Inflammatory stimuli reprogram macrophage phagocytosis to macropinocytosis for the rapid elimination of pathogens

S-nitrosylation-triggered secretion of mycobacterial PknG leads to phosphorylation of SODD to prevent apoptosis of infected macrophages

The tuberculosis-causing agent Mycobacterium tuberculosis (M.tb) establishes its niche inside macrophages by secretion of several virulence factors and engaging many host factors. Mycobacterial infection of macrophages results in a proinflammatory trigger-mediated secretion of TNFα. Protein kinase G (PknG), a Serine/Threonine kinase, is essential for mycobacterial survival within the macrophage. Pathogenic mycobacteria, upon infection, can trigger the secretion of proinflammatory cytokine TNFα, but whether secreted PknG plays any role in TNFα secretion at early stages of infection remains undeciphered. Moreover, at early infection stages, prevention of macrophage apoptosis is vital to successful mycobacterial pathogenesis. Our studies show that mycobacteria-secreted PknG can dampen the expression and concomitant secretion of proinflammatory TNFα. During early infection, M.tb infection-induced generation of reactive nitrogen intermediates (RNI) leads to S-nitrosylation of PknG on Cys109, thereby enabling its secretion into macrophages. Upon M.tb infection, secreted S-nitrosylated PknG phosphorylates macrophage Silencer of Death Domains (SODD) at Thr405, as identified through our phosphoproteomic studies. Thereafter, phosphorylated SODD, through an irreversible binding with the TNFR1 death domain, prevents Caspase8 activation and concomitant extrinsic apoptotic trigger. Moreover, alveolar macrophages from mice infected with PknG-knockout M.tb also exhibited SODD phosphorylation and hindered Caspase8 activation to prevent extrinsic macrophage apoptosis. Therefore, this work exhibits S-nitrosylation-mediated secretion of PknG to induce phosphorylation of macrophage SODD, which, through irreversible interaction with TNFR1, prevented extrinsic macrophage apoptosis at the early stages of infection.

Staphylococcus aureus in Inflammation and Pain: Update on Pathologic Mechanisms

Staphylococcus aureus (S. aureus) is a Gram-positive bacterium of significant clinical importance, known for its versatility and ability to cause a wide array of infections, such as osteoarticular, pulmonary, cardiovascular, device-related, and hospital-acquired infections. This review describes the most recent evidence of the pathogenic potential of S. aureus, which is commonly part of the human microbiota but can lead to severe infections. The prevalence of pathogenic S. aureus in hospital and community settings contributes to substantial morbidity and mortality, particularly in individuals with compromised immune systems. The immunopathogenesis of S. aureus infections involves intricate interactions with the host immune and non-immune cells, characterized by various virulence factors that facilitate adherence, invasion, and evasion of the host's defenses. This review highlights the complexity of S. aureus infections, ranging from mild to life-threatening conditions, and underscores the growing public health concern posed by multidrug-resistant strains, including methicillin-resistant S. aureus (MRSA). This article aims to provide an updated perspective on S. aureus-related infections, highlighting the main diseases linked to this pathogen, how the different cell types, virulence factors, and signaling molecules are involved in the immunopathogenesis, and the future perspectives to overcome the current challenges to treat the affected individuals.

The tryptophan-aspartate (WD) repeat domain of bovine Coronin-1A promotes mycobacterial survival by inhibiting calcium signaling-mediated phagosome-lysosome fusion

Bovine tuberculosis is a chronic consumptive zoonosis, causing significant economic losses and critical public health risks. Coronin-1A is a host cytoskeleton-associated protein that is crucial for understanding the inhibition of phagosome-lysosome fusion by Mycobacterium tuberculosis (M.tb) to evade host innate immune clearance. However, the involvement of bovine Coronin-1A (bCoronin-1A) in M.tb infection and whether it can be manipulated so as to enhance host resistance against bovine tuberculosis remains to be seen. Here, we explored the role of bCoronin-1A in phagosome-lysosome fusion in M.tb-infected macrophages. We found that bCoronin-1A was upregulated at both the transcriptional and protein levels following M.tb infection of embryonic bovine lung (EBL) cells. Notably, bCoronin-1A was recruited to M.tb-containing phagosomes where it hindered phagosome-lysosome fusion, leading to increased intracellular mycobacterial survival. Further investigation revealed that mycobacterial lipoamide dehydrogenase C (LpdC) interacted with a single tryptophan-aspartate (WD) unit within the WD repeat domain of bCoronin-1A to sequester it on the phagosomes. The WD repeat domain mediated a decrease in intracellular calcium levels, which reduced levels of calmodulin-dependent kinase II (CaMKII) and its activated forms, thereby inhibiting lysosomal delivery. Overall, our findings revealed that bCoronin-1A had a critical impact on mycobacterial survival in macrophages by inhibiting calcium-mediated phagosome-lysosome fusion. This suggests that targeting bCoronin-1A as a key factor influencing mycobacterial survival may be an effective breeding strategy to develop tuberculosis-resistant dairy cows.

TLR4 promotes smooth muscle cell-derived foam cells formation by inducing receptor-independent macropinocytosis

Foam cells are primarily formed through scavenger receptors that mediate the uptake of various modified low-density lipoproteins (LDL) into cells. In addition to the receptor-dependent pathway, macropinocytosis is an essential nonreceptor endocytic pathway for vascular smooth muscle cells (VSMCs) to take up lipids. However, the molecular mechanisms underlying this process remain unclear. Primary cultured VSMCs were stimulated with 200 ng/mL lipopolysaccharide (LPS) and 200 µg/mL native LDL (nLDL). We observed a significant increase in Toll-like receptor 4 (TLR4) protein expression and a significant activation of macropinocytosis, which correlated with the highest uptake of nLDL and intracellular lipid deposition in WT VSMCs. However, macropinocytosis was inhibited and lipid accumulation decreased after treatment with macropinocytosis inhibitors and Syk inhibitors in WT VSMCs. Consistently, TLR4 knockout significantly suppressed macropinocytosis and lipid droplets accumulation in VSMCs. Taken together, our findings suggest a critical role of TLR4/Syk signaling in promoting receptor-independent macropinocytosis leading to VSMC-derived foam cells formation.

Activation of receptor-independent fluid-phase pinocytosis promotes foamy monocyte formation in atherosclerotic mice

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death worldwide. Clinical and experimental data demonstrated that circulating monocytes internalize plasma lipoproteins and become lipid-laden foamy cells in hypercholesterolemic subjects. This study was designed to identify the endocytic mechanisms responsible for foamy monocyte formation, perform functional and transcriptomic analysis of foamy and non-foamy monocytes relevant to ASCVD, and characterize specific monocyte subsets isolated from the circulation of normocholesterolemic controls and hypercholesterolemic patients. We hypothesized that activation of fluid-phase macropinocytosis contributes to foamy monocyte formation in vitro and in hypercholesterolemic mice in vivo. High resolution scanning electron microscopy (SEM) and quantification of FITC/TRITC-dextran internalization demonstrated macropinocytosis stimulation in human (THP-1) and wild type murine monocytes. Stimulation of macropinocytosis induced foamy monocyte formation in the presence of unmodified, native LDL (nLDL) and oxidized LDL (ox-LDL) in vitro. Genetic blockade of macropinocytosis (LysMCre+ Nhe1f/f) inhibited foamy monocyte formation in hypercholesterolemic mice in vivo and attenuated monocyte adhesion to atherosclerotic aortas ex vivo. Mechanistic studies identified NADPH oxidase 2 (Nox2)-derived superoxide anion (O2⋅-) as an important downstream signaling molecule stimulating macropinocytosis in monocytes. qRT-PCR identified CD36 as a major scavenger receptor that increases in response to lipid loading in monocytes and deletion of CD36 (Cd36-/-) inhibited foamy monocyte formation in hypercholesterolemic mice. Bulk RNA-sequencing characterized transcriptional differences between non-foamy and foamy monocytes versus macrophages. Finally, flow cytometry analysis of CD14 and CD16 expression demonstrated a significant increase in intermediate monocytes in hypercholesterolemic patients compared to normocholesterolemic controls. These results provide novel insights into the mechanisms of foamy monocyte formation and potentially identify new therapeutic targets for the treatment of atherosclerosis.

