Short-Term High-Salt Diet Increases Corin Level to Regulate the Salt-Water Balance in Humans and Rodents

Corin Deficiency Diminishes Intestinal Sodium Excretion in Mice

Sodium excretion, a critical process in sodium homeostasis, occurs in many tissues, including the kidney and intestine. Unlike in the kidney, the hormonal regulation of intestinal sodium excretion remains unclear. Atrial natriuretic peptide (ANP) is a crucial hormone in renal natriuresis. Corin is a protease critical for ANP activation. Corin and ANP are expressed mainly in the heart. In this study, we investigated corin, ANP, and natriuretic peptide receptor A (Npra) expression in mouse intestines. Corin and ANP expression was co-localized in enteroendocrine cells, whereas Npra expression was on the luminal epithelial cells. In Corin knockout (KO) mice, fecal Na⁺ and Cl^- excretion decreased compared with that in wild-type (WT) mice. Such a decrease was not found in conditional Corin KO mice lacking cardiac corin selectively. In kidney conditional Corin KO mice lacking renal corin, fecal Na⁺ and Cl^- excretion increased, compared to that in WT mice. When WT, Corin KO, and the kidney conditional KO mice were treated with aldosterone, the differences in fecal Na⁺ and Cl^- levels disappeared. These results suggest that intestinal corin may promote fecal sodium excretion in a paracrine mechanism independent of the cardiac corin function. The increased fecal sodium excretion in the kidney conditional Corin KO mice likely reflected an intestinal compensatory response to renal corin deficiency. Our results also suggest that intestinal corin activity may antagonize aldosterone action in the promotion of fecal sodium excretion. These findings help us understand the hormonal mechanism controlling sodium excretion the intestinal tract.

Proprotein Convertase Subtilisin/Kexin 6 in Cardiovascular Biology and Disease

Proprotein convertase subtilisin/kexin 6 (PCSK6) is a secreted serine protease expressed in most major organs, where it cleaves a wide range of growth factors, signaling molecules, peptide hormones, proteolytic enzymes, and adhesion proteins. Studies in Pcsk6-deficient mice have demonstrated the importance of Pcsk6 in embryonic development, body axis specification, ovarian function, and extracellular matrix remodeling in articular cartilage. In the cardiovascular system, PCSK6 acts as a key modulator in heart formation, lipoprotein metabolism, body fluid homeostasis, cardiac repair, and vascular remodeling. To date, dysregulated PCSK6 expression or function has been implicated in major cardiovascular diseases, including atrial septal defects, hypertension, atherosclerosis, myocardial infarction, and cardiac aging. In this review, we describe biochemical characteristics and posttranslational modifications of PCSK6. Moreover, we discuss the role of PCSK6 and related molecular mechanisms in cardiovascular biology and disease.

Renal Corin Is Essential for Normal Blood Pressure and Sodium Homeostasis

Atrial natriuretic peptide (ANP)-mediated natriuresis is known as a cardiac endocrine function in sodium and body fluid homeostasis. Corin is a protease essential for ANP activation. Here, we studied the role of renal corin in regulating salt excretion and blood pressure. We created corin conditional knockout (cKO), in which the Corin gene was selectively disrupted in the kidney (kcKO) or heart (hcKO). We examined the blood pressure, urinary Na⁺ and Cl⁻ excretion, and cardiac hypertrophy in wild-type, corin global KO, kcKO, and hcKO mice fed normal- and high-salt diets. We found that on a normal-salt diet (0.3% NaCl), corin kcKO and hcKO mice had increased blood pressure, indicating that both renal and cardiac corin is necessary for normal blood pressure in mice. On a high-salt diet (4% NaCl), reduced urinary Na⁺ and Cl⁻ excretion, increased body weight, salt-exacerbated hypertension, and cardiac hypertrophy were observed in corin kcKO mice. In contrast, impaired urinary Na⁺ and Cl⁻ excretion and salt-exacerbated hypertension were not observed in corin hcKO mice. These results indicated that renal corin function is important in enhancing natriuresis upon high salt intakes and that this function cannot be compensated by the cardiac corin function in mice.

