Discovery and Characterization of the ddx41 Gene in Atlantic Salmon: Evolutionary Implications, Structural Functions, and Innate Immune Responses to Piscirickettsia salmonis and Renibacterium salmoninarum Infections.

The innate immune response in Salmo salar, mediated by pattern recognition receptors (PRRs), is crucial for defending against pathogens. This study examined DDX41 protein functions as a cytosolic/nuclear sensor for cyclic dinucleotides, RNA, and DNA from invasive intracellular bacteria. The investigation determined the existence, conservation, and functional expression of the ddx41 gene in S. salar. In silico predictions and experimental validations identified a single ddx41 gene on chromosome 5 in S. salar, showing 83.92% homology with its human counterpart. Transcriptomic analysis in salmon head kidney confirmed gene transcriptional integrity. Proteomic identification through mass spectrometry characterized three unique peptides with 99.99% statistical confidence. Phylogenetic analysis demonstrated significant evolutionary conservation across species. Functional gene expression analysis in SHK-1 cells infected by Piscirickettsia salmonis and Renibacterium salmoninarum indicated significant upregulation of DDX41, correlated with increased proinflammatory cytokine levels and activation of irf3 and interferon signaling pathways. In vivo studies corroborated DDX41 activation in immune responses, particularly when S. salar was challenged with P. salmonis, underscoring its potential in enhancing disease resistance. This is the first study to identify the DDX41 pathway as a key component in S. salar innate immune response to invading pathogens, establishing a basis for future research in salmonid disease resistance.

Genomic and proteomic aspects of p57 protein from Renibacterium salmoninarum: Characteristics in virulence patterns.

Renibacterium salmoninarum is one of the oldest known fish bacterial pathogens. This Gram-positive bacterium is the causative agent of Bacterial Kidney Disease (BKD), a chronic infection that primarily infects salmonids at low temperatures. Externally, infected fish may show exophthalmos, skin blisters, ulcerations, and hemorrhages at the base of the fins and along the lateral line. Internally, the kidney, heart, spleen, and liver may show signs of inflammation. The best characterized virulence factor of R. salmoninarum is p57, a 57 kDa protein located on the bacterial cell surface and secreted into surrounding fish tissue. The p57 protein in fish is the main mediator in suppressing the immune system, reducing antibody production, and intervening in cytokine activity. In this review, we will discuss aspects such as single nucleotide polymorphisms (SNPs) that modify the DNA sequence, variants in the number of copies of MSA genes, physical-chemical properties of the signal peptides, and the limited iron conditions that can modify p57 expression and increase the virulence of R. salmoninarum.

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.

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 ß-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.

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.

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.

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.

Molecular characterization of infectious pancreatic necrosis virus strains isolated from the three types of salmonids farmed in Chile.

BACKGROUND: The infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming. For effective sanitary management, the IPNV strains present in Chile need to be fully studied, characterized, and constantly updated at the molecular level. METHODS: In this study, 36 Chilean IPNV isolates collected over 6 years (2006-2011) from Salmo salar, Oncorhynchus mykiss, and Oncorhynchus kisutch were genotypically characterized. Salmonid samples were obtained from freshwater, estuary, and seawater sources from central, southern, and the extreme-south of Chile (35° to 53°S). RESULTS: Sequence analysis of the VP2 gene classified 10 IPNV isolates as genogroup 1 and 26 as genogroup 5. Analyses indicated a preferential, but not obligate, relationship between genogroup 5 isolates and S. salar infection. Fifteen genogroup 5 and nine genogroup 1 isolates presented VP2 gene residues associated with high virulence (i.e. Thr, Ala, and Thr at positions 217, 221, and 247, respectively). Four genogroup 5 isolates presented an oddly long VP5 deduced amino acid sequence (29.6 kDa). Analysis of the VP2 amino acid motifs associated with clinical and subclinical infections identified the clinical fingerprint in only genogroup 5 isolates; in contrast, the genogroup 1 isolates presented sequences predominantly associated with the subclinical fingerprint. Predictive analysis of VP5 showed an absence of transmembrane domains and plasma membrane tropism signals. WebLogo analysis of the VP5 BH domains revealed high identities with the marine birnavirus Y-6 and Japanese IPNV strain E1-S. Sequence analysis for putative 25 kDa proteins, coded by the ORF between VP2 and VP4, exhibited three putative nuclear localization sequences and signals of mitochondrial tropism in two isolates. CONCLUSIONS: This study provides important advances in updating the characterizations of IPNV strains present in Chile. The results from this study will help in identifying epidemiological links and generating specific biotechnological tools for controlling IPNV outbreaks in Chilean salmon farming.

