Rapid unleashing of macrophage efferocytic capacity via transcriptional pause release

Efferocytosis at the frontline of homeostasis: Shaping the bone microenvironment and therapeutic implications in related diseases

Bone is a dynamic tissue that constantly undergoes remodeling processes throughout life to maintain its structure and integrity. During this process, physiological bone turnover, which is shaped by apoptosis, occurs in cells in the bone microenvironment. The clearance of these apoptotic cells (ACs) is executed by phagocytes through a process called efferocytosis, which simply means taking to the grave "burial." Efferocytosis is a multistage process involving the recognition, binding, internalization, and digestion of ACs, culminating in the resolution of inflammation. Critically, aberrations in efferocytosis lead to the accumulation of apoptotic corpses, impairing tissue homeostasis and contributing to various pathologies as well as bone-related diseases. Emerging evidence suggests that modulating/activating efferocytosis at any stage represents a promising therapeutic strategy for managing bone-related diseases, especially those associated with aging and inflammation. This review discusses the current understanding of the cellular and molecular mechanisms of efferocytosis, its roles within the bone microenvironment, and potential therapeutic interventions targeting efferocytosis in age-related bone diseases.

Enhance Efferocytosis and Block the Macrophages-Platelets Feedback Loop for Targeted Treatment of Psoriasis

Efferocytosis of macrophages infiltrated in psoriatic lesions is mostly impaired, thus promoting the progression of psoriasis. Herein, we reveal that there exists a feedback loop between activated platelets and efferocytosis-impaired macrophages in psoriatic. Or rather, efferocytosis-impaired macrophages stimulate platelet activation, which in turn down-regulates the expression of the phagocytic receptor Mer on macrophages and polarizes macrophages to the M1-phenotype of weaker efferocytosis ability. Therefore, we construct a combined nanoplatform for more precise targeting to efferocytosis-impaired macrophages and activated platelets. The macrophage-targeting part of the nanoplatform efficiently orientates to efferocytosis-impaired macrophages through macrophage membrane encapsulation and targeting peptide modification. This increases the expression of Mer, simultaneously enhances the acidification and maturation of efferosomes, ultimately restores efferocytosis of macrophages, and promotes the phagocytosis and clearance of apoptotic cells. On the other hand, the activated platelet-targeting nanoparticles inhibit the activation of platelets, thus blocking the feedback loop and eventually preventing the down-regulation of Mer expression on macrophages. Furthermore, the combined nanoplatform suppresses the infiltration of macrophages and platelets in psoriatic lesions, reduces the release of pro-inflammatory factors such as IL-17A, and consequently improves the therapeutic effect of psoriasis and prevention of its recurrence in vivo. Collectively, this two-pronged strategy with multifunctionality in repairing efferocytosis, inhibiting platelet activation, and blocking the feedback loop may provide options available for the treatment of psoriasis.

Dys-regulated phosphatidylserine externalization as a cell intrinsic immune escape mechanism in cancer

The negatively charged aminophospholipid, phosphatidylserine (PS), is typically restricted to the inner leaflet of the plasma membrane under normal, healthy physiological conditions. PS is irreversibly externalized during apoptosis, where it serves as a signal for elimination by efferocytosis. PS is also reversibly and transiently externalized during cell activation such as platelet and immune cell activation. These events associated with physiological PS externalization are tightly controlled by the regulated activation of flippases and scramblases. Indeed, improper regulation of PS externalization results in thrombotic diseases such as Scott Syndrome, a defect in coagulation and thrombin production, and in the case of efferocytosis, can result in autoimmunity such as systemic lupus erythematosus (SLE) when PS-mediated apoptosis and efferocytosis fails. The physiological regulation of PS is also perturbed in cancer and during viral infection, whereby PS becomes persistently exposed on the surface of such stressed and diseased cells, which can lead to chronic thrombosis and chronic immune evasion. In this review, we summarize evidence for the dysregulation of PS with a main focus on cancer biology and the pathogenic mechanisms for immune evasion and signaling by PS, as well as the discussion of new therapeutic strategies aimed to target externalized PS. We posit that chronic PS externalization is a universal and agnostic marker for diseased tissues, and in cancer, likely reflects a cell intrinsic form of immune escape. The continued development of new therapeutic strategies for targeting PS also provides rationale for their co-utility as adjuvants and with immune checkpoint therapeutics.

