Challenges and Approach to Identifying Individuals with Salt Sensitivity of Blood Pressure

BACKGROUND

Salt sensitivity of blood pressure (SSBP) is a trait observed in both humans and animals, characterized by an increase in blood pressure (BP) following salt loading or a drop in BP following salt depletion.

SUMMARY

This "intermediate" phenotype has been reported in a sizable portion of individuals regardless of their hypertensive status; hypertensives (27-51%), normotensives (18-47%). Further, in epidemiological studies, this phenotype is associated with increased adverse cardiovascular outcomes, risk factors, and reduced survival rates. Herein, we review the challenges in the assessment of SSBP, heterogeneity in the assessment method and protocols, and how these differences could affect the results. Further, we review how to identify individuals with SSBP in the clinic by using clinical and genetic data. No clinical approach has yet provided sufficient sensitivity and specificity to identify those with SSBP. Thus, SSBP is not routinely identified in the clinic. Current genetic data suggest that genotyping may support such an office approach. To date, studies in 18 genes have provided sufficient evidence and reproducible data to identify potential mechanisms involved in subsets of subjects with hypertension and SSBP.

KEY MESSAGE

Proof-of-concept clinical trials using genetic biomarkers to determine and treat individuals with SSBP are ongoing. Their results will provide critical evidence to support genetic-focused, mechanistically driven algorithms to identify and treat, specifically, individuals with SSBP - personalized medicine.

Association study of fasting blood glucose and salt sensitivity of blood pressure in community population: The EpiSS study

BACKGROUND AND AIMS

To evaluate the association between fasting blood glucose (FBG) and salt sensitivity of blood pressure (SSBP).

METHODS AND RESULTS

This study is based on the baseline survey of systemic epidemiology of salt sensitivity study. Subjects were classified into salt sensitive (SS) and salt resistant groups according to blood pressure (BP) changes during the modified Sullivan's acute oral saline load and diuresis shrinkage test. Multivariate logistic and linear regression were used to evaluate associations between FBG with SS or BP changes. A total of 2051 participants were included in the analyses with 581 (28.33%) for SS. Multiple analysis showed that for every interquartile range increase in FBG, the OR (95%CI) for SS was 1.140 (1.069, 1.215), β (95%CI) for mean arterial pressure change (ΔMAP₁), systolic and diastolic BP changes during saline load were 0.421 (0.221, 0.622), 0.589 (0.263, 0.914) and 0.340 (0.149, 0.531), respectively. Compared to the lowest FBG quartile (Q₁), the OR (95%CI) for SS in Q₃ and Q₄ were 1.342 (1.014, 1.776) and 1.577 (1.194, 2.084), respectively. Compared to subjects with normal FBG, the β (95%CI) for ΔMAP₁ was 0.973 (0.055, 1.891) in subjects with impaired FBG, and was 1.449 (0.602, 2.296) in patients with diabetes mellitus. Stratified analyses showed significant and stronger associations between FBG with SSBP in youngers, females, hypertensives, non-diabetics, non-current smokers and non-current drinkers.

CONCLUSION

Our findings suggest FBG is an independent, dose-dependent associated factor for SSBP, and prevention of SS focusing on controlling FBG elevation in the early stage is important.

Overexpression of wheat α-mannosidase gene TaMP impairs salt tolerance in transgenic Brachypodium distachyon

The TaMP gene from wheat encodes an α-mannosidase induced by salt stress that functions as negative regulator of salt tolerance in plants. Salt stress significantly affects growth and yield of crop plants. The α-mannosidases function in protein folding, trafficking, and endoplasmic reticulum-associated degradation in eukaryotic cells, and they are involved in abiotic stress tolerance in plants. Previously, we identified the α-mannosidase gene TaMP in wheat (Triticum aestivum). In this study, we investigated the function of TaMP in salt stress tolerance. TaMP expression was induced in wheat leaves by salt, drought, abscisic acid, and H₂O₂ treatments. Overexpressing TaMP in Brachypodium distachyon was associated with a salt-sensitive phenotype. Under salt stress, the overexpressing plants had reduced height, delayed growth status, low photosynthetic rate, decreased survival rate, and diminished yield. Moreover, the overexpression of TaMP aggravated the tendency for ions to become toxic under salt stress by significantly affecting the Na⁺ and K⁺ contents in cells. In addition, TaMP could negatively regulate salt tolerance by affecting the antioxidant enzyme system capacity and increasing the reactive oxygen species accumulation. Our study was helpful to understand the underlying physiological and molecular mechanisms of salt stress tolerance in plants.

