Signalling pathway involving GULP, MAPK and Rac1 for SR-BI-induced phagocytosis of apoptotic cells

The APC/C E3 ligase subunit ANAPC11 mediates FOXO3 protein degradation to promote cell proliferation and lymph node metastasis in urothelial bladder cancer

Urothelial bladder cancer (UBC) is one of the most prevalent malignancies worldwide, with striking tumor heterogeneity. Elucidating the molecular mechanisms that can be exploited for the treatment of aggressive UBC is a particularly relevant goal. Protein ubiquitination is a critical post-translational modification (PTM) that mediates the degradation of target protein via the proteasome. However, the roles of aberrant protein ubiquitination in UBC development and the underlying mechanisms by which it drives tumor progression remain unclear. In this study, taking advantage of clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) 9 technology, we identified the ubiquitin E3 ligase ANAPC11, a critical subunit of the anaphase-promoting complex/cyclosome (APC/C), as a potential oncogenic molecule in UBC cells. Our clinical analysis showed that elevated expression of ANAPC11 was significantly correlated with high T stage, positive lymph node (LN) metastasis, and poor outcomes in UBC patients. By employing a series of in vitro experiments, we demonstrated that ANAPC11 enhanced the proliferation and invasiveness of UBC cells, while knockout of ANAPC11 inhibited the growth and LN metastasis of UBC cells in vivo. By conducting immunoprecipitation coupled with mass spectrometry, we confirmed that ANAPC11 increased the ubiquitination level of the Forkhead transcription factor FOXO3. The resulting decrease in FOXO3 protein stability led to the downregulation of the cell cycle regulator p21 and decreased expression of GULP1, a downstream effector of androgen receptor signaling. Taken together, these findings indicated that ANAPC11 plays an oncogenic role in UBC by modulating FOXO3 protein degradation. The ANAPC11-FOXO3 regulatory axis might serve as a novel therapeutic target for UBC.

The regulatory role of BMP4 in testicular Sertoli cells of Tibetan sheep

This study aimed to determine the regulatory mechanism of bone morphogenetic protein 4 (BMP4) gene in the testes of Tibetan sheep and its role in the blood-testis barrier (BTB). First, we cloned BMP4 gene for bioinformatics analysis, and detected the mRNA and protein expression levels of BMP4 in the testes of Tibetan sheep pre-puberty (3-mo-old), during sexual maturity (1-yr-old), and in adulthood (3-yr-old) by qRT-PCR and Western blot. In addition, the subcellular localization of BMP4 was analyzed by immunohistochemical staining. Next, BMP4 overexpression and silencing vectors were constructed and transfected into primary Sertoli cells (SCs) to promote and inhibit the proliferation of BMP4, respectively. Then, CCK-8 was used to detect the proliferation effect of SCs. The expression of BMP4 and downstream genes, pathway receptors, tight junction-related proteins, and cell proliferation and apoptosis-related genes in SCs were studied using qRT-PCR and Western blot. The results revealed that the relative expression of BMP4 mRNA and protein in testicular tissues of 1Y group and 3Y group was dramatically higher than that of 3M group (P < 0.01), and BMP4 protein is mainly located in SCs and Leydig cells at different development stages. The CDS region of the Tibetan sheep BMP4 gene was 1,229 bp. CCK-8 results demonstrated that the proliferation rate of BMP4 was significantly increased in the overexpression group (pc-DNA-3.1(+)-BMP4; P < 0.05). In addition, the mRNA and protein expressions of SMAD5, BMPR1A, and BMPR1B and tight junction-related proteins Claudin11, Occludin, and ZO1 were significantly increased (P < 0.05). The mRNA expression of cell proliferation-related gene Bcl2 was significantly enhanced (P < 0.05), and the expression of GDNF was enhanced (P > 0.05). The mRNA expression of apoptosis-related genes Caspase3 and Bax decreased significantly (P < 0.05), while the mRNA expression of cell cycle-related genes CyclinA2 and CDK2 increased significantly (P < 0.05). It is worth noting that the opposite results were observed after transfection with si-BMP4. In summary, what should be clear from the results reported here is that BMP4 affects testicular development by regulating the Sertoli cells and BTB, thereby modulating the spermatogenesis of Tibetan sheep.

Androgen Receptor Signaling Induces Cisplatin Resistance via Down-Regulating GULP1 Expression in Bladder Cancer

The underlying molecular mechanisms of resistance to cisplatin-based systemic chemotherapy in bladder cancer patients remain to be elucidated, while the link between androgen receptor (AR) activity and chemosensitivity in urothelial cancer has been implicated. Our DNA microarray analysis in control vs. AR knockdown bladder cancer lines identified GULP1 as a potential target of AR signaling. We herein determined the relationship between AR activity and GULP1 expression in bladder cancer cells and then assessed the functional role of GULP1 in cisplatin sensitivity. Androgen treatment in AR-positive cells or AR overexpression in AR-negative cells considerably reduced the levels of GULP1 expression. Chromatin immunoprecipitation further showed direct interaction of AR with the promoter region of GULP1. Meanwhile, GULP1 knockdown sublines were significantly more resistant to cisplatin treatment compared with respective controls. GULP1 knockdown also resulted in a significant decrease in apoptosis, as well as a significant increase in G2/M phases, when treated with cisplatin. In addition, GULP1 was immunoreactive in 74% of muscle-invasive bladder cancers from patients who had subsequently undergone neoadjuvant chemotherapy, including 53% of responders showing moderate (2+)/strong (3+) expression vs. 23% of non-responders showing 2+/3+ expression (P = 0.044). These findings indicate that GULP1 represents a key downstream effector of AR signaling in enhancing sensitivity to cisplatin treatment.