Aquaporins: Important players in the cardiovascular pathophysiology

Aquaporin is a membrane channel protein widely expressed in body tissues, which can control the input and output of water in cells. AQPs are differentially expressed in different cardiovascular tissues and participate in water transmembrane transport, cell migration, metabolism, inflammatory response, etc. The aberrant expression of AQPs highly correlates with the onset of ischemic heart disease, myocardial ischemia-reperfusion injury, heart failure, etc. Despite much attention to the regulatory role of AQPs in the cardiovascular system, the translation of AQPs into clinical application still faces many challenges, including clarification of the localization of AQPs in the cardiovascular system and mechanisms mediating cardiovascular pathophysiology, as well as the development of cardiovascular-specific AQPs modulators.Therefore, in this study, we comprehensively reviewed the critical roles of AQP family proteins in maintaining cardiovascular homeostasis and described the underlying mechanisms by which AQPs mediated the outcomes of cardiovascular diseases. Meanwhile, AQPs serve as important therapeutic targets, which provide a wide range of opportunities to investigate the mechanisms of cardiovascular diseases and the treatment of those diseases.

Chronic Kidney Disease Is Associated With Increased Cardiac Corin Expression But Decreased Proatrial Natriuretic Peptide Conversion Activity

Background

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular disease. Corin converts proatrial natriuretic peptide into its active form after being activated by PCSK6 (proprotein convertase subtilisin/kexin type 6) protease. It remains unknown whether the PCSK6/corin/atrial natriuretic peptide pathway plays a role in CKD‐induced cardiomyopathy.

Methods and Results

Serum corin, left ventricular mass index, and corin–left ventricular mass index correlation were compared between outpatients with versus without CKD. Cardiac corin expression and activity as well as serum corin were compared between 5/6 nephrectomy CKD animal models and sham controls. The effects of indoxyl sulfate, a uremic toxin, on cardiomyocytes were examined in vitro in H9c2 cells. A total of 543 patients were enrolled in this study. Serum corin levels were elevated in patients with CKD compared with levels in patients without CKD. Serum corin levels correlated negatively with left ventricular mass index in participants without CKD, but not in patients with CKD. Compared with sham controls, CKD mice had higher serum corin levels and increased cardiac expression of corin but reduced cardiac corin conversion activity. Indoxyl sulfate stimulated corin expression while suppressing serine protease activity in H9c2 cardiomyoblasts. Lower PCSK6 expression in CKD mouse hearts and indoxyl sulfate–treated H9c2 cardiomyoblasts may explain, at least partly, the observed CKD‐associated reduction in corin activity.

Conclusions

In CKD, cardiac and serum levels of corin are increased, yet corin activity is suppressed. The latter may be attributable to reduced PCSK6 expression. These findings suggest that corin dysfunction may play a significant role in the pathogenesis of CKD‐associated cardiomyopathy.

Corin: A Key Mediator in Sodium Homeostasis, Vascular Remodeling, and Heart Failure

Simple Summary

Atrial natriuretic peptide (ANP) is an important hormone that regulates many physiological and pathological processes, including electrolyte and body fluid balance, blood volume and pressure, cardiac channel activity and function, inflammatory response, lipid metabolism, and vascular remodeling. Corin is a transmembrane serine protease that activates ANP. Variants in the CORIN gene are associated with cardiovascular disease, including hypertension, cardiac hypertrophy, atrial fibrillation, heart failure, and preeclampsia. The current data indicate a key role of corin-mediated ANP production and signaling in the maintenance of cardiovascular homeostasis. In this review, we discuss the latest findings regarding the molecular and cellular mechanisms underlying the role of corin in sodium homeostasis, uterine spiral artery remodeling, and heart failure.