A novel beta-1,4 glucanase produced by symbiotic Bacillus sp. CF96 isolated from termite (Anacanthotermes)

A novel beta-1,4-glucanase was purified and characterized from symbiotic Bacillus sp. CF96 of termite. The SDS-PAGE and zymogram analyses revealed a molecular mass of 35.6 kDa. Optimal activity was at 50 °C and pH 5.5, while the enzyme was active over a wide range of temperature 20-80 °C and pH 4-10 and interestingly more than 60% of the maximum activity remained up to pH 9. The enzyme activity increased in the presence of hexane, chloroform and methanol (20% v/v). while, the enzyme activity was inhibited by metal ions such as Mn²⁺, Hg²⁺, Cu²⁺, Zn²⁺, Mg²⁺, Fe²⁺. The isolated enzyme was able to degrade carboxymethyl cellulose (CMC), avicel and cellulose. Cellobiose was the hydrolytic product of enzymatic reaction based on thin layer chromatography (TLC) analysis. Regarding beta-1,4 endo/exoglucanase activity and high temperature, pH and solvent stability, the enzyme has potential for various industrial applications especially in designing pesticide for termite.

Tissue-specific effects of targeted mutation of Mir29b1 in rats

BACKGROUND

miR-29 is a master regulator of extracellular matrix genes, but conflicting data on its anti-fibrotic effect have been reported. miR-29 improves nitric oxide (NO) production in arterioles by targeting Lypla1. Mir29b1 targeted mutation exacerbates hypertension in a model derived from the Dahl salt-sensitive rat. We examined the effect of Mir29b1 mutation on tissue fibrosis and NO levels with a focus on kidney regions.

METHODS

Mir29b1 targeted mutant rats on the genetic background of SS-Chr13^BN rats were studied. Masson trichrome staining, molecular and biochemical assays, metabolic cage studies, and bioinformatic analysis of human genomic data were performed.

FINDINGS

The abundance of miR-29b and the co-transcribed miR-29a was substantially lower in mutant rats. Tissue fibrosis was significantly increased in the renal outer medulla, but not in the renal cortex, heart or liver in mutant rats on a 0.4% NaCl diet. Lypla1 protein abundance was significantly higher and NO levels lower in the renal outer medulla, but not in the renal cortex. After 14 days of a 4% NaCl diet, 24 h urine volume and urinary sodium excretion was significantly lower in mutant rats, and tissue fibrosis became higher in the heart. NO levels were lower in the renal outer medulla and heart, but not in the renal cortex. Human miR-29 genes are located in proximity with blood pressure-associated single nucleotide polymorphisms.

INTERPRETATION

The renal outer medulla might be particularly susceptible to the injurious effects of a miR-29 insufficiency, which might contribute to the development of hypertension in Mir29b1 mutant rats.

A guanine insert in OsBBS1 leads to early leaf senescence and salt stress sensitivity in rice (Oryza sativa L.)

A rice receptor-like kinase gene OSBBS1/OsRLCK109 was identified; this gene played vital roles in leaf senescence and the salt stress response. Early leaf senescence can cause negative effects on rice yield, but the underlying molecular regulation is not fully understood. bilateral blade senescence 1 (bbs1), an early leaf senescence mutant with a premature senescence phenotype that occurs mainly performing at the leaf margins, was isolated from a rice mutant population generated by ethylmethane sulfonate (EMS) treatment. The mutant showed premature leaf senescence beginning at the tillering stage and exhibited severe symptoms at the late grain-filling stage. bbs1 showed accelerated dark-induced leaf senescence. The OsBBS1 gene was cloned by a map-based cloning strategy, and a guanine (G) insertion was found in the first exon of LOC_Os03g24930. This gene encodes a receptor-like cytoplasmic kinase and was named OsRLCK109 in a previous study. Transgenic LOC_Os03g24930 knockout plants generated by a CRISPR/Cas9 strategy exhibited similar early leaf senescence phenotypes as did the bbs1 mutant, which confirmed that LOC_Os03g24930 was the OsBBS1 gene. OsBBS1/OsRLCK109 was expressed in all detected tissues and was predominantly expressed in the main vein region of mature leaves. The expression of OsBBS1 could be greatly induced by salt stress, and the bbs1 mutant exhibited hypersensitivity to salt stress. In conclusion, this is the first identification of OsRLCKs participating in leaf senescence and playing critical roles in the salt stress response in rice (Oryza sativa L.).