In salt-sensitive hypertension, the accumulation of Na(+) in tissue has been presumed to be accompanied by a commensurate retention of water to maintain the isotonicity of body fluids. We show here that a high-salt diet (HSD) in rats leads to interstitial hypertonic Na(+) accumulation in skin, resulting in increased density and hyperplasia of the lymphcapillary network. The mechanisms underlying these effects on lymphatics involve activation of tonicity-responsive enhancer binding protein (TonEBP) in mononuclear phagocyte system (MPS) cells infiltrating the interstitium of the skin. TonEBP binds the promoter of the gene encoding vascular endothelial growth factor-C (VEGF-C, encoded by Vegfc) and causes VEGF-C secretion by macrophages. MPS cell depletion or VEGF-C trapping by soluble VEGF receptor-3 blocks VEGF-C signaling, augments interstitial hypertonic volume retention, decreases endothelial nitric oxide synthase expression and elevates blood pressure in response to HSD. Our data show that TonEBP-VEGF-C signaling in MPS cells is a major determinant of extracellular volume and blood pressure homeostasis and identify VEGFC as an osmosensitive, hypertonicity-driven gene intimately involved in salt-induced hypertension.

Gene expression in human tissue has primarily been studied on the transcriptional level, largely neglecting translational regulation. Here, we analyze the translatomes of 80 human hearts to identify new translation events and quantify the effect of translational regulation. We show extensive translational control of cardiac gene expression, which is orchestrated in a process-specific manner. Translation downstream of predicted disease-causing proteintruncating variants appears to be frequent, suggesting inefficient translation termination. We identify hundreds of previously undetected microproteins, expressed from lncRNAs and circRNAs, for which we validate the protein products in vivo. The translation of microproteins is not restricted to the heart and prominent in the translatomes of human kidney and liver. We associate these microproteins with diverse cellular processes and compartments and find that many locate to the mitochondria. Importantly, dozens of microproteins are translated from lncRNAs with well-characterized noncoding functions, indicating previously unrecognized biology.

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Abstract-Renin secretion and synthesis in renal juxtaglomerular cells are controlled by short feed back loops involving angiotensin II and the intrarenal blood pressure. The operating mechanisms of these negative feed back regulators are widely unknown, except for the fact that both require calcium to exert their inhibitory action. We here show that in the absence of connexin40 (Cx40), which form gap junctions between juxtaglomerular and endothelial cells, the negative control of renin secretion and synthesis by angiotensin II and by intravasal pressure is abrogated, while the regulation by salt intake and ␤-adrenergic stimulation is maintained. Renin secretion from Cx40-deficient kidneys or wild-type kidneys treated with the nonselective gap junction blocker 18␣-glycyrrhetinic acid (10 mol/L) resembles the situation in wild-type kidneys in the absence of extracellular calcium. This disturbed regulation is reflected by an enhanced plasma renin concentration despite an elevated blood pressure in Cx40-deficient mice. These findings indicate that Cx40 connexins and likely intercellular communication via Cx40-dependent gap junctions mediate the calcium-dependent inhibitor effects of angiotensin II and of intrarenal pressure on renin secretion and synthesis. Because Cx40 gap junctions are also formed between renin producing cells and endothelial cells our finding could provide additional information to suggest that the endothelium may be strongly involved in the control of the renin system. (Circ Res. 2007;100:556-563.)

The term Bartter syndrome encompasses a heterogeneous group of autosomal recessive salt-losing nephropathies that are caused by disturbed transepithelial sodium chloride reabsorption in the distal nephron. Mutations have been identified in the NKCC2 (Na(+)-K(+)-2Cl(-)) cotransporter and ROMK potassium channel, which cooperate in the process of apical sodium chloride uptake, and ClC-Kb chloride channels, which mediate basolateral chloride release. Recently, mutations in barttin, a protein not related to any known ion transporter or channel, were described in BSND, a variant of Bartter syndrome associated with sensorineural deafness. Here we show that barttin functions as an activator of ClC-K chloride channels. Expression of barttin together with ClC-K in Xenopus oocytes increased ClC-K current amplitude, changed ClC-K biophysical properties, and enhanced ClC-K abundance in the cell membrane. Co-immunoprecipitation revealed a direct interaction of barttin with ClC-K. We performed in situ hybridization on rat kidney slices and RT-PCR analysis on microdissected nephron segments to prove co-expression of barttin, ClC-K1 and ClC-K2 along the distal nephron. Functional analysis of BSND-associated point mutations revealed impaired ClC-K activation by barttin. The results demonstrate regulation of a CLC chloride channel by an accessory protein and indicate that ClC-K activation by barttin is required for adequate tubular salt reabsorption.

