Renin-like immunoreactivity in human placenta and fetal membranes

Expression of a renin/GFP transgene in mouse embryonic, extra-embryonic, and adult tissues

A reporter construct was assembled with 4-kb of renin 5'-flanking sequence fused to humanized green fluorescent protein (GFP) cDNA. Transgenic mice carrying this construct were produced and assayed for GFP expression. In the adult, expression was detected in juxtaglomerular (JG) cells of the kidney and granular convoluted tubular cells of the submandibular gland. Furthermore, treatment of mice with captopril induced GFP expression in renal vascular smooth muscle cells. During embryogenesis, GFP expression was first detected at embryonic day E13 in the adrenal gland and Wolffian duct. Expression was also seen in the developing renal vasculature as early as E14 and remained detectable through birth. Renal GFP expression became restricted to JG cells in adults. Fetal adrenal and gonadal arteries also expressed GFP. In the placenta, GFP was observed in giant cell trophoblasts, consistent with reports of renin expression in chorionic cells of both humans and mice. We conclude that 4 kb of renin 5' flank is sufficient to direct multiple known renin expression patterns. Furthermore, the renin-GFP construct characterized here will provide a useful vital reporter for renin expression.

Definitive molecular evidence of renin-angiotensin system in human uterine decidual cells

The tissue renin-angiotensin system (RAS) has been suggested to be present in human gestational tissues, but uncertainty exists about the authenticity of this RAS, and the cellular origin of this RAS has not been defined. In the present study, we confirmed the presence of authentic renin and angiotensinogen in the prolactin-producing decidual tissue by sequencing the cDNAs generated through reverse transcription-polymerase chain reaction, confirming cDNA product sizes, and by performing Northern blot analysis of the RNA. Our comparative data demonstrate that prolactin has the highest expression in the decidual tissue, followed by renin, and that angiotensinogen has the least expression. We demonstrated with fluorescent in situ hybridization that prolactin-expressing endocrine decidual cells are the same cells that express both renin and angiotensinogen. These results have implications in regard to how the decidual RAS may be regulated and what potential role this local RAS may have in the pathogenesis of preeclampsia.

Renin-like immunoreactivity in uterus and placenta from normotensive and hypertensive pregnancies

OBJECTIVES

(1) To identify the distribution of renin-like immunoreactivity in placental bed, placenta-free uterine wall, placenta, fetal membranes, and intertwin membranes obtained from normal pregnancies and (2) to compare the findings in normal pregnancies with those in pregnancies complicated by various hypertensive disorders.

STUDY DESIGN

Biopsies were taken from 31 normotensive pregnant women, eight of whom had twin pregnancies, and from 28 women with various hypertensive disorders of pregnancy. The anti-human renal renin monoclonal antibody, F37.1A1, was used for immunostaining. Histological structures were identified with standard H&E and PAS techniques, supplemented with immunostaining using the specific cell markers CD68 and cytokeratin.

RESULTS

Renin-like immunoreactivity was found in cytokeratin immunolabelled placental syncytiotrophoblast, amnionic and glandular epithelium, but most consistently in CD68 immunolabelled maternal and fetal macrophages. The distribution of renin-like immunoreactivity throughout the pregnant uterus roughly parallelled reported renin concentrations in the various tissues, while its localization conforms also with that of cathepsin D. There were no obvious differences in renin-like immunolabelling between normotensive or hypertensive women. Renin-like immunoreactivity was particularly common in the atherotic lesions that are observed more often in pregnancies complicated with hypertensive disorders of pregnancy and/or intra-uterine growth restriction.

CONCLUSIONS

The data complement earlier findings showing that only two of four anti-renal renin monoclonal antibodies, both of which cross-react with cathepsin D, give a positive immunostaining in placental tissue. They question whether classical concepts on renin localisation in uteroplacental tissues all relate to one and the same enzyme. The demonstration of renin-like enzymes in different cell types, including macrophages, may explain the diversity of functions that has been attributed to uterine renin. There were no differences between tissues obtained from normotensive and hypertensive pregnancies, except for the consistent presence of renin-like immunoreactivity in atherotic lesions.

Human spiral artery renin-angiotensin system

Pregnancy induces uterine spiral arteries to remodel into dilated uteroplacental vessels by an unknown mechanism called "physiological change." In women who develop preeclampsia, however, many spiral arteries remain unchanged or develop medial hyperplasia and atherosis. We recently demonstrated that angiotensinogen is expressed by remodeling spiral arteries in first-trimester decidua. We hypothesize that a local spiral artery renin-angiotensin system mediates pregnancy-induced remodeling of these vessels. In this study we tested for expression of renin, angiotensin-converting enzyme, and angiotensin II type 1 receptor genes in the first-trimester uterus using reverse-transcription polymerase chain reaction. Expression was localized by in situ hybridization and immunohistochemistry. Renin, angiotensin-converting enzyme, and the angiotensin II type 1 receptor are all expressed in and around remodeling spiral arteries. These observations suggest that a local spiral artery renin-angiotensin system may play a role in pregnancy-induced remodeling of these vessels. Elevated angiotensinogen expression in women homozygous for the A(-6) variant in the angiotensinogen promoter may promote abnormal remodeling, whereas relatively lower levels in women homozygous for G(-6) may permit enough normal remodeling to protect these women from preeclampsia.

Identification of 'renin'-containing cells in the choriodecidua

Chorionic trophoblast, decidual cells, and macrophages have all been named as the site of renin in the placental membranes. To establish more clearly the nature of the renin-containing cells in the placental membranes, double immunostaining techniques were used to stain renin and specific cell markers in the same tissue sections. Cytokeratin was selected as an ectodermal cell marker and CD68 as a cytoplasmic macrophage marker. Cross-binding between antibodies was prevented by blocking species-related binding sites between the first and second sequence of the double-immunostaining procedures and by using highly selective immunostaining techniques in the second sequence. The results clearly show renin immunostaining in CD68-positive macrophages and not in cytokeratin-positive trophoblast. The anti-renal renin monoclonal antibody showed high affinity cross-reactivity with cathepsin D, another aspartic proteinase that can release angiotensin I from angiotensinogen. This should be seen in the context of earlier findings that only two of four anti-renal renin monoclonal antibodies showed staining in uterine and placental tissues and both cross-reacted with cathepsin D. The results indicate that differentiation between renin and cathepsin D and, possibly, other substances with shared properties and epitope homology deserves more attention than it has received thus far.