High blood pressure induced by vitamin D deficiency is associated with renal overexpression and hyperphosphorylation of Na+-K+-2Cl- cotransporter type 2

Research hotspots and trends regarding microRNAs in hypertension: a bibliometric analysis

To investigate the research levels, hotspots, and development trends regarding microRNAs in hypertension, this study conducted a visual analysis of studies on miRNA in hypertension based on the Web of Science core collection database using CiteSpace and VOSviewer analysis software along with literature from 2005-2023 as information data. Using citation frequency, centrality, and starting year as metrics, this study analyzed the research objects. It revealed the main research bodies and hotspots and evaluated the sources of literature and the distribution of knowledge from journals and authors. Finally, the potential research directions for miRNAs in hypertension are discussed. The results showed that the research field is in a period of vigorous development, and scholars worldwide have shown strong interest in this research field. A comprehensive summary and analysis of the current research status and application trends will prove beneficial for the advancement of this field.

Impact of Proximal Tubule-Specific Deletion of Dipeptidyl Peptidase 4 on Blood Pressure, Renal Sodium Handling, and NHE3 Phosphorylation

Dipeptidyl peptidase 4 (DPP4) is a transmembrane serine exopeptidase abundantly expressed in the kidneys, predominantly in the proximal tubule (PT); however, its non-enzymatic functions in this nephron segment remain poorly understood. While DPP4 physically associates with the Na+/H+ exchanger isoform 3 (NHE3) and its inhibitors exert natriuretic effects, the DPP4 role in blood pressure (BP) regulation remains controversial. This study investigated the effects of PT-specific Dpp4 deletion (Dpp4 ΔPT) and global Dpp4 deletion (Dpp4 -/-) on systolic blood pressure (SBP), natriuresis, and NHE3 regulation under baseline and angiotensin II (Ang II)-stimulated conditions in both male and female mice. Global and PT-specific Dpp4 deletion increased diuretic and natriuretic responses to acute saline loading, correlating with enhanced phosphorylation of NHE3 at serine 552 (pS552-NHE3). However, baseline SBP remained unchanged. Ang II stimulation increased DPP4 activity in control mice, with a greater effect in males than in females, reflecting sex-dependent regulation of renal DPP4. In Dpp4 ΔPT mice, residual kidney DPP4 was unresponsive to Ang II, indicating that PT DPP4, rather than DPP4 in other nephron segments, is regulated by Ang II. Ang II administration increased SBP in all groups; however, the pressor response was significantly attenuated in both Dpp4 ΔPT and Dpp4 -/- mice, coinciding with sustained elevated levels of pS552-NHE3. Collectively, these findings demonstrate that PT DPP4 modulates NHE3 activity through mechanisms that prevent the accumulation of pS552-NHE3, exerting an anti-natriuretic effect. In the absence of DPP4, these mechanisms are disrupted, reducing Ang II sensitivity and maintaining high pS552-NHE3 levels, underscoring the role of DPP4 in PT signaling and function.

High Apolipoprotein B/Apolipoprotein A1 is Associated with Vitamin D Deficiency Among Type 2 Diabetes Patients

Purpose

To explore the relationship between vitamin D (VitD) deficiency and the apolipoprotein B/apolipoprotein A1 (apo B/A1) in type 2 diabetes mellitus (T2DM) patients.

Methods

This was a retrospective study that lasted 2 years and 6 months, collecting information and laboratory data from 784 patients with T2DM. Patients were divided into VitD deficiency group (n = 433) and non-VitD deficiency group (n = 351) based on VitD levels. Calculated apo B/A1 ratio, and patients were further divided into high-apo B/A1 group (n = 392) and low-apo B/A1 group (n = 392) based on the median of the apo B/A1. All data were analyzed using Prism 8.0.1 and R version 4.3.1 software.

