Sites of renin production in fetal, neonatal, and postnatal Syrian hamster kidneys

Renin expression in large renal vessels during fetal development depends on functional beta1/beta2-adrenergic receptors

During nephrogenesis, renin expression shifts from large renal arteries toward smaller vessels in a defined spatiotemporal pattern, finally becoming restricted to the juxtaglomerular position. Chronic stimulation in adult kidneys leads to a recruitment of renin expression in the upstream vasculature. The mechanisms that control this characteristic switch-on and switch-off in the immature and adult kidney are not well-understood. Previous studies in mice with juxtaglomerular cell-specific deletion of the adenylyl cyclase-stimulatory G protein Gsα suggested that signaling along the cAMP pathway plays an essential role for renin expression during nephrogenesis and in the adult kidney. To identify the Gsα-dependent receptor that might be involved in activating this pathway, the present studies were performed to compare renin expression in wild types with that in mice with targeted deletions of β(1) and β(2)-adrenoceptors. The sympathetic nervous system is an important regulator of the renin system in the adult kidney so that activation of β-adrenenoceptors may also participate in the activation of renin expression along the developing arterial tree and in upstream vasculature in adulthood. Compared with wild-types, renin expression was found to be significantly lower at all developmental stages in the kidneys of β(1)/β(2) Adr(-/-) mice. Three-dimensional analysis showed reduced renin expression in all segments of the vascular tree in mutants and a virtual absence of renin expression in the large arcuate arteries. Adult mutant kidneys showed the typical upstream renin expression after chronic stimulation. Tyrosine hydroxylase staining in fetal and postnatal kidneys revealed that sympathetic innervation of renin-producing cells occurs early in fetal development. Our data indicate that genetic disruption of β-adrenergic receptors reduces basal renin expression along the developing preglomerular tree and in adult kidneys. Furthermore, β-adrenergic receptor input is critical for the expression of renin in large renal vessels during early fetal development.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Development of vascular renin expression in the kidney critically depends on the cyclic AMP pathway

During metanephric kidney development, renin expression in the renal vasculature begins in larger vessels, shifting to smaller vessels and finally remaining restricted to the terminal portions of afferent arterioles at the entrance into the glomerular capillary network. The mechanisms determining the successive expression of renin along the vascular axis of the kidney are not well understood. Since the cAMP signaling cascade plays a central role in the regulation of both renin secretion and synthesis in the adult kidney, it seemed feasible that this pathway might also be critical for renin expression during kidney development. In the present study we determined the spatiotemporal development of renin expression and the development of the preglomerular arterial tree in mouse kidneys with renin cell-specific deletion of G(s)alpha, a core element for receptor activation of adenylyl cyclases. We found that in the absence of the G(s)alpha protein, renin expression was largely absent in the kidneys at any developmental stage, accompanied by alterations in the development of the preglomerular arterial tree. These data indicate that the maintenance of renin expression following a specific spatiotemporal pattern along the preglomerular vasculature critically depends on the availability of G(s)alpha. We infer from our data that the cAMP signaling pathway is not only critical for the regulation of renin synthesis and secretion in the mature kidney but that it also is critical for establishing the juxtaglomerular expression site of renin during development.

Development of renin expression in the mouse kidney

During metanephric kidney development, renin is expressed in the walls of larger intrarenal arteries, but is restricted to the terminal part of the preglomerular arterioles in the adult kidney. Our study describes the three-dimensional development of renin expression in mouse kidneys during fetal and postnatal life. Renin immunoreactivity first appeared at day 14 of development in the cells expressing alpha-smooth muscle actin (alphaSMA) in the arcuate arteries. Before adulthood, the branching of the arcuate arterial tree increased exponentially and renin expression shifted from proximal to distal parts of the tree. Renin expression at branching points or in the cones of growing vessels was not seen. Instead, renin expression appeared after vessel walls and branches were already established, disappeared a few days later, and remained only in the juxtaglomerular regions of afferent arterioles. In these arterioles, coexpression of renin and alphaSMA disappeared gradually, with the terminal cells expressing only renin. At all stages of kidney development, renin expression among comparable vessel segments was heterogeneous. Renin expression remained stable after it reached the terminal parts of afferent arterioles.

Renin-angiotensin system genes in kidney development

The renin-angiotensin system (RAS) plays a key role in cardiovascular homeostasis through the interactions of angiotensin II with its receptors. All components of the RAS are developmentally regulated in the kidney. The functions of the system in the maturing kidney overlap those of the adult, but higher levels of expression and novel locations of expression in the fetus suggest that the RAS has alternate functions as well. Increasing evidence suggests that the RAS may regulate renal growth and development by initiating a complex cascade of events, involving growth factors and proto-oncogenes and other unidentified factors. These same cascades may also be important in renal disease states. Recent advances in the field of molecular and cell biology are providing new tools and strategies to elucidate the intimate mechanism whereby the RAS regulates growth processes and disease states.

Review of microscopic studies on the fetal and neonatal kidney

The developing mammalian kidney has been studied by light microscopic, electron microscopic, immunohistochemical, and autoradiographic techniques. The microscopic studies have been conducted on in vivo samples and in vitro samples. The cellular biology and molecular biology of the developmental steps have been clarified, but more investigations are needed. Information has also been collected concerning the influence of the environment on the microscopic development of the kidney.

