Immediate early gene and HSP70 expression in hyperosmotic stress in MDCK cells

Heat Shock Proteins (Hsps) in Cellular Homeostasis: A Promising Tool for Health Management in Crustacean Aquaculture

Heat shock proteins (Hsps) are a family of ubiquitously expressed stress proteins and extrinsic chaperones that are required for viability and cell growth in all living organisms. These proteins are highly conserved and produced in all cellular organisms when exposed to stress. Hsps play a significant role in protein synthesis and homeostasis, as well as in the maintenance of overall health in crustaceans against various internal and external environmental stresses. Recent reports have suggested that enhancing in vivo Hsp levels via non-lethal heat shock, exogenous Hsps, or plant-based compounds, could be a promising strategy used to develop protective immunity in crustaceans against both abiotic and biotic stresses. Hence, Hsps as the agent of being an immune booster and increasing disease resistance will present a significant advancement in reducing stressful conditions in the aquaculture system.

Forensic Diagnosis of Freshwater or Saltwater Drowning Using the Marker Aquaporin 5: An Immunohistochemical Study

Background and Objectives: Aquaporins are a family of water channel proteins. In this study, the renal and intrapulmonary expression of aquaporin-5 (AQP5) was examined in forensic autopsy cases to evaluate it as a drowning marker and to differentiate between freshwater drowning and saltwater drowning. Materials and Methods: Cases were classified into three groups: freshwater drowning (FWD), saltwater drowning (SWD), and controls (CTR). Samples were obtained from forensic autopsies at less than 72 h postmortem (15 FWD cases, 15 SWD cases, and 17 other cases) and were subjected to histological and immunohistochemical investigations. Results: In FWD group, intrapulmonary AQP5 expression was significantly suppressed compared with SWD and CTR; there was no significant difference in AQP5 expression among the other two groups. The same differences in expression were also observed in the kidney. Conclusions: These observations suggest that AQP5 expression in alveolar cells was suppressed by hypotonic water to prevent hemodilution. Moreover, it is possible to hypothesize that in the kidney, with the appearance of hypo-osmotic plasma, AQP5 is hypo-expressed, as a vital reaction, to regulate the renal reabsorption of water. In conclusion, the analysis of renal and intrapulmonary AQP5 expression would be forensically useful for differentiation between FWD and SWD, or between FWD and death due to other causes.

The renal antioxidative effect of losartan involves heat shock protein 70 in proximal tubule cells

Angiotensin II exerts a cardinal role in the pathogenesis of hypertension and renal injury via action of angiotensin II type 1 (AT1) receptors. Local renin-angiotensin system (RAS) activity is essential for the mechanisms mediating pathophysiological functions. Proximal tubular angiotensinogen and tubular AT1 receptors are augmented by intrarenal angiotensin II. Caveolin 1 plays an important role as a regulatory molecule for the compartmentalization of redox signaling events through angiotensin II-induced NADPH oxidase activation in the kidney. A role for the renin-angiotensin system in the development and/or maintenance of hypertension has been demonstrated in spontaneously hypertensive rats (SHRs). Many effects of angiotensin II are dependent on the AT1 stimulation of reactive oxygen species (ROS) production by NADPH oxidase. Angiotensin II upregulation stimulates oxidative stress in proximal tubules from SHR. The NADPH oxidase 4 (Nox4) is abundantly expressed in kidney proximal tubule cells. Induction of the stress response includes synthesis of heat shock protein 70, a molecular chaperone that has a critical role in the recovery of cells from stress and in cytoprotection, guarding cells from subsequent insults. HSP70 chaperones function in part by driving the molecular triage decision, which determines whether proteins enter the productive folding pathway or result in client substrate ubiquitination and proteasomal degradation. This review examines regulation of losartan-mediated antioxidative stress responses by the chaperone HSP70 in proximal tubule cells of spontaneously hypertensive rats.

Hypertonicity counteracts MCL-1 and renders BCL-XL a synthetic lethal target in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is an aggressive and difficult-to-treat cancer entity. Current therapies ultimately aim to activate the mitochondria-controlled (intrinsic) apoptosis pathway, but complex alterations in intracellular signaling cascades and the extracellular microenvironment hamper treatment response. On the one hand, proteins of the BCL-2 family set the threshold for cell death induction and prevent accidental cellular suicide. On the other hand, controlling a cell's readiness to die also determines whether malignant cells are sensitive or resistant to anticancer treatments. Here, we show that HNSCC cells upregulate the proapoptotic BH3-only protein NOXA in response to hyperosmotic stress. Induction of NOXA is sufficient to counteract the antiapoptotic properties of MCL-1 and switches HNSCC cells from dual BCL-XL/MCL-1 protection to exclusive BCL-XL addiction. Hypertonicity-induced functional loss of MCL-1 renders BCL-XL a synthetically lethal target in HNSCC, and inhibition of BCL-XL efficiently kills HNSCC cells that poorly respond to conventional therapies. We identify hypertonicity-induced upregulation of NOXA as link between osmotic pressure in the tumor environment and mitochondrial priming, which could perspectively be exploited to boost efficacy of anticancer drugs.

Expression analysis of the heat shock protein genes and cellular reaction in dojo loach (Misgurnus anguillicaudatus) under the different pathogenic invasion

As molecular chaperones, heat shock proteins (HSPs) play essential roles in cells in response to stress conditions. Recent studies about immune functions of HSPs in fish have also been reported. In this study, based on the reported cDNA sequences of the four HSP genes, HSP70, HSC70, HSP90α and HSP90β, the temporal expression patterns of the four genes during embryonic development of dojo loach(Misgurnus anguillicaudatus) was assayed with qRT-PCR. All of the four genes were ubiquitously expressed in all detected embryonic developmental stages. Among of them, HSP70, HSC70 and HSP90β were highly expressed in the organ formation stage, while HSP90α was the highest expressed in myotome formation stage. Further, the immune responses of the four HSP genes were assayed when loach were infected with three different pathogens, bacterium (Flavobacterium cloumnare G4), parasite (Ichthyophthirius multifiliis) and fungus (Saprolegnia). All of the four genes were differentially expressed in four tissues such as skin, gills, spleen and kidney in response to the pathogenic invasion, but both HSP70 and HSP90α expressions were dramatically up-regulated. Further, the cellular responses of the loach skinand gill tissues were observed, in which the number of the skin goblet cells were significantly increased, and the gill lamellae became shorter and wider after infected. Thus, our work indicated that the HSPs may directly or indirectly involved in immune defense in fish, at least in the loach.