Rate of erythropoietin formation in humans in response to acute hypobaric hypoxia. J. Appl. Physiol. 66(4): [1785][1786][1787][1788] 1989.-This study was carried out to investigate the early changes in erythropoietin (EPO) formation in humans in response to hypoxia. Six volunteers were exposed to simulated altitudes of 3,000 and 4,000 m in a decompression chamber for 5.5 h. EPO was measured by radioimmunoassay in serum samples withdrawn every 30 min during altitude exposure and also in two subjects after termination of hypoxia (4,000 m). EPO levels during hypoxia were significantly elevated after 114 and 84 min (3,000 and 4,000 m), rising thereafter continuously for the period investigated. Mean values increased from 16.0 to 22.5 mu/ml (3,000 m) and from 16.7 to 28.0 mu/ml (4,000 m). This rise in EPO levels corresponds to 1.8-fold (3,000 m) and 3.0-fold (4,000 m) increases in the calculated production rate of the hormone. After termination of hypoxia, EPO levels continued to rise for ~1.5 h and after 3 h declined exponentially with an average half-life time of 5.2 h. simulated altitude; half-life time; radioimmunoassay THE ADJUSTMENT OF THE erythrocyte mass to the availability of 02 in the mammalian organism is brought about by renal secretion of erythropoietin (EPO). However, the regulation of renal EPO production is not completely understood. Present knowledge is mainly based on experiments in laboratory animals. Direct data related to the regulation of EPO production in humans are confined to two observations. First, it has been shown that in anemias serum EPO levels are inversely correlated with the hematocrit (5,7,9), and, second, it was demonstrated that a sojourn at high altitude increases EPO concentrations in blood and urine (1, 3, 8,(12)(13)(14) 17). However, when subjects travel to high altitude (1, 3,8, 12, 14), the interval required for ascent does not allow the precise study of early increase in EPO formation, because the onset of hypoxia is gradual and not clearly defined. During mountaineering expeditions (1, 12) additional factors, e.g., physical exercise, may also influence EPO formation in an unpredictable manner. Furthermore, with the exception of one study (12), in previous investigations in humans only bioassays for EPO that indicate a change in the serum EPO level at least threefold above the normal value were available.The present study was therefore carried out to show a more definitive association between hypoxia and EPO formation in humans. We measured serum EPO levels with a sensitive radioimmunoassay in healthy volunteers exposed to simulated altitudes of 3,000 (9,840 ft) and 4,000 m (13,120 ft) under controlled conditions in a decompression chamber. The changes in serum EPO levels after acute onset and after termination of hypoxia, as well as the relationship between alveolar partial pressure of 02 and EPO formation were determined. SUBJECTSANDMETHODSSubjects. Six male volunteers (24-39 yr) participated in the study after being informed about the aim of the investigation and the ex...