Renin and angiotensin II receptor expression in the brains of DES-treated Syrian hamsters

BACKGROUND

The renin angiotensin system (RAS) promotes vasoconstriction. Expression of RAS is induced by different factors.

METHODS

In this study, forebrain sections of hamster brains were studied by immunohistochemical methods to determine the location of renin-positive and angiotensin II receptor-positive cells. The brain sections were obtained from diethylstilbesterol- (DES-) treated hamsters, adult non-DES-treated hamsters, elderly non-DES-treated hamsters, neonatal hamsters, and 15-day fetal hamsters. Circulating renin activity was determined for all but the neonatal and 15-day fetal hamsters.

RESULTS

Renin-positive and angiotensin II receptor-positive vascular smooth muscle cells were observed in DES-treated hamsters. No positive cells were observed in neonatal, 15-day fetal, and adult non-DES-treated hamsters. Some expression was observed in elderly hamsters.

CONCLUSIONS

Therefore, focal expression of the renin angiotensin system in brain vasculature was induced by the synthetic estrogen DES.

Developmental consequences of the renin-angiotensin system

Molecular, cellular, and physiological studies indicate that the renin-angiotensin system (RAS) is highly expressed during early kidney development. We propose that a major function of the RAS during early embryonic development is the modulation of growth processes that lead the primitive kidney into a properly differentiated and architecturally organized organ suited for independent extrauterine life. As development progresses, the RAS acquires new and overlapping functions such as the endocrine and paracrine regulation of blood pressure and renal hemodynamics. Disease states in adult mammals often result in expression of RAS genes and phenotypic changes resembling the embryonic pattern, emphasizing the importance of undertaking developmental studies. Because of their importance in health and disease, the immediate challenge is to identify the mechanisms that regulate the unique development of the RAS and its role(s) in normal and abnormal growth processes.

Expression of renin in coagulating glands is regulated by testosterone

BACKGROUND

The presence of extrarenal or local renin-angiotensin system (RAS) has been noted in several tissues, although its functions have not yet been clarified. Renin from the coagulating gland (CG) is the most recently discovered local RAS and is a significant subject for investigation because large amounts of both mRNA and proteins are detected in this organ. Recently, it has been reported that testosterone influences renin synthesis in several extrarenal tissues, although it has no effect on intrarenal renin. Therefore, it is possible that CG renin is also regulated by testosterone.

METHODS

Forty-four male C57BL/6 mice, aged 3 wk to 6 mo, were used in studies on the ontogeny and androgen regulation of the RAS in the CG. The tissues were fixed with Bouin's solution and paraffin sections were stained with immunohistochemical methods using antirenin antiserum. In each immunostained section, the relative number of renin-containing cells in terminal portions of the CG were counted.

RESULTS

Immunoreactivity for renin was first detected at 6 wk after birth. After that time, the number of renin-containing cells gradually increased throughout the experiment. In adults, several patterns of renin immunoreactivity were demonstrated in almost all epithelial cells of CGs, specifically; (1) basolateral granular reaction, (2) diffuse immunoreactivity throughout the cytoplasm, and (3) restricted nuclear reaction. Excretory products of some terminal lumina were also found to be positive for renin. At 10 days after castration, renin-containing cells in ductal termini were decreased and remained at low levels until at 4 wk after castration. After testosterone injection, numerical values of renin-containing cells were high at 1 wk and then decreased at 2-3 wk.

CONCLUSION

It is suggested that CG renin of the mouse is expressed together with sexual maturation during development and that it depends on the testis, possibly the male sex hormone.

Immunohistochemical studies of renin-containing cells in the developing sheep kidney

BACKGROUND

Renin-containing (RC) cells in small ruminant kidneys have been known to be widely distributed along the blood vessels. In the present study, RC cells in developing sheep kidneys were studied to investigate not only the appearance but distribution with the potential physiological significance using immunohistochemical and histoplanimetrical techniques.

METHODS

Seven fetal, 12 newborn, and 3 adult metanephric kidneys were used and immunostained by anti-renin antiserum. In the histoplanimetrical analysis, the numerical values of RC cells existing at the walls of 3 major arterial types in the kidneys were calculated.

RESULTS

At day 44 of gestation, RC cells were already demonstrated in the walls of renal, interlobar, and afferent vessels, located in the deep cortex and the medulla. In intermediate gestational periods, RC cells were detected throughout the intrarenal arterial trees. In late gestational periods, RC cells expressed in the walls of interlobar/arcuate and interlobular arteries tended to decrease or disappear gradually, while they were distributed predominantly in the afferent glomerular vessels. In newborn lambs, especially days 1 to 3 after birth, increased numbers of RC cells were demonstrated throughout the arterial trees in the kidneys. In older lambs, RC cells located in the interlobar/arcuate arteries and the proximal region of the interlobular arteries decreased in number and gradually disappeared. Some RC cells were still distributed in the distal portion of the interlobular artery even in the adult sheep.

CONCLUSIONS

These results suggest that the wide distribution of RC cells in sheep kidney is formed in perinatal life, and that the neuronal regulation is associated with the maintenance of this distribution.