Clearance Of Apoptotic Cells Research Articles

Abstract 10706: Alpha Aminoadipic Acid Down-Regulates Sr-bi Abca1 and Abcg1 Expression and May Regulate Plasma Lipid Profiles, Cellular Cholesterol Efflux, and Efferocytosis

Introduction: The metabolite α-aminoadipic acid (2-AAA) has been identified as a predictor of diabetes and atherosclerosis in large human prospective studies. However, the mechanisms linking this metabolite to disease pathophysiology remain unknown. Efferocytosis, a macrophage-mediated process for clearance of apoptotic cells (ACs), is critical in preventing necrosis of dead cells and triggers anti-inflammatory and pro-resolving responses in phagocytes. Cholesterol efflux from peripheral cells in atherosclerotic plaque is a critical step in Reverse Cholesterol Transport (RCT). We hypothesized that the 2-AAA pathway relates to atherosclerosis through modulation of plasma lipid profiles, cholesterol efflux, and macrophage efferocytosis. Results: We found a significant negative correlation between plasma 2-AAA and HDL cholesterol (r=-0.53, P<0.0001), and a significant positive correlation with triglycerides (r=0.35, P=0.006), in two separate samples of individuals with and without cardiometabolic disease (N=98), suggesting a relationship between 2-AAA and cardiovascular risk. We investigated the consequences of 2-AAA stimulation in several primary cells and cell lines. We found that 2-AAA stimulation downregulates three key genes (SR-BI (up to 86% reduction, P=0.005), ABCA1 (up to 92% reduction, P=0.007), ABCG1 (up to 94% reduction, P=0.008)) that directly relate to cholesterol efflux in THP-1 macropohages, suggesting an important role of 2-AAA in cholesterol efflux. Next, we found that treatment with 2-AAA at physiologically-relevant doses (30μM and 100μM) for times ranging from 30 minutes to 6 hours led to consistent reductions of efferocytosis of up to 60% (P<0.001) in mouse macrophages, J774 cells and Raw 264.7 cells, suggesting a pivotal role of 2-AAA in efferocytosis. Conclusions: Our data suggest 2-AAA is associated with plasma lipid profiles (HDL, triglycerides), cholesterol efflux, and macrophage efferocytosis. These novel data could provide a new target for the treatment of atherosclerosis.

Efferocytosis induces macrophage proliferation to help resolve tissue injury

Apoptotic cell clearance by macrophages (efferocytosis) promotes resolution signaling pathways, which can be triggered by molecules derived from the phagolysosomal degradation of apoptotic cells. We show here that nucleotides derived from the hydrolysis of apoptotic cell DNA by phagolysosomal DNase2a activate a DNA-PKcs-mTORC2/Rictor pathway that increases Myc to promote non-inflammatory macrophage proliferation. Efferocytosis-induced proliferation expands the pool of resolving macrophages invitro and in mice, including zymosan-induced peritonitis, dexamethasone-induced thymocyte apoptosis, and atherosclerosis regression. In the dexamethasone-thymus model, hematopoietic Rictor deletion blocked efferocytosing macrophage proliferation, apoptotic cell clearance, and tissue resolution. In atherosclerosis regression, silencing macrophage Rictor or DNase2a blocked efferocyte proliferation, apoptotic cell clearance, and plaque stabilization. In view of previous work showing that other types of apoptotic cell cargo can promote resolution in individual efferocytosing macrophages, the findings here suggest that signaling-triggered apoptotic cell-derived nucleotides can amplify this benefit by increasing the number of these macrophages.

Gas6 Ameliorates Inflammatory Response and Apoptosis in Bleomycin-Induced Acute Lung Injury.

