Dissecting the role of transforming growth factor-β1 in topmouth culter immunobiological activity: a fundamental functional analysis

Proteomic insights into extracellular matrix dynamics in the intestine of Labeo rohita during Aeromonas hydrophila infection

In the aquaculture sector, one of the challenges includes disease outbreaks such as bacterial infections, particularly from Aeromonas hydrophila (Ah), impacting both wild and farmed fish. In this study, we conducted a proteomic analysis of the intestinal tissue in Labeo rohita following Ah infection to elucidate the protein alterations and its implications for immune response. Our findings indicate significant dysregulation in extracellular matrix (ECM)-associated proteins during Ah infection, with increased abundance of elastin and collagen alpha-3(VI). Pathway and enrichment analysis of differentially expressed proteins highlights the involvement of ECM-related pathways, including focal adhesions, integrin cell surface interactions, and actin cytoskeleton organization. Focal adhesions, crucial for connecting intracellular actin bundles to the ECM, play a pivotal role in immune response during infections. Increased abundance of integrin alpha 1, integrin beta 1, and tetraspanin suggests their involvement in the host's response to Ah infection. Proteins associated with actin cytoskeleton reorganization, such as myosin, tropomyosin, and phosphoglucomutase, exhibit increased abundance, influencing changes in cell behavior. Additionally, upregulated proteins like LTBP1 and fibrillin-2 contribute to TGF-β signaling and focal adhesion, indicating their potential role in immune regulation. The study also identifies elevated levels of laminin, galectin 3, and tenascin-C, which interact with integrins and other ECM components, potentially influencing immune cell migration and function. These proteins, along with decorin and lumican, may act as immunomodulators, coordinating pro- and anti-inflammatory responses. ECM fragments released during pathogen invasion could serve as "danger signals," initiating pathogen clearance and tissue repair through Toll-like receptor signaling.

IMPORTANCE

The study underscores the critical role of the extracellular matrix (ECM) and its associated proteins in the immune response of aquatic organisms during bacterial infections like Aeromonas hydrophila. Understanding the intricate interplay between ECM alterations and immune response pathways provides crucial insights for developing effective disease control strategies in aquaculture. By identifying key proteins and pathways involved in host defense mechanisms, this research lays the groundwork for targeted interventions to mitigate the impact of bacterial infections on fish health and aquaculture production.

Repeated exposure affects susceptibility and responses of Atlantic salmon (Salmo salar) towards the ectoparasitic salmon lice (Lepeophtheirus salmonis)

Atlantic salmon (Salmo salar) is repeatedly exposed to and infected with ectoparasitic salmon lice (Lepeophtheirus salmonis) both in farms and in nature. However, this is not reflected in laboratory experiments where fish typically are infected only once. To investigate if a previous lice infection affects host response to subsequent infections, fish received 4 different experimental treatments; including 2 groups of fish that had previously been infected either with adult or infective salmon lice larvae (copepodids). Thereafter, fish in all treatment groups were infected with either a double or a single dose of copepodids originating from the same cohort. Fish were sampled when lice had developed into the chalimus, the pre-adult and the adult stage, respectively. Both the specific growth rate and cortisol levels (i.e. a proxy for stress) of the fish differed between treatments. Lice success (i.e. ability to infect and survive on the host) was higher in naïve than in previously infected fish (pre-adult stage). The expression of immune and wound healing transcripts in the skin also differed between treatments, and most noticeable was a higher upregulation early in the infection in the group previously infected with copepodids. However, later in the infection, the least upregulation was observed in this group, suggesting that previous exposure to salmon lice affects the response of Atlantic salmon towards subsequent lice infections.

Temperature affects settlement success of ectoparasitic salmon lice (Lepeophtheirus salmonis) and impacts the immune and stress response of Atlantic salmon (Salmo salar)

In this study, the effect of temperature on Atlantic salmon (Salmo salar) stress and immune response to the ectoparasitic salmon lice (Lepeophtheirus salmonis) was investigated. We found that infestation affected the expression of several immune and wound healing transcripts in the skin especially at the site of lice attachment compared to un-infested control fish. Moreover, expression patterns in the skin of infested fish suggest that host immune responses towards salmon lice are impaired at low temperatures. However, reduced lice infestation success and survival at the lowest investigated temperatures suggest that cold water temperatures are more detrimental to the lice than their fish hosts. Finally, temperature affected the stress response of the fish and infected fish had a higher increase in cortisol levels in response to handling (a stressor) than un-infested controls.

Structural and Functional Aspects of the Spleen in Molly Fish Poecilia sphenops (Valenciennes, 1846): Synergistic Interactions of Stem Cells, Neurons, and Immune Cells

In fish, the spleen is the prime secondary lymphoid organ. It has a role in the induction of adaptive immune responses, in addition to its significance in the elimination of immune complexes. This study was conducted on 18 randomly obtained adult molly fish (Poecilia sphenops) of both sexes using histological, immunohistochemical, and ultrastructural studies to highlight the cellular components of the spleen and their potential role in the immune system. The spleen of molly fish was characterized by the presence of well-distinct melanomacrophage centers, and other basic structures present in higher vertebrates including red and white pulps, blood vessels, and ellipsoids. Some mitotic cells could also be identified in the red pulp. Mast cells with characteristic metachromatic granules could be seen among the splenic cells. Rodlet cells were randomly distributed in the spleen and were also observed around the ellipsoids. The white pulp of the spleen expressed APG5. The expressions were well distinct in the melanomacrophages, leukocytes, and macrophages. Myostatin was expressed in leukocytes and epithelial reticular cells. IL-1β showed immunoreactivity in monocytes and macrophages around the ellipsoids. NF-κB and TGF-β were expressed in macrophages and epithelial reticular cells. Nrf2 expression was detected in stem cells and rodlet cells. Sox-9 had a higher expression in epithelial reticular cells and stem cells. The high frequency of immune cells in the spleen confirmed its role in the regulation of both innate and adaptive immunity, cell proliferation, and apoptosis.