Sequential and synchronized hypertonicity-induced activation of Rel-family transcription factors is required for osmoprotection in renal cells

NF-κB and TonEBP belong to the Rel-superfamily of transcription factors. Several specific stimuli, including hypertonicity which is a key factor for renal physiology, are able to activate them. It has been reported that, after hypertonic challenge, NF-κB activity can be modulated by TonEBP, considered as the master regulator of transcriptional activity in the presence of changes in environmental tonicity. In the present work we evaluated whether hypertonicity-induced gene transcription mediated by p65/RelA and TonEBP occurs by an independent action of each transcription factor or by acting together. To do this, we evaluated the expression of their specific target genes and cyclooxygenase-2 (COX-2), a common target of both transcription factors, in the renal epithelial cell line Madin-Darby canine kidney (MDCK) subjected to hypertonic environment. The results herein indicate that hypertonicity activates the Rel-family transcription factors p65/RelA and TonEBP in MDCK cells, and that both are required for hypertonic induction of COX-2 and of their specific target genes. In addition, present data show that p65/RelA modulates TonEBP expression and both colocalize in nuclei of hypertonic cultures of MDCK cells. Thus, a sequential and synchronized action p65/RelA → TonEBP would be necessary for the expression of hypertonicity-induced protective genes.

Salt stress in the renal tubules is linked to TAL-specific expression of uromodulin and an upregulation of heat shock genes

Previously, our comprehensive cardiovascular characterization study validated Uromodulin as a blood pressure gene. Uromodulin is a glycoprotein exclusively synthesized at the thick ascending limb of the loop of Henle and is encoded by the Umod gene. Umod-/- mice have significantly lower blood pressure than Umod+/+ mice, are resistant to salt-induced changes in blood pressure, and show a leftward shift in pressure-natriuresis curves reflecting changes of sodium reabsorption. Salt stress triggers transcription factors and genes that alter renal sodium reabsorption. To date there are no studies on renal transcriptome responses to salt stress. Here we aimed use RNA-Seq to delineate salt stress pathways in tubules isolated from Umod+/+ mice (a model of sodium retention) and Umod-/- mice (a model of sodium depletion) ± 300 mosmol sodium chloride ( n = 3 per group). In response to salt stress, the tubules of Umod+/+ mice displayed an upregulation of heat shock transcripts. The greatest changes occurred in the expression of: Hspa1a (Log2 fold change 4.35, P = 2.48 e-12) and Hspa1b (Log2 fold change 4.05, P = 2.48 e-12). This response was absent in tubules of Umod-/- mice. Interestingly, seven of the genes discordantly expressed in the Umod-/- tubules were electrolyte transporters. Our results are the first to show that salt stress in renal tubules alters the transcriptome, increasing the expression of heat shock genes. This direction of effect in Umod+/+ tubules suggest the difference is due to the presence of Umod facilitating greater sodium entry into the tubule cell reflecting a specific response to salt stress.

Evolution in chronic cold: varied loss of cellular response to heat in Antarctic notothenioid fish

Background

Confined within the freezing Southern Ocean, the Antarctic notothenioids have evolved to become both cold adapted and cold specialized. A marked signature of cold specialization is an apparent loss of the cellular heat shock response (HSR). As the HSR has been examined in very few notothenioid species to-date, it remains unknown whether HSR loss pervades the Antarctic radiation, or whether the broader cellular responses to heat stress has sustained similar loss. Understanding the evolutionary status of these responses in this stenothermal taxon is crucial for evaluating its adaptive potential to ocean warming under climate change.

Results

In this study, we used an acute heat stress protocol followed by RNA-Seq analyses to study the evolution of cellular-wide transcriptional responses to heat stress across three select notothenioid lineages - the basal temperate and nearest non-Antarctic sister species Eleginops maclovinus serving as ancestral proxy, the cryopelagic Pagothenia borchgrevinki and the icefish Chionodraco rastrospinosus representing cold-adapted red-blooded and hemoglobinless Antarctic notothenioids respectively. E. maclovinus displayed robust cellular stress responses including the ER Unfolded Protein Response and the cytosolic HSR, cementing the HSR as a plesiomorphy that preceded Antarctic notothenioid radiation. While the transcriptional response to heat stress was minimal in P. borchgrevinki, C. rastrospinosus exhibited robust responses in the broader cellular networks especially in inflammatory responses despite lacking the classic HSR and UPR.

Conclusion

The disparate patterns observed in these two archetypal Antarctic species indicate the evolutionary status in cellular ability to mitigate acute heat stress varies even among Antarctic lineages, which may affect their adaptive potential in coping with a warming world.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1254-6) contains supplementary material, which is available to authorized users.

Heat shock proteins and kidney disease: perspectives of HSP therapy

Heat shock proteins (HSPs) mediate a diverse range of cellular functions, prominently including folding and regulatory processes of cellular repair. A major property of these remarkable proteins, dependent on intracellular or extracellular location, is their capacity for immunoregulation that optimizes immune activity while avoiding hyperactivated inflammation. In this review, recent investigations are described, which examine roles of HSPs in protection of kidney tissue from various traumatic influences and demonstrate their potential for clinical management of nephritic disease. The HSP70 class is particularly attractive in this respect due to its multiple protective effects. The review also summarizes current understanding of HSP bioactivity in the pathophysiology of various kidney diseases, including acute kidney injury, diabetic nephropathy, chronic glomerulonephritis, and lupus nephritis-along with other promising strategies for their remediation, such as DNA vaccination.

NFAT5 and SLC4A10 Loci Associate with Plasma Osmolality

Disorders of water balance, an excess or deficit of total body water relative to body electrolyte content, are common and ascertained by plasma hypo- or hypernatremia, respectively. We performed a two-stage genome-wide association study meta-analysis on plasma sodium concentration in 45,889 individuals of European descent (stage 1 discovery) and 17,637 additional individuals of European descent (stage 2 replication), and a transethnic meta-analysis of replicated single-nucleotide polymorphisms in 79,506 individuals (63,526 individuals of European descent, 8765 individuals of Asian Indian descent, and 7215 individuals of African descent). In stage 1, we identified eight loci associated with plasma sodium concentration at P<5.0 × 10^-6 Of these, rs9980 at NFAT5 replicated in stage 2 meta-analysis (P=3.1 × 10^-5), with combined stages 1 and 2 genome-wide significance of P=5.6 × 10^-10 Transethnic meta-analysis further supported the association at rs9980 (P=5.9 × 10^-12). Additionally, rs16846053 at SLC4A10 showed nominally, but not genome-wide, significant association in combined stages 1 and 2 meta-analysis (P=6.7 × 10^-8). NFAT5 encodes a ubiquitously expressed transcription factor that coordinates the intracellular response to hypertonic stress but was not previously implicated in the regulation of systemic water balance. SLC4A10 encodes a sodium bicarbonate transporter with a brain-restricted expression pattern, and variant rs16846053 affects a putative intronic NFAT5 DNA binding motif. The lead variants for NFAT5 and SLC4A10 are cis expression quantitative trait loci in tissues of the central nervous system and relevant to transcriptional regulation. Thus, genetic variation in NFAT5 and SLC4A10 expression and function in the central nervous system may affect the regulation of systemic water balance.

