Effect of low-dose Piscirickettsia salmonis infection on haematological-biochemical blood parameters in Atlantic salmon (Salmo salar)

Piscirickettsia salmonis is the etiological agent of Piscirickettsiosis, a severe disease that affects Atlantic salmon (Salmo salar) farmed in Chile and many other areas (Norway, Scotland, Ireland, Canada and the USA). This study investigated the effects of low-dose P. salmonis infection (1 × 10²  CFU/ml) on Atlantic salmon. In this study, we challenged fish with an isolated representative of the EM-90 genogroup via intraperitoneal injection for 42 days. Infected fish displayed decreased haematocrit and haemoglobin levels at day 13 post-infection, indicating erythropenia, haemolysis and haemodilution. Conversely, their white blood cell counts increased on days 13 and 21 post-infection. Additionally, their iron levels decreased from day 2 post-infection, indicating iron deficiency and an inability to retrieve stored iron before infection. Their magnesium levels also decreased at day 28 post-infection, possibly due to osmoregulatory problems. Also, we observed an increase in lactate dehydrogenase activity on days 5, 21, and 28 post-infection, suggesting early symptoms of hepatotoxicity. Later analyses determined a decrease in plasma glucose levels from day 2 post-infection. This may be attributed to the hypoxic conditions caused by P. salmonis, leading to an excess utilization of stored carbohydrates. Our results suggest that the blood parameters we studied are useful for monitoring the physiological status of Atlantic salmon infected with P. salmonis.

Protein-Based Vaccine Protect Against Piscirickettsia salmonis in Atlantic Salmon (Salmo salar)

An effective and economical vaccine against the Piscirickettsia salmonis pathogen is needed for sustainable salmon farming and to reduce disease-related economic losses. Consequently, the aquaculture industry urgently needs to investigate efficient prophylactic measures. Three protein-based vaccine prototypes against Piscirickettsia salmonis were prepared from a highly pathogenic Chilean isolate. Only one vaccine effectively protected Atlantic salmon (Salmo salar), in correlation with the induction of Piscirickettsia-specific IgM antibodies and a high induction of transcripts encoding pro-inflammatory cytokines (i.e., Il-1β and TNF-α). In addition, we studied the proteome fraction protein of P. salmonis strain Austral-005 using multidimensional protein identification technology. The analyzes identified 87 proteins of different subcellular origins, such as the cytoplasmic and membrane compartment, where many of them have virulence functions. The other two prototypes activated only the innate immune responses, but did not protect Salmo salar against P. salmonis. These results suggest that the knowledge of the formulation of vaccines based on P. salmonis proteins is useful as an effective therapy, this demonstrates the importance of the different research tools to improve the study of the different immune responses, resistance to diseases in the Atlantic salmon. We suggest that this vaccine can help prevent widespread infection by P. salmonis, in addition to being able to be used as a booster after a primary vaccine to maintain high levels of circulating protective antibodies, greatly helping to reduce the economic losses caused by the pathogen.

Subcellular Location of Piscirickettsia salmonis Heat Shock Protein 60 (Hsp60) Chaperone by Using Immunogold Labeling and Proteomic Analysis

Piscirickettsia salmonis is the causative bacterial agent of piscirickettsiosis, a systemic fish disease that significantly impacts the Chilean salmon industry. This bacterium possesses a type IV secretion system (T4SS), several proteins of the type III secretion system (T3SS), and a single heat shock protein 60 (Hsp60/GroEL). It has been suggested that due to its high antigenicity, the P. salmonis Hsp60 could be surface-exposed, translocated across the membrane, and (or) secreted into the extracellular matrix. This study tests the hypothesis that P. salmonis Hsp60 could be located on the bacterial surface. Immunogold electron microscopy and proteomic analyses suggested that although P. salmonis Hsp60 was predominantly associated with the bacterial cell cytoplasm, Hsp60-positive spots also exist on the bacterial cell envelope. IgY antibodies against P. salmonis Hsp60 protected SHK-1 cells against infection. Several bioinformatics approaches were used to assess Hsp60 translocation by the T4SS, T3SS, and T6SS, with negative results. These data support the hypothesis that small amounts of Hsp60 must reach the bacterial cell surface in a manner probably not mediated by currently characterized secretion systems, and that they remain biologically active during P. salmonis infection, possibly mediating adherence and (or) invasion.

Analysis of single nucleotide polymorphisms (SNPs) associated with antibiotic resistance genes in Chilean Piscirickettsia salmonis strains

The aetiological agent of Piscirickettsiosis is Piscirickettsia salmonis, a Gram-negative intracellular pathogen, and high doses of antibiotics have regularly been employed to treat this infection. Seven florfenicol and/or oxytetracycline resistance genes (tet pump, tetE, Tclor/flor, Tbcr, TfloR, ompF and mdtN) were identified in strains by in silico genome analyses. Later, the number of single nucleotide polymorphisms (SNPs) and its relationship with the resistance to these antibiotics were identified and analysed, using the original LF-89 strain as reference. Trials to determine and compare the minimum inhibitory concentration (MIC) of oxytetracycline and florfenicol in each strain, as well as to quantify the gPCR transcripts levels in the selected genes, were performed. Therefore, variations in the resistance to both antibiotics were observed, where the strain with fewer SNPs showed the highest susceptibility. Consistently, the in silico 3D analyses of proteins encoded by the selected genes revealed structural changes, evident in the sequences with the highest number of SNPs. These results showed that the bacterial resistance to oxytetracycline was mainly linked to the presence of SNPs in relevant sites, antibiotic resistance genes and an OmpF porin, leading to important changes in the protein structure.