Transcriptome analysis reveals the molecular mechanisms of heterosis on thermal resistance in hybrid abalone

BACKGROUND

Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive.

RESULTS

Heterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone.

CONCLUSION

More alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.

Having an Old Friend for Dinner: The Interplay between Apoptotic Cells and Efferocytes

Apoptosis, the programmed and intentional death of senescent, damaged, or otherwise superfluous cells, is the natural end-point for most cells within multicellular organisms. Apoptotic cells are not inherently damaging, but if left unattended, they can lyse through secondary necrosis. The resulting release of intracellular contents drives inflammation in the surrounding tissue and can lead to autoimmunity. These negative consequences of secondary necrosis are avoided by efferocytosis—the phagocytic clearance of apoptotic cells. Efferocytosis is a product of both apoptotic cells and efferocyte mechanisms, which cooperate to ensure the rapid and complete removal of apoptotic cells. Herein, we review the processes used by apoptotic cells to ensure their timely removal, and the receptors, signaling, and cellular processes used by efferocytes for efferocytosis, with a focus on the receptors and signaling driving this process.

Testicular Lmcd1 regulates phagocytosis by Sertoli cells through modulation of NFAT1/Txlna signaling pathway

Increased oxidative stress is well known to cause testicular dysfunction in aging males, but the detailed relationships between aging, oxidative stress, and testicular function remain to be elucidated. LIM and cysteine‐rich domains 1 (LMCD1) regulates fundamentally cellular process by interacting with transcription factors. A recent study has identified Lmcd1 as one of the most upregulated nuclear proteins associated with Sertoli cell (SC) differentiation, raising the possibility that testicular actions of LMCD1 are likely to take place. Herein, we reported that LMCD1 was exclusively expressed in the nuclei of SCs. This expression was regulated by TNF‐α signaling produced by apoptotic germ cells (GCs) and was suppressed by oxidative stress in a STAT3‐dependent manner. Ablation of endogenous LMCD1 expression caused lipid accumulation and senescence in GC co‐incubated SCs. Using a previously validated in vivo siRNA approach, we showed that LMCD1 depletion significantly impaired male fertility by inducing oligozoospermia and asthenospermia. Mechanistically, LMCD1 upregulation was associated with the nuclear enrichment of the nuclear factor of activated T cells 1 (NFAT1), a core component of Ca²⁺/calmodulin‐dependent pathway. LMCD1 facilitated the dephosphorylation and nuclear translocation of NFAT1, which consequently expedited the transactivation of Txlna, a binding partner of the syntaxin family essential for testicular phagocytosis, and thus promoted the removal of apoptotic GCs by phagocytic SCs. Collectively, LMCD1 may operate as a novel pretranscriptional integrator linking SC phagocytosis, lipid homeostasis, and cell senescence.

GULP1 regulates the NRF2-KEAP1 signaling axis in urothelial carcinoma

Disruption of the KEAP1-NRF2 pathway results in the transactivation of NRF2 target genes, consequently inducing cell proliferation and other phenotypic changes in cancer cells. Here, we demonstrated that GULP1 was a KEAP1-binding protein that maintained actin cytoskeleton architecture and helped KEAP1 to sequester NRF2 in the cytoplasm. In urothelial carcinoma of the bladder (UCB), silencing of GULP1 facilitated the nuclear accumulation of NRF2, led to constitutive activation of NRF2 signaling, and conferred resistance to the platinum drug cisplatin. Knockdown of GULP1 in UCB cells promoted tumor cell proliferation in vitro and enhanced tumor growth in vivo. In primary UCB, GULP1 silencing was more prevalent in muscle-invasive UCB compared to nonmuscle-invasive UCB. GULP1 knockdown cells showed resistance to cisplatin treatment. In parallel with decreased GULP1 expression, we observed increased expression of NRF2, HMOX1, and other candidate antioxidant genes in cisplatin-resistant cells. Furthermore, low or no expression of GULP1 was observed in most cisplatin nonresponder cases. Silencing of GULP1 was associated with GULP1 promoter hypermethylation in cell lines and primary tumors, and a high frequency of GULP1 promoter methylation was observed in multiple sets of primary clinical UCB samples. Together, our findings demonstrate that GULP1 is a KEAP1-binding protein that regulates KEAP1-NRF2 signaling in UCB and that promoter hypermethylation of GULP1 is a potential mechanism of GULP1 silencing.

