Mitochondrial Fission Promotes the Continued Clearance of Apoptotic Cells by Macrophages

Drp1 Promotes Macrophage M1 Polarization and Inflammatory Response in Autoimmune Myocarditis by Driving Mitochondrial Fission

Autoimmune myocarditis (AM) is characterized by an intricate inflammatory response within the myocardium. Dynamin-related protein 1 (Drp1), a pivotal modulator of mitochondrial fission, plays a role in the pathogenesis of various diseases. A myosin-induced experimental autoimmune myocarditis (EAM) mouse model was successfully established. Flow cytometry was employed to detect M1/M2-like macrophages. Mitochondrial fragmentation was assessed using Mito-Tracker Red CMXRos. Drp1 was upregulated and activated in EAM mice. Depletion of Drp1 was observed to mitigate inflammation, macrophage infiltration and M1 polarization within the cardiac tissue of EAM mice. In M1-like macrophages derived from the hearts of EAM mice, Drp1 was found to promote mitochondrial fission and diminish mitochondrial fusion. Furthermore, the depletion of Drp1 reduced the NF-κB-related pro-inflammatory response in EAM-associated M1-like macrophages. Drp1 drives mitochondrial fission in macrophages, driving their M1 polarization and the subsequent inflammatory response. Drp1 may represent an effective target for the prevention and treatment of AM.

Multifaceted roles of mitochondria in asthma

Mitochondria are essential organelles within cells, playing various roles in numerous cellular processes, including differentiation, growth, apoptosis, energy conversion, metabolism, and cellular immunity. The phenotypic variation of mitochondria is specific to different tissues and cell types, resulting in significant differences in their function, morphology, and molecular characteristics. Asthma is a chronic, complex, and heterogeneous airway disease influenced by external factors such as environmental pollutants and allergen exposure, as well as internal factors at the tissue, cellular, and genetic levels, including lung and airway structural cells, immune cells, granulocytes, and mast cells. Therefore, a comprehensive understanding of the specific responses of mitochondria to various external environmental stimuli and internal changes are crucial for elucidating the pathogenesis of asthma. Previous research on mitochondrial-targeted therapy for asthma has primarily focused on antioxidants. Consequently, it is necessary to summarize the multifaceted roles of mitochondria in the pathogenesis of asthma to discover additional strategies targeting mitochondria in this context. In this review, our goal is to describe the changes in mitochondrial function in response to various exposure factors across different cell types and other relevant factors in the context of asthma, utilizing a new mitochondrial terminology framework that encompasses cell-dependent mitochondrial characteristics, molecular features, mitochondrial activity, function, and behavior.

Mechanism of Efferocytosis in Determining Ischaemic Stroke Resolution-Diving into Microglia/Macrophage Functions and Therapeutic Modality

After ischaemic cerebral vascular injury, efferocytosis-a process known as the efficient clearance of apoptotic cells (ACs) by various phagocytes in both physiological and pathological states-is crucial for maintaining central nervous system (CNS) homeostasis and regaining prognosis. The mechanisms of efferocytosis in ischaemic stroke and its influence on preventing inflammation progression from secondary injury were still not fully understood, despite the fact that the fundamental process of efferocytosis has been described in a series of phases, including AC recognition, phagocyte engulfment, and subsequent degradation. The genetic reprogramming of macrophages and brain-resident microglia after an ischaemic stroke has been equated by some researchers to that of the peripheral blood and brain. Based on previous studies, some molecules, such as signal transducer and activator of transcription 6 (STAT6), peroxisome proliferator-activated receptor γ (PPARG), CD300A, and sigma non-opioid intracellular receptor 1 (SIGMAR1), were discovered to be largely associated with aspects of apoptotic cell elimination and accompanying neuroinflammation, such as inflammatory cytokine release, phenotype transformation, and suppressing of antigen presentation. Exacerbated stroke outcomes are brought on by defective efferocytosis and improper modulation of pertinent signalling pathways in blood-borne macrophages and brain microglia, which also results in subsequent tissue inflammatory damage. This review focuses on recent researches which contain a number of recently discovered mechanisms, such as studies on the relationship between benign efferocytosis and the regulation of inflammation in ischaemic stroke, the roles of some risk factors in disease progression, and current immune approaches that aim to promote efferocytosis to treat some autoimmune diseases. Understanding these pathways provides insight into novel pathophysiological processes and fresh characteristics, which can be used to build cerebral ischaemia targeting techniques.

Efferocytosis and Bone Dynamics

PURPOSE OF REVIEW

This review summarizes the recently published scientific evidence regarding the role of efferocytosis in bone dynamics and skeletal health.

RECENT FINDINGS

Several types of efferocytes have been identified within the skeleton, with macrophages being the most extensively studied. Efferocytosis is not merely a 'clean-up' process vital for maintaining skeletal homeostasis; it also plays a crucial role in promoting resolution pathways and orchestrating bone dynamics, such as osteoblast-osteoclast coupling during bone remodeling. Impaired efferocytosis has been associated with aging-related bone loss and various skeletal pathologies, including osteoporosis, osteoarthritis, rheumatoid arthritis, and metastatic bone diseases. Accordingly, emerging evidence suggests that targeting efferocytic mechanisms has the potential to alleviate these conditions. While efferocytosis remains underexplored in the skeleton, recent discoveries have shed light on its pivotal role in bone dynamics, with important implications for skeletal health and pathology. However, there are several knowledge gaps and persisting technical limitations that must be addressed to fully unveil the contributions of efferocytosis in bone.

Crosstalk between ferroptosis and macrophages: potential value for targeted treatment in diseases

Ferroptosis is a newly identified form of programmed cell death that is connected to iron-dependent lipid peroxidization. It involves a variety of physiological processes involving iron metabolism, lipid metabolism, oxidative stress, and biosynthesis of nicotinamide adenine dinucleotide phosphate, glutathione, and coenzyme Q10. So far, it has been discovered to contribute to the pathological process of many diseases, such as myocardial infarction, acute kidney injury, atherosclerosis, and so on. Macrophages are innate immune system cells that regulate metabolism, phagocytize pathogens and dead cells, mediate inflammatory reactions, promote tissue repair, etc. Emerging evidence shows strong associations between macrophages and ferroptosis, which can provide us with a deeper comprehension of the pathological process of diseases and new targets for the treatments. In this review, we summarized the crosstalk between macrophages and ferroptosis and anatomized the application of this association in disease treatments, both non-neoplastic and neoplastic diseases. In addition, we have also addressed problems that remain to be investigated, in the hope of inspiring novel therapeutic strategies for diseases.

Young small extracellular vesicles rejuvenate replicative senescence by remodeling Drp1 translocation-mediated mitochondrial dynamics

BACKGROUND

Human mesenchymal stem cells have attracted interest in regenerative medicine and are being tested in many clinical trials. In vitro expansion is necessary to provide clinical-grade quantities of mesenchymal stem cells; however, it has been reported to cause replicative senescence and undefined dysfunction in mesenchymal stem cells. Quality control assessments of in vitro expansion have rarely been addressed in ongoing trials. Young small extracellular vesicles from the remnant pulp of human exfoliated deciduous teeth stem cells have demonstrated therapeutic potential for diverse diseases. However, it is still unclear whether young small extracellular vesicles can reverse senescence-related declines.

RESULTS

We demonstrated that mitochondrial structural disruption precedes cellular dysfunction during bone marrow-derived mesenchymal stem cell replication, indicating mitochondrial parameters as quality assessment indicators of mesenchymal stem cells. Dynamin-related protein 1-mediated mitochondrial dynamism is an upstream regulator of replicative senescence-induced dysfunction in bone marrow-derived mesenchymal stem cells. We observed that the application of young small extracellular vesicles could rescue the pluripotency dissolution, immunoregulatory capacities, and therapeutic effects of replicative senescent bone marrow-derived mesenchymal stem cells. Mechanistically, young small extracellular vesicles could promote Dynamin-related protein 1 translocation from the cytoplasm to the mitochondria and remodel mitochondrial disruption during replication history.

