Mitochondrial Membrane Potential Regulates Nuclear Gene Expression in Macrophages Exposed to Prostaglandin E2

TREM2-mediated Macrophage Glycolysis Promotes Skin Wound Angiogenesis via the Akt/mTOR/HIF-1α Signaling Axis

OBJECTIVE

The trigger receptor expressed on myeloid cells-2 (TREM2) pathway in myeloid cells is a key disease-inducing immune signaling hub that is essential for detecting tissue damage and limiting its pathological spread. However, the role and potential mechanisms of TREM2 in wound repair remain unclear. The purpose of this study was to determine the role and mechanism of TREM2 in skin wound healing in mice.

METHODS

Immunofluorescence staining was used to determine the expression and cellular localization of TREM2 and test the effects of TREM2 knockout on angiogenesis, glycolysis, and lactylation in skin tissue. Western blotting was used to analyze the expression of the Akt/mTOR/HIF-1α signaling pathway in the wounded skin tissues of wild-type (WT) and TREM2 knockout mice. A coimmunoprecipitation assay was used to determine whether HIF-1α, which mediates angiogenesis, is modified by lactylation.

RESULTS

The number of TREM2+ macrophages was increased, and TREM2+ macrophages mediated angiogenesis after skin injury. TREM2 promoted glycolysis and lactylation in macrophages during wound healing. Mechanistically, TREM2 promoted macrophage glycolysis and angiogenesis in wounded skin tissues by activating the Akt/mTOR/HIF-1α signaling pathway. HIF-1α colocalized with Klac to mediate lactylation in macrophages, and lactate could stabilize the expression of the HIF-1α protein through lactylation. Lactate treatment ameliorated the impaired angiogenesis and delayed wound healing in wounded skin in TREM2 knockout mice.

CONCLUSION

TREM2+ macrophage-mediated glycolysis can promote angiogenesis and wound healing. Our findings provide an effective strategy and target for promoting skin wound healing.

Metabolic adaptations of ILC2 and Th2 cells in type 2 immunity

Type 2 immune responses play a crucial role in host defense against parasitic infections but can also promote the development of allergies and asthma. This response is orchestrated primarily by group 2 innate lymphoid cells (ILC2) and helper type 2 (Th2) cells, both of which undergo substantial metabolic reprogramming as they transition from resting to activated states. Understanding these metabolic adaptations not only provides insights into the fundamental biology of ILC2 and Th2 cells but also opens up potential therapeutic avenues for the identification of novel metabolic targets that can extend the current treatment regimens for diseases in which type 2 immune responses play pivotal roles. By integrating recent findings, this review underscores the significance of cellular metabolism in orchestrating immune functions and highlights future directions for research in this evolving field.

Spinster homolog 2/S1P signaling ameliorates macrophage inflammatory response to bacterial infections by balancing PGE2 production

BACKGROUND

Mitochondria play a crucial role in shaping the macrophage inflammatory response during bacterial infections. Spinster homolog 2 (Spns2), responsible for sphingosine-1-phosphate (S1P) secretion, acts as a key regulator of mitochondrial dynamics in macrophages. However, the link between Spns2/S1P signaling and mitochondrial functions remains unclear.

METHODS

Peritoneal macrophages were isolated from both wild-type and Spns2 knockout rats, followed by non-targeted metabolomics and RNA sequencing analysis to identify the potential mediators through which Spns2/S1P signaling influences the mitochondrial functions in macrophages. Various agonists and antagonists were used to modulate the activation of Spns2/S1P signaling and its downstream pathways, with the underlying mechanisms elucidated through western blotting. Mitochondrial functions were assessed using flow cytometry and oxygen consumption assays, as well as morphological analysis. The impact on inflammatory response was validated through both in vitro and in vivo sepsis models, with the specific role of macrophage-expressed Spns2 in sepsis evaluated using Spns2flox/floxLyz2-Cre mice. Additionally, the regulation of mitochondrial functions by Spns2/S1P signaling was confirmed using THP-1 cells, a human monocyte-derived macrophage model.

RESULTS

In this study, we unveil prostaglandin E2 (PGE2) as a pivotal mediator involved in Spns2/S1P-mitochondrial communication. Spns2/S1P signaling suppresses PGE2 production to support malate-aspartate shuttle activity. Conversely, excessive PGE2 resulting from Spns2 deficiency impairs mitochondrial respiration, leading to intracellular lactate accumulation and increased reactive oxygen species (ROS) generation through E-type prostanoid receptor 4 activation. The overactive lactate-ROS axis contributes to the early-phase hyperinflammation during infections. Prolonged exposure to elevated PGE2 due to Spns2 deficiency culminates in subsequent immunosuppression, underscoring the dual roles of PGE2 in inflammation throughout infections. The regulation of PGE2 production by Spns2/S1P signaling appears to depend on the coordinated activation of multiple S1P receptors rather than any single one.

CONCLUSIONS

These findings emphasize PGE2 as a key effector of Spns2/S1P signaling on mitochondrial dynamics in macrophages, elucidating the mechanisms through which Spns2/S1P signaling balances both early hyperinflammation and subsequent immunosuppression during bacterial infections.

The S341P mutant MYOC renders the trabecular meshwork sensitive to cyclic mechanical stretch

The trabecular meshwork (TM) plays an essential role in the circulation of aqueous humor by sensing mechanical stretch. The balance between the outflow and inflow of aqueous humor is critical in regulating intraocular pressure (IOP). A dysfunctional TM leads to resistance to the outflow of aqueous humor, resulting in an elevated IOP, a major risk factor for glaucoma. It is widely accepted that mutant myocilin (MYOC) can cause damage to the TM. However, few studies have investigated how TM cells carrying mutant MYOC respond to cyclic mechanical stretch (CMS) and whether these cells are more sensitive to CMS under this genetic background. In this study, we applied mechanical stretch to TM cells using the Flexcell system to mimic physiological stress. In addition, we performed genome-wide transcriptome analysis and oxidized lipidomics to systematically compare the gene expression and oxylipin profiles of non-stretched control human primary TM cells, human primary TM cells under CMS (TM-CMS), and human primary TM cells overexpressing MYOCS341P under CMS (S341P-CMS). We found that TM cells that overexpressed MYOCS341P were more sensitive to mechanical stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that downregulated genes were most enriched in oxidative phosphorylation, indicating mitochondria dysfunction and the likelihood of oxidative stress. Oxidized lipidomics analysis revealed significant changes in oxylipin profiles between the S341P-CMS and TM-CMS groups. Through further genome-wide transcriptomic analysis, we identified several genes that may be involved in the sensitivity of TM cells that overexpressed MYOCS341P to mechanical stress, including SARM1, AHNAK2, NT5C, and SOX8. The importance of these genes was validated by quantitative real-time PCR. Collectively, our findings indicate that mitochondrial dysfunction may contribute to the damage that occurs to TM cells with a MYOCS341P background under mechanical stretch.

Monocyte-macrophages modulate intestinal homeostasis in inflammatory bowel disease

BACKGROUND

Monocytes and macrophages play an indispensable role in maintaining intestinal homeostasis and modulating mucosal immune responses in inflammatory bowel disease (IBD). Although numerous studies have described macrophage properties in IBD, the underlying mechanisms whereby the monocyte-macrophage lineage modulates intestinal homeostasis during gut inflammation remain elusive.

MAIN BODY

In this review, we decipher the cellular and molecular mechanisms governing the generation of intestinal mucosal macrophages and fill the knowledge gap in understanding the origin, maturation, classification, and functions of mucosal macrophages in intestinal niches, particularly the phagocytosis and bactericidal effects involved in the elimination of cell debris and pathogens. We delineate macrophage-mediated immunoregulation in the context of producing pro-inflammatory and anti-inflammatory cytokines, chemokines, toxic mediators, and macrophage extracellular traps (METs), and participating in the modulation of epithelial cell proliferation, angiogenesis, and fibrosis in the intestine and its accessory tissues. Moreover, we emphasize that the maturation of intestinal macrophages is arrested at immature stage during IBD, and the deficiency of MCPIP1 involves in the process via ATF3-AP1S2 signature. In addition, we confirmed the origin potential of IL-1B+ macrophages and defined C1QB+ macrophages as mature macrophages. The interaction crosstalk between the intestine and the mesentery has been described in this review, and the expression of mesentery-derived SAA2 is upregulated during IBD, which contributes to immunoregulation of macrophage. Moreover, we also highlight IBD-related susceptibility genes (e.g., RUNX3, IL21R, GTF2I, and LILRB3) associated with the maturation and functions of macrophage, which provide promising therapeutic opportunities for treating human IBD.

