Classically and alternatively activated bone marrow derived macrophages differ in cytoskeletal functions and migration towards specific CNS cell types

Focusing on Formyl Peptide Receptors after Traumatic Spinal Cord Injury: from Immune Response to Neurogenesis

The intricate pathophysiological cascades following spinal cord injury (SCI), encompassing cellular demise, axonal degeneration, and the formation of glial scars, pose formidable barriers to neural regeneration and restoration. Notably, neuroinflammation and glial scars emerge as pivotal barrier to post-SCI repair. Formyl peptide receptors (FPRs) emerge as critical regulators of immune responses, exerting significant influence over inflammatory modulation and nerve regeneration subsequent to SCI. Beyond their classical expression in myeloid cells, FPRs demonstrate a pronounced presence within the central nervous system (CNS) with roles in the progression of neurodegenerative disorders and neurological malignancies. Post-SCI, the equilibrium of the inflammatory microenvironment is recalibrated through the strategic modulation of FPRs, including facilitating a balance in microglial polarization, stimulating neural stem cells (NSCs) migration, and promoting neural axon elongation. These observations enlighten the potential of FPRs as innovative targets for neuronal regenerations bolstering SCI repair. This review endeavors to delineate the distribution and function of FPRs in the aftermath of SCI, with a special attention to their roles in inflammatory regulation, NSCs mobilization, and synaptic growth. By elucidating these mechanisms, we aspire to contribute novel insights and strategies for SCI therapy.

Single-nucleus RNA-seq dissection of choroid plexus tumor cell heterogeneity

The genomic, genetic and cellular events regulating the onset, growth and survival of rare, choroid plexus neoplasms remain poorly understood. Here, we examine the heterogeneity of human choroid plexus tumors by single-nucleus transcriptome analysis of 23,906 cells from four disease-free choroid plexus and eleven choroid plexus tumors. The resulting expression atlas profiles cellular and transcriptional diversity, copy number alterations, and cell-cell interaction networks in normal and cancerous choroid plexus. In choroid plexus tumor epithelial cells, we observe transcriptional changes that correlate with genome-wide methylation profiles. We further characterize tumor type-specific stromal microenvironments that include altered macrophage and mesenchymal cell states, as well as changes in extracellular matrix components. This first single-cell dataset resource from such scarce samples should be valuable for divising therapies against these little-studied neoplasms.

Tumor-associated macrophages and tumor-infiltrating lymphocytes in canine cutaneous and subcutaneous mast cell tumors

Cutaneous and subcutaneous mast cell tumors (MCTs) are common canine neoplasms characterized by variable biological behavior. Tumor-associated macrophages (TAMs) and tumor-infiltrating lymphocytes (TILs) can be effective prognostic markers in numerous human neoplasms and are increasingly investigated in dogs. The aim of this study was to characterize immune cells in canine MCTs and their relationship with histological location (cutaneous, subcutaneous) and histologic nodal metastatic status (HN0-3). Thirty-eight MCTs (26 cutaneous, 12 subcutaneous) from 33 dogs with known sentinel lymph node (SLN) metastatic status were immunolabeled for Iba1 (macrophages), CD20 (B cells), CD3 (T cells), and Foxp3 (regulatory T cells). Semiquantitative scoring of interstitial and perivascular CD3+, CD20+, and Foxp3+ cells and morphological evaluation of Iba1+ cells were performed. For each marker, the percent immunopositive area was evaluated by image analysis. All MCTs were diffusely infiltrated by Iba1+ cells and variably infiltrated by CD20+, CD3+, and rare Foxp3+ cells. Stellate/spindle Iba1+ cells were associated with HN2 and HN3 SLNs. Perivascular Foxp3+ cells, CD3+ cells, and percent CD3+ areas were increased in subcutaneous MCTs. Interstitial CD3+ cells were increased in cutaneous MCTs with HN0 SLNs. No differences in CD20+ cells were identified between cutaneous and subcutaneous MCTs and among SLN classes. MCTs were markedly infiltrated by TAMs and variably infiltrated by TILs. Stellate/spindle morphology of TAMs associated with HN2 and HN3 SLNs is suggestive of a pro-tumoral (M2) phenotype. Cutaneous and subcutaneous MCTs have different tumor-immune microenvironments, and T-cell infiltration might contribute to prevention of nodal metastatic spread of cutaneous MCTs.

Targeting foamy macrophages by manipulating ABCA1 expression to facilitate lesion healing in the injured spinal cord

Spinal cord injury (SCI) triggers a complex cascade of events, including myelin loss, neuronal damage, neuroinflammation, and the accumulation of damaged cells and debris at the injury site. Infiltrating bone marrow derived macrophages (BMDMϕ) migrate to the epicenter of the SCI lesion, where they engulf cell debris including abundant myelin debris to become pro-inflammatory foamy macrophages (foamy Mϕ), participate neuroinflammation, and facilitate the progression of SCI. This study aimed to elucidate the cellular and molecular mechanisms underlying the functional changes in foamy Mϕ and their potential implications for SCI. Contusion at T10 level of the spinal cord was induced using a New York University (NYU) impactor (5 g rod from a height of 6.25 mm) in male mice. ABCA1, an ATP-binding cassette transporter expressed by Mϕ, plays a crucial role in lipid efflux from foamy cells. We observed that foamy Mϕ lacking ABCA1 exhibited increased lipid accumulation and a higher presence of lipid-accumulated foamy Mϕ as well as elevated pro-inflammatory response in vitro and in injured spinal cord. We also found that both genetic and pharmacological enhancement of ABCA1 expression accelerated lipid efflux from foamy Mϕ, reduced lipid accumulation and inhibited the pro-inflammatory response of foamy Mϕ, and accelerated clearance of cell debris and necrotic cells, which resulted in functional recovery. Our study highlights the importance of understanding the pathologic role of foamy Mϕ in SCI progression and the potential of ABCA1 as a therapeutic target for modulating the inflammatory response, promoting lipid metabolism, and facilitating functional recovery in SCI.

Xanthohumol, a prenylated flavonoid from hops (Humulus lupulus L.) exerts multidirectional pro-healing properties towards damaged zebrafish hair cells by regulating the innate immune response

Xanthohumol (XN) is a prominent prenylated flavonoid present in the hop plant (Humulus lupulus L.). Despite undoubted pro-healing properties of hop plant, there is still a need for clinical investigations confirming these effects as well as the underlying molecular mechanisms. The present study was designed to (1) establish the role of XN in non-invasive inflammation induced by chemical damage to zebrafish hair cells, (2) clarify if it influences cell injury severity, neutrophil migration, macrophage activation, cell regeneration, and (3) find out whether it modulates the gene expression profile of chosen immune and stress response markers. All experiments were performed on 3 dpf zebrafish larvae. After fertilization the embryos were transferred to appropriate XN solutions (0.1 μM, 0.3 μM and 0.5 μM). The 40 min 10 μM CuSO4 exposure evoked severe damage to posterior lateral line hair cells triggering a robust acute inflammatory response. Four readouts were selected as the indicators of XN role in the process of inflammation: 1) hair cell death, 2) neutrophil migration towards damaged hair cells, 3) macrophage activation and recruitment to damaged hair cells, 4) hair cell regeneration. The assessments involved in vivo confocal microscopy imaging and qPCR based molecular analysis. It was demonstrated that XN (1) influences death pathway of damaged hair cells by redirecting their severe necrotic phenotype into apoptotic one, (2) impacts the immune response via regulating neutrophil migration, macrophage recruitment and activation (3) modulates gene expression of immune system markers and (4) accelerates hair cell regeneration.

Plastic response of macrophages to metal ions and nanoparticles in time mimicking metal implant body environment

The paradigm of using metal biomaterials could be viewed from two sides - treatment of wide spectrum of degenerative diseases, and debris release from materials. After implant insertion, metal nanoparticles (NPs) and ions are released not only upon the first contact with cells/tissues, but in continual manner, which is immediately recognized by immune cells. In this work, the effects of metal nanoparticles (TiO2, Ni) and ions (Ni2+, Co2+, Cr3+, Mo6+) on primary human M0 macrophages from the blood samples of osteoarthritic patients undergoing total arthroplasty were studied in order to monitor immunomodulatory effects on the cells in a real-time format. The highest NiNPs concentration of 10 µg/ml had no effect on any of macrophage parameters, while the Ni2+ ions cytotoxicity limit for the cells is 0.5 mM. The cytotoxic effects of higher Ni2+ concentration revealed mitochondrial network fragmentation leading to mitochondrial dysfunction, accompanied by increased lysosomal activity and changes in pro-apoptotic markers. The suppression of M2 cell formation ability was connected to presence of Ni2+ ions (0.5 mM) and TiO2NPs (10 µg/ml). The immunomodulatory effect of Mo6+ ions, controversially, inhibit the formation of the cells with M1 phenotype and potentiate the thread-like shape M2s with increased chaotic cell movement. To summarize, metal toxicity depends on the debris form. Both, metal ions and nanoparticles affect macrophage size, morphological and functional parameters, but the effect of ions is more complex and likely more harmful, which has potential impact on healing and determines post-implantation reactions.