Activation of osmolyte pathways in inflammatory myopathy and Duchenne muscular dystrophy points to osmoregulation as a contributing pathogenic mechanism

Alongside well-known nuclear factor κB (NFκB) and its associated cytokine networks, nuclear factor of activated T cells 5 (NFAT5), the master regulator of cellular osmoprotective programs, comes forward as an inflammatory regulator. To gain insight into its yet unexplored role in muscle disease, we studied the expression of NFAT5 target proteins involved in osmolyte accumulation: aldose reductase (AR), taurine transporter (TauT), and sodium myo-inositol co-transporter (SMIT). We analyzed idiopathic inflammatory myopathy and Duchenne muscular dystrophy muscle biopsies and myotubes in culture, using immunohistochemistry, immunofluorescence, and western blotting. We report that the level of constitutive AR was upregulated in patients, most strongly so in Duchenne muscular dystrophy. TauT and SMIT expression levels were induced in patients' muscle fibers, mostly representing regenerating and atrophic fibers. In dermatomyositis, strong staining for AR, TauT, and SMIT in atrophic perifascicular fibers was accompanied by staining for other molecular NFAT5 targets, including chaperones, chemokines, and inducible nitric oxide synthase. In these fibers, NFAT5 and NFκB p65 staining coincided, linking both transcription factors with this important pathogenic hallmark. In sporadic inclusion body myositis, SMIT localized to inclusions inside muscle fibers. In addition, SMIT was expressed by a substantial subset of muscle-infiltrating macrophages and T cells in patient biopsies. Our results indicate that osmolyte pathways may contribute to normal muscle functioning, and that activation of AR, TauT, and SMIT in muscle inflammation possibly contributes to the tissue's failing program of damage control.

Stress alters the expression of aquaporins in cultured rat intestinal epithelial cells

Aquaporins (AQPs) are widely-expressed small water channel proteins that provide the major route for water transport across plasma membranes in various cell types. Although the quantity of water transported in the intestinal tract is second only to that in the kidney, the precise role of AQPs in this organ remains largely uncertain. The present study reports the effects of hypertonic stress and ischemia/reperfusion injury on the expression of AQPs in intestinal epithelial cells. Cultured rat intestinal epithelial cells were incubated in 300 mM mannitol-containing, hypertonic culture medium or subjected to simulated ischemia/reperfusion treatment. The cell viability was evaluated by MTT assay, and the expression of AQPs was determined by semi-quantitative reverse transcription polymerase chain reaction and western blotting. Despite reduced viability, the cells exposed to hypertonic stress for 16 h demonstrated enhanced expression of AQP1 mRNA and protein. AQP9 and glycosylated AQP11 proteins were also markedly upregulated. Ischemia alone did not affect the cell viability, but subsequent reperfusion significantly reduced viability. The mRNA expression levels of all the tested AQPs were not altered by ischemia alone or by ischemia/reperfusion; however, AQP8 protein was markedly reduced by ischemic injury. In addition, treatment with ischemia alone eradicated the normally-expressed, non-glycosylated AQP11 protein whilst inducing pronounced expression of the glycosylated form. These observations may indicate that AQPs function in the intestinal epithelia in response to stress.

Global discovery of high-NaCl-induced changes of protein phosphorylation

High extracellular NaCl, such as in the renal medulla, can perturb and even kill cells, but cells mount protective responses that enable them to survive and function. Many high-NaCl-induced perturbations and protective responses are known, but the signaling pathways involved are less clear. Change in protein phosphorylation is a common mode of cell signaling, but there was no unbiased survey of protein phosphorylation in response to high NaCl. We used stable isotopic labeling of amino acids in cell culture coupled to mass spectrometry to identify changes in protein phosphorylation in human embryonic kidney (HEK 293) cells exposed to high NaCl. We reproducibly identify >8,000 unique phosphopeptides in 4 biological replicate samples with a 1% false discovery rate. High NaCl significantly changed phosphorylation of 253 proteins. Western analysis and targeted ion selection mass spectrometry confirm a representative sample of the phosphorylation events. We analyze the affected proteins by functional category to infer how altered protein phosphorylation might signal cellular responses to high NaCl, including alteration of cell cycle, cyto/nucleoskeletal organization, DNA double-strand breaks, transcription, proteostasis, metabolism of mRNA, and cell death.

Transcriptome-based analysis of kidney gene expression changes associated with diabetes in OVE26 mice, in the presence and absence of losartan treatment

Diabetes is among the most common causes of end-stage renal disease, although its pathophysiology is incompletely understood. We performed next-generation sequencing-based transcriptome analysis of renal gene expression changes in the OVE26 murine model of diabetes (age 15 weeks), relative to non-diabetic control, in the presence and absence of short-term (seven-day) treatment with the angiotensin receptor blocker, losartan (n = 3-6 biological replicates per condition). We detected 1438 statistically significant changes in gene expression across conditions. Of the 638 genes dysregulated in diabetes relative to the non-diabetic state, >70% were downregulation events. Unbiased functional annotation of genes up- and down-regulated by diabetes strongly associated (p<1 × 10(-8)) with terms for oxidative stress and for endoplasmic reticulum stress/protein folding. Most of the individual gene products up- or down-regulated with diabetes were unaffected by losartan treatment; however, of the gene products dysregulated in diabetes and influenced by losartan treatment, the vast majority of changes were in the direction of amelioration rather than exacerbation of the diabetic dysregulation. This group of losartan-protected genes associated strongly with annotation terms for endoplasmic reticulum stress, heat shock proteins, and chaperone function, but not oxidative stress; therefore, the losartan-unaffected genes suggest avenues for additional therapeutic opportunity in diabetes. Interestingly, the gene product most highly upregulated by diabetes (>52-fold), encoded by the cationic amino acid transporter Slc7a12, and the gene product most highly downregulated by diabetes (>99%)--encoded by the "pseudogene" Gm6300--are adjacent in the murine genome, are members of the SLC7 gene family, and are likely paralogous. Therefore, diabetes activates a near-total genetic switch between these two paralogs. Other individual-level changes in gene expression are potentially relevant to diabetic pathophysiology, and novel pathways are suggested. Genes unaffected by diabetes alone but exhibiting increased renal expression with losartan produced a signature consistent with malignant potential.

