AMP-activated protein kinase enhances the phagocytic ability of macrophages and neutrophils

Innate immune response in acute critical illness: a narrative review

BACKGROUND

Activation of innate immunity is a first line of host defense during acute critical illness (ACI) that aims to contain injury and avoid tissue damages. Aberrant activation of innate immunity may also participate in the occurrence of organ failures during critical illness. This review aims to provide a narrative overview of recent advances in the field of innate immunity in critical illness, and to consider future potential therapeutic strategies.

MAIN TEXT

Understanding the underlying biological concepts supporting therapeutic strategies modulating immune response is essential in decision-making. We will develop the multiple facets of innate immune response, especially its cellular aspects, and its interaction with other defense mechanisms. We will first describe the pathophysiological mechanisms of initiation of innate immune response and its implication during ACI. We will then develop the amplification of innate immunity mediated by multiple effectors. Our review will mainly focus on myeloid and lymphoid cellular effectors, the major actors involved in innate immune-mediated organ failure. We will third discuss the interaction and integration of innate immune response in a global view of host defense, thus considering interaction with non-immune cells through immunothrombosis, immunometabolism and long-term reprogramming via trained immunity. The last part of this review will focus on the specificities of the immune response in children and the older population.

CONCLUSIONS

Recent understanding of the innate immune response integrates immunity in a highly dynamic global vision of host response. A better knowledge of the implicated mechanisms and their tissue-compartmentalization allows to characterize the individual immune profile, and one day eventually, to develop individualized bench-to-bedside immunomodulation approaches as an adjuvant resuscitation strategy.

Metabolic regulation of neutrophil functions in homeostasis and diseases

Neutrophils are the most abundant leukocytes in humans and play a role in the innate immune response by being the first cells attracted to the site of infection. While early studies presented neutrophils as almost exclusively glycolytic cells, recent advances show that these cells use several metabolic pathways other than glycolysis, such as the pentose phosphate pathway, oxidative phosphorylation, fatty acid oxidation, and glutaminolysis, which they modulate to perform their functions. Metabolism shifts from fatty acid oxidation-mediated mitochondrial respiration in immature neutrophils to glycolysis in mature neutrophils. Tissue environments largely influence neutrophil metabolism according to nutrient sources, inflammatory mediators, and oxygen availability. Inhibition of metabolic pathways in neutrophils results in impairment of certain effector functions, such as NETosis, chemotaxis, degranulation, and reactive oxygen species generation. Alteration of these neutrophil functions is implicated in certain human diseases, such as antiphospholipid syndrome, coronavirus disease 2019, and bronchiectasis. Metabolic regulators such as AMPK, HIF-1α, mTOR, and Arf6 are linked to neutrophil metabolism and function and could potentially be targeted for the treatment of diseases associated with neutrophil dysfunction. This review details the effects of alterations in neutrophil metabolism on the effector functions of these cells.

The CAMKK/AMPK Pathway Contributes to Besnoitia besnoiti-Induced NETosis in Bovine Polymorphonuclear Neutrophils

Besnoitia besnoiti is an obligate intracellular apicomplexan parasite and the causal agent of bovine besnoitiosis. Bovine besnoitiosis has a considerable economic impact in Africa and Asia due to reduced milk production, abortions, and bull infertility. In Europe, bovine besnoitiosis is classified as an emerging disease. Polymorphonuclear neutrophils (PMN) are one of the most abundant leukocytes in cattle blood and amongst the first immunological responders toward invading pathogens. In the case of B. besnoiti, bovine PMN produce reactive oxygen species (ROS), release neutrophil extracellular traps (NETs), and show increased autophagic activities upon exposure to tachyzoite stages. In that context, the general processes of NETosis and autophagy were previously reported as associated with AMP-activated protein kinase (AMPK) activation. Here, we study the role of AMPK in B. besnoiti tachyzoite-induced NET formation, thereby expanding the analysis to both upstream proteins, such as the calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK), and downstream signaling and effector molecules, such as the autophagy-related proteins ULK-1 and Beclin-1. Current data revealed early AMPK activation (<30 min) in both B. besnoiti-exposed and AMPK activator (AICAR)-treated bovine PMN. This finding correlated with upstream responses on the level of CAMKK activation. Moreover, these reactions were accompanied by an augmented autophagic activity, as represented by enhanced expression of ULK-1 but not of Beclin-1. Referring to neutrophil effector functions, AICAR treatments induced both AMPK phosphorylation and NET formation, without affecting cell viability. In B. besnoiti tachyzoite-exposed PMN, AICAR treatments failed to affect oxidative responses, but led to enhanced NET formation, thereby indicating that AMPK and autophagic activation synergize with B. besnoiti-driven NETosis.

Macrophage α7nAChR alleviates the inflammation of neonatal necrotizing enterocolitis through mTOR/NLRP3/IL-1β pathway

BACKGROUND

Neonatal necrotizing enterocolitis (NEC) is one of the most prevalent and severe intestinal emergencies in newborns. The inflammatory activation of macrophages is associated with the intestinal injury of NEC. The neuroimmune regulation mediated by α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulating macrophage activation and inflammation progression, but in NEC remains unclear. This study aims to explore the effect of macrophage α7nAChR on NEC.

METHODS

Mice NEC model were conducted with high-osmolarity formula feeding, hypoxia, and cold stimulation. The α7nAChR agonist PNU-282987 and mTOR inhibitor rapamycin were treated by intraperitoneal injections in mice. The expression and distribution of macrophages, α7nAChR, and phospho-mammalian target of rapamycin (p-mTOR) in the intestines of NEC patients and mice was assessed using immunohistochemistry, immunofluorescence, and flow cytometry. The expression of NLRP3, activated caspase-1 and IL-1β in mice intestines was detected by flow cytometry, western blot or ELISA. In vitro, the mouse RAW264.7 macrophage cell line was also cultured followed by various treatments. Expression of p-mTOR, NLRP3, activated caspase-1, and IL-1β in macrophages was determined.

RESULTS

Macrophages accumulated in the intestines and the expression of α7nAChR in the mucosal and submucosal layers of the intestines was increased in both the NEC patients and mice. The p-mTOR and CD68 were increased and co-localized in intestines of NEC patients. In vitro, α7nAChR agonist PNU-282987 significantly reduced the increase of NLRP3, activated caspase-1, and IL-1β in macrophages. PNU-282987 also significantly reduced the increase of p-mTOR. The effect was blocked by AMPK inhibitor compound C. The expression of NLRP3, activated caspase-1, and IL-1β was inhibited after mTOR inhibitor rapamycin treatment. In NEC model mice, PNU-282987 reduced the expression of p-mTOR, NLRP3, activated caspase-1, and IL-1β in the intestine. Meanwhile, rapamycin significantly attenuated NLRP3 activation and the release of IL-1β. Moreover, the proportion of intestinal macrophages and intestinal injury decreased after PNU-282987 treatment.

CONCLUSION

Macrophage α7nAChR activation mitigates NLRP3 inflammasome activation by modulating mTOR phosphorylation, and subsequently alleviates intestinal inflammation and injury in NEC.

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

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

Geniposide ameliorates acute kidney injury via enhancing the phagocytic ability of macrophages towards neutrophil extracellular traps

Acute kidney injury (AKI) is a clinically serious disorder associated with high mortality rates and an increased risk of progression to end-stage renal disease. As an essential supportive treatment for patients with respiratory failure, mechanical ventilation not only save many critically ill patients, but also affect glomerular filtration function by changing renal hemodynamics, neurohumoral and positive end-expiratory pressure, eventually leading to AKI. AMP-activated protein kinase (AMPK), a crucial energy homeostasis regulator, could enhance macrophage phagocytic ability and inhibit inflammation, but whether it can engulf neutrophil extracellular traps (NETs) and alleviate mechanical ventilation-associated AKI is still unclear. In this study, we found that geniposide significantly ameliorated histopathological damage, reduced serum Cre and BUN levels. Besides, geniposide can also induce AMPK activation and enhance macrophage phagocytic ability toward NETs. Moreover, geniposide can markedly reduce the levels of high mobility group box 1 (HMGB1), and these effects were dependent on AMPK-PI3K/Akt signaling. Altogether, these results indicated that geniposide promoted macrophage efferocytosis by inducing AMPK-PI3K/Akt signaling activation, clearing NETs and ameliorating AKI.