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.

SGLT2 Inhibitors: Glucotoxicity and Tumorigenesis Downstream the Renal Proximal Tubule?

At present, diabetes mellitus is the main cause of end-stage renal disease. Effective glycaemic management is the most powerful tool to delay the establishment of diabetic complications, such as diabetic kidney disease. Together with reducing blood glucose levels, new anti-diabetic agents are expected not only to control the progression but also to restore known defects of the diabetic kidney. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are promising anti-diabetic agents that reduce hyperglycaemia by impairing glucose reabsorption in proximal tubule of the kidney and increasing glucosuria. SGLT2 inhibitors have shown to reduce glucotoxicity in isolated proximal tubule cells and also to attenuate expression of markers of overall kidney damage in experimental animal models of diabetes, but the actual renoprotective effect for downstream nephron segments is still unknown and deserves further attention. Here, we briefly discuss possible undesired effects of enhanced glucosuria and albuminuria in nephron segments beyond the proximal tubule after SGLT2 inhibitor treatment, offering new lines of research to further understand the renoprotective action of these anti-diabetic agents. Strategies blocking glucose reabsorption by renal proximal tubule epithelial cells (RPTEC) may be protective for RPTEC, but downstream nephron segments will still be exposed to high glucose and albumin levels through the luminal face. The actual effect of constant enhanced glucosuria over distal nephron segments remains to be established. J. Cell. Physiol. 231: 1635-1637, 2016. © 2015 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.

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.

A new level of regulation in gluconeogenesis: metabolic state modulates the intracellular localization of aldolase B and its interaction with liver fructose-1,6-bisphosphatase.

Understanding how glucose metabolism is finely regulated at molecular and cellular levels in the liver is critical for knowing its relationship to related pathologies, such as diabetes. In order to gain insight into the regulation of glucose metabolism, we studied the liver-expressed isoforms aldolase B and fructose-1,6-bisphosphatase-1 (FBPase-1), key enzymes in gluconeogenesis, analysing their cellular localization in hepatocytes under different metabolic conditions and their protein-protein interaction in vitro and in vivo. We observed that glucose, insulin, glucagon and adrenaline differentially modulate the intracellular distribution of aldolase B and FBPase-1. Interestingly, the in vitro protein-protein interaction analysis between aldolase B and FBPase-1 showed a specific and regulable interaction between them, whereas aldolase A (muscle isozyme) and FBPase-1 showed no interaction. The affinity of the aldolase B and FBPase-1 complex was modulated by intermediate metabolites, but only in the presence of K(+). We observed a decreased association constant in the presence of adenosine monophosphate, fructose-2,6-bisphosphate, fructose-6-phosphate and inhibitory concentrations of fructose-1,6-bisphosphate. Conversely, the association constant of the complex increased in the presence of dihydroxyacetone phosphate (DHAP) and non-inhibitory concentrations of fructose-1,6-bisphosphate. Notably, in vivo FRET studies confirmed the interaction between aldolase B and FBPase-1. Also, the co-expression of aldolase B and FBPase-1 in cultured cells suggested that FBPase-1 guides the cellular localization of aldolase B. Our results provide further evidence that metabolic conditions modulate aldolase B and FBPase-1 activity at the cellular level through the regulation of their interaction, suggesting that their association confers a catalytic advantage for both enzymes.

Subunit interactions in pig-kidney fructose-1,6-bisphosphatase: binding of substrate induces a second class of site with lowered affinity and catalytic activity.

BACKGROUND: Fructose-1,6-bisphosphatase, a major enzyme of gluconeogenesis, is inhibited by AMP, Fru-2,6-P2 and by high concentrations of its substrate Fru-1,6-P2. The mechanism that produces substrate inhibition continues to be obscure. METHODS: Four types of experiments were used to shed light on this: (1) kinetic measurements over a very wide range of substrate concentrations, subjected to detailed statistical analysis; (2) fluorescence studies of mutants in which phenylalanine residues were replaced by tryptophan; (3) effect of Fru-2,6-P2 and Fru-1,6-P2 on the exchange of subunits between wild-type and Glu-tagged oligomers; and (4) kinetic studies of hybrid forms of the enzyme containing subunits mutated at the active site residue tyrosine-244. RESULTS: The kinetic experiments with the wild-type enzyme indicate that the binding of Fru-1,6-P2 induces the appearance of catalytic sites with lower affinity for substrate and lower catalytic activity. Binding of substrate to the high-affinity sites, but not to the low-affinity sites, enhances the fluorescence emission of the Phe219Trp mutant; the inhibitor, Fru-2,6-P2, competes with the substrate for the high-affinity sites. Binding of substrate to the low-affinity sites acts as a "stapler" that prevents dissociation of the tetramer and hence exchange of subunits, and results in substrate inhibition. CONCLUSIONS: Binding of the first substrate molecule, in one dimer of the enzyme, produces a conformational change at the other dimer, reducing the substrate affinity and catalytic activity of its subunits. GENERAL SIGNIFICANCE: Mimics of the substrate inhibition of fructose-1,6-bisphosphatase may provide a future option for combatting both postprandial and fasting hyperglycemia.