Results

Apo B/A1 levels of T2DM patients combined with VitD deficiency was significantly higher than that of non-VitD deficiency patients, and the VitD levels of patients with high apo B/A1 was significantly lower than that patients with low apo B/A1 (all P<0.001). Spearman correlation analysis showed that VitD levels were negatively correlated with apo B/A1 (r=-0.238, P<0.001). Multiple linear regression analysis revealed after adjusting other factors, VitD levels were significantly negatively associated with apo B/A1 (β=-0.123, P=0.001). Binary logistic regression analysis showed apoB/A1 was an independent risk factor for VitD deficiency in T2DM patients. Restrictive cubic spline indicated a significant linear relationship between apoB/A1 and VitD deficiency (P general trend <0.0001, P nonlinear = 0.0896), after stratification of gender, the results showed that apo B/A1 was more susceptible to VitD deficiency in female patients. The receiver operating characteristic (ROC) curve analysis showed that the area under the curve, sensitivity and specificity of the apo B/A1 for VitD deficiency were 0.654, 66.3% and 59.8%, respectively.

Conclusion

The apo B/A1 was significantly negatively associated with VitD levels and an independent risk factor for VitD deficiency in patients with T2DM.

Renal upregulation of NCC counteracts empagliflozin-mediated NHE3 inhibition in normotensive but not in hypertensive male rat

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) reduce blood pressure (BP) in patients with hypertension, yet the precise molecular mechanisms remain elusive. SGLT2i inhibits proximal tubule (PT) NHE3-mediated sodium reabsorption in normotensive rodents, yet no hypotensive effect is observed under this scenario. This study examined the effect of empagliflozin (EMPA) on renal tubular sodium transport in normotensive and spontaneously hypertensive rats (SHRs). It also tested the hypothesis that EMPA-mediated PT NHE3 inhibition in normotensive rats is associated with upregulation of distal nephron apical sodium transporters. EMPA administration for 14 days reduced BP in 12-wk-old SHRs but not in age-matched Wistar rats. PT NHE3 activity was inhibited by EMPA treatment in both Wistar and SHRs. In Wistar rats, EMPA increased NCC activity, mRNA expression, protein abundance, and phosphorylation levels, but not in SHRs. SHRs showed higher NKCC2 activity and an abundance of cleaved ENaC α and γ subunits compared with Wistar rats, none of which were affected by EMPA. Another set of male Wistar rats was treated with EMPA, the NCC inhibitor hydrochlorothiazide (HCTZ), and EMPA combined with HCTZ or vehicle for 14 days. In these rats, BP reduction was observed only with combined EMPA and HCTZ treatment, not with either drug alone. These findings suggest that NCC upregulation counteracts EMPA-mediated inhibition of PT NHE3 in male normotensive rats, maintaining their baseline BP. Moreover, the reduction of NHE3 activity without further upregulation of major apical sodium transporters beyond the PT may contribute to the BP-lowering effect of SGLT2i in experimental models and patients with hypertension.NEW & NOTEWORTHY This study suggests that reduced NHE3-mediated sodium reabsorption in the renal proximal tubule may account, at least in part, for the BP-lowering effect of SGLT2 inhibitors in the setting of hypertension. It also demonstrates that chronic treatment with SGLT2 inhibitors upregulates NCC activity, phosphorylation, and expression in the distal tubule of normotensive but not hypertensive rats. SGLT2 inhibitor-mediated upregulation of NCC seems crucial to counteract proximal tubule natriuresis in subjects with normal BP.

Relative Contribution of Blood Pressure and Renal Sympathetic Nerve Activity to Proximal Tubular Sodium Reabsorption via NHE3 Activity

We examined the effects of an acute increase in blood pressure (BP) and renal sympathetic nerve activity (rSNA) induced by bicuculline (Bic) injection in the paraventricular nucleus of hypothalamus (PVN) or the effects of a selective increase in rSNA induced by renal nerve stimulation (RNS) on the renal excretion of sodium and water and its effect on sodium-hydrogen exchanger 3 (NHE3) activity. Uninephrectomized anesthetized male Wistar rats were divided into three groups: (1) Sham; (2) Bic PVN: (3) RNS + Bic injection into the PVN. BP and rSNA were recorded, and urine was collected prior and after the interventions in all groups. RNS decreased sodium (58%) and water excretion (53%) independently of BP changes (p < 0.05). However, after Bic injection in the PVN during RNS stimulation, the BP and rSNA increased by 30% and 60% (p < 0.05), respectively, diuresis (5-fold) and natriuresis (2.3-fold) were increased (p < 0.05), and NHE3 activity was significantly reduced, independently of glomerular filtration rate changes. Thus, an acute increase in the BP overcomes RNS, leading to diuresis, natriuresis, and NHE3 activity inhibition.