Crk1/2 and CrkL play critical roles in maintaining podocyte morphology and function

Podocytes are actin-rich epithelial cells whose effacement and detachment are the main cause of glomerular disease. Crk family proteins: Crk1/2 and CrkL are reported to be important intracellular signaling proteins that are involved in many biological processes. However, the roles of them in maintaining podocyte morphology and function remain poorly understood. In this study, specific knocking down of Crk1/2 and CrkL in podocytes caused abnormal cell morphology, actin cytoskeleton rearrangement and dysfunction in cell adhesion, spreading, migration, and viability. The p130Cas, focal adhesion kinase, phosphatidylinositol 3-kinase/Akt, p38 and JNK signaling pathways involved in these alterations. Furthermore, knocking down CrkL alone conferred a more modest phenotype than did the Crk1/2 knockdown and the double knockdown. Kidney biopsy specimens from patients with focal segmental glomerulosclerosis and minimal change nephropathy showed downregulation of Crk1/2 and CrkL in glomeruli. In zebrafish embryos, Crk1/2 and CrkL knockdown compromised the morphology and caused abnormal glomerular development. Thus, our results suggest that Crk1/2 and CrkL expression are important in podocytes; loss of either will cause podocyte dysfunction, leading to foot process effacement and podocyte detachment.

Characterization of class B scavenger receptor type 1 (SRB1) in turbot (Scophthalmus maximus L.)

Class B scavenger receptor type 1 (SRB1) serves as a high-density lipoprotein (HDL) receptor essential for HDL metabolism, and plays vital roles in innate immunity. In this study, the turbot (Scophthalmus maximus) SRB1 was cloned and characterized. The gene structure consists of a coding region of 1,527 bp nucleotides dividing into 13 exons and 12 introns. Such genome structure is highly conserved among teleost fishes. The deduced SRB1 encodes 508 amino acids that mainly has a CD36 transmembrane domain. Tissue distribution of SRB1 showed the lowest expression in liver, while the highest expression was found in intestine. Significantly down-regulation pattern of SmSRB1 expression in intestine was shared after infection with Vibrio anguillarum and Streptococcus iniae. Brach and site models in CODEML program showed that SmSRB1 underwent a conservative evolutionary and three potential positive selected sites 470K, 496E, and 501Y were detected, which requires further investigation and confirmation using base-editing technologies. Subcellular localization demonstrated that turbot SRB1 was distributed in the membrane and cytoplasm. rSmSRB1 showed binding ability in vitro to bacteria, LPS, PGN, LTA and virus. Protein-protein interaction network agrees the function of SRB1 as lipoprotein receptor. Our results indicated SmSRB1 might act as co-receptors to TLRs and NLRs to modulate the immune response to pathogens. Further studies should pay attention to evaluate the specific co-receptor for SRB1 in recognition of different pathogens and selective mechanisms involved.

Stabilin Receptors: Role as Phosphatidylserine Receptors

Phosphatidylserine is a membrane phospholipid that is localized to the inner leaflet of the plasma membrane. Phosphatidylserine externalization to the outer leaflet of the plasma membrane is an important signal for various physiological processes, including apoptosis, platelet activation, cell fusion, lymphocyte activation, and regenerative axonal fusion. Stabilin-1 and stabilin-2 are membrane receptors that recognize phosphatidylserine on the cell surface. Here, we discuss the functions of Stabilin-1 and stabilin-2 as phosphatidylserine receptors in apoptotic cell clearance (efferocytosis) and cell fusion, and their ligand-recognition and signaling pathways.

Characterisation of scavenger receptor class B type 1 in rare minnow (Gobiocypris rarus)

Scavenger receptor class B type 1 (SRB1) is a transmembrane protein belonging to the scavenger receptors (SRs) family and it plays an important role in viral entry. Not much is known on SRB1 in teleost fish. Grass carp reovirus (GCRV) cause huge economic losses in grass carp industry. In this study, rare minnow (Gobiocypris rarus) was used as a model fish to investigate the mechanism of GCRV infection, which is sensitive to GCRV. The structure of SRB1 gene in G. rarus (GrSRB1) was cloned and elucidated. GrSRB1 is composed of 13 exons and 12 introns, and its full-length cDNA is 2296 bp in length, with 1521 bp open reading frame (ORF) that encodes a 506 amino acid protein. The GrSRB1 protein is predicted to contain a typical CD36 domain and two transmembrane regions. In G. rarus, GrSRB1 is expressed strongly in the liver (L), intestines (I), brain (B) and muscle (M), while it is expressed poorly in the heart (H), middle kidney (MK), head kidney (HK) and gills (G). After infection with GCRV, GrSRB1 expression was up-regulated in main immune tissues during the early infection period. Moreover, co-immunoprecipitation assays revealed that GrSRB1 could interact with the outer capsid protein of GCRV (VP5 and VP7). These results suggest that GrSRB1 could be a receptor for GCRV. We have managed to characterize the GrSRB1 gene and provide evidence for its potential functions for GCRV entry into host cells.

Dual role of DMXL2 in olfactory information transmission and the first wave of spermatogenesis

