Elevated levels of endogenous angiotensin can cause hypertensive nephrosclerosis as a result of the potent vasopressor action of the peptide. We have produced by gene targeting mice homozygous for a null mutation in the angiotensinogen gene (Atg-'-). Postnatally, Atg-'-animals show a modest delay in glomerular maturation. Although Atg-'-animals are hypotensive by 7 wk of age, they develop, by 3 wk of age, pronounced lesions in the renal cortex, similar to those of hypertensive nephrosclerosis. In addition, the papillae of homozygous mutant kidneys are reduced in size. These lesions are accompanied by local up-regulation of PDGF-B and TGF-fi1 mRNA in the cortex and down-regulation of PDGF-A mRNA in the papilla. The study demonstrates an important requirement for angiotensin in achieving and maintaining the normal morphology of the kidney. The mechanism through which angiotensin maintains the volume homeostasis in mammals includes promotion of the maturational growth of the papilla. (J. Clin. Invest. 1995.

The cellular distribution of angiotensin II type 1 (AT1) and type 2 (AT2) receptor mRNA was examined in mouse kidneys at several embryonic stages (12 to 18 days; 19 days = full term) and up to three weeks after birth by in situ hybridization. The expression of both AT1 and AT2 mRNAs appeared simultaneously at 14 days of gestation. However, their distributions were contrasting: AT1 mRNA was expressed in mature glomeruli and maturing S-shaped bodies throughout the stages examined. AT1 expression was also detected at 16 days of gestation in the proximal and distal tubules and peaked at the end of gestation. Both the temporal and spatial expression of AT1 coincide with the differentiation and proliferation of glomerular mesangial and tubular cells during nephrogenesis. In contrast, AT2 mRNA was present only in the mesenchymal cells adjacent to the stalk of the ureter bud at early developmental stages, and, later, extended to the mesenchymal cells located near, but outside, the nephrogenic area of superficial cortex and also the cells between collecting ducts. AT2 expression in these regions decreased markedly within three weeks after birth. Temporally and spatially, AT2 mRNA expression coincides with the epithelial-mesenchymal interactions that take place during early phases of nephrogenesis. The site of AT2 expression also overlaps closely with that of a specific group of cells which undergo apoptosis following nephrogenesis. Thus, contrary to current belief, the activation of AT1 and AT2 genes takes place in different cell types of the kidney during embryonic development, and thereby conceivably contributes to the ontogeny of those specific renal cells.

We have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse ( Agtr1a Ϫ / Ϫ ↔ ϩ / ϩ ) is made up of wild-type ( Agtr1a ϩ / ϩ ) cells or cells homozygous for Agtr1a deletion (Agtr1a Ϫ / Ϫ ). In the latter, the AT1A coding exon was replaced with a reporter gene,

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This study aimed to identify the intracellular signaling pathway in angiotensin II (Ang II)-induced upregulation of plasminogen activator inhibitor type 1 (PAI-1) mRNA expression in cultured rat glomerular mesangial cells, and to examine the interaction between Ang II and TGF-beta signaling. Ang II-induced upregulation of PAI-1 mRNA expression was prevented by a protein kinase C (PKC) inhibitor, bisindorylmaleimide I. While phorbol 12-myristate 13-acetate (PMA) upregulated the PAI-1 mRNA expression, a calcium ionophore, ionomycin, had little effect. Mesangial cells pretreated with PMA for 24 h to downregulate PKC demonstrated attenuated response to Ang II. A protein tyrosine kinase inhibitor, genistein, completely blocked both Ang II- and PMA-induced PAI-1 mRNA expression. Transforming growth factor-beta1 (TGF-beta1) alone induced the expression, and in the presence of Ang II, TGF-beta1 superinduced PAI-1 mRNA expression to a higher extent. Both bisindorylmaleimide I and genistein suppressed the Ang II plus TGF-beta1-induced PAI-1 mRNA upregulation to the basal level, while downregulation of PKC attenuated the synergistic upregulation of PAI-1 mRNA expression to the level comparable to TGF-beta1 alone. These data suggest that, in rat mesangial cells, (1) PKC and protein tyrosine kinase(s) are involved in the Ang II signaling cascade, (2) protein tyrosine kinase(s) works downstream from PKC in the cascade, and (3) there is an interaction between the Ang II and TGF-beta signal pathways downstream from PKC. In in vivo settings, local activation of renin-angiotensin and TGF-beta systems in the glomeruli may synergistically augment PAI-1 expression, promote mesangial matrix accumulation and progression of glomerular injury.

Administration of a selective angiotensin I type 1 receptor (AT1) antagonist in animals not only nullifies the vasopressor action of angiotensin II, but also induces chloriduria and kaliuria, juxtoglomerular apparatus (JGA) hypertrophy and hyperreninemia, features characteristic of human Bartter's syndrome. We, therefore, explored the possibility that Bartter's syndrome may involve an AT1 abnormality. Using a pair of AT1-specific oligonucleotide primers and two different DNA polymerases (Taq and Pfu), we amplified the approximately 1 kb AT1 coding region of genomic DNA isolated from leukocytes of five patients with Bartter's syndrome by PCR and analyzed the sequence of the product. While the sequence of all clones from four patients were identical to that already reported for the normal human AT1 DNA sequence, 50% of the clones from one patient with Bartter's syndrome were found to have A-->G transition at nucleotide 931 which causes an amino acid substitution (arg-->gly) on the carboxy-terminal cytosolic tail of AT1. This mutation was not found in DNA from 50 normal controls which were screened by restriction enzyme digestion pattern of the PCR products of this region. As PCR-amplified AT1 DNA clones from four other individuals with Bartter's syndrome did not display any abnormality in the coding region, the possibility exists that Bartter's syndrome consists of multiple disease entities, where an AT1 gene abnormality represents a specific subgroup of the syndrome and/or some abnormality includes mutations outside of the coding region.

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