CONCLUSIONS

Our findings show that Dynamin-related protein 1-mediated mitochondrial disruption is associated with the replication history of bone marrow-derived mesenchymal stem cells. Young small extracellular vesicles from human exfoliated deciduous teeth stem cells alleviate replicative senescence by promoting Dynamin-related protein 1 translocation onto the mitochondria, providing evidence for a potential rejuvenation strategy.

Macrophages in vascular disease: Roles of mitochondria and metabolic mechanisms

Macrophages are a dynamic cell type of the immune system implicated in the pathophysiology of vascular diseases and are a major contributor to pathological inflammation. Excessive macrophage accumulation, activation, and polarization is observed in aortic aneurysm (AA), atherosclerosis, and pulmonary arterial hypertension. In general, macrophages become activated and polarized to a pro-inflammatory phenotype, which dramatically changes cell behavior to become pro-inflammatory and infiltrative. These cell types become cumbersome and fail to be cleared by normal mechanisms such as autophagy. The result is a hyper-inflammatory environment causing the recruitment of adjacent cells and circulating immune cells to further augment the inflammatory response. In AA, this leads to excessive ECM degradation and chemokine secretion, ultimately causing macrophages to dominate the immune cell landscape in the aortic wall. In atherosclerosis, monocytes are recruited to the vascular wall, where they polarize to the pro-inflammatory phenotype and induce inflammatory pathway activation. This leads to the development of foam cells, which significantly contribute to neointima and necrotic core formation in atherosclerotic plaques. Pro-inflammatory macrophages, which affect other vascular diseases, present with fragmented mitochondria and corresponding metabolic dysfunction. Targeting macrophage mitochondrial dynamics has proved to be an exciting potential therapeutic approach to combat vascular disease. This review will summarize mitochondrial and metabolic mechanisms of macrophage activation, polarization, and accumulation in vascular diseases.

Efferocytosis drives a tryptophan metabolism pathway in macrophages to promote tissue resolution

Macrophage efferocytosis prevents apoptotic cell (AC) accumulation and triggers inflammation-resolution pathways. The mechanisms linking efferocytosis to resolution often involve changes in macrophage metabolism, but many gaps remain in our understanding of these processes. We now report that efferocytosis triggers an indoleamine 2,3-dioxygenase-1 (IDO1)-dependent tryptophan (Trp) metabolism pathway that promotes several key resolution processes, including the induction of pro-resolving proteins, such interleukin-10, and further enhancement of efferocytosis. The process begins with upregulation of Trp transport and metabolism, and it involves subsequent activation of the aryl hydrocarbon receptor (AhR) by the Trp metabolite kynurenine (Kyn). Through these mechanisms, macrophage IDO1 and AhR contribute to a proper resolution response in several different mouse models of efferocytosis-dependent tissue repair, notably during atherosclerosis regression induced by plasma low-density lipoprotein (LDL) lowering. These findings reveal an integrated metabolism programme in macrophages that links efferocytosis to resolution, with possible therapeutic implications for non-resolving chronic inflammatory diseases, notably atherosclerosis.

Aberrant mitochondrial DNA synthesis in macrophages exacerbates inflammation and atherosclerosis

There is a large body of evidence that cellular metabolism governs inflammation, and that inflammation contributes to the progression of atherosclerosis. However, whether mitochondrial DNA synthesis affects macrophage function and atherosclerosis pathology is not fully understood. Here we show, by transcriptomic analyzes of plaque macrophages, spatial single cell transcriptomics of atherosclerotic plaques, and functional experiments, that mitochondrial DNA (mtDNA) synthesis in atherosclerotic plaque macrophages are triggered by vascular cell adhesion molecule 1 (VCAM-1) under inflammatory conditions in both humans and mice. Mechanistically, VCAM-1 activates C/EBPα, which binds to the promoters of key mitochondrial biogenesis genes - Cmpk2 and Pgc1a. Increased CMPK2 and PGC-1α expression triggers mtDNA synthesis, which activates STING-mediated inflammation. Consistently, atherosclerosis and inflammation are less severe in Apoe-/- mice lacking Vcam1 in macrophages. Downregulation of macrophage-specific VCAM-1 in vivo leads to decreased expression of LYZ1 and FCOR, involved in STING signalling. Finally, VCAM-1 expression in human carotid plaque macrophages correlates with necrotic core area, mitochondrial volume, and oxidative damage to DNA. Collectively, our study highlights the importance of macrophage VCAM-1 in inflammation and atherogenesis pathology and proposes a self-acerbating pathway involving increased mtDNA synthesis.

Transcriptional analysis of efferocytosis in mouse skin wounds

Defects in apoptotic cell clearance, or efferocytosis, can cause inflammatory diseases and prevent tissue repair due in part to inducing a pro-repair transcriptional program in phagocytic cells like macrophages. While the cellular machinery and metabolic pathways involved in efferocytosis have been characterized, the precise efferocytic response of macrophages is dependent on the identity and macromolecular cues of apoptotic cells, and the complex tissue microenvironment in which efferocytosis occurs. Here, we find that macrophages undergoing active efferocytosis in mid-stage mouse skin wounds in vivo display a pro-repair gene program, while efferocytosis of apoptotic skin fibroblasts in vitro also induces an inflammatory transcription response. These data provide a resource for understanding how the skin wound environment influences macrophage efferocytosis and will be useful for future investigations that define the role of efferocytosis during tissue repair.

Therapeutic implication of targeting mitochondrial drugs designed for efferocytosis dysfunction

Efferocytosis refers to the process by which phagocytes remove apoptotic cells and related apoptotic products. It is essential for the growth and development of the body, the repair of damaged or inflamed tissues, and the balance of the immune system. Damaged efferocytosis will cause a variety of chronic inflammation and immune system diseases. Many studies show that efferocytosis is a process mediated by mitochondria. Mitochondrial metabolism, mitochondrial dynamics, and communication between mitochondria and other organelles can all affect phagocytes' clearance of apoptotic cells. Therefore, targeting mitochondria to modulate phagocyte efferocytosis is an anticipated strategy to prevent and treat chronic inflammatory diseases and autoimmune diseases. In this review, we introduced the mechanism of efferocytosis and the pivoted role of mitochondria in efferocytosis. In addition, we focused on the therapeutic implication of drugs targeting mitochondria in diseases related to efferocytosis dysfunction.

PIEZO1 targeting in macrophages boosts phagocytic activity and foam cell apoptosis in atherosclerosis

The rising incidences of atherosclerosis have necessitated efforts to identify novel targets for therapeutic interventions. In the present study, we observed increased expression of the mechanosensitive calcium channel Piezo1 transcript in mouse and human atherosclerotic plaques, correlating with infiltration of PIEZO1-expressing macrophages. In vitro administration of Yoda1, a specific agonist for PIEZO1, led to increased foam cell apoptosis and enhanced phagocytosis by macrophages. Mechanistically, PIEZO1 activation resulted in intracellular F-actin rearrangement, elevated mitochondrial ROS levels and induction of mitochondrial fragmentation upon PIEZO1 activation, as well as increased expression of anti-inflammatory genes. In vivo, ApoE-/- mice treated with Yoda1 exhibited regression of atherosclerosis, enhanced stability of advanced lesions, reduced plaque size and necrotic core, increased collagen content, and reduced expression levels of inflammatory markers. Our findings propose PIEZO1 as a novel and potential therapeutic target in atherosclerosis.

Interplay Between Skeletal and Hematopoietic Cells in the Bone Marrow Microenvironment in Homeostasis and Aging

PURPOSE OF THE REVIEW

In this review, we discuss the most recent scientific advances on the reciprocal regulatory interactions between the skeletal and hematopoietic stem cell niche, focusing on immunomodulation and its interplay with the cell's mitochondrial function, and how this impacts osteoimmune health during aging and disease.

RECENT FINDINGS

Osteoimmunology investigates interactions between cells that make up the skeletal stem cell niche and immune system. Much work has investigated the complexity of the bone marrow microenvironment with respect to the skeletal and hematopoietic stem cells that regulate skeletal formation and immune health respectively. It has now become clear that these cellular components cooperate to maintain homeostasis and that dysfunction in their interaction can lead to aging and disease. Having a deeper, mechanistic appreciation for osteoimmune regulation will lead to better research perspective and therapeutics with the potential to improve the aging process, skeletal and hematologic regeneration, and disease targeting.