AMPK and the Endocrine Control of Metabolism

Complex multicellular organisms require a coordinated response from multiple tissues to maintain whole-body homeostasis in the face of energetic stressors such as fasting, cold, and exercise. It is also essential that energy is stored efficiently with feeding and the chronic nutrient surplus that occurs with obesity. Mammals have adapted several endocrine signals that regulate metabolism in response to changes in nutrient availability and energy demand. These include hormones altered by fasting and refeeding including insulin, glucagon, glucagon-like peptide-1, catecholamines, ghrelin, and fibroblast growth factor 21; adipokines such as leptin and adiponectin; cell stress-induced cytokines like tumor necrosis factor alpha and growth differentiating factor 15, and lastly exerkines such as interleukin-6 and irisin. Over the last 2 decades, it has become apparent that many of these endocrine factors control metabolism by regulating the activity of the AMPK (adenosine monophosphate-activated protein kinase). AMPK is a master regulator of nutrient homeostasis, phosphorylating over 100 distinct substrates that are critical for controlling autophagy, carbohydrate, fatty acid, cholesterol, and protein metabolism. In this review, we discuss how AMPK integrates endocrine signals to maintain energy balance in response to diverse homeostatic challenges. We also present some considerations with respect to experimental design which should enhance reproducibility and the fidelity of the conclusions.

Adenosine 5'-monophosphate-activated protein kinase (AMPK) negatively regulates the immunity and resistance to Vibrio alginolyticus of white shrimp, Penaeus vannamei

Shrimp immunology is vital in establishing prophylactic and therapeutic strategies for controlling pathological problems that threaten shrimp production. Apart from dietary treatments, the adenosine 5'-monophosphate-activated protein kinase (AMPK), an important regulatory enzyme that restores cellular energy balance during metabolic and physiological stress, is known to have therapeutic potential to improve shrimp's defense mechanism. Despite this, studies targeting the AMPK pathway in shrimp exposed to stressful conditions are vastly limited. In this study, AMPK was knocked down to assess the immunological changes and white shrimp, Penaeus vannamei resistance to Vibrio alginolyticus infection. Shrimps were injected individually and simultaneously with dsRNA targeting specific genes such as AMPK, Rheb, and TOR, after which the hepatopancreas was analyzed for the different gene expressions. The gene expressions of AMPK, Rheb, and TOR were effectively suppressed after being treated with dsRNAs. The Western blot analysis further confirmed a reduction in the protein concentration of AMPK and Rheb in the hepatopancreas. The suppression of AMPK gene led to a robust increase in the shrimp's resistance to V. alginolyticus, whereas the activation of AMPK by metformin decreased the shrimp's disease resistance. Among the mTOR downstream targets, the HIF-1α expression in shrimp treated with dsAMPK significantly increased at 48 h but returned to normal levels when shrimp were treated with dsAMPK and either dsRheb or dsTOR. Immune responses such as respiratory burst, lysozyme activity, and phagocytic activity increased, while superoxide dismutase activity decreased following the knockdown of the AMPK gene compared to the control group. However, co-injection with dsAMPK and dsTOR or dsRheb restored immune responses to normal levels. Collectively, these results demonstrate that the inactivation of AMPK may ameliorate shrimp's innate immune response to recognize and defend against pathogens via the AMPK/mTOR1 pathway.

Cardiovascular Functions of Ena/VASP Proteins: Past, Present and Beyond

Actin binding proteins are of crucial importance for the spatiotemporal regulation of actin cytoskeletal dynamics, thereby mediating a tremendous range of cellular processes. Since their initial discovery more than 30 years ago, the enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family has evolved as one of the most fascinating and versatile family of actin regulating proteins. The proteins directly enhance actin filament assembly, but they also organize higher order actin networks and link kinase signaling pathways to actin filament assembly. Thereby, Ena/VASP proteins regulate dynamic cellular processes ranging from membrane protrusions and trafficking, and cell-cell and cell-matrix adhesions, to the generation of mechanical tension and contractile force. Important insights have been gained into the physiological functions of Ena/VASP proteins in platelets, leukocytes, endothelial cells, smooth muscle cells and cardiomyocytes. In this review, we summarize the unique and redundant functions of Ena/VASP proteins in cardiovascular cells and discuss the underlying molecular mechanisms.

Promoting AMPK/SR-A1-mediated clearance of HMGB1 attenuates chemotherapy-induced peripheral neuropathy

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious side effect of chemotherapy with poorly understood mechanisms and few treatments. High-mobility group box 1 (HMGB1)-induced neuroinflammation is the main cause of CIPN. Here, we aimed to illustrate the role of the macrophage scavenger receptor A1 (SR-A1) in HMGB1 clearance and CIPN resolution.

METHODS

Oxaliplatin (L-OHP) was used to establish a CIPN model. Recombinant HMGB1 (rHMGB1) (his tag) was used to evaluate the phagocytosis of HMGB1 by macrophages.

RESULTS

In the clinic, HMGB1 expression and MMP-9 activity were increased in the plasma of patients with CIPN. Plasma HMGB1 expression was positively correlated with the cumulative dose of L-OHP and the visual analog scale. In vitro, engulfment and degradation of rHMGB1 increased and inflammatory factor expression decreased after AMP-activated protein kinase (AMPK) activation. Neutralizing antibodies, inhibitors, or knockout of SR-A1 abolished the effects of AMPK activation on rHMGB1 engulfment. In vivo, AMPK activation increased SR-A1 expression in the dorsal root ganglion, decreased plasma HMGB1 expression and MMP-9 activity, and attenuated CIPN, which was abolished by AMPK inhibition or SR-A1 knockout in the CIPN mice model.

CONCLUSION

Activation of the AMPK/SR-A1 axis alleviated CIPN by increasing macrophage-mediated HMGB1 engulfment and degradation. Therefore, promoting HMGB1 clearance may be a potential treatment strategy for CIPN. Video abstract.

Cellular mechanisms underlying the impairment of macrophage efferocytosis

The phagocytosis and clearance of dying cells by macrophages, a process termed efferocytosis, is essential for both maintaining homeostasis and promoting tissue repair after infection or sterile injury. If not removed in a timely manner, uncleared cells can undergo secondary necrosis, and necrotic cells lose membrane integrity, release toxic intracellular components, and potentially induce inflammation or autoimmune diseases. Efferocytosis also initiates the repair process by producing a wide range of pro-reparative factors. Accumulating evidence has revealed that macrophage efferocytosis defects are involved in the development and progression of a variety of inflammatory and autoimmune diseases. The underlying mechanisms of efferocytosis impairment are complex, disease-dependent, and incompletely understood. In this review, we will first summarize the current knowledge about the normal signaling and metabolic processes of macrophage efferocytosis and its importance in maintaining tissue homeostasis and repair. We then will focus on analyzing the molecular and cellular mechanisms underlying efferocytotic abnormality (impairment) in disease or injury conditions. Next, we will discuss the potential molecular targets for enhanced efferocytosis in animal models of disease. To provide a balanced view, we will also discuss some deleterious effects of efferocytosis.