CONCLUSION

In summary, this review provides a comprehensive, comprehensive, in-depth and novel description of the characteristics and functions of macrophages in IBD, and highlights the important role of macrophages in the molecular and cellular process during IBD.

Oxylipins and metabolites from pyroptotic cells act as promoters of tissue repair

Pyroptosis is a lytic cell death mode that helps limit the spread of infections and is also linked to pathology in sterile inflammatory diseases and autoimmune diseases1-4. During pyroptosis, inflammasome activation and the engagement of caspase-1 lead to cell death, along with the maturation and secretion of the inflammatory cytokine interleukin-1β (IL-1β). The dominant effect of IL-1β in promoting tissue inflammation has clouded the potential influence of other factors released from pyroptotic cells. Here, using a system in which macrophages are induced to undergo pyroptosis without IL-1β or IL-1α release (denoted Pyro-1), we identify unexpected beneficial effects of the Pyro-1 secretome. First, we noted that the Pyro-1 supernatants upregulated gene signatures linked to migration, cellular proliferation and wound healing. Consistent with this gene signature, Pyro-1 supernatants boosted migration of primary fibroblasts and macrophages, and promoted faster wound closure in vitro and improved tissue repair in vivo. In mechanistic studies, lipidomics and metabolomics of the Pyro-1 supernatants identified the presence of both oxylipins and metabolites, linking them to pro-wound-healing effects. Focusing specifically on the oxylipin prostaglandin E2 (PGE2), we find that its synthesis is induced de novo during pyroptosis, downstream of caspase-1 activation and cyclooxygenase-2 activity; further, PGE2 synthesis occurs late in pyroptosis, with its release dependent on gasdermin D pores opened during pyroptosis. As for the pyroptotic metabolites, they link to immune cell infiltration into the wounds, and polarization to CD301+ macrophages. Collectively, these data advance the concept that the pyroptotic secretome possesses oxylipins and metabolites with tissue repair properties that may be harnessed therapeutically.

Multifaceted mitochondria in innate immunity

The ability of mitochondria to transform the energy we obtain from food into cell phosphorylation potential has long been appreciated. However, recent decades have seen an evolution in our understanding of mitochondria, highlighting their significance as key signal-transducing organelles with essential roles in immunity that extend beyond their bioenergetic function. Importantly, mitochondria retain bacterial motifs as a remnant of their endosymbiotic origin that are recognised by innate immune cells to trigger inflammation and participate in anti-microbial defence. This review aims to explore how mitochondrial physiology, spanning from oxidative phosphorylation (OxPhos) to signalling of mitochondrial nucleic acids, metabolites, and lipids, influences the effector functions of phagocytes. These myriad effector functions include macrophage polarisation, efferocytosis, anti-bactericidal activity, antigen presentation, immune signalling, and cytokine regulation. Strict regulation of these processes is critical for organismal homeostasis that when disrupted may cause injury or contribute to disease. Thus, the expanding body of literature, which continues to highlight the central role of mitochondria in the innate immune system, may provide insights for the development of the next generation of therapies for inflammatory diseases.

PGE2 inhibits TIL expansion by disrupting IL-2 signalling and mitochondrial function

Expansion of antigen-experienced CD8+ T cells is critical for the success of tumour-infiltrating lymphocyte (TIL)-adoptive cell therapy (ACT) in patients with cancer1. Interleukin-2 (IL-2) acts as a key regulator of CD8+ cytotoxic T lymphocyte functions by promoting expansion and cytotoxic capability2,3. Therefore, it is essential to comprehend mechanistic barriers to IL-2 sensing in the tumour microenvironment to implement strategies to reinvigorate IL-2 responsiveness and T cell antitumour responses. Here we report that prostaglandin E2 (PGE2), a known negative regulator of immune response in the tumour microenvironment4,5, is present at high concentrations in tumour tissue from patients and leads to impaired IL-2 sensing in human CD8+ TILs via the PGE2 receptors EP2 and EP4. Mechanistically, PGE2 inhibits IL-2 sensing in TILs by downregulating the IL-2Rγc chain, resulting in defective assembly of IL-2Rβ-IL2Rγc membrane dimers. This results in impaired IL-2-mTOR adaptation and PGC1α transcriptional repression, causing oxidative stress and ferroptotic cell death in tumour-reactive TILs. Inhibition of PGE2 signalling to EP2 and EP4 during TIL expansion for ACT resulted in increased IL-2 sensing, leading to enhanced proliferation of tumour-reactive TILs and enhanced tumour control once the cells were transferred in vivo. Our study reveals fundamental features that underlie impairment of human TILs mediated by PGE2 in the tumour microenvironment. These findings have therapeutic implications for cancer immunotherapy and cell therapy, and enable the development of targeted strategies to enhance IL-2 sensing and amplify the IL-2 response in TILs, thereby promoting the expansion of effector T cells with enhanced therapeutic potential.

The metabolic cofactor Coenzyme A enhances alternative macrophage activation via MyD88-linked signaling

Metabolites and metabolic co-factors can shape the innate immune response, though the pathways by which these molecules adjust inflammation remain incompletely understood. Here we show that the metabolic cofactor Coenzyme A (CoA) enhances IL-4 driven alternative macrophage activation [m(IL-4)] in vitro and in vivo. Unexpectedly, we found that perturbations in intracellular CoA metabolism did not influence m(IL-4) differentiation. Rather, we discovered that exogenous CoA provides a weak TLR4 signal which primes macrophages for increased receptivity to IL-4 signals and resolution of inflammation via MyD88. Mechanistic studies revealed MyD88-linked signals prime for IL-4 responsiveness, in part, by reshaping chromatin accessibility to enhance transcription of IL-4-linked genes. The results identify CoA as a host metabolic co-factor that influences macrophage function through an extrinsic TLR4-dependent mechanism, and suggests that damage-associated molecular patterns (DAMPs) can prime macrophages for alternative activation and resolution of inflammation.

Mitochondrial electron transport chain in macrophage reprogramming: Potential role in antibacterial immune response

Macrophages restrain microbial infection and reinstate tissue homeostasis. The mitochondria govern macrophage metabolism and serve as pivot in innate immunity, thus acting as immunometabolic regulon. Metabolic pathways produce electron flows that end up in mitochondrial electron transport chain (mtETC), made of super-complexes regulating multitude of molecular and biochemical processes. Cell-intrinsic and extrinsic factors influence mtETC structure and function, impacting several aspects of macrophage immunity. These factors provide the macrophages with alternate fuel sources and metabolites, critical to gain functional competence and overcoming pathogenic stress. Mitochondrial reactive oxygen species (mtROS) and oxidative phosphorylation (OXPHOS) generated through the mtETC are important innate immune attributes, which help macrophages in mounting antibacterial responses. Recent studies have demonstrated the role of mtETC in governing mitochondrial dynamics and macrophage polarization (M1/M2). M1 macrophages are important for containing bacterial pathogens and M2 macrophages promote tissue repair and wound healing. Thus, mitochondrial bioenergetics and metabolism are intimately coupled with innate immunity. In this review, we have addressed mtETC function as innate rheostats that regulate macrophage reprogramming and innate immune responses. Advancement in this field encourages further exploration and provides potential novel macrophage-based therapeutic targets to control unsolicited inflammation.