In vitro genomic and proteomic evidence of a type IV pili-like structure in the fish pathogen Piscirickettsia salmonis

Piscirickettsia salmonis is an intracellular γ-proteobacteria and the etiological agent of piscirickettsiosis, which causes massive economic losses in the Chilean salmon industry. The type IV pili (T4P) play an important role in adherence to host cell surfaces and bacterial pathogenicity. T4P contains a variable number of components, as predicted in P. salmonis genomes. However, no studies have determined if P. salmonis possesses T4P. The aims of this investigation were to identify T4P components in the P. salmonis type strain LF-89T, evaluate respective transcript expressions, and analyze the main putative T4P proteins using bioinformatics and proteomic approaches. Two main clusters of P. salmonis T4P genes were found. Expression of the pilA gene was upregulated at 4 h post-infection (hpi), while pilQ was upregulated 4 days post-infection. At 16 hpi, pilB and pilD were strongly upregulated. The PilA amino acid sequence analysis showed a conserved N-terminal domain and sequence motifs critical for T4P biosynthesis. MudPIT analysis revealed PilA in the P. salmonis LF-89T proteome, and TEM showed pili-like filamentous structures on the P. salmonis surface. These results strongly suggest the presence of a T4P-like structure in P. salmonis.

High doses of Francisella noatunensis induces an immune response in Eleginops maclovinus

Francisella noatunensis subsp. noatunensis, the etiological agent of Francisellosis, affects a large number of farmed species such as Salmo salar. This species coexists with several native species in the same ecosystem, including Eleginops maclovinus. Our objective was to evaluate the susceptibility, presence of clinical symptoms, and the ability of Eleginops maclovinus to respond to Francisella infection. For this, healthy individuals were inoculated with 1.5 × 10¹, 1.5 × 10⁵, and 1.5 × 10¹⁰ bact/μL of Francisella by intraperitoneal injection, subsequently the fish were sampled on days 1, 3, 7, 14, 21, and 28 post injection (dpi). At the end of the experiment, no mortality, nor internal and external clinical signs were observed, although in the high dose anaemia was detected. Additionally, bacteria were detected in all three doses, however there was replication at day 28 only in the liver in the high dose. Analysis of gene expression by qPCR showed that the spleen generated an immune response against infection from day 1 dpi, however at day 7 dpi most of the genes suffered repressed expression; observing over expression of the genes C3, NLRC3, NLRC5, MHCI, IgM. In contrast, expression in the anterior kidney did not vary significantly during the challenge. IgM quantification showed the production of antibodies in the medium and high doses. This study provides new knowledge about Francisella infection and the long-lasting and specific immune response generated by Eleginops maclovinus. It also demonstrates its susceptibility to Francisellosis where there is a difference in the immune response according to the tissue.

Cytosolic phosphoenolpyruvate carboxykinase is expressed in α-cells from human and murine pancreas

The pancreatic islets of Langerhans, mainly formed by glucagon-producing α-cells and insulin-producing β-cells, are critical for glucose homeostasis. Insulin and glucagon oppositely modulate blood glucose levels in health, but a combined decline in insulin secretion together with increased glucagon secretion contribute to hyperglycemia in diabetes. Despite this bi-hormonal dysregulation, most studies have focused on insulin secretion and much less is known about glucagon secretion. Therefore, a deeper understanding of α-cell metabolism and glucagon secretion is of great interest. Here, we show that phosphoenolpyruvate carboxykinase (PCK1), an essential cataplerotic enzyme involved in metabolism and long considered to be absent from the pancreatic islet, is expressed in pancreatic α-cells of both murine and human. Furthermore, PCK1 transcription is induced by fasting and diabetes in rat pancreas, which indicates that the PCK1 activity is required for α-cell adaptation to different metabolic states. To our knowledge, this is the first evidence implicating PCK1 expression in α-cell metabolism.

Comparative Genomic Analysis of Two Chilean Renibacterium salmoninarum Isolates and the Type Strain ATCC 33209T

Renibacterium salmoninarum, a slow-growing facultative intracellular pathogen belonging to the high C + G content Actinobacteria phylum, is the causative agent of bacterial kidney disease, a progressive granulomatous infection affecting salmonids worldwide. This Gram-positive bacterium has existed in the Chilean salmonid industry for >30 years, but little or no information is available regarding the virulence mechanisms and genomic characteristics of Chilean isolates. In this study, the genomes of two Chilean isolates (H-2 and DJ2R) were sequenced, and a search was conducted for genes and proteins involved in virulence and pathogenicity, and we compare with the type strain ATCC 33209 ^T genome. The genome sizes of H-2 and DJ2R are 3,155,332 bp and 3,155,228 bp, respectively. They genomes presented six ribosomal RNA, 46 transcription RNA, and 25 noncodingRNA, and both had the same 56.27% G + C content described for the type strain ATCC 33209 ^T. A total of 3,522 and 3,527 coding sequences were found for H-2 and DJ2R, respectively. Meanwhile, the ATCC 33209 ^T type strain had 3,519 coding sequences. The in silico genome analysis revealed a genes related to tricarboxylic acid cycle, glycolysis, iron transport and others metabolic pathway. Also, the data indicated that R salmoninarum may have a variety of possible virulence-factor and antibiotic-resistance strategies. Interestingly, many of genes had high identities with Mycobacterium species, a known pathogenic Actinobacteria bacterium. In summary, this study provides the first insights into and initial steps towards understanding the molecular basis of antibiotic resistance, virulence mechanisms and host/environment adaptation in two Chilean R. salmoninarum isolates that contain proteins of which were similar to those of Mycobacterium. Furthermore, important information is presented that could facilitate the development of preventive and treatment measures against R. salmoninarum in Chile and worldwide.