Retinoids Promote Mouse Bone Marrow-Derived Macrophage Differentiation and Efferocytosis via Upregulating Bone Morphogenetic Protein-2 and Smad3

Clearance of apoptotic cells by bone marrow-derived macrophages differentiated from monocytes plays a central role in the resolution of inflammation, as the conversion of pro-inflammatory M1 macrophages to M2 macrophages that mediate the resolution process occurs during efferocytosis. Thus, proper efferocytosis is a prerequisite for proper resolution of inflammation, and failure in efferocytosis is associated with the development of chronic inflammatory diseases. Previous studies from our laboratory have shown that (13R)-all-trans-13,14-dihydroretinol (DHR), the product of retinol saturase, acting from day 4 of monocyte differentiation enhances the efferocytosis capacity of the resulted macrophages. Loss of retinol saturase in mice leads to impaired efferocytosis, and to development of autoimmunity. In the present paper, we report that in differentiating monocytes DHR, retinol, and all-trans retinoic acid all act directly on retinoic acid receptors and enhance the clearance of apoptotic cells by upregulating the expression of several efferocytosis-related genes. The effect of retinoids seems to be mediated by bone morphogenetic protein (BMP)-2, and the Smad3 transcription factor. In addition, retinoids also upregulate the expression of the vitamin D receptor and that of vascular endothelial growth factor A, indicating that altogether retinoids promote the generation of a pro-reparative M2 macrophage population during monocyte differentiation.

The effects of SARS-CoV-2 infection on modulating innate immunity and strategies of combating inflammatory response for COVID-19 therapy

The global pandemic of COVID-19 has caused huge causality and unquantifiable loss of social wealth. The innate immune response is the first line of defense against SARS-CoV-2 infection. However, strong inflammatory response associated with dysregulation of innate immunity causes severe acute respiratory syndrome (SARS) and death. In this review, we update the current knowledge on how SARS-CoV-2 modulates the host innate immune response for its evasion from host defense and its corresponding pathogenesis caused by cytokine storm. We emphasize Type I interferon response and the strategies of evading innate immune defense used by SARS-CoV-2. We also extensively discuss the cells and their function involved in the innate immune response and inflammatory response, as well as the promises and challenges of drugs targeting excessive inflammation for antiviral treatment. This review would help us to figure out the current challenge questions of SARS-CoV-2 infection on innate immunity and directions for future studies.

Signaling Pathways that Regulate Macropinocytosis in Mammalian Cells

Macropinocytosis is an evolutionarily conserved endocytic pathway that mediates non-selective uptake of extracellular fluid in bulk. Macropinocytosis is initiated by localized polymerization of the actin cytoskeleton, which generates plasma membrane protrusions that enclose part of the environment into large endocytic vesicles. From amoebae to mammalian cells, the actin dynamics that drive macropinosome formation are regulated by a conserved set of intracellular signaling proteins including Ras superfamily GTPases and PI3-kinases. In mammalian cells, multiple upstream signaling pathways control activity of these core regulators in response to cell-extrinsic and cell-intrinsic stimuli. Growth factor signaling pathways play a central role in macropinocytosis induction. In addition, an increasing number of functionally diverse processes has been identified as macropinocytosis regulators, including several nutrient-sensing and developmental signaling pathways. Many of these signaling pathways have proto-oncogenic properties, and their dysregulation drives the high macropinocytic activity that is commonly observed in cancer cells. These regulatory principles illustrate how macropinocytosis is controlled by complex upstream inputs to exert diverse cellular functions in physiological and pathological contexts.

Targeting Neutrophils for Promoting the Resolution of Inflammation

Acute inflammation is a localized and self-limited innate host-defense mechanism against invading pathogens and tissue injury. Neutrophils, the most abundant immune cells in humans, play pivotal roles in host defense by eradicating invading pathogens and debris. Ideally, elimination of the offending insult prompts repair and return to homeostasis. However, the neutrophils` powerful weaponry to combat microbes can also cause tissue damage and neutrophil-driven inflammation is a unifying mechanism for many diseases. For timely resolution of inflammation, in addition to stopping neutrophil recruitment, emigrated neutrophils need to be disarmed and removed from the affected site. Accumulating evidence documents the phenotypic and functional versatility of neutrophils far beyond their antimicrobial functions. Hence, understanding the receptors that integrate opposing cues and checkpoints that determine the fate of neutrophils in inflamed tissues provides insight into the mechanisms that distinguish protective and dysregulated, excessive inflammation and govern resolution. This review aims to provide a brief overview and update with key points from recent advances on neutrophil heterogeneity, functional versatility and signaling, and discusses challenges and emerging therapeutic approaches that target neutrophils to enhance the resolution of inflammation.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

Efferocytosis during Skeletal Muscle Regeneration

Efferocytosis, i.e., engulfment of dead cells by macrophages, is a crucial step during tissue repair after an injury. Efferocytosis delineates the transition from the pro-inflammatory phase of the inflammatory response to the recovery phase that ensures tissue reconstruction. We present here the role of efferocytosis during skeletal muscle regeneration, which is a paradigm of sterile tissue injury followed by a complete regeneration. We present the molecular mechanisms that have been described to control this process, and particularly the metabolic control of efferocytosis during skeletal muscle regeneration.

Statins and Bempedoic Acid: Different Actions of Cholesterol Inhibitors on Macrophage Activation

Statins represent the most prescribed class of drugs for the treatment of hypercholesterolemia. Effects that go beyond lipid-lowering actions have been suggested to contribute to their beneficial pharmacological properties. Whether and how statins act on macrophages has been a matter of debate. In the present study, we aimed at characterizing the impact of statins on macrophage polarization and comparing these to the effects of bempedoic acid, a recently registered drug for the treatment of hypercholesterolemia, which has been suggested to have a similar beneficial profile but fewer side effects. Treatment of primary murine macrophages with two different statins, i.e., simvastatin and cerivastatin, impaired phagocytotic activity and, concurrently, enhanced pro-inflammatory responses upon short-term lipopolysaccharide challenge, as characterized by an induction of tumor necrosis factor (TNF), interleukin (IL) 1β, and IL6. In contrast, no differences were observed under long-term inflammatory (M1) or anti-inflammatory (M2) conditions, and neither inducible NO synthase (iNOS) expression nor nitric oxide production was altered. Statin treatment led to extracellular-signal regulated kinase (ERK) activation, and the pro-inflammatory statin effects were abolished by ERK inhibition. Bempedoic acid only had a negligible impact on macrophage responses when compared with statins. Taken together, our data point toward an immunomodulatory effect of statins on macrophage polarization, which is absent upon bempedoic acid treatment.

First we eat, then we do everything else: The dynamic metabolic regulation of efferocytosis

Clearance of apoptotic cells, or "efferocytosis," is essential for diverse processes including embryonic development, tissue turnover, organ regeneration, and immune cell development. The human body is estimated to remove approximately 1% of its body mass via apoptotic cell clearance daily. This poses several intriguing cell metabolism problems. For instance, phagocytes such as macrophages must induce or suppress metabolic pathways to find, engulf, and digest apoptotic cells. Then, phagocytes must manage the potentially burdensome biomass of the engulfed apoptotic cell. Finally, phagocytes reside in complex tissue architectures that vary in nutrient availability, the types of dying cells or debris that require clearance, and the neighboring cells they interact with. Here, we review advances in our understanding of these three key areas of phagocyte metabolism. We end by proposing a model of efferocytosis that integrates recent findings and establishes a new paradigm for testing how efferocytosis prevents chronic inflammatory disease and autoimmunity.

