SUN-130 A Not-So-Simple Work-Up of Diabetes: A Case of MODY 5

Introduction: Maturity-onset diabetes of the young 5 (MODY-5) is a rare type of inherited diabetes mellitus. It is an autosomal dominant disease, manifesting as a clinically heterogeneous disorder with a lack of autoantibodies. On the molecular level, MODY 5 is due to defects of hepatocyte nuclear factors 1B (HNF1B), which not only cause structural abnormalities, but also intrinsic organ dysfunction in the kidneys, liver, and pancreas as well. Case: This is a 33 year old female presented for diabetes type 2 management. Her past medical history originated at the age of 7, diagnosed with short ureters with reflux leading to frequent pyelonephritis, requiring reconstructive surgery. At 15, found to have high liver enzymes, which have had variable and persistent elevation; she had 4 liver biopsies, which were pathologically unremarkable and no cause found. At 27, diagnosed with type 2 DM based on her HbA1c being >7 and initiated on metformin. Recently was also diagnosed with PCOS after a first trimester missed abortion and subsequent infertility. Abdominal US subsequently revealed bilateral renal cysts. Family history was remarkable for type 1 diabetes in her father, type 2 diabetes in her sister and maternal uncle, and renal dysfunction in her niece. Physical exam was unremarkable, and BMI was 19.53 kg/m2. Laboratory workup revealed elevated liver enzymes (Alkaline Phosphatase: 445 U/l; Bilirubin: 1.7 mg/dl, ASL: 106 U/L, ALT 248 U/L). A1C was 5.3% at that time. Based off the presentation and exam, it was felt that her disease process did not fit the classic paradigm of type 2 diabetes mellitus, no obesity, no hypertension and no dyslipidemia. This prompted autoimmune diabetes screening which was negative. A MODY Sequencing Panel was then performed, which was positive for MODY type 5; she was found to be heterozygous in the HNF1B gene, c.544+1G>A variant. Given her diagnosis, an insulin regimen was initiated but due to allergic reaction, she was then converted to glipizide orally. She is now following with medical genetics. Conclusion: MODY is not commonly seen in the diabetes population, where prevalence accounts for 2 to 5 % of known diabetics. MODY-5 is a more uncommon subset in the population with MODY, manifesting as 5-10% of such cases. As such, many MODY patients are often misclassified has having either type 1 or type 2 diabetes. Given other organ dysfunctions affected by MODY-5, a lack of diagnosis of this condition can delay monitoring and treatment of the disease. As such, recognition of MODY should be increased, as is need for early screening for patients if the disease is suspected. Citation: Dubois-Laforgue, D,. et al. (2017). Diabetes, Associated Clinical Spectrum, Long-term Prognosis, and Genotype/Phenotype Correlations in 201 Adult Patients With Hepatocyte Nuclear Factor 1B ( HNF1B ) Molecular Defects. Diabetes Care, 40(11), 1436-1443. doi:10.2337/dc16-2462. PMID: 28420700

Correction to: Combination Glucose-Lowering Therapy Plans in T2DM: Case-Based Considerations

The article "Combination Glucose-Lowering Therapy Plans in T2DM: Case-Based Considerations".

Combination Glucose-Lowering Therapy Plans in T2DM: Case-Based Considerations

Type 2 diabetes mellitus (T2DM) is a complex disease, and while lifestyle interventions remain the cornerstone of therapy, most patients will also require pharmacotherapy. Current diabetes treatment guidelines and algorithms recommend an individualized approach to setting glycemic goals and selecting treatment. Although a single antihyperglycemic agent may be appropriate as the initial T2DM pharmacotherapy, the progressive nature of the disease due to declining pancreatic β-cell function will result in the vast majority of T2DM patients eventually requiring two or more antihyperglycemic agents. The American Association of Clinical Endocrinologists/American College of Clinical Endocrinology T2DM management algorithm recommends initial dual agent combination therapy when a single agent is unlikely to achieve their target glycemia, i.e., for those patients with an HbA1c ≥ 7.5 and an individualized HbA1c target of < 7.5%. The American Diabetes Association Standards of Care recommend combination pharmacotherapy for those patients presenting with very elevated HbA1c levels (e.g., ≥ 9% and < 10%). Metformin (if well tolerated and not contraindicated) is the initial pharmacologic choice for most patients; selection of another antihyperglycemic agent to the regimen will depend on the presence of atherosclerotic cardiovascular disease and other patient-specific factors (e.g., age, known duration of T2DM, history of or risk for hypoglycemia and/or adverse consequences from hypoglycemia, other comorbidities, and available resources), along with drug-specific factors (e.g., risk for hypoglycemia, potential effects on weight, drug adverse event profiles, and cost). Combination therapy may be administered as a multi-pill regimen, a single-pill combination (i.e., fixed-dose combination oral therapy), or as a combination of oral and/or injectable therapies. This paper provides two illustrative case presentations to demonstrate how current treatment recommendations and algorithms can be used to guide the selection of non-insulin-based combination therapy for patients with T2DM in primary care settings and discusses the relative merits of several possible approaches for each patient.