Excitatory amino acid transporter supports inflammatory macrophage responses

Excitatory amino acid transporters (EAATs) are responsible for excitatory amino acid transportation and are associated with auto-immune diseases in the central nervous system and peripheral tissues. However, the subcellular location and function of EAAT2 in macrophages are still obscure. In this study, we demonstrated that LPS stimulation increases expression of EAAT2 (coded by Slc1a2) via NF-κB signaling. EAAT2 is necessary for inflammatory macrophage polarization through sustaining mTORC1 activation. Mechanistically, lysosomal EAAT2 mediates lysosomal glutamate and aspartate efflux to maintain V-ATPase activation, which sustains macropinocytosis and mTORC1. We also found that mice with myeloid depletion of Slc1a2 show alleviated inflammatory responses in LPS-induced systemic inflammation and high-fat diet induced obesity. Notably, patients with type II diabetes (T2D) have a higher level of expression of lysosomal EAAT2 and activation of mTORC1 in blood macrophages. Taken together, our study links the subcellular location of amino acid transporters with the fate decision of immune cells, which provides potential therapeutic targets for the treatment of inflammatory diseases.

Breaking the Cycle: Matrix Metalloproteinase Inhibitors as an Alternative Approach in Managing Tuberculosis Pathogenesis and Progression

Mycobacterium tuberculosis (Mtb) has long posed a significant challenge to global public health, resulting in approximately 1.6 million deaths annually. Pulmonary tuberculosis (TB) instigated by Mtb is characterized by extensive lung tissue damage, leading to lesions and dissemination within the tissue matrix. Matrix metalloproteinases (MMPs) exhibit endopeptidase activity, contributing to inflammatory tissue damage and, consequently, morbidity and mortality in TB patients. MMP activities in TB are intricately regulated by various components, including cytokines, chemokines, cell receptors, and growth factors, through intracellular signaling pathways. Primarily, Mtb-infected macrophages induce MMP expression, disrupting the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thereby impairing extracellular matrix (ECM) deposition in the lungs. Recent research underscores the significance of immunomodulatory factors in MMP secretion and granuloma formation during Mtb pathogenesis. Several studies have investigated both the activation and inhibition of MMPs using endogenous MMP inhibitors (i.e., TIMPs) and synthetic inhibitors. However, despite their promising pharmacological potential, few MMP inhibitors have been explored for TB treatment as host-directed therapy. Scientists are exploring novel strategies to enhance TB therapeutic regimens by suppressing MMP activity to mitigate Mtb-associated matrix destruction and reduce TB induced lung inflammation. These strategies include the use of MMP inhibitor molecules alone or in combination with anti-TB drugs. Additionally, there is growing interest in developing novel formulations containing MMP inhibitors or MMP-responsive drug delivery systems to suppress MMPs and release drugs at specific target sites. This review summarizes MMPs' expression and regulation in TB, their role in immune response, and the potential of MMP inhibitors as effective therapeutic targets to alleviate TB immunopathology.

The anti-infective and immunologic effect of babassu (Attalea speciosa, Mart. ex Spreng) reduces mortality induced by MRSA-Staphylococcus aureus

ETHNOPHARMACOLOGICAL RELEVANCE

Babassu mesocarp, derived from the Attalea speciosa fruits, is used in folk medicine for infections, inflammatory diseases, and skin wounds.

AIM OF THE STUDY

To investigate the antimicrobial and immunological effect of babassu mesocarp aqueous extract (BAE) in Swiss mice lethally infected with methicillin-resistant Staphylococcus aureus (MRSA).

MATERIALS AND METHODS

The animals (n = 14/group) received an overload of MRSA (3.0 × 108 CFU/mL, via intraperitoneal) and were treated 6 h later with the BAE (125 and 250 mg/kg, subcutaneously). Two experiments were performed with four groups each (Control, ATB, BAE125 and BAE 250). The first was to determine the survival (n = 7 animals/group). The second is to evaluate 24h after infection the number of Colony Forming Units (CFU) and cells in the blood, peritoneum and bronchoalveolar fluid. Cytometric Bead Assay - CBA quantified the cytokines and flow cytometry to determine the cellular distribution in the mesenteric lymph node.

RESULTS

Treatment with BAE improved the survival (60%) in all groups, reduced the number of colony-forming units in the peritoneum and blood, the number of peritoneal and bronchoalveolar cells, and the levels of pro-inflammatory IL-6, TNF-α, and IL-17 cytokines. Additionally, BAE increased: IL-10 and INF-γ levels, nitric oxide release, CD4+ T helper cells, CD14+/IaIe + activated macrophages and Ly6G + neutrophils in the mesenteric lymph node.

CONCLUSIONS

BAE can be used as a complementary treatment during infections due to its antimicrobial and immunomodulatory effect and the ability to protect animals from death after MRSA lethal infection.

Age-Associated KLF9 Enhances the Inflammatory Response of Alveolar Macrophages Via Regulating TLR2 Expression

Staphylococcus aureus pneumonia is a severe infection in infant and young children. Toll-like receptor 2 (TLR2)-mediated inflammation plays essential roles in S. aureus pneumonia. Krueppel-like factor 9 (KLF9) is a transcriptional factor participating in multiple cellular aspects including inflammation. In this study, the potential roles of KLF9 in S. aureus pneumonia were evaluated. The expression of KLF9 in peripheral blood mononuclear cells (PBMCs) from healthy donors with different ages and in alveolar macrophages from mice with different ages was measured. Pam3CK4-induced expression of inflammatory cytokines was compared in alveolar macrophages from young and old mice and in wild-type (WT) and KLF9-deficient macrophages. The survival rate, body weight loss, lung pathology were compared between WT and KLF9-deficient mice after S. aureus infection. The TLR2 expression was compared between WT and KLF9-deficient macrophages after Pam3CK4 treatment. Decreased expression of KLF9 was detected in PBMCs from elder donor and in macrophages from old mice. Impaired expression of pro-inflammatory cytokines was observed in macrophages from old mice and KLF9-deficient macrophages after Pam3CK4 treatment. KLF9-deficient mice had elevated survival rate, decreased lung injury after S. aureus infection. Decreased expression of TLR2 was detected in KLF9-deficient macrophages and overexpression of TLR2 rescued the impaired expression of inflammatory cytokines in KLF9-deficient macrophages. KLF9 regulated inflammatory responses in macrophages through TLR2.