Temperature modulates the immunological response of the sub-antarctic notothenioid fish Eleginops maclovinus injected with Piscirickettsia salmonis

Eleginops maclovinus is a eurythermic fish that under natural conditions lives in environments with temperatures ranging from 4 to 18 °C and can be usually captured near salmon farming areas. The aim of this study was to evaluate the effect of temperature over the innate and adaptive immune response of E. maclovinus challenged with Piscirickettsia salmonis following different treatments: C (control injection with culture medium at 12 °C), C+ (bacterial injection at 12 °C), 18 °C c/A + B (injection with culture medium in acclimation at 18 °C), 18 °C c/A + B (bacterial injection in acclimation at 18 °C), 18 °C s/A + M (injection with culture medium without acclimation at 18 °C) and 18 °C s/A + B (bacterial injection without acclimation at 18 °C). Each injection had 100 μL of culture medium or with 100 μL at a concentration 1 × 10⁸ of live bacteria, sampling six fish per group at 4, 8, 12, 16 and 20 days post-injection (dpi). Expression of the mRNA related with the innate immune response gene (TLR1, TLR5, TLR8, NLRC3, NLRC5, MyD88 and IL-1β) as well as the adaptive immune response gene (MHCI, MHCII, IgMs and IgD) were measured in spleen and head kidney. Gene expression profiles were treatment-type and time dependent. Levels of Immunoglobulin M (IgM) increased in challenged groups with P. salmonis from day 8-20 post challenge, which suggest activation of B cells IgM + through P. salmonis epitope detection. Additionally, a rise in temperature from 12 °C (C+) to 18 °C (with/without acclimation) also resulted in antibody increment detected in serum with significant differences between "18 °C c/A + B" and "18 °C s/A + B" groups. This is the first study that evaluates the effect of temperature changes and mRNA expression related with immune system gene over time on E. maclovinus, a native wild life fish that cohabits in the salmon farming environment.

Immunological response of the Sub-Antarctic Notothenioid fish Eleginops maclovinus injected with two strains of Piscirickettsia salmonis

Eleginops maclovinus is an endemic fish to Chile that lives in proximity to salmonid culture centers, feeding off of uneaten pellet and salmonid feces. Occurring in the natural environment, this interaction between native and farmed fish could result in the horizontal transmission of pathogens affecting the aquaculture industry. The aim of this study was to evaluate the innate and adaptive immune responses of E. maclovinus challenged with P. salmonis. Treatment injections (in duplicate) were as follows: control (100 μL of culture medium), wild type LF-89 strain (100 μL, 1 × 10⁸ live bacteria), and antibiotic resistant strain Austral-005 (100 μL, 1 × 10⁸ live bacteria). The fish were sampled at various time-points during the 35-day experimental period. The gene expression of TLRs (1, 5, and 8), NLRCs (3 and 5), C3, IL-1β, MHCII, and IgMs were significantly modulated during the experimental period in both the spleen and gut (excepting TLR1 and TLR8 spleen expressions), with tissue-specific expression profiles and punctual differences between the injected strains. Anti-P. salmonis antibodies increased in E. maclovinus serum from day 14-28 for the LF-89 strain and from day 14-35 for the Austral-005 strain. These results suggest temporal activation of the innate and adaptive immune responses in E. maclovinus tissues when injected by distinct P. salmonis strains. The Austral-005 strain did not always cause the greatest increases/decreases in the number of transcripts, so the magnitude of the observed immune response (mRNA) may not be related to antibiotic resistance. This is the first immunological study to relate a pathogen widely studied in salmonids with a native fish.

The Antidiabetic Agent Sodium Tungstate Induces Abnormal Glycogen Accumulation in Renal Proximal Tubules from Diabetic IRS2-Knockout Mice

The kidney is an insulin-sensitive organ involved in glucose homeostasis. One major effect of insulin is to induce glycogen storage in the liver and muscle. However, no significant glycogen stores are detected in normal kidneys, but diabetic subjects present a characteristic renal histopathological feature resulting from extensive glycogen deposition mostly in nonproximal tubules. The mechanism of renal glycogen accumulation is yet poorly understood. Here, we studied in situ glycogen accumulation in the kidney from diabetic IRS2-knockout mice and the effect of the insulin-mimetic agent sodium tungstate (NaW). IRS2-knockout mice displayed hyperglycemia and hyperinsulinemia. NaW only normalized glycemia. There was no evident morphological difference between kidneys from untreated wild-type (WT), NaW-treated WT, and untreated IRS2-knockout mice. However, NaW-treated IRS2-knockout mice showed tubular alterations resembling clear cells in the cortex, but not in the outer medulla, that were correlated with glycogen accumulation. Immunohistochemical detection of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase, mostly expressed by renal proximal tubules, showed that altered tubules were of proximal origin. Our preliminary study suggests that IRS2 differentially regulates glycogen accumulation in renal tubules and that NaW treatment in the context of IRS2 ablation induces abnormal glycogen accumulation in cortical proximal tubules.

