Syntaxin 11 regulates the stimulus-dependent transport of Toll-like receptor 4 to the plasma membrane by cooperating with SNAP-23 in macrophages

ASO-mediated knockdown or kinase inhibition of G2019S-Lrrk2 modulates lysosomal tubule-associated antigen presentation in macrophages

Genetic variation around the LRRK2 gene affects risk for both familial and sporadic Parkinson's disease (PD). LRRK2 levels have become an appealing target for potential PD therapeutics with LRRK2 antisense oligonucleotides (ASOs) now moving toward clinical trials. However, LRRK2 has been suggested to play a fundamental role in peripheral immunity, and it is currently unknown if targeting increased LRRK2 levels in peripheral immune cells will be beneficial or deleterious. Here it was observed that G2019S macrophages exhibited increased stimulation-dependent lysosomal tubule formation (LTF) and MHC-II trafficking from the perinuclear lysosome to the plasma membrane in an mTOR-dependent manner with concomitant increases in pro-inflammatory cytokine release. Both ASO-mediated knockdown of mutant Lrrk2 and LRRK2 kinase inhibition ameliorated this phenotype and decreased these immune responses in control cells. Given the critical role of antigen presentation, lysosomal function, and cytokine release in macrophages, it is likely LRRK2-targeting therapies with systemic activity may have therapeutic value with regard to mutant LRRK2, but deleterious effects on the peripheral immune system, such as altered pathogen control in these cells, should be considered when reducing levels of non-mutant LRRK2.

Lactoferrin deficiency during lactation increases the risk of depressive-like behavior in adult mice

BACKGROUND

Lactoferrin is an active protein in breast milk that plays an important role in the growth and development of infants and is implicated as a neuroprotective agent. The incidence of depression is currently increasing, and it is unclear whether the lack of lactoferrin during lactation affects the incidence of depressive-like behavior in adulthood.

RESULTS

Lack of lactoferrin feeding during lactation affected the barrier and innate immune functions of the intestine, disrupted the intestinal microflora, and led to neuroimmune dysfunction and neurodevelopmental delay in the hippocampus. When exposed to external stimulation, adult lactoferrin feeding-deficient mice presented with worse depression-like symptoms; the mechanisms involved were activation of the LPS-TLR4 signalling pathway in the intestine and hippocampus, reduced BDNF-CREB signaling pathway in hippocampus, increased abundance of depression-related bacteria, and decreased abundance of beneficial bacteria.

CONCLUSIONS

Overall, our findings reveal that lactoferrin feeding deficient during lactation can increase the risk of depressive-like behavior in adults. The mechanism is related to the regulatory effect of lactoferrin on the development of the "microbial-intestinal-brain" axis.

Distinct transcriptional profiles of maternal and fetal placental macrophages at term are associated with gravidity

Maternal intervillous monocytes (MIMs) and fetal Hofbauer cells (HBCs) are myeloid-derived immune cells at the maternal-fetal interface. Little is known regarding the molecular phenotypes and roles of these distinct monocyte/macrophage populations. Here, we used RNA sequencing to investigate the transcriptional profiles of MIMs and HBCs in six normal term pregnancies. Our analyses revealed distinct transcriptomes of MIMs and HBCs. Genes involved in differentiation and cell organization pathways were more highly expressed in MIMs vs. HBCs. In contrast, HBCs had higher expression of genes involved in inflammatory responses and cell surface receptor signaling. Maternal gravidity influenced monocyte programming, as expression of pro-inflammatory molecules was significantly higher in MIMs from multigravidas compared to primigravidas. In HBCs, multigravidas displayed enrichment of gene pathways involved in cell-cell signaling and differentiation. In summary, our results demonstrated that MIMs and HBCs have highly divergent transcriptional signatures, reflecting their distinct origins, locations, functions, and roles in inflammatory responses. Our data further suggested that maternal gravidity influences the gene signatures of MIMs and HBCs, potentially modulating the interplay between tolerance and trained immunity. The phenomenon of reproductive immune memory may play a novel role in the differential susceptibility of primigravidas to pregnancy complications.