IL-17A/IL-17RA interaction blockade sensitizes synovial macrophages to efferocytosis and PD-L1 signaling via rewiring STAT-3/ADAM17/MERTK axis in rheumatoid arthritis animal model

Defective clearance of apoptotic cells due to impaired efferocytosis sustains error in self-tolerance that exacerbates rheumatoid arthritis (RA). However, the molecular determinant that directly or specifically impairs efferocytosis in RA is not yet studied. We identified a new perspective that IL-17A significantly impedes efferocytosis via preferential activation of the JAK/STAT-3/ADAM17 signaling axis. In contrast, disruption of the IL-17A/IL-17RA interaction using cyanidin or silencing of IL-17RA obstructed JAK/STAT-3 activation that further abolished ADAM17 expression. Subsequent depletion of ADAM17 inhibited the shedding of Mer tyrosine kinase receptor (MERTK), which significantly increased apoptotic cell intake and restored efferocytosis in adjuvant-induced arthritic (AA) model. Concomitantly, the amplification of the efferocytosis process due to IL-17A/IL-17RA interaction disruption was sensitive to mitochondrial fission mediated via Drp-1 phosphorylation downstream of STAT-3 inhibition. As expected, cyanidin treated AA synovial macrophages that exhibited increased efferocytosis demonstrated a phenotypic shift towards CD163 anti-inflammatory phenotype in a STAT-5 dependent manner. Similar results were obtained in IL-17A-sensitized AA synovial macrophages treated with S3I-201 (a STAT-3 inhibitor) indicating that IL-17A influences efferocytosis via the STAT-3 pathway. In view of our previous work where cyanidin restored Th17/Treg balance, our present investigation fulfils a critical gap by providing scientific validation that cyanidin escalated PD-L1 expression during the efferocytosis process that could have impacted the restoration of Th17/Treg balance in an AA model. Together, these data corroborate the hypothesis that IL-17A signaling can impair efferocytosis via regulating STAT-3/ADAM17/FL-MERTK axis and that its inhibition can amplify a pro-resolution signal against RA progression.

Oxidized LDL regulates efferocytosis through the CD36-PKM2-mtROS pathway

Macrophage efferocytosis, the process by which phagocytes engulf and remove apoptotic cells (ACs), plays a critical role in maintaining tissue homeostasis. Efficient efferocytosis prevents secondary necrosis, mitigates chronic inflammation, and impedes atherosclerosis progression. However, the regulatory mechanisms of efferocytosis under atherogenic conditions remain poorly understood. We previously demonstrated that oxidized LDL (oxLDL), an atherogenic lipoprotein, induces mitochondrial reactive oxygen species (mtROS) in macrophages via CD36. In this study, we demonstrate that macrophage mtROS facilitate continual efferocytosis through a positive feedback mechanism. However, oxLDL disrupts continual efferocytosis by dysregulating the internalization of ACs. This disruption is mediated by an overproduction of mtROS. Mechanistically, oxLDL/CD36 signaling promotes the translocation of cytosolic PKM2 to mitochondria, facilitated by the chaperone GRP75. Mitochondrial PKM2 then binds to Complex III of the electron transport chain, inducing mtROS production. This study elucidates a novel regulatory mechanism of efferocytosis in atherosclerosis, providing potential therapeutic targets for intervention.

SUMMARY

Macrophages clear apoptotic cells through a process called efferocytosis, which involves mitochondrial ROS. However, the atherogenic oxidized LDL overstimulates mitochondrial ROS via the CD36-PKM2 pathway, disrupting continual efferocytosis. This finding elucidates a novel molecular mechanism that explains defects in efferocytosis, driving atherosclerosis progression.

Retinoic acid tiers mitochondrial metabolism to Sertoli Cell-Mediated efferocytosis via a non-RAR-dependent mechanism

Efferocytosis of massive non-viable germ cells by Sertoli cells (SCs), the specialized phagocytes, is essential for maintaining testis homeostasis. What elusive is the contribution of mitochondrial metabolism to this energy-consuming process, as SC has a preference of aerobic glycolysis. All-trans retinoic acid (ATRA, hereafter referred to as RA) is a well-known morphogen that primarily acts through the nuclear RA receptor (RAR). It sustains SC blood-testisbarrier integrity, and it's SC-derived RA sets the timing of meiotic commitment. In this study, we revisited RA in SC biology, from the perspective of SC-mediated efferocytosis. We provide evidence that RA induces transcriptional programming of multiple regulators involved in efferocytosis, which thereby represses SC-mediated efferocytosis, via a RAR-independent mechanism, as blocking pan-RAR activity fails to rescue RA-induced defective efferocytosis. RA-treated SCs exhibit alternations in mitochondrial dynamics and metabolism, and the hindered efferocytosis can be rescued by stimulating mitochondrial OXPHOS via pharmacological targeting of AMPK and PDK. We thus prefer to propose a signaling axis of RA-mitochondrial metabolism-efferocytosis. Our study uncovers a hitherto unappreciated role of RA in SC biology and tiers mitochondria metabolism to SC-mediated efferocytosis, contributing a deeper understanding of SC in male reproduction.

Activating Macrophage Continual Efferocytosis via Microenvironment Biomimetic Short Fibers for Reversing Inflammation in Bone Repair

Efferocytosis-mediated inflammatory reversal plays a crucial role in bone repairing process. However, in refractory bone defects, the macrophage continual efferocytosis may be suppressed due to the disrupted microenvironment homeostasis, particularly the loss of apoptotic signals and overactivation of intracellular oxidative stress. In this study, a polydopamine-coated short fiber matrix containing biomimetic "apoptotic signals" to reconstruct the microenvironment and reactivate macrophage continual efferocytosis for inflammatory reversal and bone defect repair is presented. The "apoptotic signals" (AM/CeO2) are prepared using CeO2 nanoenzymes with apoptotic neutrophil membrane coating for macrophage recognition and oxidative stress regulation. Additionally, a short fiber "biomimetic matrix" is utilized for loading AM/CeO2 signals via abundant adhesion sites involving π-π stacking and hydrogen bonding interactions. Ultimately, the implantable apoptosis-mimetic nanoenzyme/short-fiber matrixes (PFS@AM/CeO2), integrating apoptotic signals and biomimetic matrixes, are constructed to facilitate inflammatory reversal and reestablish the pro-efferocytosis microenvironment. In vitro and in vivo data indicate that the microenvironment biomimetic short fibers can activate macrophage continual efferocytosis, leading to the suppression of overactivated inflammation. The enhanced repair of rat femoral defect further demonstrates the osteogenic potential of the pro-efferocytosis strategy. It is believed that the regulation of macrophage efferocytosis through microenvironment biomimetic materials can provide a new perspective for tissue repair.

Functional transformation of macrophage mitochondria in cardiovascular diseases

Mitochondria are pivotal in the modulation of macrophage activation, differentiation, and survival. Furthermore, macrophages are instrumental in the onset and progression of cardiovascular diseases. Hence, it is imperative to investigate the role of mitochondria within macrophages in the context of cardiovascular disease. In this review, we provide an updated description of the origin and classification of cardiac macrophages and also focused on the relationship between macrophages and mitochondria in cardiovascular diseases with respect to (1) proinflammatory or anti-inflammatory macrophages, (2) macrophage apoptosis, (3) macrophage pyroptosis, and (4) macrophage efferocytosis. Clarifying the relationship between mitochondria and macrophages can aid the exploration of novel therapeutic strategies for cardiovascular disease.