Impact of endogenous and exogenous nitrogen species on macrophage extracellular trap (MET) formation by bone marrow-derived macrophages

Macrophage extracellular traps (METs) represent a novel defense mechanism in the antimicrobial arsenal of macrophages. However, mechanisms of MET formation are still poorly understood and this is at least partially due to the lack of reliable and reproducible models. Thus, we aimed at establishing a protocol of MET induction by bone marrow-derived macrophages (BMDMs) obtained from cryopreserved and then thawed bone marrow (BM) mouse cells. We report that BMDMs obtained in this way were morphologically (F4/80+) and functionally (expression of inducible nitric oxide (NO) synthase and NO production) differentiated and responded to various stimuli of bacterial (lipopolysaccharide, LPS), fungal (zymosan) and chemical (PMA) origin. Importantly, BMDMs were successfully casting METs composed of extracellular DNA (extDNA) serving as their backbone to which proteins such as H2A.X histones and matrix metalloproteinase 9 (MMP-9) were attached. In rendered 3D structure of METs, extDNA and protein components were embedded in each other. Since studies had shown the involvement of oxygen species in MET release, we aimed at studying if reactive nitrogen species (RNS) such as NO are also involved in MET formation. By application of NOS inhibitor - L-NAME or nitric oxide donor (SNAP), we studied the involvement of endogenous and exogenous RNS in traps release. We demonstrated that L-NAME halted MET formation upon stimulation with LPS while SNAP alone induced it. The latter phenomenon was further enhanced in the presence of LPS. Taken together, our findings demonstrate that BMDMs obtained from cryopreserved BM cells are capable of forming METs in an RNS-dependent manner.

Sex-specific impact of maternal obesity on fetal placental macrophages and cord blood triglycerides

INTRODUCTION

Maternal obesity is associated with increased risk of offspring obesity and cardiometabolic disease. Altered fetoplacental immune programming is a potential candidate mechanism. Differences in fetal placental macrophages, or Hofbauer cells (HBCs), have been observed in maternal obesity, and lipid metabolism is a key function of resident macrophages that may be deranged in inflammation/immune activation. We sought to test the following hypotheses: 1) maternal obesity is associated with altered HBC density and phenotype in the term placenta and 2) obesity-associated HBC changes are associated with altered placental lipid transport to the fetus. The impact of fetal sex was evaluated in all experiments.

METHODS

We quantified the density and morphology of CD163-and CD68-positive HBCs in placental villi in 34 full-term pregnancies undergoing cesarean delivery (N = 15, maternal BMI ≥30 kg/m2; N = 19, BMI <30 kg/m2). Antibody-positive cells in terminal villi were detected and cell size and circularity analyzed using a semi-automated method for thresholding of bright-field microscopy images (ImageJ). Placental expression of lipid transporter genes was quantified using RTqPCR, and cord plasma triglycerides (TGs) were profiled using modified Wahlefeld method. The impact of maternal obesity and fetal sex on HBC features, lipid transporters, and cord TGs were evaluated by two-way ANOVA. Spearman correlations of cord TGs, HBC metrics and gene expression levels were calculated.

RESULTS

Maternal obesity was associated with significantly increased density of HBCs, with male placentas most affected (fetal sex by maternal obesity interaction p = 0.04). CD163+ HBCs were larger and rounder in obesity-exposed male placentas. Sexually dimorphic expression of placental FATP4, FATP6, FABPPM, AMPKB1 and AMPKG and cord TGs was noted in maternal obesity, such that levels were higher in males and lower in females relative to sex-matched controls. Cord TGs were positively correlated with HBC density and FATP1 expression.

DISCUSSION

Maternal obesity is associated with sex-specific alterations in HBC density and placental lipid transporter expression, which may impact umbilical cord blood TG levels and offspring cardiometabolic programming.

ATF2 orchestrates macrophage differentiation and activation to promote antibacterial responses

The differentiation and activation of macrophages are critical regulatory programs that are central to host inflammation and pathogen defense. However, the transcriptional regulatory pathways involved in these programs are not well understood. Herein, we demonstrate that the activity and expression of the transcription factor ATF2 is precisely regulated during primary human monocyte-to-macrophage differentiation and that its activation is linked to M1 polarization and antibacterial responses. Genetic perturbation experiments demonstrated that deletion of ATF2 (THP-ΔATF2) resulted in irregular and abnormal macrophage morphology, whereas macrophages overexpressing ATF2 (THP-ATF2) developed round and pancake-like morphology, resembling classically activated (M1) macrophages. Mechanistically, we show that ATF2 binds to the core promoter of PPM1A, a phosphatase that regulates monocyte-to-macrophage differentiation, to regulate its expression. Functionally, overexpression of ATF2 sensitized macrophages to M1 polarization, resulting in increased production of major histocompatibility complex class II, IL-1β, and IP-10; improved phagocytic capacity; and enhanced control of the intracellular pathogen Mycobacterium tuberculosis. Gene expression profiling revealed that overexpression of ATF2 reprogramed macrophages to promote antibacterial pathways enriched in chemokine signaling, metabolism, and antigen presentation. Consistent with pathways analysis, metabolic profiling revealed that genetic overexpression or stimuli-induced activation of ATF2 alters the metabolic capacity of macrophages and primes these cells for glycolytic metabolism during M1 polarization or bacterial infection. Our findings reveal that ATF2 plays a central role during macrophage differentiation and M1 polarization to enhance the functional capacities of macrophages.

The significance of M1 macrophage should be highlighted in peripheral nerve regeneration

Macrophage influences peripheral nerve regeneration. According to the classical M1/M2 paradigm, the M1 macrophage is an inhibitor of regeneration, while the M2 macrophage is a promoter. However, several studies have shown that M1 macrophages are indispensable for peripheral nerve repair and facilitate many critical processes in axonal regeneration. In this review, we summarized the information on macrophage polarization and focused on the activities of M1 macrophages in regeneration. We also provided some examples where the macrophage phenotypes were regulated to help regeneration. We argued that the coordination of both macrophage phenotypes might be effective in peripheral nerve repair, and a more comprehensive view of macrophages might contribute to macrophage-based immunomodulatory therapies.

A macrophage subpopulation promotes airineme-mediated intercellular communication in a matrix metalloproteinase-9 dependent manner

Tissue-resident macrophages are heterogeneous and perform location-dependent functions. Skin resident macrophages play intriguing roles in long-distance intercellular signaling by mediating cellular protrusions called airinemes in zebrafish. These macrophages relay signaling molecules containing airineme vesicles between pigment cells, and their absence disrupts airineme-mediated signaling and pigment pattern formation. It is unknown if the same macrophages control both these signaling and typical immune functions or if a separate subpopulation functions in intercellular communication. With high-resolution imaging and genetic ablation approaches, we identify a macrophage subpopulation responsible for airineme-mediated signaling. These seem to be distinct from conventional skin-resident macrophages by their ameboid morphology and faster or expansive migratory behaviors. They resemble ectoderm-derived macrophages termed metaphocytes. Metaphocyte ablation markedly decreases airineme extension and signaling. In addition, these ameboid/metaphocytes require matrix metalloproteinase-9 for their migration and airineme-mediated signaling. These results reveal a macrophage subpopulation with specialized functions in airineme-mediated signaling, which may play roles in other aspects of intercellular communication.

Composite Fibrin and Carbon Microfibre Implant to Modulate Postraumatic Inflammation after Spinal Cord Injury

Poor functional recovery after spinal cord injury (SCI) drives the development of novel strategies to manage this devastating condition. We recently showed promising immunomodulatory and pro-regenerative actions of bio-functionalized carbon microfibres (MFs) implanted in a rodent model of SCI. In order to maximize tissue repair while easing MF implantation, we produced a composite implant based on the embedding of several MFs within a fibrin hydrogel. We used intravital imaging of fluorescent reporter mice at the early stages and spinal sections of the same animals 3 months later to characterize the neuroinflammatory response to the implant and its impact on axonal regeneration. Whereas fibrin alone was inert in the first week, its enzymatic degradation drove the chronic activation of microglial cells and axonal degeneration within 3 months. However, the presence of MFs inside the fibrin hydrogel slowed down fibrin degradation and boosted the early recruitment of immune cells. Noteworthy, there was an enhanced contribution of monocyte-derived dendritic cells (moDCs), preceding a faster transition toward an anti-inflammatory environment with increased axonal regeneration over 3 months. The inclusion of MF here ensured the long-term biocompatibility of fibrin hydrogels, which would otherwise preclude successful spinal cord regeneration.