Abstract

Atrial natriuretic peptide (ANP) is a crucial element of the cardiac endocrine function that promotes natriuresis, diuresis, and vasodilation, thereby protecting normal blood pressure and cardiac function. Corin is a type II transmembrane serine protease that is highly expressed in the heart, where it converts the ANP precursor to mature ANP. Corin deficiency prevents ANP activation and causes hypertension and heart disease. In addition to the heart, corin is expressed in other tissues, including those of the kidney, skin, and uterus, where corin-mediated ANP production and signaling act locally to promote sodium excretion and vascular remodeling. These results indicate that corin and ANP function in many tissues via endocrine and autocrine mechanisms. In heart failure patients, impaired natriuretic peptide processing is a common pathological mechanism that contributes to sodium and body fluid retention. In this review, we discuss most recent findings regarding the role of corin in non-cardiac tissues, including the kidney and skin, in regulating sodium homeostasis and body fluid excretion. Moreover, we describe the molecular mechanisms underlying corin and ANP function in supporting orderly cellular events in uterine spiral artery remodeling. Finally, we assess the potential of corin-based approaches to enhance natriuretic peptide production and activity as a treatment of heart failure.

Urine peptidome in combination with transcriptomics analysis highlights MMP7, MMP14 and PCSK5 for further investigation in chronic kidney disease

Chronic kidney disease (CKD) is characterized by the loss of kidney function. The molecular mechanisms underlying the development and progression of CKD are still not fully understood. Among others, the urinary peptidome has been extensively studied, with several urinary peptides effectively detecting disease progression. However, their link to proteolytic events has not been made yet. This study aimed to predict the proteases involved in the generation of CKD-associated urinary excreted peptides in a well-matched (for age, sex, lack of heart disease) case-control study. The urinary peptide profiles from CKD (n = 241) and controls (n = 240) were compared and statistically analyzed. The in-silico analysis of the involved proteases was performed using Proteasix and proteases activity was predicted based on the abundance changes of the associated peptides. Predictions were cross-correlated to transcriptomics datasets by using the Nephroseq database. Information on the respective protease inhibitors was also retrieved from the MEROPS database. Totally, 303 urinary peptides were significantly associated with CKD. Among the most frequently observed were fragments of collagen types I, II and III, uromodulin, albumin and beta-2-microglobulin. Proteasix predicted 16 proteases involved in their generation. Through investigating CKD-associated transcriptomics datasets, several proteases are highlighted including members of matrix metalloproteinases (MMP7, MMP14) and serine proteases (PCSK5); laying the foundation for further studies towards elucidating their role in CKD pathophysiology.

Associations of corin genetic polymorphisms with salt sensitivity, blood pressure changes, and hypertension incidence in Chinese adults

Corin, a transmembrane serine protease that can cleave pro‐atrial natriuretic peptide (Pro‐ANP) into smaller bioactive molecule atrial natriuretic peptide, has been shown to be involved in the pathophysiology of hypertension, cardiac hypertrophy. We sought to examine the associations of corin genetic variations with salt sensitivity, blood pressure (BP) changes and hypertension incidence. We studied participants of the original Baoji Salt‐Sensitive cohort, recruited from 124 families from seven Chinese villages in 2004 who sequentially received a usual baseline salt diet, a 7‐day low salt diet (3 g/day) and a 7‐day high salt diet (18 g/day), respectively. They were followed up for 8 years (in 2009, 2012) to evaluate the development of hypertension. Corin SNP rs3749584 was significantly associated with diastolic BP (DBP) and mean arterial pressure (MAP) response to low‐salt diet, while rs4695253, rs17654278 were associated with pulse pressure (PP) response to low‐salt diet. SNPs rs4695253, rs12509275, rs2351783, rs2271036, rs2271037 were significantly associated with systolic BP (SBP), DBP, and MAP responses to high‐salt diet. In addition, SNPs rs12641823, rs6834933, rs2271036, and rs22710367 were significantly associated with the longitudinal changes in SBP, DBP, MAP, or PP over 8 years of follow‐up. SNP rs73814824 was significantly associated with the incidence of hypertension over 8 years. Gene‐based analysis showed that corin gene was significantly associated with longitudinal BP changes and hypertension incidence after 8‐year follow‐up. This study suggests that corin may play a role in salt sensitivity, BP progression, and development of hypertension.

