Raptor/mTORC1 Acts as a Modulatory Center to Regulate Anti-bacterial Immune Response in Rockfish

Arthropod autophagy molecules facilitate Anaplasma phagocytophilum infection of Ixodes scapularis tick cells

Ixodes scapularis ticks transmit several medically important pathogens including Anaplasma phagocytophilum to humans and animals. In this study, we provide evidence that A. phagocytophilum modulates autophagy molecules for its survival in tick cells. qRT-PCR analysis revealed that A. phagocytophilum infection results in the upregulation of tyrosine phosphatase, shp-2, and serine/threonine-protein kinase, mTOR, in ticks and tick cells. RNAi-mediated knockdown of shp-2 or functional blocking with SHP-2 inhibitor resulted in significantly increased bacterial burden and reduced phospho-mTOR levels in A. phagocytophilum-infected tick cells. In addition, treatment of A. phagocytophilum-infected tick cells with rapamycin (mTOR inhibitor) resulted in significantly increased bacterial burden and reduced phospho-mTOR levels. Furthermore, expression of autophagy molecules such as atg14 and ulk1 were noted to be upregulated in both A. phagocytophilum-infected unfed ticks and tick cells. RNAi-mediated silencing of atg14 or ulk1 affected bacterial growth in tick cells. Collectively, these results not only indicate distinct host and pathogen responses in tick-A. phagocytophilum interactions but also suggest that this bacterium modulates autophagy molecules for its survival in ticks.

Cellular evidence and spatial distribution of endosomal biosynthesis and autophagy in intestinal immune barrier cells of crucian carp (Carassiuscarassius)

Crucian carp (Carassius carassius) is an important aquatic economic animal, and the immune barrier function of its intestine has been a focus of research into oral vaccines and drugs. However, the histological structures of the intestinal barrier and its adjacent areas have not been clearly established, and little subcellular evidence is available to elucidate the spatial distribution of intracellular biological processes. In this study, the spatial distribution of autophagy and endosome formation in the intestinal epithelial cells (IECs) of crucian carp were analyzed. These two biological activities are closely related to intestinal homeostasis, immunity, and cell communication. Periodic acid-Schiff (PAS) and Masson's trichrome staining were employed to elucidate the distinctive histological framework of the Crucian carp's myoid cell network, which resides within the subepithelial layer and is characterized by gap junctions. Transmission electron microscopy (TEM), immunohistochemistry (IHC), and immunofluorescence (IF) were used to detect the structural and functional aspects of the IEC in different intestinal segments. TEM and immunohistochemical analyses captured the biogenesis and maturation of early and late endosomes as well as multivesicular bodies (MVBs), as well as the initiation and progression of autophagy, including macroautophagy and mitophagy. The endosome and MVBs-specific marker CD63 and autophagy-related protein LC3 were highly expressed in IECs and were correlated with autophagy and endosome biosynthesis in the apical and basal regions of individual cells, and differed between different intestinal segments. In summary, this study elucidated the ubiquity and morphological characteristics of autophagy and endosome formation across different intestinal segments of crucian carp. A unique myoid cell network beneath the intestinal epithelium in crucian carp was also identified, expanding the histological understanding of this animal's intestinal tract.

mTOR (Mammalian Target of Rapamycin): Hitting the Bull's Eye for Enhancing Neurogenesis After Cerebral Ischemia?

Ischemic stroke remains a leading cause of morbidity and disability around the world. The sequelae of serious neurological damage are irreversible due to body's own limited repair capacity. However, endogenous neurogenesis induced by cerebral ischemia plays a critical role in the repair and regeneration of impaired neural cells after ischemic brain injury. mTOR (mammalian target of rapamycin) kinase has been suggested to regulate neural stem cells ability to self-renew and differentiate into proliferative daughter cells, thus leading to improved cell growth, proliferation, and survival. In this review, we summarized the current evidence to support that mTOR signaling pathways may enhance neurogenesis, angiogenesis, and synaptic plasticity following cerebral ischemia, which could highlight the potential of mTOR to be a viable therapeutic target for the treatment of ischemic brain injury.