Butyrate induces oxidative burst mediated apoptosis via Glucose-6-Phosphate Dehydrogenase (G6PDH) in macrophages during mycobacterial infection

Microorganisms present in the gut modulate host defence responses against infections in order to maintain immune homeostasis. This host-microbe crosstalk is regulated by gut metabolites. Butyrate is one such small chain fatty acid produced by gut microbes upon fermentation that has the potential to influence immune responses. Here we investigated the role of butyrate in macrophages during mycobacterial infection. Results demonstrate that butyrate significantly suppresses the growth kinetics of mycobacteria in culture medium as well as inhibits mycobacterial survival inside macrophages. Interestingly, butyrate alters the pentose phosphate pathway by inducing higher expression of Glucose-6-Phosphate Dehydrogenase (G6PDH) resulting in a higher oxidative burst via decreased Sod-2 and increased Nox-2 (NADPH oxidase-2) expression. Butyrate-induced G6PDH also mediated a decrease in mitochondrial membrane potential. This in turn lead to an induction of apoptosis as measured by lower expression of the anti-apoptotic protein Bcl-2 and a higher release of Cytochrome C as a result of induction of apoptosis. These results indicate that butyrate alters the metabolic status of macrophages and induces protective immune responses against mycobacterial infection.

Prostaglandin E2 affects mitochondrial function in adult mouse cardiomyocytes and hearts

Prostaglandin E2 (PGE2) signals differently through 4 receptor subtypes (EP1-EP4) to elicit diverse physiologic/pathologic effects. We previously reported that PGE2 via its EP3 receptor reduces cardiac contractility and male mice with cardiomyocyte-specific deletion of the EP4 receptor (EP4 KO) develop dilated cardiomyopathy. The aim of this study was to identify pathways responsible for this phenotype. We performed ingenuity pathway analysis (IPA) and found that genes differentiating WT mice and EP4 KO mice were significantly overrepresented in mitochondrial (adj. p value = 6.28 × 10-26) and oxidative phosphorylation (adj. p value = 1.58 × 10-27) pathways. Electron microscopy from the EP4 KO hearts show substantial mitochondrial disarray and disordered cristae. Not surprisingly, isolated adult mouse cardiomyocytes (AVM) from these mice have reduced ATP levels compared to their WT littermates and reduced expression of key genes involved in the electron transport chain (ETC) in older mice. Moreover, treatment of AVM from C57Bl/6 mice with PGE2 or the EP3 agonist sulprostone resulted in changes of various genes involved in the ETC, measured by the Mitochondrial Energy Metabolism RT2-profiler assay. Lastly, the EP4 KO mice have reduced expression of superoxide dismuatse-2 (SOD2), whereas treatment of AVM with PGE2 or sulprostone increase superoxide production, suggesting increased oxidative stress levels in these EP4 KO mice. Altogether the current study supports the premise that PGE2 acting via its EP4 receptor is protective, while signaling through its other receptors, likely EP3, is deleterious.

Prostaglandin E2 controls the metabolic adaptation of T cells to the intestinal microenvironment

Immune cells must adapt to different environments during the course of an immune response. Here we study the adaptation of CD8+ T cells to the intestinal microenvironment and how this process shapes the establishment of the CD8+ T cell pool. CD8+ T cells progressively remodel their transcriptome and surface phenotype as they enter the gut wall, and downregulate expression of mitochondrial genes. Human and mouse intestinal CD8+ T cells have reduced mitochondrial mass, but maintain a viable energy balance to sustain their function. We find that the intestinal microenvironment is rich in prostaglandin E2 (PGE2), which drives mitochondrial depolarization in CD8+ T cells. Consequently, these cells engage autophagy to clear depolarized mitochondria, and enhance glutathione synthesis to scavenge reactive oxygen species (ROS) that result from mitochondrial depolarization. Impairing PGE2 sensing promotes CD8+ T cell accumulation in the gut, while tampering with autophagy and glutathione negatively impacts the T cell pool. Thus, a PGE2-autophagy-glutathione axis defines the metabolic adaptation of CD8+ T cells to the intestinal microenvironment, to ultimately influence the T cell pool.

A moderate dosage of prostaglandin E2-mediated annexin A1 upregulation promotes alkali-burned corneal repair

Corneal alkali burn remains a clinical challenge in ocular emergency, necessitating the development of effective therapeutic drugs. Here, we observed the arachidonic acid metabolic disorders of corneas induced by alkali burns and aimed to explore the role of Prostaglandin E2 (PGE2), a critical metabolite of arachidonic acid, in the repair of alkali-burned corneas. We found a moderate dosage of PGE2 promoted the alkali-burned corneal epithelial repair, whereas a high dosage of PGE2 exhibited a contrary effect. This divergent effect is attributed to different dosages of PGE2 regulating ANXA1 expression differently. Mechanically, a high dosage of PGE2 induced higher GATA3 expression, followed by enhanced GATA3 binding to the ANXA1 promoter to inhibit ANXA1 expression. In contrast, a moderate dosage of PGE2 increased CREB1 phosphorylation and reduced GATA3 binding to the ANXA1 promoter, promoting ANXA1 expression. We believe PGE2 and its regulatory target ANXA1 could be potential drugs for alkali-burned corneas.

Tussilagone inhibits osteoclastogenesis by modulating mitochondrial function and ROS production involved Nrf2 activation

Reactive Oxygen Species (ROS) play an essential role in the pathogenesis of osteoporosis mainly characterized by excessive osteoclasts (OCs) activity. OCs are rich in mitochondria for energy support, which is a major source of total ROS. Tussilagone (TSG), a natural Sesquiterpenes from the flower of Tussilago farfara, has plentiful beneficial pharmacological characteristics with anti-inflammatory and anti-oxidative activity, but its effects and mechanism in osteopathology are still unclear. In our study, we investigated the regulation of ROS generated from the mitochondria in OCs. We found that TSG inhibited OCs differentiation and bone resorption without any cytotoxicity. Mechanistically, TSG reduced RANKL-mediated total ROS level by down-regulating intracellular ROS production and mitochondrial function, leading to the suppression of NFATc1 transcription. We also found that nuclear factor erythroid 2-related factor 2 (Nrf2) could enhance ROS scavenging enzymes in response to RANKL-induced oxidative stress. Furthermore, TSG up-regulated the expression of Nrf2 by inhibiting its proteosomal degradation. Interestingly, Nrf2 deficiency reversed the suppressive effect of TSG on mitochondrial activity and ROS signaling in OCs. Consistent with this finding, TSG attenuated post-ovariectomy (OVX)- and lipopolysaccharide (LPS) induced bone loss by ameliorating osteoclastogenesis. Taken together, TSG has an anti-bone resorptive effect by modulating mitochondrial function and ROS production involved Nrf2 activation.

Differential response of mesenchymal stromal cells (MSCs) to type 1 ex vivo cytokine priming: implications for MSC therapy

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are polymorphic, adherent cells with the capability to stimulate tissue regeneration and modulate immunity. MSCs have been broadly investigated for potential therapeutic applications, particularly immunomodulatory properties, wound healing and tissue regeneration. The exact physiologic role of MSCs, however, remains poorly understood, and this gap in knowledge significantly impedes the rational development of therapeutic cells. Here, we considered interferon γ (IFN-γ) and tumor necrosis factor alpha (TNF-α), two cytokines likely encountered physiologically and commonly used in cell manufacturing. For comparison, we studied interleukin-10 (IL-10) (anti-inflammatory) and interleukin-4 (IL-4) (type 2 cytokine).

METHODS

We directly assessed the effects of these cytokines on bone marrow MSCs by comparing RNA Seq transcriptional profiles. Western blotting and flow cytometry were also used to evaluate effects of cytokine priming.

RESULTS

The type 1 cytokines (IFN-γ and TNF-α) induced striking changes in gene expression and remarkably different profiles from one another. Importantly, priming MSCs with either of these cytokines did not increase variability among multiple donors beyond what is intrinsic to non-primed MSCs from different donors. IFN-γ-primed MSCs expressed IDO1 and chemokines that recruit activated T cells. In contrast, TNF-α-primed MSCs expressed genes in alternate pathways, namely PGE2 and matrix metalloproteinases synthesis, and chemokines that recruit neutrophils. IL-10 and IL-4 priming had little to no effect.