Acute lung injury (ALI) is characterized by alveolar damage, lung edema, and exacerbated inflammatory response. Growth arrest-specific protein 6 (Gas6) mediates many different functions, including cell survival, proliferation, inflammatory signaling, and apoptotic cell clearance (efferocytosis). The role of Gas6 in bleomycin (BLM)-induced ALI is unknown. We investigated whether exogenous administration of mouse recombinant Gas6 (rGas6) has anti-inflammatory and anti-apoptotic effects on BLM-induced ALI. Compared to mice treated with only BLM, the administration of rGas6 reduced the secretion of proinflammatory cytokines, including tumor necrosis factor-α, interleukin-1β, and macrophage inflammatory protein-2, and increased the secretion of hepatocyte growth factor in bronchoalveolar lavage (BAL) fluid. rGas6 administration also reduced BLM-induced inflammation and apoptosis as evidenced by reduced neutrophil recruitment into the lungs, total protein levels in BAL fluid, caspase-3 activity, and TUNEL-positive lung cells in lung tissue. Apoptotic cell clearance by alveolar macrophages was also enhanced in mice treated with both BLM and rGas6 compared with mice treated with only BLM. rGas6 also had pro-resolving and anti-apoptotic effects in mouse bone marrow-derived macrophages and alveolar epithelial cell lines stimulated with BLM in vitro. These findings indicate that rGas6 may play a protective role in BLM-induced ALI.

Phagocyte Chemoattraction Is Induced through the Mcp-1-Ccr2 Axis during Efferocytosis.

Apoptotic cells generated during development and for tissue homeostasis are swiftly and continuously removed by phagocytes via a process called efferocytosis. Efficient efferocytosis can be achieved via transcriptional modulation in phagocytes that have engulfed apoptotic cells. However, such modulation and its effect on efferocytosis are not completely understood. Here, we report that phagocytes are recruited to apoptotic cells being cleared through the Mcp-1–Ccr2 axis, which facilitates clearance of apoptotic cells. We identified Mcp-1 as a modulated transcript using a microarray and found that Mcp-1 secretion was augmented in phagocytes engulfing apoptotic cells. This augmented Mcp-1 secretion was impaired by blocking phagolysosomal degradation of apoptotic cells. Conditioned medium from wild type (WT) phagocytes promoted cell migration, but that from Mcp-1−/− phagocytes did not. In addition, blockade of Ccr2, the receptor for Mcp-1, abrogated cell migration to conditioned medium from phagocytes incubated with apoptotic cells. The intrinsic efferocytosis activity of Mcp-1−/− and Ccr2−/− phagocytes was unaltered, but clearance of apoptotic cells was less efficient in the peritoneum of Mcp-1−/− and Ccr2−/− mice than in that of WT mice because fewer Ccr2-positive phagocytes were recruited. Taken together, our findings demonstrate a mechanism by which not only apoptotic cells but also phagocytes induce chemoattraction to recruit phagocytes to sites where apoptotic cells are cleared for efficient efferocytosis.

Lymphocyte Cytosolic Protein 1 I232F Mutation Impairs Granulocytic Proliferation with a G2/M Block in Severe Neutropenia

