Adrenal renin: a possible local hormonal regulator of aldosterone production

Six Decades of History of Hypertension Research at the University of Toledo: Highlighting Pioneering Contributions in Biochemistry, Genetics, and Host-Microbiota Interactions

PURPOSE OF REVIEW

The study aims to capture the history and lineage of hypertension researchers from the University of Toledo in Ohio and showcase their collective scientific contributions dating from their initial discoveries of the physiology of adrenal and renal systems and genetics regulating blood pressure (BP) to its more contemporary contributions including microbiota and metabolomic links to BP regulation.

RECENT FINDINGS

The University of Toledo College of Medicine and Life Sciences (UTCOMLS), previously known as the Medical College of Ohio, has contributed significantly to our understanding of the etiology of hypertension. Two of the scientists, Patrick Mulrow and John Rapp from UTCOMLS, have been recognized with the highest honor, the Excellence in Hypertension award from the American Heart Association for their pioneering work on the physiology and genetics of hypertension, respectively. More recently, Bina Joe has continued their legacy in the basic sciences by uncovering previously unknown novel links between microbiota and metabolites to the etiology of hypertension, work that has been recognized by the American Heart Association with multiple awards. On the clinical research front, Christopher Cooper and colleagues lead the CORAL trials and contributed importantly to the investigations on renal artery stenosis treatment paradigms. Hypertension research at this institution has not only provided these pioneering insights, but also grown careers of scientists as leaders in academia as University Presidents and Deans of Medical Schools. Through the last decade, the university has expanded its commitment to Hypertension research as evident through the development of the Center for Hypertension and Precision Medicine led by Bina Joe as its founding Director. Hypertension being the top risk factor for cardiovascular diseases, which is the leading cause of human mortality, is an important area of research in multiple international universities. The UTCOMLS is one such university which, for the last 6 decades, has made significant contributions to our current understanding of hypertension. This review is a synthesis of this rich history. Additionally, it also serves as a collection of audio archives by more recent faculty who are also prominent leaders in the field of hypertension research, including John Rapp, Bina Joe, and Christopher Cooper, which are cataloged at Interviews .

Exploration of cardiometabolic and developmental significance of angiotensinogen expression by cells expressing the leptin receptor or agouti-related peptide

Angiotensin II (ANG II) Agtr1a receptor (AT_1A) is expressed in cells of the arcuate nucleus of the hypothalamus that express the leptin receptor (Lepr) and agouti-related peptide (Agrp). Agtr1a expression in these cells is required to stimulate resting energy expenditure in response to leptin and high-fat diets (HFDs), but the mechanism activating AT_1A signaling by leptin remains unclear. To probe the role of local paracrine/autocrine ANG II generation and signaling in this mechanism, we bred mice harboring a conditional allele for angiotensinogen (Agt, encoding AGT) with mice expressing Cre-recombinase via the Lepr or Agrp promoters to cause cell-specific deletions of Agt (Agt^Lepr-KO and Agt^Agrp-KO mice, respectively). Agt^Lepr-KO mice were phenotypically normal, arguing against a paracrine/autocrine AGT signaling mechanism for metabolic control. In contrast, Agt^Agrp-KO mice exhibited reduced preweaning survival, and surviving adults exhibited altered renal structure and steroid flux, paralleling previous reports of animals with whole body Agt deficiency or Agt disruption in albumin (Alb)-expressing cells (thought to cause liver-specific disruption). Surprisingly, adult Agt^Agrp-KO mice exhibited normal circulating AGT protein and hepatic Agt mRNA expression but reduced Agt mRNA expression in adrenal glands. Reanalysis of RNA-sequencing data sets describing transcriptomes of normal adrenal glands suggests that Agrp and Alb are both expressed in this tissue, and fluorescent reporter gene expression confirms Cre activity in adrenal gland of both Agrp-Cre and Alb-Cre mice. These findings lead to the iconoclastic conclusion that extrahepatic (i.e., adrenal) expression of Agt is critically required for normal renal development and survival.

Renin gene expression in the aging kidney: effect of sodium restriction

The activity of the renin-angiotensin system as well as the ability of the kidney to retain sodium following salt restriction are reduced with age. The relationship between these age-related changes in renal function and the renin gene expression was presently investigated. The concentrations of renin and its mRNA were measured in kidney of 10- and 30-month-old control female WAG/Rij rats and of animals which were salt restricted for 4 days. In the senescent rats, the kidney renin concentration, like the plasma concentration of angiotensin II, was half that in adult rats. The intrarenal content of renin mRNA did not differ between 10- and 30-month-old animals, suggesting that the transcriptional rate of the renin gene is unchanged with age. During the early phase of adaptation to sodium depletion, the systemic angiotensin II concentration was not modified in either age groups. Four-days salt restriction did not significantly change the renal storage of renin. In contrast, this short term salt restriction induced a 2.3-fold increase in the renin mRNA in adult kidney, and a 1.9-fold increase in the senescent kidney. These data suggest that the age-related decrease in renal concentration of renin is linked to a modification in the rate of translation of renin mRNA, or to an alteration in the protein maturation. The difference in adaptation to the early phase of salt restriction with age should not be linked to changes in renin gene transcription, but more likely to a change in the tissue response to the local renin-angiotensin system.

Quantitation of renal renin and renin mRNA in Dahl rats in response to provocative stimuli

It is known that inbred Dahl salt-sensitive (S) rats carry a different renin allele than inbred Dahl salt-resistant (R) rats. The levels of, and responses of, renal renin and renal renin mRNA to sodium deficient diet and to sodium deficient diet plus Captopril treatment were compared in S and R rats. S rats had lower renal renin and lower renal renin mRNA than R rats on control (1% NaCl) diet. Sodium deficient diet caused a modest increase, and sodium deficient diet plus Captopril caused a very large increase in both renal renin and renal renin mRNA in both strains. In general, both S and R strains appeared to regulate renin similarly in response to provocative stimuli.