Antigen Presentation and Autophagy in Teleost Adaptive Immunity

Infectious diseases are a burden for aquaculture. Antigen processing and presentation (APP) to the immune effector cells that fight pathogens is key in the adaptive immune response. At the core of the adaptive immunity that appeared in lower vertebrates during evolution are the variable genes encoding the major histocompatibility complex (MHC). MHC class I molecules mainly present peptides processed in the cytosol by the proteasome and transported to the cell surface of all cells through secretory compartments. Professional antigen-presenting cells (pAPC) also express MHC class II molecules, which normally present peptides processed from exogenous antigens through lysosomal pathways. Autophagy is an intracellular self-degradation process that is conserved in all eukaryotes and is induced by starvation to contribute to cellular homeostasis. Self-digestion during autophagy mainly occurs by the fusion of autophagosomes, which engulf portions of cytosol and fuse with lysosomes (macroautophagy) or assisted by chaperones (chaperone-mediated autophagy, CMA) that deliver proteins to lysosomes. Thus, during self-degradation, antigens can be processed to be presented by the MHC to immune effector cells, thus, linking autophagy to APP. This review is focused on the essential components of the APP that are conserved in teleost fish and the increasing evidence related to the modulation of APP and autophagy during pathogen infection.

Matrix metalloproteinase-25 from Japanese sea bass (Lateolabrax japonicus) is involved in pro-inflammatory responses

Matrix metalloproteinases (MMPs) are highly expressed in leukocytes and macrophages, which play a role in the innate immune response. Here, the cDNA sequence of MMP25 from Japanese sea bass (Lateolabrax japonicus) (LjMMP25) was identified. Phylogenetic analysis revealed that LjMMP25 was most closely related to large yellow croaker MMP25. Multiple sequence alignment of LjMMP25 with MMP25 sequences from other teleosts revealed that regions of known functional importance were highly conserved. Expression analysis revealed that LjMMP25 was highly expressed in the head kidney and widely expressed in other tissues including gill, spleen, and liver. LjMMP25 was found to regulate inflammatory cytokine production and promote phagocytosis and bacterial killing in monocytes/macrophages (MO/MФ). Furthermore, LjMMP25 regulated the inflammatory response by modulating NF-κB signaling. These findings reveal new information about the role of LjMMP25 in regulating pro-inflammatory responses in this species.

Modulation of Sirt1-mTORC1 Pathway in Microglia Attenuates Retinal Ganglion Cell Loss After Optic Nerve Injury

Purpose

Optic nerve injury (ONI) causes neuroinflammation and neurodegeneration leading to visual deficits. The response of microglia has emerged as an impactful component of etiology in neurodegeneration. This study aimed to investigate the effect of SIRT1-mTORC1 signaling pathway in microglia regulation after ONI.

Methods

Cx3Cr1-Cre^ERT2/Raptor^F/F and Cx3Cr1-Cre^ERT2/Sirt1^F/F mice were used to delete Raptor and Sirt1 in microglia, respectively. Optic nerve crush (ONC) model was established to mimic ONI. PLX5622, a highly specific inhibitor of the colony-stimulating factor 1 receptor (CSF1R), is used to eliminate microglia in optic nerve. Ionized calcium binding adaptor molecule 1 (Iba1) immunostaining was used to detect microglial activation. Retinal ganglion cells (RGCs) were quantified by Nissl staining and retinal whole-mount immunostaining with RNA-binding protein with multiple splicing (RBPMS). Axonal damage was valued by transmission electron microscopy (TEM).

Results

Microglial activation emerged on day 3 post ONC and was earlier than RGCs loss which occurred at day 5 after injury. Depleting microglia with PLX5622 could attenuate the loss of RGCs and axon damage after ONC. Gain- and loss-of-function studies revealed that SIRT1 determined the activation of microglia in optic nerve. In addition, microglia-specific deletion of Raptor resulted in decreased microglial activation. Interestingly, activating mTORC1 with CCT007093 could reverse the function of SIRT1 in regulating the process of microglial activation mediated RGCs loss.

Conclusion

Our study reveals a potential novel mechanism of SIRT1-mTORC1 pathway in microglia regulation, and indicates a therapeutic potential for the protection of RGCs in ONI.