Exploring the effect of salinity changes on the levels of Hsp60 in the tropical coral Seriatopora caliendrum

Osmotic stress represents a limiting physical parameter for marine organisms and especially for sessile scleractinian corals which are known to be basically stenohaline and osmoconformers. The salinity changes may cause important cellular damage since corals lack any developed physiological regulatory system. One mechanism of reaction to deleterious conditions is the rapid increase of the induction of heat shock proteins. This study highlights the modulation of the expression of a mitochondrial heat shock protein, such as the chaperonin Hsp60, in the animal tissues of the scleractinian coral Seriatopora caliendrum under three salinity scenarios (hypersalinity of 45 ppt, hyposalinity of 25 ppt and extreme hyposalinity of 15 ppt). The study was performed during the time course of a 2-day period and accompanied also by the assessment of the coral health condition. For each salinity stress S. caliendrum responds differently at the morphological and cellular levels, since the Hsp60 exhibited specific patterns of expression and the coral showed different tissue appearance. Furthermore, the response reflects the severity and exposure length of the disturbance. However, the results indicate that S. caliendrum seems able to tolerates high salinity better than low salinity. In particular, in extreme hyposalinity conditions, a considerable gradual down-regulation of Hsp60 was detected accompanied by necrosis and degradation of the coral tissues. The study suggests that Hsp60 may be involved in the mechanisms of cellular response to stress caused by exposure to adverse salinity.

Expression of Hsp70 in the mud crab, Scylla paramamosain in response to bacterial, osmotic, and thermal stress

Hsp70 is involved in immune responses against infectious pathogens, thermal, and osmotic stress. To understand the immune defense mechanisms of the mud crab Scylla paramamosain, genomic DNA, transcript level and antimicrobial activities of Hsp70 were analyzed. Genomic DNA sequence analysis revealed one intron in this gene. Furthermore, six SNPs were detected by direct sequencing from 30 samples in this study. Hsp70 mRNA was expressed in almost all tissues examined. By using the quantitative real-time PCR, the expression level of Hsp70 in hemocytes showed a clear time-dependent expression pattern during the 96 h after stimulated by Vibrio alginolyticus. Then, recombinant Hsp70 was obtained by using the bacterial expression system, but no obvious antimicrobial activity has been found for the protein in the antimicrobial tests. After osmotic stress, the expression of Hsp70 in hemocytes showed this gene was induced by the high salinity (30 ‰) for at least 96 h. Hsp70 mRNA expression in hemocytes was analyzed after thermal stress at 6 h, the highest and the lowest expression level of Hsp70 was observed at 36 and 15 °C, respectively. These results indicated that Hsp70 was inducible by bacterial, osmotic, and thermal stress, and therefore plays an important role, different from antibacterial peptide, in innate immune responses of S. paramamosain.

Hyperosmotic stress induces aquaporin-dependent cell shrinkage, polyphosphate synthesis, amino acid accumulation, and global gene expression changes in Trypanosoma cruzi

The protist parasite Trypanosoma cruzi has evolved the ability to transit between completely different hosts and to replicate in adverse environments. In particular, the epimastigote form, the replicative stage inside the vector, is subjected to nutritional and osmotic stresses during its development. In this work, we describe the biochemical and global gene expression changes of epimastigotes under hyperosmotic conditions. Hyperosmotic stress resulted in cell shrinking within a few minutes. Depending on the medium osmolarity, this was followed by lack of volume recovery for at least 2 h or by slow recovery. Experiments with inhibitors, or with cells in which an aquaporin gene (TcAQP1) was knocked down or overexpressed, revealed its importance for the cellular response to hyperosmotic stress. Furthermore, the adaptation to this new environment was shown to involve the regulation of the polyphosphate polymerization state as well as changes in amino acid catabolism to generate compatible osmolytes. A genome-wide transcriptional analysis of stressed parasites revealed down-regulation of genes belonging to diverse functional categories and up-regulation of genes encoding trans-sialidase-like and ribosomal proteins. Several of these changes were confirmed by Northern blot analyses. Sequence analysis of the 3'UTRs of up- and down-regulated genes allowed the identification of conserved structural RNA motifs enriched in each group, suggesting that specific ribonucleoprotein complexes could be of great importance in the adaptation of this parasite to different environments through regulation of transcript abundance.

Osmoadaptation of Mammalian cells - an orchestrated network of protective genes

In mammals, the cells of the renal medulla are physiologically exposed to interstitial osmolalities several-fold higher that found in any other tissue. Nevertheless, these cells not only have the ability to survive in this harsh environment, but also to function normally, which is critical for maintenance of systemic electrolyte and fluid homeostasis. Over the last two decades, a substantial body of evidence has accumulated, indicating that sequential and well orchestrated genomic responses are required to provide tolerance to osmotic stress. This includes the enhanced expression and action of immediate-early genes, growth arrest and DNA damage inducible genes (GADDs), genes involved in cell cycle control and apoptosis, heat shock proteins, and ultimately that of genes involved in the intracellular accumulation of nonperturbing organic osmolytes. The present review summarizes the sequence of genomic responses conferring resistance against osmotic stress. In addition, the regulatory mechanisms mediating the coordinated genomic response to osmotic stress will be highlighted.

NA+/H+ Exchanger 1-and Aquaporin-1-Dependent Hyperosmolarity Changes Decrease Nitric Oxide Production and Induce VCAM-1 Expression in Endothelial Cells Exposed to High Glucose

Since diabetic hyperglycaemia causes hyperosmolarity, we investigated the contribution of hyperosmolarity in the proinflammatory endothelial effects of hyperglycemia, and sought to unravel the mechanisms involved. Human aortic endothelial cells (HAEC) were incubated for short-term (1–3 days) or long-term (1–2 weeks) exposures to 5.5 mmol/L glucose (normoglycemia, basal), high glucose (25 and 45 mmol/L, HG), or a hyperosmolar control (mannitol 25 and 45 mmol/L, HM), in the presence or absence of the aquaporin-1 (AQP1) inihibitor dimethylsulfoxide (DMSO), the Na+/H+ exchanger 1 (NHE-1) inihibitor cariporide (CA), the protein kinase C (PKC) inihibitor calphostin C or the PKCβ isoform inhibitor LY379196 (LY). Both short- and long-term exposures to HG and HM decreased the expression of the active, phosphorylated form of endothelial nitric oxide synthase (Ser1146-eNOS) and, in parallel, increased vascular cell adhesion molecule(VCAM)-1 protein at immunoblotting. After 24 h incubation with HG/HM, we observed a significant similar and concentration-dependent enhancement of AQP1 expression. DMSO and CA inhibited hyperosmolarity-induced VCAM-1 expressions, while increasing nitrite levels and Ser1146-eNOS expression. Gene silencing by small interfering RNA reduced the expression of AQP1, and suppressed HG- and HM-stimulated VCAM-1 expression. Calphostin C and LY blunted hyperosmolarity-induced VCAM-1 expression, while increasing the expression of Ser1146-eNOS and nitrite production. Thus HG decreases eNOS activation and induces total VCAM-1 expression in HAEC through a hyperosmolar mechanism. These effects are mediated by activation of the water channels AQP1 and NHE-1, and a PKCβ-mediated intracellular signaling pathway. Targeting osmosignaling pathways may represent a novel strategy to reduce vascular effects of hyperglycemia.