Totally tubular: ASO-mediated knock-down of G2019S -Lrrk2 modulates lysosomal tubule-associated antigen presentation in macrophages

Genetic variation around the LRRK2 gene affects risk of both familial and sporadic Parkinson's disease (PD). LRRK2 levels have become an appealing target for potential PD-therapeutics with LRRK2 antisense oligonucleotides (ASOs) now in clinical trials. However, LRRK2 has been suggested to play a fundamental role in peripheral immunity, and it is currently unknown if targeting increased LRRK2 levels in peripheral immune cells will be beneficial or deleterious. Furthermore, the precise role of LRRK2 in immune cells is currently unknown, although it has been suggested that LRRK2-mediated lysosomal function may be crucial to immune responses. Here, it was observed that G2019S macrophages exhibited increased stimulation-dependent lysosomal tubule formation (LTF) and MHC-II trafficking from the perinuclear lysosome to the plasma membrane in an mTOR dependent manner with concomitant increases in pro-inflammatory cytokine release. Both ASO-mediated knock down of mutant Lrrk 2 and LRRK2 kinase inhibition ameliorated this phenotype and decreased these immune responses in control cells. Given the critical role of antigen presentation, lysosomal function, and cytokine release in macrophages, it is likely LRRK2-targetting therapies may have therapeutic value with regards to mutant LRRK2 but deleterious effects on the peripheral immune system, such as altered pathogen control and infection resolution.

Syntaxin 11 Contributes to the Interferon-Inducible Restriction of Coxiella burnetii Intracellular Infection

There is a limited understanding of host defense mechanisms targeting intracellular pathogens that proliferate in a lysosome. Coxiella burnetii is a model bacterial pathogen capable of replicating in the hydrolytic and acidic environment of the lysosome. It has been shown that gamma interferon (IFNγ)-stimulated host cells restrict C. burnetii replication by a mechanism that involves host IDO1 depletion of tryptophan. Host cells deficient in IDO1 activity, however, retain the ability to restrict C. burnetii replication when stimulated with IFNγ, which suggests additional mechanisms of host defense. This study identified syntaxin 11 (STX11) as a host protein that contributes to IFNγ-mediated suppression of C. burnetii replication. STX11 is a SNARE protein; SNARE proteins are proteins that mediate fusion of host vesicles with specific subcellular organelles. Depletion of STX11 using either small interfering RNA (siRNA)- or CRISPR-based approaches enhanced C. burnetii replication intracellularly. Stable expression of STX11 reduced C. burnetii replication in epithelial cells and macrophages, which indicates that this STX11-dependent cell-autonomous response is operational in multiple cell types and can function independently of other IFNγ-induced factors. Fluorescently tagged STX11 localized to the Coxiella-containing vacuole (CCV), and STX11 restriction was found to involve an interaction with STX8. Thus, STX11 regulates a vesicle fusion pathway that limits replication of this intracellular pathogen in a lysosome-derived organelle. IMPORTANCE Cell intrinsic defense mechanisms are used by eukaryotic cells to restrict the replication and dissemination of pathogens. This study identified a human protein called syntaxin 11 (STX11) as a host restriction factor that inhibits the intracellular replication of Coxiella burnetii. Syntaxins regulate the delivery of cargo inside vesicles by promoting specific membrane fusion events between donor and acceptor vesicles. Data presented here demonstrate that STX11 regulates an immunological defense pathway that controls replication of pathogens in lysosome-derived organelles, which provides new insight into the function of this SNARE protein.

Trihydroxyxanthones from the heartwood of Maclura cochinchinensis modulate M1/M2 macrophage polarisation and enhance surface TLR4