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A p53-Pax2 pathway in kidney development: implications for nephrogenesis

Congenital reduction in nephron number (renal hypoplasia) is a predisposing factor for chronic kidney disease and hypertension. Despite identification of specific genes and pathways in nephrogenesis, determinants of final nephron endowment are poorly understood. Here, we report that mice with germ-line p53 deletion (p53(-/-)) manifest renal hypoplasia; the phenotype can be recapitulated by conditional deletion of p53 from renal progenitors in the cap mesenchyme (CM(p53-/-)). Mice or humans with germ-line heterozygous mutations in Pax2 exhibit renal hypoplasia. Since both transcription factors are developmentally expressed in the metanephros, we tested the hypothesis that p53 and Pax2 cooperate in nephrogenesis. In this study, we provide evidence for the presence of genetic epistasis between p53 and Pax2: a) p53(-/-) and CM(p53-/-)embryos express lower Pax2 mRNA and protein in nephron progenitors than their wild-type littermates; b) ChIP-Seq identified peaks of p53 occupancy in chromatin regions of the Pax2 promoter and gene in embryonic kidneys; c) p53 binding to Pax2 gene is significantly more enriched in Pax2 -expressing than non-expressing metanephric mesenchyme cells; d) in transient transfection assays, Pax2 promoter activity is stimulated by wild-type p53 and inhibited by a dominant negative mutant p53; e) p53 knockdown in cultured metanephric mesenchyme cells down-regulates endogenous Pax2 expression; f) reduction of p53 gene dosage worsens the renal hypoplasia in Pax2(+/-) mice. Bioinformatics identified a set of developmental renal genes likely to be co-regulated by p53 and Pax2. We propose that the cross-talk between p53 and Pax2 provides a transcriptional platform that promotes nephrogenesis, thus contributing to nephron endowment.

Histone deacetylase (HDAC) activity is critical for embryonic kidney gene expression, growth, and differentiation

Histone deacetylases (HDACs) regulate fundamental biological processes such as cellular proliferation, differentiation, and survival via genomic and nongenomic effects. This study examined the importance of HDAC activity in the regulation of gene expression and differentiation of the developing mouse kidney. Class I HDAC1-3 and class II HDAC4, -7, and -9 genes are developmentally regulated. Moreover, HDAC1-3 are highly expressed in nephron precursors. Short term treatment of cultured mouse embryonic kidneys with HDAC inhibitors (HDACi) induced global histone H3 and H4 hyperacetylation and H3K4 hypermethylation. However, genome-wide profiling revealed that the HDAC-regulated transcriptome is restricted and encompasses regulators of the cell cycle, Wnt/β-catenin, TGF-β/Smad, and PI3K-AKT pathways. Further analysis demonstrated that base-line expression of key developmental renal regulators, including Osr1, Eya1, Pax2/8, WT1, Gdnf, Wnt9b, Sfrp1/2, and Emx2, is dependent on intact HDAC activity. Treatment of cultured embryonic kidney cells with HDACi recapitulated these gene expression changes, and chromatin immunoprecipitation assays revealed that HDACi is associated with histone hyperacetylation of Pax2/Pax8, Gdnf, Sfrp1, and p21. Gene knockdown studies demonstrated that HDAC1 and HDAC2 play a redundant role in regulation of Pax2/8 and Sfrp1 but not Gdnf. Long term treatment of embryonic kidneys with HDACi impairs the ureteric bud branching morphogenesis program and provokes growth arrest and apoptosis. We conclude that HDAC activity is critical for normal embryonic kidney homeostasis, and we implicate class I HDACs in the regulation of early nephron gene expression, differentiation, and survival.