The roles of microglia and astrocytes in myelin phagocytosis in the central nervous system

Myelination is an important process in the central nervous system (CNS). Oligodendrocytes (OLs) extend multiple layers to densely sheath on axons, composing the myelin to achieve efficient electrical signal conduction. The myelination during developmental stage maintains a balanced state. However, numerous CNS diseases including neurodegenerative and cerebrovascular diseases cause demyelination and disrupt the homeostasis, resulting in inflammation and white matter deficits. Effective clearance of myelin debris is needed in the region of demyelination, which is a key step for remyelination and tissue regeneration. Microglia and astrocytes are the major resident phagocytic cells in the brain, which may play different or collaborative roles in myelination. Microglia and astrocytes participate in developmental myelination through engulfing excessive unneeded myelin. They are also involved in the clearance of degenerated myelin debris for accelerating remyelination, or engulfing healthy myelin sheath for inhibiting remyelination. This review focuses on the roles of microglia and astrocytes in phagocytosing myelin in the developmental brain and diseased brain. In addition, the interaction between microglia and astrocytes to mediate myelin engulfment is also summarized.

Cellulose nanocrystals vs. cellulose nanospheres: A comparative study of cytotoxicity and macrophage polarization potential

Nanocellulose application has been increasing owing to its appealing physicochemical properties. Monitoring of the crystallinity, surface topography, and reactivity of this high-aspect-ratio nanomaterial is crucial for efficient tissue engineering. Controlling macrophage polarization phenotype remains a challenge in regenerative medicine and tissue engineering. Herein, we monitored the effects of shape-regulated (rod and spherical) nanocellulose on the macrophage modulatory potential of RAW 246.7 cells in vitro. Spherical nanocellulose (s-NC) exhibited higher thermal stability and biocompatibility than rod nanocellulose. Macrophage polarization was profoundly affected by nanocellulose topography and incubation period. M2 polarization was observed in vitro after 1 day of treatment with s-NC, followed by M1 polarization after treatment for longer periods. Transcriptome analysis similarly revealed that M1 polarization was dominant after 1 day h of incubation with both nanocellulose types. These findings demonstrate that macrophage polarization can be controlled by selecting suitable nanocellulose shape and incubation time for desired applications.

Human Umbilical Cord Mesenchymal Stem Cells Improve the Status of Hypoxic/Ischemic Cerebral Palsy Rats by Downregulating NogoA/NgR/Rho Pathway

Human umbilical cord mesenchymal stem cells (hUCMSC) have shown promising potential in ameliorating brain injury, but the mechanism is unclear. We explore the role of NogoA/NgR/Rho pathway in mediating hUCMSC to improve neurobehavioral status and alleviate brain injury in hypoxia/ischemia-induced CP (cerebral palsy) rat model in order to promote the clinical application of stem cell therapy in CP. The injury model of HT22 cells was established after 3 h hypoxia, and then co-cultured with hUCMSC. The rat model of CP was established by ligation of the left common carotid artery for 2.5 h. Subsequently, hUCMSC was administered via the tail vein once a week for a total of four times. The neurobehavioral status of CP rats was determined by behavioral experiment, and the pathological brain injury was determined by pathological staining method. The mRNA and protein expressions of NogoA, NgR, RhoA, Rac1, and CDC42 in brain tissues of rats in all groups and cell groups were detected by real-time quantitative polymerase chain reaction (RT-qPCR), Western blot, and immunofluorescence. The CP rats exhibited obvious motor function abnormalities and pathological damage. Compared with the control group, hUCMSC transplantation could significantly improve the neurobehavioral situation and attenuate brain pathological injury in CP rats. The relative expression of NogoA, NgR, RhoA mRNA, and protein in brain tissues of rats in the CP group was significantly higher than the rats in the sham and CP+hUCMSC group. The relative expression of Rac1, CDC42 mRNA, and protein in brain tissues of rats in the CP group was significantly lower than the rats in the sham and CP+hUCMSC group. The animal experiment results were consistent with the experimental trend of hypoxic injury of HT22 cells. This study confirmed that hUCMSC can efficiently improve neurobehavioral status and alleviate brain injury in hypoxia/ischemia-induced CP rat model and HT22 cell model through downregulating the NogoA/NgR/Rho pathway.

Macrophages undergo a behavioural switch during wound healing in zebrafish

In response to wound signals, macrophages are immediately recruited to the injury where they acquire distinct phenotypes and functions, playing crucial roles both in host defense and healing process. Although macrophage phenotypes have been intensively studied during wound healing, mostly using markers and expression profiles, the impact of the wound environment on macrophage shape and behaviour, and the underlying mechanisms deserve more in-depth investigation. Here, we sought to characterize the dynamics of macrophage recruitment and behaviour during aseptic wounding of the caudal fin fold of the zebrafish larva. Using a photo-conversion approach, we demonstrated that macrophages are recruited to the wounded fin fold as a single wave where they switch their phenotype. Intravital imaging of macrophage shape and trajectories revealed that wound-macrophages display a highly stereotypical set of behaviours and change their shape from amoeboid to elongated shape as wound healing proceeds. Using a pharmacological inhibitor of 15-lipoxygenase and protectin D1, a specialized pro-resolving lipid, we investigated the role of polyunsaturated fatty acid metabolism in macrophage behaviour. While inhibition of 15-lipoxygenase using PD146176 or Nordihydroguaiaretic acid (NDGA) decreases the switch from amoeboid to elongated shape, protectin D1 accelerates macrophage reverse migration and favours elongated morphologies. Altogether, our findings suggest that individual macrophages at the wound switch their phenotype leading to important changes in behaviour and shape to adapt to changing environment, and highlight the crucial role of lipid metabolism in the control of macrophage behaviour plasticity during inflammation in vivo.

Engineering physical microenvironments to study innate immune cell biophysics

Innate immunity forms the core of the human body's defense system against infection, injury, and foreign objects. It aims to maintain homeostasis by promoting inflammation and then initiating tissue repair, but it can also lead to disease when dysregulated. Although innate immune cells respond to their physical microenvironment and carry out intrinsically mechanical actions such as migration and phagocytosis, we still do not have a complete biophysical description of innate immunity. Here, we review how engineering tools can be used to study innate immune cell biophysics. We first provide an overview of innate immunity from a biophysical perspective, review the biophysical factors that affect the innate immune system, and then explore innate immune cell biophysics in the context of migration, phagocytosis, and phenotype polarization. Throughout the review, we highlight how physical microenvironments can be designed to probe the innate immune system, discuss how biophysical insight gained from these studies can be used to generate a more comprehensive description of innate immunity, and briefly comment on how this insight could be used to develop mechanical immune biomarkers and immunomodulatory therapies.

A tailored bioactive 3D porous poly(lactic-acid)-exosome scaffold with osteo-immunomodulatory and osteogenic differentiation properties

Polylactic acid (PLA) is a versatile and biodegradable scaffold widely used in biomedical fields to repair tissue defects. Exosomes derived from mesenchymal stem cells (MSCs) are nano-sized extracellular vesicles, which play an important role in tissue engineering in recent years. The primary focus of this study was to develop a bioactive 3D PLA scaffold using exosome-based strategy to improve its osteogenic and immunoregulatory potential. We firstly successfully isolated MSC-derived exosomes (MSC-Exo). Morphological analysis revealed that MSC-Exo exhibits a typical cup-shaped morphology with high expression of exosomal marker CD63. MSC-Exo internalization into recipient cells were also investigated using flow cytometry and confocal laser scanning microscopy. Porous 3D PLA scaffold coated MSC-Exo were used for immunoregulatory and osteogenic testing. Exosomes released from 3D PLA scaffold were validated in RAW264.7 and hBMSCs. The cell proliferation and live/dead assay indicated high biocompatibility for PLA-Exo scaffold. Additionally, PLA-Exo scaffold could reduce the pro-inflammatory marker expression and reactive oxygen species (ROS) production, indicating potential immunoregulatory potential. It is also confirmed that PLA-Exo scaffold could potentiate osteogenic differentiation in the osteogenesis assay. In conclusion, our results demonstrate this bioactive 3D-printed PLA scaffolds with MSC-Exo modification holds immunoregulatory potential and favor osteogenic differentiation, thus having potential applications in bone tissue regeneration.

Creatine promotes the repair of peripheral nerve injury by affecting macrophage polarization

The present study aimed to explore whether creatine promotes the repair of peripheral nerve injury and its possible mechanism. In vitro: RAW264.7 cells were used to investigate the role of proteins related to the JAK2/STAT1 pathway in the polarization of macrophages treated with creatine. In vivo: A sciatic nerve crush model was used. After the injury, IL-4 or creatine was injected. The recovery of motor function was assessed by the rotarod test and sciatic function index at 2, 6, 10, and 16 days after injury. At 16 days after injury, the ultrastructure of the nerve tissue was observed under a transmission electron microscope. Immunostaining were performed at 4 and 16 days to investigate the expression levels of macrophage-related markers as well as the distribution of macrophages after injury. Compared with the IFN-γ group, the group pretreated with creatine showed a significant decrease in p-JAK2 and p-STAT1 in vitro. The motor function of mice in the creatine group (CR₁) and creatine 4 days group (CR₂) was significantly improved compared to the control group (CON). The improvement in the CR₂ group was more significant. Immunostaining showed that infiltrating macrophages mainly comprised M1 macrophages in the CON group and M2 macrophages in the CR group. Our study shows that creatine promotes the repair of peripheral nerve injury by affecting macrophage polarization, possibly through decreasing M1 polarization by inhibiting the JAK2/STAT1 pathway.