Receptor-independent fluid-phase macropinocytosis promotes arterial foam cell formation and atherosclerosis

Accumulation of lipid-laden foam cells in the arterial wall plays a central role in atherosclerotic lesion development, plaque progression, and late-stage complications of atherosclerosis. However, there are still fundamental gaps in our knowledge of the underlying mechanisms leading to foam cell formation in atherosclerotic arteries. Here, we investigated the role of receptor-independent macropinocytosis in arterial lipid accumulation and pathogenesis of atherosclerosis. Genetic inhibition of fluid-phase macropinocytosis in myeloid cells (LysMCre+ Nhe1fl/fl) and repurposing of a Food and Drug Administration (FDA)-approved drug that inhibits macrophage macropinocytosis substantially decreased atherosclerotic lesion development in low-density lipoprotein (LDL) receptor-deficient and Apoe-/- mice. Stimulation of macropinocytosis using genetic (H-RASG12V) and physiologically relevant approaches promoted internalization of unmodified native (nLDL) and modified [e.g., acetylated (ac) and oxidized (ox) LDL] lipoproteins in both wild-type and scavenger receptor (SR) knockout (Cd36-/-/Sra-/-) macrophages. Pharmacological inhibition of macropinocytosis in hypercholesterolemic wild-type and Cd36-/-/Sra-/- mice identified an important role of macropinocytosis in LDL uptake by lesional macrophages and development of atherosclerosis. Furthermore, serial section high-resolution imaging, LDL immunolabeling, and three-dimensional (3D) reconstruction of subendothelial foam cells provide visual evidence of lipid macropinocytosis in both human and murine atherosclerotic arteries. Our findings complement the SR paradigm of atherosclerosis and identify a therapeutic strategy to counter the development of atherosclerosis and cardiovascular disease.

Nanoparticle entry into cells; the cell biology weak link

Nanoparticles (NP) are attractive options for the therapeutic delivery of active pharmaceutical drugs, proteins and nucleic acids into cells, tissues and organs. Research into the development and application of NP most often starts with a diverse group of scientists, including chemists, bioengineers and material and pharmaceutical scientists, who design, fabricate and characterize NP in vitro (Stage 1). The next step (Stage 2) generally investigates cell toxicity as well as the processes by which NP bind, are internalized and deliver their cargo to appropriate model tissue culture cells. Subsequently, in Stage 3, selected NP are tested in animal systems, mostly mouse. Whereas the chemistry-based development and analysis in Stage 1 is increasingly sophisticated, the investigations in Stage 2 are not what could be regarded as 'state-of-the-art' for the cell biology field and the quality of research into NP interactions with cells is often sub-standard. In this review we describe our current understanding of the mechanisms by which particles gain entry into mammalian cells via endocytosis. We summarize the most important areas for concern, highlight some of the most common mis-conceptions, and identify areas where NP scientists could engage with trained cell biologists. Our survey of the different mechanisms of uptake into cells makes us suspect that claims for roles for caveolae, as well as macropinocytosis, in NP uptake into cells have been exaggerated, whereas phagocytosis has been under-appreciated.

Aging alters antiviral signaling pathways resulting in functional impairment in innate immunity in response to pattern recognition receptor agonists

The progressive impairment of immunity to pathogens and vaccines with aging is a significant public health problem as the world population shifts to an increased percentage of older adults (> 65). We have previously demonstrated that cells obtained from older volunteers have delayed and defective induction of type I interferons and T cell and B cell helper cytokines in response to TLR ligands when compared to those from adult subjects. However, the underlying intracellular mechanisms are not well described. Herein, we studied two critical pathways important in the production of type I interferon (IFN), the interferon response factor 7 (pIRF7), and TANK-binding kinase (pTBK-1). We show a decrease in pIRF7 and pTBK-1 in cross-priming dendritic cells (cDC1s), CD4⁺ T cell priming DCs (cDC2s), and CD14^dimCD16⁺ vascular patrolling monocytes from older adults (n = 11) following stimulation with pathway-specific agonists in comparison with young individuals (n = 11). The decrease in these key antiviral pathway proteins correlates with decreased phagocytosis, suggesting impaired function in Overall, our findings describe molecular mechanisms which explain the innate functional impairment in older adults and thus could inform us of novel approaches to restore these defects.

Klf10 favors Mycobacterium tuberculosis survival by impairing IFN-γ production and preventing macrophages reprograming to macropinocytosis

Mycobacterium tuberculosis has developed diverse mechanisms to survive inside phagocytic cells, such as macrophages. Phagocytosis is a key process in eliminating invading pathogens; thus, M. tuberculosis efficiently disrupts phagosome maturation to ensure infection. However, inflammatory cytokines produced by macrophages in response to early M. tuberculosis infection are key to promoting bacterial clarification. IFN-γ enhances M. tuberculosis engulfment and destruction by reprogramming macrophages from phagocytosis to macropinocytosis. Here, we show that the transcription factor Krüppel-like factor 10 (Klf10) plays a positive role in M. tuberculosis survival and infection by negatively modulating IFN-γ levels. Naïve Klf10-deficient macrophages produce more IFN-γ upon stimulation than wild-type macrophages, thus enhancing bacterial uptake and bactericidal activity achieved by macropinocytosis. Moreover, Klf10⁻^/ ⁻ macrophages showed cytoplasmic distribution of coronin 1 correlated with increased pseudopod count and length. In agreement with these observations, Klf10⁻^/ ⁻ mice showed improved bacterial clearance from the lungs and increased viability. Altogether, our data indicate that Klf10 plays a critical role in M. tuberculosis survival by preventing macrophage reprogramming from phagocytosis to macropinocytosis by negatively regulating IFN-γ production upon macrophage infection.

Suppression of caspase 8 activity by a coronin 1-PI3Kδ pathway promotes T cell survival independently of TCR and IL-7 signaling

The control of T cell survival is crucial for defense against infectious pathogens or emerging cancers. Although the survival of peripheral naïve T cells has been proposed to be controlled by interleukin-7 (IL-7) signaling and T cell receptor (TCR) activation by peptide-loaded major histocompatibility complexes (pMHC), the essential roles for these pathways in thymic output and T cell proliferation have complicated the analysis of their contributions to T cell survival. Here, we showed that the WD repeat–containing protein coronin 1, which is dispensable for thymic selection and output, promoted naïve T cell survival in the periphery in a manner that was independent of TCR and IL-7 signaling. Coronin 1 was required for the maintenance of the basal activity of phosphoinositide 3-kinase δ (PI3Kδ), thereby suppressing caspase 8–mediated apoptosis. These results therefore reveal a coronin 1–dependent PI3Kδ pathway that is independent of pMHC:TCR and IL-7 signaling and essential for peripheral T cell survival.

Three-dimensional morphodynamic simulations of macropinocytic cups

Macropinocytosis refers to the non-specific uptake of extracellular fluid, which plays ubiquitous roles in cell growth, immune surveillance, and virus entry. Despite its widespread occurrence, it remains unclear how its initial cup-shaped plasma membrane extensions form without any external solid support, as opposed to the process of particle uptake during phagocytosis. Here, by developing a computational framework that describes the coupling between the bistable reaction-diffusion processes of active signaling patches and membrane deformation, we demonstrated that the protrusive force localized to the edge of the patches can give rise to a self-enclosing cup structure, without further assumptions of local bending or contraction. Efficient uptake requires a balance among the patch size, magnitude of protrusive force, and cortical tension. Furthermore, our model exhibits cyclic cup formation, coexistence of multiple cups, and cup-splitting, indicating that these complex morphologies self-organize via a common mutually-dependent process of reaction-diffusion and membrane deformation.