The Proteome of Biologically Active Membrane Vesicles from Piscirickettsia salmonis LF-89 Type Strain Identifies Plasmid-Encoded Putative Toxins

Piscirickettsia salmonis is the predominant bacterial pathogen affecting the Chilean salmonid industry. This bacterium is the etiological agent of piscirickettsiosis, a significant fish disease. Membrane vesicles (MVs) released by P. salmonis deliver several virulence factors to host cells. To improve on existing knowledge for the pathogenicity-associated functions of P. salmonis MVs, we studied the proteome of purified MVs from the P. salmonis LF-89 type strain using multidimensional protein identification technology. Initially, the cytotoxicity of different MV concentration purified from P. salmonis LF-89 was confirmed in an in vivo adult zebrafish infection model. The cumulative mortality of zebrafish injected with MVs showed a dose-dependent pattern. Analyses identified 452 proteins of different subcellular origins; most of them were associated with the cytoplasmic compartment and were mainly related to key functions for pathogen survival. Interestingly, previously unidentified putative virulence-related proteins were identified in P. salmonis MVs, such as outer membrane porin F and hemolysin. Additionally, five amino acid sequences corresponding to the Bordetella pertussis toxin subunit 1 and two amino acid sequences corresponding to the heat-labile enterotoxin alpha chain of Escherichia coli were located in the P. salmonis MV proteome. Curiously, these putative toxins were located in a plasmid region of P. salmonis LF-89. Based on the identified proteins, we propose that the protein composition of P. salmonis LF-89 MVs could reflect total protein characteristics of this P. salmonis type strain.

Nutritional Immunity Triggers the Modulation of Iron Metabolism Genes in the Sub-Antarctic Notothenioid Eleginops maclovinus in Response to Piscirickettsia salmonis

Iron deprivation is a nutritional immunity mechanism through which fish can limit the amount of iron available to invading bacteria. The aim of this study was to evaluate the modulation of iron metabolism genes in the liver and brain of sub-Antarctic notothenioid Eleginops maclovinus challenged with Piscirickettsia salmonis. The specimens were inoculated with two P. salmonis strains: LF-89 (ATCC^® VR-1361™) and Austral-005 (antibiotic resistant). Hepatic and brain samples were collected at intervals over a period of 35 days. Gene expression (by RT-qPCR) of proteins involved in iron storage, transport, and binding were statistically modulated in infected fish when compared with control counterparts. Specifically, the expression profiles of the transferrin and hemopexin genes in the liver, as well as the expression profiles of ferritin-M, ferritin-L, and transferrin in the brain, were similar for both experimental groups. Nevertheless, the remaining genes such as ferritin-H, ceruloplasmin, hepcidin, and haptoglobin presented tissue-specific expression profiles that varied in relation to the injected bacterial strain and sampling time-point. These results suggest that nutritional immunity could be an important immune defense mechanism for E. maclovinus against P. salmonis injection. This study provides relevant information for understanding iron metabolism of a sub-Antarctic notothenioid fish.

In vitro expression of Sec-dependent pathway and type 4B secretion system in Piscirickettsia salmonis

Piscirickettsia salmonis is an intracellular bacterium and the causative agent of Piscirickettsiosis, a disease responsible for considerable mortalities in the Chilean salmon farming industry. Currently, P. salmonis protein translocation across the membrane and the mechanisms by which virulence factors are delivered to host cells are poorly understood. However, it is known that Gram-negative bacteria possess several mechanisms that transport proteins to the periplasmic and extracellular compartments. The aim of this study was to evaluate the expressional changes of several genes in the P. salmonis Sec-dependent pathway and type 4B secretion system during in vitro infection. Genes homologous and the main proteins belonging to Sec-dependent pathway and Type 4 Dot/Icm secretion system were found in the genome and proteome of P. salmonis AUSTRAL-005 strain. Additionally, several genes of these protein transport mechanisms were overexpressed during in vitro P. salmonis infection in SHK-1 cell line. The obtained data indicate that the Sec-dependent pathway and Type 4B secretion system are biologically active during P. salmonis infection. These mechanisms could contribute to the recycling of proteins into the inner and outer bacterial membrane and in translocate virulence factors to infected cell, which would favor the structural integrity and virulence of this bacterium.

Membrane vesicles from Piscirickettsia salmonis induce protective immunity and reduce development of salmonid rickettsial septicemia in an adult zebrafish model

Infections caused by the facultative intracellular bacterial pathogen Piscirickettsia salmonis remains an unsolved problem for the aquaculture as no efficient treatments have been developed. As a result, substantial amounts of antibiotic have been used to limit salmonid rickettsial septicemia (SRS) disease outbreaks. The antibiotic usage has not reduced the occurrence, but lead to an increase in resistant strains, underlining the need for new treatment strategies. P. salmonis produce membrane vesicles (MVs); small spherical structures know to contain a variety of bacterial components, including proteins, lipopolysaccharides (LPS), DNA and RNA. MVs mimics' in many aspects their mother cell, and has been reported as alternative vaccine candidates. Here, MVs from P. salmonis was isolated and evaluated as a vaccine candidate against SRS in an adult zebrafish infection model. When zebrafish was immunized with MVs they were protected from subsequent challenge with a lethal dose of P. salmonis. Histological analysis showed a reduced bacterial load upon challenge in the MV immunized group, and the mRNA expression levels of several immune related genes altered, including mpeg1.1, tnfα, il1b, il10 and il6. The MVs induced the secretion of IgM upon immunization, indicating an immunogenic effect of the vesicles. Taken together, the data demonstrate a vaccine potential of MVs against P. salmonis.

Identification, characterization and modulation of ferritin-H in the sub-Antarctic Notothenioid Eleginops maclovinus challenged with Piscirickettsia salmonis

Ferritin is a major iron storage protein essential not only in the infectious process, but also in any circumstance generating oxidative stress. In this study, the cDNA coding sequence of ferritin-H was obtained from the sub-Antarctic Notothenioid fish Eleginops maclovinus through transcriptomic analysis of the head kidney. This sequence contained a 534 bp open reading frame that coded for a 177 amino acid protein with a molecular weight of 20,786.2 Da and a theoretical pI of 5.56. The protein displayed a region of iron putative response elements in the 5'UTR, two putative ferritin iron-binding region signatures, and seven characteristic amino acids with ferroxidase functions. Phylogenetic analysis related this sequence to ferritin-H sequences of other Antarctic Notothenioid fish, sharing 96.61% similarity. Constitutive gene expression analysis in different organs revealed increased ferritin-H gene expression in the gills, spleen, muscle, and liver. After infection with two bacterial strains of Piscirickettsia salmonis (LF-89 and Austral-005), ferritin-H was differentially expressed depending on bacterial strain and tissue. This study provides relevant information towards understanding the iron metabolism of a sub-Antarctic Notothenioid fish.