Titanium surface with nanospikes tunes macrophage polarization to produce inhibitory factors for osteoclastogenesis through nanotopographic cues

Definitive prevention of inflammatory osteolysis around peri-implant bone tissue remains unestablished. M1 macrophages play a key role in the host defense against inflammatory osteolysis, and their polarization depends on cell shape. Macrophage polarization is controlled by environmental stimuli, particularly physicochemical cues and hence titanium nanosurface might tune macrophage polarization and function. This study determined whether titanium nanosurfaces with anisotropically patterned nanospikes regulates macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors. Alkaline-etching treatment with different protocols created two types of titanium nanosurfaces that had anisotropically patterned nanospikes with high or low distribution density, together with superhydrophilicity and the presence of hydroxyl groups. J774A.1 cells (mouse macrophage-like cell line), cultured on both titanium nanosurfaces, exhibited truly circulated shapes and highly expressed M1, but less M2, markers, without loss of viability. M1-like polarization of macrophages on both titanium nanosurfaces was independent of protein-mediated ligand stimulation or titanium surface hydrophilic or chemical status. In contrast, other smooth or micro-roughened titanium surfaces with little or no nanospikes did not activate macrophages under any culture conditions. Macrophage culture supernatants on both titanium nanosurfaces inhibited osteoclast differentiation of RAW264.7 cells (mouse osteoclast precursor cell line), even when co-incubated with osteoclast differentiation factors. The inhibitory effects on osteoclast differentiation tended to be higher in macrophages cultured on titanium nanosurfaces with denser nanospikes. These results showed that titanium nanosurfaces with anisotropically patterned nanospikes tune macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors, with nanotopographic cues rather than other physicochemical properties. STATEMENT OF SIGNIFICANCE: Peri-implant inflammatory osteolysis is one of the serious issues for dental and orthopedic implants. Macrophage polarization and function are key for prevention of peri-implant inflammatory osteolysis. Macrophage polarization can be regulated by the biomaterial's surface physicochemical properties such as hydrophilicity or topography. However, there was no titanium surface modification to prevent inflammatory osteolysis through immunomodulation. The present study showed for the first time that the titanium nanosurfaces with anisotropically patterned nanospikes, created by the simple alkali-etching treatment polarized macrophages into M1-like type producing the inhibitory factor on osteoclast differentiation. This phenomenon attributed to nanotopographic cues, but not hydrophilicity on the titanium nanosurfaces. This nanotechnology might pave the way to develop the smart implant surface preventing peri-implant inflammatory osteolysis through immunomodulation.

Polypharmacological reprogramming of tumor-associated macrophages towards an inflammatory phenotype

Tumor-associated macrophages (TAM) are an important component of the tumor microenvironment (TME) that can promote tumor progression, metastasis, and resistance to therapies. Although TAMs represent a promising target for therapeutic intervention, the complexity of the TME has made the study of TAMs challenging. Here, we established a physiologically relevant in vitro TAM polarization system that recapitulates TAM pro-tumoral activities. This system was used to characterize dynamic changes in gene expression and protein phosphorylation during TAM polarization and to screen phenotypic kinase inhibitors that impact TAM programming. BMS-794833, a multi-targeted compound, was identified as a potent inhibitor of TAM polarization. BMS-794833 decreased pro-tumoral properties of TAMs in vitro and suppressed tumor growth in mouse triple-negative breast cancer models. The effect of BMS-794833 was independent of its primary targets (MET and VEGFR2) but was dependent on its effect on multiple signaling pathways, including focal adhesion kinases, SRC family kinases, STAT3, and p38 MAP kinases. Collectively, these findings underline the efficacy of polypharmacological strategies in reprogramming complex signaling cascades activated during TAM polarization.

NogoA-expressing astrocytes limit peripheral macrophage infiltration after ischemic brain injury in primates

Astrocytes play critical roles after brain injury, but their precise function is poorly defined. Utilizing single-nuclei transcriptomics to characterize astrocytes after ischemic stroke in the visual cortex of the marmoset monkey, we observed nearly complete segregation between stroke and control astrocyte clusters. Screening for the top 30 differentially expressed genes that might limit stroke recovery, we discovered that a majority of astrocytes expressed RTN4A/ NogoA, a neurite-outgrowth inhibitory protein previously only associated with oligodendrocytes. NogoA upregulation on reactive astrocytes post-stroke was significant in both the marmoset and human brain, whereas only a marginal change was observed in mice. We determined that NogoA mediated an anti-inflammatory response which likely contributes to limiting the infiltration of peripheral macrophages into the surviving parenchyma.

The Effects of Simulated Microgravity on Macrophage Phenotype

The effects of spaceflight, including prolonged exposure to microgravity, can have significant effects on the immune system and human health. Altered immune cell function can lead to adverse health events, though precisely how and to what extent a microgravity environment impacts these cells remains uncertain. Macrophages, a key immune cell, effect the inflammatory response as well as tissue remodeling and repair. Specifically, macrophage function can be dictated by phenotype that can exist between spectrums of M0 macrophage: the classically activated, pro-inflammatory M1, and the alternatively activated, pro-healing M2 phenotypes. This work assesses the effects of simulated microgravity via clinorotation on M0, M1, and M2 macrophage phenotypes. We focus on phenotypic, inflammatory, and angiogenic gene and protein expression. Our results show that across all three phenotypes, microgravity results in a decrease in TNF-α expression and an increase in IL-12 and VEGF expression. IL-10 was also significantly increased in M1 and M2, but not M0 macrophages. The phenotypic cytokine expression profiles observed may be related to specific gravisensitive signal transduction pathways previously implicated in microgravity regulation of macrophage gene and protein expression. Our results highlight the far-reaching effects that simulated microgravity has on macrophage function and provides insight into macrophage phenotypic function in microgravity.

Macrophage-derived cholesterol contributes to therapeutic resistance in prostate cancer

Castration-resistant prostate cancer (CRPC) is a lethal stage of disease in which androgen receptor (AR) signaling is persistent despite androgen deprivation therapy (ADT). Most studies have focused on investigating cell-autonomous alterations in CRPC, while the contributions of the tumor microenvironment are less well understood. Here we sought to determine the role of tumor-associated macrophages in CRPC, based upon their role in cancer progression and therapeutic resistance. In a syngeneic model that reflected the mutational landscape of CRPC, macrophage depletion resulted in a reduced transcriptional signature for steroid and bile acid synthesis, indicating potential perturbation of cholesterol metabolism. As cholesterol is the precursor of the five major types of steroid hormones, we hypothesized that macrophages were regulating androgen biosynthesis within the prostate tumor microenvironment. Macrophage depletion reduced androgen levels within prostate tumors and restricted androgen receptor (AR) nuclear localization in vitro and in vivo. Macrophages were also cholesterol-rich and were able to transfer cholesterol to tumor cells in vitro. AR nuclear translocation was inhibited by activation of Liver X Receptor (LXR)-β, the master regulator of cholesterol homeostasis. Consistent with these data, macrophage depletion extended survival during ADT and the presence of macrophages correlated with therapeutic resistance in patient-derived explants. Taken together, these findings support the therapeutic targeting of macrophages in CRPC.

Evaluation of the immunomodulatory effects of cobalt, copper and magnesium ions in a pro inflammatory environment

Biomaterials and scaffolds for Tissue Engineering are widely used for an effective healing and regeneration. However, the implantation of these scaffolds causes an innate immune response in which the macrophage polarization from M1 (pro-inflammatory) to M2 (anti-inflammatory) phenotype is crucial to avoid chronic inflammation. Recent studies have showed that the use of bioactive ions such as cobalt (Co²⁺), copper (Cu²⁺) and magnesium (Mg²⁺) could improve tissue regeneration, although there is limited evidence on their effect on the macrophage response. Therefore, we investigated the immunomodulatory potential of Co²⁺, Cu²⁺ and Mg²⁺ in macrophage polarization. Our results indicate that Mg²⁺ and concentrations of Cu²⁺ lower than 10 μM promoted the expression of M2 related genes. However, higher concentrations of Cu²⁺ and Co²⁺ (100 μM) stimulated pro-inflammatory marker expression, indicating a concentration dependent effect of these ions. Furthermore, Mg²⁺ were able to decrease M1 marker expression in presence of a mild pro-inflammatory stimulus, showing that Mg²⁺ can be used to modulate the inflammatory response, even though their application can be limited in a strong pro-inflammatory environment.