Gonad differentiation is a crucial step conditioning the future fertility of individuals and most of the master genes involved in this process have been investigated in detail. However, transcriptomic analyses of developing gonads from different animal models have revealed that hundreds of genes present sexually dimorphic expression patterns. DMXL2 was one of these genes and its function in mammalian gonads was unknown. We therefore investigated the phenotypes of total and gonad-specific Dmxl2 knockout mouse lines. The total loss-of-function of Dmxl2 was lethal in neonates, with death occurring within 12 hours of birth. Dmxl2-knockout neonates were weak and did not feed. They also presented defects of olfactory information transmission and severe hypoglycemia, suggesting that their premature death might be due to global neuronal and/or metabolic deficiencies. Dmxl2 expression in the gonads increased after birth, during follicle formation in females and spermatogenesis in males. DMXL2 was detected in both the supporting and germinal cells of both sexes. As Dmxl2 loss-of-function was lethal, only limited investigations of the gonads of Dmxl2 KO pups were possible. They revealed no major defects at birth. The gonadal function of Dmxl2 was then assessed by conditional deletions of the gene in gonadal supporting cells, germinal cells, or both. Conditional Dmxl2 ablation in the gonads did not impair fertility in males or females. By contrast, male mice with Dmxl2 deletions, either throughout the testes or exclusively in germ cells, presented a subtle testicular phenotype during the first wave of spermatogenesis that was clearly detectable at puberty. Indeed, Dmxl2 loss-of-function throughout the testes or in germ cells only, led to sperm counts more than 60% lower than normal and defective seminiferous tubule architecture. Transcriptomic and immunohistochemichal analyses on these abnormal testes revealed a deregulation of Sertoli cell phagocytic activity related to germ cell apoptosis augmentation. In conclusion, we show that Dmxl2 exerts its principal function in the testes at the onset of puberty, although its absence does not compromise male fertility in mice.

RhoG-ELMO1-RAC1 is involved in phagocytosis suppressed by mono-butyl phthalate in TM4 cells

Di-n-butyl phthalate (DBP) is one of the most dominant phthalate esters and is ubiquitous in the environment. Male reproductive toxicity of DBP and its active metabolite mono-butyl phthalate (MBP) has been demonstrated in in vivo and in vitro studies. The objective of this study was to explore the roles of RhoG-ELMO1-RAC1 in phagocytosis disrupted by MBP in TM4 cells. Mouse Sertoli cell lines (TM4 cells) were maintained and treated by various levels of MBP (1, 10, and 100 μM) for 24 h. Then, cells were harvested for further experiments. Phagocytic capacity of TM4 cells was detected by flow cytometry, immunofluorescence, and oil red O staining. RAC1 activity (GTP-RAC1) was measured by RAC1 pull-down assay. Expression of mRNA and protein related to phagocytosis including ELMO1, RhoG, and RAC1 was analyzed by qRT-PCR and Western blots, respectively. MBP inhibited phagocytosis of TM4 cells and downregulated GTP-RAC1 expression and movement to membrane markedly. Furthermore, ELMO1 protein expression was downregulated in a dose-dependent manner after MBP treatments. Additionally, expression of proteins relating to phagocytosis, including RhoG and GTP-RAC1, was decreased significantly, but expression of total-RAC1 remained unchanged. GTP-RAC1 expression increased dramatically after TM4 cells were transfected with ELMO1 or RhoG plasmid, but restored under co-treatments with MBP and ELMO1/RhoG plasmid. This study suggests that MBP can reduce the phagocytosis of Sertoli cells through RhoG-ELMO1-RAC1 pathway.

[Advances in macrophage function and its anti-inflammatory and proresolving activity and role in periodontitis development]

Macrophage plays an important role in human innate immune system. It has powerful functions, such as recognition, phagocytosis, and bacteria and foreign body removal. Periodontitis, which is a chronic infectious disease characterized by gum inflammation and bone loss, is a major cause of tooth loss in adults. Several studies demonstrated that periodontal tissue destruction is caused by the host immune response defending against infections. As an important part of host immune response, macrophage is also involved in periodontitis pathogenesis. Recently, anti-inflammatory and proresolving activities of macrophage was discovered. Thus, the complex function of macrophage in the occurrence, development, and resolution of inflammation and its potential role in periodontitis were reviewed.

SR-B1: A Unique Multifunctional Receptor for Cholesterol Influx and Efflux

The scavenger receptor, class B type 1 (SR-B1), is a multiligand membrane receptor protein that functions as a physiologically relevant high-density lipoprotein (HDL) receptor whose primary role is to mediate selective uptake or influx of HDL-derived cholesteryl esters into cells and tissues. SR-B1 also facilitates the efflux of cholesterol from peripheral tissues, including macrophages, back to liver. As a regulator of plasma membrane cholesterol content, SR-B1 promotes the uptake of lipid soluble vitamins as well as viral entry into host cells. These collective functions of SR-B1 ultimately affect programmed cell death, female fertility, platelet function, vasculature inflammation, and diet-induced atherosclerosis and myocardial infarction. SR-B1 has also been identified as a potential marker for cancer diagnosis and prognosis. Finally, the SR-B1-linked selective HDL-cholesteryl ester uptake pathway is now being evaluated as a gateway for the delivery of therapeutic and diagnostic agents. In this review, we focus on the regulation and functional significance of SR-B1 in mediating cholesterol movement into and out of cells.

