The role of renal transporters and novel regulatory interactions in the TAL that control blood pressure

Hypertension (HTN), a major public health issue is currently the leading factor in the global burden of disease, where associated complications account for 9.4 million deaths worldwide every year (98). Excessive dietary salt intake is among the environmental factors that contribute to HTN, known as salt sensitivity. The heterogeneity of salt sensitivity and the multiple mechanisms that link high salt intake to increases in blood pressure are of upmost importance for therapeutic application. A continual increase in the kidney's reabsorption of sodium (Na+) relies on sequential actions at various segments along the nephron. When the distal segments of the nephron fail to regulate Na+, the effects on Na+ homeostasis are unfavourable. We propose that the specific nephron region where increased active uptake occurs as a result of variations in Na+ reabsorption is at the thick ascending limb of the loop of Henle (TAL). The purpose of this review is to urge the consideration of the TAL that contributes to the pathophysiology of salt sensitive HTN. Further research in this area will enable development of a therapeutic application for targeted treatment

Characterisation of Uromodulin as a candidate gene for human essential hypertension

Essential hypertension is a highly hereditable trait of complex aetiology, where multiple environmental and life style factors contribute to blood pressure variation. Family health studies of blood pressure suggest that heritability accounts for 30 – 50 % of variation. Consequently the study of genetic architecture has proven useful to detect a small number of genes, loci, and single nucleotide polymorphisms (SNPs) that have appreciable effects on blood pressure. Genetic linkage and association methods have long provided the foundation of gene identification in humans. Although linkage studies have proven to be highly successful in identifying genes of monogenic (or Mendelian) disorders, this analysis has minimal or limited power to detect gene of complex traits and disease. Furthermore, candidate gene approaches have not yet reported any reproducible associations with hypertension. Accordingly, gene identification efforts have become increasingly reliant on association approaches. A recent genome wide association study (GWAS) identified a locus upstream of the Uromodulin (UMOD) gene transcriptional start site, which was associated with hypertension. This group used an extreme case - control design in a discovery sample of 1,621 hypertension cases and 1,699 hypercontrols, representing the top 2% and bottom 20% of the BP distribution. The minor G allele of rs13333226 when adjusted for estimated glomerular filtration rate (eGFR) was associated with a 7 % lower risk of developing hypertension. UMOD encodes the protein uromodulin which is interchangeably known as Tamm Horsfall protein (THP). It is a kidney specific protein and is exclusively synthesised at the level of the thick ascending limb of the loop of Henle (TAL) and is the most abundant protein in human urine. The biological role of uromodulin still remains unclear; however other UMOD variants have been associated with chronic kidney disease. Due to UMODs exclusive expression at the kidney it may have a role in regulating blood pressure via sodium homeostasis mechanisms. As hypertension is characterised by a disturbance of renal function that subsequently leads to an augmented Na+ reabsorption, the present study aimed to follow up the GWAS signal to assess whether altered 18 UMOD expression and/or function impacts on sodium homeostasis and influence blood pressure phenotypes. Promoter activity assays here demonstrate that the index SNP (rs13333226) is not a functional variant causing altered transcription, however the minor G allele of rs13333226 is associated with reduced promoter activity. These findings are consistent with the original GWAS study that this allele is associated with lower risk of hypertension. In this study we reported a SNP in LD with rs13333226 within the 2 Kb promoter region (rs4997081) that may be a causal variant altering transcriptional activity of UMOD. Furthermore, with computational and experimental evidence we show that binding of rs4997081 to TFAP2A in a genotype dependent manner leads to transcriptional changes of UMOD which were associated with altered sodium reabsorption via downstream signalling of Tumor necrosis factor alpha (TNF-α). Cardiovascular characterisation of UMOD knockout mice (KO) revealed significantly lower systolic blood pressure (SBP) in comparison to the wild type (WT) counterparts. The reported novel blood pressure phenotypes in the KO mice were not sensitive to change by salt loading (2% NaCl) over a six week period. KO mice displayed increased concentrations of sodium in the urine upon salt loading, to greater levels than the WT mice (± 2% NaCl). Urinary electrolyte analysis corrected to creatinine levels revealed augmented sodium loss in the KO mice during the high salt diet. Chronic renal function curves demonstrate that the reduced SBP is attained by increased natriuresis via augmented GFR in the KO mice. Histological examination illustrated cellular swelling and papillary oedema in the KO mice before and after salt loading which may be triggered by the pro-inflammatory cytokines TNF-α and Interleukin 1 (IL-1) according to metabolomic analysis. These inflammatory signals may affect Na+ homeostasis at the TAL in the KO mice by reducing NKCC2 expression. Expression analysis studied in outer medulla tissue illustrated down regulation of the major NaCl transporters in the absence of UMOD which were further attenuated upon salt loading conditions possibly by increased levels of TNF-α at the TAL. KO mice displayed increased levels of urinary TNF-α in addition to augmented mRNA abundance in the outer medulla tissue. In addition, immunohistochemical analysis revealed reduced NKCC2 staining with increased TNF-α staining in renal tissue of the KO mice during normal and high salt diets. These results were 19 confirmed in vitro and suggest UMOD acts as a negative regulator of TNF-α production by the TAL to maintain NaCl/volume homeostasis. We have confirmed with a small pilot study using human renal tissue samples from normotensive and hypertensive individuals, that in times of altered UMOD expression there are changes in NKCC2 and NHE3 expression levels, but not TNF- α. More interestingly we have demonstrated that UMOD, NKCC2, and NHE3 expression levels are altered in a genotype dependant manner, in that the minor G allele of rs13333226 appears to be associated with blood pressure via altered sodium homeostasis