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) ß-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 TGFß-1 and serum from diabetic rat induced a similar reduction in E-cadherin expression. However, E-cadherin loss induced by TGFß-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 TGFß isoforms and vascular endothelial growth factor (VEGF)-A, which have opposite actions on EMT. One millimolar NaW alone reduced secretion of both TGFß-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 TGFß and VEGF-A functions.

Over-expression of muscle glycogen synthase in human diabetic nephropathy.

Diabetic nephropathy (DN) is a major complication of diabetic patients and the leading cause of end-stage renal disease. Glomerular dysfunction plays a critical role in DN, but deterioration of renal function also correlates with tubular alterations. Human DN is characterized by glycogen accumulation in tubules. Although this pathological feature has long been recognized, little information exists about the triggering mechanism. In this study, we detected over-expression of muscle glycogen synthase (MGS) in diabetic human kidney. This enhanced expression suggests the participation of MGS in renal metabolic changes associated with diabetes. HK2 human renal cell line exhibited an intrinsic ability to synthesize glycogen, which was enhanced after over-expression of protein targeting to glycogen. A correlation between increased glycogen amount and cell death was observed. Based on a previous transcriptome study on human diabetic kidney disease, significant differences in the expression of genes involved in glycogen metabolism were analyzed. We propose that glucose, but not insulin, is the main modulator of MGS activity in HK2 cells, suggesting that blood glucose control is the best approach to modulate renal glycogen-induced damage during long-term diabetes.

Sodium Tungstate (NaW) Decreases Inflammation and Renal Fibrosis in Diabetic Nephropathy.

BACKGROUND: Diabetic Nephropathy is one of the most severe complications of Diabetes Mellitus and the main cause of end-stage kidney disease worldwide. Despite the therapies available to control blood glucose and blood pressure, many patients continue to suffer from progressive kidney damage. Chronic hyperglycemia is the main driver of changes observed in diabetes; however, it was recently discovered that inflammation and oxidative stress contribute to the development and progression of kidney damage. Therefore, it is important to search for new pharmacological therapies that stop the progression of DN. Sodium tungstate (NaW) is an effective short and long-term antidiabetic agent in both type 1 and type 2 diabetes models. METHODS: In this study, the effect of NaW on proinflammatory signalling pathways, proinflammatory proteins and fibrosis in the streptozotocin (STZ)-induced type 1 diabetic rat model was analysed using histological analysis, western blotting and immunohistochemistry. RESULTS: NaW treatment in diabetic rats normalize parameters such as glycemia, glucosuria, albuminuria/creatinuria, glomerular damage, and tubulointerstitial damage. NaW decreased the proinflammatory signaling pathway NF-κB, inflammatory markers (ICAM-1, MCP-1 and OPN), profibrotic pathways (TGFß1/Smad2/3), reduced epithelial-mesenchymal transition (α -SMA), and decreased renal fibrosis (type IV collagen). CONCLUSION: NaW could be an effective drug therapy for treating human diabetic nephropathy.

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 GSK3ß 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.

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.

Sodium Tungstate (NaW) Decreases Reactive Oxygen Species (ROS) Production in Cells: New Cellular Antioxidant.

Diabetic nephropathy (DN) is the leading cause of end-stage renal failure worldwide. Hyperglycemia generates reactive oxygen species (ROS), contributing to diabetic complications, especially in DN. Sodium Tungstate (NaW) is an effective antidiabetic agent for short and long-term treatments of both type 1 and type 2 diabetes models. In this study, we evaluated the effect of NaW on ROS production in bovine neutrophils incubated with platelet-activating factor (PAF) and in HK-2 cells induced by high glucose or H2O2. In addition, we evaluated the effect on iNOS expression in the type 1 diabetic rat model induced with streptozotocin (STZ). NaW inhibited ROS production in PAF-induced bovine neutrophils, and human tubular cells (HK-2) were incubated in high glucose or H2O2. In addition, NaW inhibited iNOS expression in glomeruli and tubular cells in the type 1 diabetic rat. This study demonstrates a new role for NaW as an active antioxidant and its potential use in treating DN.