CONCLUSIONS

Our data suggest that IFN-γ-primed MSCs may be a more efficacious immunosuppressive therapy aimed at diseases that target T cells (ie, graft-versus-host disease) compared with TNF-α-primed or non-primed MSCs, which may be better suited for therapies in other disease settings. These results contribute to our understanding of MSC bioactivity and suggest rational ex vivo cytokine priming approaches for MSC manufacturing and therapeutic applications.

Engineering the IL-4/IL-13 axis for targeted immune modulation

The structurally and functionally related interleukin-4 (IL-4) and IL-13 cytokines play pivotal roles in shaping immune activity. The IL-4/IL-13 axis is best known for its critical role in T helper 2 (Th2) cell-mediated Type 2 inflammation, which protects the host from large multicellular pathogens, such as parasitic helminth worms, and regulates immune responses to allergens. In addition, IL-4 and IL-13 stimulate a wide range of innate and adaptive immune cells, as well as non-hematopoietic cells, to coordinate various functions, including immune regulation, antibody production, and fibrosis. Due to its importance for a broad spectrum of physiological activities, the IL-4/IL-13 network has been targeted through a variety of molecular engineering and synthetic biology approaches to modulate immune behavior and develop novel therapeutics. Here, we review ongoing efforts to manipulate the IL-4/IL-13 axis, including cytokine engineering strategies, formulation of fusion proteins, antagonist development, cell engineering approaches, and biosensor design. We discuss how these strategies have been employed to dissect IL-4 and IL-13 pathways, as well as to discover new immunotherapies targeting allergy, autoimmune diseases, and cancer. Looking ahead, emerging bioengineering tools promise to continue advancing fundamental understanding of IL-4/IL-13 biology and enabling researchers to exploit these insights to develop effective interventions.

Enhancing Spns2/S1P in macrophages alleviates hyperinflammation and prevents immunosuppression in sepsis

Sepsis is a leading cause of in-hospital mortality resulting from a dysregulated response to infection. Novel immunomodulatory therapies targeting macrophage metabolism have emerged as an important focus for current sepsis research. However, understanding the mechanisms underlying macrophage metabolic reprogramming and how they impact immune response requires further investigation. Here, we identify macrophage-expressed Spinster homolog 2 (Spns2), a major transporter of sphingosine-1-phosphate (S1P), as a crucial metabolic mediator that regulates inflammation through the lactate-reactive oxygen species (ROS) axis. Spns2 deficiency in macrophages significantly enhances glycolysis, thereby increasing intracellular lactate production. As a key effector, intracellular lactate promotes pro-inflammatory response by increasing ROS generation. The overactivity of the lactate-ROS axis drives lethal hyperinflammation during the early phase of sepsis. Furthermore, diminished Spns2/S1P signaling impairs the ability of macrophages to sustain an antibacterial response, leading to significant innate immunosuppression in the late stage of infection. Notably, reinforcing Spns2/S1P signaling contributes to balancing the immune response during sepsis, preventing both early hyperinflammation and later immunosuppression, making it a promising therapeutic target for sepsis.

IL-4 and IL-13: Regulators and Effectors of Wound Repair

Type 2 immunity mediates protective responses to helminths and pathological responses to allergens, but it also has broad roles in the maintenance of tissue integrity, including wound repair. Type 2 cytokines are known to promote fibrosis, an overzealous repair response, but their contribution to healthy wound repair is less well understood. This review discusses the evidence that the canonical type 2 cytokines, IL-4 and IL-13, are integral to the tissue repair process through two main pathways. First, essential for the progression of effective tissue repair, IL-4 and IL-13 suppress the initial inflammatory response to injury. Second, these cytokines regulate how the extracellular matrix is modified, broken down, and rebuilt for effective repair. IL-4 and/or IL-13 amplifies multiple aspects of the tissue repair response, but many of these pathways are highly redundant and can be induced by other signals. Therefore, the exact contribution of IL-4Rα signaling remains difficult to unravel.

Peptidoglycan-induced modulation of metabolic and inflammatory responses

Bacterial cell wall peptidoglycan is composed of innate immune ligands and, due to its important structural role, also regulates access to many other innate immune ligands contained within the bacteria. There is a growing body of literature demonstrating how innate immune recognition impacts the metabolic functions of immune cells and how metabolic changes are not only important to inflammatory responses but are often essential. Peptidoglycan is primarily sensed in the context of the whole bacteria during lysosomal degradation; consequently, the innate immune receptors for peptidoglycan are primarily intracellular cytosolic innate immune sensors. However, during bacterial growth, peptidoglycan fragments are shed and can be found in the bloodstream of humans and mice, not only during infection but also derived from the abundant bacterial component of the gut microbiota. These peptidoglycan fragments influence cells throughout the body and are important for regulating inflammation and whole-body metabolic function. Therefore, it is important to understand how peptidoglycan-induced signals in innate immune cells and cells throughout the body interact to regulate how the body responds to both pathogenic and nonpathogenic bacteria. This mini-review will highlight key research regarding how cellular metabolism shifts in response to peptidoglycan and how systemic peptidoglycan sensing impacts whole-body metabolic function.

Prostaglandin E 2 controls the metabolic adaptation of T cells to the intestinal microenvironment

Immune cells must adapt to different environments during the course of an immune response. We studied the adaptation of CD8 + T cells to the intestinal microenvironment and how this process shapes their residency in the gut. CD8 + T cells progressively remodel their transcriptome and surface phenotype as they acquire gut residency, and downregulate expression of mitochondrial genes. Human and mouse gut-resident CD8 + T cells have reduced mitochondrial mass, but maintain a viable energy balance to sustain their function. We found that the intestinal microenvironment is rich in prostaglandin E 2 (PGE 2 ), which drives mitochondrial depolarization in CD8 + T cells. Consequently, these cells engage autophagy to clear depolarized mitochondria, and enhance glutathione synthesis to scavenge reactive oxygen species (ROS) that result from mitochondrial depolarization. Impairing PGE 2 sensing promotes CD8 + T cell accumulation in the gut, while tampering with autophagy and glutathione negatively impacts the T cell population. Thus, a PGE 2 -autophagy-glutathione axis defines the metabolic adaptation of CD8 + T cells to the intestinal microenvironment, to ultimately influence the T cell pool.

ETS transcription factors: Multifaceted players from cancer progression to tumor immunity

The E26 transformation specific (ETS) family comprises 28 transcription factors, the majority of which are involved in tumor initiation and development. Serving as a group of functionally heterogeneous gene regulators, ETS factors possess a structurally conserved DNA-binding domain. As one of the most prominent families of transcription factors that control diverse cellular functions, ETS activation is modulated by multiple intracellular signaling pathways and post-translational modifications. Disturbances in ETS activity often lead to abnormal changes in oncogenicity, including cancer cell survival, growth, proliferation, metastasis, genetic instability, cell metabolism, and tumor immunity. This review systematically addresses the basics and advances in studying ETS factors, from their tumor relevance to clinical translational utility, with a particular focus on elucidating the role of ETS family in tumor immunity, aiming to decipher the vital role and clinical potential of regulation of ETS factors in the cancer field.

