Aldosterone: Renal Action and Physiological Effects

Sex differences in the adrenal circadian clock: a role for BMAL1 in the regulation of urinary aldosterone excretion and renal electrolyte balance in mice

Brain and muscle ARNT-Like 1 (BMAL1) is a circadian clock transcription factor that regulates physiological functions. Male adrenal-specific Bmal1 (ASCre/+::Bmal1) KO mice displayed blunted serum corticosterone rhythms, altered blood pressure rhythm, and altered timing of eating, but there is a lack of knowledge in females. This study investigates the role of adrenal BMAL1 in renal electrolyte handling and urinary aldosterone levels in response to low salt in male and female mice. Mice were placed in metabolic cages to measure 12-h urinary aldosterone after a standard diet and 7 days low-salt diet, as well as daily body weight, 12-h food and water intake, and renal sodium and potassium balance. Adrenal glands and kidneys were collected at ZT0 or ZT12 to measure the expression of aldosterone synthesis genes and clock genes. Compared with littermate controls, ASCre/+::Bmal1 KO male and female mice displayed increased urinary aldosterone in response to a low-salt diet, although mRNA expression of aldosterone synthesis genes was decreased. Timing of food intake was altered in ASCre/+::Bmal1 KO male and female mice, with a blunted night/day ratio. ASCre/+::Bmal1 KO female mice displayed decreases in renal sodium excretion in response to low salt, but both male and female KO mice had changes in sodium balance that were time-of-day-dependent. In addition, sex differences were found in adrenal and kidney clock gene expression. Notably, this study highlights sex differences in clock gene expression that could contribute to sex differences in physiological functions.NEW & NOTEWORTHY Our findings highlight the importance of sex as well as time-of-day in understanding the role of the circadian clock in the regulation of homeostasis. Time-of-day is a key biological variable that is often ignored in research, particularly in preclinical rodent studies. Our findings demonstrate important differences in several measures at 6 AM compared with 6 PM. Consideration of time-of-day is critical for the translation of findings in nocturnal rodent physiology to diurnal human physiology.

Mineralocorticoid Receptor and Sleep Quality in Chronic Kidney Disease

The classical function of the mineralocorticoid receptor (MR) is to maintain electrolytic homeostasis and control extracellular volume and blood pressure. The MR is expressed in the central nervous system (CNS) and is involved in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis as well as sleep physiology, playing a role in the non-rapid eye movement (NREM) phase of sleep. Some patients with psychiatric disorders have very poor sleep quality, and a relationship between MR dysregulation and this disorder has been found in them. In addition, the MR is involved in the regulation of the renal peripheral clock. One of the most common comorbidities observed in patients with chronic kidney disease (CKD) is poor sleep quality. Patients with CKD experience sleep disturbances, including reduced sleep duration, sleep fragmentation, and insomnia. To date, no studies have specifically investigated the relationship between MR activation and CKD-associated sleep disturbances. However, in this review, we analyzed the environment that occurs in CKD and proposed two MR-related mechanisms that may be responsible for these sleep disturbances: the circadian clock disruption and the high levels of MR agonist observed in CKD.

Going with the flow: New insights regarding flow induced K+ secretion in the distal nephron

K+ secretion in the distal nephron has a critical role in K+ homeostasis and is the primary route by which K+ is lost from the body. Renal K+ secretion is enhanced by increases in dietary K+ intake and by increases in tubular flow rate in the distal nephron. This review addresses new and important insights regarding the mechanisms underlying flow-induced K+ secretion (FIKS). While basal K+ secretion in the distal nephron is mediated by renal outer medullary K+ (ROMK) channels in principal cells (PCs), FIKS is mediated by large conductance, Ca2+/stretch activated K+ (BK) channels in intercalated cells (ICs), a distinct cell type. BK channel activation requires an increase in intracellular Ca2+ concentration ([Ca2+]i), and both PCs and ICs exhibit increases in [Ca2+]i in response to increases in tubular fluid flow rate, associated with an increase in tubular diameter. PIEZO1, a mechanosensitive, nonselective cation channel, is expressed in the basolateral membranes of PCs and ICs, where it functions as a mechanosensor. The loss of flow-induced [Ca2+]i transients in ICs and BK channel-mediated FIKS in microperfused collecting ducts isolated from mice with IC-specific deletion of Piezo1 in the CCD underscores the importance of PIEZO1 in the renal regulation of K+ transport.