The anti-inflammatory actions of phytochemicals have attracted much attention due to the current state of numerous inflammatory disorders. Thai traditional medicine uses Maclura cochinchinensis (Lour.) Corner to treat chronic fever and various inflammatory diseases, as well as to maintain normal lymphatic function. Five flavonoids and five xanthones were isolated from the heartwood of M. cochinchinensis and we investigated the anti-inflammatory properties of the isolated compounds. All isolated compounds possessed an anti-inflammatory effect by decreasing prostaglandin E₂ (PGE₂) synthesis in lipopolysaccharide (LPS)-activated murine macrophages with varying degrees of potency. The greatest decrease in M1 inflammatory mediators, nitric oxide, PGE₂, and proinflammatory cytokines was observed with 1,3,7-trihydroxyxanthone and 1,3,5-trihydroxyxanthone treatment of LPS-activated macrophages. The anti-inflammatory mechanism of the two xanthones is mediated by the suppression of inducible nitric oxide synthase, cyclooxygenase-2, and phosphatidylinositol 3-kinase/protein kinase B expression and the upregulation of M2 anti-inflammatory signalling proteins phosphorylated signal transducer and activator of transcription 6 and peroxisome proliferator-activated receptors-γ. 1,3,7-Trihydroxyxanthone exhibits superior induction of anti-inflammatory M2 mediator of LPS-activated macrophages by upregulating arginase1 expression. Following the resolution of inflammation, the two xanthones enhanced surface TLR4 expression compared to LPS-stimulated cells, possibly preserving macrophage function. Our research highlights the role of the two xanthones in modulating the M1/M2 macrophage polarisation to reduce inflammation and retain surface TLR4 once inflammation has been resolved. These findings support the use of xanthones for their anti-inflammatory effects in treating inflammatory dysregulation.

Cell Junction and Vesicle Trafficking-Mediated Melanosome/Melanin Transfer Are Involved in the Dynamic Transformation of Goldfish Carassius auratus Skin Color

Goldfish are one of the most popular models for studying the genetic diversity of skin color. Transcriptome sequencing (RNA-seq) and whole genome bisulfate sequencing (WGBS) of skin tissues from the third filial (F3) cyan (CN), black (BK), and white (WH) goldfish were conducted to analyze the molecular mechanism of color transformation in fish. The RNA-seq yielded 56 Gb of clean data and 56,627 transcripts from nine skin samples. The DEGs (differentially expressed genes) were enriched in cell junction cellular components and the tight junction pathway. Ninety-five homologs of the claudin family were predicted and 16 claudins were identified in correlation with skin color transformation. WGBS yielded 1079 Gb of clean data from 15 samples. Both the DEGs and the DMRs (differentially methylated regions) in the BK_CN group were found to be enriched in cytoskeleton reorganization and vesicle trafficking. Masson staining and TEM (transmission electron microscopy) confirmed the varied distribution and processes of melanosome/melanin in skin tissues. Our results suggested that cytoskeleton reorganization, cell junction, and the vesicle trafficking system played key roles in the transfer of the melanosome/melanin, and it was the extracellular translocation rather than the biosynthesis or metabolism of the melanin process that resulted in the color transformation of cyan goldfish. The data will facilitate the understanding of the molecular mechanisms underlying dynamic skin color transformation in goldfish.

TLR4 and CD14 trafficking and its influence on LPS-induced pro-inflammatory signaling

Toll-like receptor (TLR) 4 belongs to the TLR family of receptors inducing pro-inflammatory responses to invading pathogens. TLR4 is activated by lipopolysaccharide (LPS, endotoxin) of Gram-negative bacteria and sequentially triggers two signaling cascades: the first one involving TIRAP and MyD88 adaptor proteins is induced in the plasma membrane, whereas the second engaging adaptor proteins TRAM and TRIF begins in early endosomes after endocytosis of the receptor. The LPS-induced internalization of TLR4 and hence also the activation of the TRIF-dependent pathway is governed by a GPI-anchored protein, CD14. The endocytosis of TLR4 terminates the MyD88-dependent signaling, while the following endosome maturation and lysosomal degradation of TLR4 determine the duration and magnitude of the TRIF-dependent one. Alternatively, TLR4 may return to the plasma membrane, which process is still poorly understood. Therefore, the course of the LPS-induced pro-inflammatory responses depends strictly on the rates of TLR4 endocytosis and trafficking through the endo-lysosomal compartment. Notably, prolonged activation of TLR4 is linked with several hereditary human diseases, neurodegeneration and also with autoimmune diseases and cancer. Recent studies have provided ample data on the role of diverse proteins regulating the functions of early, late, and recycling endosomes in the TLR4-induced inflammation caused by LPS or phagocytosis of E. coli. In this review, we focus on the mechanisms of the internalization and intracellular trafficking of TLR4 and CD14, and also of LPS, in immune cells and discuss how dysregulation of the endo-lysosomal compartment contributes to the development of diverse human diseases.

