation, the loss of autophagy-dependent microglia leads to neural and glial cell death and increased mortality. Conversely, microglial expansion mediated by IL-34 exhibits a protective effect. These findings shed light on an autophagy-dependent neuroprotective microglia population as a potential target for treating age-related neuroinflammatory conditions, including progressive MS.

Novel nano-carriers with N-formylmethionyl-leucyl-phenylalanine-modified liposomes improve effects of C16-angiopoietin 1 in acute animal model of multiple sclerosis

Gradual loss of neuronal structure and function due to impaired blood-brain barrier (BBB) and neuroinflammation are important factors in multiple sclerosis (MS) progression. Our previous studies demonstrated that the C16 peptide and angiopoietin 1 (Ang-1) compound (C + A) could modulate inflammation and vascular protection in many models of MS. In this study, nanotechnology and a novel nanovector of the leukocyte chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) were used to examine the effects of C + A on MS. The acute experimental autoimmune encephalomyelitis (EAE) model of MS was established in Lewis rats. The C + A compounds were conjugated to control nano-carriers and fMLP-nano-carriers and administered to animals by intravenous injection. The neuropathological changes in the brain cortex and spinal cord were examined using multiple approaches. The stimulation of vascular injection sites was examined using rabbits. The results showed that all C + A compounds (C + A alone, nano-carrier C + A, and fMLP-nano-carrier C + A) reduced neuronal inflammation, axonal demyelination, gliosis, neuronal apoptosis, vascular leakage, and BBB impairment induced by EAE. In addition, the C + A compounds had minimal side effects on liver and kidney functions. Furthermore, the fMLP-nano-carrier C + A compound had better effects compared to C + A alone and the nano-carrier C + A. This study indicated that the fMLP-nano-carrier C + A could attenuate inflammation-related pathological changes in EAE and may be a potential therapeutic strategy for the treatment of MS and EAE.

High-affinity decoy protein, nFD164, with an inactive Fc region as a potential therapeutic drug targeting CD47

CD47, as an innate immune checkpoint molecule, is an important target of cancer immunotherapy. We previously reported that a high-affinity SIRPα variant FD164 fused with IgG1 subtype Fc showed a better antitumor effect than wild-type SIRPα in an immunodeficient tumor-bearing model. However, CD47 is widely expressed in blood cells, and the drugs targeting CD47 may cause potential hematological toxicity. Herein, we modified the FD164 molecule by Fc mutation (N²⁹⁷A) to inactivate the Fc-related effector function and named it nFD164. Moreover, we further studied the potential of nFD164 as a candidate drug targeting CD47, including the stability, in vitro activity, antitumor activity of single or combined drugs in vivo, and hematological toxicity in humanized CD47/SIRPα transgenic mouse model. The results show that nFD164 maintains strong binding activity to CD47 on tumor cells, but has weak binding activity with red blood cells or white blood cells, and nFD164 has good drug stability under accelerated conditions (high temperature, bright light and freeze-thaw cycles). More importantly, in the immunodeficient or humanized CD47/SIRPα transgenic mice bearing tumor model, the combination of nFD164 and anti-CD20 antibody or anti-mPD-1 antibody had a synergistic antitumor effect. Especially in transgenic mouse models, nFD164 combined with anti-mPD-1 significantly enhanced tumor suppressive activity compared with anti-mPD-1 (P < 0.01) or nFD164 (P < 0.01) as a single drug and had fewer hematology-related side effects than FD164 or Hu5F9-G4. When these factors are taken together, nFD164 is a promising high-affinity CD47-targeting drug candidate with better stability, potential antitumor activity, and improved safety profile.

Very-long-chain fatty acids induce glial-derived sphingosine-1-phosphate synthesis, secretion, and neuroinflammation

VLCFAs (very-long-chain fatty acids) are the most abundant fatty acids in myelin. Hence, during demyelination or aging, glia are exposed to higher levels of VLCFA than normal. We report that glia convert these VLCFA into sphingosine-1-phosphate (S1P) via a glial-specific S1P pathway. Excess S1P causes neuroinflammation, NF-κB activation, and macrophage infiltration into the CNS. Suppressing the function of S1P in fly glia or neurons, or administration of Fingolimod, an S1P receptor antagonist, strongly attenuates the phenotypes caused by excess VLCFAs. In contrast, elevating the VLCFA levels in glia and immune cells exacerbates these phenotypes. Elevated VLCFA and S1P are also toxic in vertebrates based on a mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). Indeed, reducing VLCFA with bezafibrate ameliorates the phenotypes. Moreover, simultaneous use of bezafibrate and fingolimod synergizes to improve EAE, suggesting that lowering VLCFA and S1P is a treatment avenue for MS.

Contribution of adaptive immunity to human COPD and experimental models of emphysema

The pathophysiology of chronic obstructive pulmonary disease (COPD) and the undisputed role of innate immune cells in this condition have dominated the field in the basic research arena for many years. Recently, however, compelling data suggesting that adaptive immune cells may also contribute to the progressive nature of lung destruction associated with COPD in smokers have gained considerable attention. The histopathological changes in the lungs of smokers can be limited to the large or small airways, but alveolar loss leading to emphysema, which occurs in some individuals, remains its most significant and irreversible outcome. Critically, however, the question of why emphysema progresses in a subset of former smokers remained a mystery for many years. The recognition of activated and organized tertiary T- and B-lymphoid aggregates in emphysematous lungs provided the first clue that adaptive immune cells may play a crucial role in COPD pathophysiology. Based on these findings from human translational studies, experimental animal models of emphysema were used to determine the mechanisms through which smoke exposure initiates and orchestrates adaptive autoreactive inflammation in the lungs. These models have revealed that T helper (Th)1 and Th17 subsets promote a positive feedback loop that activates innate immune cells, confirming their role in emphysema pathogenesis. Results from genetic studies and immune-based discoveries have further provided strong evidence for autoimmunity induction in smokers with emphysema. These new findings offer a novel opportunity to explore the mechanisms underlying the inflammatory landscape in the COPD lung and offer insights for development of precision-based treatment to halt lung destruction.

Neuronal signal-regulatory protein alpha drives microglial phagocytosis by limiting microglial interaction with CD47 in the retina

Microglia utilize their phagocytic activity to prune redundant synapses and refine neural circuits during precise developmental periods. However, the neuronal signals that control this phagocytic clockwork remain largely undefined. Here, we show that neuronal signal-regulatory protein alpha (SIRPα) is a permissive cue for microglial phagocytosis in the developing murine retina. Removal of neuronal, but not microglial, SIRPα reduced microglial phagocytosis, increased synpase numbers, and impaired circuit function. Conversely, prolonging neuronal SIRPα expression extended developmental microglial phagocytosis. These outcomes depended on the interaction of presynaptic SIRPα with postsynaptic CD47. Global CD47 deficiency modestly increased microglial phagocytosis, while CD47 overexpression reduced it. This effect was rescued by coexpression of neuronal SIRPα or codeletion of neuronal SIRPα and CD47. These data indicate that neuronal SIRPα regulates microglial phagocytosis by limiting microglial SIRPα access to neuronal CD47. This discovery may aid our understanding of synapse loss in neurological diseases.