Metformin, Macrophage Dysfunction and Atherosclerosis

Metformin is one of the most widely prescribed hypoglycemic drugs and has the potential to treat many diseases. More and more evidence shows that metformin can regulate the function of macrophages in atherosclerosis, including reducing the differentiation of monocytes and inhibiting the inflammation, oxidative stress, polarization, foam cell formation and apoptosis of macrophages. The mechanisms by which metformin regulates the function of macrophages include AMPK, AMPK independent targets, NF-κB, ABCG5/8, Sirt1, FOXO1/FABP4 and HMGB1. On the basis of summarizing these studies, we further discussed the future research directions of metformin: single-cell RNA sequencing, neutrophil extracellular traps (NETs), epigenetic modification, and metformin-based combination drugs. In short, macrophages play an important role in a variety of diseases, and improving macrophage dysfunction may be an important mechanism for metformin to expand its pleiotropic pharmacological profile. In addition, the combination of metformin with other drugs that improve the function of macrophages (such as SGLT2 inhibitors, statins and IL-1β inhibitors/monoclonal antibodies) may further enhance the pleiotropic therapeutic potential of metformin in conditions such as atherosclerosis, obesity, cancer, dementia and aging.

Resveratrol suppresses the reprogramming of macrophages into an endotoxin-tolerant state through the activation of AMP-activated protein kinase

Resveratrol has been reported to have beneficial effects on sepsis by regulating the inflammatory response. However, it remains unclear if resveratrol plays a role in the development of endotoxin tolerance. Treatment with resveratrol in macrophages stimulated with primary lipopolysaccharide (LPS) resulted in the increased production of TNF-α and IL-6 induced by a 2^nd dose of LPS (by 74.5 ± 12.9% and 63.4 ± 12%, respectively, compared to untreated cells, P < 0.05). This effect was inhibited by compound C, an AMPK inhibitor, and STO609, a calcium/calmodulin-dependent protein kinase-kinase (CaMKK) inhibitor. Resveratrol diminished the expression of interleukin-1 receptor-associated kinase M (IRAK-M) and Src homology 2 (SH2) domain-containing inositol-5-phosphatase 1 (SHIP1) by prolonging the exposure of cells to LPS (by 60.8 ± 16.3% and 70.3 ± 18.1%, respectively, compared to LPS only). The effect of resveratrol on the LPS-induced expression of IRAK-M and SHIP1 was inhibited by compound C or STO609. After a 2^nd dose of LPS, resveratrol increased phosphorylation of ERK1/2, p38, and JNK in endotoxin tolerant macrophages. In vivo systemic administration of resveratrol prevented a significant increase in mortality rate by cecal ligation and puncture in LPS-induced endotoxin-tolerant mice. These results indicate that resveratrol induces AMPK activation through the Ca²⁺/CaMKKβ pathway and suppresses the development of endotoxin tolerance by inhibiting LPS-induced expression of IRAK-M and SHIP1.

Neutrophil dysfunction in bronchiectasis: an emerging role for immunometabolism

Bronchiectasis is a heterogenous disease with multiple underlying causes. The pathophysiology is poorly understood but neutrophilic inflammation and dysfunctional killing of pathogens is believed to be key. There are, however, no licensed therapies for bronchiectasis that directly target neutrophilic inflammation. In this review, we discuss our current understanding of neutrophil dysfunction and therapeutic targeting in bronchiectasis. Immunometabolic reprogramming, a process through which inflammation changes inflammatory cell behaviour by altering intracellular metabolic pathways, is increasingly recognised across multiple inflammatory and autoimmune diseases. Here, we show evidence that much of the neutrophil dysfunction observed in bronchiectasis is consistent with immunometabolic reprogramming. Previous attempts at developing therapies targeting neutrophils have focused on reducing neutrophil numbers, resulting in increased frequency of infections. New approaches are needed and we propose that targeting metabolism could theoretically reverse neutrophil dysfunction and dysregulated inflammation. As an exemplar, 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) activation has already been shown to reverse phagocytic dysfunction and neutrophil extracellular trap (NET) formation in models of pulmonary disease. AMPK modulates multiple metabolic pathways, including glycolysis which is critical for energy generation in neutrophils. AMPK activators can reverse metabolic reprogramming and are already in clinical use and/or development. We propose the need for a new immunomodulatory approach, rather than an anti-inflammatory approach, to enhance bacterial clearance and reduce bronchiectasis disease severity.

Propofol suppresses microglial phagocytosis through the downregulation of MFG-E8

BACKGROUND

Microglia are highly motile phagocytic cells in the healthy brain with surveillance and clearance functions. Although microglia have been shown to engulf cellular debris following brain insult, less is known about their phagocytic function in the absence of injury. Propofol can inhibit microglial activity, including phagocytosis. Milk fat globule epidermal growth factor 8 (MFG-E8), as a regulator of microglia, plays an essential role in the phagocytic process. However, whether MFG-E8 affects the alteration of phagocytosis by propofol remains unknown.

METHODS

Microglial BV2 cells were treated with propofol, with or without MFG-E8. Phagocytosis of latex beads was evaluated by flow cytometry and immunofluorescence. MFG-E8, p-AMPK, AMPK, p-Src, and Src levels were assessed by western blot analysis. Compound C (AMPK inhibitor) and dasatinib (Src inhibitor) were applied to determine the roles of AMPK and Src in microglial phagocytosis under propofol treatment.

RESULTS

The phagocytic ability of microglia was significantly decreased after propofol treatment for 4 h (P < 0.05). MFG-E8 production was inhibited by propofol in a concentration- and time-dependent manner (P < 0.05). Preadministration of MFG-E8 dose-dependently (from 10 to 100 ng/ml) reversed the suppression of phagocytosis by propofol (P < 0.05). Furthermore, the decline in p-AMPK and p-Src levels induced by propofol intervention was reversed by MFG-E8 activation (P < 0.05). Administration of compound C (AMPK inhibitor) and dasatinib (Src inhibitor) to microglia blocked the trend of enhanced phagocytosis induced by MFG-E8 (P < 0.05).

CONCLUSIONS

These findings reveal the intermediate role of MFG-E8 between propofol and microglial phagocytic activity. Moreover, MFG-E8 may reverse the suppression of phagocytosis induced by propofol through the regulation of the AMPK and Src signaling pathways.

Myosin 10 Regulates Invasion, Mitosis, and Metabolic Signaling in Glioblastoma

Invasion and proliferation are defining phenotypes of cancer, and in glioblastoma blocking one stimulates the other, implying that effective therapy must inhibit both, ideally through a single target that is also dispensable for normal tissue function. The molecular motor myosin 10 meets these criteria. Myosin 10 knockout mice can survive to adulthood, implying that normal cells can compensate for its loss; its deletion impairs invasion, slows proliferation, and prolongs survival in murine models of glioblastoma. Myosin 10 deletion also enhances tumor dependency on the DNA damage and the metabolic stress responses and induces synthetic lethality when combined with inhibitors of these processes. Our results thus demonstrate that targeting myosin 10 is active against glioblastoma by itself, synergizes with other clinically available therapeutics, may have acceptable side effects in normal tissues, and has potential as a heretofore unexplored therapeutic approach for this disease.

Crbn modulates calcium influx by regulating Orai1 during efferocytosis

Calcium flux regulating intracellular calcium levels is essential and modulated for efficient efferocytosis. However, the molecular mechanism by which calcium flux is modulated during efferocytosis remains elusive. Here, we report that Orai1, a Crbn substrate, is upregulated via its attenuated interaction with Crbn during efferocytosis, which increases calcium influx into phagocytes and thereby promotes efferocytosis. We found that Crbn deficiency promoted phagocytosis of apoptotic cells, which resulted from facilitated phagocytic cup closure and was nullified by a CRAC channel inhibitor. In addition, Orai1 associated with Crbn, resulting in ubiquitination and proteasomal degradation of Orai1 and alteration of SOCE-mediated calcium influx. The association of Orai1 with Crbn was attenuated during efferocytosis, leading to reduced ubiquitination of Orai1 and consequently upregulation of Orai1 and calcium influx. Collectively, our study reveals a regulatory mechanism by which calcium influx is modulated by a Crbn-Orai1 axis to facilitate efferocytosis.