COX-2/PGE2 upregulation contributes to the chromosome 17p-deleted lymphoma

Deletions of chromosome 17p, where TP53 gene locates, are the most frequent chromosome alterations in human cancers and associated with poor outcomes in patients. Our previous work suggested that there were p53-independent mechanisms involved in chromosome 17p deletions-driven cancers. Here, we report that altered arachidonate metabolism, due to the deficiency of mouse Alox8 on chromosome 11B3 (homologous to human ALOX15B on chromosome 17p), contributes to the B cell malignancy. While the metabolites produced from lipoxygenase pathway reduced, chromosome 11B3 deletions or Alox8 loss, lead to upregulating its paralleling cyclooxygenase pathway, indicated by the increased levels of oncometabolite prostaglandin E2. Ectopic PGE2 prevented the apoptosis and differentiation of pre-B cells. Further studies revealed that Alox8 deficiency dramatically and specifically induced Cox-2(Ptgs2) gene expression. Repressing Cox-2 by its shRNAs impaired the tumorigenesis driven by Alox8 loss. And, in turn, tumor cells with Alox8 or 11B3 loss were sensitive to the COX-2 inhibitor celecoxib. This correlation between COX-2 upregulation and chromosome 17p deletions was consistent in human B-cell lymphomas. Hence, our studies reveal that the arachidonate metabolism abnormality with unbalanced ALOX and COX pathways underlies human cancers with 17p deletions and suggest new susceptibility for this disease.

Chronic Diclofenac Exposure Increases Mitochondrial Oxidative Stress, Inflammatory Mediators, and Cardiac Dysfunction

PURPOSE

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among one of the most commonly prescribed medications for pain and inflammation. Diclofenac (DIC) is a commonly prescribed NSAID that is known to increase the risk of cardiovascular diseases. However, the mechanisms underlying its cardiotoxic effects remain largely unknown. In this study, we tested the hypothesis that chronic exposure to DIC increases oxidative stress, which ultimately impairs cardiovascular function.

METHODS AND RESULTS

Mice were treated with DIC for 4 weeks and subsequently subjected to in vivo and in vitro functional assessments. Chronic DIC exposure resulted in not only systolic but also diastolic dysfunction. DIC treatment, however, did not alter blood pressure or electrocardiographic recordings. Importantly, treatment with DIC significantly increased inflammatory cytokines and chemokines as well as cardiac fibroblast activation and proliferation. There was increased reactive oxygen species (ROS) production in cardiomyocytes from DIC-treated mice, which may contribute to the more depolarized mitochondrial membrane potential and reduced energy production, leading to a significant decrease in sarcoplasmic reticulum (SR) Ca2+ load, Ca2+ transients, and sarcomere shortening. Using unbiased metabolomic analyses, we demonstrated significant alterations in oxylipin profiles towards inflammatory features in chronic DIC treatment.

CONCLUSIONS

Together, chronic treatment with DIC resulted in severe cardiotoxicity, which was mediated, in part, by an increase in mitochondrial oxidative stress.

Deleterious effects of cardiomyocyte-specific prostaglandin E2 EP3 receptor overexpression on cardiac function after myocardial infarction

AIMS

Prostaglandin E2 (PGE2) is a lipid hormone that signals through 4 different G-protein coupled receptor subtypes which act to regulate key physiological processes. Our laboratory has previously reported that PGE2 through its EP3 receptor reduces cardiac contractility at the level of isolated cardiomyocytes and in the isolated working heart preparation. We therefore hypothesized that cardiomyocyte specific overexpression of the PGE2 EP3 receptor further decreases cardiac function in a mouse model of heart failure produced by myocardial infarction.

MAIN METHODS

Our study tested this hypothesis using EP3 transgenic mice (EP3 TG), which overexpress the porcine analogue of human EP3 in the cardiomyocytes, and their wildtype (WT) littermates. Mice were analyzed 2 wks after myocardial infarction (MI) or sham operation by echocardiography, RT-PCR, immunohistochemistry, and histology.

KEY FINDINGS

We found that the EP3 TG sham controls had a reduced ejection fraction, reduced fractional shortening, and an increased left ventricular dimension at systole and diastole compared to the WT sham controls. Moreover, there was a further reduction in the EP3 TG mice after myocardial infarction. Additionally, single-cell analysis of cardiomyocytes isolated from EP3 TG mice showed reduced contractility under basal conditions. Overexpression of EP3 significantly increased cardiac hypertrophy, interstitial collagen fraction, macrophage, and T-cell infiltration in the sham operated group. Interestingly, after MI, there were no changes in hypertrophy but there were changes in collagen fraction, and inflammatory cell infiltration.

SIGNIFICANCE

Overexpression of EP3 reduces cardiac function under basal conditions and this is exacerbated after myocardial infarction.

Functional Potassium Channels in Macrophages

Macrophages are the predominant component of innate immunity, which is an important protective barrier of our body. Macrophages are present in all organs and tissues of the body, their main functions include immune surveillance, bacterial killing, tissue remodeling and repair, and clearance of cell debris. In addition, macrophages can present antigens to T cells and facilitate inflammatory response by releasing cytokines. Macrophages are of high concern due to their crucial roles in multiple physiological processes. In recent years, new advances are emerging after great efforts have been made to explore the mechanisms of macrophage activation. Ion channel is a class of multimeric transmembrane protein that allows specific ions to go through cell membrane. The flow of ions through ion channel between inside and outside of cell membrane is required for maintaining cell morphology and intracellular signal transduction. Expressions of various ion channels in macrophages have been detected. The roles of ion channels in macrophage activation are gradually caught attention. K⁺ channels are the most studied channels in immune system. However, very few of published papers reviewed the studies of K⁺ channels on macrophages. Here, we will review the four types of K⁺ channels that are expressed in macrophages: voltage-gated K⁺ channel, calcium-activated K⁺ channel, inwardly rectifying K⁺ channel and two-pore domain K⁺ channel.

Role of prostaglandin E2 in macrophage polarization: Insights into atherosclerosis

Atherosclerosis, a trigger of cardiovascular disease, poses grave threats to human health. Although atherosclerosis depends on lipid accumulation and vascular wall inflammation, abnormal phenotypic regulation of macrophages is considered the pathological basis of atherosclerosis. Macrophage polarization mainly refers to the transformation of macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, which has recently become a much-discussed topic. Increasing evidence has shown that M2 macrophage polarization can alleviate atherosclerosis progression. PGE₂ is a bioactive lipid that has been observed to be elevated in atherosclerosis and to play a pro-inflammatory role, yet recent studies have reported that PGE₂ promotes anti-inflammatory M2 macrophage polarization and mitigates atherosclerosis progression. However, the mechanisms by which PGE₂ acts remain unclear. This review summarizes current knowledge of PGE₂ and macrophages in atherosclerosis. Additionally, we discuss potential PGE₂ mechanisms of macrophage polarization, including CREB, NF-κB, and STAT signaling pathways, which may provide important therapeutic strategies based on targeting PGE₂ pathways to modulate macrophage polarization for atherosclerosis treatment.

Cytotoxicity, Mitochondrial Functionality, and Redox Status of Human Conjunctival Cells after Short and Chronic Exposure to Preservative-Free Bimatoprost 0.03% and 0.01%: An In Vitro Comparative Study

Prostaglandin analogues (PGAs), including bimatoprost (BIM), are generally the first-line therapy for glaucoma due to their greater efficacy, safety, and convenience of use. Commercial solutions of preservative-free BIM (BIM 0.03% and 0.01%) are already available, although their topical application may result in ocular discomfort. This study aimed to evaluate the in vitro effects of preservative-free BIM 0.03% vs. 0.01% in the human conjunctival epithelial (HCE) cell line. Our results showed that long-term exposure to BIM 0.03% ensues a significant decrease in cell proliferation and viability. Furthermore, these events were associated with cell cycle arrest, apoptosis, and alterations of ΔΨ_m. BIM 0.01% does not exhibit cytotoxicity, and no negative influence on conjunctival cell growth and viability or mitochondrial activity has been observed. Short-time exposure also demonstrates the ability of BIM 0.03% to trigger reactive oxygen species (ROS) production and mitochondrial hyperpolarisation. An in silico drug network interaction was also performed to explore known and predicted interactions of BIM with proteins potentially involved in mitochondrial membrane potential dissipation. Our findings overall strongly reveal better cellular tolerability of BIM 0.01% vs. BIM 0.03% in HCE cells.