A Bumpy Ride of Mycobacterial Phagosome Maturation: Roleplay of Coronin1 Through Cofilin1 and cAMP

Phagosome-lysosome fusion in innate immune cells like macrophages and neutrophils marshal an essential role in eliminating intracellular microorganisms. In microbe-challenged macrophages, phagosome-lysosome fusion occurs 4 to 6 h after the phagocytic uptake of the microbe. However, live pathogenic mycobacteria hinder the transfer of phagosomes to lysosomes, up to 20 h post-phagocytic uptake. This period is required to evade pro-inflammatory response and upregulate the acid-stress tolerant proteins. The exact sequence of events through which mycobacteria retards phagolysosome formation remains an enigma. The macrophage coat protein Coronin1(Cor1) is recruited and retained by mycobacteria on the phagosome membrane to retard its maturation by hindering the access of phagosome maturation factors. Mycobacteria-infected macrophages exhibit an increased cAMP level, and based on receptor stimulus, Cor1 expressing cells show a higher level of cAMP than non-Cor1 expressing cells. Here we have shown that infection of bone marrow-derived macrophages with H37Rv causes a Cor1 dependent rise of intracellular cAMP levels at the vicinity of the phagosomes. This increased cAMP fuels cytoskeletal protein Cofilin1 to depolymerize F-actin around the mycobacteria-containing phagosome. Owing to reduced F-actin levels, the movement of the phagosome toward the lysosomes is hindered, thus contributing to the retarded phagosome maturation process. Additionally, Cor1 mediated upregulation of Cofilin1 also contributes to the prevention of phagosomal acidification, which further aids in the retardation of phagosome maturation. Overall, our study provides first-hand information on Cor1 mediated retardation of phagosome maturation, which can be utilized in developing novel peptidomimetics as part of host-directed therapeutics against tuberculosis.

Mycobacterium tuberculosis PE17 (Rv1646) promotes host cell apoptosis via host chromatin remodeling mediated by reduced H3K9me3 occupancy

Tuberculosis caused by Mycobacterium tuberculosis remains a serious global public health threat. M. tuberculosis PE and PPE proteins are closely involved in pathogen-host interaction. To explore the predicted function of the M. tuberculosis PE17 (Rv1646), we heterologously expressed PE17 in a non-pathogenic Mycobacterium smegmatis strain (Ms_PE17). PE17 can reduce the survival of M. smegmatis within macrophages associated with altering the transcription levels of inflammatory cytokines IL1β, IL6, TNFα, and IL10 in Ms_PE17 infected macrophages through JNK signaling. Furthermore, macrophages apoptosis was increased upon Ms_PE17 infection in a caspases-dependent manner, accompanied by the activation of the Endoplasmic Reticulum stress IRE1α/ASK1/JNK signaling pathway. This can be largely interpreted by the epigenetic changes through reduced H3K9me3 chromatin occupancy post Ms_PE17 infection. To our knowledge, this is the first report that PE17 altered the macrophages apoptosis via H3K9me3 mediated chromatin remodeling.

Understanding nanoparticle endocytosis to improve targeting strategies in nanomedicine

Nanoparticles (NPs) have attracted considerable attention in various fields, such as cosmetics, the food industry, material design, and nanomedicine. In particular, the fast-moving field of nanomedicine takes advantage of features of NPs for the detection and treatment of different types of cancer, fibrosis, inflammation, arthritis as well as neurodegenerative and gastrointestinal diseases. To this end, a detailed understanding of the NP uptake mechanisms by cells and intracellular localization is essential for safe and efficient therapeutic applications. In the first part of this review, we describe the several endocytic pathways involved in the internalization of NPs and we discuss the impact of the physicochemical properties of NPs on this process. In addition, the potential challenges of using various inhibitors, endocytic markers and genetic approaches to study endocytosis are addressed along with the principal (semi) quantification methods of NP uptake. The second part focuses on synthetic and bio-inspired substances, which can stimulate or decrease the cellular uptake of NPs. This approach could be interesting in nanomedicine where a high accumulation of drugs in the target cells is desirable and clearance by immune cells is to be avoided. This review contributes to an improved understanding of NP endocytic pathways and reveals potential substances, which can be used in nanomedicine to improve NP delivery.

Intercellular Mitochondria Transfer to Macrophages Regulates White Adipose Tissue Homeostasis and Is Impaired in Obesity

Recent studies suggest that mitochondria can be transferred between cells to support the survival of metabolically compromised cells. However, whether intercellular mitochondria transfer occurs in white adipose tissue (WAT) or regulates metabolic homeostasis in vivo remains unknown. We found that macrophages acquire mitochondria from neighboring adipocytes in vivo and that this process defines a transcriptionally distinct macrophage subpopulation. A genome-wide CRISPR-Cas9 knockout screen revealed that mitochondria uptake depends on heparan sulfates (HS). High-fat diet (HFD)-induced obese mice exhibit lower HS levels on WAT macrophages and decreased intercellular mitochondria transfer from adipocytes to macrophages. Deletion of the HS biosynthetic gene Ext1 in myeloid cells decreases mitochondria uptake by WAT macrophages, increases WAT mass, lowers energy expenditure, and exacerbates HFD-induced obesity in vivo. Collectively, this study suggests that adipocytes and macrophages employ intercellular mitochondria transfer as a mechanism of immunometabolic crosstalk that regulates metabolic homeostasis and is impaired in obesity.

The Role of Macrophages in Staphylococcus aureus Infection

Staphylococcus aureus is a member of the human commensal microflora that exists, apparently benignly, at multiple sites on the host. However, as an opportunist pathogen it can also cause a range of serious diseases. This requires an ability to circumvent the innate immune system to establish an infection. Professional phagocytes, primarily macrophages and neutrophils, are key innate immune cells which interact with S. aureus, acting as gatekeepers to contain and resolve infection. Recent studies have highlighted the important roles of macrophages during S. aureus infections, using a wide array of killing mechanisms. In defense, S. aureus has evolved multiple strategies to survive within, manipulate and escape from macrophages, allowing them to not only subvert but also exploit this key element of our immune system. Macrophage-S. aureus interactions are multifaceted and have direct roles in infection outcome. In depth understanding of these host-pathogen interactions may be useful for future therapeutic developments. This review examines macrophage interactions with S. aureus throughout all stages of infection, with special emphasis on mechanisms that determine infection outcome.

"It Takes Two to Tango": Role of Neglected Macrophage Manipulators Coronin 1 and Protein Kinase G in Mycobacterial Pathogenesis

Macrophages being the connecting link between innate and adaptive immune system plays a crucial role in microbial antigen presentation and orchestrates the subsequent clearance of microorganisms. Microbial invasion of macrophages trigger a plethora of signaling cascades, which interact among them to generate a dynamically altered hostile environment, that ultimately leads to disruption of microbial pathogenesis. Paradoxically, Mycobacterium sp. exploits macrophage proteins such as Coronin 1, Calcineurin, LRG47, SOCS1, CISH, Gbp5 etc. and secretes virulence proteins such as PknG, PtpA, SapM, Eis etc. to hijack these intra-macrophage, signaling cascades and thereby develop its own niche. Coronin 1, being a cortical protein is transiently recruited to all mycobacteria containing phagosomes, but only pathogenic mycobacteria can retain it on the phagosome, to hinder its maturation. Additionally, mycobacterial infection linked secretion of virulence factor Protein Kinase G through its phosphorylation, manipulates several macrophage signaling pathways and thus promotes pathogenesis at various stages, form early infection to latency to granuloma formation. Here we discuss the present status of mycobacteria engaged Coronin 1-dependent signaling cascades and secreted PknG related sequence of events promoting mycobacterial pathogenesis. Current knowledge about these two proteins in context of macrophage signaling manipulation encompassing diverse mechanisms like calcium-calcineurin signaling, reduced proinflamtory cytokine secretion, cytoskeletal changes, and adaptation in acidic environment, which ultimately converge toward mycobacterial survival inside the macrophages has been discussed.