Identification and expressional analysis of NLRC5 inflammasome gene in smolting Atlantic salmon (Salmo salar)

The NOD-like receptors (NLRs) were recently identified as an intracellular pathogen recognition receptor family in vertebrates. While the immune system participation of NLRs has been characterized and analyzed in various mammalian models, few studies have considered NLRs in teleost species. Therefore, this study analyzed the Atlantic salmon (Salmo salar) NLRC5. Structurally, Atlantic salmon NLRC5 presented leucine-rich repeat subfamily genes. Phylogenetically, NLRC5 was moderately conserved between S. salar and other species. Real-time quantitative PCR revealed NLRC5 expression in almost all analyzed organs, with greatest expressions in the head kidney, spleen, and hindgut. Furthermore, NLRC5 gene expression decreased during smolt stage. These data suggest that NLRC5 participates in the Atlantic salmon immune response and is regulated, at least partly, by the smoltification process, suggesting that there is a depression of immune system from parr at smolt stage. This is the first report on the NLRC5 gene in salmonid smolts.

Anti-Diabetic Agent Sodium Tungstate Induces the Secretion of Pro- and Anti-Inflammatory Cytokines by Human Kidney Cells

Diabetic kidney disease (DKD) is the major cause of end stage renal disease. Sodium tungstate (NaW) exerts anti-diabetic and immunomodulatory activities in diabetic animal models. Here, we used primary cultures of renal proximal tubule epithelial cells derived from type-2-diabetic (D-RPTEC) and non-diabetic (N-RPTEC) subjects as in vitro models to study the effects of NaW on cytokine secretion, as these factors participate in intercellular regulation of inflammation, cell growth and death, differentiation, angiogenesis, development, and repair, all processes that are dysregulated during DKD. In basal conditions, D-RPTEC cells secreted higher levels of prototypical pro-inflammatory IL-6, IL-8, and MCP-1 than N-RPTEC cells, in agreement with their diabetic phenotype. Unexpectedly, NaW further induced IL-6, IL-8, and MCP-1 secretion in both N- and D-RPTEC, together with lower levels of IL-1 RA, IL-4, IL-10, and GM-CSF, suggesting that it may contribute to the extent of renal damage/repair during DKD. Besides, NaW induced the accumulation of IκBα, the main inhibitor protein of one major pathway involved in cytokine production, suggesting further anti-inflammatory effect in the long-term. A better understanding of the mechanisms involved in the interplay between the anti-diabetic and immunomodulatory properties of NaW will facilitate future studies about its clinical relevance. J. Cell. Physiol. 232: 355-362, 2017. © 2016 Wiley Periodicals, Inc.

Comparative analysis of innate immune responses to Streptococcus phocae strains in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)

Streptococcus phocae subsp. salmonis is a Gram-positive bacterium that causes mortality only in Atlantic salmon (Salmo salar) farmed in Chile, even when this species is co-cultured with rainbow trout (Oncorhynchus mykiss). This susceptibility could be determined by innate immune response components and their responses to bacterial infection. This fish pathogen shares subspecies status with Streptococcus phocae subsp. phocae isolated from seals. The present study compared innate immune system mechanisms in Atlantic salmon and rainbow trout when challenged with different S. phocae, including two isolates from Atlantic salmon (LM-08-Sp and LM-13-Sp) and two from seal (ATCC 51973(T) and P23). Streptococcus phocae growth was evaluated in the mucus and serum of both species, with rainbow trout samples evidencing inhibitory effects. Lysozyme activity supported this observation, with significantly higher (p < 0.01) expression in rainbow trout serum and mucus as compared to Atlantic salmon. No differences were found in phagocytic capacity between fish species when stimulated with ATCC 51973(T) and P23. Against all S. phocae strains, rainbow trout and Atlantic salmon showed up to two-fold increased bactericidal activity, and rainbow trout demonstrated up to three-fold greater reactive oxygen species production in macrophages. In conclusion, the non-specific humoral and cellular barriers of Atlantic salmon were immunologically insufficient against S. phocae subsp. salmonis, thereby facilitating streptococcosis. Moreover, the more robust response of rainbow trout to S. phocae could not be attributed to any specific component of the innate immune system, but was rather the consequence of a combined response by the evaluated components.

Case Report: Strawberry Disease in Farmed Chilean Rainbow Trout

Strawberry disease is a chronic, nonlethal skin condition that affects Rainbow Trout Oncorhynchus mykiss in the United States and several European countries, where it is also known as red-mark syndrome. We provide the first identification and characterization of three strawberry disease outbreaks occurring at two aquaculture farms in southern Chile. Clinically affected fish weighing an average of 400 g presented multiple bright-red, usually raised, skin lesions on the flank, ventral surface, and dorsal surface. A PCR using Rickettsia-like-organism (RLO)-specific primers was performed on nine affected fish, and all skin samples were positive for the RLO 16S ribosomal RNA sequence. All PCR results for Flavobacterium psychrophilum and other bacterial and viral pathogens were negative. Histopathological examination of the skin lesions revealed extensive dermatitis, with severe lymphocytic infiltration in advanced cases. This report is the first to describe strawberry disease in farmed Chilean Rainbow Trout. Additional studies are needed to evaluate the risk for Rainbow Trout culture; fish challenge experiments should be performed to fulfill Koch's postulates and to demonstrate that RLO is the cause of this disease. Received December 27, 2014; accepted October 23, 2015.