Macrophages in cardiovascular diseases: molecular mechanisms and therapeutic targets

The immune response holds a pivotal role in cardiovascular disease development. As multifunctional cells of the innate immune system, macrophages play an essential role in initial inflammatory response that occurs following cardiovascular injury, thereby inducing subsequent damage while also facilitating recovery. Meanwhile, the diverse phenotypes and phenotypic alterations of macrophages strongly associate with distinct types and severity of cardiovascular diseases, including coronary heart disease, valvular disease, myocarditis, cardiomyopathy, heart failure, atherosclerosis and aneurysm, which underscores the importance of investigating macrophage regulatory mechanisms within the context of specific diseases. Besides, recent strides in single-cell sequencing technologies have revealed macrophage heterogeneity, cell-cell interactions, and downstream mechanisms of therapeutic targets at a higher resolution, which brings new perspectives into macrophage-mediated mechanisms and potential therapeutic targets in cardiovascular diseases. Remarkably, myocardial fibrosis, a prevalent characteristic in most cardiac diseases, remains a formidable clinical challenge, necessitating a profound investigation into the impact of macrophages on myocardial fibrosis within the context of cardiac diseases. In this review, we systematically summarize the diverse phenotypic and functional plasticity of macrophages in regulatory mechanisms of cardiovascular diseases and unprecedented insights introduced by single-cell sequencing technologies, with a focus on different causes and characteristics of diseases, especially the relationship between inflammation and fibrosis in cardiac diseases (myocardial infarction, pressure overload, myocarditis, dilated cardiomyopathy, diabetic cardiomyopathy and cardiac aging) and the relationship between inflammation and vascular injury in vascular diseases (atherosclerosis and aneurysm). Finally, we also highlight the preclinical/clinical macrophage targeting strategies and translational implications.

LPS exposure alleviates multiple tissues damage by facilitating macrophage efferocytosis

Toll-like receptors (TLRs) play a crucial role in mediating immune responses by recognizing pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), as well as facilitating apoptotic cell (ACs) clearance (efferocytosis), thus contributing significantly to maintaining homeostasis and promoting tissue resolution. In this study, we investigate the impact of TLR agonists on macrophage efferocytosis. Our findings demonstrate that pretreatment with the TLR agonist lipopolysaccharide (LPS) significantly enhances macrophage phagocytic ability, thereby promoting efferocytosis both in vitro and in vivo. Moreover, LPS pretreatment confers tissue protection against damage by augmenting macrophage efferocytic capacity in murine models. Further examination reveals that LPS modulates efferocytosis by upregulating the expression of Tim4.These results underscore the pivotal role of TLR agonists in regulating the efferocytosis process and suggest potential therapeutic avenues for addressing inflammatory diseases. Overall, our study highlights the intricate interplay between LPS pretreatment and efferocytosis in maintaining tissue homeostasis and resolving inflammation.

Mitochondrial fusion-fission dynamics and its involvement in colorectal cancer

The incidence and mortality rates of colorectal cancer have elevated its status as a significant public health concern. Recent research has elucidated the crucial role of mitochondrial fusion-fission dynamics in the initiation and progression of colorectal cancer. Elevated mitochondrial fission or fusion activity can contribute to the metabolic reprogramming of tumor cells, thereby activating oncogenic pathways that drive cell proliferation, invasion, migration, and drug resistance. Nevertheless, excessive mitochondrial fission can induce apoptosis, whereas moderate mitochondrial fusion can protect cells from oxidative stress. This imbalance in mitochondrial dynamics can exert dual roles as both promoters and inhibitors of colorectal cancer progression. This review provides an in-depth analysis of the fusion-fission dynamics and the underlying pathological mechanisms in colorectal cancer cells. Additionally, it offers partial insights into the mitochondrial kinetics in colorectal cancer-associated cells, such as immune and endothelial cells. This review is aimed at identifying key molecular events involved in colorectal cancer progression and highlighting the potential of mitochondrial dynamic proteins as emerging targets for pharmacological intervention.

epHero - a tandem-fluorescent probe to track the fate of apoptotic cells during efferocytosis

The efficient removal of apoptotic cells via efferocytosis is critical for maintaining optimal tissue function. This involves the binding and engulfment of apoptotic cells by phagocytes and the subsequent maturation of the phagosome, culminating in lysosomal fusion and cargo destruction. However, current approaches to measure efferocytosis rely on labelling apoptotic targets with fluorescent dyes, which do not sufficiently distinguish between changes to the engulfment and acidification of apoptotic material. To address this limitation, we have developed a genetically coded ratiometric probe epHero which when expressed in the cytoplasm of target cells, bypasses the need for additional labelling steps. We demonstrate that epHero is a pH-sensitive reporter for efferocytosis and can be used to simultaneously track changes to apoptotic cell uptake and acidification, both in vitro and in mice. As proof-of-principle, we modify extracellular nutrition to show how epHero can distinguish between changes to cargo engulfment and acidification. Thus, tracking efferocytosis with epHero is a simple, cost-effective improvement on conventional techniques.

Generating PET scan patterns in Alzheimer's by a mathematical model

Alzheimer disease (AD) is the most common form of dementia. The cause of the disease is unknown, and it has no cure. Symptoms include cognitive decline, memory loss, and impairment of daily functioning. The pathological hallmarks of the disease are aggregation of plaques of amyloid-β (Aβ) and neurofibrillary tangles of tau proteins (τ), which can be detected in PET scans of the brain. The disease can remain asymptomatic for decades, while the densities of Aβ and τ continue to grow. Inflammation is considered an early event that drives the disease. In this paper, we develop a mathematical model that can produce simulated patterns of (Aβ,τ) seen in PET scans of AD patients. The model is based on the assumption that early inflammations, R and [Formula: see text], drive the growth of Aβ and τ, respectively. Recently approved drugs can slow the progression of AD in patients, provided treatment begins early, before significant damage to the brain has occurred. In line with current longitudinal studies, we used the model to demonstrate how to assess the efficacy of such drugs when given years before the disease becomes symptomatic.

Efferocytosis: Current status and future prospects in the treatment of autoimmune diseases

Billions of apoptotic cells are swiftly removed from the human body daily. This clearance process is regulated by efferocytosis, an active anti-inflammatory process during which phagocytes engulf and remove apoptotic cells. However, impaired clearance of apoptotic cells is associated with the development of various autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease. In this review, we conducted a comprehensive search of relevant studies published from January 1, 2000, to the present, focusing on efferocytosis, autoimmune disease pathogenesis, regulatory mechanisms governing efferocytosis, and potential treatments targeting this process. Our review highlights the key molecules involved in different stages of efferocytosis-namely, the "find me," "eat me," and "engulf and digest" phases-while elucidating their relevance to autoimmune disease pathology. Furthermore, we explore the therapeutic potential of modulating efferocytosis to restore immune homeostasis and mitigate autoimmune responses. By providing theoretical underpinnings for the targeting of efferocytosis in the treatment of autoimmune diseases, this review contributes to the advancement of therapeutic strategies in this field.

Dysregulated cellular metabolism in atherosclerosis: mediators and therapeutic opportunities

Accumulating evidence over the past decades has revealed an intricate relationship between dysregulation of cellular metabolism and the progression of atherosclerotic cardiovascular disease. However, an integrated understanding of dysregulated cellular metabolism in atherosclerotic cardiovascular disease and its potential value as a therapeutic target is missing. In this Review, we (1) summarize recent advances concerning the role of metabolic dysregulation during atherosclerosis progression in lesional cells, including endothelial cells, vascular smooth muscle cells, macrophages and T cells; (2) explore the complexity of metabolic cross-talk between these lesional cells; (3) highlight emerging technologies that promise to illuminate unknown aspects of metabolism in atherosclerosis; and (4) suggest strategies for targeting these underexplored metabolic alterations to mitigate atherosclerosis progression and stabilize rupture-prone atheromas with a potential new generation of cardiovascular therapeutics.

Targeting mitochondrial dynamics and redox regulation in cardiovascular diseases

Accumulating evidence highlights the pivotal role of mitochondria in cardiovascular diseases (CVDs). Understanding the molecular mechanisms underlying mitochondrial dysfunction is crucial for developing targeted therapeutics. Recent years have seen substantial advancements in unraveling mitochondrial regulatory pathways in both normal and pathological states and the development of potent drugs. However, specific delivery of drugs into the mitochondria is still a challenge. We present recent findings on regulators of mitochondrial dynamics and reactive oxygen species (ROS), critical factors influencing mitochondrial function in CVDs. We also discuss advancements in drug delivery strategies aimed at overcoming the technical barrier in targeting mitochondria for CVD treatment.