Lipid Receptor G2A-Mediated Signal Pathway Plays a Critical Role in Inflammatory Response by Promoting Classical Macrophage Activation

Macrophage polarization is a dynamic and integral process in tissue inflammation and remodeling. In this study, we describe that lipoprotein-associated phospholipase A₂ (Lp-PLA₂) plays an important role in controlling inflammatory macrophage (M1) polarization in rodent experimental autoimmune encephalomyelitis (EAE) and in monocytes from multiple sclerosis (MS) patients. Specific inhibition of Lp-PLA₂ led to an ameliorated EAE via markedly decreased inflammatory and demyelinating property of M1. The effects of Lp-PLA₂ on M1 function were mediated by lysophosphatidylcholine, a bioactive product of oxidized lipids hydrolyzed by Lp-PLA₂ through JAK2-independent activation of STAT5 and upregulation of IRF5. This process was directed by the G2A receptor, which was only found in differentiated M1 or monocytes from MS patients. M1 polarization could be inhibited by a G2A neutralizing Ab, which led to an inhibited disease in rat EAE. In addition, G2A-deficient rats showed an ameliorated EAE and an inhibited autoimmune response. This study has revealed a mechanism by which lipid metabolites control macrophage activation and function, modification of which could lead to a new therapeutic approach for MS and other inflammatory disorders.

Macrophages in microgravity: the impact of space on immune cells

The effects of a microgravity environment on the myriad types of immune cells present within the human body have been assessed both by bench-scale simulation and suborbital methods, as well as in true spaceflight. Macrophages have garnered increased research interest in this context in recent years. Their functionality in both immune response and tissue remodeling makes them a unique cell to investigate in regards to gravisensitive effects as well as parameters of interest that could impact astronaut health. Here, we review and summarize the literature investigating the effects of microgravity on macrophages and monocytes regarding the microgravity environment simulation/generation methods, cell sources, experiment durations, and parameters of interest utilized within the field. We discuss reported findings on the impacts of microgravity on macrophage/monocyte structure, adhesion and migration, proliferation, genetic expression, cytokine secretion, and reactive oxygen species production, as well as polarization. Based on this body of data, we make recommendations to the field for careful consideration of experimental design to complement existing reports, as the multitude of disparate study methods previously published can make drawing direct comparisons difficult. However, the breadth of different testing methodologies can also lend itself to attempting to identify the most robust and consistent responses to microgravity across various testing conditions.

Sex Differences in Macrophage Responses to Obesity-Mediated Changes Determine Migratory and Inflammatory Traits

The mechanisms whereby obesity differentially affects males and females are unclear. Because macrophages are functionally the most important cells in obesity-induced inflammation, we sought to determine reasons for male-specific propensity in macrophage migration. We previously determined that male mice fed a high-fat diet exhibit macrophage infiltration into the hypothalamus, whereas females were protected irrespective of ovarian estrogen, in this study, we show that males accumulate more macrophages in adipose tissues that are also more inflammatory. Using bone marrow cells or macrophages differentiated in vitro from male and female mice fed control or high-fat diet, we demonstrated that macrophages derived from male mice are intrinsically more migratory. We determined that males have higher levels of leptin in serum and adipose tissue. Serum CCL2 levels, however, are the same in males and females, although they are increased in obese mice compared with lean mice of both sexes. Leptin receptor and free fatty acid (FFA) receptor, GPR120, are upregulated only in macrophages derived from male mice when cultured in the presence of FFA to mimic hyperlipidemia of obesity. Unless previously stimulated with LPS, CCL2 did not cause migration of macrophages. Leptin, however, elicited migration of macrophages from both sexes. Macrophages from male mice maintained migratory capacity when cultured with FFA, whereas female macrophages failed to migrate. Therefore, both hyperlipidemia and hyperleptinemia contribute to male macrophage-specific migration because increased FFA induce leptin receptors, whereas higher leptin causes migration. Our results may explain sex differences in obesity-mediated disorders caused by macrophage infiltration.

Adherent Intestinal Cells From Atlantic Salmon Show Phagocytic Ability and Express Macrophage-Specific Genes

Our knowledge of the intestinal immune system of fish is rather limited compared to mammals. Very little is known about the immune cells including the phagocytic cells in fish intestine. Hence, employing imaging flow cytometry and RNA sequencing, we studied adherent cells isolated from healthy Atlantic salmon. Phagocytic activity and selected gene expression of adherent cells from the distal intestine (adherent intestinal cells, or AIC) were compared with those from head kidney (adherent kidney cells, or AKC). Phagocytic activity of the two cell types was assessed based on the uptake of Escherichia coli BioParticles^TM. AIC showed phagocytic ability but the phagocytes were of different morphology compared to AKC. Transcriptomic analysis revealed that AIC expressed genes associated with macrophages, T cells, and endothelial cells. Heatmap analysis of selected genes indicated that the adherent cells from the two organs had apparently higher expression of macrophage-related genes. We believe that the adherent intestinal cells have phagocytic characteristics and high expression of genes commonly associated with macrophages. We envisage the possibilities for future studies on enriched populations of adherent intestinal cells.

The influenza virus NS1A binding protein gene modulates macrophages response to cytokines and phagocytic potential in inflammation

Macrophages show remarkable phenotypic plasticity in response to environmental signals. Although it is generally less considered, cytoskeletal changes in macrophages influence their phenotype, including phagocytosis and secretion of soluble cytokines. Influenza virus NS1A-binding protein (Ivns1abp) belongs to the Kelch family of proteins that play a central role in actin cytoskeleton dynamics by directly associating with F-actin and by protecting against actin derangement. Due to its role in cytoskeleton preservation, the Ivns1abp gene might be a critical regulator of the macrophage phenotype and function under inflammatory conditions. In this study, we determine that the modulation of the Ivns1abp gene in macrophages could modify resistance to macrophages against inflammation and maintain functional phagocytosis. Our results indicate that inflammatory insults inhibit the Ivns1abp gene, whereby phagocytosis is inhibited and the ability of macrophages to induce proliferation and repair of damaged cells is compromised. Furthermore, our results show that inflammatory insults alter the activity of the transcription factor c-myc, a factor which directly modulates the expression of the Ivns1abp gene. In conclusion, this study demonstrates a central role of lvns1abp in promoting and preserving a reparative macrophage phenotype and resistance to this inflammatory environment.

Cathepsin Inhibition Modulates Metabolism and Polarization of Tumor-Associated Macrophages

Simple Summary

Stroma-infiltrating tumor-associated macrophages (TAM) play an important role in regulating tumor progression and chemoresistance. Many tumor-infiltrating macrophage populations can be identified by preferential expression of distinct marker genes associated with an M2 phenotype and may execute tumor-promoting functions by enhancing tissue remodeling, facilitating angiogenesis, and suppressing immune responses. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype. For this purpose, we investigated the molecular effects of cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to a polarization shift from M2- to M1 macrophages, associated with distinct alterations in lysosomal signaling and lipid metabolism. This could be therapeutically exploited in tumors with strong infiltration of M2-macrophages, thereby possibly reverting M2 polarization, overcoming drug resistance, and improving the prognosis of our patients.

Abstract

Stroma-infiltrating immune cells, such as tumor-associated macrophages (TAM), play an important role in regulating tumor progression and chemoresistance. These effects are mostly conveyed by secreted mediators, among them several cathepsin proteases. In addition, increasing evidence suggests that stroma-infiltrating immune cells are able to induce profound metabolic changes within the tumor microenvironment. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype in more detail. For this purpose, we investigated the molecular effects of pharmacological cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to changes in cellular recycling processes characterized by an increased expression of autophagy- and lysosome-associated marker genes and reduced adenosine triphosphate (ATP) content. Decreased cathepsin activity in primary macrophages further led to distinct changes in fatty acid metabolites associated with increased expression of key modulators of fatty acid metabolism, such as fatty acid synthase (FASN) and acid ceramidase (ASAH1). The altered fatty acid profile was associated with an increased synthesis of the pro-inflammatory prostaglandin PGE₂, which correlated with the upregulation of numerous NF_kB-dependent pro-inflammatory mediators, including interleukin-1 (IL-1), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-alpha (TNFα). Our data indicate a novel link between cathepsin activity and metabolic reprogramming in macrophages, demonstrated by a profound impact on autophagy and fatty acid metabolism, which facilitates a pro-inflammatory micromilieu generally associated with enhanced tumor elimination. These results provide a strong rationale for therapeutic cathepsin inhibition to overcome the tumor-promoting effects of the immune-evasive tumor micromilieu.