▪Introduction: As critical effectors of innate immune response, neutrophils migrate from the vasculature into inflamed tissue, where they engage in phagocytosis and clearance of pathogens and apoptotic cells. Migration, phagocytosis, and granule release require multiple well-coordinated events involving remodeling of the actin cytoskeleton. While mutations of some regulators of actin polymerization, such as Wiskott-Aldrich Syndrome gene (WAS) result in Severe Congenital Neutropenia (SCN), the role of actin cytoskeleton in regulating neutrophil ontogeny and functions remain poorly understood. Lymphocyte Cytosolic Protein 1 (LCP1) is an actin bundling protein encoded by LCP1 gene. A 7-year-old girl presented at age of 2 years with chronic severe neutropenia and frequent infections. Next generation sequencing did not reveal a variant in genes known to cause neutropenia. Whole exome sequencing identified a novel LCP1 p.I232F variant of unknown significance, which was not present in either parent. Bone marrow examination revealed a granulocytic hypoplasia with significant dysmorphic giant granulocytes with complex hypersegmentation and increased apoptosis. (Figure 1A) Based on these observations, we hypothesized that missense mutation in LCP1 (I232F) impairs granulocytic proliferation, and causes neutropenia.Aims: To investigate the role of LCP1 I232F, discovered in a child with severe symptomatic neutropenia, in granulopoiesis.Methods: in vitro experiments involving the expression of wild type and mutant LCP1 I232F in murine myeloblast cell (32D cells) and human cervical cancer HeLa cell. We deployed various biologic and functional studies to investigate the role of LCP1 I232F in granulocyte proliferation, differentiation, survival, and function.Results: To determine the pathophysiologic significance of LCP1 I232F, we stably transduced interleukin 3-dependent murine myeloblast 32D and human cervical cancer HeLa cell lines with a doxycycline-inducible lentiviral constructs containing the cDNA for either wild type LCP1 or LCP1 I232F. The mutant LCP1 I232F expressing 32D cells showed impaired proliferation with the appearance of dysplastic granulocytic cells. (Figure 1A, B) However, we did not observe block in differentiation. A cell cycle arrest at G2/M phase occurred only in the LCP1 I232F expressing cells (Figure 1B) and was associated with an upregulation of markers of cell cycle arrest (Cdkn1a and Tp53). LCP1 I232F overexpression did not lead to increased expression of genes involved in apoptosis or the unfolded protein response. The LCP1 I232F cells with dysplastic features were further analyzed by confocal microscopy, which demonstrated increased level of F-actin and enrichment of F-actin and LCP1 at the cell cortex. Flow cytometric evaluation of these cells further confirmed the presence of increased level of F actin. (Figure 1C) Expression of LCP1 I232F impaired cell motility and invasiveness in both 32D and HeLa cells. However, mutant LCP1 expressing 32D cells demonstrated normal oxidative burst upon treatment with N-formyl-Met-Leu-Phe (fMLP) and phorbol myristate acetate (PMA). Confocal imaging and subcellular fractionation revealed diffuse localization of LCP1, but only the mutant form was found in the nucleus. (Figure 1C) In LCP1, two tandem CH domains (CH1-CH2 and CH3-CH4) formed two actin-binding domains (ABD1 and ABD2) that bind to actin to participate in actin bundling. I232F is located at LCP1-CH1 that interacts with actin. To study how the mutation impacts LCP1-actin binding, we constructed a model of LCP1-ABD1 based on the cryo-EM structure of F-actin/LCP1-ABD2 and performed 40 ns of molecular dynamics (MD) simulations of LCP1-ABD1 and LCP1-ABD1 I232F alone to study their dynamical motions. We found that LCP1-ABD1 I232F adopted a more stable open conformation than LCP1-ABD1 to bind effectively with F-actin. The model implies a prolonged association of LCP1 I232F with actin than wild-type LCP1, and the consequence is the increased stabilization of actin bundles.Conclusions: Like the WAS gain-of-function mutations in SCN, LCP1 I232F resulted in severe neutropenia with dysplastic granulocytic precursors, cell cycle arrest, impaired motility, and increased F actin. We also found decreased proliferation of granulocytic progenitor and precursor cells. Our findings suggest that LCP1 is an important gene involved in granulopoiesis. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Geranylgeraniol Restores Zoledronic Acid-Induced Efferocytosis Inhibition in Bisphosphonate-Related Osteonecrosis of the Jaw.

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a severe side effect of long-term administration of bisphosphonates such as zoledronic acid (ZA), but its pathogenesis remains unclear. Impairment of the clearance of apoptotic cells (termed “efferocytosis”) by ZA may be associated with the pathogenesis of BRONJ. The aim of this study was to investigate whether ZA might inhibit macrophage efferocytosis and promote osteocytic apoptosis, and the underlying mechanisms responsible for the disturbing balance between clean and generation of osteocytic apoptosis. We found that ZA significantly promoted the apoptosis of osteocyte and pre-osteoblast via BRONJ mouse models and in vitro MC3T3-E1 but also inhibited the efferocytosis of macrophage on apoptotic cells. Moreover, supplement with geranylgeraniol (GGOH), a substrate analog for geranylgeranylation of Rac1, could restore Rac1 homeostasis and rescue macrophage efferocytosis. GGOH partially inhibits MC3T3-E1 apoptosis induced by ZA via downregulation of Rac1/JNK pathway. We also examined the Rac1 distribution and activation conditions in bone marrow-derived macrophages (BMDMs) and MC3T3-E1 under ZA treatment, and we found that ZA impaired Rac1 migration to BMDM membrane, leading to round appearance with less pseudopodia and efferocytosis inhibition. Moreover, ZA simultaneously activated Rac1, causing overexpression of P-JNK and cleaved caspase 3 in MC3T3-E1. Finally, the systemic administration of GGOH decreased the osteocytic apoptosis and improved the bone healing of the extraction sockets in BRONJ mouse models. Taken together, our findings provided a new insight and experimental basis for the application of GGOH in the treatment of BRONJ.