Rapid unleashing of macrophage efferocytic capacity via transcriptional pause release

During development, inflammation or tissue injury, macrophages may successively engulf and process multiple apoptotic corpses via efferocytosis to achieve tissue homeostasis1. How macrophages may rapidly adapt their transcription to achieve continuous corpse uptake is incompletely understood. Transcriptional pause/release is an evolutionarily conserved mechanism, in which RNA polymerase (Pol) II initiates transcription for 20-60 nucleotides, is paused for minutes to hours and is then released to make full-length mRNA2. Here we show that macrophages, within minutes of corpse encounter, use transcriptional pause/release to unleash a rapid transcriptional response. For human and mouse macrophages, the Pol II pause/release was required for continuous efferocytosis in vitro and in vivo. Interestingly, blocking Pol II pause/release did not impede Fc receptor-mediated phagocytosis, yeast uptake or bacterial phagocytosis. Integration of data from three genomic approaches-precision nuclear run-on sequencing, RNA sequencing, and assay for transposase-accessible chromatin using sequencing (ATAC-seq)-on efferocytic macrophages at different time points revealed that Pol II pause/release controls expression of select transcription factors and downstream target genes. Mechanistic studies on transcription factor EGR3, prominently regulated by pause/release, uncovered EGR3-related reprogramming of other macrophage genes involved in cytoskeleton and corpse processing. Using lysosomal probes and a new genetic fluorescent reporter, we identify a role for pause/release in phagosome acidification during efferocytosis. Furthermore, microglia from egr3-deficient zebrafish embryos displayed reduced phagocytosis of apoptotic neurons and fewer maturing phagosomes, supporting defective corpse processing. Collectively, these data indicate that macrophages use Pol II pause/release as a mechanism to rapidly alter their transcriptional programs for efficient processing of the ingested apoptotic corpses and for successive efferocytosis.

The efferocytosis process in aging: Supporting evidence, mechanisms, and therapeutic prospects for age-related diseases

BACKGROUND

Aging is characterized by an ongoing struggle between the buildup of damage caused by a combination of external and internal factors. Aging has different effects on phagocytes, including impaired efferocytosis. A deficiency in efferocytosis can cause chronic inflammation, aging, and several other clinical disorders.

AIM OF REVIEW

Our review underscores the possible feasibility and extensive scope of employing dual targets in various age-related diseases to reduce the occurrence and progression of age-related diseases, ultimately fostering healthy aging and increasing lifespan. Key scientific concepts of review Hence, the concurrent implementation of strategies aimed at augmenting efferocytic mechanisms and anti-aging treatments has the potential to serve as a potent intervention for extending the duration of a healthy lifespan. In this review, we comprehensively discuss the concept and physiological effects of efferocytosis. Subsequently, we investigated the association between efferocytosis and the hallmarks of aging. Finally, we discuss growing evidence regarding therapeutic interventions for age-related disorders, focusing on the physiological processes of aging and efferocytosis.

Mitochondrial dynamics and colorectal cancer biology: mechanisms and potential targets

Colorectal cancer (CRC) is a significant public health concern, and its development is associated with mitochondrial dysfunction. Mitochondria can adapt to the high metabolic demands of cancer cells owing to their plasticity and dynamic nature. The fusion-fission dynamics of mitochondria play a crucial role in signal transduction and metabolic functions of CRC cells. Enhanced mitochondrial fission promotes the metabolic reprogramming of CRC cells, leading to cell proliferation, metastasis, and chemoresistance. Excessive fission can also trigger mitochondria-mediated apoptosis. In contrast, excessive mitochondrial fusion leads to adenosine triphosphate (ATP) overproduction and abnormal tumor proliferation, whereas moderate fusion protects intestinal epithelial cells from oxidative stress-induced mitochondrial damage, thus preventing colitis-associated cancer (CAC). Therefore, an imbalance in mitochondrial dynamics can either promote or inhibit CRC progression. This review provides an overview of the mechanism underlying mitochondrial fusion-fission dynamics and their impact on CRC biology. This revealed the dual role of mitochondrial fusion-fission dynamics in CRC development and identified potential drug targets. Additionally, this study partially explored mitochondrial dynamics in immune and vascular endothelial cells in the tumor microenvironment, suggesting promising prospects for targeting key fusion/fission effector proteins against CRC.

Efferocyte-Derived MCTRs Metabolically Prime Macrophages for Continual Efferocytosis via Rac1-Mediated Activation of Glycolysis

Clearance of multiple rounds of apoptotic cells (ACs) through continual efferocytosis is critical in the maintenance of organ function, the resolution of acute inflammation, and tissue repair. To date, little is known about the nature of mechanisms and factors that govern this fundamental process. Herein, the authors reported that breakdown of ACs leads to upregulation of 12-lipoxygenase in macrophages. This enzyme converts docosahexaenoic acid to maresin conjugates in tissue regeneration (MCTRs). The levels of these autacoids are elevated at sites of high apoptotic burden in vivo and in efferocytosing macrophages in vitro. Abrogation of MCTR production using genetic approaches limits the ability of macrophages to perform continual efferocytosis both in vivo and in vitro, an effect that is rescued by add-back of MCTRs. Mechanistically, MCTR-mediated priming of macrophages for continual efferocytosis is dependent on alterations in Rac1 signalling and glycolytic metabolism. Inhibition of Rac1 abolishes the ability of MCTRs to increase glucose uptake and efferocytosis in vitro, whereas inhibition of glycolysis limits the MCTR-mediated increases in efferocytosis and tissue repair. Together, these findings demonstrate that upregulation of MCTRs by efferocytosing macrophages plays a central role in the regulation of continual efferocytosis via the autocrine and paracrine modulation of metabolic pathways.

Mitochondrial Mechanisms in Immunity and Inflammatory Conditions: Beyond Energy Management

Significance: The growing importance of mitochondria in the immune response and inflammation is multifaceted. Unraveling the different mechanisms by which mitochondria have a relevant role in the inflammatory response beyond the energy management of the process is necessary for improving our understanding of the host immune defense and the pathogenesis of various inflammatory diseases and syndromes. Critical Issues: Mitochondria are relevant in the immune response at different levels, including releasing activation molecules, changing its structure and function to accompany the immune response, and serving as a structural base for activating intermediates as NLRP3 inflammasome. In this scientific journey of dissecting mitochondrial mechanisms, new questions and interesting aspects arise, such as the involvement of mitochondrial-derived vesicles in the immune response with the putative role of preventing uncontrolled situations. Recent Advances: Researchers are continuously rethinking the role of mitochondria in acute and chronic inflammation and related disorders. As such, mitochondria have important roles as centrally positioned signaling hubs in regulating inflammatory and immune responses. In this review, we present the current understanding of mitochondrial mechanisms involved, beyond the largely known mitochondrial dysfunction, in the onset and development of inflammatory situations. Future Directions: Mitochondria emerge as an interesting and multifaceted platform for studying and developing pharmaceutical and therapeutic approaches. There are many ongoing studies aimed to describe the effects of specific mitochondrial targeted molecules and treatments to ameliorate the consequences of exacerbated inflammatory components of pathologies and syndromes, resulting in an open area of increasing research interest.

Targeting Efferocytosis in Inflammaging

Rapid removal of apoptotic cells by phagocytes, a process known as efferocytosis, is key for the maintenance of tissue homeostasis, the resolution of inflammation, and tissue repair. However, impaired efferocytosis can result in the accumulation of apoptotic cells, subsequently triggering sterile inflammation through the release of endogenous factors such as DNA and nuclear proteins from membrane permeabilized dying cells. Here, we review the molecular basis of the three key phases of efferocytosis, that is, the detection, uptake, and degradation of apoptotic materials by phagocytes. We also discuss how defects in efferocytosis due to the alteration of phagocytes and dying cells can contribute to the low-grade chronic inflammation that occurs during aging, described as inflammaging. Lastly, we explore opportunities in targeting and harnessing the efferocytic machinery to limit aging-associated inflammatory diseases.