In vivo sodium tungstate treatment prevents E-cadherin loss induced by diabetic serum in HK-2 cell line

Diabetic nephropathy (DN) is characterized by interstitial inflammation and fibrosis, which is the result of chronic accumulation of extracellular matrix produced by activated fibroblasts in the renal tubulointerstitium. Renal proximal tubular epithelial cells (PTECs), through the process of epithelial-to-mesenchymal transition (EMT), are the source of fibroblasts within the interstitial space, and loss of E-cadherin has shown to be one of the earliest steps in this event. Here, we studied the effect of the anti-diabetic agent sodium tungstate (NaW) in the loss of E-cadherin induced by transforming growth factor (TGF) β-1, the best-characterized in vitro EMT promoter, and serum from untreated or NaW-treated diabetic rats in HK-2 cell line, a model of human kidney PTEC. Our results showed that both TGFβ-1 and serum from diabetic rat induced a similar reduction in E-cadherin expression. However, E-cadherin loss induced by TGFβ-1 was not reversed by NaW, whereas sera from NaW-treated rats were able to protect HK-2 cells. Searching for soluble mediators of NaW effect, we compared secretion of TGFβ isoforms and vascular endothelial growth factor (VEGF)-A, which have opposite actions on EMT. One millimolar NaW alone reduced secretion of both TGFβ-1 and -2, and stimulated secretion of VEGF-A after 48 h. However, these patterns of secretion were not observed after diabetic rat serum treatment, suggesting that protection from E-cadherin loss by serum from NaW-treated diabetic rats originates from an indirect rather than a direct effect of this salt on HK-2 cells, via a mechanism independent of TGFβ and VEGF-A functions.

Cell-surface properties of Vibrio ordalii strains isolated from Atlantic salmon Salmo salar in Chilean farms

Vibrio ordalii is the causative agent of atypical vibriosis and has the potential to cause severe losses in salmonid aquaculture, but the factors determining its virulence have not yet been elucidated. In this work, cell-surface-related properties of the isolates responsible for outbreaks in Atlantic salmon were investigated. We also briefly examined whether pathogenicity against fish varied for V. ordalii strains with differing cell-surface properties. Hydrocarbon adhesions indicated the hydrophobic character of V. ordalii, although only 4 of 18 isolates induced haemagglutination in Atlantic salmon erythrocytes. A minority of the studied isolates (6 of 18) and the type strain ATCC 33509T produced low-grade biofilm formation on polyethylene surface after 2 h post-inoculation (hpi), but no strains were slime producers. Interestingly, V. ordalii isolates showed wide differences in hydrophobicity. Therefore, we chose 3 V. ordalii isolates (Vo-LM-03, Vo-LM-18 and Vo-LM-16) as representative of each hydrophobicity group (strongly hydrophobic, relatively hydrophobic and quasi-hydrophilic, respectively) and ATCC 33509T was used in the pathogenicity studies. All tested V. ordalii strains except the type strain resisted the killing activity of Atlantic salmon mucus and serum, and could proliferate in these components. Moreover, all V. ordalii isolates adhered to SHK-1 cells, causing damage to fish cell membrane permeability after 16 hpi. Virulence testing using rainbow trout revealed that isolate Vo-LM-18 was more virulent than isolates Vo-LM-03 and Vo-LM-16, indicating some relationship between haemagglutination and virulence, but not with hydrophobicity.

Preclinical and Clinical Studies for Sodium Tungstate: Application in Humans

Diabetes is a complex metabolic disorder triggered by the deficient secretion of insulin by the pancreatic β-cell or the resistance of peripheral tissues to the action of the hormone. Chronic hyperglycemia is the major consequence of this failure, and also the main cause of diabetic problems. Indeed, several clinical trials have agreed in that tight glycemic control is the best way to stop progression of the disease. Many anti-diabetic drugs for treatment of type 2 diabetes are commercially available, but no ideal normoglycemic agent has been developed yet. Moreover, weight gain is the most common side effect of many oral anti-diabetic agents and insulin, and increased weight has been shown to worsen glycemic control and increase the risk of diabetes progression. In this sense, the inorganic salt sodium tungstate (NaW) has been studied in different animal models of metabolic syndrome and diabetes, proving to have a potent effect on normalizing blood glucose levels and reducing body weight, without any hypoglycemic action. Although the liver has been studied as the main site of NaW action, positive effects have been also addressed in muscle, pancreas, brain, adipose tissue and intestine, explaining the effective anti-diabetic action of this salt. Here, we review NaW research to date in these different target organs. We believe that NaW deserves more attention, since all available anti-diabetic treatments remain suboptimal and new therapeutics are urgently needed.

Altered expression and localization of insulin receptor in proximal tubule cells from human and rat diabetic kidney

Diabetes is the major cause of end stage renal disease, and tubular alterations are now considered to participate in the development and progression of diabetic nephropathy (DN). Here, we report for the first time that expression of the insulin receptor (IR) in human kidney is altered during diabetes. We detected a strong expression in proximal and distal tubules from human renal cortex, and a significant reduction in type 2 diabetic patients. Moreover, isolated proximal tubules from type 1 diabetic rat kidney showed a similar response, supporting its use as an excellent model for in vitro study of human DN. IR protein down-regulation was paralleled in proximal and distal tubules from diabetic rats, but prominent in proximal tubules from diabetic patients. A target of renal insulin signaling, the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK), showed increased expression and activity, and localization in compartments near the apical membrane of proximal tubules, which was correlated with activation of the GSK3β kinase in this specific renal structure in the diabetic condition. Thus, expression of IR protein in proximal tubules from type 1 and type 2 diabetic kidney indicates that this is a common regulatory mechanism which is altered in DN, triggering enhanced gluconeogenesis regardless the etiology of the disease.