COMMD10 is critical for Kupffer cell survival and controls Ly6Chi monocyte differentiation and inflammation in the injured liver.

Liver-resident macrophages Kupffer cells (KCs) and infiltrating Ly6Chi monocytes both contribute to liver tissue regeneration in various pathologies but also to disease progression upon disruption of orderly consecutive regeneration cascades. Little is known about molecular pathways that regulate their differentiation, maintenance, or inflammatory behavior during injury. Here, we show that copper metabolism MURR1 domain (COMMD)10-deficient KCs adopt liver-specific identity. Strikingly, COMMD10 deficiency in KCs and in other tissue-resident macrophages impedes their homeostatic survival, leading to their continuous replacement by Ly6Chi monocytes. While COMMD10 deficiency in KCs mildly worsens acetaminophen-induced liver injury (AILI), its deficiency in Ly6Chi monocytes results in exacerbated and sustained hepatic damage. Monocytes display unleashed inflammasome activation and a reduced type I interferon response and acquire "neutrophil-like" and lipid-associated macrophage differentiation fates. Collectively, COMMD10 appears indispensable for KC and other tissue-resident macrophage survival and is an important regulator of Ly6Chi monocyte fate decisions and reparative behavior in the diseased liver.

Macrophages and Iron: A Special Relationship.

Macrophages perform a variety of different biological functions and are known for their essential role in the immune response. In this context, a principal function is phagocytic clearance of pathogens, apoptotic and senescent cells. However, the major targets of homeostatic phagocytosis by macrophages are old/damaged red blood cells. As such, macrophages play a crucial role in iron trafficking, as they recycle the large quantity of iron obtained by hemoglobin degradation. They also seem particularly adapted to handle and store amounts of iron that would be toxic to other cell types. Here, we examine the specific and peculiar iron metabolism of macrophages.

Physiological Roles of Apoptotic Cell Clearance: Beyond Immune Functions

The clearance of apoptotic cells is known to be a critical step in maintaining tissue and organism homeostasis. This process is rapidly/promptly mediated by recruited or resident phagocytes. Phagocytes that engulf apoptotic cells have been closely linked to the release of anti-inflammatory cytokines to eliminate inflammatory responses. Defective clearance of apoptotic cells can cause severe inflammation and autoimmune responses due to secondary necrosis of apoptotic cells. Recently accumulated evidence indicates that apoptotic cells and their clearance have important physiological roles in addition to immune-related functions. Herein, we review the current understanding of the mechanisms and fundamental roles of apoptotic cell clearance and the beneficial roles of apoptotic cells in physiological processes such as differentiation and development.