Targeting Neutrophils to Treat Acute Respiratory Distress Syndrome in Coronavirus Disease

This review describes targeting neutrophils as a potential therapeutic strategy for acute respiratory distress syndrome (ARDS) associated with coronavirus disease 2019 (COVID-19), a pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Neutrophil counts are significantly elevated in patients with COVID-19 and significantly correlated with disease severity. The neutrophil-to-lymphocyte ratio can serve as a clinical marker for predicting fatal complications related to ARDS in patients with COVID-19. Neutrophil-associated inflammation plays a critical pathogenic role in ARDS. The effector functions of neutrophils, acting as respiratory burst oxidants, granule proteases, and neutrophil extracellular traps, are linked to the pathogenesis of ARDS. Hence, neutrophils can not only be used as pathogenic markers but also as candidate drug targets for COVID-19 associated ARDS.

An Overview of the Cytoskeleton-Associated Role of PDLIM5

Regenerative medicine represented by stem cell technology has become one of the pillar medical technologies for human disease treatment. Cytoskeleton plays important roles in maintaining cell morphology, bearing external forces, and maintaining the effectiveness of cell internal structure, among which cytoskeleton related proteins are involved in and play an indispensable role in the changes of cytoskeleton. PDLIM5 is a cytoskeleton-related protein that, like other cytoskeletal proteins, acts as a binding protein. PDZ and LIM domain 5 (PDLIM5), also known as ENH (Enigma homolog), is a cytoplasmic protein with a molecular mass of about 63 KDa that consists of a PDZ domain at the N-terminus and three LIM domains at the C-terminus. PDLIM5 binds to the cytoskeleton and membrane proteins through its PDZ domain and interacts with various signaling molecules, including protein kinases and transcription factors, through its LIM domain. As a cytoskeleton-related protein, PDLIM5 plays an important role in regulating cell proliferation, differentiation and cell fate decision in multiple tissues and cell types. In this review, we briefly summarize the state of knowledge on the PDLIM5 gene, structural properties, and molecular functional mechanisms of the PDLIM5 protein, and its role in cells, tissues, and organ systems, and describe the possible underlying molecular signaling pathways. In the last part of this review, we will focus on discussing the limitations of existing research and the future prospects of PDLIM5 research in turn.

Down-regulation of AMPK signaling pathway rescues hearing loss in TFB1 transgenic mice and delays age-related hearing loss

AMP-activated protein kinase (AMPK) integrates the regulation of cell growth and metabolism. AMPK activation occurs in response to cellular energy decline and mitochondrial dysfunction triggered by reactive oxygen species (ROS). In aged Tg-mtTFB1 mice, a mitochondrial deafness mouse model, hearing loss is accompanied with cochlear pathology including reduced endocochlear potential (EP) and loss of spiral ganglion neurons (SGN), inner hair cell (IHC) synapses and outer hair cells (OHC). Accumulated ROS and increased apoptosis signaling were also detected in cochlear tissues, accompanied by activation of AMPK. To further explore the role of AMPK signaling in the auditory phenotype, we used genetically knocked out AMPKα1 as a rescue to Tg-mtTFB1 mice and observed: improved ABR wave I, EP and IHC function, normal SGNs, IHC synapses morphology and OHC survivals, with decreased ROS, reduced pro-apoptotic signaling (Bax) and increased anti-apoptotic signaling (Bcl-2) in the cochlear tissues, indicating that reduced AMPK attenuated apoptosis via ROS-AMPK-Bcl2 pathway in the cochlea. To conclude, AMPK hyperactivation causes accelerated presbycusis in Tg-mtTFB1 mice by redox imbalance and dysregulation of the apoptosis pathway. The effects of AMPK downregulation on pro-survival function and reduction of oxidative stress indicate AMPK serves as a target to rescue or relieve mitochondrial hearing loss.

Metformin Alters Human Host Responses to Mycobacterium tuberculosis in Healthy Subjects

BACKGROUND

Metformin, the most widely administered diabetes drug, has been proposed as a candidate adjunctive host-directed therapy for tuberculosis, but little is known about its effects on human host responses to Mycobacterium tuberculosis.

METHODS

We investigated in vitro and in vivo effects of metformin in humans.

RESULTS

Metformin added to peripheral blood mononuclear cells from healthy volunteers enhanced in vitro cellular metabolism while inhibiting the mammalian target of rapamycin targets p70S6K and 4EBP1, with decreased cytokine production and cellular proliferation and increased phagocytosis activity. Metformin administered to healthy human volunteers led to significant downregulation of genes involved in oxidative phosphorylation, mammalian target of rapamycin signaling, and type I interferon response pathways, particularly following stimulation with M. tuberculosis, and upregulation of genes involved in phagocytosis and reactive oxygen species production was increased. These in vivo effects were accompanied by a metformin-induced shift in myeloid cells from classical to nonclassical monocytes. At a functional level, metformin lowered ex vivo production of tumor necrosis factor α, interferon γ, and interleukin 1β but increased phagocytosis activity and reactive oxygen species production.

CONCLUSION

Metformin has a range of potentially beneficial effects on cellular metabolism, immune function, and gene transcription involved in innate host responses to M. tuberculosis.

MiR-144 protects the heart from hyperglycemia-induced injury by regulating mitochondrial biogenesis and cardiomyocyte apoptosis

Several lines of evidence have revealed the potential of microRNAs (miRNAs, miRs) as biomarkers for detecting diabetic cardiomyopathy, although their functions in hyperglycemic cardiac dysfunction are still lacking. In this study, mitochondrial biogenesis was markedly impaired induced by high glucose (HG), as evidenced by dysregulated mitochondrial structure, reduced mitochondrial DNA contents, and biogenesis-related mRNA levels, accompanied by increased cell apoptosis. MiR-144 was identified to be decreased in HG-induced cardiomyocytes and in streptozotocin (STZ)-challenged heart samples. Forced miR-144 expression enhanced mitochondrial biogenesis and suppressed cell apoptosis, while miR-144 inhibition exhibited the opposite results. Rac-1 was identified as a target gene of miR-144. Decreased Rac-1 levels activated AMPK phosphorylation and PGC-1α deacetylation, leading to increased mitochondrial biogenesis and reduced cell apoptosis. Importantly, the systemic neutralization of miR-144 attenuated mitochondrial disorder and ventricular dysfunction following STZ treatment. Additionally, plasma miR-144 decreased markedly in diabetic patients with cardiac dysfunction. The receiver-operator characteristic curve showed that plasma miR-144 could specifically predict diabetic patients developing cardiac dysfunction. In conclusion, this study provides strong evidence suggesting that miR-144 protects heart from hyperglycemia-induced injury by improving mitochondrial biogenesis and decreasing cell apoptosis via targeting Rac-1. Forced miR-144 expression might, thus, be a protective strategy for treating hyperglycemia-induced cardiac dysfunction.

Quantum dot conjugated saporin activates microglia and induces selective substantia nigra degeneration

Parkinson's disease (PD) is characterized by profound microglial driven inflammatory processes and the loss of dopamine neurons of the substantia nigra (SNc). Both microglia and dopamine neurons that are affected in the SNc are particularly vulnerable to environmental toxicants and finding more selective ways of targeting these cell types is of importance. Quantum dots (QDs) might be a useful vehicle for selectively delivering toxicants to microglia and owing to their fluorescent capability, they can be microscopically tracked within the cell. Accordingly, we assessed the impact of QDs alone and QDs conjugated to the ribosomal toxin, saporin, upon SNc microglia and dopamine neurons. We found that intra-SNc infused QDs selectively entered microglia and induced morphological changes consistent with an activated state. QDs conjugated to saporin also caused a significant loss of dopamine neurons and motor coordination (on a rotarod test) deficits, along with an increase in the inflammatory microglial actin regulatory factors, WAVE2. These data suggest that QDs might be a viable route for toxicant delivery and also has an added advantage of being fluorescently visible. Ultimately, we found SNc neurons to be exceptionally vulnerable to QD-saporin and suggest that this could be a novel targeted approach to model PD-like inflammatory pathology.