The role of Raf-1 kinase inhibitor protein in the regulation of pancreatic beta cell proliferation in mice

AIMS/HYPOTHESIS

Manoeuvres aimed at increasing beta cell mass have been proposed as regenerative medicine strategies for diabetes treatment. Raf-1 kinase inhibitor protein 1 (RKIP1) is a common regulatory node of the mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways and therefore may be involved in regulation of beta cell homeostasis. The aim of this study was to investigate the involvement of RKIP1 in the control of beta cell mass and function.

METHODS

Rkip1 (also known as Pebp1) knockout (Rkip1 (-/-)) mice were characterised in terms of pancreatic and glucose homeostasis, including morphological and functional analysis. Glucose tolerance and insulin sensitivity were examined, followed by assessment of glucose-induced insulin secretion in isolated islets and beta cell mass quantification through morphometry. Further characterisation included determination of endocrine and exocrine proliferation, apoptosis, MAPK activation and whole genome gene expression assays. Capacity to reverse a diabetic phenotype was assessed in adult Rkip1 (-/-) mice after streptozotocin treatment.

RESULTS

Rkip1 (-/-) mice exhibit a moderately larger pancreas and increased beta cell mass and pancreatic insulin content, which correlate with an overall improvement in whole body glucose tolerance. This phenotype is established in young postnatal stages and involves enhanced cellular proliferation without significant alterations in cell death. Importantly, adult Rkip1 (-/-) mice exhibit rapid reversal of streptozotocin-induced diabetes compared with control mice.

CONCLUSIONS/INTERPRETATION

These data implicate RKIP1 in the regulation of pancreatic growth and beta cell expansion, thus revealing RKIP1 as a potential pharmacological target to promote beta cell regeneration.

Dynamic expression of the sodium-vitamin C co-transporters, SVCT1 and SVCT2, during perinatal kidney development

Isoform 1 of the sodium-vitamin C co-transporter (SVCT1) is expressed in the apical membrane of proximal tubule epithelial cells in adult human and mouse kidneys. This study is aimed at analyzing the expression and function of SVCTs during kidney development. RT-PCR and immunohistochemical analyses revealed that SVCT1 expression is increased progressively during postnatal kidney development. However, SVCT1 transcripts were barely detected, if not absent, in the embryonic kidney. Instead, the high-affinity transporter, isoform 2 (SVCT2), was strongly expressed in the developing kidney from E15; its expression decreased at postnatal stages. Immunohistochemical analyses showed a dynamic distribution of SVCT2 in epithelial cells during kidney development. In renal cortex tubular epithelial cells, intracellular distribution of SVCT2 was observed at E19 with distribution in the basolateral membrane at P1. In contrast, SVCT2 was localized to the apical and basolateral membranes between E17 and E19 in medullary kidney tubular cells but was distributed intracellularly at P1. In agreement with these findings, functional expression of SVCT2, but not SVCT1 was detected in human embryonic kidney-derived (HEK293) cells. In addition, kinetic analysis suggested that an ascorbate-dependent mechanism accounts for targeted SVCT2 expression in the developing kidney during medullary epithelial cell differentiation. However, during cortical tubular differentiation, SVCT1 was induced and localized to the apical membrane of tubular epithelial cells. SVCT2 showed a basolateral polarization only for the first days of postnatal life. These studies suggest that the uptake of vitamin C mediated by different SVCTs plays differential roles during the ontogeny of kidney tubular epithelial cells.

Nuclear accumulation of fructose 1,6-bisphosphatase is impaired in diabetic rat liver

Using a streptozotocin-induced type 1 diabetic rat model, we analyzed and separated the effects of hyperglycemia and hyperinsulinemia over the in vivo expression and subcellular localization of hepatic fructose 1,6-bisphosphatase (FBPase) in the multicellular context of the liver. Our data showed that FBPase subcellular localization was modulated by the nutritional state in normal but not in diabetic rats. By contrast, the liver zonation was not affected in any condition. In healthy starved rats, FBPase was localized in the cytoplasm of hepatocytes, whereas in healthy re-fed rats it was concentrated in the nucleus and the cell periphery. Interestingly, despite the hyperglycemia, FBPase was unable to accumulate in the nucleus in hepatocytes from streptozotocin-induced diabetic rats, suggesting that insulin is a critical in vivo modulator. This idea was confirmed by exogenous insulin supplementation to diabetic rats, where insulin was able to induce the rapid accumulation of FBPase within the hepatocyte nucleus. Besides, hepatic FBPase was found phosphorylated only in the cytoplasm, suggesting that the phosphorylation state is involved in the nuclear translocation. In conclusion, insulin and not hyperglycemia plays a crucial role in the nuclear accumulation of FBPase in vivo and may be an important regulatory mechanism that could account for the increased endogenous glucose production of liver of diabetic rodents.