Glial Draper Rescues Aβ Toxicity in a Drosophila Model of Alzheimer's Disease

Pathological hallmarks of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques, neurofibrillary tangles, and reactive gliosis. Glial cells offer protection against AD by engulfing extracellular Aβ peptides, but the repertoire of molecules required for glial recognition and destruction of Aβ are still unclear. Here, we show that the highly conserved glial engulfment receptor Draper/MEGF10 provides neuroprotection in an AD model of Drosophila (both sexes). Neuronal expression of human Aβ42^arc in adult flies results in robust Aβ accumulation, neurodegeneration, locomotor dysfunction, and reduced lifespan. Notably, all of these phenotypes are more severe in draper mutant animals, whereas enhanced expression of glial Draper reverses Aβ accumulation, as well as behavioral phenotypes. We also show that the signal transducer and activator of transcription (Stat92E), c-Jun N-terminal kinase (JNK)/AP-1 signaling, and expression of matrix metalloproteinase-1 (Mmp1) are activated downstream of Draper in glia in response to Aβ42^arc exposure. Furthermore, Aβ42-induced upregulation of the phagolysosomal markers Atg8 and p62 was notably reduced in draper mutant flies. Based on our findings, we propose that glia clear neurotoxic Aβ peptides in the AD model Drosophila brain through a Draper/STAT92E/JNK cascade that may be coupled to protein degradation pathways such as autophagy or more traditional phagolysosomal destruction methods.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) and similar dementias are common incurable neurodegenerative disorders in the aging population. As the primary immune responders in the brain, glial cells are implicated as key players in the onset and progression of AD and related disorders. Here we show that the glial engulfment receptor Draper is protective in a Drosophila model of AD, reducing levels of amyloid β (Aβ) peptides, reversing locomotor defects, and extending lifespan. We further show that protein degradation pathways are induced downstream of Draper in AD model flies, supporting a model in which glia engulf and destroy Aβ peptides to reduce amyloid-associated toxicity.

Apoptotic cell recognition receptors and scavenger receptors

Phosphatidylserine recognition receptors are a highly diverse set of receptors grouped by their ability to recognize the 'eat-me' signal phosphatidylserine on apoptotic cells. Most of the phosphatidylserine recognition receptors dampen inflammation by inducing the production of anti-inflammatory mediators during the phagocytosis of apoptotic corpses. However, many phosphatidylserine receptors are also capable of recognizing other ligands, with some receptors being categorized as scavenger receptors. It is now appreciated that these receptors can elicit different downstream events for particular ligands. Therefore, how phosphatidylserine recognition receptors mediate specific signals during recognition of apoptotic cells versus other ligands, and how this might help regulate the inflammatory state of a tissue is an important question that is not fully understood. Here, we revisit the work on signaling downstream of the phosphatidylserine recognition receptor BAI1, and evaluate how these and other signaling modules mediate signaling downstream from other receptors, including Stabilin-2, MerTK, and αvβ5. We also propose the concept that phosphatidylserine recognition receptors could be viewed as a subset of scavenger receptors that are capable of eliciting anti-inflammatory responses to apoptotic cells.

MicroRNA-34a Negatively Regulates Efferocytosis by Tissue Macrophages in Part via SIRT1

Apoptotic cell (AC) clearance (efferocytosis) is an evolutionarily conserved process essential for immune health, particularly to maintain self-tolerance. Despite identification of many recognition receptors and intracellular signaling components of efferocytosis, its negative regulation remains incompletely understood and has not previously been known to involve microRNAs (miRs). In this article, we show that miR-34a (gene ID 407040), well recognized as a p53-dependent tumor suppressor, mediates coordinated negative regulation of efferocytosis by resident murine and human tissue macrophages (Mø). The miR-34a expression varied greatly between Mø from different tissues, correlating inversely with their capacity for AC uptake. Transient or genetic knockdown of miR-34a increased efferocytosis, whereas miR-34a overexpression decreased efferocytosis, without altering recognition of live, necrotic, or Ig-opsonized cells. The inhibitory effect of miR-34a was mediated both by reduced expression of Axl, a receptor tyrosine kinase known to recognize AC, and of the deacetylase silent information regulator T1, which had not previously been linked to efferocytosis by tissue Mø. Exposure to AC downregulated Mø miR-34a expression, resulting in a positive feedback loop that increased subsequent capacity to engulf AC. These findings demonstrate that miR-34a both specifically regulates and is regulated by efferocytosis. Given the ability of efferocytosis to polarize ingesting Mø uniquely and to reduce their host-defense functions, dynamic negative regulation by miR-34a provides one means of fine-tuning Mø behavior toward AC in specific tissue environments with differing potentials for microbial exposure.

Macrophage SR-BI mediates efferocytosis via Src/PI3K/Rac1 signaling and reduces atherosclerotic lesion necrosis

Macrophage apoptosis and efferocytosis are key determinants of atherosclerotic plaque inflammation and necrosis. Bone marrow transplantation studies in ApoE- and LDLR-deficient mice revealed that hematopoietic scavenger receptor class B type I (SR-BI) deficiency results in severely defective efferocytosis in mouse atherosclerotic lesions, resulting in a 17-fold higher ratio of free to macrophage-associated dead cells in lesions containing SR-BI^−/− cells, 5-fold more necrosis, 65.2% less lesional collagen content, nearly 7-fold higher dead cell accumulation, and 2-fold larger lesion area. Hematopoietic SR-BI deletion elicited a maladaptive inflammatory response [higher interleukin (IL)-1β, IL-6, and TNF-α lower IL-10 and transforming growth factor β]. Efferocytosis of apoptotic thymocytes was reduced by 64% in SR-BI^−/− versus WT macrophages, both in vitro and in vivo. In response to apoptotic cells, macrophage SR-BI bound with phosphatidylserine and induced Src phosphorylation and cell membrane recruitment, which led to downstream activation of phosphoinositide 3-kinase (PI3K) and Ras-related C3 botulinum toxin substrate 1 (Rac1) for engulfment and clearance of apoptotic cells, as inhibition of Src decreased PI3K, Rac1-GTP, and efferocytosis in WT cells. Pharmacological inhibition of Rac1 reduced macrophage efferocytosis in a SR-BI-dependent fashion, and activation of Rac1 corrected the defective efferocytosis in SR-BI^−/− macrophages. Thus, deficiency of macrophage SR-BI promotes defective efferocytosis signaling via the Src/PI3K/Rac1 pathway, resulting in increased plaque size, necrosis, and inflammation.