α1AMPK deletion in myelomonocytic cells induces a pro-inflammatory phenotype and enhances angiotensin II-induced vascular dysfunction

Aims

Immune cell function involves energy-dependent processes including growth, proliferation, and cytokine production. Since the AMP-activated protein kinase (AMPK) is a crucial regulator of intracellular energy homeostasis, its expression and activity may also affect innate and adaptive immune cell responses. Therefore, we aimed to investigate the consequences of α1AMPK deletion in myelomonocytic cells on vascular function, inflammation, and hypertension during chronic angiotensin II (ATII) treatment.

Methods and results

We generated a mouse strain with α1AMPK deletion in lysozyme M+ myelomonocytic cells. Compared to controls, chronic ATII infusion (1 mg/kg/day for 7 days) lead to increased vascular oxidative stress and aggravated endothelial dysfunction in LysM-Cre+ x α1AMPKfl/fl mice. This was accompanied by an increased aortic infiltration of CD11b+F4/80+ macrophages and enhanced pro-inflammatory cytokine release (tumour necrosis factor-alpha, interferon-gamma, and interleukin-6). Mechanistically, we found that increased expression of C-C chemokine receptor 2 (CCR2) in α1AMPK deficient myelomonocytic cells facilitated their recruitment to the vascular wall. In addition, expression of the ATII receptor type 1a and the oxidative burst was increased in these cells, indicating an increased susceptibility towards pro-oxidant stimuli.

Conclusions

In summary, α1AMPK deletion in myelomonocytic cells aggravates vascular oxidative stress and dysfunction by enhancing their recruitment to the vascular wall and increasing their susceptibility towards pro-oxidant stimuli. Our observations suggest that metabolic control in myelomonocytic cells has profound implications for their inflammatory phenotype and may trigger the development of vascular disease.

Ginsenoside Rg3 promotes Fc gamma receptor-mediated phagocytosis of bacteria by macrophages via an extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase-dependent mechanism

Ginsenoside Rg3 is a steroidal saponin abundant in Korean red ginseng that has high anti-inflammatory activity. Rg3 exerts an immunomodulatory effect in acute inflammatory conditions such as bacterial infections. In this study, we determined the effect of Rg3 on bacterial uptake by macrophages and the related intracellular signaling pathways. Rg3 increased macrophage phagocytosis of IgG-opsonized Escherichia coli and IgG-opsonized beads (IgGbeads), but not of non-opsonized beads. Rg3 also enhanced the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinase (p38 MAPK), but not that of Akt. The inclusion of IgGbeads in macrophage cultures also increased the phosphorylation of ERK1/2 and p38, but co-culture of macrophages with non-opsonized beads did not affect the phosphorylation of ERK1/2 and p38. The Rg3-induced promotion of phagocytosis was inhibited by PD98059, an ERK1/2 inhibitor, and SB203580, a p38 inhibitor. PD98059 inhibited Rg3-induced p38 MAPK phosphorylation, but SB203580 did not suppress ERK1/2 phosphorylation. Culture of macrophages with Rg3 increased actin polymerization, and this effect was inhibited by SB203580 and PD98059. The Rg3-induced increase in phagocytosis was also inhibited by NSC23766, a Rac1 inhibitor and CASIN, a Cdc42 inhibitor. Intraperitoneal injection of Rg3 increased the phosphorylation of ERK1/2 and p38 as well as the phagocytosis of bacteria by lung cells. These results demonstrate that ginsenoside Rg3 enhances macrophage phagocytosis of bacteria by activating the ERK1/2 and p38 MAPK pathways.

Molecular characteristics of AMPK and its role in regulating the phagocytosis of oyster hemocytes

Phagocytosis is one of the fundamental cellular immune defense parameter that helps in the elimination of the invading pathogens in both vertebrates and invertebrates, which require plenty of energy for functioning. In the present study, we identified the critical energy regulator AMP-activated protein kinase (AMPK) in Crassostrea hongkongensis which is composed of three subunits, named ChAMPK-α, ChAMPK-β, and ChAMPK-γ, and then analyzed the function of AMPK in regulating hemocyte phagocytosis. All the three ChAMPK subunits mRNA were detected to be expressed at various embryological stages, and also constitutively expressed in multiple tissues with high expression in gill and mantle. The phylogenetic tree showed that the three subunits of AMPK were correspondingly clustered with its orthologue branches. Furthermore Western Blot analysis revealed that the AMPK pharmacological inhibitors Compound C could effectively down-regulate the Thr¹⁷² phosphorylation level of AMPK-α, and the hemocyte phagocytosis was inhibited by Compound C (CC), which indicate its existence in the oyster. Our results showed that treatment of AMPK inhibitors significantly attenuated the capacity of hemocytes phagocytosis. Moreover, Compound C could also change the organization of actin cytoskeleton in the oyster hemocytes, demonstrating the crucial role of AMPK signaling in control of phagocytosis.

The Photomodulation Activity of Metformin Against Oral Microbiome

Periodontitis is one of the most common inflammatory diseases of the periodontium, which results in the inflammatory destruction of supporting structures around teeth and is closely associated with the development of systemic disease. Due to a wide variety of antibiotic resistance periodontopathic bacteria, photodynamic therapy (PDT) is a non-invasive adjunctive therapeutic modality that is capable of destroying the whole range of microbes. Metformin (Metf) is an antidiabetic drug, and recent studies suggest that cancer patients who receive Metf and are exposed to radiotherapy and chemotherapy show better outcomes. Our surveys in this review introduce Metf as a potent stimulus in increasing the efficacy of PDT in the induction of destruction in microbial cells.

Enrichment of ATP Binding Proteins Unveils Proteomic Alterations in Human Macrophage Cell Death, Inflammatory Response, and Protein Synthesis after Interaction with Candida albicans

Macrophages are involved in the primary human response to Candida albicans. After pathogen recognition, signaling pathways are activated, leading to the production of cytokines, chemokines, and antimicrobial peptides. ATP binding proteins are crucial for this regulation. Here, a quantitative proteomic and phosphoproteomic approach was carried out for the study of human macrophage ATP-binding proteins after interaction with C. albicans. From a total of 547 nonredundant quantified proteins, 137 were ATP binding proteins and 59 were detected as differentially abundant. From the differentially abundant ATP-binding proteins, 6 were kinases (MAP2K2, SYK, STK3, MAP3K2, NDKA, and SRPK1), most of them involved in signaling pathways. Furthermore, 85 phosphopeptides were quantified. Macrophage proteomic alterations including an increase of protein synthesis with a consistent decrease in proteolysis were observed. Besides, macrophages showed changes in proteins of endosomal trafficking together with mitochondrial proteins, including some involved in the response to oxidative stress. Regarding cell death mechanisms, an increase of antiapoptotic over pro-apoptotic signals is suggested. Furthermore, a high pro-inflammatory response was detected, together with no upregulation of key mi-RNAs involved in the negative feedback of this response. These findings illustrate a strategy to deepen the knowledge of the complex interactions between the host and the clinically important pathogen C. albicans.