Adipose tissue-derived stromal cells stimulated macrophages-endothelial cells interactions promote effective ischemic muscle neovascularization

Neovascularization, the process of new blood vessels formation in response to hypoxia induced signals, is an essential step during wound healing or ischemia repair. It follows as a cascade of consecutive events leading to new blood vessels formation and their subsequent remodeling to a mature and functional state, enabling tissue regeneration. Any disruption in consecutive stages of neovascularization can lead to chronic wounds or impairment of tissue repair. In the study we try to explain the biological basis of accelerated blood vessels formation in ischemic tissue after adipose tissue-derived stromal cells (ADSCs) administration. Experiments were performed on mouse models of hindlimb ischemia. We have evaluated the level of immune cells (neutrophils, macrophages) infiltration. The novelty of our work was the assessment of bone marrow-derived stem/progenitor cells (BMDCs) infiltration and their contribution to the neovascularization process in ischemic tissue. We have noticed that ADSCs regulated immune response and affected the kinetics and ratio of macrophages population infiltrating ischemic tissue. Our research revealed that ADSCs promoted changes in the morphology of infiltrating macrophages and their tight association with forming blood vessels. We assume that recruited macrophages may take over the role of pericytes and stabilize the new blood vessel or even differentiate into endothelial cells, which in consequence can accelerate vascular formation upon ADSCs administration. Our findings indicate that administration of ADSCs into ischemic muscle influence spatio-temporal distribution of infiltrating cells (macrophages, neutrophils and BMDCs), which are involved in each step of vascular formation, promoting effective ischemic tissue neovascularization.

Celecoxib reduces cortical spreading depression-induced macrophage activation and dilatation of dural but not pial arteries in rodents: implications for mechanism of action in terminating migraine attacks

Nonsteroidal anti-inflammatory drugs, commonly known as COX-1/COX-2 inhibitors, can be effective in treating mild to moderate migraine headache. However, neither the mechanism by which these drugs act in migraine is known, nor is the specific contribution of COX-1 vs COX-2. We sought to investigate these unknowns using celecoxib, which selectively inhibits the enzymatic activity of COX-2, by determining its effects on several migraine-associated vascular and inflammatory events. Using in vivo 2-photon microscopy, we determined intraperitoneal celecoxib effects on cortical spreading depression (CSD)-induced blood vessel responses, plasma protein extravasation, and immune cell activation in the dura and pia of mice and rats. Compared to vehicle (control group), celecoxib reduced CSD-induced dilatation of dural arteries and activation of dural and pial macrophages significantly, but not dilatation or constriction of pial arteries and veins, or the occurrence of plasma protein extravasation. Collectively, these findings suggest that a mechanism by which celecoxib-mediated COX-2 inhibition might ease the intensity of migraine headache and potentially terminate an attack is by attenuating dural macrophages' activation and arterial dilatation outside the blood-brain barrier, and pial macrophages' activation inside the blood-brain barrier.

Cell engineering: Biophysical regulation of the nucleus

Cells live in a complex and dynamic microenvironment, and a variety of microenvironmental cues can regulate cell behavior. In addition to biochemical signals, biophysical cues can induce not only immediate intracellular responses, but also long-term effects on phenotypic changes such as stem cell differentiation, immune cell activation and somatic cell reprogramming. Cells respond to mechanical stimuli via an outside-in and inside-out feedback loop, and the cell nucleus plays an important role in this process. The mechanical properties of the nucleus can directly or indirectly modulate mechanotransduction, and the physical coupling of the cell nucleus with the cytoskeleton can affect chromatin structure and regulate the epigenetic state, gene expression and cell function. In this review, we will highlight the recent progress in nuclear biomechanics and mechanobiology in the context of cell engineering, tissue remodeling and disease development.

The shift in macrophages polarisation after tendon injury: A systematic review

Background

The role of macrophages (Mφs) in tendon injury healing is controversy. The aims of this study were to determine whether there is a shift in Mφs polarisation after an acute and chronic tendon injury ​and to assess whether the Mφs polarisation between the partial and complete rupture is different.

Methods

This systematic review of the scientific literature was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Cochrane guidelines. PubMed database and Excerpta Medica Database (EMBASE) were used for specific search criteria. Only studies measuring Mφs using specific cell markers in Achilles tendon tissue and rotator cuff tendon tissue were included, respectively.

Results

Five Achilles tendon injury studies and four rotator cuff injury studies were included. Expression of the pan Mϕs marker Cluster of Differentiation (CD) 68 was significantly upregulated in acute Achilles tendon ruptures compared to intact tendons, while no significant changes were found in Mφs polarisation markers CD80 (M1 Mφs) and CD206 (M2 Mφs). High levels of CD86 (M1 Mφs) and CD206 were observed in acute partial rupture. Expression of CD68 and CD206 were significantly upregulated in chronic rotator cuff tendinopathy and downregulated as structural failure increases. A low level of CD206 was observed in complete tendon rupture regardless of acute or chronic injury.

Discussion and conclusion

In spite of the limited number of articles included, findings from this study suggested that the process of inflammation plays an important role in acute Achilles tendon injuries, indicated by the increased expression of CD68+ Mφs. Low levels of CD206+ Mφs were constantly observed in complete Achilles tendon rupture, while high levels of CD80+ Mφs and CD206+ Mφs were observed in partial Achilles tendon rupture, which suggested the potential correlation between M2 Mφs and tendon structure. For chronic rotator cuff injury, CD68+ Mφs and CD206+ Mφs were higher in tendinopathic tissues in comparison to the intact control tissues. Both CD68+ Mφs and CD206+ Mφs has an inverse relation to the structural failure in the torn rotator cuff tendon. After tendon rupture, the time point of biopsy specimen collection is an important factor, which could occur in the acute phase or chronic phase. Collectively, the understanding of the roles in Mφs after tendon injury is inadequate, and more research efforts should be devoted to this direction.

The translational potential of this article

This article provided a potential implication on how pan Mφs or M2 Mφs might be associated with ruptured or torn tendon structure. Managing Mφs numbers and phenotypes may lead to possible novel therapeutic approaches to the management of early tendinopathy, early acute tendon rupture, hence, promote healing after restoration surgery.

Acidity promotes tumour progression by altering macrophage phenotype in prostate cancer

BACKGROUND

Tumours rapidly ferment glucose to lactic acid even in the presence of oxygen, and coupling high glycolysis with poor perfusion leads to extracellular acidification. We hypothesise that acidity, independent from lactate, can augment the pro-tumour phenotype of macrophages.

METHODS

We analysed publicly available data of human prostate cancer for linear correlation between macrophage markers and glycolysis genes. We used zwitterionic buffers to adjust the pH in series of in vitro experiments. We then utilised subcutaneous and transgenic tumour models developed in C57BL/6 mice as well as computer simulations to correlate tumour progression with macrophage infiltration and to delineate role of acidity.

RESULTS

Activating macrophages at pH 6.8 in vitro enhanced an IL-4-driven phenotype as measured by gene expression, cytokine profiling, and functional assays. These results were recapitulated in vivo wherein neutralising intratumoural acidity reduced the pro-tumour phenotype of macrophages, while also decreasing tumour incidence and invasion in the TRAMP model of prostate cancer. These results were recapitulated using an in silico mathematical model that simulate macrophage responses to environmental signals. By turning off acid-induced cellular responses, our in silico mathematical modelling shows that acid-resistant macrophages can limit tumour progression.

CONCLUSIONS

This study suggests that tumour acidity contributes to prostate carcinogenesis by altering the state of macrophage activation.

Immunoregulation of macrophages by dynamic ligand presentation via ligand-cation coordination

Macrophages regulate host responses to implants through their dynamic adhesion, release, and activation. Herein, we employ bisphosphonate (BP)-coated gold nanoparticle template (BNP) to direct the swift and convertible formation of Mg²⁺-functional Mg²⁺-BP nanoparticle (NP) on the BP-AuNP surface via reversible Mg²⁺-BP coordination, thus producing (Mg²⁺-BP)-Au dimer (MgBNP). Ethylenediaminetetraacetic acid-based Mg²⁺ chelation facilitates the dissolution of Mg²⁺-BP NP, thus enabling the reversion of the MgBNP to the BNP. This convertible nanoassembly incorporating cell-adhesive Mg²⁺ moieties directs reversible attachment and detachment of macrophages by BP and EDTA, without physical scraping or trypsin that could damage cells. The swift formation of RGD ligand- and Mg²⁺-bifunctional RGD-Mg²⁺-BP NP that yields (RGD-Mg²⁺-BP)-Au dimer (RGDBNP) further stimulates the adhesion and pro-regenerative M2-type polarization of macrophages, both in vitro and in vivo, including rho-associated protein kinase. This swift and non-toxic dimer formation can include diverse bio-functional moieties to regulate host responses to implants.

Control of macrophage adhesion and phenotype is important to biomaterial applications. Here, the authors report on the use of bisphosphonate coated gold nanoparticles by magnesium coordination for the controlled adhesion and polarisation of macrophages in vitro and in vivo and controlled cell release.