AICAR Enhances the Phagocytic Ability of Macrophages towards Apoptotic Cells through P38 Mitogen Activated Protein Kinase Activation Independent of AMP-Activated Protein Kinase

Recent studies have suggested that 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) increases macrophage phagocytosis through adenosine monophosphate-activated protein kinase (AMPK). However, little information is available on the effects of AICAR on the clearance of apoptotic cells by macrophages, known as efferocytosis, which is essential in maintaining tissue homeostasis and resolving inflammation. AICAR increased p38 MAPK activation and the phagocytosis of apoptotic cells by macrophages, which were inhibited by the p38 MAPK inhibitor, SB203580, the TGF-beta-activated kinase 1 (TAK1) inhibitor, (5Z)-7-oxozeaenol, and siRNA-mediated knock-down of p38α. AICAR increased phosphorylation of Akt, but the inhibition of PI3K/Akt activity using LY294002 did not affect the AICAR-induced changes in efferocytosis in macrophages. CGS15943, a non-selective adenosine receptor antagonist, did not affect AICAR-induced changes in efferocytosis, but dipyridamole, an adenosine transporter inhibitor, diminished the AICAR-mediated increases in efferocytosis. AICAR-induced p38 MAPK phosphorylation was not inhibited by the AMPK inhibitor, compound C, or siRNA-mediated knock-down of AMPKα1. Inhibition of AMPK using compound C or 5’-iodotubercidin did not completely block AICAR-mediated increases in efferocytosis. Furthermore, AICAR also increased the removal of apoptotic neutrophils or thymocytes in mouse lungs. These results reveal a novel mechanism by which AICAR increases macrophage-mediated phagocytosis of apoptotic cells and suggest that AICAR may be used to treat efferocytosis-related inflammatory conditions.

Scavenger receptor class B type I (SR-BI): a versatile receptor with multiple functions and actions

Scavenger receptor class B type I (SR-BI), is a physiologically relevant HDL receptor that mediates selective uptake of lipoprotein (HDL)-derived cholesteryl ester (CE) in vitro and in vivo. Mammalian SR-BI is a 509-amino acid, ~82 kDa glycoprotein that contains N- and C-terminal cytoplasmic domains, two-transmembrane domains, as well as a large extracellular domain containing 5-6 cysteine residues and multiple sites for N-linked glycosylation. The size and structural characteristics of SR-BI, however, vary considerably among lower vertebrates and insects. Recently, significant progress has been made in understanding the molecular mechanisms involved in the posttranscriptional/posttranslational regulation of SR-BI in a tissue specific manner. The purpose of this review is to summarize the current body of knowledge about the events and molecules connected with the posttranscriptional/posttranslational regulation of SR-BI and to update the molecular and functional characteristics of the insect SR-BI orthologs.

The adaptor protein GULP promotes Jedi-1-mediated phagocytosis through a clathrin-dependent mechanism

During the development of the peripheral nervous system, the large number of apoptotic neurons generated are phagocytosed by glial precursor cells. This clearance is mediated, in part, through the mammalian engulfment receptor Jedi-1. However, the mechanisms by which Jedi-1 mediates phagocytosis are poorly understood. Here we demonstrate that Jedi-1 associates with GULP, the mammalian homologue of CED-6, an adaptor protein required for phagocytosis mediated by the nematode engulfment receptor CED-1. Silencing GULP or mutating the NPXY motif in Jedi-1, which is required for GULP binding, prevents Jedi-1-mediated phagocytosis. How GULP promotes engulfment is not known. Of interest, we find that Jedi-1-induced phagocytosis requires GULP binding to clathrin heavy chain (CHC). During engulfment, CHC is tyrosine phosphorylated, which is required for Jedi-mediated engulfment. Both phosphoclathrin and actin accumulate around engulfed microspheres. Furthermore, knockdown of CHC in HeLa cells prevents Jedi-1-mediated engulfment of microspheres, and knockdown in glial precursors prevents the engulfment of apoptotic neurons. Taken together, these results reveal that Jedi-1 signals through recruitment of GULP, which promotes phagocytosis through a noncanonical phosphoclathrin-dependent mechanism.

Identification of novel candidate genes for follicle selection in the broiler breeder ovary

BACKGROUND

Broiler breeders fed ad libitum are characterised by multiple ovulation, which leads to poor shell quality and egg production. Multiple ovulation is controlled by food restriction in commercial flocks. However, the level of food restriction raises welfare concerns, including that of severe hunger. Reducing the rate of multiple ovulation by genetic selection would facilitate progress towards developing a growth profile for optimum animal welfare.