EFFECT OF M2 MACROPHAGE-DERIVED SOLUBLE FACTORS ON DIFFERENTIATION OF SH-SY5Y CELLS

Macrophages play a key role in triggering and regulation of neuroregeneration. The characteristic feature of macrophages is pronounced plasticity, which manifests itself in the ability of macrophages to change their functional phenotype depending on the micromilieu. Apoptotic cell clearance (efferocytosis) is an important inducer of a macrophage polarization to M2 phenotype under pathological settings. Previously, we have developed an original protocol for the generation of M2-like macrophages, polarized by efferocytosis under serum-deprived conditions (M2 (LS), Low Serum). The present study was aimed to assess a neuroregenerative potential of M2 (LS) macrophages. We studied their effect on the differentiation of SH-SY5Y cells in comparison with retinoic acid (RA). As the morphological criteria of differentiation we have assessed the relative content of differentiated cells, i.e., cells with a neurite length exceeding the cell body length, and the average neurite length on days 3, 7, and 13. The ratio of neuron-like (N-type) and epithelial-like (S-type) cells in cultures was also assessed. SH-SY5Y cells were characterized by a low level of spontaneous differentiation, both under standard conditions (10% FBS) and serum deprivation (1% FBS). Upon RA treatment, SH-SY5Y cells stopped proliferating and underwent neuronal differentiation. Cultivation of SH-SY5Y cells in the presence of M2 (LS) conditioned medium also led to a significant increase in the relative content of differentiated cells, the average length of neurite-like processes, as well as a change in the balance of S- and N-type cells towards a pronounced predominance of the latter. The morphological features of differentiation were significantly less pronounced at early stage (day 3) of differentiation as compared with the RA-induced changes and reached the level of positive control only at later stages (day 13) (p < 0.05). In contrast to retinoic acid, M2 (LS) conditioned medium induced neuronal differentiation of SH-SY5Y cells without suppressing their proliferative activity. The data obtained may indicate a high neuroregenerative potential of M2 macrophages in vitro, which is realized through soluble factors and manifests itself in promoting SH-SY5Y differentiation.

New Horizons for the Roles and Association of APE1/Ref-1 and ABCA1 in Atherosclerosis.

Atherosclerosis is the leading cause of death worldwide. APE1/Ref-1 and ABCA1 play key roles in the progression of atherosclerosis. APE1/Ref-1 suppresses atherosclerosis via multiple mechanisms, including reducing the IL-6-, TNF-α-, and IL-1β-mediated proinflammatory responses, suppressing ROS-mediated oxidant activity and Bax/Bcl-2-mediated vascular calcification and apoptosis, and reducing LOX-1-mediated cholesterol uptake. However, APE1/Ref-1 also promotes atherosclerosis by increasing the activity of the NK-κB and S1PR1 pathways. APE1/Ref-1 localizes to the nucleus, cytoplasm, and mitochondria and can be secreted from the cell. APE1/Ref-1 localization is dynamically regulated by the disease state and may be responsible for its proatherogenic and antiatherogenic effects. ABCA1 promotes cholesterol efflux and anti-inflammatory responses by binding to apoA-I and regulates apoptotic cell clearance and HSPC proliferation to protect against inflammatory responses. Interestingly, in addition to mediating these functions, ABCA1 promotes the secretion of acetylated APE1/Ref-1 (AcAPE1/Ref-1), a therapeutic target, which protects against atherosclerosis development. The APE1/Ref-1 inhibitor APX3330 is being evaluated in a phase II clinical trial. The LXR agonist LXR-623 (WAY-252623) is an agonist of ABCA1 and the first LXR-targeting compound to be evaluated in clinical trials. In this article, we review the roles of ABCA1 and APE1/Ref-1 in atherosclerosis and focus on new insights into the ABCA1-APE1/Ref-1 axis and its potential as a novel therapeutic target in atherosclerosis.

Non-canonical glutamine transamination sustains efferocytosis by coupling redox buffering to oxidative phosphorylation.

SummaryMacrophages rely on tightly integrated metabolic rewiring to clear dying neighboring cells by efferocytosis during homeostasis and disease. Here, we reveal that glutaminase (GLS) 1-mediated glutaminolysis is critical to promote apoptotic cell clearance by macrophages during homeostasis in mice. In addition, impaired macrophage glutaminolysis exacerbates atherosclerosis, a condition during which efficient apoptotic cell debris clearance is critical to limit disease progression. Gls1 expression strongly correlates with atherosclerotic plaque necrosis in patients with cardiovascular diseases. High-throughput transcriptional and metabolic profiling reveals that macrophage efferocytic capacity relies on a non-canonical transaminase pathway, independent from the traditional requirement of glutamate dehydrogenase (GLUD1) to fuel ɑ-ketoglutarate-dependent immunometabolism. This pathway is necessary to meet the unique requirements of efferocytosis for cellular detoxification and high energy cytoskeletal rearrangements. Thus, we uncover a role for non-canonical glutamine metabolism for efficient clearance of dying cells and maintenance of tissue homeostasis during health and disease in mouse and humans