Ontogeny of bradykinin B1 receptors in the mouse kidney

Kinins are vasoactive peptides that stimulate two G-protein coupled bradykinin receptors (B1R and B2R). B2R-knockout mice are salt sensitive and develop renal dysgenesis and hypertension if salt stressed during embryogenesis. B1R-knockout mice, on the other hand, are protected from inflammation and fibrosis. This study examined the spatiotemporal expression of B1R during renal organogenesis. The segmental nephron identity of B1R immunoreactivity was determined by costaining with markers of the collecting duct (Dolichos biflorus), proximal tubule (Dolichos tetraglonus), and nephron progenitors (Pax2). At E14.5, the B1R was confined to few cells in the metanephric mesenchyme. Abundance of B1R increased progressively during development. On E17.5, B1R was enriched in differentiating proximal tubular cells and by postnatal day 1, B1R was clearly expressed on the luminal aspect of the proximal tubule. Quantitative real-time PCR revealed that the levels of B1R mRNA more than double during renal maturation. We conclude that 1) B1R expression correlates closely with nephron maturation; 2) lack of B1R in nephron progenitors suggests that B1R is unlikely to play a role in early nephrogenesis; and 3) enrichment of B1R in maturing proximal tubule suggests a potential role for this receptor in terminal differentiation of the proximal nephron.

p53 regulates metanephric development

p53 is best known as a tumor suppressor that regulates cell-cycle, differentiation, and apoptosis pathways, but its potential role in embryonic development and organogenesis remains controversial. Here, p53(-/-) embryos bred on C57Bl6 background exhibited a spectrum of congenital abnormalities of the kidney and urinary tract, including ureteric bud (UB) ectopia, double ureters/collecting systems, delayed primary branching of the UB, and hypoplastic metanephroi. We observed ectopic UB outgrowth from the Wolffian duct (WD) in one third of p53(-/-) embryos. The prevalence of duplex was higher in embryos than in neonates, and ex vivo organ culture suggested that ectopic ureters can regress over time, leaving behind a dysplastic pole ("segmental dysgenesis"). Transgenic expression of dominant negative p53 or conditional inactivation of p53 in the UB but not in the metanephric mesenchyme lineage recapitulated the duplex phenotype. Mechanistically, p53 inactivation in the WD associated with enhanced sensitivity to glial cell line-derived neurotrophic factor (GDNF)-induced ectopic budding and potentiated phosphatidylinositol-3 kinase activation by GDNF in UB cells. Unlike several other models of UB ectopia, hypersensitivity of p53(-/-) WD to GDNF is not accompanied by reduced Sprouty-1 or anterior expansion of the GDNF domain. In summary, our data lend support for a restrictive role for p53 activity in UB outgrowth from the WD.

Bradykinin B2 receptor null mice harboring a Ser23-to-Ala substitution in the p53 gene are protected from renal dysgenesis

A physiological cross talk operates between the tumor suppressor protein p53 and the bradykinin B2 receptor (BdkrB2) during renal organogenesis. Thus, although BdkrB2 is a target for p53-mediated transcriptional activation, BdkrB2 is required to restrict p53 proapoptotic activity. We previously demonstrated that BdkrB2(-/-) embryos exposed to gestational salt stress develop renal dysgenesis as a result of p53-mediated apoptosis of nephron progenitors and repression of the terminal differentiation program. Compared with wild-type kidneys, BdkrB2(-/-) express abnormally high levels of the Checkpoint kinase (Chk1), which activates p53 via Ser23 phosphorylation. To define the functional relevance of p53S23 phosphorylation, we generated a compound strain of BdkrB2(-/-) mice harboring a homozygous Ser23-to-Ala (S23A) mutation in the p53 gene by crossing BdkrB2(-/-) with p53S23A knockin mice. Unlike salt-stressed BdkrB2(-/-) pups, which exhibit renal dysgenesis, homozygous S23A;BdkrB2(-/-) littermates are protected and have normal renal development. Heterozygous S23A;BdkrB2(-/-) mice have an intermediate phenotype. The p53-S23A substitution was associated with amelioration of apoptosis and restored markers of nephrogenesis and tubulogenesis. Real-time quantitative RT-PCR of terminal differentiation genes demonstrated that the S23A substitution restored normal expression patterns of aquaporin-2, Na-Cl cotransporter, Na-K-2Cl cotransporter, Na-bicarbonate cotransporter, and Sglt1. We conclude that p53 phosphorylation on Ser23 is an essential step in the signaling pathway mediating the susceptibility of BdkrB2(-/-) mutants to renal dysgenesis.