Differential expression of the heat shock protein Hsp70 in natural populations of the tilapia, Sarotherodon melanotheron, acclimatised to a range of environmental salinities

Background

The relationship between environmental variation and induction of heat shock proteins (Hsps) has been much documented under experimental conditions. However, very little is known about such induction in natural populations acclimatised to prevailing environmental conditions. Furthermore, while induction of stress proteins has been well documented in response to environmental contaminants and thermal stressors, little is known about whether factors, such as extreme salinity, are also potential inductors. The black-chinned tilapia Sarotherodon melanotheron is unusual for its ability to colonise estuarine environments in West Africa that are characterised by extremely high salinities. The relationships between mRNA levels of the 70 kDa heat shock protein (Hsp70) and Na⁺, K⁺-ATPase1α (Naka) in the gills, environmental salinity, and a life-history trait (condition factor) were investigated in wild populations of this species sampled from three locations in the Saloum estuary, at salinities ranging from 40 to 100 psu.

Results

The highest Hsp70 and Naka mRNA levels, and the poorest condition factors were recorded in the most saline sampling site (100 psu). The Hsp70 and Naka mRNA were correlated amongst themselves and showed a direct positive correlation with environmental salinity, and a negative correlation with fish condition factor. Thus, the Hsp70 is constitutively overexpressed by S. melanotheron acclimatised to extreme hypersalinity.

Conclusions

These results indicate that, although S. melanotheron can colonise extremely saline environments, the overexpression of Hsp70 combined with the higher Naka mRNA expression reveals that this represents a chronic stress. The induction of Hsp70 was, therefore, a biomarker of chronic hyper-osmotic stress which presumably can be linked to the impaired growth performance and precocious reproduction that have been demonstrated in the populations at the extremely saline sites.

Effects of hyperosmolarity on the Na+-myo-inositol cotransporter SMIT2 stably transfected in the Madin-Darby canine kidney cell line

Myo-inositol (MI) is a compatible osmolyte used by cells to compensate for changes in the osmolarity of their surrounding milieu. In kidney, the basolateral Na+-MI cotransporter (SMIT1) and apical SMIT2 proteins are homologous cotransporters responsible for cellular uptake of MI. It has been shown in the Madin-Darby canine kidney (MDCK) cell line that SMIT1 expression was under the control of the tonicity-sensitive transcription factor, tonicity-responsive enhancer binding protein (TonEBP). We used an MDCK cell line stably transfected with SMIT2 to determine whether variations in external osmolarity could also affect SMIT2 function. Hyperosmotic conditions (+200 mosM raffinose or NaCl but not urea) generated an increase in SMIT2-specific MI uptake by three- to ninefold in a process that required protein synthesis. Using quantitative RT-PCR, we have determined that hyperosmotic conditions augment both the endogenous SMIT1 and the transfected SMIT2 mRNAs. Transport activities for both SMIT1 and SMIT2 exhibited differences in their respective induction profiles for both their sensitivities to raffinose, as well as in their time course of induction. Application of MG-132, which inhibits nuclear translocation of TonEBP, showed that the effect of osmolarity on transfected SMIT2 was unrelated to TonEBP, unlike the effect observed with SMIT1. Inhibition studies involving the hyperosmolarity-related MAPK suggested that p38 and JNK play a role in the induction of SMIT2. Further studies have shown that hyperosmolarity also upregulates another transfected transporter (Na+-glucose), as well as several endogenously expressed transport systems. This study shows that hyperosmolarity can stimulate transport in a TonEBP-independent manner by increasing the amount of mRNA derived from an exogenous DNA segment.

Modulation of Gene Expression Profiles by Hyperosmolarity and Insulin

Cell hydration changes play a key role in the regulation of cell function and critically affect insulin sensitivity of carbohydrate- and protein metabolism. Here, the modulation of gene expression profiles by hyperosmolarity and insulin was examined in H4IIE rat hepatoma cells by cDNA/oligonucleotiode array-, Northern- and Western blot analysis. Osmosensitive expression of the insulin-like growth factor binding protein Igfbp1, the multidrug resistance protein Mrp5 (Abcc5a) and cyclin D1 (Ccnd1) was established at the mRNA and protein level. Despite a hyperosmotic increase of cyclin D1 mRNA induction by insulin, the cyclin D1 protein expression was decreased by hyperosmolarity, suggesting a hyperosmotic interference with cyclin D1 mRNA translation. Hyperosmolarity at the mRNA level blunted the insulin response of betaine homocysteine-S-methyl transferase, the multidrug resistance proteins Mdr1a (Abcb1a) and 2 (Abcb4), the Igfbp 2 and 5, cyclin G1, dual specificity phosphatase Dusp1, signal transducers and activators of transcription Stat3 and 5, catalase and the bile salt export pump Bsep (Abcb11), whereas the insulin response was increased for Mrp5, cyclin D1 and the phosphoenolpyruvate carboxykinase. Insulin effects on the mRNA expression of the eukaryotic initiation factor 4E binding protein 4e-bp1, tubulin, gene 33, growth hormone receptor, keratin18, ornithine decarboxylase and heme oxygenase 1 were largely insensitive to hyperosmolarity. The data indicate that hyperosmolarity differentially modulates insulin sensitivity at the level of gene expression.

High salt culture conditions inhibit serum- and NGF- but not PMA-induced Egr-1 gene transcription in rat C6 glioma cells

Recent studies have suggested that glial cells may play a physiologically important role in the retention and restoration of neuronal cell integrity, proposing the possibility that the proliferation and/or differentiation of glial cells may be related to pathological changes in neural functions in neurodegenerative diseases, and hence, it seems interesting to investigate the expression of genes related to the proliferation and differentiation of glial cells. Following this basic concept, we have previously examined the influence of culture conditions on egr-1 gene expression in rat C6 glioma cells and have shown that brief exposure of these cells to high salt culture medium can induce the down-regulation of egr-1 gene expression. In contrast, the long-term culture of these cells in high salt medium has been shown to primarily reduce their proliferation and secondarily elevate egr-1 gene transcription as a consequence of arresting the cell-cycle progression. Therefore, the effect of high salt culture medium on egr-1 gene expression seems practically unconfirmed, and remains to be further investigated. Then, the effects of various egr-1 gene inducers, such as serum, NGF and phorbol ester PMA, on Egr-1 mRNA levels in the glioma cells were examined under the high salt culture conditions. The brief exposure to high salt culture medium inhibited the elevation of Egr-1 mRNA levels induced by serum replenishment and NGF, but not induced by PMA. These results suggest that the suppression of serum action on egr-1 gene transcription may be the primary and essential event leading to the down-regulation of egr-1 gene expression under the high salt culture conditions.