Retroviral elements are found in abundance throughout the human genome but only rarely have alterations of endogenous genes by retroviral insertions been described. Herein we report that a human endogenous retrovirus (HERV) type C is inserted in the human growth factor gene pleiotrophin (PTN) between the 5 untranslated and the coding region. This insert in the human genome expands the region relative to the murine gene. Studies with promoterreporter constructs show that the HERV insert in the human PTN gene generates an additional promoter with trophoblastspecific activity. Due to this promoter function, fusion transcripts between HERV and the open reading frame of PTN (HERV-PTN) were detected in all normal human trophoblast cell cultures as early as 9 weeks after gestation (n ‫؍‬ 7) and in all term placenta tissues (n ‫؍‬ 5) but not in other normal adult tissues. Furthermore, only trophoblast-derived choriocarcinoma cell lines expressed HERV-PTN mRNA whereas tumor cell lines derived from the embryoblast (teratocarcinoma) or from other lineages failed to do so. We investigated the significance of HERV-PTN mRNA in a choriocarcinoma model by targeting this transcript with ribozymes and found that the depletion of HERV-PTN mRNA prevents human choriocarcinoma growth, invasion, and angiogenesis in mice. This suggests that the tissue-specific expression of PTN due to the HERV insertion in the human genome supports the highly aggressive growth of human choriocarcinoma and possibly of the human trophoblast.Pleiotrophin (PTN) is a secreted heparin-binding polypeptide growth factor (1) with mitogenic (1-3) and transforming effects (3) on fibroblasts and growth factor activity on epithelial (2, 4, 5) and endothelial (2, 5, 6) cells. Furthermore, PTN induces the release of proteolytic enzymes from endothelial cells (7) and stimulates neurite outgrowth (8) and tube formation by endothelial cells in vitro (5) as well as angiogenesis in the rabbit corneal pocket assay (6). PTN gene expression is regulated in a time-and tissue-specific manner during rodent development and PTN mRNA is found at high levels in the central nervous system during the perinatal period, is downregulated thereafter, and is present at low levels in a few adult tissues (1, 9-11). On the other hand, the PTN gene is upregulated in several human tumor tissues and tumor cell lines (2) but little is known about the regulatory elements in this gene (12).To understand the mechanisms that regulate expression of the human PTN gene, we studied 5Ј ends of PTN mRNA isolated from various human tissues that express the PTN gene. To our surprise we found that all placenta samples, in contrast to brain, expressed PTN mRNA with 5Ј exons that are homologous to a human endogenous retrovirus (HERV) and are spliced onto the intact open reading frame (ORF) of PTN. Upon analysis of human genomic DNA, we located the insertion of an HERV fragment into the intron region upstream of the ORF of the human PTN gene expanding this region relative to the ancestral PTN gene share...

Sepsis-associated acute renal failure is characterized by decreased GFR and tubular dysfunction. The pathogenesis of endotoxemic tubular dysfunction with failure in urine concentration and increased fractional sodium excretion is poorly understood. This study investigated the regulation of renal sodium transporters during severe inflammation in vivo and in vitro. Injection of high-dosage LPS reduced BP and GFR, increased fractional sodium excretion, and strongly decreased the expression of Na . ARF is present in 20% of patients with severe sepsis and 50% of patients with septic shock (2) and is clinically defined as a deterioration of GFR and tubular function. Little is known about the pathophysiology of endotoxemic tubular dysfunction with failure in urine concentration and increased fractional sodium excretion.Urine concentration requires establishment and maintenance of a hypertonic medullary interstitium, which depends on the NaCl reabsorption (3). The Na ϩ /H ϩ -exchanger (NHE3) and the functional unit of ROMK and Na ϩ -K ϩ -2Cl Ϫ co-transporter (NKCC2) are key components that are responsible for sodium reabsorption by the thick ascending limb (3,4). ROMK, also located in the cortical collecting duct (CCD), is responsible for recycling K ϩ across the apical membrane, which is critical for continuous sodium uptake by NKCC2 (5-8). In the collecting duct, the vasopressin-regulated epithelial sodium channel (ENaC), composed of three homologous subunits (9,10), accounts for the fine adjustment of the sodium reabsorption. The Na ϩ /K ϩ -ATPase in the basolateral membrane is essential for the efficient sodium reabsorption along the whole nephron.Findings that endotoxemia diminishes expression of renal V 2 receptors and aquaporin-2 (11) directed our interest toward the regulation of tubular sodium transporters during experimental sepsis. We hypothesized that endotoxemia downregulates tubular sodium transporters. On the basis of our previous findings that proinflammatory cytokines downregulate several vasoconstrictive receptors in renal tissue (12-15), we assumed that cytokines affect the expression of renal sodium transporters.To test our hypotheses, we performed in vivo experiments with (1) mice that were administered an injection of LPS as a model for severe experimental Gram-negative sepsis; (2) mice that were administered injections the cytokines TNF-␣, IL-1␤, or IFN-␥; (3) knockout mice that had a deficiency for TNF-␣, IL-1 receptor-1 (IL-1R1), or IFN-␥ and were administered an injection of LPS; (4) mice that did or did not have glucocorticoid pretreatment, which attenuates LPS-induced cytokine production (16 -18) and were administered an injection of LPS; (5) mice that were administered an injection of low-dosage LPS using as a model of inflammation without systemic hypotension and renal ischemia; (6) mice with renal artery clipping to reduce renocortical flux to 40% of controls to imitate LPS-induced renal hypoperfusion (19); and (7) mice with renal ischemia-reperfusion injury by complete renal artery occlus...