Exposure of a specific pleioform of multifunctional glyceraldehyde 3-phosphate dehydrogenase initiates CD14-dependent clearance of apoptotic cells

Rapid clearance of apoptotic cells by phagocytes is crucial for organogenesis, tissue homeostasis, and resolution of inflammation. This process is initiated by surface exposure of various ‘eat me’ ligands. Though phosphatidylserine (PS) is the best recognized general recognition ligand till date, recent studies have shown that PS by itself is not sufficient for clearance of apoptotic cells. In this study, we have identified a specific pleioform of GAPDH (Glyceraldehyde 3-phosphate dehydrogenase) that functions as an ‘eat me’ signal on apoptotic cell surface. This specific form of GAPDH which is exposed on surface of apoptotic cells was found to interact with CD14 present on plasma membrane of phagocytes leading to their engulfment. This is the first study demonstrating the novel interaction between multifunctional GAPDH and the phagocytic receptor CD14 resulting in apoptotic cell clearance (efferocytosis).

CX3CL1(+) Microparticles-Induced MFG-E8 Enhances Apoptotic Cell Clearance by Alveolar Macrophages.

During the resolution phase of acute lung injury, apoptotic cells release CX3CL1 as a “find-me” signal to attract alveolar macrophage transmigration toward apoptotic cells for phagocytosis. However, it is still not clear whether CX3CL1 has pro-phagocytic activity on alveolar macrophage. In this study, we investigated the role of apoptotic NB4 cells-derived CX3CL1(+) microparticles (apo-MP) on the phagocytic activity of NR8383 cells. We demonstrate that exogenous CX3CL1 and apo-MP enhanced the phagocytic activity of NR8383 cells in a CX3 CR1-dependent manner. The apo-MP-enhanced phagocytic activity on NR8383 was attenuated when apo-MP and NR8383 cells were pre-treated with anti-CX3CL1 antibodies and anti-CX3CR1 antibody, respectively, before incubating both for phagocytic assay. Further studies demonstrate that exogenous CX3CL1 and apo-MP also enhanced NR8383 cells in their surface expression and release of MFG-E8 in a CX3CR1 dependent manner. The enhanced phagocytic activity of CX3CL1-treated NR8383 cells was attenuated when NR8383 cells were pre-treated with an anti-MFG-E8 antibody before CX3CL1 treatment. We conclude that apoptotic cell-derived CX3CL1(+) microparticles enhance the phagocytic activity of NR8383 cells by up-regulating their MFG-E8 as a bridge molecule, and these contribute to the formation of phagocytic synapses between apoptotic cells and alveolar macrophages for the subsequent phagocytic clearance of apoptotic cells.

Pattern Recognition Proteins: First Line of Defense Against Coronaviruses.

The rapid outbreak of COVID-19 caused by the novel coronavirus SARS-CoV-2 in Wuhan, China, has become a worldwide pandemic affecting almost 204 million people and causing more than 4.3 million deaths as of August 11 2021. This pandemic has placed a substantial burden on the global healthcare system and the global economy. Availability of novel prophylactic and therapeutic approaches are crucially needed to prevent development of severe disease leading to major complications both acutely and chronically. The success in fighting this virus results from three main achievements: (a) Direct killing of the SARS-CoV-2 virus; (b) Development of a specific vaccine, and (c) Enhancement of the host’s immune system. A fundamental necessity to win the battle against the virus involves a better understanding of the host’s innate and adaptive immune response to the virus. Although the role of the adaptive immune response is directly involved in the generation of a vaccine, the role of innate immunity on RNA viruses in general, and coronaviruses in particular, is mostly unknown. In this review, we will consider the structure of RNA viruses, mainly coronaviruses, and their capacity to affect the lungs and the cardiovascular system. We will also consider the effects of the pattern recognition protein (PRP) trident composed by (a) Surfactant proteins A and D, mannose-binding lectin (MBL) and complement component 1q (C1q), (b) C-reactive protein, and (c) Innate and adaptive IgM antibodies, upon clearance of viral particles and apoptotic cells in lungs and atherosclerotic lesions. We emphasize on the role of pattern recognition protein immune therapies as a combination treatment to prevent development of severe respiratory syndrome and to reduce pulmonary and cardiovascular complications in patients with SARS-CoV-2 and summarize the need of a combined therapeutic approach that takes into account all aspects of immunity against SARS-CoV-2 virus and COVID-19 disease to allow mankind to beat this pandemic killer.