A change in temperature modulates defence to yellow (stripe) rust in wheat line UC1041 independently of resistance gene Yr36

Background Rust diseases are of major importance in wheat production worldwide. With the constant evolution of new rust strains and their adaptation to higher temperatures, consistent and durable disease resistance is a key challenge. Environmental conditions affect resistance gene performance, but the basis for this is poorly understood. Results Here we show that a change in day temperature affects wheat resistance to Puccinia striiformis f. sp tritici (Pst), the causal agent of yellow (or stripe) rust. Using adult plants of near-isogenic lines UC1041 +/- Yr36, there was no significant difference between Pst percentage uredia coverage in plants grown at day temperatures of 18°C or 25°C in adult UC1041 + Yr36 plants. However, when plants were transferred to the lower day temperature at the time of Pst inoculation, infection increased up to two fold. Interestingly, this response was independent of Yr36, which has previously been reported as a temperature-responsive resistance gene as Pst development in adult UC1041 -Yr36 plants was similarly affected by the plants experiencing a temperature reduction. In addition, UC1041 -Yr36 plants grown at the lower temperature then transferred to the higher temperature were effectively resistant and a temperature change in either direction was shown to affect Pst development up to 8 days prior to inoculation. Results for seedlings were similar, but more variable compared to adult plants. Enhanced resistance to Pst was observed in seedlings of UC1041 and the cultivar Shamrock when transferred to the higher temperature. Resistance was not affected in seedlings of cultivar Solstice by a temperature change in either direction. Conclusions Yr36 is effective at 18°C, refining the lower range of temperature at which resistance against Pst is conferred compared to previous studies. Results reveal previously uncharacterised defence temperature sensitivity in the UC1041 background which is caused by a change in temperature and independently of Yr36. This novel phenotype is present in some cultivars but absent in others, suggesting that Pst defence may be more stable in some cultivars than others when plants are exposed to varying temperatures

Inflammation and salt in young adults: the African-PREDICT study

Purpose: Low-grade inflammation and a diet high in salt are both established risk factors for cardiovascular disease. High potassium (K+) intake was found to counter increase in blood pressure due to high salt intake and may potentially also have protective anti-inflammatory effects. To better understand these interactions under normal physiological conditions, we investigated the relationships between 22 inflammatory mediators with 24-h urinary K+ in young healthy adults stratified by low, medium and high salt intake (salt tertiles). We stratified by ethnicity due to potential salt sensitivity in black populations. Methods: In 991 healthy black (N = 457) and white (N = 534) adults, aged 20–30 years, with complete data for 24-h urinary sodium and K+, we analysed blood samples for 22 inflammatory mediators. Results: We found no differences in inflammatory mediators between low-, mid- and high-sodium tertiles in either the black or white groups. In multivariable-adjusted regression analyses in white adults, we found only in the lowest salt tertile that K+ associated negatively with pro-inflammatory mediators, namely interferon gamma, interleukin (IL) -7, IL-12, IL-17A, IL-23 and tumour necrosis factor alpha (all p ≤ 0.046). In the black population, we found no independent associations between K+ and any inflammatory mediator. Conclusion: In healthy white adults, 24-h urinary K+ associated independently and negatively with specific pro-inflammatory mediators, but only in those with a daily salt intake less than 6.31 g, suggesting K+ to play a protective, anti-inflammatory role in a low-sodium environment. No similar associations were found in young healthy black adults

