Sex Specific Adaptations to High Salt Diet Preserve Electrolyte Homeostasis with Distinct Sodium Transporter Profiles

Kidneys continuously filter an enormous amount of sodium and adapt kidney Na+ reabsorption to match Na+ intake to maintain circulatory volume and electrolyte homeostasis. Males (M) respond to high salt (HS) diet by translocating proximal tubule Na+/H+ exchanger 3 (NHE3) to the base of the microvilli, reducing activated forms of the distal NaCl cotransporter (NCC) and epithelial Na+ channel (ENaC). Males and females (M, F) on normal salt (NS) diets present sex-specific profiles of "transporters" (co-transporters, channels, pumps and claudins) along the nephron, e.g., F exhibit 40% lower NHE3 and 200% higher NCC abundance vs. M. We tested the hypothesis that adaptations to HS diet along the nephron will, likewise, exhibit sexual dimorphisms. C57BL/6J mice were fed 15 d with 4% NaCl diet (HS) vs. 0.26% NaCl diet (NS). On HS, M and F exhibited normal plasma [Na+] and [K+], and similar urine volume, Na+, K+, and osmolal excretion rates normalized to body weight. In F, like M, HS lowered abundance of distal NCC, phosphorylated NCC, and cleaved (activated) forms of ENaC. The adaptations associated with achieving electrolyte homeostasis exhibit sex-dependent and independent mechanisms: Sex differences in baseline "transporters" abundance persist during HS diet, yet the fold changes during HS diet (normalized to NS) are similar along the distal nephron and collecting duct. Sex dependent differences observed along the proximal tubule during HS show that female kidneys adapt differently from patterns reported in males yet achieve and maintain fluid and electrolyte homeostasis.

Vascular Control of Kidney Epithelial Transporters

A major pathway in hypertension pathogenesis involves direct activation of Ang II (AT1) receptors in the kidney, stimulating sodium reabsorption. AT1 receptors in tubular epithelia control expression and stimulation of sodium transporters and channels. Recently, we found reduced blood pressure and enhanced natriuresis in mice with cell-specific deletion of AT1 receptors in smooth muscle (SMKOs). While impaired vasoconstriction and preserved renal blood flow might contribute to exaggerated urinary sodium excretion in SMKOs, we considered whether alterations in sodium transporter expression might also play a role and therefore carried out a proteomic analysis of key sodium transporters and associated proteins. Here we show that levels of Na+-K+-2Cl- cotransporter isoform 2 (NKCC2) and Na+/H+ exchanger isoform 3 (NHE3) are reduced at baseline in SMKOs, accompanied by attenuated natriuretic and diuretic responses to furosemide. During Ang II hypertension, we find widespread remodeling of transporter expression in wild-type mice with significant increases in levels of total NCC, phosphorylated-NCCps71, and NKCC2-P, along with the cleaved, activated forms of the a- and g-ENaC. However, the increases in a- and g-ENaC with Ang II were substantially attenuated in SMKOs. This was accompanied by reduced natriuretic response to amiloride. Thus, enhanced urinary sodium excretion observed after cell-specific deletion of AT1 receptors from smooth muscle cells is associated with altered sodium transporter abundance across epithelia in multiple nephron segments. These findings suggest a system of vascular-epithelial cross-talk in the kidney, modulating expression of sodium transporters and contributing to regulation of pressure-natriuresis.

Rationale and Design of the Genotype-Blinded Trial of Torasemide for the Treatment of Hypertension (BHF UMOD)

BACKGROUND Genome-wide association studies have identified single nucleotide polymorphisms (SNPs) near the uromodulin gene (UMOD) affecting uromodulin excretion and blood pressure (BP). Uromodulin is almost exclusively expressed in the thick ascending limb (TAL) of the loop of Henle and its effect on BP appears to be mediated via the TAL sodium transporter, NKCC2. Loop-diuretics block NKCC2 but are not commonly used in hypertension management. Volume overload is one of the primary drivers for uncontrolled hypertension, so targeting loop-diuretics to individuals who are more likely to respond to this drug class, using the UMOD genotype, could be an efficient precision medicine strategy. METHODS The BHF UMOD Trial is a genotype-blinded, multicenter trial comparing BP response to torasemide between individuals possessing the AA genotype of the SNP rs13333226 and those possessing the G allele. 240 participants (≥18 years) with uncontrolled BP, on ≥1 antihypertensive agent for ≥3 months, will receive treatment with Torasemide, 5 mg daily for 16 weeks. Uncontrolled BP is average home systolic BP (SBP) >135 mmHg and/or diastolic BP >85 mmHg. The primary outcome is the change in 24-hour ambulatory SBP area under the curve between baseline and end of treatment. Sample size was calculated to detect a 4 mmHg difference between groups at 90% power. Approval by West of Scotland Research Ethics Committee 5 (16/WS/0160). RESULTS The study should conclude August 2021. CONCLUSIONS If our hypothesis is confirmed, a genotype-based treatment strategy for loop diuretics would help reduce the burden of uncontrolled hypertension. CLINICAL TRIALS REGISTRATION https://clinicaltrials.gov/ct2/show/NCT03354897.

Transcriptional variation and divergence of host-finding behaviour in Steinernema carpocapsae infective juveniles

Background Steinernema carpocapsae is an entomopathogenic nematode that employs nictation and jumping behaviours to find potential insect hosts. Here we aimed to investigate the transcriptional basis of variant host-finding behaviours in the infective juvenile (IJ) stage of three S. carpocapsae strains (ALL, Breton and UK1), with a focus on neuronal genes known to influence behaviour in other nematode species. Identifying gene expression changes that correlate with variant host-finding behaviours will further our understanding of nematode biology. Results RNA-seq analysis revealed that whilst up to 28% of the S. carpocapsae transcriptome was differentially expressed (P < 0.0001) between strains, remarkably few of the most highly differentially expressed genes (> 2 log2 fold change, P < 0.0001) were from neuronal gene families. S. carpocapsae Breton displays increased chemotaxis toward the laboratory host Galleria mellonella, relative to the other strains. This correlates with the up-regulation of four srsx chemosensory GPCR genes, and a sodium transporter gene, asic-2, relative to both ALL and UK1 strains. The UK1 strain exhibits a decreased nictation phenotype relative to ALL and Breton strains, which correlates with co-ordinate up-regulation of neuropeptide like protein 36 (nlp-36), and down-regulation of an srt family GPCR gene, and a distinct asic-2-like sodium channel paralogue. To further investigate the link between transcriptional regulation and behavioural variation, we sequenced microRNAs across IJs of each strain. We have identified 283 high confidence microRNA genes, yielding 321 predicted mature microRNAs in S. carpocapsae, and find that up to 36% of microRNAs are differentially expressed (P < 0.0001) between strains. Many of the most highly differentially expressed microRNAs (> 2 log2 fold, P < 0.0001) are predicted to regulate a variety of neuronal genes that may contribute to variant host-finding behaviours. We have also found evidence for differential gene isoform usage between strains, which alters predicted microRNA interactions, and could contribute to the diversification of behaviour. Conclusions These data provide insight to the transcriptional basis of behavioural variation in S. carpocapsae, supporting efforts to understand the molecular basis of complex behaviours in nematodes.

A role for the OsHKT 2;1 sodium transporter in potassium use efficiency in rice

Genome-wide association studies were used to analyse potassium use efficiency in rice. Novel associations were found along with a role for sodium replacement via the OsHKT2;1 sodium transporter.