Influence of hormonal imbalance on the integrity of seminiferous epithelium in the testes of adult rats chronically exposed to letrozole and rats exposed to soya isoflavones during the prenatal period, lactation, and up to sexual maturity

The structural integrity of the germ cells in the seminiferous epithelium and the correct process of spermatogenesis are made possible by proteins that participate in the formation of different types of junctions. This study was performed on samples of the testes of 4 groups (2 experimental and 2 corresponding control) of male Wistar rats. In the first experimental group, the adult rats received letrozole – a nonsteroidal inhibitor of cytochrome P450 aromatase (P450arom). The second experimental group was exposed to soya isoflavones during the prenatal period, lactation, and up to sexual maturity. The aim of this study was to examine the immunoexpression of β-catenin, N-cadherin, occludin, connexin43, annexin V, and advanced glycation end products (AGE) in the seminiferous epithelium of rat testes with chronic estrogen deficiency and of rats exposed to soya isoflavones. Series of sections of the testes were stained using PAS and silver impregnation. Moreover, immunohistochemistry tests were performed. A semi-quantitative determination of protein immunoexpression was performed using Image J. The number of annexin V positive Sertoli cells per tubule were counted manually. Comparisons between the experimental and corresponding control groups were performed using a non-parametric Mann-Whitney U test. The most common alterations were prematurely sloughed germ cells in the lumen of the seminiferous tubules and invaginations of the seminiferous tubules. We observed a lower number of annexin V positive Sertoli cells and a lower expression of N-cadherin and occludin in the seminiferous epithelium of both groups of rats with hormonal imbalances. Moreover, a higher expression of AGE, a lower expression of connexin 43 and a lower amount of reticular fibers in the basal lamina of seminiferous tubules was present in rats treated with letrozole and a higher expression of β-catenin was found in rats exposed to soya isoflavones. The hormonal imbalance between androgens and estrogens resulted in a decreased number of annexin V positive Sertoli cells. This may be associated with a failed clearance of apoptotic germ cells that leads to disturbances in the blood-testis-barrier (BTB) by affecting the expression of junctional proteins in the seminiferous epithelium. Moreover, a decreased level of estrogens was also associated with an increased expression of AGEs and with a changed composition of basal lamina in the seminiferous tubules of rats. These changes could lead to germ cell sloughing and invaginations of the seminiferous tubules.

Properdin Deficiency Impairs Phagocytosis and Enhances Injury at Kidney Repair Phase Post Ischemia-Reperfusion.

Properdin, a positive regulator of complement alternative pathway, participates in renal ischemia–reperfusion (IR) injury and also acts as a pattern-recognition molecule affecting apoptotic T-cell clearance. However, the role of properdin in tubular epithelial cells (TECs) at the repair phase post IR injury is not well defined. This study revealed that properdin knockout (PKO) mice exhibited greater injury in renal function and histology than wild-type (WT) mice post 72-h IR, with more apoptotic cells and macrophages in tubular lumina, increased active caspase-3 and HMGB1, but better histological structure at 24 h. Raised erythropoietin receptor by IR was furthered by PKO and positively correlated with injury and repair markers. Properdin in WT kidneys was also upregulated by IR, while H2O2-increased properdin in TECs was reduced by its small-interfering RNA (siRNA), with raised HMGB1 and apoptosis. Moreover, the phagocytic ability of WT TECs, analyzed by pHrodo Escherichia coli bioparticles, was promoted by H2O2 but inhibited by PKO. These results were confirmed by counting phagocytosed H2O2-induced apoptotic TECs by in situ end labeling fragmented DNAs but not affected by additional serum with/without properdin. Taken together, PKO results in impaired phagocytosis at the repair phase post renal IR injury. Properdin locally produced by TECs plays crucial roles in optimizing damaged cells and regulating phagocytic ability of TECs to effectively clear apoptotic cells and reduce inflammation.