RESULTS

The study utilised 3 models of ovarian follicle development; laying hens fed ad libitum (experiment 2) and broiler breeders fed ad libitum or a restricted diet (experiments 1 & 3). This allowed us to investigate gene candidates for follicular development by comparing normal, abnormal and "controlled" follicle hierarchies at different stages of development. Several candidate genes for multiple ovulation were identified by combining microarray analysis of restricted vs. ad libitum feeding, literature searches and QPCR expression profiling throughout follicle development. Three candidate genes were confirmed by QPCR as showing significant differential expression between restricted and ad libitum feeding: FSHR, GDF9 and PDGFRL. PDGFRL, a candidate for steroidogenesis, showed significantly up-regulated expression in 6-8 mm follicles of ad libitum fed broiler breeders (P = 0.016), the period at which follicle recruitment occurs.

CONCLUSIONS

Gene candidates have been identified and evidence provided to support a possible role in regulation of ovarian function and follicle number. Further characterisation of these genes will be required to assess their potential for inclusion into breeding programmes to improve the regulation of follicle selection and reduce the need for feed restriction.

Toll-like receptor 3 activation differentially regulates phagocytosis of bacteria and apoptotic neutrophils by mouse peritoneal macrophages

Toll-like receptor (TLR) activation by microbial pathogens triggers inflammatory responses against microbes. The phagocytic clearance of invading microbes and apoptotic immune cells is essential to resolve inflammation. However, the relationship between TLR activation and phagocytosis is poorly understood. We found that TLR3 activation promotes bacterial uptake through the activation of interferon-regulating factor 3 (IRF3) and inhibits phagocytosis of apoptotic neutrophils through the activation of nuclear factor-κB (NF-κB) by mouse peritoneal macrophages. The TLR signals that regulate the phagocytic ability of macrophages were also induced by TLR4 and TLR5 activation. Further, we demonstrated that TLR-induced tumor necrosis factor-α and interferon-β contributed to the differential phagocytosis of apoptotic neutrophils and bacteria by macrophages. Moreover, activation of IRF3 upregulated the expression of some receptors involved in bacterial uptake, whereas activation of NF-κB downregulated the expression of molecules that facilitate the phagocytosis of apoptotic cells. These results describe an effect of TLR-triggered innate immunity on the phagocytic activity of macrophages.

Discovery of carboxyethylpyrroles (CEPs): critical insights into AMD, autism, cancer, and wound healing from basic research on the chemistry of oxidized phospholipids

Basic research, exploring the hypothesis that 2-(ω-carboxyethyl)pyrrole (CEP) modifications of proteins are generated nonenzymatically in vivo is delivering a bonanza of molecular mechanistic insights into age-related macular degeneration, autism, cancer, and wound healing. CEPs are produced through covalent modification of protein lysyl ε-amino groups by γ-hydroxyalkenal phospholipids that are formed by oxidative cleavage of docosahexaenate-containing phospholipids. Chemical synthesis of CEP-modified proteins and the production of highly specific antibodies that recognize them preceded and facilitated their detection in vivo and enabled exploration of their biological occurrence and activities. This investigational approach, from the chemistry of biomolecules to disease phenotype, is proving to be remarkably productive.

Intracellular HMGB1 negatively regulates efferocytosis

High mobility group box 1 (HMGB1) is a highly conserved protein with multiple intracellular and extracellular functions, including transcriptional regulation, as well as modulation of inflammation, cell migration, and ingestion of apoptotic cells. In these experiments, we examined a potential role for intracellular HMGB1 in modulating phagocytosis. We found that phagocytosis of apoptotic cells resulted in translocation of HMGB1 into the cytoplasm and extracellular space. Transient or stable inhibition of HMGB1 expression in bone marrow-derived macrophages or fibroblasts resulted in increased phagocytosis of apoptotic thymocytes and apoptotic neutrophils. Knockdown of HMGB1 was associated with enhanced activation of Rac-1 and cytoskeletal rearrangement. Intracellular events involved in phagocytosis and upstream of Rac-1 activation, such as phosphorylation of ERK and focal adhesion kinase (FAK), were increased after knockdown of HMGB1. Inhibition of Src kinase activity prevented the increase in phosphorylation of FAK and ERK present during phagocytosis in HMGB1 knockdown cells, and also abrogated the enhancement in phagocytosis associated with HMGB1 knockdown. Interaction between Src and FAK in the cytoplasm of HMGB1 knockdown fibroblasts was enhanced compared with that present in control fibroblasts. Under in vitro conditions, the presence of HMGB1 diminished interactions between purified FAK and Src. These studies demonstrate a novel role for HMGB1 in the regulation of phagocytosis. In particular, these experiments show that intracellular HMGB1, through associating with Src kinase and inhibiting interactions between Src and FAK, diminishes the phagocytic ability of macrophages and other cell populations.

Tolerance induced by apoptotic antigen-coupled leukocytes is induced by PD-L1+ and IL-10-producing splenic macrophages and maintained by T regulatory cells

Ag-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide Ags linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-coupled splenocytes [Ag-SP]) has been demonstrated to be a highly efficient method for inducing peripheral, Ag-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. In this study, we show that apoptotic Ag-SP accumulate in the splenic marginal zone, where their uptake by F4/80(+) macrophages induces production of IL-10, which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 that is essential for Ag-SP tolerance induction. Ag-SP infusion also induces T regulatory cells that are dispensable for tolerance induction but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. To our knowledge, we show for the first time that tolerance results from the synergistic effects of two distinct mechanisms, PD-L1-dependent T cell-intrinsic unresponsiveness and the activation of T regulatory cells. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting multiple sclerosis.