Function and regulation of corin in physiology and disease

Atrial natriuretic peptide (ANP) is of major importance in the maintenance of electrolyte balance and normal blood pressure. Reduced plasma ANP levels are associated with the increased risk of cardiovascular disease. Corin is a type II transmembrane serine protease that converts the ANP precursor to mature ANP. Corin deficiency prevents ANP generation and alters electrolyte and body fluid homeostasis. Corin is synthesized as a zymogen that is proteolytically activated on the cell surface. Factors that disrupt corin folding, intracellular trafficking, cell surface expression, and zymogen activation are expected to impair corin function. To date, CORIN variants that reduce corin activity have been identified in hypertensive patients. In addition to the heart, corin expression has been detected in non-cardiac tissues, where corin and ANP participate in diverse physiological processes. In this review, we summarize the current knowledge in corin biosynthesis and post-translational modifications. We also discuss tissue-specific corin expression and function in physiology and disease.

Risk Factors for Albuminuria in Normotensive Older Adults with Type 2 Diabetes Mellitus and Normal Renal Function: A Cross-Sectional Study

INTRODUCTION

Diabetes mellitus (DM) is prevalent in developed and developing countries, including China. However, few studies have examined the potential risk factors for albuminuria in normotensive older adults with type 2 DM and normal renal function.

METHODS

We recruited normotensive older adults (≥ 65 years) with type 2 DM and normal renal function from the First Affiliated Hospital of Soochow University from January to December 2019. We stratified participants according to their urine albumin to creatinine ratio (ACR) into the following groups: normal ACR (ACR1), microalbuminuria (ACR2), and macroalbuminuria (ACR3). Demographic characteristics, anthropometric parameters, and metabolic profiles were recorded. Creatinine clearance (Ccr) and homeostasis model assessment-insulin resistance (HOMA-IR) were calculated. Logistic regression was used to examine risk factors for albuminuria.

RESULTS

A total of 250 older adults were enrolled during the study period, including 124, 82, and 44 with normal albuminuria, microalbuminuria, and macroalbuminuria, respectively. We found that an extended duration of DM (odds ratio [OR] 1.085, 95% confidence interval [CI] 1.012-1.164, P = 0.022), elevated systolic blood pressure (OR 1.049, 95%CI 1.018-1.081, P < 0.01), elevated glycated hemoglobin (OR 1.734, 95% CI 1.332-2.258, P < 0.01), low insulin (OR 0.871, 95% CI 0.804-0.944, P < 0.01), and low C-peptide (OR 0.365, 95% CI 0.239-0.588, P < 0.01) were independent risk factors for albuminuria.

CONCLUSION

Elevated blood pressure, low insulin, low C-peptide, and poor glycemic control were significant risk factors for albuminuria. These parameters may serve as early indicators for intervention.

Soluble Neprilysin and Corin Concentrations in Relation to Clinical Outcome in Chronic Heart Failure

OBJECTIVES

This study investigated whether patients with chronic heart failure (HF) can be stratified according to the combination of soluble neprilysin and corin concentrations and whether this is related to clinical outcome.

BACKGROUND

Natriuretic peptide processing by the enzymes corin and neprilysin plays a pivotal role in conversion of pro-natriuretic peptides to active natriuretic peptides, as well as their degradation, respectively.

METHODS

A prospective cohort of patients with chronic HF (n = 1,009) was stratified into 4 equal groups based on high or low neprilysin/corin concentration relative to the median: 1) low neprilysin/low corin; 2) low neprilysin/high corin; 3) high neprilysin/low corin; and 4) high neprilysin/high corin. Cox regression survival analysis was performed for the composite primary endpoint of cardiovascular death and HF hospitalization.

RESULTS

Median neprilysin and corin concentrations were not correlated (rho: -0.04; p = 0.21). Although in univariate analysis there was no association with outcome, after correction for baseline differences in age and sex, a significant association with survival was demonstrated: with highest survival in group 1 (low neprilysin/low corin) and lowest in group 4 (high neprilysin/high corin) (adjusted hazard ratio: 1.56; p = 0.003), which remained statistically significant after comprehensive multivariable analysis (adjusted hazard ratio: 1.41; p = 0.03).