Macrophage biology in the peripheral nervous system after injury

Neuroinflammation has positive and negative effects. This review focuses on the roles of macrophage in the PNS. Transection of PNS axons leads to degeneration and clearance of the distal nerve and to changes in the region of the axotomized cell bodies. In both locations, resident and infiltrating macrophages are found. Macrophages enter these areas in response to expression of the chemokine CCL2 acting on the macrophage receptor CCR2. In the distal nerve, macrophages and other phagocytes are involved in clearance of axonal debris, which removes molecules that inhibit nerve regeneration. In the cell body region, macrophage trigger the conditioning lesion response, a process in which neurons increase their regeneration after a prior lesion. In mice in which the genes for CCL2 or CCR2 are deleted, neither macrophage infiltration nor the conditioning lesion response occurs in dorsal root ganglia (DRG). Macrophages exist in different phenotypes depending on their environment. These phenotypes have different effects on axonal clearance and neurite outgrowth. The mechanism by which macrophages affect neuronal cell bodies is still under study. Overexpression of CCL2 in DRG in uninjured animals leads to macrophage accumulation in the ganglia and to an increase in the growth potential of DRG neurons. This increased growth requires activation of neuronal STAT3. In contrast, in acute demyelinating neuropathies, macrophages are involved in stripping myelin from peripheral axons. The molecular mechanisms that trigger macrophage action after trauma and in autoimmune disease are receiving increased attention and should lead to avenues to promote regeneration and protect axonal integrity.

Fibronectin aggregates promote features of a classically and alternatively activated phenotype in macrophages

BACKGROUND

Means to promote endogenous remyelination in multiple sclerosis (MS) benefit from insights into the role of inhibitory molecules that preclude remyelination. Fibronectin assembles into aggregates in MS, which impair oligodendrocyte differentiation and remyelination. Microglia and macrophages are required for complete remyelination and normally switch from a pro-inflammatory classical phenotype upon demyelination to a supportive alternative phenotype during remyelination. Here, we investigated the role of fibronectin aggregates in modulating microglia and macrophage behavior and phenotypes.

METHODS

Bone marrow-derived macrophages and microglia from newborn rats were exposed to (a) plasma fibronectin coatings; (b) coatings of deoxycholate-insoluble fibronectin aggregates; (c) interferon-γ (IFNγ) treatment, as an inducer of the pro-inflammatory classically activated phenotype; (d) interleukin-4 (IL-4) treatment, to promote the pro-regenerative anti-inflammatory alternatively activated phenotype; or (e) left unstimulated on uncoated plastic. To examine the in vitro effects of the different stimulations on cell behavior and phenotype, proliferation, phagocytosis, morphology, and pro- and anti-inflammatory features were assessed.

RESULTS

In line with a classically activated phenotype, exposure of microglia and macrophages to both plasma fibronectin and fibronectin aggregates induced an amoeboid morphology and stimulated phagocytosis by macrophages. Furthermore, as observed upon IFNγ treatment, coatings of aggregated, but not plasma fibronectin, promoted nitric oxide release by microglia and macrophages. Remarkably, fibronectin aggregates induced nitric oxide release in an integrin-independent manner. In addition, fibronectin aggregates, but not plasma fibronectin, increased the expression of arginase-1, similarly as observed upon treatment with IL-4. Proteomic analysis revealed that aggregates of fibronectin act as a scaffold for other proteins, including Hsp70 and thrombospondin-1, which may clarify the induction of both pro-inflammatory and anti-inflammatory features in macrophages cultured on fibronectin aggregate, but not plasma fibronectin coatings.

CONCLUSIONS

Macrophages and microglia grown on aggregated fibronectin coatings adopt a distinct phenotype compared to plasma fibronectin coatings, showing pro-inflammatory and anti-inflammatory features. Therefore, the pathological fibronectin aggregates in MS lesions may impair remyelination by promoting and/or retaining several classically activated phenotypic features in microglia and macrophages.

An hPSC-Derived Tissue-Resident Macrophage Model Reveals Differential Responses of Macrophages to ZIKV and DENV Infection

Zika virus (ZIKV) and dengue virus (DENV) are two closely related flaviviruses that lead to different clinical outcomes. The mechanism for the distinct pathogenesis of ZIKV and DENV is poorly understood. Here, we investigate ZIKV and DENV infection of macrophages using a human pluripotent stem cell (hPSC)-derived macrophage model and discover key virus-specific responses. ZIKV and DENV productively infect hPSC-derived macrophages. DENV, but not ZIKV, infection of macrophages strongly activates macrophage migration inhibitory factor (MIF) secretion and decreases macrophage migration. Neutralization of MIF leads to improved migratory ability of DENV-infected macrophages. In contrast, ZIKV-infected macrophages exhibit prolonged migration and express low levels of pro-inflammatory cytokines and chemokines. Mechanistically, ZIKV disrupts the nuclear factor κB (NF-κB)-MIF positive feedback loop by inhibiting the NF-κB signaling pathway. Our results demonstrate the utility of hPSC-derived macrophages in infectious disease modeling and suggest that the distinct impact of ZIKV and DENV on macrophage immune response may underlie different pathogenesis of Zika and dengue diseases.

•

An hPSC-derived tissue-resident macrophage model for ZIKV and DENV infection

•

ZIKV-, but not DENV-, infected macrophages maintain migratory capacity

•

ZIKV, but not DENV, inhibits pro-inflammatory cytokines and chemokines expression

•

ZIKV disrupts NF-κB-MIF positive feedback loop by inhibiting NF-κB pathway

Magnetic Manipulation of Reversible Nanocaging Controls In Vivo Adhesion and Polarization of Macrophages

Macrophages are key immune cells that perform various physiological functions, such as the maintenance of homeostasis, host defense, disease progression, and tissue regeneration. Macrophages adopt distinctly polarized phenotypes, such as pro-inflammatory M1 phenotype or anti-inflammatory (pro-healing) M2 phenotype, to execute disparate functions. The remotely controlled reversible uncaging of bioactive ligands, such as Arg-Gly-Asp (RGD) peptide, is an appealing approach for temporally regulating the adhesion and resultant polarization of macrophages on implants in vivo. Here, we utilize physical and reversible uncaging of RGD by a magnetic field that allows facile tissue penetration. We first conjugated a RGD-bearing gold nanoparticle (GNP) to the substrate and then a magnetic nanocage (MNC) to the GNP via a flexible linker to form the heterodimeric nanostructure. We magnetically manipulated nanoscale displacement of MNC and thus its proximity to the GNP to reversibly uncage and cage RGD. The uncaging of RGD temporally promoted the adhesion and subsequent M2 polarization of macrophages while inhibiting their M1 polarization both in vitro and in vivo. The RGD uncaging-mediated adhesion and M2 polarization of macrophages involved rho-associated protein kinase signaling. This study demonstrates physical and reversible uncaging of RGD to regulate the adhesion and polarization of host macrophages in vivo. This approach of magnetically regulating the heterodimer conformation for physical and reversible uncaging of RGD offers the promising potential to manipulate inflammatory or tissue-regenerative immune responses to the implants in vivo.

Canine macrophages can like human macrophages be in vitro activated toward the M2a subtype relevant in allergy

The M2a subtype of macrophages plays an important role in human immunoglobulin E (IgE-mediated allergies) and other Th2 type immune reactions. In contrast, very little is known about these cells in the dog. Here we describe an in vitro method to activate canine histiocytic DH82 cells and primary canine monocyte-derived macrophages (MDMs) toward the M2a macrophages using human cytokines. For a side-by-side comparison, we compared the canine cells to human MDMs, and the human monocytic cell line U937 activated towards M1 and M2a cells on the cellular and molecular level. In analogy to activated human M2a cells, canine M2a, differentiated from both DH82 and MDMs, showed an increase in CD206 surface receptor expression compared to M1. Interestingly, canine M2a, but not M1 derived from MDM, upregulated the high-affinity IgE receptor (FcεRI). Transcription levels of M2a-associated genes (IL10, CCL22, TGFβ, CD163) showed a diverse pattern between the human and dog species, whereas M1 genes (IDO1, CXCL11, IL6, TNF-α) were similarly upregulated in canine and human M1 cells (cell lines and MDMs). We suggest that our novel in vitro method will be suitable in comparative allergology studies focussing on macrophages.

PhD AM, Burstein R. Activation of pial and dural macrophages and dendritic cells by cortical spreading depression

OBJECTIVE

Cortical spreading depression (CSD) has long been implicated in migraine attacks with aura. The process by which CSD, a cortical event that occurs within the blood-brain barrier (BBB), results in nociceptor activation outside the BBB is likely mediated by multiple molecules and cells. The objective of this study was to determine whether CSD activates immune cells inside the BBB (pia), outside the BBB (dura), or in both, and if so, when.

METHODS

Investigating cellular events in the meninges shortly after CSD, we used in vivo two-photon imaging to identify changes in macrophages and dendritic cells (DCs) that reside in the pia, arachnoid, and dura and their anatomical relationship to TRPV1 axons.

RESULTS

We found that activated meningeal macrophages retract their processes and become circular, and that activated meningeal DCs stop migrating. We found that CSD activates pial macrophages instantaneously, pial, subarachnoid, and dural DCs 6-12 minutes later, and dural macrophages 20 minutes later. Dural macrophages and DCs can appear in close proximity to TRPV1-positive axons.