The polycystic kidney disease-1 gene is a target for p53-mediated transcriptional repression

This study provides evidence that the tumor suppressor protein, p53, is a transcriptional repressor of PKD1. Kidneys of p53-null mice expressed higher Pkd1 mRNA levels than wild-type littermates; gamma-irradiation suppressed PKD1 gene expression in p53+/+ but not p53-/- cells; and chromatin immunoprecipitation assays demonstrated the binding of p53 to the PKD1 promoter in vivo. In transient transfection assays, p53 repressed PKD1 promoter activity independently of endogenous p21. Deletion analysis mapped p53-mediated repression to the proximal promoter region of PKD1. Mutations of the DNA binding or C-terminal minimal repression domains of p53 abolished its ability to repress PKD1. Moreover, trichostatin A, an inhibitor of histone deacetylase activity, attenuated p53-induced repression of the PKD1 promoter. These findings, together with previous reports showing that dedifferentiated Pkd1-deficient cells express lower p53 and p21 levels, suggest a model whereby PKD1 signaling activates the p53-p21 differentiation pathway. In turn, p53 cooperates with histone deacetylases to repress PKD1 gene transcription. Loss of a p53-mediated negative feedback loop in PKD1 mutant cells may therefore contribute to deregulated PKD1 expression and cystogenesis.

Spatiotemporal Switch from ΔNp73 to TAp73 Isoforms during Nephrogenesis

p73 is a member of the p53 gene family, which also includes p53 and p63. These proteins share sequence similarity and target genes but also have divergent roles in cancer and development. Unlike p53, transcription of the p73 gene yields multiple full-length (transactivation (TA) domain) and amino terminus-truncated (DeltaN) isoforms. DeltaNp73 acts in a dominant negative fashion to inhibit the actions of TAp73 and p53 on their target genes, promoting cell survival and proliferation and suppressing apoptosis. The balance between TAp73 and its negative regulator, DeltaNp73, may therefore represent an important determinant of developmental cell fate. There is little if anything known regarding the developmental regulation of the p73 gene. In this study, we showed that TAp73 and DeltaNp73 exhibit reciprocal spatiotemporal expression and functions during nephrogenesis. TAp73 was predominantly expressed in the differentiation domain of the renal cortex in an overlapping manner with the vasopressin-sensitive water channel aquaporin-2 (AQP-2). Chromatin immunoprecipitation assays demonstrated that the endogenous AQP-2 promoter was occupied by TAp73 in a developmentally regulated manner. Furthermore TAp73 stimulated AQP-2 promoter-driven reporter expression. TAp73 also activated the bradykinin B2 receptor (B2R) promoter, a developmentally regulated gene involved in regulation of sodium excretion. The transcriptional effects of TAp73 on AQP-2 and B2R were independent of p53. In marked contrast to TAp73, DeltaNp73 isoforms were induced early in development and were preferentially expressed in proliferating nephron precursors. Moreover DeltaNp73 was a potent repressor of B2R gene transcription. We conclude that the p73 gene is developmentally regulated during kidney organogenesis. The spatiotemporal switch from DeltaNp73 to TAp73 may play an important role in the terminal differentiation program of the developing nephron.

Combinatorial control of the bradykinin B2 receptor promoter by p53, CREB, KLF-4, and CBP: implications for terminal nephron differentiation