Phagocytic removal of cells that have become unwanted: implications for animal development and tissue homeostasis

Cells that have become unwanted need to be promptly, selectively, and safely removed. This is made possible by apoptosis-dependent phagocytosis, in which cells unnecessary, obstructive, or dangerous to organisms are induced to undergo apoptosis so that they are earmarked for phagocytosis. The phagocytic elimination occurs so quickly that cells with hallmarks of apoptosis are barely detectable in vivo. The removal of particular types of cells at appropriate stages of development not only contributes to the disposal of spent cells, the creation of space for morphogenesis, and the exclusion of pathogenic or noxious cells, but seems to actively control tissue renewal, tissue remodeling, tissue function, and pathogenic state. This event thus plays an indispensable role in the maintenance of animal development and tissue homeostasis.

Impact of interleukin-17 on macrophage phagocytosis of apoptotic neutrophils and particles

There is now substantial evidence that the cytokine interleukin-17 orchestrates the accumulation of neutrophils in mammals and thereby contributes to host defense. However, the role of IL-17 in controlling neutrophil turnover is not fully understood. Here, we demonstrate that IL-17 stimulates the apoptosis of mouse neutrophils and, simultaneously, the release of the microbicidal compound, myeloperoxidase. IL-17 also stimulates mouse macrophages to phagocytose aged neutrophils and latex beads, and it induces an increase in a soluble form of the phagocytic receptor, lectin-like oxidized low-density lipoprotein receptor-1 as well. In contrast, IL-17 does not markedly increase the release of the archetype neutrophil-recruiting cytokine, macrophage inflammatory protein-2 in mouse macrophages. Importantly, IL-17 also stimulates the phagocytosis of latex beads in human monocyte-derived macrophages. Thus, IL-17 bears the potential to control both phagocytosis and neutrophil turnover during activation of host defense.

Galactose specific adhesin of enteroaggregative E. coli induces IL-8 secretion via activation of MAPK and STAT-3 in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is one of the most common bacterial pathogens associated with the etiology of persistent diarrhea. A characteristic feature of EAEC-pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. The present study was designed to investigate the underlying mechanism of inflammatory responses induced by a novel galactose specific adhesin of T7 strain of EAEC (EAEC-T7) in human intestinal epithelial cell line (INT-407).

METHODS

INT-407 cells were stimulated with the adhesin in the absence and presence of anti-adhesin (IgG(AD))/d-galactose/H7/staurosporin (inhibitor of PKC)/PD098059 (inhibitor of MEK)/SB203580 (inhibitor of p38-MAPkinase)/AG490 (inhibitor of JAK (-2,-3)/STAT-3 pathway). The expression of activated Raf-1, MEK-1, ERK1/2, JNK, p38-MAPK and STAT-3 was analyzed by Western immunoblot. Release of interleukin-8 (IL-8) was measured by ELISA.

RESULTS

The adhesin was found to induce activation of Raf-1, MEK-1, ERK1/2, p38-MAPK and STAT-3, which was reduced in the presence of IgG(AD)/d-galactose. The activation of Raf-1 was found to be attenuated in the presence of H7/staurosporin. The expression of phosphorylated STAT-3 was downregulated in the presence of AG490 and PD098059. Further, the adhesin induced IL-8 secretion was reduced in the presence of the inhibitors of MEK (PD098059), p38-MAPK (SB203580) and JAK (-2,-3)/STAT-3 pathway (AG490).

CONCLUSIONS

We propose that STAT-3 activation is quintessential for the galactose specific adhesin induced IL-8 secretion by INT-407 cells and must occur in concert with the activation of ERK1/2.

GENERAL SIGNIFICANCE

Our contribution regarding the galactose specific adhesin mediated signaling leads to an improved understanding of the EAEC-pathogenesis and may provide novel therapeutic approaches to combat EAEC infection.

CD14 and toll-like receptors 2 and 4 are required for fibrillar A{beta}-stimulated microglial activation

Microglia are the brain's tissue macrophages and are found in an activated state surrounding beta-amyloid plaques in the Alzheimer's disease brain. Microglia interact with fibrillar beta-amyloid (fAbeta) through an ensemble of surface receptors composed of the alpha(6)beta(1) integrin, CD36, CD47, and the class A scavenger receptor. These receptors act in concert to initiate intracellular signaling cascades and phenotypic activation of these cells. However, it is unclear how engagement of this receptor complex is linked to the induction of an activated microglial phenotype. We report that the response of microglial cells to fibrillar forms of Abeta requires the participation of Toll-like receptors (TLRs) and the coreceptor CD14. The response of microglia to fAbeta is reliant upon CD14, which act together with TLR4 and TLR2 to bind fAbeta and to activate intracellular signaling. We find that cells lacking these receptors could not initiate a Src-Vav-Rac signaling cascade leading to reactive oxygen species production and phagocytosis. The fAbeta-mediated activation of p38 MAPK also required CD14, TLR4, and TLR2. Inhibition of p38 abrogated fAbeta-induced reactive oxygen species production and attenuated the induction of phagocytosis. Microglia lacking CD14, TLR4, and TLR2 showed no induction of phosphorylated IkappaBalpha following fAbeta. These data indicate these innate immune receptors function as members of the microglial fAbeta receptor complex and identify the signaling mechanisms whereby they contribute to microglial activation.