CONCLUSIONS

Stratification of patients with chronic HF based on circulating neprilysin and corin concentrations is associated with clinical outcomes. These results suggest that regulation of these enzymes is of importance in chronic HF and may offer an interesting approach for classification of patients with HF in a step toward individualized HF patient management.

Dietary Sodium Intake and Health Indicators: A Systematic Review of Published Literature between January 2015 and December 2019

As the science surrounding population sodium reduction evolves, monitoring and evaluating new studies on intake and health can help increase our understanding of the associated benefits and risks. Here we describe a systematic review of recent studies on sodium intake and health, examine the risk of bias (ROB) of selected studies, and provide direction for future research. Seven online databases were searched monthly from January 2015 to December 2019. We selected human studies that met specified population, intervention, comparison, outcome, time, setting/study design (PICOTS) criteria and abstracted attributes related to the study population, design, intervention, exposure, and outcomes, and evaluated ROB for the subset of studies on sodium intake and cardiovascular disease risks or indicators. Of 41,601 abstracts reviewed, 231 studies were identified that met the PICOTS criteria and ROB was assessed for 54 studies. One hundred and fifty-seven (68%) studies were observational and 161 (70%) focused on the general population. Five types of sodium interventions and a variety of urinary and dietary measurement methods were used to establish and quantify sodium intake. Five observational studies used multiple 24-h urine collections to assess sodium intake. Evidence mainly focused on cardiovascular-related indicators (48%) but encompassed an assortment of outcomes. Studies varied in ROB domains and 87% of studies evaluated were missing information on ≥1 domains. Two or more studies on each of 12 outcomes (e.g., cognition) not previously included in systematic reviews and 9 new studies at low ROB suggest the need for ongoing or updated systematic reviews of evidence on sodium intake and health. Summarizing evidence from assessments on sodium and health outcomes was limited by the various methods used to measure sodium intake and outcomes, as well as lack of details related to study design and conduct. In line with research recommendations identified by the National Academies of Science, future research is needed to identify and standardize methods for measuring sodium intake.

Synthesis and Excretion of Atrial Natriuretic Peptide in Secretory Cardiomyocytes in Experimental Hypertension

The intensity of accumulation and excretion of atrial natriuretic peptide in myocytes of the right atrium in rat models of renovascular hypertension and salt loading was studied by immunocytochemical analysis and transmission electron microscopy. The data suggest that high BP is not the decisive factor affecting secretion of atrial natriuretic peptide in atrial cardiomyocytes. The regulatory mechanisms of the accumulation and release of the peptide from myocyte granules can vary and depend on the pathogenesis of hypertension.

Corin Is Downregulated in Renal Ischemia/Reperfusion Injury and Is Associated with Delayed Graft Function after Kidney Transplantation

Renal ischemia/reperfusion (IR) injury is one of the most important risk factors for the occurrence of delayed graft function (DGF) after kidney transplantation; however, its mechanism remains not fully understood. In the present study, we screened differentially expressed genes in a murine model of renal IR injury by using high-throughput assays. We identified Corin as one of the most significantly downregulated genes among 2218 differentially expressed genes (≥2-fold, P < 0.05). By using a real-time qPCR assay, we observed that the expression of renal Corin in IR-injured mice was reduced to 11.5% of the sham-operated mice and that the protein level of renal Corin in IR-injured mice was also downregulated. Interestingly, renal IR injury in mice induced the downregulation of Corin in heart tissues, suggesting that the overall synthesis of Corin may be suppressed. We recruited 11 recipients complicated with DGF and 16 without DGF, and plasma Corin concentrations were determined by ELISA. We observed that the plasma Corin levels were indeed reduced in recipients complicated with DGF (0.98 vs. 1.95 ng/ml, P < 0.05). These findings demonstrate that Corin may be a potential biomarker of DGF after kidney transplantation and may participate in the regulation of renal IR injury.