Macrophage SREBP1 regulates skeletal muscle regeneration

Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have demonstrated close links between the function of activated macrophages and their cellular metabolism. Sterol regulatory element-binding protein 1 (SREBP1) is a key regulator of lipid metabolism and has been shown to affect the activated states of macrophages. However, its role in tissue repair and regeneration is poorly understood. Here we show that systemic deletion of Srebf1, encoding SREBP1, or macrophage-specific deletion of Srebf1a, encoding SREBP1a, delays resolution of inflammation and impairs skeletal muscle regeneration after injury. Srebf1 deficiency impairs mitochondrial function in macrophages and suppresses the accumulation of macrophages at sites of muscle injury. Lipidomic analyses showed the reduction of major phospholipid species in Srebf1 -/- muscle myeloid cells. Moreover, diet supplementation with eicosapentaenoic acid restored the accumulation of macrophages and their mitochondrial gene expression and improved muscle regeneration. Collectively, our results demonstrate that SREBP1 in macrophages is essential for repair and regeneration of skeletal muscle after injury and suggest that SREBP1-mediated fatty acid metabolism and phospholipid remodeling are critical for proper macrophage function in tissue repair.

Macrophage-specific deletion of MIC26 (APOO) mitigates advanced atherosclerosis by increasing efferocytosis

BACKGROUND AND AIMS

Recent studies have suggested that MIC26 (apolipoprotein O, APOO), a novel mitochondrial inner membrane protein, is involved in inflammation. Thus, the role of macrophage MIC26 in acute inflammation and chronic inflammatory disease atherosclerosis was investigated.

METHODS

Macrophage-specific MIC26 knockout mice (MIC26LysM) were generated by crossing Apooflox/flox and LysMcre+/- mice. An endotoxemia mouse model was generated to explore the effects of macrophage MIC26 deficiency on acute inflammation, while an atherosclerosis mouse model was constructed by crossing MIC26LysM mice with Apoe-/- mice and challenged with a Western diet. Atherosclerotic plaques, primary macrophage function, and mitochondrial structure and function were analyzed.

RESULTS

MIC26 knockout did not affect the median survival time and post-injection serum interleukin 1β concentrations in mice with endotoxemia. Mice with MIC26 deficiency in an Apoe-/- background had smaller atherosclerotic lesions and necrotic core than the control group. In vitro studies found that the loss of MIC26 did not affect macrophage polarization, apoptosis, or lipid handling capacity, but increased efferocytosis (the ability to clear apoptotic cells). An in situ efferocytosis assay of plaques also showed that the ratio of macrophage-associated apoptotic cells to free apoptotic cells was higher in the MIC26-deficient group than in the control group, indicating increased efferocytosis. In addition, an in vivo thymus efferocytosis assay indicated that MIC26 deletion promoted efferocytosis. Mechanistically, the loss of MIC26 resulted in an abnormal mitochondrial inner membrane structure, increased mitochondrial fission, and decreased mitochondrial membrane potential. Loss of MIC26 reduced mitochondria optic atrophy type 1 (OPA1) protein, and OPA1 silencing in macrophages promoted efferocytosis. Overexpression of OPA1 abolished the increase in efferocytosis produced by MIC26 deficiency.

CONCLUSIONS

Macrophage MIC26 deletion alleviated advanced atherosclerosis and necrotic core expansion by promoting efferocytosis. This mechanism may be related to the increased mitochondrial fission caused by reduced mitochondrial OPA1.

Efferocytosis-induced lactate enables the proliferation of pro-resolving macrophages to mediate tissue repair

The clearance of apoptotic cells by macrophages (efferocytosis) prevents necrosis and inflammation and activates pro-resolving pathways, including continual efferocytosis. A key resolution process in vivo is efferocytosis-induced macrophage proliferation (EIMP), in which apoptotic cell-derived nucleotides trigger Myc-mediated proliferation of pro-resolving macrophages. Here we show that EIMP requires a second input that is integrated with cellular metabolism, notably efferocytosis-induced lactate production. Lactate signalling via GPR132 promotes Myc protein stabilization and subsequent macrophage proliferation. This mechanism is validated in vivo using a mouse model of dexamethasone-induced thymocyte apoptosis, which elevates apoptotic cell burden and requires efferocytosis to prevent inflammation and necrosis. Thus, EIMP, a key process in tissue resolution, requires inputs from two independent processes: a signalling pathway induced by apoptotic cell-derived nucleotides and a cellular metabolism pathway involving lactate production. These findings illustrate how seemingly distinct pathways in efferocytosing macrophages are integrated to carry out a key process in tissue resolution.

Myeloid Drp1 Deficiency Limits Revascularization in Ischemic Muscles via Inflammatory Macrophage Polarization and Metabolic Reprograming

In the preclinical model of peripheral arterial disease (PAD), M2-like anti-inflammatory macrophage polarization and angiogenesis are required for revascularization. The regulation of cell metabolism and inflammation in macrophages is tightly linked to mitochondrial dynamics. Drp1, a mitochondrial fission protein, has shown context-dependent macrophage phenotypes with both pro- and anti-inflammatory characteristics. However, the role of macrophage Drp1 in reparative neovascularization remains unexplored. Here we show that Drp1 expression was significantly increased in F4/80+ macrophages within ischemic muscle at day 3 following hindlimb ischemia (HLI), an animal model of PAD. Myeloid-specific Drp1 -/- mice exhibited reduced limb perfusion recovery, angiogenesis and muscle regeneration after HLI. These effects were concomitant with enhancement of pro-inflammatory M1-like macrophages, p-NFkB, and TNFα levels, while showing reduction in anti-inflammatory M2-like macrophages and p-AMPK in ischemic muscle of myeloid Drp1 -/- mice. In vitro, Drp1 -/- macrophages under hypoxia serum starvation (HSS), an in vitro PAD model, demonstrated enhanced glycolysis via reducing p-AMPK as well as mitochondrial dysfunction and excessive mitochondrial ROS, resulting in increased M1-gene and reduced M2-gene expression. Conditioned media from HSS-treated Drp1 -/- macrophages exhibited increased secretion of pro-inflammatory cytokines and suppressed angiogenic responses in cultured endothelial cells. Thus, Drp1 deficiency in macrophages under ischemia drives inflammatory metabolic reprogramming and macrophage polarization, thereby limiting revascularization in experimental PAD.

Efferocytosis: An accomplice of cancer immune escape

The clearance of apoptotic cells by efferocytes such as macrophages and dendritic cells is termed as "efferocytosis", it plays critical roles in maintaining tissue homeostasis in multicellular organisms. Currently, available studies indicate that efferocytosis-related molecules and pathways are tightly associated with cancer development, metastasis and treatment resistance, efferocytosis also induces an immunosuppressive tumor microenvironment and assists cancer cells escape from immune surveillance. In this study, we reviewed the underlying mechanisms of efferocytosis in mediating the occurrence of cancer immune escape, and then emphatically summarized the strategies of using efferocytosis as therapeutic target to enhance the anti-tumor efficacies of immune checkpoint inhibitors, hoping to provide powerful evidences for more effective therapeutic regimens of malignant tumors.

The Role of Macrophages in Atherosclerosis: Participants and Therapists

Currently, atherosclerosis, characterized by the dysfunction of lipid metabolism and chronic inflammation in the intimal space of the vessel, is considered to be a metabolic disease. As the most abundant innate immune cells in the body, macrophages play a key role in the onset, progression, or regression of atherosclerosis. For example, macrophages exhibit several polarization states in response to microenvironmental stimuli; an increasing proportion of macrophages, polarized toward M2, can suppress inflammation, scavenge cell debris and apoptotic cells, and contribute to tissue repair and fibrosis. Additionally, specific exosomes, generated by macrophages containing certain miRNAs and effective efferocytosis of macrophages, are crucial for atherosclerosis. Therefore, macrophages have emerged as a novel potential target for anti-atherosclerosis therapy. This article reviews the role of macrophages in atherosclerosis from different aspects: origin, phenotype, exosomes, and efferocytosis, and discusses new approaches for the treatment of atherosclerosis.