Gene expression profiling in brain following acute systemic hypertonicity: novel genes possibly involved in osmoadaptation

In brain osmoprotective genes known to be involved in cellular osmoadaptation to hypertonicity, as well as the related transcription factor tonicity-responsive enhancer binding protein (TonEBP) are only expressed in some cell subsets. In the search for other genes possibly involved in osmoadaptation of brain cells we have analyzed, through microarray, the transcriptional profile of forebrain from rats subjected to 45 min, 90 min, and 6 h systemic hypertonicity. Microarray data were validated by quantitative real-time PCR. Around 23 000 genes gave a reliable hybridization signal. The number of genes showing a higher expression increased from around 15 (45 min) up to nearly 200 (6 h). Among about 30 immediate early genes (IEGs) encoding transcription factors, only Atf3, Verge, and Klf4 showed a rapid increased expression. TonEBP-mRNA tissue level and TonEBP-mRNA labeling in neurons remained unchanged whereas TonEBP labeling was rapidly increased in neurons. Sodium-dependent neutral amino acid transporter-2 (SNAT2) encoded by gene Slc38a2 showed a delayed increased expression. The rapid tonicity-induced activation of Atf3, Verge, and Klf4 may regulate genes involved in osmoadaptation. Nfat5 encoding TonEBP is not an IEG and the early tonicity-induced expression of TonEBP in neurons may result from translational activation. Increased expression of sodium-dependent neutral amino-acid transporter 2 may lead to the cellular accumulation of amino acids for adaptation to hypertonicity.

Oxalate exposure provokes HSP 70 response in LLC-PK1 cells, a line of renal epithelial cells: protective role of HSP 70 against oxalate toxicity

We investigated the effects of oxalate on immediate early genes (IEGs) and stress protein HSP 70, commonly induced genes in response to a variety of stresses. LLC-PK1 cells were exposed to oxalate. Gene transcription and translation were monitored by Northern and Western blot analysis. RNA and DNA synthesis were assessed by [(3)H]-uridine and [(3)H]-thymidine incorporation, respectively. Oxalate exposure selectively increased the levels of mRNA encoding IEGs c-myc and c-jun as well as stress protein HSP 70. While expression of c-myc and c-jun was rapid (within 15 min to 2 h) and transient, HSP 70 expression was delayed (approximately 8 h) and stable. Furthermore, oxalate exposure resulted in delayed induction of generalized transcription by 18 h and reinitiation of the DNA synthesis by 24 h of oxalate exposure. Moreover, we show that prior induction of HSP 70 by mild hypertonic exposure protected the cells from oxalate toxicity. To the best of our knowledge this is the first study to demonstrate rapid IEG response and delayed heat-shock response to oxalate toxicity and protective role of HSP 70 against oxalate toxicity to renal epithelial cells. Oxalate, a metabolic end product, induces IEGs c-myc and c-jun and a delayed HSP 70 expression; While IEG expression may regulate additional genetic responses to oxalate, increased HSP 70 expression would serve an early protective role during oxalate stress.

Activator protein-1 contributes to high NaCl-induced increase in tonicity-responsive enhancer/osmotic response element-binding protein transactivating activity

Tonicity-responsive enhancer/osmotic response element-binding protein (TonEBP/OREBP) is a Rel protein that activates transcription of osmoprotective genes at high extracellular NaCl. Other Rel proteins NFAT1-4 and NF-kappaB complex with activator protein-1 (AP-1) to transactivate target genes through interaction at composite NFAT/NF-kappaB.AP-1 sites. TonEBP/OREBP target genes commonly have one or more conserved AP-1 binding sites near TonEBP/OREBP cognate elements (OREs). Also, TonEBP/OREBP and the AP-1 proteins c-Fos and c-Jun are all activated by high NaCl. We now find, using an ORE.AP-1 reporter from the target aldose reductase gene or the same reporter with a mutated AP-1 site, that upon stimulation by high extracellular NaCl, 1) the presence of a wild type, but not a mutated, AP-1 site contributes to TonEBP/OREBP-dependent transcription and 2) AP-1 dominant negative constructs inhibit TonEBP/OREBP-dependent transcription provided the AP-1 site is not mutated. Using supershifts and an ORE.AP-1 probe, we find c-Fos and c-Jun present in combination with TonEBP/OREBP. Also, c-Fos and c-Jun coimmunoprecipitate with TonEBP/OREBP, indicating physical association. Small interfering RNA knockdown of either c-Fos or c-Jun inhibits high NaCl-induced increase of mRNA abundance of the TonEBP/OREBP target genes AR and BGT1. Furthermore, a dominant negative AP-1 also reduces high NaCl-induced increase of TonEBP/OREBP transactivating activity. Inhibition of p38, which is known to stimulate TonEBP/OREBP transcriptional activity, reduces high NaCl-dependent transcription of an ORE.AP-1 reporter only if the AP-1 site is intact. Thus, AP-1 is part of the TonEBP/OREBP enhanceosome, and its role in high NaCl-induced activation of TonEBP/OREBP may require p38 activity.

Tonicity-regulated gene expression

Hypertonicity activates several different transcription factors, including TonEBP/OREBP, that in turn increase transcription of numerous genes. Hypertonicity elevates TonEBP/OREBP transcriptional activity by moving it into the nucleus, where it binds to its cognate DNA element (ORE), and by increasing its transactivational activity. This chapter presents protocols for measuring the transcriptional activity of TonEBP/OREBP and determining its subcellular localization, its binding to OREs, and activity of its transactivation domain.

Cellular Response to Hyperosmotic Stresses

Cells in the renal inner medulla are normally exposed to extraordinarily high levels of NaCl and urea. The osmotic stress causes numerous perturbations because of the hypertonic effect of high NaCl and the direct denaturation of cellular macromolecules by high urea. High NaCl and urea elevate reactive oxygen species, cause cytoskeletal rearrangement, inhibit DNA replication and transcription, inhibit translation, depolarize mitochondria, and damage DNA and proteins. Nevertheless, cells can accommodate by changes that include accumulation of organic osmolytes and increased expression of heat shock proteins. Failure to accommodate results in cell death by apoptosis. Although the adapted cells survive and function, many of the original perturbations persist, and even contribute to signaling the adaptive responses. This review addresses both the perturbing effects of high NaCl and urea and the adaptive responses. We speculate on the sensors of osmolality and document the multiple pathways that signal activation of the transcription factor TonEBP/OREBP, which directs many aspects of adaptation. The facts that numerous cellular functions are altered by hyperosmolality and remain so, even after adaptation, indicate that both the effects of hyperosmolality and adaptation to it involve profound alterations of the state of the cells.