SNAREs and developmental disorders

Members of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family mediate membrane fusion processes associated with vesicular trafficking and autophagy. SNAREs mediate core membrane fusion processes essential for all cells, but some SNAREs serve cell/tissue type-specific exocytic/endocytic functions, and are therefore critical for various aspects of embryonic development. Mutations or variants of their encoding genes could give rise to developmental disorders, such as those affecting the nervous system and immune system in humans. Mutations to components in the canonical synaptic vesicle fusion SNARE complex (VAMP2, STX1A/B, and SNAP25) and a key regulator of SNARE complex formation MUNC18-1, produce variant phenotypes of autism, intellectual disability, movement disorders, and epilepsy. STX11 and MUNC18-2 mutations underlie 2 subtypes of familial hemophagocytic lymphohistiocytosis. STX3 mutations contribute to variant microvillus inclusion disease. Chromosomal microdeletions involving STX16 play a role in pseudohypoparathyroidism type IB associated with abnormal imprinting of the GNAS complex locus. In this short review, I discuss these and other SNARE gene mutations and variants that are known to be associated with a variety developmental disorders, with a focus on their underlying cellular and molecular pathological basis deciphered through disease modeling. Possible pathogenic potentials of other SNAREs whose variants could be disease predisposing are also speculated upon.

Regulatory Mechanism of SNAP23 in Phagosome Formation and Maturation

Synaptosomal associated protein of 23 kDa (SNAP23), a plasma membrane-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), is a ubiquitously expressed protein that is generally involved in fusion of the plasma membrane and secretory or endosomal recycling vesicles during several types of exocytosis. SNAP23 is expressed in phagocytes, such as neutrophils, macrophages, and dendritic cells, and functions in both exocytosis and phagocytosis. This review focuses on the function of SNAP23 in immunoglobulin G Fc receptor-mediated phagocytosis by macrophages. SNAP23 and its partner SNAREs mediate fusion of the plasma membrane with intracellular organelles or vesicles to form phagosomes as well as the fusion of phagosomes with endosomes or lysosomes to induce phagosome maturation, characterized by reactive oxygen species production and acidification. During these processes, SNAP23 function is regulated by phosphorylation. In addition, microtubule-associated protein 1A/1B light chain 3 (LC3)-associated phagocytosis, which tightly promotes or suppresses phagosome maturation depending on the foreign target, requires SNAP23 function. SNAP23 that is enriched on the phagosome membrane during LC3-associated phagocytosis may be phosphorylated or dephosphorylated, thereby enhancing or inhibiting subsequent phagosome maturation, respectively. These findings have increased our understanding of the SNAP23-associated membrane trafficking mechanism in phagocytes, which has important implications for microbial pathogenesis and innate and adaptive immune responses.

Characterization of MORN2 stability and regulatory function in LC3-associated phagocytosis in macrophages

Microtubule-associated protein A1/B1-light chain 3 (LC3)-associated phagocytosis (LAP) is a type of non-canonical autophagy that regulates phagosome maturation in macrophages. However, the role and regulatory mechanism of LAP remain largely unknown. Recently, the membrane occupation and recognition nexus repeat-containing-2 (MORN2) was identified as a key component of LAP for the efficient formation of LC3-recruiting phagosomes. To characterize MORN2 and elucidate its function in LAP, we established a MORN2-overexpressing macrophage line. At a steady state, MORN2 was partially cleaved by the ubiquitin-proteasome system. MORN2 overexpression promoted not only LC3-II production but also LAP phagosome (LAPosome) acidification during Escherichia coli uptake. Furthermore, the formation of LAPosomes containing the yeast cell wall component zymosan was enhanced in MORN2-overexpressing cells and depended on reactive oxygen species (ROS). Finally, MORN2-mediated LAP was regulated by plasma membrane-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) such as SNAP-23 and syntaxin 11. Taken together, these findings demonstrate that MORN2, whose expression is downregulated via proteasomal digestion, is a limiting factor for LAP, and that membrane trafficking by SNARE proteins is involved in MORN2-mediated LAP.