INTERPRETATION

The findings suggest that activation of pial macrophages may be more relevant to cases where aura and migraine begin simultaneously, that activation of dural macrophages may be more relevant to cases where headache begins 20 to 30 minutes after aura, and that activation of dural macrophages may be mediated by activation of migratory DCs in the subarachnoid space and dura. The anatomical relationship between TRPV1-positive meningeal nociceptors, and dural macrophages and DCs supports a role for these immune cells in the modulation of head pain. Ann Neurol 2018;83:508-521.

P2Y6 Receptors Regulate CXCL10 Expression and Secretion in Mouse Intestinal Epithelial Cells

In this study, we investigated the role of extracellular nucleotides in chemokine (KC, MIP-2, MCP-1, and CXCL10) expression and secretion by murine primary intestinal epithelial cells (IECs) with a focus on P2Y₆ receptors. qRT-PCR experiments showed that P2Y₆ was the dominant nucleotide receptor expressed in mouse IEC. In addition, the P2Y₆ ligand UDP induced expression and secretion of CXCL10. For the other studies, we took advantage of mice deficient in P2Y₆ (P2ry6^-/-). Similar expression levels of P2Y₁, P2Y₂, P2X2, P2X4, and A_2A were detected in P2ry6^-/- and WT IEC. Agonists of TLR3 (poly(I:C)), TLR4 (LPS), P2Y₁, and P2Y₂ increased the expression and secretion of CXCL10 more prominently in P2ry6^-/- IEC than in WT IEC. CXCL10 expression and secretion induced by poly(I:C) in both P2ry6^-/- and WT IEC were inhibited by general P2 antagonists (suramin and Reactive-Blue-2), by apyrase, and by specific antagonists of P2Y₁, P2Y₂, P2Y₆ (only in WT), and P2X4. Neither adenosine nor an A_2A antagonist had an effect on CXCL10 expression and secretion. Macrophage chemotaxis was induced by the supernatant of poly(I:C)-treated IEC which was consistent with the level of CXCL10 secreted. Finally, the non-nucleotide agonist FGF2 induced MMP9 mRNA expression also at a higher level in P2ry6^-/- IEC than in WT IEC. In conclusion, extracellular nucleotides regulate CXCL10 expression and secretion by IEC. In the absence of P2Y₆, these effects are modulated by other P2 receptors also present on IEC. These data suggest that the presence of P2Y₆ regulates chemokine secretion and may also regulate IEC homeostasis.

Agmatine Modulates the Phenotype of Macrophage Acute Phase after Spinal Cord Injury in Rats

Agmatine is a decarboxylated arginine by arginine decarboxylase. Agmatine is known to be a neuroprotective agent. It has been reported that agmatine works as a NMDA receptor blocker or a competitive nitric oxide synthase inhibitor in CNS injuries. In spinal cord injury, agmatine showed reduction of neuropathic pain, improvement of locomotor function, and neuroprotection. Macrophage is a key cellular component in neuroinflammation, a major cause of impairment after spinal cord injury. Macrophage has subtypes, M1 and M2 macrophages. M1 macrophage induces a pro-inflammatory response, but M2 inspires an anti-inflammatory response. In this study, it was clarified whether the neuroprotective effect of agmatine is related with the modulation of macrophage subdivision after spinal cord injury. Spinal cord injury was induced in rats with contusion using MASCIS. Animals received agmatine (100 mg/kg, IP) daily for 6 days beginning the day after spinal cord injury. The proportion of M1 and M2 macrophages are confirmed with immunohistochemistry and FACS. CD206⁺ & ED1⁺ cells were counted as M2 macrophages. The systemic treatment of agmatine increased M2 macrophages caudal side to epicenter 1 week after spinal cord injury in immunohistochemistry. M2 macrophage related markers, Arginase-1 and CD206 mRNA, were increased in the agmatine treatment group and M2 macrophage expressing and stimulated cytokine, IL-10 mRNA, also was significantly overexpressed by agmatine injection. Among BMPs, BMP2/4/7, agmatine significantly increased only the expression of BMP2 known to reduce M1 macrophage under inflammatory status. These results suggest that agmatine reduces impairment after spinal cord injury through modulating the macrophage phenotype.

Remote Manipulation of Ligand Nano-Oscillations Regulates Adhesion and Polarization of Macrophages in Vivo

Macrophages play crucial roles in various immune-related responses, such as host defense, wound healing, disease progression, and tissue regeneration. Macrophages perform distinct and dynamic functions in vivo, depending on their polarization states, such as the pro-inflammatory M1 phenotype and pro-healing M2 phenotype. Remote manipulation of the adhesion of host macrophages to the implants and their subsequent polarization in vivo can be an attractive strategy to control macrophage polarization-specific functions but has rarely been achieved. In this study, we grafted RGD ligand-bearing superparamagnetic iron oxide nanoparticles (SPIONs) to a planar matrix via a long flexible linker. We characterized the nanoscale motion of the RGD-bearing SPIONs grafted to the matrix, in real time by in situ magnetic scanning transmission electron microscopy (STEM) and in situ atomic force microscopy. The magnetic field was applied at various oscillation frequencies to manipulate the frequency-dependent ligand nano-oscillation speeds of the RGD-bearing SPIONs. We demonstrate that a low oscillation frequency of the magnetic field stimulated the adhesion and M2 polarization of macrophages, whereas a high oscillation frequency suppressed the adhesion of macrophages but promoted their M1 polarization, both in vitro and in vivo. Macrophage adhesion was also temporally regulated by switching between the low and high frequencies of the oscillating magnetic field. To the best of our knowledge, this is the first demonstration of the remote manipulation of the adhesion and polarization phenotype of macrophages, both in vitro and in vivo. Our system offers the promising potential to manipulate host immune responses to implanted biomaterials, including inflammation or tissue reparative processes, by regulating macrophage adhesion and polarization.

Morphologic, phenotypic, and transcriptomic characterization of classically and alternatively activated canine blood-derived macrophages in vitro

Macrophages are a heterogeneous cell population playing a pivotal role in tissue homeostasis and inflammation, and their phenotype strongly depends on the micromilieu. Despite its increasing importance as a translational animal model for human diseases, there is a considerable gap of knowledge with respect to macrophage polarization in dogs. The present study comprehensively investigated the morphologic, phenotypic, and transcriptomic characteristics of unstimulated (M0), M1- (GM-CSF, LPS, IFNγ-stimulated) and M2- (M-CSF, IL-4-stimulated)-polarized canine blood-derived macrophages in vitro. Scanning electron microscopy revealed distinct morphologies of polarized macrophages with formation of multinucleated cells in M2-macrophages, while immunofluorescence employing literature-based prototype-antibodies against CD16, CD32, iNOS, MHC class II (M1-markers), CD163, CD206, and arginase-1 (M2-markers) demonstrated that only CD206 was able to discriminate M2-macrophages from both other phenotypes, highlighting this molecule as a promising marker for canine M2-macrophages. Global microarray analysis revealed profound changes in the transcriptome of polarized canine macrophages. Functional analysis pointed out that M1-polarization was associated with biological processes such as "respiratory burst", whereas M2-polarization was associated with processes such as "mitosis". Literature-based marker gene selection revealed only minor overlaps in the gene sets of the dog compared to prototype markers of murine and human macrophages. Biomarker selection using supervised clustering suggested latexin (LXN) and membrane-spanning 4-domains, subfamily A, member 2 (MS4A2) to be the most powerful predicting biomarkers for canine M1- and M2-macrophages, respectively. Immunofluorescence for both markers demonstrated expression of both proteins by macrophages in vitro but failed to reveal differences between canine M1 and M2-macrophages. The present study provides a solid basis for future studies upon the role of macrophage polarization in spontaneous diseases of the dog, a species that has emerging importance for translational research.

Image based Machine Learning for identification of macrophage subsets

Macrophages play a crucial rule in orchestrating immune responses against pathogens and foreign materials. Macrophages have remarkable plasticity in response to environmental cues and are able to acquire a spectrum of activation status, best exemplified by pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes at the two ends of the spectrum. Characterisation of M1 and M2 subsets is usually carried out by quantification of multiple cell surface markers, transcription factors and cytokine profiles. These approaches are time-consuming, require large numbers of cells and are resource intensive. In this study, we used machine learning algorithms to develop a simple and fast imaging-based approach that enables automated identification of different macrophage functional phenotypes using their cell size and morphology. Fluorescent microscopy was used to assess cell morphology of different cell types which were stained for nucleus and actin distribution using DAPI and phalloidin respectively. By only analysing their morphology we were able to identify M1 and M2 phenotypes effectively and could distinguish them from naïve macrophages and monocytes with an average accuracy of 90%. Thus we suggest high-content and automated image analysis can be used for fast phenotyping of functionally diverse cell populations with reasonable accuracy and without the need for using multiple markers.