Prostaglandin E2 stimulates expression of osmoprotective genes in MDCK cells and promotes survival under hypertonic conditions

The cells of the renal medulla produce large amounts of prostaglandin E2 (PGE2) via cyclooxygenases (COX)-1 and -2. PGE2 is well known to play a critical role in salt and water balance and maintenance of medullary blood flow. Since renal medullary PGE2 production increases in antidiuresis, and since COX inhibition is associated with damage to the renal medulla during water deprivation, PGE2 may promote the adaptation of renal papillary cells to high interstitial solute concentrations. To address this question, MDCK cells were exposed to a gradual tonicity increase in the presence or absence of 20 microM PGE2 prior to analysis of (i) cell survival, (ii) expression of osmoprotective genes (AR, BGT1, SMIT, HSP70 and COX-2), (iii) subcellular TonEBP/NFAT5 abundance, (iv) TonEBP/NFAT5 transcriptional activity and (v) aldose reductase promoter activity. Cell survival and apoptotic indices after raising the medium tonicity improved markedly in the presence of PGE2. PGE2 significantly increased tonicity-mediated up-regulation of AR, SMIT and HSP70 mRNAs. However, neither nuclear abundance nor TonEBP/NFAT5-driven reporter activity were elevated by PGE2, but aldose reductase promoter activity was significantly increased by PGE2. Interestingly, tonicity-induced COX-2 expression and activity was also stimulated by PGE2, suggesting the existence of a positive feedback loop. These results demonstrate that the major medullary prostanoid, PGE2, stimulates the expression of osmoprotective genes and favours the adaptation of medullary cells to increasing interstitial tonicities, an effect that is not explained directly by the presence of TonEs in the promoter region of the respective target genes. These findings may be relevant in the pathophysiology of medullary damage associated with analgesic drugs.

Osmoregulation in anthozoan-dinoflagellate symbiosis

Endosymbiosis creates a unique osmotic circumstance. Hosts are not only responsible for balancing their internal osmolarity with respect to the external environment, but they must also maintain a compatible osmotic environment for their endosymbionts, which may themselves contribute to the net osmolarity of the host cell through molecular fluxes and/or exchange. Cnidarian hosts that harbor intracellular dinoflagellates (zooxanthellae) are excellent examples of such a symbiosis. These associations are characterized by the exchange of osmotically active compounds, but they are temporally stable under normal environmental conditions indicating that these osmotically driven exchanges are effectively and rapidly regulated. Although we have some knowledge about how asymbiotic anthozoans and algae osmoregulate, our understanding of the physiological mechanisms involved in regulating an intact anthozoan-dinoflagellate symbiosis is poor. Large-scale expulsion of endosymbiotic zooxanthellae, or bleaching, is currently considered to be one of the greatest threats to coral reefs worldwide. To date, there has been little consideration of the osmotic scenarios that occur when these symbioses are exposed to the conditions that normally elicit bleaching, such as increased seawater temperatures and UV radiation. Here we review what is known about osmoregulation and osmotic stress in anthozoans and dinoflagellates and discuss the osmotic implications of exposure to environmental stress in these globally distributed and ecologically important symbioses.

Hyperosmotic stress response: comparison with other cellular stresses

Cellular responses induced by stress are essential for the survival of cells under adverse conditions. These responses, resulting in cell adaptation to the stress, are accomplished by a variety of processes at the molecular level. After an alteration in homeostatic conditions, intracellular signalling processes link the sensing mechanism to adaptive or compensatory changes in gene expression. The ability of cells to adapt to hyperosmotic stress involves early responses in which ions move across cell membranes and late responses characterized by increased synthesis of either membrane transporters essential for uptake of organic osmolytes or of enzymes involved in their synthesis. The goal of these responses is to return the cell to its normal size and maintain cellular homeostasis. The enhanced synthesis of molecular chaperones, such as heat shock proteins, is another important component of the adaptive process that contributes to cell survival. Some responses are common to different stresses, whereas others are specific. In the first part of the review, we illustrate the characteristic and specific features of adaptive response to hypertonicity; we then describe similarities to and differences from other cellular stresses, such as genotoxic agents, nutrient starvation and heat shock.

Proteomic identification of proteins associated with the osmoregulatory transcription factor TonEBP/OREBP: functional effects of Hsp90 and PARP-1

Hypertonicity (e.g., high NaCl) activates the transcription factor tonicity-responsive enhancer/osmotic response element-binding protein (TonEBP/OREBP), increasing transcription of protective genes. In the present studies, by stably expressing amino acids 1-547 of TonEBP/OREBP in HEK 293 cells and immunoprecipitating it plus associated proteins from the nuclei of cells exposed to high NaCl, we identify 14 proteins that are physically associated with TonEBP/OREBP. The associated proteins fall into several classes: 1) DNA-dependent protein kinase, both its catalytic subunit and regulatory subunit, Ku86; 2) RNA helicases, namely RNA helicase A, nucleolar RNA helicase II/Gu, and DEAD-box RNA helicase p72; 3) small or heterogeneous nuclear ribonucleoproteins (snRNPs or hnRNPs), namely U5 snRNP-specific 116 kDa protein, U5 snRNP-specific 200 kDa protein, hnRNP U, hnRNP M, hnRNP K, and hnRNP F; 4) heat shock proteins, namely Hsp90beta and Hsc70; and 5) poly(ADP-ribose) polymerase-1 (PARP-1). We confirm identification of most of the proteins by Western analysis and also demonstrate by electrophoretic mobility-shift assay that they are present in the large complex that binds specifically along with TonEBP/OREBP to its cognate DNA element. In addition, we find that PARP-1 and Hsp90 modulate TonEBP/OREBP activity. PARP-1 expression reduces TonEBP/OREBP transcriptional activity and the activity of its transactivating domain. Hsp90 enhances those activities and sustains the increased abundance of TonEBP/OREBP protein in cells exposed to high NaCl.

Stimulation of aquaporin-5 and transepithelial water permeability in human airway epithelium by hyperosmotic stress

Osmotic water permeability (P(f )) was measured in spheroid-shaped human nasal airway epithelial explants pre-exposed to increasing levels of hyperosmotic stress. The fluid-filled spheroids, derived from nasal polyps, were lined by a single cell layer with the ciliated apical cell membrane facing the outside. The P(f ) was determined from diameter changes of the spheroids in response to changes in bathing medium osmolarity forth and back between 300 and 225 mOsm x l(-1). Continuous diameter measurements also allowed determination of spontaneous fluid absorption. Hyperosmotic pretreatment (increase from 300 up to 600 mOsm x l(-1)) caused a time- and osmolarity-dependent increase (up to approximately 1.5 times) in epithelial P(f ) which was of similar magnitude in cystic fibrosis (CF) and non-CF spheroids. The effect saturated at approximately 450 mOsm x l(-1) and at approximately 24 h. Expression of aquaporin-5 (AQP5), studied by immunofluorescence and confocal microscopy, showed an increase in parallel with the increase in P(f ) following hyperosmotic stress. The AQP5 was localized both in cytoplasmic vesicles and in apical cell membranes. Spontaneous fluid absorption rates were equal in CF and non-CF spheroids and were not significantly influenced by hyperosmotic stress. The results suggest that hyperosmotic stress is an important activator of AQP-5 in human airway epithelium, leading to significantly increased transepithelial water permeability.