Tumor-associated macrophages are shaped by intratumoral high potassium via Kir2.1

The tumor microenvironment (TME) is a unique niche governed by constant crosstalk within and across all intratumoral cellular compartments. In particular, intratumoral high potassium (K⁺) has shown immune-suppressive potency on T cells. However, as a pan-cancer characteristic associated with local necrosis, the impact of this ionic disturbance on innate immunity is unknown. Here, we reveal that intratumoral high K⁺ suppresses the anti-tumor capacity of tumor-associated macrophages (TAMs). We identify the inwardly rectifying K⁺ channel Kir2.1 as a central modulator of TAM functional polarization in high K⁺ TME, and its conditional depletion repolarizes TAMs toward an anti-tumor state, sequentially boosting local anti-tumor immunity. Kir2.1 deficiency disturbs the electrochemically dependent glutamine uptake, engendering TAM metabolic reprogramming from oxidative phosphorylation toward glycolysis. Kir2.1 blockade attenuates both murine tumor- and patient-derived xenograft growth. Collectively, our findings reveal Kir2.1 as a determinant and potential therapeutic target for regaining the anti-tumor capacity of TAMs within ionic-imbalanced TME.

Aminooxyacetic acid hemihydrochloride inhibits osteoclast differentiation and bone resorption by attenuating oxidative phosphorylation

Osteoclasts undergo active metabolic reprogramming to acquire the energy needed during differentiation and bone resorption. Compared with immature osteoclasts, mature osteoclasts comprise higher levels of electron transport chain enzymes and more metabolically active mitochondria. Of all energy metabolism pathways, oxidative phosphorylation is considered to be the most efficient in supplying energy to osteoclasts. We found that the malate-aspartate shuttle inhibitor aminooxyacetic acid hemihydrochloride inhibits osteoclastogenesis and bone resorption by inhibiting exchange of reducing equivalents between the cytosol and the mitochondrial matrix and attenuating mitochondrial oxidative phosphorylation in vitro. The weakening of the oxidative phosphorylation pathway resulted in reduced mitochondrial function and inadequate energy supply along with reduced reactive oxygen species production. Furthermore, treatment with aminooxyacetic acid hemihydrochloride helped recover bone loss in ovariectomized mice. Our findings highlight the potential of interfering with the osteoclast intrinsic energy metabolism pathway as a treatment for osteoclast-mediated osteolytic diseases.

SILAC-based quantitative proteomics to investigate the eicosanoid associated inflammatory response in activated macrophages

BACKGROUND

Macrophages play a central role in inflammation by phagocytosing invading pathogens, apoptotic cells and debris, as well as mediating repair of tissues damaged by trauma. In order to do this, these dynamic cells generate a variety of inflammatory mediators including eicosanoids such as prostaglandins, leukotrienes and hydroxyeicosatraenoic acids (HETEs) that are formed through the cyclooxygenase, lipoxygenase and cytochrome P450 pathways. The ability to examine the effects of eicosanoid production at the protein level is therefore critical to understanding the mechanisms associated with macrophage activation.

RESULTS

This study presents a stable isotope labelling with amino acids in cell culture (SILAC) -based proteomics strategy to quantify the changes in macrophage protein abundance following inflammatory stimulation with Kdo2-lipid A and ATP, with a focus on eicosanoid metabolism and regulation. Detailed gene ontology analysis, at the protein level, revealed several key pathways with a decrease in expression in response to macrophage activation, which included a promotion of macrophage polarisation and dynamic changes to energy requirements, transcription and translation. These findings suggest that, whilst there is evidence for the induction of a pro-inflammatory response in the form of prostaglandin secretion, there is also metabolic reprogramming along with a change in cell polarisation towards a reduced pro-inflammatory phenotype.

CONCLUSIONS

Advanced quantitative proteomics in conjunction with functional pathway network analysis is a useful tool to investigate the molecular pathways involved in inflammation.

Single-cell RNA-Seq reveals changes in immune landscape in post-traumatic osteoarthritis

Osteoarthritis (OA) is the most common joint disease, affecting over 300 million people world-wide. Accumulating evidence attests to the important roles of the immune system in OA pathogenesis. Understanding the role of various immune cells in joint degeneration or joint repair after injury is vital for improving therapeutic strategies for treating OA. Post-traumatic osteoarthritis (PTOA) develops in ~50% of individuals who have experienced an articular trauma like an anterior cruciate ligament (ACL) rupture. Here, using the high resolution of single-cell RNA sequencing, we delineated the temporal dynamics of immune cell accumulation in the mouse knee joint after ACL rupture. Our study identified multiple immune cell types in the joint including neutrophils, monocytes, macrophages, B cells, T cells, NK cells and dendritic cells. Monocytes and macrophage populations showed the most dramatic changes after injury. Further characterization of monocytes and macrophages reveled 9 major subtypes with unique transcriptomics signatures, including a tissue resident Lyve1hiFolr2hi macrophage population and Trem2hiFcrls+ recruited macrophages, both showing enrichment for phagocytic genes and growth factors such as Igf1, Pdgfa and Pdgfc. We also identified several genes induced or repressed after ACL injury in a cell type-specific manner. This study provides new insight into PTOA-associated changes in the immune microenvironment and highlights macrophage subtypes that may play a role in joint repair after injury.

Depletion of oocyte dynamin-related protein 1 shows maternal-effect abnormalities in embryonic development

Eggs contain about 200,000 mitochondria that generate adenosine triphosphate and metabolites essential for oocyte development. Mitochondria also integrate metabolism and transcription via metabolites that regulate epigenetic modifiers, but there is no direct evidence linking oocyte mitochondrial function to the maternal epigenome and subsequent embryo development. Here, we have disrupted oocyte mitochondrial function via deletion of the mitochondrial fission factor Drp1. Fission-deficient oocytes exhibit a high frequency of failure in peri- and postimplantation development. This is associated with altered mitochondrial function, changes in the oocyte transcriptome and proteome, altered subcortical maternal complex, and a decrease in oocyte DNA methylation and H3K27me3. Transplanting pronuclei of fertilized Drp1 knockout oocytes to normal ooplasm fails to rescue embryonic lethality. We conclude that mitochondrial function plays a role in establishing the maternal epigenome, with serious consequences for embryo development.

Prostaglandin 2α Promotes Autophagy and Mitochondrial Energy Production in Fish Hepatocytes

Fatty liver, characterized by excessive lipid droplet (LD) accumulation in hepatocytes, is a common physiological condition in humans and aquaculture species. Lipid mobilization is an important strategy for modulating the number and size of cellular LDs. Cyclooxygenase (COX)-mediated arachidonic acid derivatives are known to improve lipid catabolism in fish; however, the specific derivatives remain unknown. In the present study, we showed that serum starvation induced LD degradation via autophagy, lipolysis, and mitochondrial energy production in zebrafish hepatocytes, accompanied by activation of the COX pathway. The cellular concentration of PGF2α, but not other prostaglandins, was significantly increased. Administration of a COX inhibitor or interference with PGF2α synthase abolished serum deprivation-induced LD suppression, LD-lysosome colocalization, and expression of autophagic genes. Additionally, exogenous PGF2α suppressed the accumulation of LDs, promoted the accumulation of lysosomes with LD and the autophagy marker protein LC3A/B, and augmented the expression of autophagic genes. Moreover, PGF2α enhanced mitochondrial accumulation and ATP production, and increased the transcript levels of β-oxidation- and mitochondrial respiratory chain-related genes. Collectively, these findings demonstrate that the COX pathway is implicated in lipid degradation induced by energy deprivation, and that PGF2α is a key molecule triggering autophagy, lipolysis, and mitochondrial development in zebrafish hepatocytes.

A common framework of monocyte-derived macrophage activation

Macrophages populate every organ during homeostasis and disease, displaying features of tissue imprinting and heterogeneous activation. The disconnected picture of macrophage biology that has emerged from these observations is a barrier for integration across models or with in vitro macrophage activation paradigms. We set out to contextualize macrophage heterogeneity across mouse tissues and inflammatory conditions, specifically aiming to define a common framework of macrophage activation. We built a predictive model with which we mapped the activation of macrophages across 12 tissues and 25 biological conditions, finding a notable commonality and finite number of transcriptional profiles, in particular among infiltrating macrophages, which we modeled as defined stages along four conserved activation paths. These activation paths include a "phagocytic" regulatory path, an "inflammatory" cytokine-producing path, an "oxidative stress" antimicrobial path, or a "remodeling" extracellular matrix deposition path. We verified this model with adoptive cell transfer experiments and identified transient RELMɑ expression as a feature of monocyte-derived macrophage tissue engraftment. We propose that this integrative approach of macrophage classification allows the establishment of a common predictive framework of monocyte-derived macrophage activation in inflammation and homeostasis.