Identification of Antimicrobial Peptide Genes in Black Rockfish Sebastes schlegelii and Their Responsive Mechanisms to Edwardsiella tarda Infection

The black rockfish, Sebastes schlegelii, is a typical viviparous teleost, which belongs to the family Scorpaenidae. Due to its high economic and ecological values, S. schlegelii has been widely cultured in East Asian countries. With the enlargement of cultivation scale, bacterial and viral diseases have become the main threats to the farming industry of S. schlegelii, which have resulted in significant economic losses. In this study, Illumina shotgun sequencing, single-molecule real-time (SMRT) sequencing, 10× genomics and high-throughput chromosome conformation capture (Hi-C) technologies were collectively applied to assemble the genome of S. schlegelii. Then, we identified the antimicrobial peptide genes (AMPs) in the S. schlegelii genome. In total, 214 AMPs were identified in the S. schlegelii genome, which can be divided into 33 classes according to the annotation and cataloging of the Antimicrobial Peptides Database (APD3). Among these AMPs, thrombin-derived C-terminal peptide (TCP) was the dominant type, followed by RegIIIgamma and chemokine. The amino acid sequences of the TCP, cgUbiquitin, RegIIIalpha, RegIIIgamma, chemokine shared 32.55%, 42.63%, 29.87%, 28.09%, and 32.15% similarities among the same type in S. schlegelii. Meanwhile, the expression patterns of these AMPs in nine healthy tissues and at different infection time points in intestine were investigated. The results showed that the numbers and types of AMPs that responded to Edwardsiella tarda infection gradually increased as the infection progressed. In addition, we analyzed the phylogenetic relationships of hepcidins in teleost. The identification of AMPs based on the whole genome could provide a comprehensive database of potential AMPs, and benefit for the understanding of the molecular mechanisms of immune responses to E. tarda infection in S. schlegelii. This would further offer insights into an accurate and effective design and development of AMP for aquaculture therapy in the future.

The Amino Acid-mTORC1 Pathway Mediates APEC TW-XM-Induced Inflammation in bEnd.3 Cells

The blood-brain barrier (BBB) is key to establishing and maintaining homeostasis in the central nervous system (CNS); meningitis bacterial infection can disrupt the integrity of BBB by inducing an inflammatory response. The changes in the cerebral uptake of amino acids may contribute to inflammatory response during infection and were accompanied by high expression of amino acid transporters leading to increased amino acid uptake. However, it is unclear whether amino acid uptake is changed and how to affect inflammatory responses in mouse brain microvascular endothelial (bEnd.3) cells in response to Avian Pathogenic Escherichia coli TW-XM (APEC XM) infection. Here, we firstly found that APEC XM infection could induce serine (Ser) and glutamate (Glu) transport from extracellular into intracellular in bEnd.3 cells. Meanwhile, we also shown that the expression sodium-dependent neutral amino acid transporter 2 (SNAT2) for Ser and excitatory amino acid transporter 4 (EAAT4) for Glu was also significantly elevated during infection. Then, in amino acid deficiency or supplementation medium, we found that Ser or Glu transport were involving in increasing SNAT2 or EAAT4 expression, mTORC1 (mechanistic target of rapamycin complex 1) activation and inflammation, respectively. Of note, Ser or Glu transport were inhibited after SNAT2 silencing or EAAT4 silencing, resulting in inhibition of mTORC1 pathway activation, and inflammation compared with the APEC XM infection group. Moreover, pEGFP-SNAT2 overexpression and pEGFP-EAAT4 overexpression in bEnd.3 cells all could promote amino acid uptake, activation of the mTORC1 pathway and inflammation during infection. We further found mTORC1 silencing could inhibit inflammation, the expression of SNAT2 and EAAT4, and amino acid uptake. Taken together, our results demonstrated that APEC TW-XM infection can induce Ser or Glu uptake depending on amino acid transporters transportation, and then activate amino acid-mTORC1 pathway to induce inflammation in bEnd.3 cells.