Expression of the heat shock protein Hsp70 in chloride target cells of mayfly larvae from motorway retention pond: a biomarker of osmotic shock

The aim of this work was to study, by an in toto immunohistochemical technique, the expression pattern of the heat shock protein, Hsp70, in the widely used bioindicator species Cloeon dipterum (Linnaeus 1761) (Ephemeroptera, Baetidae), living in a motorway retention pond. All sampling and measurements have been performed from March 2002 to March 2003. The water physicochemical analyses have revealed a large increase in Na(+) and Cl(-) concentrations after the de-icing road surface in winter related to motorway maintenance that correspond to an osmotic shock (from 3.1 to 105.7 mg L(-1) for Na(+) and from 3.5 to 193.9 mg L(-1) for Cl(-)). An expression of Hsp70 was observed in the chloride cells only during the osmotic shock. In contrast, the gill insertions were Hsp70 immunoreactive in specimens collected all along the year. For comparison, the expression of Hsp70 was investigated in specimens collected in a temporary pond. C. dipterum larvae living in this pond, not submitted to such osmotic shock, do not express Hsp70 neither in chloride cells nor in gill insertions. Likewise, the expression of Hsp70 was not detected in these structures during the drying period when the abiotic conditions become progressively stressful (elevation of temperature and anoxia). As chloride cells play a key role in osmoregulation, their functional integrity is crucial for the survival of the mayfly larvae in occasionally salty freshwaters. According to the well known protective role of the Hsp70 stress proteins, it is likely that the induction of Hsp70 may protect the chloride cells from osmotic shock injuries resulting from the increase in salinity. So, the Hsp70 induction in chloride cells is designed as a useful biomarker of osmotic shock. The in toto immunohistochemical detection of Hsp70 allows to characterize both the exposure situation and biological effects in target cells induced by stresses. This method could be used as a complementary qualitative approach in the biomarker actual concept. Finally, this investigation that combines this osmotic shock biomarker and this kind of bioindicator species would be a helpful tool for the monitoring of freshwater ecological systems.

Survival in Hostile Environments: Strategies of Renal Medullary Cells

Cells in the renal medulla exist in a hostile milieu characterized by wide variations in extracellular solute concentrations, low oxygen tensions, and abundant reactive oxygen species. This article reviews the strategies adopted by these cells to allow them to survive and fulfill their functions under these extreme conditions.

High-throughput identification of IMCD proteins using LC-MS/MS

The inner medullary collecting duct (IMCD) is an important site of vasopressin-regulated water and urea transport. Here we have used protein mass spectrometry to investigate the proteome of the IMCD cell and how it is altered in response to long-term vasopressin administration in rats. IMCDs were isolated from inner medullas of rats, and IMCD proteins were identified by liquid chromatography/tandem mass spectrometry (LC-MS/MS). We present a WWW-based "IMCD Proteome Database" containing all IMCD proteins identified in this study (n = 704) and prior MS-based identification studies (n = 301). We used the isotope-coded affinity tag (ICAT) technique to identify IMCD proteins that change in abundance in response to vasopressin. Vasopressin analog (dDAVP) or vehicle was infused subcutaneously in Brattleboro rats for 3 days, and IMCDs were isolated for proteomic analysis. dDAVP and control samples were labeled with different cleavable ICAT reagents (mass difference 9 amu) and mixed. This was followed by one-dimensional SDS-PAGE separation, in-gel trypsin digestion, biotin-avidin affinity purification, and LC-MS/MS identification and quantification. Responses to vasopressin for a total of 165 proteins were quantified. Quantification, based on semiquantitative immunoblotting of 16 proteins for which antibodies were available, showed a high degree of correlation with ICAT results. In addition to aquaporin-2 and gamma-epithelial Na channel (gamma-ENaC), five of the immunoblotted proteins were substantially altered in abundance in response to dDAVP, viz., syntaxin-7, Rap1, GAPDH, heat shock protein (HSP)70, and cathepsin D. A 28-protein vasopressin signaling network was constructed using literature-based network analysis software focusing on the newly identified proteins, providing several new hypotheses for future studies.

Hypoglycemia in newborn infants: Features associated with adverse outcomes

The purpose of this review article is to document from the literature values of blood/plasma glucose concentration and associated clinical signs and conditions in newborn infants (both term and preterm) that indicate a reasonable clinical probability that hypoglycemia is a proximate cause of acute and/or sustained neurological injury and to review the physiological and pathophysiological responses to hypoglycemia that may influence the ultimate outcome of newborns with low blood glucose. Our overall conclusion is that there is inadequate information in the literature to define any one value of glucose below which irreparable hypoglycemic injury to the central nervous system occurs, at any one time or for any defined period of time, in a population of infants or in any given infant. Clinical signs of prolonged and severe neurological disturbance (coma, seizures), extremely and persistently low plasma/blood glucose concentrations (0 to <1.0 mmol/l [0 to <18-20 mg/dl] for more than 1-2 h), and the absence of other obvious central nervous system (CNS) pathology (hypoxia-ischemia, intracranial hemorrhage, infection, etc.) are important for the diagnosis of injury due to glucose deficiency. Specific conditions, such as persistent hyperinsulinemia with severe hypoglycemic episodes that include seizures, also contribute to the diagnosis of hypoglycemic injury. Such lack of definitive measures of injury specific to glucose deficiency indicates that clinicians should be on the alert for infants at risk of hypoglycemia and for clinical signs and conditions that might herald severe hypoglycemia; they should have a low threshold for investigating and diagnosing 'hypoglycemia' with frequent measurements of plasma/blood glucose concentration; and they should treat low glucose concentrations promptly and maintain them in a safe range. Because there is no conclusive evidence or consensus in the literature that defines an absolute value or duration of 'hypoglycemia' that must occur, with our without related clinical complications, to produce neurological injury, clinicians should consider the information currently available, determine a 'target' plasma or blood glucose concentration that is acceptable, and treat infants with glucose concentrations below this value accordingly. Our intent in this review article is to highlight the studies relevant to this issue and help clinicians formulate a safe and, hopefully, effective strategy for the diagnosis and treatment of hypoglycemia.