Increased Uptake of Silica Nanoparticles in Inflamed Macrophages but Not upon Co-Exposure to Micron-Sized Particles

Silica nanoparticles (NPs) are widely used in various industrial and biomedical applications. Little is known about the cellular uptake of co-exposed silica particles, as can be expected in our daily life. In addition, an inflamed microenvironment might affect a NP’s uptake and a cell’s physiological response. Herein, prestimulated mouse J774A.1 macrophages with bacterial lipopolysaccharide were post-exposed to micron- and nanosized silica particles, either alone or together, i.e., simultaneously or sequentially, for different time points. The results indicated a morphological change and increased expression of tumor necrosis factor alpha in lipopolysaccharide prestimulated cells, suggesting a M1-polarization phenotype. Confocal laser scanning microscopy revealed the intracellular accumulation and uptake of both particle types for all exposure conditions. A flow cytometry analysis showed an increased particle uptake in lipopolysaccharide prestimulated macrophages. However, no differences were observed in particle uptakes between single- and co-exposure conditions. We did not observe any colocalization between the two silica (SiO₂) particles. However, there was a positive colocalization between lysosomes and nanosized silica but only a few colocalized events with micro-sized silica particles. This suggests differential intracellular localizations of silica particles in macrophages and a possible activation of distinct endocytic pathways. The results demonstrate that the cellular uptake of NPs is modulated in inflamed macrophages but not in the presence of micron-sized particles.

Hypersensitivity of Vps33B mutant flies to non-pathogenic infections is dictated by aberrant activation of p38b MAP kinase

Loss of the arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome-linked Vps33B protein results in exaggerated inflammatory responses upon activation of receptors of the innate immune system in both vertebrates and flies. However, little is known about the signaling elements downstream of these receptors that are critical for the hypersensitivity of Vps33B mutants. Here, we show that p38b MAP kinase contributes to the enhanced inflammatory responses in flies lacking Vps33B. Loss of p38b mitogen-activated protein kinase (MAPK) reduces enhanced inflammatory responses and prolongs the survival of infected Vps33B deficient flies. The function of p38 MAPK is not limited to its proinflammatory effects downstream of the PGRP-LC receptor as p38 also modulates endosomal trafficking of PGRP-LC and phagocytosis of bacteria. Expression of constitutively active p38b MAPK, but not dominant negative p38b MAPK enhances accumulation of endocytosed PGRP-LC receptors or phagocytosed bacteria within cells. Moreover, p38 MAPK is required for induction of macropinocytosis, an alternate pathway for the downregulation of immune receptors. Together, our data indicate that p38 MAPK activates multiple pathways that can contribute to the dysregulation of innate immune signaling in ARC syndrome.

Humoral immune responses against gut bacteria in dogs with inflammatory bowel disease

Inflammatory bowel disease (IBD) in dogs is associated with clinical signs of intestinal dysfunction, as well as abnormal lymphocytic and myeloid cell infiltrates in the small and/or large intestine. Thus, in many respects IBD in dogs resembles IBD in humans. However, the factors that trigger intestinal inflammation in dogs with IBD are not well understood and have been variously attributed to immune responses against dietary antigens or intestinal antigens. Previous studies in humans with IBD have documented increased production of IgG and IgA antibodies specific to intestinal bacteria, and this abnormal immune response has been linked to disease pathogenesis. Therefore, we investigated the humoral immune response against gut bacteria in dogs with IBD, using flow cytometry to quantitate IgG and IgA binding. Studies were also done to investigate the source of these antibodies (locally produced versus systemic production) and whether greater antibody binding to bacteria is associated with increased inflammatory responses. We found that dogs with IBD had significantly higher percentages and overall amounts of IgG bound to their intestinal bacteria compared to healthy dogs. Similarly, significantly higher percentages of bacteria were IgA+ bacteria were also found in dogs with IBD. Serum antibody recognition of gut bacteria was not different between healthy dogs and dogs with IBD, suggesting that anti-bacterial antibodies were primarily produced locally in the gut rather than systemically. Importantly, bacteria in the Actinobacteria phylum and in particular the genus Collinsella had significantly greater levels of antibody binding in dogs with IBD. Based on these findings, we concluded that antibody binding to commensal gut bacteria was significantly increased in dogs with IBD, that particular phyla were preferential targets for gut antibodies, and that anti-bacterial antibody responses may play an important role in regulating gut inflammation.

Intracellular protozoan parasites: living probes of the host cell surface molecular repertoire

Intracellular protozoans co-evolved with their mammalian host cells a range of strategies to cope with the composite and dynamic cell surface features they encounter during migration and infection. Therefore, these single-celled eukaryotic parasites represent a fascinating source of living probes for precisely capturing the dynamic coupling between the membrane and contractile cortex components of the cell surface. Such biomechanical changes drive a constant re-sculpting of the host cell surface, enabling rapid adjustments that contribute to cellular homeostasis. As emphasized in this review, through the design of specific molecular devices and stratagems to interfere with the biomechanics of the mammalian cell surface these parasitic microbes escape from dangerous or unfavourable microenvironments by breaching host cell membranes, directing the membrane repair machinery to wounded membrane areas, or minimizing membrane assault using discretion and speed when invading host cells for sustained residence.

Matrix metalloproteinases: Expression, regulation and role in the immunopathology of tuberculosis

Mycobacterium tuberculosis (Mtb) leads to approximately 1.5 million human deaths every year. In pulmonary tuberculosis (TB), Mtb must drive host tissue destruction to cause pulmonary cavitation and dissemination in the tissues. Matrix metalloproteinases (MMPs) are endopeptidases capable of degrading all components of pulmonary extracellular matrix (ECM). It is well established that Mtb infection leads to upregulation of MMPs and also causes disturbance in the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thus altering the extracellular matrix deposition. In TB, secretion of MMPs is mainly regulated by NF-κB, p38 and MAPK signalling pathways. In addition, recent studies have demonstrated the immunomodulatory roles of MMPs in Mtb pathogenesis. Researchers have proposed a new regimen of improved TB treatment by inhibition of MMP activity to hinder matrix destruction and to minimize the TB-associated morbidity and mortality. The proposed regimen involves adjunctive use of MMP inhibitors such as doxycycline, marimastat and other related drugs along with front-line anti-TB drugs to reduce granuloma formation and bacterial load. These findings implicate the possible addition of economical and well-tolerated MMP inhibitors to current multidrug regimens as an attractive mean to increase the drug potency. Here, we will summarize the recent advancements regarding expression of MMPs in TB, their immunomodulatory role, as well as their potential as therapeutic targets to control the deadly disease.

Class II MHC antigen processing in immune tolerance and inflammation

Presentation of peptide antigens by MHC-II proteins is prerequisite to effective CD4 T cell tolerance to self and to recognition of foreign antigens. Antigen uptake and processing pathways as well as expression of the peptide exchange factors HLA-DM and HLA-DO differ among the various professional and non-professional antigen-presenting cells and are modulated by cell developmental state and activation. Recent studies have highlighted the importance of these cell-specific factors in controlling the source and breadth of peptides presented by MHC-II under different conditions. During inflammation, increased presentation of selected self-peptides has implications for maintenance of peripheral tolerance and autoimmunity.

Macrophage-microbe interaction: lessons learned from the pathogen Mycobacterium tuberculosis

Macrophages, being the cornerstone of the immune system, have adapted the ancient nutrient acquisition mechanism of phagocytosis to engulf various infectious organisms thereby helping to orchestrate an appropriate host response. Phagocytosis refers to the process of internalization and degradation of particulate material, damaged and senescent cells and microorganisms by specialized cells, after which the vesicle containing the ingested particle, the phagosome, matures into acidic phagolysosomes upon fusion with hydrolytic enzyme-containing lysosomes. The destructive power of the macrophage is further exacerbated through the induction of macrophage activation upon a variety of inflammatory stimuli. Despite being the end-point for many phagocytosed microbes, the macrophage can also serve as an intracellular survival niche for a number of intracellular microorganisms. One microbe that is particularly successful at surviving within macrophages is the pathogen Mycobacterium tuberculosis, which can efficiently manipulate the macrophage at several levels, including modulation of the phagocytic pathway as well as interfering with a number of immune activation pathways that normally would lead to eradication of the internalized bacilli. M. tuberculosis excels at circumventing destruction within macrophages, thus establishing itself successfully for prolonged times within the macrophage. In this contribution, we describe a number of general features of macrophages in the context of their function to clear an infection, and highlight the strategies employed by M. tuberculosis to counter macrophage attack. Interestingly, research on the evasion tactics employed by M. tuberculosis within macrophages not only helps to design strategies to curb tuberculosis, but also allows a better understanding of host cell biology.