Cytokines Studied in Carp (Cyprinus carpio L.) in Response to Important Diseases

Cytokines belong to the most widely studied group of intracellular molecules involved in the function of the immune system. Their secretion is induced by various infectious stimuli. Cytokine release by host cells has been extensively used as a powerful tool for studying immune reactions in the early stages of viral and bacterial infections. Recently, research attention has shifted to the investigation of cytokine responses using mRNA expression, an essential mechanism related to pathogenic and nonpathogenic-immune stimulants in fish. This review represents the current knowledge of cytokine responses to infectious diseases in the common carp (Cyprinus carpio L.). Given the paucity of literature on cytokine responses to many infections in carp, only select viral diseases, such as koi herpesvirus disease (KHVD), spring viremia of carp (SVC), and carp edema virus disease (CEVD), are discussed. Aeromonas hydrophila is one of the most studied bacterial pathogens associated with cytokine responses in common carp. Therefore, the cytokine-based immunoreactivity raised by this specific bacterial pathogen is also highlighted in this review.

A novel invertebrate toll-like receptor with broad recognition spectrum from thick shell mussel Mytilus coruscus

Toll-like receptors (TLRs) are a category of most well recognized pattern recognition molecules that act on a vital role in both innate and adaptive immunity. In the present study, a novel toll-like receptor (McTLRw) was identified and characterized in thick shell mussel Mytilus coruscus. McTLRw possesses one intracellular Toll/interleukin-1 (IL-1) receptor (TIR) domain, one transmembrane region (TM), one leucine rich repeat N-terminal domain (LRR_NT) and a few of leucine-rich repeats (LRRs), which all are common in typical TLRs. McTLRw transcripts were constitutively expressed in all examined tissues with higher expression levels in immune related tissues, and were significantly induced in haemocytes with the challenges of live Vibrio alginolyticus, lipopolysaccharide (LPS), peptidoglycans (PGN) and β-glucan (GLU), but not induced by polyinosinic-polycytidylic acid (poly I:C). rMcTLRw exhibited affinity to LPS, PGN and GLU while no affinity to poly I:C. Further, the downstream of TLR signaling pathway myeloid differentiation factor 88a (MyD88a), interleukin-1 receptor-associated kinase-4 (IRAK4) and tumor necrosis factor receptor-associated factor 6 (TRAF6) were significantly repressed in McTLRw silenced mussels while challenged with LPS. These results collectively indicated that McTLRw is one member of TLR family and involved in immune response to against invaders by taking participate in TLR mediated signaling pathway.

The receptor for activated C kinase 1 (RACK1) mediating immune response in thick shell mussel Mytilus coruscus

The receptor for activated C kinase 1 (RACK1) is a intracellular receptor for the protein kinase C family which mediates various biological processes. Here, a novel RACK1 gene termed Mc-RACK1 was identified from thick shell mussel, Mytilus coruscus. Mc-RACK1 shared typical RACK1 domains containing WD repeats, PKC phosphorylation sites, N-myristoylation sites, PKC activation sites, TK phosphorylation site and WD motifs. Mc-RACK1 was constitutively expressed in all examined tissues, and its expression in gills, haemocytes and digestive glands were significantly up-regulated upon LPS challenge. Mc-RACK1 showed a significantly down-regulated expression in gills and haemocytes at the early phase upon copper exposure. Mc-RACK1 in haemocytes was silenced after receiving its dsRNA, meanwhile, the increases of SOD and CAT activity were investigated. Further, Mc-RACK1 could activate the NF-κB and ISRE reporter in HEK-293T cells. These suggested that Mc-RACK1 had a deeper involvement in mollusc immunity, and played an important role in antioxidant system.

The complement factor H (CFH) and its related protein 2 (CFHR2) mediating immune response in large yellow croaker Larimichthys crocea

Complement is a complex innate immune surveillance system, playing a key role in host homeostasis, inflammation, and in the defense against pathogens. Complement regulators are crucial to prevent the injudicious production of these mediators and potential injury to self tissues. Here, we identified the complement factor H (CFH) and its related gene 2 (CFHR2) homologs from large yellow croaker (Larimichthys crocea), named LcCfh and LcCfhr2, respectively. The deduced LcCfh and LcCfhr2 proteins shared significant structural similarities and identified codes for a polypeptide consisting of various numbers of highly conserved SCR domains. LcCfh, LcCfhr1 and LcCfhr2 genes were detected in all examined tissues with predominantly expressions in liver, spleen and kidney, and their expressions all increased upon Vibrio alginolyticus challenge. In vitro assays showed that recombinant LcCfh was likely to act as a cofactor of CFI and played a negative regulation role in complement system, when recombinant LcCfhr2 seemed to play mechanisms independent of the activity of CFH. Both recombinant LcCfh and LcCfhr2 took participate in inflammatory reaction despite of the inequal ability to mediate pro-inflammation response. These data provide a new insight into the functional activities of teleost complement system.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.