Mitochondrial Fragmentation Promotes Inflammation Resolution Responses in Macrophages via Histone Lactylation

During the inflammatory response, macrophage phenotypes can be broadly classified as pro-inflammatory/classically activated "M1", or pro-resolving/alternatively "M2" macrophages. Although the classification of macrophages is general and assumes there are distinct phenotypes, in reality macrophages exist across a spectrum and must transform from a pro-inflammatory state to a proresolving state following an inflammatory insult. To adapt to changing metabolic needs of the cell, mitochondria undergo fusion and fission, which have important implications for cell fate and function. We hypothesized that mitochondrial fission and fusion directly contribute to macrophage function during the pro-inflammatory and proresolving phases. In the present study, we find that mitochondrial length directly contributes to macrophage phenotype, primarily during the transition from a pro-inflammatory to a proresolving state. Phenocopying the elongated mitochondrial network (by disabling the fission machinery using siRNA) leads to a baseline reduction in the inflammatory marker IL-1β, but a normal inflammatory response to LPS, similar to control macrophages. In contrast, in macrophages with a phenocopied fragmented phenotype (by disabling the fusion machinery using siRNA) there is a heightened inflammatory response to LPS and increased signaling through the ATF4/c-Jun transcriptional axis compared to control macrophages. Importantly, macrophages with a fragmented mitochondrial phenotype show increased expression of proresolving mediator arginase 1 and increased phagocytic capacity. Promoting mitochondrial fragmentation caused an increase in cellular lactate, and an increase in histone lactylation which caused an increase in arginase 1 expression. These studies demonstrate that a fragmented mitochondrial phenotype is critical for the proresolving response in macrophages and specifically drive epigenetic changes via lactylation of histones following an inflammatory insult.

LRRK2 aggravates kidney injury through promoting MFN2 degradation and abnormal mitochondrial integrity

Mitochondrial dysfunction is one of the key features of acute kidney injury (AKI) and associated fibrosis. Leucine-rich repeat kinase 2 (LRRK2) is highly expressed in kidneys and regulates mitochondrial homeostasis. How it functions in AKI is unclear. Herein we reported that LRRK2 was dramatically downregulated in AKI kidneys. Lrrk2-/- mice exhibited less severity of AKI when compared to wild-type counterparts with less mitochondrial fragmentation and decreased reactive oxygen species (ROS) production in proximal renal tubular cells (PTCs) due to mitofusin 2 (MFN2) accumulation. Overexpression of LRRK2 in human PTC cell lines promoted LRRK2-MKK4/JNK-dependent phosphorylation of MFN2Ser27 and subsequently ubiquitination-mediated MFN2 degradation, which in turn exaggerated mitochondrial damage upon ischemia/reperfusion (I/R) mimicry treatment. Lrrk2 deficiency also alleviated AKI-to-chronic kidney disease (CKD) transition with less fibrosis. In vivo pretreatment of LRRK2 inhibitors attenuated the severity of AKI as well as CKD, potentiating LRRK2 as a novel target to alleviate AKI and fibrosis.

The role of efferocytosis-fueled macrophage metabolism in the resolution of inflammation

The phagocytosis of dying cells by macrophages, termed efferocytosis, is a tightly regulated process that involves the sensing, binding, engulfment, and digestion of apoptotic cells. Efferocytosis not only prevents tissue necrosis and inflammation caused by secondary necrosis of dying cells, but it also promotes pro-resolving signaling in macrophages, which is essential for tissue resolution and repair following injury or inflammation. An important factor that contributes to this pro-resolving reprogramming is the cargo that is released from apoptotic cells after their engulfment and phagolysosomal digestion by macrophages. The apoptotic cell cargo contains amino acids, nucleotides, fatty acids, and cholesterol that function as metabolites and signaling molecules to bring about this re-programming. Here, we review efferocytosis-induced changes in macrophage metabolism that mediate the pro-resolving functions of macrophages. We also discuss various strategies, challenges, and future perspectives related to drugging efferocytosis-fueled macrophage metabolism as strategy to dampen inflammation and promote resolution in chronic inflammatory diseases.

Hijacking homeostasis: Regulation of the tumor microenvironment by apoptosis

Cancers are genetically driven, rogue tissues which generate dysfunctional, obdurate organs by hijacking normal, homeostatic programs. Apoptosis is an evolutionarily conserved regulated cell death program and a profoundly important homeostatic mechanism that is common (alongside tumor cell proliferation) in actively growing cancers, as well as in tumors responding to cytotoxic anti-cancer therapies. Although well known for its cell-autonomous tumor-suppressive qualities, apoptosis harbors pro-oncogenic properties which are deployed through non-cell-autonomous mechanisms and which generally remain poorly defined. Here, the roles of apoptosis in tumor biology are reviewed, with particular focus on the secreted and fragmentation products of apoptotic tumor cells and their effects on tumor-associated macrophages, key supportive cells in the aberrant homeostasis of the tumor microenvironment. Historical aspects of cell loss in tumor growth kinetics are considered and the impact (and potential impact) on tumor growth of apoptotic-cell clearance (efferocytosis) as well as released soluble and extracellular vesicle-associated factors are discussed from the perspectives of inflammation, tissue repair, and regeneration programs. An "apoptosis-centric" view is proposed in which dying tumor cells provide an important platform for intricate intercellular communication networks in growing cancers. The perspective has implications for future research and for improving cancer diagnosis and therapy.

Mitochondrial Dynamics and Cristae Shape Changes During Metabolic Reprogramming

Significance: The architecture of the mitochondrial network and cristae critically impact cell differentiation and identity. Cells undergoing metabolic reprogramming to aerobic glycolysis (Warburg effect), such as immune cells, stem cells, and cancer cells, go through controlled modifications in mitochondrial architecture, which is critical for achieving the resulting cellular phenotype. Recent Advances: Recent studies in immunometabolism have shown that the manipulation of mitochondrial network dynamics and cristae shape directly affects T cell phenotype and macrophage polarization through altering energy metabolism. Similar manipulations also alter the specific metabolic phenotypes that accompany somatic reprogramming, stem cell differentiation, and cancer cells. The modulation of oxidative phosphorylation activity, accompanied by changes in metabolite signaling, reactive oxygen species generation, and adenosine triphosphate levels, is the shared underlying mechanism. Critical Issues: The plasticity of mitochondrial architecture is particularly vital for metabolic reprogramming. Consequently, failure to adapt the appropriate mitochondrial morphology often compromises the differentiation and identity of the cell. Immune, stem, and tumor cells exhibit striking similarities in their coordination of mitochondrial morphology with metabolic pathways. However, although many general unifying principles can be observed, their validity is not absolute, and the mechanistic links thus need to be further explored. Future Directions: Better knowledge of the molecular mechanisms involved and their relationships to both mitochondrial network and cristae morphology will not only further deepen our understanding of energy metabolism but may also contribute to improved therapeutic manipulation of cell viability, differentiation, proliferation, and identity in many different cell types. Antioxid. Redox Signal. 39, 684-707.