Micelle-Forming Dexamethasone Prodrug Attenuates Nephritis in Lupus-Prone Mice without Apparent Glucocorticoid Side Effects

Nephritis is one of the major complications of systemic lupus erythematosus. While glucocorticoids (GCs) are frequently used as the first-line treatment for lupus nephritis (LN), long-term GC usage is often complicated by severe adverse effects. To address this challenge, we have developed a polyethylene glycol-based macromolecular prodrug (ZSJ-0228) of dexamethasone, which self-assembles into micelles in aqueous media. When compared to the dose equivalent daily dexamethasone 21-phosphate disodium (Dex) treatment, monthly intravenous administration of ZSJ-0228 for two months significantly improved the survival of lupus-prone NZB/W F1 mice and was much more effective in normalizing proteinuria, with clear histological evidence of nephritis resolution. Different from the dose equivalent daily Dex treatment, monthly ZSJ-0228 administration has no impact on the serum anti-double-stranded DNA (anti-dsDNA) antibody level but can significantly reduce renal immune complex deposition. No significant systemic toxicities of GCs ( e. g., total IgG reduction, adrenal gland atrophy, and osteopenia) were found to be associated with ZSJ-0228 treatment. In vivo imaging and flow cytometry studies revealed that the fluorescent-labeled ZSJ-0228 primarily distributed to the inflamed kidney after systemic administration, with renal myeloid cells and proximal tubular epithelial cells mainly responsible for its kidney retention. Collectively, these data suggest that the ZSJ-0228's potent local anti-inflammatory/immunosuppressive effects and improved safety may be attributed to its nephrotropicity and cellular sequestration at the inflamed kidney tissues. Pending further optimization, it may be developed into an effective and safe therapy for improved clinical management of LN.

PtpA, a secreted tyrosine phosphatase from Staphylococcus aureus, contributes to virulence and interacts with coronin-1A during infection

Secretion of bacterial signaling proteins and adaptation to the host, especially during infection, are processes that are often linked in pathogenic bacteria. The human pathogen Staphylococcus aureus is equipped with a large arsenal of immune-modulating factors, allowing it to either subvert the host immune response or to create permissive niches for its survival. Recently, we showed that one of the low-molecular-weight protein tyrosine phosphatases produced by S. aureus, PtpA, is secreted during growth. Here, we report that deletion of ptpA in S. aureus affects intramacrophage survival and infectivity. We also observed that PtpA is secreted during macrophage infection. Immunoprecipitation assays identified several host proteins as putative intracellular binding partners for PtpA, including coronin-1A, a cytoskeleton-associated protein that is implicated in a variety of cellular processes. Of note, we demonstrated that coronin-1A is phosphorylated on tyrosine residues upon S. aureus infection and that its phosphorylation profile is linked to PtpA expression. Our results confirm that PtpA has a critical role during infection as a bacterial effector protein that counteracts host defenses.

Getting in and Staying Alive: Role for Coronin 1 in the Survival of Pathogenic Mycobacteria and Naïve T Cells

There are many different pathogenic stimuli that are able to activate the immune system, ranging from microbes that include bacteria, viruses, fungi, and parasites to host-derived triggers such as autoantigens that can induce autoimmunity as well as neoantigens involved in tumorigenesis. One of the key interactions shaping immunity toward these triggers involves the encounter of antigen-processing and -presenting cells such as macrophages and dendritic cells with T cells, resulting in immune responses that are highly selective for the antigenic trigger. Research over the past few years has implicated members of the coronin protein family, in particular coronin 1, in responses against several pathogenic triggers. While coronin 1 was initially described as a host factor allowing the intracellular survival of the pathogen Mycobacterium tuberculosis, subsequent work showed it to be a crucial factor for naïve T cell homeostasis. The activity of coronin 1 in allowing the intracellular survival of pathogenic mycobacteria is relatively well characterized, involving the activation of the Ca²⁺/calcineurin pathway, while coronin 1’s role in modulating naïve T cell homeostasis remains more enigmatic. In this mini review, we discuss the knowledge on the role for coronin 1 in immune cell functioning and provide a number of potential scenarios via which coronin 1 may be able to regulate naïve T cell homeostasis.

NGF steers microglia toward a neuroprotective phenotype

Microglia are the sentinels of the brain but a clear understanding of the factors that modulate their activation in physiological and pathological conditions is still lacking. Here we demonstrate that Nerve Growth Factor (NGF) acts on microglia by steering them toward a neuroprotective and anti-inflammatory phenotype. We show that microglial cells express functional NGF receptors in vitro and ex vivo. Our transcriptomic analysis reveals how, in primary microglia, NGF treatment leads to a modulation of motility, phagocytosis and degradation pathways. At the functional level, NGF induces an increase in membrane dynamics and macropinocytosis and, in vivo, it activates an outward rectifying current that appears to modulate glutamatergic neurotransmission in nearby neurons. Since microglia are supposed to be a major player in Aβ peptide clearance in the brain, we tested the effects of NGF on its phagocytosis. NGF was shown to promote TrkA-mediated engulfment of Aβ by microglia, and to enhance its degradation. Additionally, the proinflammatory activation induced by Aβ treatment is counteracted by the concomitant administration of NGF. Moreover, by acting specifically on microglia, NGF protects neurons from the Aβ-induced loss of dendritic spines and inhibition of long term potentiation. Finally, in an ex-vivo setup of acute brain slices, we observed a similar increase in Aβ engulfment by microglial cells under the influence of NGF. Our work substantiates a role for NGF in the regulation of microglial homeostatic activities and points toward this neurotrophin as a neuroprotective agent in Aβ accumulation pathologies, via its anti-inflammatory activity on microglia.

From Phagocytes to Immune Defense: Roles for Coronin Proteins in Dictyostelium and Mammalian Immunity

Microbes have interacted with eukaryotic cells for as long as they have been co-existing. While many of these interactions are beneficial for both the microbe as well as the eukaryotic cell, several microbes have evolved into pathogenic species. For some of these pathogens, host cell invasion results in irreparable damage and thus host cell destruction, whereas others use the host to avoid immune detection and elimination. One of the latter pathogens is Mycobacterium tuberculosis, arguably one of the most notorious pathogens on earth. In mammalian macrophages, M. tuberculosis manages to survive within infected macrophages by avoiding intracellular degradation in lysosomes using a number of different strategies. One of these is based on the recruitment and phagosomal retention of the host protein coronin 1, that is a member of the coronin protein family and a mammalian homolog of coronin A, a protein identified in Dictyostelium. Besides mediating mycobacterial survival in macrophages, coronin 1 is also an important regulator of naïve T cell homeostasis. How, exactly, coronin 1 mediates its activity in immune cells remains unclear. While in lower eukaryotes coronins are involved in cytoskeletal regulation, the functions of the seven coronin members in mammals are less clear. Dictyostelium coronins may have maintained multiple functions, whereas the mammalian coronins may have evolved from regulators of the cytoskeleton to modulators of signal transduction. In this minireview, we will discuss the different studies that have contributed to understand the molecular and cellular functions of coronin proteins in mammals and Dictyostelium.