Prostaglandin E2 receptor 3 (EP3) promotes M1 macrophages polarization in unexplained recurrent pregnancy loss (uRPL)

Unexplained Recurrent Pregnancy Loss (uRPL) is associated with macrophage polarization, which can be modulated by prostaglandin E2 (PGE2). Our previous study demonstrated that PGE2 receptor 3 (EP3) signaling is induced in the first trimester placentas of uRPL patients compared to its expression in healthy controls. However, whether EP3 plays a role in macrophage polarization at the maternal-fetal interface of uRPL women remains unknown. The positive expression of EP3 in decidual macrophages was confirmed by double immunofluorescence staining in the first trimester placentas collected from uRPL patients and healthy controls. CD68, iNOS and CD163 were used as immunofluorescence marker for decidual macrophages, M1 and M2 macrophages. To clarify the effects of EP3 on macrophage polarization, THP-1 monocyte cells were applied as M0 macrophages after phorbol 12-myristate 13-acetate (PMA) treatment for in vitro study. The mRNA levels of representative M1 markers (interleukin-1β and interleukin-6) and M2 markers (interleukin-10 and arginase-1) were quantified with qPCR in M0 macrophages being stimulated with sulprostone (an EP3 agonist) or L-798, 106 (an EP3 antagonist). We found that EP3 expression was upregulated in the decidual macrophages of first trimester placentas from uRPL patients compared to healthy controls. Furthermore, EP3 expression was increased in M1 macrophages compared to in M2 macrophages in first trimester placentas of uRPL patients. Sulprostone intensified the mRNA levels of IL-6 together with interferon-γ (IFN-γ), while L-798,106 stimulated the mRNA expression of IL-10 and Arg-1 in a dose-dependent manner.

Oocyte mitochondria – Key regulators of oocyte function and potential therapeutic targets for improving fertility

The development of oocytes and early embryos is dependent on mitochondrial ATP production. This reliance on mitochondrial activity, together with the exclusively maternal inheritance of mitochondria in development, places mitochondria as central regulators of both fertility and transgenerational inheritance mechanisms. Mitochondrial mass and mtDNA content massively increase during oocyte growth. They are highly dynamic organelles and oocyte maturation is accompanied by mitochondrial trafficking around subcellular compartments. Due to their key roles in generation of ATP and reactive oxygen species, oocyte mitochondrial defects have largely been linked with energy deficiency and oxidative stress. Pharmacological treatments and mitochondrial supplementation have been proposed to improve oocyte quality and fertility by enhancing ATP generation and reducing reactive oxygen species levels. More recently, the role of mitochondria-derived metabolites in controlling epigenetic modifiers has provided a mechanistic basis for mitochondria-nuclear crosstalk, allowing adaptation of gene expression to specific metabolic states. Here, we discuss the multi-faceted mechanisms by which mitochondrial function influence oocyte quality, as well as longer-term developmental events within and across generations.

Translation and emerging functions of non-coding RNAs in inflammation and immunity

Regulatory non‐coding RNAs (ncRNAs) including small non‐coding RNAs (sRNAs), long non‐coding RNAs (lncRNAs), and circular RNAs (circRNAs) have gained considerable attention in the last few years. This is mainly due to their condition‐ and tissue‐specific expression and their various modes of action, which suggests them as promising biomarkers and therapeutic targets. One important mechanism of ncRNAs to regulate gene expression is through translation of short open reading frames (sORFs). These sORFs can be located in lncRNAs, in non‐translated regions of mRNAs where upstream ORFs (uORFs) represent the majority, or in circRNAs. Regulation of their translation can function as a quick way to adapt protein production to changing cellular or environmental cues, and can either depend solely on the initiation and elongation of translation, or on the roles of the produced functional peptides. Due to the experimental challenges to pinpoint translation events and to detect the produced peptides, translational regulation through regulatory RNAs is not well studied yet. In the case of circRNAs, they have only recently started to be recognized as regulatory molecules instead of mere artifacts of RNA biosynthesis. Of the many roles described for regulatory ncRNAs, we will focus here on their regulation during inflammation and in immunity.

Myeloid cyclooxygenase-2/prostaglandin E2/E-type prostanoid receptor 4 promotes transcription factor MafB-dependent inflammatory resolution in acute kidney injury

Following acute injury to the kidney, macrophages play an important role in recovery of functional and structural integrity, but organ fibrosis and progressive functional decline occur with incomplete recovery. Pro-resolving macrophages are characterized by increased cyclooxygenase 2 (COX-2) expression and this expression was selectively increased in kidney macrophages following injury and myeloid-specific COX-2 deletion inhibited recovery. Deletion of the myeloid prostaglandin E2 (PGE2) receptor, E-type prostanoid receptor 4 (EP4), mimicked effects seen with myeloid COX-2-/- deletion. PGE2-mediated EP4 activation induced expression of the transcription factor MafB in kidney macrophages, which upregulated anti-inflammatory genes and suppressed pro-inflammatory genes. Myeloid Mafb deletion recapitulated the effects seen with either myeloid COX-2 or EP4 deletion following acute kidney injury, with delayed recovery, persistent presence of pro-inflammatory kidney macrophages, and increased kidney fibrosis. Thus, our studies identified a previously unknown mechanism by which prostaglandins modulate macrophage phenotype following acute organ injury and provide new insight into mechanisms underlying detrimental kidney effects of non-steroidal anti-inflammatory drugs that inhibit cyclooxygenase activity.

Mitochondrial metabolism coordinates stage-specific repair processes in macrophages during wound healing

Wound healing is a coordinated process that initially relies on pro-inflammatory macrophages, followed by a pro-resolution function of these cells. Changes in cellular metabolism likely dictate these distinct activities, but the nature of these changes has been unclear. Here, we profiled early- versus late-stage skin wound macrophages in mice at both the transcriptional and functional levels. We found that glycolytic metabolism in the early phase is not sufficient to ensure productive repair. Instead, by combining conditional disruption of the electron transport chain with deletion of mitochondrial aspartyl-tRNA synthetase, followed by single-cell sequencing analysis, we found that a subpopulation of early-stage wound macrophages are marked by mitochondrial ROS (mtROS) production and HIF1α stabilization, which ultimately drives a pro-angiogenic program essential for timely healing. In contrast, late-phase, pro-resolving wound macrophages are marked by IL-4Rα-mediated mitochondrial respiration and mitohormesis. Collectively, we identify changes in mitochondrial metabolism as a critical control mechanism for macrophage effector functions during wound healing.

Mitochondrial matrix protein C14orf159 attenuates colorectal cancer metastasis by suppressing Wnt/β-catenin signalling

BACKGROUND

The mechanisms underlying metastasis of colorectal cancer (CRC) remain unclear. C14orf159 is a mitochondrial matrix protein converting D-glutamate to 5-oxo-D-proline. Other metabolic functions of C14orf159, especially on mitochondrial metabolism, and its contribution to CRC metastasis, are not elucidated.

METHODS

Metabolome analysis by gas chromatography-mass spectrometry, RNA-sequencing analysis, flow cytometry, migration and invasion assay, sphere-formation assay using C14orf159-knockout and -stable expressing cells, immunohistochemistry of C14orf159 in human CRC specimens, and xenograft experiments using Balb/c nude mice were conducted.

