Identification of Bona Fide Alternative Renin Transcripts Expressed Along Cortical Tubules and Potential Roles in Promoting Insulin Resistance In Vivo Without Significant Plasma Renin Activity Elevation

Abstract

Abstract-Renin belongs to a family of aspartyl proteases and is the rate-limiting enzyme in the synthesis of the potent vasoactive peptide angiotensin II. Processing of renal renin has been extensively investigated in juxtaglomerular granular cells, in which prorenin and active renin are present in secretory condensed granules. Previous studies demonstrated alternative renin transcription in rat adrenal glands. Different studies reported novel intracellular forms of renin deduced from novel 5′ variants derived from renin mRNA in both mice and humans. Comprehensive detailed studies in genetically engineered mice showed that both a secreted and an intracellular form of renin plays divergent mechanism regulating fluid intake and metabolism by the brain renin-angiotensin system; however, the presence, regulation, and functions of these renin isoforms in kidney and adrenal gland are not fully understood in mice. To investigate the characteristics of renin isoforms in mice, we performed a systematic inventory of renin transcripts of mice with and without a duplication of the renin gene alternatively from previous studies. We discovered a novel isoform of renin of the Ren2 gene, which conserved functionally important residues of the prosegment and incomplete isoforms of the Ren1C/D gene lacking a pre-pro segment. In situ hybridization assays revealed alternative renin isoforms expressed along cortical tubules. Newly generated transgenic mice with systemic overexpression of alternative renin transcript showed enhanced local angiotensin II generation without elevation of plasma renin activity and systemic insulin resistance in vivo, providing new pathophysiological insights into insulin resistance exaggerated by bona fide renin isoform. Correspondence to Tomoaki Ishigami, Department of Medical Science and Cardio-Renal Medicine, Yokohama City University, Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, Kanagawa, Japan. E-mail tommmish@hotmail.com Identification of Bona Fide Alternative Renin Transcripts Expressed Along Cortical Tubules and Potential Roles in Promoting Insulin Resistance In Vivo Without Significant Plasma Renin Activity ElevationTomoaki Ishigami, Tabito Kino,* Lin Chen,* Shintaro Minegishi, Naomi Araki, Masanari Umemura, Kaito Abe, Rie Sasaki, Hisako Yamana, Satoshi Umemura © 2014 American Heart Association, Inc. Materials and Methods Cloning and Identification of Alternative Renin Transcripts AnimalsAll animals were purchased from Oriental Yeast Company (Mihama, Chiba, Japan) and were housed and maintained under conditions approved by the Institution Animal Care and Use Committee of Yokohama City University. Rapid Amplification of cDNA Ends ProtocolTo investigate whether alternative renin expression is found in mouse adrenal glands, we performed 5′ rapid amplification of cDNA ends (RACE) analysis in adrenal tissue from 129 mice that endogenously have both Ren1D and Ren2 renin 6 and C57BL/6J mice with Ren1C renin. RNA was isolated from the mice with the use of Trizol reagent (Invitrogen, C...

Biochemical evaluation of the renin-angiotensin system: the good, bad, and absolute?

“…A second source of renal renin is the collecting duct cells that secrete active renin into the tubular fluid (52,71,82,92,113). There is evidence for alternative gene products of intracellular renin in the kidney, brain, and adrenal that may imply a renin-dependent pathway for the intracellular expression of angiotensin peptides (65,76,106,107,142). Apart from its catalytic activity, prorenin may constitute an additional circulating hormone of the RAS through binding and activation of the prorenin receptor within various tissues (52,71,94).…”

Peptidases and the Renin-Angiotensin System: The Alternative Angiotensin-(1-7) Cascade

“…Renin activity as measured by aliskerin-sensitive inhibition of Ang I formation from angiotensinogen was also evident in isolated nuclei in the renal epithelial NRK-52 cells, as well as quantifiable levels of Ang I, Ang II, and Ang-(1-7) [22]. In confirmation of intracellular renin within the kidney, Ishigami and colleagues report a truncated renin transcript expressed in the proximal tubules of the mouse kidney [16]. Overexpression of the renin isoform within the proximal tubules was associated with a sustained elevation in blood pressure and no change in the circulating levels of renin [16].…”

“…In confirmation of intracellular renin within the kidney, Ishigami and colleagues report a truncated renin transcript expressed in the proximal tubules of the mouse kidney [16]. Overexpression of the renin isoform within the proximal tubules was associated with a sustained elevation in blood pressure and no change in the circulating levels of renin [16]. Although the intracellular distribution of the renin isoform was not ascertained, the fact that overexpression of tubular renin augmented blood pressure is consistent with previous studies demonstrating that the increased expression of proximal tubule angiotensinogen, the AT 1 R, or intracellular Ang II also resulted in a sustained increase in blood pressure [23][24][25][26][27][28].…”

“…There is evidence for alternative gene products of renin expressed in the kidney, brain, heart, and adrenal gland [14][15][16][17]. These products arise from an alternative start site for renin transcription that is situated downstream from the typical start site and yields a shorter, but active form of the enzyme.…”

Renin, Genes, MicroRNAs, and Renal Mechanisms Involved in Hypertension

“…47 In the kidney, a truncated intracellular renin isoform has been identified in collecting ducts and generates local angiotensin II, leading to inflammation and systemic insulin resistance without an elevation in plasma renin. 47 After localizing renin mRNA in the kidney, 48 we showed that stimuli known to affect renin secretion had similar effects on renal renin mRNA levels. [49][50][51][52] Perturbations in renin mRNA were then documented in the kidney and other tissues in models of hypertension.…”