Neutrophil Microvesicles from Healthy Control and Rheumatoid Arthritis Patients Prevent the Inflammatory Activation of Macrophages

Microvesicles (MVs) are emerging as a novel means to enact cell-to-cell communication in inflammation. Here, we aimed to ascertain the ability of neutrophil-derived MVs to modulate target cell behaviour, the focus being the macrophage. MVs were generated in response to tumour necrosis factor-α, from healthy control neutrophils or those from rheumatoid arthritis patients. MVs were used to stimulate human monocyte-derived macrophages in vitro, or administered intra-articularly in the K/BxN mouse model of arthritis. A macrophage/fibroblast-like synoviocyte co-culture system was used to study the effects of vesicles on the crosstalk between these cells. We demonstrate a direct role for phosphatidylserine and annexin-A1 exposed by the MVs to counteract classical activation of the macrophages, and promote the release of transforming growth factor-β, respectively. Classically-activated macrophages exposed to neutrophil MVs no longer activated fibroblast-like synoviocytes in subsequent co-culture settings. Finally, intra-articular administration of neutrophil MVs from rheumatoid arthritis patients in arthritic mice affected the phenotype of joint macrophages. Altogether these data, with the identification of specific MV determinants, open new opportunities to modulate on-going inflammation in the synovia - mainly by affecting macrophage polarization and potentially also fibroblast-like synoviocytes - through the delivery of autologous or heterologous MVs produced from neutrophils.

Activation of MMPs in Macrophages by Mycobacterium tuberculosis via the miR-223-BMAL1 Signaling Pathway

An interaction between Mycobacterium tuberculosis and macrophages constitutes an essential step in tuberculosis development, as macrophages exert both positive and negative effects on M. tuberculosis-triggered organ lesions. In this study, we focused on the regulation of the expression of matrix metalloproteinases (MMPs), which is responsible for lung matrix degradation and bacteria dissection, in macrophages following M. tuberculosis infection. Female BALB/c mice were intravenously injected with the M. tuberculosis strain H37Rv at 0 h zeitgeber time (ZT0) or 12 h zeitgeber time (ZT12). The expression and activity of MMP-1, -2, -3, and -9 in lungs and spleens were then evaluated. In vitro, peritoneal macrophages were harvested at ZT0 or at ZT12 and infected with 10 MOI M. tuberculosis. The expression of MMPs, microRNA-223 and BMAL1 was analyzed by qRT-PCR and/or Western blot. The binding of BMAL1 3'-UTR by miR-223 was confirmed by luciferase activity assay. Additionally, wild-type BMAL1 or NLSmut BMAL1 plasmids were transfected to evaluate the effect of BMAL1 on MMPs. The results showed a differential expression of MMPs in mice tissues infected at different times. M. tuberculosis infection caused enhanced MMP-1, -9, and miR-223 expression, with inhibited BMAL1 expression. MiR-223 modulated BMAL1 expression via the direct binding of BMAL1 3'-UTR. Furthermore, wild-type BMAL1 other than NLSmut BMAL1 attenuated MMPs expression in M. tuberculosis-infected macrophages. Overall, this study demonstrated a potential involvement of circadian rhythm in MMP activation by M. tuberculosis in macrophages. J. Cell. Biochem. 118: 4804-4812, 2017. © 2017 Wiley Periodicals, Inc.

Vacuolar ATPase in phago(lyso)some biology

Many eukaryotic cells ingest extracellular particles in a process termed phagocytosis which entails the generation of a new intracellular compartment, the phagosome. Phagosomes change their composition over time and this maturation process culminates in their fusion with acidic, hydrolase-rich lysosomes. During the maturation process, degradation and, when applicable, killing of the cargo may ensue. Many of the events that are pathologically relevant depend on strong acidification of phagosomes by the 'vacuolar' ATPase (V-ATPase). This protein complex acidifies the lumen of some intracellular compartments at the expense of ATP hydrolysis. We discuss here the roles and importance of V-ATPase in intracellular trafficking, its distribution, inhibition and activities, its role in the defense against microorganisms and the counteractivities of pathogens.

An Essential Role for TAGLN2 in Phagocytosis of Lipopolysaccharide-activated Macrophages

Activated macrophages have a greater ability of phagocytosis against pathogens that is mediated by large-scale actin rearrangement. However, molecular machineries that conduct this task have not been fully identified. Here, we demonstrate an unanticipated role of TAGLN2, a 22-kDa actin-binding protein, in Toll-like receptor (TLR)-stimulated phagocytosis. TAGLN2 was greatly induced in macrophages in response to lipopolysaccharide (LPS), a ligand for TLR4, partly via the NF-κB pathway. TAGLN2-deficient macrophages (TAGLN2^−/−) showed defective phagocytic functions of IgM- and IgG-coated sheep red blood cells as well as bacteria. Cell signaling pathways involved in actin rearrangement—PI3 kinase/AKT and Ras-ERK—were also down-regulated in LPS-stimulated TAGLN2-deficient macrophages. Moreover, TAGLN2^−/− mice showed higher mortality after bacterial infection than wild-type littermates. Thus, our results revealed a novel function of TAGLN2 as a molecular armament required for host defense.

Antigen Processing and Presentation Mechanisms in Myeloid Cells

Unlike B cells, CD8-positive and CD4-positive T cells of the adaptive immune system do not recognize intact foreign proteins but instead recognize polypeptide fragments of potential antigens. These antigenic peptides are expressed on the surface of antigen presenting cells bound to MHC class I and MHC class II proteins. Here, we review the basics of antigen acquisition by antigen presenting cells, antigen proteolysis into polypeptide fragments, antigenic peptide binding to MHC proteins, and surface display of both MHC class I-peptide and MHC class II-peptide complexes.

Actin-binding protein coronin 1A controls osteoclastic bone resorption by regulating lysosomal secretion of cathepsin K

Osteoclasts degrade bone matrix proteins via the secretion of lysosomal enzymes. However, the precise mechanisms by which lysosomal components are transported and fused to the bone-apposed plasma membrane, termed ruffled border membrane, remain elusive. Here, we identified coronin 1A as a negative regulator of exocytotic release of cathepsin K, one of the most important bone-degrading enzymes in osteoclasts. The modulation of coronin 1A expression did not alter osteoclast differentiation and extracellular acidification, but strongly affected the secretion of cathepsin K and osteoclast bone-resorption activity, suggesting the coronin 1A-mediated regulation of lysosomal trafficking and protease exocytosis. Further analyses suggested that coronin 1A prevented the lipidation-mediated sorting of the autophagy-related protein LC3 to the ruffled border and attenuated lysosome-plasma membrane fusion. In this process, the interactions between coronin 1A and actin were crucial. Collectively, our findings indicate that coronin 1A is a pivotal component that regulates lysosomal fusion and the secretion pathway in osteoclast-lineage cells and may provide a novel therapeutic target for bone diseases.