Exploring CAR-macrophages in non-tumor diseases: Therapeutic potential beyond cancer

BACKGROUND

After significant advancements in tumor treatment, personalized cell therapy based on chimeric antigen receptors (CAR) holds promise for transforming the management of various diseases. CAR-T therapy, the first approved CAR cell therapy product, has demonstrated therapeutic potential in treating infectious diseases, autoimmune disorders, and fibrosis. CAR-macrophages (CAR-Ms) are emerging as a promising approach in CAR immune cell therapy, particularly for solid tumor treatment, highlighting the feasibility of using macrophages to eliminate pathogens and abnormal cells.

AIM OF REVIEW

This review summarizes the progress of CAR-M therapy in non-tumor diseases and discusses various CAR intracellular activation domain designs and their potential to optimize therapeutic effects by modulating interactions between cellular components in the tissue microenvironment and CAR-M. Additionally, we discuss the characteristics and advantages of CAR-M therapy compared to traditional medicine and CAR-T/NK therapy, as well as the challenges and prospects for the clinical translation of CAR-M.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review provides a comprehensive understanding of CAR-M for the treatment of non-tumor diseases, analyzes the advantages and characteristics of CAR-M therapy, and highlights the important impact of CAR intracellular domain design on therapeutic efficacy. In addition, the challenges and clinical translation prospects of developing CAR-M as a new cell therapy are discussed.

Biochemical and biophysical mechanisms macrophages use to tune phagocytic appetite

Macrophages phagocytose, or eat, pathogens, dead cells and cancer cells. To activate phagocytosis, macrophages recognize 'eat me' signals like IgG and phosphatidylserine on the target cell surface. Macrophages must carefully adjust their phagocytic appetite to ignore non-specific or transient eat me signal exposure on healthy cells while still rapidly recognizing pathogens and debris. Depending on the context, macrophages can increase their appetite for phagocytosis, to prioritize an effective immune response, or decrease their appetite, to avoid damage to healthy tissue during homeostasis. In this Review, we discuss the biochemical and biophysical mechanisms that macrophages employ to increase or decrease their sensitivity or capacity for phagocytosis. We discuss evidence that macrophages tune their sensitivity via several mechanisms, including altering the balance of activating and inhibitory receptor expression, altering the availability of activating receptors, as well as influencing their clustering and mobility, and modulating inhibitory receptor location. We also highlight how membrane availability limits the capacity of macrophages for phagocytosis and discuss potential mechanisms to promote membrane recycling and increase phagocytic capacity. Overall, this Review highlights recent work detailing the molecular toolkit that macrophages use to alter their appetite.

Extracellular Vesicles From Bone Marrow-Derived Macrophages Enriched in ARG1 Enhance Microglial Phagocytosis and Haematoma Clearance Following Intracerebral Haemorrhage

Microglial phagocytosis of haematomas is crucial for neural functional recovery following intracerebral haemorrhage (ICH), a process regulated by various factors from within and outside the central nervous system (CNS). Extracellular vesicles (EVs), significant mediators of intercellular communication, have been demonstrated to play a pivotal role in the pathogenesis and progression of CNS diseases. However, the regulatory role of endogenous EVs on the phagocytic capacity of microglia post-ICH remains elusive. Utilising multi-omics analysis of brain tissue-derived EVs proteomics and single-cell RNA sequencing, this study identified that bone marrow-derived macrophages (BMDMs) potentially enhance microglial phagocytosis via EVs following ICH. By blocking BMDMs and reducing ARG1 in BMDM-derived EVs, we demonstrated that BMDMs facilitate erythrophagocytosis by delivering ARG1 to microglia via EVs post-ICH. EVs-carried ARG1 was found to augment phagocytosis by promoting RAC1-dependent cytoskeletal remodelling in microglia. Collectively, this research uncovers an intercellular communication pathway from BMDMs to microglia mediated by EVs post-ICH. This provides a novel paradigm for EV-mediated intercellular communication mechanisms and suggests a promising therapeutic potential for BMDM-derived EVs in the treatment of ICH.