Interplay between efferocytosis and atherosclerosis

In an adult human, billions of cells die and turn over daily. During this process, many apoptotic cells are produced and subsequently cleared by phagocytes - a process termed efferocytosis, which plays a critical role in tissue homeostasis. Efferocytosis is an important mechanism in the control of inflammatory processes. Efficient efferocytosis inhibits accumulation of apoptotic cells/debris and maintains homeostasis before the onset of necrosis (secondary necrosis), which promotes inflammation or injury. During efferocytosis, mitochondrial fission and the oxidative stress process are linked through reactive oxygen species production and oxidative stress control. Autophagy plays an important role in inhibiting inflammation and apoptosis, and in promoting efferocytosis by activated inflammatory cells, particularly neutrophils and macrophages. Autophagy in neutrophils is activated by phagocytosis of pathogens or activation of pattern recognition receptors. Autophagy is essential for major neutrophil functions, including degranulation, reactive oxygen species production, oxidative stress and release of neutrophil extracellular cytokines. Failed efferocytosis is a key mechanism driving the development and progression of chronic inflammatory diseases, including atherosclerosis, cardiometabolic pathology, neurodegenerative disease and cancer. Impairment of efferocytosis in apoptotic macrophages is a determinant of atherosclerosis severity and the vulnerability of plaques to rupture. Recent results suggest that inhibition of efferocytosis in the protection of the myocardium results in reduced infiltration of reparatory macrophages into the tissue, in association with oxidative stress reduction. Activated macrophages play a central role in the development and resolution of inflammation. The resolution of inflammation through efferocytosis is an endogenous process that protects host tissues from prolonged or excessive inflammation. Accordingly, therapeutic strategies that ameliorate efferocytosis control would be predicted to dampen inflammation and improve resolution. Thus, therapies targeting efferocytosis will provide a new means of treating and preventing cardiovascular and metabolic diseases involving the chronic inflammatory state.

Macrophage immunometabolism in diabetes-associated atherosclerosis

Macrophages play fundamental roles in atherosclerotic plaque formation, growth, and regression. These cells are extremely plastic and perform different immune functions depending on the stimuli they receive. Initial in vitro studies have identified specific metabolic pathways that are crucial for the proper function of pro-inflammatory and pro-resolving macrophages. However, the plaque microenvironment, especially in the context of insulin resistance and type 2 diabetes, constantly challenges macrophages with several simultaneous inflammatory and metabolic stimuli, which may explain why atherosclerosis is accelerated in diabetic patients. In this mini review, we discuss how macrophage mitochondrial function and metabolism of carbohydrates, lipids, and amino acids may be affected by this complex plaque microenvironment and how risk factors associated with type 2 diabetes alter the metabolic rewiring of macrophages and disease progression. We also briefly discuss current challenges in assessing macrophage metabolism and identify future tools and possible strategies to alter macrophage metabolism to improve treatment options for diabetes-associated atherosclerosis.

A bibliometric analysis of efferocytosis in cardiovascular diseases from 2001 to 2022

INTRODUCTION

In recent years, efferocytosis in cardiovascular diseases has become an intense area of research. However, only a few bibliometric analyses have been conducted in this area. In this review, we used CiteSpace 5.7. R2 and VOSviewer 1.6.17 software to perform text mining and knowledge map analysis. This study summarizes the latest progress, development paths, frontier research hotspots, and future research trends in this field.

MATERIALS AND METHODS

Studies on efferocytosis in cardiovascular diseases were downloaded from the Web of Science Core Collection.

RESULTS

In total, 327 studies published by 506 institutions across 42 countries and regions were identified. The number of studies on efferocytosis in cardiovascular diseases has increased over time. Arteriosclerosis Thrombosis and Vascular Biology published the highest number of articles and was the top co-cited journal. Tabas Ira. was the most prolific researcher and co-cited the most. The most productive countries were the United States and China. Columbia University, Harvard Medical School, and Brigham Women's Hospital were the 3 most productive institutions in the field of research. Keyword Co-occurrence, Clusters, and Burst analyses showed that inflammation, atherosclerosis, macrophages, and phagocytosis appeared with the highest frequency in these studies.

CONCLUSION

Multinational cooperation and multidisciplinary intersections are characteristic trends of development in the field, and the immune microenvironment, glycolysis, and lipid metabolism will be the focus of future research.

Cardiac macrophages and emerging roles for their metabolism after myocardial infarction

Interest in cardioimmunology has reached new heights as the experimental cardiology field works to tap the unrealized potential of immunotherapy for clinical care. Within this space is the cardiac macrophage, a key modulator of cardiac function in health and disease. After a myocardial infarction, myeloid macrophages both protect and harm the heart. To varying degrees, such outcomes are a function of myeloid ontogeny and heterogeneity, as well as functional cellular plasticity. Diversity is further shaped by the extracellular milieu, which fluctuates considerably after coronary occlusion. Ischemic limitation of nutrients constrains the metabolic potential of immune cells, and accumulating evidence supports a paradigm whereby macrophage metabolism is coupled to divergent inflammatory consequences, although experimental evidence for this in the heart is just emerging. Herein we examine the heterogeneous cardiac macrophage response following ischemic injury, with a focus on integrating putative contributions of immunometabolism and implications for therapeutically relevant cardiac injury versus cardiac repair.

SIRT3 Regulates Clearance of Apoptotic Cardiomyocytes by Deacetylating Frataxin

BACKGROUND

Efferocytosis is an activity of macrophages that is pivotal for the resolution of inflammation in hypertension. The precise mechanism by which macrophages coordinate efferocytosis and internalize apoptotic cardiomyocytes remains unknown. The aim of this study was to determine whether SIRT3 (sirtuin-3) is required for both apoptotic cardiomyocyte engulfment and anti-inflammatory responses during efferocytosis.

METHODS

We generated myeloid SIRT3 knockout mice and FXN (frataxin) knock-in mice carrying an acetylation-defective lysine to arginine K189R mutation (FXNK189R). The mice were given Ang II (angiotensin II) infusion for 7 days. We analyzed cardiac macrophages' mitochondrial iron levels, efferocytosis activity, and phenotype both in vivo and in vitro.

RESULTS

We showed that SIRT3 deficiency exacerbated Ang II-induced downregulation of the efferocytosis receptor MerTK (c-Mer tyrosine kinase) and proinflammatory cytokine production, accompanied by disrupted mitochondrial iron homeostasis in cardiac macrophages. Quantitative acetylome analysis revealed that SIRT3 deacetylated FXN at lysine 189. Ang II attenuated SIRT3 activity and enhanced the acetylation level of FXNK189. Acetylated FXN further reduced the synthesis of ISCs (iron-sulfur clusters), resulting in mitochondrial iron accumulation. Phagocytic internalization of apoptotic cardiomyocytes increased myoglobin content, and derived iron ions promoted mitochondrial iron overload and lipid peroxidation. An iron chelator deferoxamine improved the levels of MerTK and efferocytosis, thereby attenuating proinflammatory macrophage activation. FXNK189R mice showed improved macrophage efferocytosis, reduced cardiac inflammation, and suppressed cardiac fibrosis.

CONCLUSIONS

The SIRT3-FXN axis has the potential to resolve cardiac inflammation by increasing macrophage efferocytosis and anti-inflammatory activities.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Mitochondrial dynamics modulate the allergic inflammation in a murine model of allergic rhinitis

OBJECTIVE

Allergic rhinitis (AR) is a common allergic disorder, afflicting thousands of human beings. Aberrant mitochondrial dynamics are important pathological elements for various immune cell dysfunctions and allergic diseases. However, the connection between mitochondrial dynamics and AR remains poorly understood. This study aimed to determine whether mitochondrial dynamics influence the inflammatory response in AR.

METHODS

In the present study, we established a murine model of AR by sensitization with ovalbumin (OVA). Then, we investigated the mitochondrial morphology in mice with AR by transmission electron microscopy and confocal fluorescence microscopy, and evaluated the role of Mdivi-1 (an inhibitor of mitochondrial fission) on allergic symptoms, inflammatory responses, allergic-related signals, and reactive oxygen species formation.

RESULTS

There was a notable enhancement in mitochondrial fragmentation in the nasal mucosa of mice following OVA stimulation, whereas Mdivi-1 prevented aberrant mitochondrial morphology. Indeed, Mdivi-1 alleviated the rubbing and sneezing responses in OVA-sensitized mice. Compared with vehicle-treated ones, mice treated with Mdivi-1 exhibited a reduction in interleukin (IL)-4, IL-5, and specific IgE levels in both serum and nasal lavage fluid, and shown an amelioration in inflammatory response of nasal mucosa. Meanwhile, Mdivi-1 treatment was associated with a suppression in JAK2 and STAT6 activation and reactive oxygen species generation, which act as important signaling for allergic response.

CONCLUSION

Our findings reveal mitochondrial dynamics modulate the allergic responses in AR. Mitochondrial dynamics may represent a promising target for the treatment of AR.