RESULTS

C14orf159 maintained the mitochondrial membrane potential of human CRC cells, and its involvement in amino acid and glutathione metabolism was demonstrated. In human CRC specimens, a decrease in C14orf159 expression at the invasive front of the tumour and in metastasis was determined. C14orf159 was also shown to attenuate the migration, invasion, and spheroid growth of CRC cells in vitro and colorectal tumour growth and metastasis in vivo. Mechanistically, C14orf159 reduced the expression of genes involved in CRC metastasis, including members of the Wnt and MMP family, by maintaining the mitochondrial membrane potential.

CONCLUSIONS

Our findings link mitochondrial membrane potential to Wnt/β-catenin signalling and reveal a previously unrecognised function of the mitochondrial matrix protein C14orf159 as a suppressor of CRC metastasis.

Microbiota-derived acetate enables the metabolic fitness of the brain innate immune system during health and disease

As tissue macrophages of the central nervous system (CNS), microglia constitute the pivotal immune cells of this organ. Microglial features are strongly dependent on environmental cues such as commensal microbiota. Gut bacteria are known to continuously modulate microglia maturation and function by the production of short-chain fatty acids (SCFAs). However, the precise mechanism of this crosstalk is unknown. Here we determined that the immature phenotype of microglia from germ-free (GF) mice is epigenetically imprinted by H3K4me3 and H3K9ac on metabolic genes associated with substantial functional alterations including increased mitochondrial mass and specific respiratory chain dysfunctions. We identified acetate as the essential microbiome-derived SCFA driving microglia maturation and regulating the homeostatic metabolic state, and further showed that it is able to modulate microglial phagocytosis and disease progression during neurodegeneration. These findings indicate that acetate is an essential bacteria-derived molecule driving metabolic pathways and functions of microglia during health and perturbation.

Macrophage monocarboxylate transporter 1 promotes peripheral nerve regeneration after injury in mice

Peripheral nerves have the capacity for regeneration, but the rate of regeneration is so slow that many nerve injuries lead to incomplete recovery and permanent disability for patients. Macrophages play a critical role in the peripheral nerve response to injury, contributing to both Wallerian degeneration and nerve regeneration, and their function has recently been shown to be dependent on intracellular metabolism. To date, the impact of their intracellular metabolism on peripheral nerve regeneration has not been studied. We examined conditional transgenic mice with selective ablation in macrophages of solute carrier family 16, member 1 (Slc16a1), which encodes monocarboxylate transporter 1 (MCT1), and found that MCT1 contributed to macrophage metabolism, phenotype, and function, specifically in regard to phagocytosis and peripheral nerve regeneration. Adoptive cell transfer of wild-type macrophages ameliorated the impaired nerve regeneration in macrophage-selective MCT1-null mice. We also developed a mouse model that overexpressed MCT1 in macrophages and found that peripheral nerves in these mice regenerated more rapidly than in control mice. Our study provides further evidence that MCT1 has an important biological role in macrophages and that manipulations of macrophage metabolism can enhance recovery from peripheral nerve injuries, for which there are currently no approved medical therapies.

Macrophage metabolic regulation in atherosclerotic plaque

Metabolism plays a key role in controlling immune cell functions. In this review, we will discuss the diversity of plaque resident myeloid cells and will focus on their metabolic demands that could reflect on their particular intraplaque localization. Defining the metabolic configuration of plaque resident myeloid cells according to their topologic distribution could provide answers to key questions regarding their functions and contribution to disease development.

SREBP1-induced fatty acid synthesis depletes macrophages antioxidant defences to promote their alternative activation

Macrophages exhibit a spectrum of activation states ranging from classical to alternative activation¹. Alternatively, activated macrophages are involved in diverse pathophysiological processes such as confining tissue parasites², improving insulin sensitivity³ or promoting an immune-tolerant microenvironment that facilitates tumour growth and metastasis⁴. Recently, the metabolic regulation of macrophage function has come into focus as both the classical and alternative activation programmes require specific regulated metabolic reprogramming⁵. While most of the studies regarding immunometabolism have focussed on the catabolic pathways activated to provide energy, little is known about the anabolic pathways mediating macrophage alternative activation. In this study, we show that the anabolic transcription factor sterol regulatory element binding protein 1 (SREBP1) is activated in response to the canonical T helper 2 cell cytokine interleukin-4 to trigger the de novo lipogenesis (DNL) programme, as a necessary step for macrophage alternative activation. Mechanistically, DNL consumes NADPH, partitioning it away from cellular antioxidant defences and raising reactive oxygen species levels. Reactive oxygen species serves as a second messenger, signalling sufficient DNL, and promoting macrophage alternative activation. The pathophysiological relevance of this mechanism is validated by showing that SREBP1/DNL is essential for macrophage alternative activation in vivo in a helminth infection model.

Macrophage Responses to Environmental Stimuli During Homeostasis and Disease

Work over the last 40 years has described macrophages as a heterogeneous population that serve as the frontline surveyors of tissue immunity. As a class, macrophages are found in almost every tissue in the body and as distinct populations within discrete microenvironments in any given tissue. During homeostasis, macrophages protect these tissues by clearing invading foreign bodies and/or mounting immune responses. In addition to varying identities regulated by transcriptional programs shaped by their respective environments, macrophage metabolism serves as an additional regulator to temper responses to extracellular stimuli. The area of research known as "immunometabolism" has been established within the last decade, owing to an increase in studies focusing on the crosstalk between altered metabolism and the regulation of cellular immune processes. From this research, macrophages have emerged as a prime focus of immunometabolic studies, although macrophage metabolism and their immune responses have been studied for centuries. During disease, the metabolic profile of the tissue and/or systemic regulators, such as endocrine factors, become increasingly dysregulated. Owing to these changes, macrophage responses can become skewed to promote further pathophysiologic changes. For instance, during diabetes, obesity, and atherosclerosis, macrophages favor a proinflammatory phenotype; whereas in the tumor microenvironment, macrophages elicit an anti-inflammatory response to enhance tumor growth. Herein we have described how macrophages respond to extracellular cues including inflammatory stimuli, nutrient availability, and endocrine factors that occur during and further promote disease progression.

The expanding world of tissue-resident macrophages

The term 'macrophage' encompasses tissue cells that typically share dependence on the same transcriptional regulatory pathways (e.g. the transcription factor PU.1) and growth factors (e.g. CSF1/IL-34). They share a core set of functions that largely arise from a uniquely high phagocytic capacity manifest in their ability to clear dying cells, pathogens and scavenge damaged, toxic or modified host molecules. However, macrophages demonstrate a remarkable degree of tissue-specific functionality and have diverse origins that vary by tissue site and inflammation status. With our understanding of this diversity has come an appreciation of the longevity and replicative capacity of tissue-resident macrophages and thus the realisation that macrophages may persist through tissue perturbations and inflammatory events with important consequences for cell function. Here, we discuss our current understanding of the parameters that regulate macrophage survival and function, focusing on the relative importance of the tissue environment versus cell-intrinsic factors, such as origin, how long a cell has been resident within a tissue and prior history of activation. Thus, we reconsider the view of macrophages as wholly plastic cells and raise many unanswered questions about the relative importance of cell life-history versus environment in macrophage programming and function.

Mitochondrial metabolism regulates macrophage biology

Mitochondria are critical for regulation of the activation, differentiation, and survival of macrophages and other immune cells. In response to various extracellular signals, such as microbial or viral infection, changes to mitochondrial metabolism and physiology could underlie the corresponding state of macrophage activation. These changes include alterations of oxidative metabolism, mitochondrial membrane potential, and tricarboxylic acid (TCA) cycling, as well as the release of mitochondrial reactive oxygen species (mtROS) and mitochondrial DNA (mtDNA) and transformation of the mitochondrial ultrastructure. Here, we provide an updated review of how changes in mitochondrial metabolism and various metabolites such as fumarate, succinate, and itaconate coordinate to guide macrophage activation to distinct cellular states, thus clarifying the vital link between mitochondria metabolism and immunity. We also discuss how in disease settings, mitochondrial dysfunction and oxidative stress contribute to dysregulation of the inflammatory response. Therefore, mitochondria are a vital source of dynamic signals that regulate macrophage biology to fine-tune immune responses.