The neurotrophin receptor signaling endosome: Where trafficking meets signaling

Neurons are the largest cells in the body and form subcellular compartments such as axons and dendrites. During both development and adulthood building blocks must be continually trafficked long distances to maintain the different regions of the neuron. Beyond building blocks, signaling complexes are also transported, allowing for example, axons to communicate with the soma. The critical roles of signaling via ligand-receptor complexes is perhaps best illustrated in the context of development, where they are known to regulate polarization, survival, axon outgrowth, dendrite development, and synapse formation. However, knowing 'when' and 'how much' signaling is occurring does not provide the complete story. The location of signaling has a significant impact on the functional outcomes. There are therefore complex and functionally important trafficking mechanisms in place to control the precise spatial and temporal aspects of many signal transduction events. In turn, many of these signaling events affect trafficking mechanisms, setting up an intricate connection between trafficking and signaling. In this review we will use neurotrophin receptors, specifically TrkA and TrkB, to illustrate the cell biology underlying the links between trafficking and signaling. Briefly, we will discuss the concepts of how trafficking and signaling are intimately linked for functional and diverse signaling outputs, and how the same protein can play different roles for the same receptor depending on its localization. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Role for coronin 1 in mouse NK cell function

Coronin 1, a member of the evolutionary conserved WD repeat protein family of coronin proteins is expressed in all leukocytes, but a role for coronin 1 in natural killer (NK) cell homeostasis and function remains unclear. Here, we have analyzed the number and functionality of NK cells in the presence and absence of coronin 1. In coronin 1-deficient mice, absolute NK cell numbers and phenotype were comparable to wild type mice in blood, spleen and liver. Following in vitro stimulation of the activating NK cell receptors NK1.1, NKp46, Ly49D and NKG2D, coronin 1-deficient NK cells were functional with respect to interferon-γ production, degranulation and intracellular Ca2+ mobilization. Also, both wild type as well as coronin 1-deficient NK cells showed comparable cytotoxic activity. Furthermore, activation and functionality of NK cells following Vesicular Stomatitis Virus (VSV) infection was similar between wild type and coronin 1-deficient mice. Taken together these data suggest that coronin 1 is dispensable for mouse NK cell homeostasis and function.

Macropinocytosis of Nab-paclitaxel Drives Macrophage Activation in Pancreatic Cancer

Pancreatic cancer is a devastating disease that is largely refractory to currently available treatment strategies. Therapeutic resistance is partially attributed to the dense stromal reaction of pancreatic ductal adenocarcinoma tumors that includes a pervasive infiltration of immunosuppressive (M2) macrophages. Nab-paclitaxel (trade name Abraxane) is a nanoparticle albumin-bound formulation of paclitaxel that, in combination with gemcitabine, is currently the first-line treatment for pancreatic cancer. Here, we show that macrophages internalized nab-paclitaxel via macropinocytosis. The macropinocytic uptake of nab-paclitaxel induced macrophage immunostimulatory (M1) cytokine expression and synergized with IFNγ to promote inducible nitric oxide synthase expression in a TLR4-dependent manner. Nab-paclitaxel was internalized by tumor-associated macrophages in vivo, and therapeutic doses of nab-paclitaxel alone, and in combination with gemcitabine, increased the MHCII⁺CD80⁺CD86⁺ M1 macrophage population. These data revealed an unanticipated role for nab-paclitaxel in macrophage activation and rationalized its potential use to target immune evasion in pancreatic cancer. Cancer Immunol Res; 5(3); 182-90. ©2017 AACR.

Effect of partial PEGylation on particle uptake by macrophages

Controlling the internalization of synthetic particles by immune cells remains a grand challenge for developing successful drug carrier systems. Polyethylene glycol (PEG) is frequently used as a protective coating on particles to evade immune clearance, but it also hinders the interactions of particles with their intended target cells. In this study, we investigate a spatial decoupling strategy, in which PEGs are coated on only one hemisphere of particles, so that the other hemisphere is available for functionalization of cell-targeting ligands without the hindrance effect from the PEGs. The partial coating of PEGs is realized by creating two-faced Janus particles with different surface chemistries on opposite sides. We show that a half-coating of PEGs reduces the macrophage uptake of particles as effectively as a complete coating. Owing to the surface asymmetry, Janus particles that are internalized enter macrophage cells via a combination of ligand-guided phagocytosis and macropinocytosis. By spatially segregating PEGs and ligands for targeting T cells on Janus particles, we demonstrate that the Janus particles bind T cells uni-directionally from the ligand-coated side, bypassing the hindrance from the PEGs on the other hemisphere. The results reveal a new mechanistic understanding on how a spatial coating of PEGs on particles changes the phagocytosis of particles. This study also suggests a new design principle for therapeutic particles - the spatial decoupling of PEGs and cell-targeting moieties reduces the interference between the two functions while attaining the protective effect of PEGs for macrophage evasion.

Mycobacteria Manipulate G-Protein-Coupled Receptors to Increase Mucosal Rac1 Expression in the Lungs

Mycobacterium bovis bacille Calmette-Guérin (BCG) is currently the only approved vaccine against tuberculosis (TB). BCG mimics M. tuberculosis (Mtb) in its persistence in the body and is used as a benchmark to compare new vaccine candidates. BCG was originally designed for mucosal vaccination, but comprehensive knowledge about its interaction with epithelium is currently lacking. We used primary airway epithelial cells (AECs) and a murine model to investigate the initial events of mucosal BCG interactions. Furthermore, we analysed the impact of the G-protein-coupled receptors (GPCRs), CXCR1 and CXCR2, in this process, as these receptors were previously shown to be important during TB infection. BCG infection of AECs induced GPCR-dependent Rac1 up-regulation, resulting in actin redistribution. The altered distribution of the actin cytoskeleton involved the MAPK signalling pathway. Blocking of the CXCR1 or CXCR2 prior to infection decreased Rac1 expression, and increased epithelial transcriptional activity and epithelial cytokine production. BCG infection did not result in epithelial cell death as measured by p53 phosphorylation and annexin. This study demonstrated that BCG infection of AECs manipulated the GPCRs to suppress epithelial signalling pathways. Future vaccine strategies could thus be improved by targeting GPCRs.

Emergent Role of Coronin-1a in Neuronal Signaling

The Coronin family of proteins were first noted for their role in pathogen-host interactions and for modulating actin dynamics. Recently, however, Coronins have been found in a greater variety of cell types, and novel roles for the Coronins within the nervous system have been discovered. In the immune system, Coronin-1a enables Mycobacterium tuberculosis to evade lysosomal destruction. This activity appears to be analogous to protection of the NGF-TrkA signaling endosome during sympathetic nervous system development that is required for survival signaling. Similarly, others have implicated Coronin-1a in GPCR signaling during the formation of excitatory connections in the central nervous system. Its role in multiple signaling pathways suggests that it may influence cross talk between key pathways (TrkA, GPCRs) during neurodevelopment. Here, we review the role of Coronin-1a in neural development and function.

PPE26 induces TLR2-dependent activation of macrophages and drives Th1-type T-cell immunity by triggering the cross-talk of multiple pathways involved in the host response

The pathophysiological functions and the underlying molecular basis of PE /PPE proteins of M. tuberculosis remain largely unknown. In this study, we focused on the link between PPE26 and host response. We demonstrated that PPE26 can induce extensive inflammatory responses in macrophages through triggering the cross-talk of multiple pathways involved in the host response, as revealed by iTRAQ-based subcellular quantitative proteomics. We observed that PPE26 is able to specifically bind to TLR2 leading to the subsequent activation of MAPKs and NF-κB signaling. PPE26 functionally stimulates macrophage activation by augmenting pro-inflammatory cytokine production (TNF-α, IL-6 and IL-12 p40) and the expression of cell surface markers (CD80, CD86, MHC class I and II). We observed that PPE26-treated macrophages effectively polarizes naïve CD4⁺ T cells to up-regulate CXCR3 expression, and to secrete IFN-γ and IL-2, indicating PPE26 contributes to the Th1 polarization during the immune response. Importantly, rBCG::PPE26 induces stronger antigen-specific TNF-α and IFN-γ activity, and higher levels of the Th1 cytokines TNF-α and IFN-γ comparable to BCG. Moreover, PPE26 effectively induces the reciprocal expansion of effector/memory CD4⁺/CD8⁺ CD44^highCD62L^low T cells in the spleens of mice immunized with this strain. These results suggest that PPE26 may be a TLR2 agonist that stimulates innate immunity and adaptive immunity, indicating that PPE26 is a potential antigen for the rational design of an efficient vaccine against M. tuberculosis.