The Hidden Cost of Modern Medical Interventions: How Medical Advances Have Shaped the Prevalence of Human Fungal Disease

Life expectancy in the West is the highest it has ever been, due to the introduction of better hygiene practices and sophisticated medical interventions for cancer, autoimmunity and infectious disease. With these modern advances, a rise in the prevalence of opportunistic infections has also been observed. These include several fungal infections, which present a particular clinical challenge due to the lack of fungal vaccines, limited diagnostics and increasing antifungal drug resistance. This mini-review outlines how modern-day clinical practices have shaped the recent increase in fungal diseases observed in the last few decades. We discuss new research that has implicated the use of immune-modulating drugs in the enhanced susceptibility of vulnerable patients to life-threatening fungal infections.

Neutrophils in the initiation and resolution of acute pulmonary inflammation: understanding biological function and therapeutic potential

Acute respiratory distress syndrome (ARDS) is the often fatal sequelae of a broad range of precipitating conditions. Despite decades of intensive research and clinical trials there remain no therapies in routine clinical practice that target the dysregulated and overwhelming inflammatory response that characterises ARDS. Neutrophils play a central role in the initiation, propagation and resolution of this complex inflammatory environment by migrating into the lung and executing a variety of pro-inflammatory functions. These include degranulation with liberation of bactericidal proteins, release of cytokines and reactive oxygen species as well as production of neutrophil extracellular traps. Although these functions are advantageous in clearing bacterial infection, the consequence of associated tissue damage, the contribution to worsening acute inflammation and prolonged neutrophil lifespan at sites of inflammation are deleterious. In this review, the importance of the neutrophil will be considered, together with discussion of recent advances in understanding neutrophil function and the factors that influence them throughout the phases of inflammation in ARDS. From a better understanding of neutrophils in this context, potential therapeutic targets are identified and discussed. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

SIRT3 diminishes inflammation and mitigates endotoxin-induced acute lung injury

Acute lung injury (ALI) is characterized by exuberant proinflammatory responses and mitochondrial dysfunction. However, the link between mitochondrial dysfunction and inflammation in ALI is not well understood. In this report, we demonstrate a critical role for the mitochondrial NAD+-dependent deacetylase, sirtuin-3 (SIRT3), in regulating macrophage mitochondrial bioenergetics, ROS formation, and proinflammatory responses. We found that SIRT3 expression was significantly diminished in lungs of mice subjected to LPS-induced ALI. SIRT3-deficient mice (SIRT3-/-) develop more severe ALI compared with wild-type controls (SIRT3+/+). Macrophages obtained from SIRT3-/- mice show significant alterations in mitochondrial bioenergetic and redox homeostasis, in association with a proinflammatory phenotype characterized by NLRP3 inflammasome activation. The SIRT3 activator viniferin restored macrophage bioenergetic function in LPS-treated macrophages. Viniferin also reduced NLRP3 activation and the production of proinflammatory cytokines, effects that were absent in SIRT3-/- macrophages. In-vivo administration of viniferin reduced production of inflammatory mediators TNF-α, MIP-2, IL-6, IL-1β, and HMGB1, and diminished neutrophil influx and severity of endotoxin-mediated ALI; this protective effect of vinferin was abolished in SIRT3-/- mice. Taken together, our results show that the induction/activation of SIRT3 may serve as a new therapeutic strategy in ALI by modulating cellular bioenergetics, controlling inflammatory responses, and reducing the severity of lung injury.

AMP-Activated Protein Kinase and Host Defense against Infection

5′-AMP-activated protein kinase (AMPK) plays diverse roles in various physiological and pathological conditions. AMPK is involved in energy metabolism, which is perturbed by infectious stimuli. Indeed, various pathogens modulate AMPK activity, which affects host defenses against infection. In some viral infections, including hepatitis B and C viral infections, AMPK activation is beneficial, but in others such as dengue virus, Ebola virus, and human cytomegaloviral infections, AMPK plays a detrimental role. AMPK-targeting agents or small molecules enhance the antiviral response and contribute to the control of microbial and parasitic infections. In addition, this review focuses on the double-edged role of AMPK in innate and adaptive immune responses to infection. Understanding how AMPK regulates host defenses will enable development of more effective host-directed therapeutic strategies against infectious diseases.

The Mitochondrial Isoform of FASTK Modulates Nonopsonic Phagocytosis of Bacteria by Macrophages via Regulation of Respiratory Complex I

Phagocytosis is a pivotal process by which innate immune cells eliminate bacteria. In this study, we explore novel regulatory mechanisms of phagocytosis driven by the mitochondria. Fas-activated serine/threonine kinase (FASTK) is an RNA-binding protein with two isoforms, one localized to the mitochondria (mitoFASTK) and the other isoform to cytosol and nucleus. The mitoFASTK isoform has been reported to be necessary for the biogenesis of the mitochondrial ND6 mRNA, which encodes an essential subunit of mitochondrial respiratory complex I (CI, NADH:ubiquinone oxidoreductase). This study investigates the role and the mechanisms of action of FASTK in phagocytosis. Macrophages from FASTK^─/─ mice exhibited a marked increase in nonopsonic phagocytosis of bacteria. As expected, CI activity was specifically reduced by almost 50% in those cells. To explore if decreased CI activity could underlie the phagocytic phenotype, we tested the effect of CI inhibition on phagocytosis. Indeed, treatment with CI inhibitor rotenone or short hairpin RNAs against two CI subunits (NDUFS3 and NDUFS4) resulted in a marked increase in nonopsonic phagocytosis of bacteria. Importantly, re-expression of mitoFASTK in FASTK-depleted macrophages was sufficient to rescue the phagocytic phenotype. In addition, we also report that the decrease in CI activity in FASTK^─/─ macrophages is associated with an increase in phosphorylation of the energy sensor AMP-activated protein kinase (AMPK) and that its inhibition using Compound C reverted the phagocytosis phenotype. Taken together, our results clearly demonstrate for the first time, to our knowledge, that mitoFASTK plays a negative regulatory role on nonopsonic phagocytosis of bacteria in macrophages through its action on CI activity.

Embigin Promotes Prostate Cancer Progression by S100A4-Dependent and-Independent Mechanisms

Embigin, a transmembrane glycoprotein belonging to the immunoglobulin superfamily, is involved in prostate and mammary gland development. As embigin’s roles in cancer remain elusive, we studied its biological functions and interaction with extracellular S100A4 in prostate cancer progression. We found by a pull-down assay that embigin is a novel receptor for S100A4, which is one of the vital cancer microenvironment milleu. Binding of extracellular S100A4 to embigin mediates prostate cancer progression by inhibition of AMPK activity, activation of NF-κB, MMP9 and mTORC1 signaling, and inhibition of autophagy, which increase prostate cancer cell motility. We also found that embigin promotes prostate cancer growth, spheroid- and colony-forming ability, and survival upon chemotherapy independently of S100A4. An in vivo growth mouse model confirmed the importance of embigin and its cytoplasmic tail in mediating prostate tumor growth. Moreover, embigin and p21^WAF1 can be used to predict survival of prostate cancer patients. Our results demonstrated for the first time that the S100A4-embigin/AMPK/mTORC1/p21^WAF1 and NF-κB/MMP9 axis is a vital oncogenic molecular cascade for prostate cancer progression. We proposed that embigin and p21^WAF1 could be used as prognostic biomarkers and a strategy to inhibit S100A4-embigin binding could be a therapeutic approach for prostate cancer patients.