Phloem connectivity and transport are not involved in mature plant resistance (MPR) to Potato Virus Y in different potato cultivars, and MPR does not protect tubers from recombinant strains of the virus

This research was funded by UK Research and Innovation (BBSRC Grant # BB/L011840/1; Ecology and Epidemiology of Infectious Diseases), by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS) Division, and by the James Hutton Institute.The aims of this study were: i) to investigate mature plant resistance (MPR) against four strains of Potato virus Y (PVYO, PVYN, PVYNTN and PVYN−Wi) in potato cultivars that differ in maturity (e.g. early or maincrop) at different developmental stages, and ii) to determine whether phloem translocation of photoassimilates at different stages including the source-sink transition influences MPR. The data showed that MPR was functional by the flowering stage in all cultivars, and that the host-pathogen interaction is highly complex, with all three variables (potato cultivar, virus strain and developmental stage of infection) having a significant effect on the outcome. However, virus strain was the most important factor, and MPR was less effective in protecting tubers from recombinant virus strains (PVYNTN and PVYN−Wi). Development of MPR was unrelated to foliar phloem connectivity, which was observed at all developmental stages, but a switch from symplastic to apoplastic phloem unloading early in tuber development may be involved in the prevention of tuber infections with PVYO. Recombinant virus strains were more infectious than parental strains and PVYNTN has a more effective silencing suppressor than PVYO, another factor that may contribute to the efficiency of MPR. The resistance conferred by MPR against PVYO or PVYN may be associated with or enhanced by the presence of the corresponding strain-specific HR resistance gene in the cultivar.Publisher PDFPeer reviewe

Characterization of the Myocardial Inflammatory Response in Acute Stress-Induced (Takotsubo) Cardiomyopathy

This work was supported by grants from NHS Grampian Endowments and British Heart Foundation Project Grant no. PG/15/108/31928 The authors have reported that they have no relationships relevant to the contents of this paper to disclose.Peer reviewedPublisher PD

Effect of increasing fruit and vegetable intake by dietary intervention on nutritional biomarkers and attitudes to dietary change : a randomised trial

This work was funded by The Scottish Government Rural and Environmental Science and Analytical Sciences Division (RESAS) and supported by the Rank Prize Funds.Peer reviewedPublisher PD

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 characterisation study validated Uromodulin as a blood pressure gene. Uromodulin is a glycoprotein exclusively synthesised 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 to delineate salt stress pathways in tubules isolated from Umod(+/+) mice (a model of sodium retention) and Umod(-/-) mice (a model of sodium depletion) +/-300mOsmol sodium chloride (n=3 per group) performing RNA-Seq. In response to salt stress, the tubules of Umod(+/+) mice displayed an up regulation of heat shock transcripts. The greatest changes occurred in the expression of: Hspa1a (Log2 fold change 4.35, p=2.48e-12) and Hspa1b (Log2 fold change 4.05, p=2.48e-12). This response was absent in tubules of Umod(-/-) mice. Interestingly, 7 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

Natural resistance to Potato virus Y in <i>Solanum tuberosum</i> Group Phureja

This work was supported by funding from the Scottish Government’s Rural and Environmental Science and Analytical Services (RESAS) Division.A new source of genetic resistance derived from Solanum tuberosum Group Phureja against Potato virus Y (PVY) was identified and genetically characterised in three diploid biparental potato populations. Segregation data for two populations (05H1 and 08H1) suggested the presence of a single dominant gene for resistance to PVY which, following DaRT analysis of the 08H1 cross, was mapped to chromosome 9. More detailed genetic analysis of resistance utilised a well-characterised SNP-linkage map for the 06H1 population, together with newly generated marker data. In these plants, which have both S. tuberosum Group Phureja and S. tuberosum Group Tuberosum in their pedigree, the resistance was shown to map to chromosome 9 at a locus not previously associated with PVY resistance, although there is evidence for at least one other genetic factor controlling PVY infection. The resistance factor location on chromosome 9 (named as Ry(o)phu) suggests a potential role of NB-LRR genes in this resistance. Phenotypic analysis using a GUS-tagged virus revealed that a small amount of PVY replication occurred in occasional groups of epidermal cells in inoculated leaves of resistant plants, without inducing any visible hypersensitive response. However, the virus did not enter the vascular system and systemic spread was completely prevented.Publisher PDFPeer reviewe