Expression of key substrate cycle enzymes in rat spermatogenic cells: Fructose 1,6 bisphosphatase and 6 phosphofructose 1-kinase

A substrate cycle composed of phosphofructo 1-kinase I (PFK) and fructose 1,6 bisphosphatase I (FBPase) has been proposed in rat spermatids. This substrate cycle can explain the ability of glucose to induce a decrease in intracellular ATP, a phenomenon that was related to regulation of [Ca(2+)]i in these cells. In spite of the importance of this metabolic cycle, the expression and activities of the enzymes that compose such cycle have not been systematically studied in spermatogenic cells. Here, we show that PFK and FBPase activities were present in pachytene spermatocytes and round spermatids extracts. Expression of PFK at the mRNA and protein levels showed a relatively similar expression in spermatogenic cells, but a stronger expression in Sertoli cells. Instead, expression of FBPase at the mRNA and protein levels was stronger in round and elongating spermatids as compared to other spermatogenic cells. A similar pattern was observed when evidencing FBPase activity by a NADPH-nitroblue tetrazolium-linked cytochemical assay in isolated pachytene spermatocytes and round spermatids. Rat spermatids also showed the ability to convert lactate to fructose- and glucose-6-P, indicating that both glycolytic and gluconeogenic fluxes are present in these cells. Our results indicate that a coordinated expression of key substrate cycle enzymes, at the level of PFK/FBPase, appear in the last stages of spermatogenic cell differentiation, suggesting that the co-regulation of these enzymes are required for the ability of these cells to respond to glucose and induce metabolic and Ca(2+) signals that can be important for sperm development and function.

Hexose transporters GLUT1 and GLUT3 are colocalized with hexokinase I in caveolae microdomains of rat spermatogenic cells

Postmeiotic spermatogenic cells, but not meiotic spermatogenic cells respond differentially with glucose-induced changes in [Ca2+]i indicating a differential transport of glucose via facilitative hexose transporters (GLUTs) specifically distributed in the plasma membrane. Several studies have indicated that plasma membrane in mammalian cells is not homogeneously organized, but contains specific microdomains known as detergent-resistant membrane domains (DRMDs), lipid rafts or caveolae. The association of these domains and GLUTs isoforms has not been characterized in spermatogenic cells. We analyzed the expression and function of GLUT1 and GLUT3 in isolated spermatocytes and spermatids. The results showed that spermatogenic cells express both glucose transporters, with spermatids exhibiting a higher affinity glucose transport system. In addition, spermatogenic cells express caveolin-1, and glucose transporters colocalize with caveolin-1 in caveolin-enriched membrane fractions. Experiments in which the integrity of caveolae was disrupted by pretreatment with methyl-beta-cyclodextrin, indicated that the involvement of cholesterol-enriched plasma membrane microdomains were involved in the localization of GLUTs and uptake of 2-deoxyglucose. We also observed cofractionation of GLUT3 and caveolin-1 in low-buoyant density membranes together with their shift to higher densities after methyl-beta-cyclodextrin treatment. GLUT1 was found in all fractions isolated. Immunofluorescent studies indicated that caveolin-1, GLUT1, and hexokinase I colocalize in spermatocytes while caveolin-1, GLUT3, and hexokinase I colocalize in spermatids. These findings suggest the presence of hexose transporters in DRMDs, and further support a role for intact caveolae or cholesterol-enriched membrane microdomains in relation to glucose uptake and glucose phosphorylation. The results would also explain the different glucose-induced changes in [Ca2+]i in both cells.

Novel expression of liver FBPase in Langerhans islets of human and rat pancreas

Several reports have indicated the absence of gluconeogenic enzymes in pancreatic islet cells. In contrast, here we demonstrate that liver fructose-1,6-bisphosphatase (FBPase) is highly expressed both in human and rat pancreas. Interestingly, pancreatic FBPase is active and functional, and is inhibited by AMP and fructose-2,6-bisphosphate (Fru-2,6-P2). These results suggest that FBPase may participate as a component of a metabolic sensing mechanism present in the pancreas. Immunolocalization analysis showed that FBPase is expressed both in human and rat Langerhans islets, specifically in beta cells. In humans, FBPase was also located in the canaliculus and acinar cells. These results indicate that FBPase coupled with phosphofructokinase (PFK) plays a crucial role in the metabolism of pancreatic islet cells. The demonstration of gluconeogenic recycling of trioses as a new metabolic signaling pathway may contribute to our understanding of the differences between the insulin secretagogues trioses, fructose, and glucose in pancreas.

Subcellular localization of liver FBPase is modulated by metabolic conditions

In primary cultured hepatocytes, fructose-1,6-bisphosphatase (FBPase) localization is modulated by glucose, dihydroxyacetone (DHA) and insulin. In the absence of these substrates, FBPase was present in the cytoplasm, but the addition of glucose or DHA induced its translocation to the nucleus. As expected, we observed the opposite effect of glucose on glucokinase localization. The addition of insulin in the absence of glucose largely increased the amount of nuclear FBPase. Moreover, at high concentrations of glucose or DHA, FBPase shifted from the cytosol to the cell periphery and co-localized with GS. Interestingly, the synthesis of Glu-6-P and glycogen induced by DHA was not inhibited by insulin. These results indicate that FBPase is involved in glycogen synthesis from gluconeogenic precursors. Overall, these findings show that translocation may be a new integrative mechanism for gluconeogenesis and glyconeogenesis.

Nuclear localization of liver FBPase isoenzyme in kidney and liver

Nuclear localization has been observed for glycolytic enzymes but not for key gluconeogenic enzymes. We report our findings on the intracellular localization of liver FBPase in rat liver and kidney, the main organs in the endogenous glucose production. Immunofluorescence and confocal analysis revealed that FBPase was present in the cytosol and, unexpectedly, inside the nucleus of hepatocytes and proximal cells of the nephron. Additionally, FBPase was found in the plasma membrane area of adjacent hepatocytes where glycogen is synthesized and in the apical region of proximal kidney cells. This subcellular distribution in multiple compartments suggests the presence of different localization signals on FBPase for diverse metabolic functions.