Complement genes in black rockfish (Sebastods schlegelii): genome-wide identification, evolution and their potential functions in response to Vibrio anguillarum infection

As complex components of innate immune system, members of complement system play crucial roles during the process of defensing against pathogens. Black rockfish (Sebastes schlegelii) is one of the important aquaculture species in East Asian. However, studies of complement genes in black rockfish and its related immune activities are still lacking. Therefore, a total of 112 members of the complement genes were identified from the genome of black rockfish and were classified into five subgroups. According to their functional annotations, 30 genes belonged to pattern recognition, 6 genes belonged to proteases, 14 genes belonged to complement components, 36 genes belonged to receptors, and 26 genes belonged to regulators. It can be found that many complement genes evolved into multi-copies, especially in teleost, which may be influenced by whole-genome duplication or tandem duplication events. Complement genes were randomly distributed on 22 chromosomes. The number of introns of complement genes varied from 1 to 70. Results of the expression patterns of 10 randomly selected genes from 5 subtypes response to Vibrio anguillarum infection revealed that most of the members of the complement genes were induced in gill and skin. In contrast, most genes in intestine showed downregulation. This study systematically characterized and analyzed the complement genes in black rockfish and provided new insights into their functions responding to bacterial infection.

Prepubertal gonad investment modulates thymus function: evidence in a teleost fish

Thymus plasticity following gonadectomy or sex hormone replacement has long since exemplified sex hormone effects on the immune system in mammals and, to a lesser extent, in 'lower vertebrates', including amphibians and fish. Nevertheless, the underlying physiological significances as well as the ontogenetic establishment of this crosstalk remain largely unknown. Here, we used a teleost fish, the European sea bass, Dicentrarchus labrax, to investigate: (1) whether the regulation of thymus plasticity relies on resource trade-off with somatic growth and reproductive investment and (2) if the gonad-thymus interaction takes place during gonadal differentiation and development. Because gonadal development and, supposedly, thymus function in sea bass depend on environmental changes associated with the winter season, we evaluated thymus changes (foxn1 expression, and thymocyte and T cell content) in juvenile D. labrax raised for 1 year under either constant or fluctuating photoperiod and temperature. Importantly, in both conditions, intensive gonadal development following sex differentiation coincided with a halt of thymus growth, while somatic growth continued. To the best of our knowledge, this is the first study showing that gonadal development during prepuberty regulates thymus plasticity. This finding may provide an explanation for the initiation of the thymus involution related to ageing in mammals. Comparing fixed and variable environmental conditions, our work also demonstrates that the extent of the effects on the thymus, which are related to reproduction, depend on ecophysiological conditions, rather than being directly related to sexual maturity and sex hormone levels.

S6K1/S6 axis-regulated lymphocyte activation is important for adaptive immune response of Nile tilapia

Ribosomal protein S6 kinase beta-1 (S6K1) is a serine/threonine kinase downstream of the mechanistic target of rapamycin (mTOR) pathway, and plays crucial roles in immune regulation. Although remarkable progress has been achieved with a mouse model, how S6K1 regulates adaptive immunity is largely unknown in early vertebrates. In this study, we identified an S6K1 from Nile tilapia Oreochromis niloticus (OnS6K1), and further investigated its potential regulatory role on the adaptive immunity of this fish species. Both sequence and structure of OnS6K1 were highly conserved with its homologs from other vertebrates and invertebrates. OnS6K1 was widely expressed in immune tissues, and with a relative higher expression level in the liver, spleen and head kidney. At the adaptive immune stage of Nile tilapia that infected with Aeromonas hydrophila, mRNA expression of OnS6K1 and its downstream effector S6 was significantly up-regulated in spleen lymphocytes. Meanwhile, their phosphorylation level was also enhanced during this process, suggesting that S6K1/S6 axis participated in the primary response of anti-bacterial adaptive immunity in Nile tilapia. Furthermore, after spleen lymphocytes were activated by the T cell-specific mitogen PHA or lymphocytes agonist PMA in vitro, mRNA and phosphorylation levels of S6K1 were elevated, and phosphorylation of S6 was also enhanced. Once S6K1 activity was blocked by a specific inhibitor, both mRNA and phosphorylation levels of S6 were severely impaired. More importantly, blockade of S6K1/S6 axis reduced the expression of T cell activation marker IFN-γ and CD122 in PHA-activated spleen lymphocytes, indicating the essential role of S6K1/S6 axis in regulating T cell activation of Nile tilapia. Together, our study suggests that S6K1 and its effector S6 regulate lymphocyte activation of Nile tilapia, and in turn promote lymphocyte-mediated adaptive immunity. This study enriched the mechanism of adaptive immune response in teleost and provided useful clues to understand the evolution of adaptive immune system.