Adipose Tissue Immunometabolism and Apoptotic Cell Clearance.

The safe removal of apoptotic debris by macrophages—often referred to as efferocytosis—is crucial for maintaining tissue integrity and preventing self-immunity or tissue damaging inflammation. Macrophages clear tissues of hazardous materials from dying cells and ultimately adopt a pro-resolving activation state. However, adipocyte apoptosis is an inflammation-generating process, and the removal of apoptotic adipocytes by so-called adipose tissue macrophages triggers a sequence of events that lead to meta-inflammation and obesity-associated metabolic diseases. Signals that allow apoptotic cells to control macrophage immune functions are complex and involve metabolites released by the apoptotic cells and also metabolites produced by the macrophages during the digestion of apoptotic cell contents. This review provides a concise summary of the adipocyte-derived metabolites that potentially control adipose tissue macrophage immune functions and, hence, may induce or alleviate adipose tissue inflammation.

KLF13 induces apoptotic cell clearance in Penaeus vannamei as an essential part of shrimp innate immune response to pathogens

Although, in mammals, the Krüppel-like transcription factor 13 (KLF13) plays an essential role in cell proliferation, survival, differentiation, apoptosis, tumorigenesis, immune regulation, and inflammation, its role in penaeid shrimp is unclear. In the current study, we characterized a KLF13 homolog in Penaeus vannamei (PvKLF13), with full-length cDNA of 1677 bp and 1068 bp open reading frame (ORF) encoding a putative protein of 355 amino acids, which contains three ZnF_C2H2 domains. Sequence and phylogenetic analysis revealed that PvKLF13 shares a close evolutionary relationship with KLF13 from invertebrates. Transcript levels of PvKLF13 were ubiquitously expressed in shrimp and induced in hemocytes upon challenge with Vibrio parahaemolyticus, Streptococcus iniae, and white spot syndrome virus (WSSV), suggesting the involvement of PvKLF13 in shrimp immune response to pathogens. Besides, knockdown of PvKLF13 decreased hemocytes apoptosis in terms of increased expression of pro-survival PvBcl-2, but decreased expression of pro-apoptotic PvBax and PvCytochrome C, coupled with high PvCaspase3/7 activity, especially upon V. parahaemolyticus challenge. The findings here indicate the involvement of PvKLF13 in apoptotic cell clearance as an essential part of shrimp innate immune response to pathogens.

Conserved and Distinct Elements of Phagocytosis in Human and C. elegans.

Endocytosis provides the cellular nutrition and homeostasis of organisms, but pathogens often take advantage of this entry point to infect host cells. This is counteracted by phagocytosis that plays a key role in the protection against invading microbes both during the initial engulfment of pathogens and in the clearance of infected cells. Phagocytic cells balance two vital functions: preventing the accumulation of cell corpses to avoid pathological inflammation and autoimmunity, whilst maintaining host defence. In this review, we compare elements of phagocytosis in mammals and the nematode Caenorhabditis elegans. Initial recognition of infection requires different mechanisms. In mammals, pattern recognition receptors bind pathogens directly, whereas activation of the innate immune response in the nematode rather relies on the detection of cellular damage. In contrast, molecules involved in efferocytosis—the engulfment and elimination of dying cells and cell debris—are highly conserved between the two species. Therefore, C. elegans is a powerful model to research mechanisms of the phagocytic machinery. Finally, we show that both mammalian and worm studies help to understand how the two phagocytic functions are interconnected: emerging data suggest the activation of innate immunity as a consequence of defective apoptotic cell clearance.