PTEN Deficiency and AMPK Activation Promote Nutrient Scavenging and Anabolism in Prostate Cancer Cells

We report that PTEN-deficient prostate cancer cells use macropinocytosis to survive and proliferate under nutrient stress. PTEN loss increased macropinocytosis only in the context of AMPK activation, revealing a general requirement for AMPK in macropinocytosis and a novel mechanism by which AMPK promotes survival under stress. In prostate cancer cells, albumin uptake did not require macropinocytosis, but necrotic cell debris proved a specific macropinocytic cargo. Isotopic labeling confirmed that macropinocytosed necrotic cell proteins fueled new protein synthesis in prostate cancer cells. Supplementation with necrotic debris, but not albumin, also maintained lipid stores, suggesting that macropinocytosis can supply nutrients other than amino acids. Nontransformed prostatic epithelial cells were not macropinocytic, but patient-derived prostate cancer organoids and xenografts and autochthonous prostate tumors all exhibited constitutive macropinocytosis, and blocking macropinocytosis limited prostate tumor growth. Macropinocytosis of extracellular material by prostate cancer cells is a previously unappreciated tumor-microenvironment interaction that could be targeted therapeutically.Significance: As PTEN-deficient prostate cancer cells proliferate in low-nutrient environments by scavenging necrotic debris and extracellular protein via macropinocytosis, blocking macropinocytosis by inhibiting AMPK, RAC1, or PI3K may have therapeutic value, particularly in necrotic tumors and in combination with therapies that cause nutrient stress. Cancer Discov; 8(7); 866-83. ©2018 AACR.See related commentary by Commisso and Debnath, p. 800This article is highlighted in the In This Issue feature, p. 781.

Ginsenoside Rb1 increases macrophage phagocytosis through p38 mitogen-activated protein kinase/Akt pathway

Background

Ginsenoside Rb1, a triterpene saponin, is derived from the Panax ginseng root and has potent antiinflammatory activity. In this study, we determined if Rb1 can increase macrophage phagocytosis and elucidated the underlying mechanisms.

Methods

To measure macrophage phagocytosis, mouse peritoneal macrophages or RAW 264.7 cells were cultured with fluorescein isothiocyanate–conjugated Escherichia coli, and the phagocytic index was determined by flow cytometry. Western blot analyses were performed.

Results

Ginsenoside Rb1 increased macrophage phagocytosis and phosphorylation of p38 mitogen-activated protein kinase (MAPK), but inhibition of p38 MAPK activity with SB203580 decreased the phagocytic ability of macrophages. Rb1 also increased Akt phosphorylation, which was suppressed by LY294002, a phosphoinositide 3-kinase inhibitor. Rb1-induced Akt phosphorylation was inhibited by SB203580, (5Z)-7-oxozeaenol, and small-interfering RNA (siRNA)–mediated knockdown of p38α MAPK in macrophages. However, Rb1-induced p38 MAPK phosphorylation was not blocked by LY294002 or siRNA-mediated knockdown of Akt. The inhibition of Akt activation with siRNA or LY294002 also inhibited the Rb1-induced increase in phagocytosis. Rb1 increased macrophage phagocytosis of IgG-opsonized beads but not unopsonized beads. The phosphorylation of p21 activated kinase 1/2 and actin polymerization induced by IgG-opsonized beads and Rb1 were inhibited by SB203580 and LY294002. Intraperitoneal injection of Rb1 increased phosphorylation of p38 MAPK and Akt and the phagocytosis of bacteria in bronchoalveolar cells.

Conclusion

These results suggest that ginsenoside Rb1 enhances the phagocytic capacity of macrophages for bacteria via activation of the p38/Akt pathway. Rb1 may be a useful pharmacological adjuvant for the treatment of bacterial infections in clinically relevant conditions.

Novel drug discovery strategies for atherosclerosis that target necrosis and necroptosis

INTRODUCTION

Formation and enlargement of a necrotic core play a pivotal role in atherogenesis. Since the discovery of necroptosis, which is a regulated form of necrosis, prevention of necrotic cell death has become an attractive therapeutic goal to reduce plaque formation. Areas covered: This review highlights the triggers and consequences of (unregulated) necrosis and necroptosis in atherosclerosis. The authors discuss different pharmacological strategies to inhibit necrotic cell death in advanced atherosclerotic plaques. Expert opinion: Addition of a necrosis or necroptosis inhibitor to standard statin therapy could be a promising strategy for primary prevention of cardiovascular disease. However, a necrosis inhibitor cannot block all necrosis stimuli in atherosclerotic plaques. A necroptosis inhibitor could be more effective, because necroptosis is mediated by specific proteins, termed receptor-interacting serine/threonine-protein kinases (RIPK) and mixed lineage kinase domain-like pseudokinase (MLKL). Currently, only RIPK1 inhibitors have been successfully used in atherosclerotic mouse models to inhibit necroptosis. However, because RIPK1 is involved in both necroptosis and apoptosis, and also RIPK1-independent necroptosis can occur, we feel that targeting RIPK3 and MLKL could be a more attractive therapeutic approach to inhibit necroptosis. Therefore, future challenges will consist of developing RIPK3 and MLKL inhibitors applicable in both preclinical and clinical settings.

Berberine augments ATP-induced inflammasome activation in macrophages by enhancing AMPK signaling

The isoquinoline alkaloid berberine possesses many pharmacological activities including antibacterial infection. Although the direct bactericidal effect of berberine has been documented, its influence on the antibacterial functions of macrophages is largely unknown. As inflammasome activation in macrophages is important for the defense against bacterial infection, we aimed to investigate the influence of berberine on inflammasome activation in murine macrophages. Our results showed that berberine significantly increased ATP-induced inflammasome activation as reflected by enhanced pyroptosis as well as increased release of caspase-1p10 and mature interleukin-1β (IL-1β) in macrophages. Such effects of berberine could be suppressed by AMP-activated protein kinase (AMPK) inhibitor compound C or by knockdown of AMPKα expression, indicating the involvement of AMPK signaling in this process. In line with increased IL-1β release, the ability of macrophages to kill engulfed bacteria was also intensified by berberine. This was corroborated by the in vivo finding that the peritoneal live bacterial load was decreased by berberine treatment. Moreover, berberine administration significantly improved survival of bacterial infected mice, concomitant with increased IL-1β levels and elevated neutrophil recruitment in the peritoneal cavity. Collectively, these data suggested that berberine could enhance bacterial killing by augmenting inflammasome activation in macrophages through AMPK signaling.

Metformin Mediates Protection against Legionella Pneumonia through Activation of AMPK and Mitochondrial Reactive Oxygen Species

In Legionella pneumophila infection, macrophages play a critical role in the host defense response. Metformin, an oral drug for type 2 diabetes, is attracting attention as a new supportive therapy against a variety of diseases, such as cancer and infectious diseases. The novel mechanisms for metformin actions include modulation of the effector functions of macrophages and other host immune cells. In this study, we have examined the effects of metformin on L. pneumophila infection in vitro and in vivo. Metformin treatment suppressed growth of L. pneumophila in a time- and concentration-dependent fashion in bone marrow-derived macrophages, RAW cells (mouse), and U937 cells (human). Metformin induced phosphorylation of AMP-activated protein kinase (AMPK) in L. pneumophila-infected bone marrow-derived macrophages, and the AMPK inhibitor Compound C negated metformin-mediated growth suppression. Also, metformin induced mitochondrial reactive oxygen species but not phagosomal NADPH oxidase-derived reactive oxygen species. Metformin-mediated growth suppression was mitigated in the presence of the reactive oxygen species scavenger glutathione. In a murine L. pneumophila pneumonia model, metformin treatment improved survival of mice, which was associated with a significant reduction in bacterial number in the lung. Similar to in vitro observations, induction of AMPK phosphorylation and mitochondrial ROS was demonstrated in the infected lungs of mice treated with metformin. Finally, glutathione treatment abolished metformin effects on lung bacterial clearance. Collectively, these data suggest that metformin promotes mitochondrial ROS production and AMPK signaling and enhances the bactericidal activity of macrophages, which may contribute to improved survival in L. pneumophila pneumonia.