The Interaction of Vasopressin with Hormones of the Hypothalamo-Pituitary-Adrenal Axis: The Significance for Therapeutic Strategies in Cardiovascular and Metabolic Diseases

A large body of evidence indicates that vasopressin (AVP) and steroid hormones are frequently secreted together and closely cooperate in the regulation of blood pressure, metabolism, water-electrolyte balance, and behavior, thereby securing survival and the comfort of life. Vasopressin cooperates with hormones of the hypothalamo-pituitary-adrenal axis (HPA) at several levels through regulation of the release of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and multiple steroid hormones, as well as through interactions with steroids in the target organs. These interactions are facilitated by positive and negative feedback between specific components of the HPA. Altogether, AVP and the HPA cooperate closely as a coordinated functional AVP-HPA system. It has been shown that cooperation between AVP and steroid hormones may be affected by cellular stress combined with hypoxia, and by metabolic, cardiovascular, and respiratory disorders; neurogenic stress; and inflammation. Growing evidence indicates that central and peripheral interactions between AVP and steroid hormones are reprogrammed in cardiovascular and metabolic diseases and that these rearrangements exert either beneficial or harmful effects. The present review highlights specific mechanisms of the interactions between AVP and steroids at cellular and systemic levels and analyses the consequences of the inappropriate cooperation of various components of the AVP-HPA system for the pathogenesis of cardiovascular and metabolic diseases.

Tetrandrine inhibits aldosterone synthesis by covalently targeting CYP11A1 to attenuate hypertension

Introduction

Tetrandrine (Tet) is the main pharmacological component of Stephania tetrandra S. Moore, which is a well-documented traditional Chinese medicine known for its diuretic and antihypertensive properties. Unraveling the specific targets and mechanisms of Tet involved in inducing diuresis and mitigating hypertension can provide valuable insights into its therapeutic effects. This study aimed to explore the diuretic and antihypertensive targets and mechanisms of Tet using chemical biology coupled with activity analyses in vivo and in vitro.

Methods

The diuretic effects of Tet were evaluated using a water-loaded mouse model. The direct target proteins for the diuretic and antihypertensive effects of Tet were determined using chemical biology. Furthermore, the molecular mechanism of Tet binding to target proteins was analyzed using a multidisciplinary approach based on the structure and function of the proteins. Finally, the effects of the Tet-targeted protein on downstream signaling pathways and blood pressure were evaluated in hypertensive model rats.

Results

Tet exhibited significant antihypertensive and potassium-preserving diuretic effects. The mechanism underlying these effects involves the modulation of the enzyme activity by covalent binding of Tet to Cys423 of CYP11A1. This interaction alters the stability of heme within CYP11A1, subsequently impeding electron transfer and inhibiting aldosterone biosynthesis.

Discussion

This study not only revealed the mechanism of the diuretic and antihypertensive effects of Tet but also discovered a novel covalent inhibitor of CYP11A1. These findings contribute significantly to our understanding of the therapeutic potential of Tet and provide a foundation for future research in the development of targeted treatments for hypertension.

Adverse Effects of Aldosterone: Beyond Blood Pressure

Aldosterone is a steroid hormone that primarily acts through activation of the mineralocorticoid receptor (MR), a nuclear receptor responsible for downstream genomic regulation. Classically, activation of the MR in the renal tubular epithelium is responsible for sodium retention and volume expansion, raising systemic blood pressure. However, activation of the MR across a wide distribution of tissue types has been implicated in multiple adverse consequences for cardiovascular, cerebrovascular, renal, and metabolic disease, independent of blood pressure alone. Primary aldosteronism, heart failure, and chronic kidney disease are states of excessive aldosterone production and MR activity where targeting MR activation has had clinical benefits out of proportion to blood pressure lowering. The growing list of established and emerging therapies that target aldosterone and MR activation may provide new opportunities to improve clinical outcomes and enhance cardiovascular and renal health.