Despite a wealth of knowledge regarding the early steps of epithelial differentiation, little is known about the mechanisms responsible for terminal nephron differentiation. The bradykinin B2 receptor (B2R) regulates renal function and integrity, and its expression is induced during terminal nephron differentiation. This study investigates the transcriptional regulation of the B2R during kidney development. The rat B2R 5′-flanking region has a highly conserved cis-acting enhancer in the proximal promoter consisting of contiguous binding sites for the transcription factors cAMP response element binding protein (CREB), p53, and Krüppel-like factor (KLF-4). The B2R enhancer drives reporter gene expression in inner medullary collecting duct-3 cells but is considerably weaker in other cell types. Site-directed mutagenesis and expression of dominant negative mutants demonstrated the requirement of CREB DNA binding and Ser-133 phosphorylation for optimal enhancer function. Moreover, helical phasing experiments showed that disruption of the spatial organization of the enhancer inhibits B2R promoter activity. Several lines of evidence indicate that cooperative interactions among the three transcription factors occur in vivo during terminal nephron differentiation: 1) CREB, p53, and KLF-4 are coexpressed in B2R-positive differentiating cells; 2) the maturational expression of B2R correlates with CREB/p53/KLF-4 DNA-binding activity; 3) assembly of CREB, p53, and KLF-4 on chromatin at the endogenous B2R promoter is developmentally regulated and is accompanied by CBP recruitment and histone hyperacetylation; and 4) CREB and p53 occupancy of the B2R enhancer is cooperative. These results demonstrate that combinatorial interactions among the transcription factors, CREB, p53, and KLF-4, and the coactivator CBP, may be critical for the regulation of B2R gene expression during terminal nephron differentiation.

A novel pathological role of p53 in kidney development revealed by gene-environment interactions

Gene-environment interactions are implicated in congenital human disorders. Accordingly, there is a pressing need to develop animal models of human disease, which are the product of defined gene-environment interactions. Previously, our laboratory demonstrated that gestational salt stress of bradykinin B(2) receptor (B(2)R)-null mice induces renal dysgenesis and early death of the offspring. In contrast, salt-stressed B(2)R +/+ or +/- littermates have normal development. The present study investigates the mechanisms underlying the susceptibility of B(2)R-null mice to renal dysgenesis. Proteomic and conventional Western blot screens identified E-cadherin among the differentially repressed proteins in B(2)R-/- kidneys, whereas the checkpoint kinase Chk1 and its substrate P-Ser(20) p53 were induced. We tested the hypothesis that p53 mediates repression of E-cadherin gene expression and is causally linked to the renal dysgenesis. Genetic crosses between B(2)R -/- and p53+/- mice revealed that germline reduction of p53 gene dosage rescues B(2)R-/- mice from renal dysgenesis and restores kidney E-cadherin gene expression. Furthermore, gamma-irradiation induces repression of E-cadherin gene expression in p53+/+ but not -/- cells. In transient transfection assays, p53 repressed human E-cadherin promoter-driven reporter activity, whereas a mutant p53, which cannot bind DNA, did not. Functional promoter analysis indicated the presence of a p53-responsive element in exon 1, which partially mediates p53-induced repression. Chromatin immunoprecipitation assays revealed that p53 inhibits histone acetylation of the E-cadherin promoter. Treatment with a histone deacetylase inhibitor reversed both p53-mediated promoter repression and deacetylation. In conclusion, this study demonstrates that gene-environment interactions cooperate to induce congenital defects through p53 activation.

Renal and blood pressure phenotype in 18-mo-old bradykinin B2R(-/-)CRD mice

Aberrant gene-environment interactions are implicated in the pathogenesis of congenital renal dysgenesis (CRD), a leading cause of renal failure in infants and children. We have recently developed an animal model of CRD that is caused by gestational salt stress (5% NaCl diet; HS) of bradykinin B2R null mice [B2R(-/-)CRD; El-Dahr SS, Harrison-Bernard LM, Dipp S, Yosipiv IV, and Meleg-Smith S. Physiol Genomics 3: 121-131, 2000.]. Developing B2R(-/-)CRD mice exhibit tubular and glomerular cysts, stromal expansion, and loss of corticomedullary differentiation. In addition, B2R(-/-)CRD mice exhibit transient hypertension from 2 to 4 mo of age. The present study was designed to determine the long-term consequences of CRD on renal morphology and salt sensitivity of blood pressure in B2R(-/-)CRD mice. One-year- and 18-mo-old B2R(-/-)CRD mice exhibited stunted renal growth, glomerular cystic abnormalities, and collecting duct ectasia. Moreover, tumors of mesenchymal cell origin emerged in the dysplastic kidneys of 90% of 1-yr-old and 100% of 18-mo-old B2R(-/-)CRD mice but not in age-matched B2R(-/-) or wild-type mice. When challenged with an HS diet, 18-mo-old B2R(-/-)CRD exhibited a significant rise in systolic and diastolic blood pressures and more pronounced natriuresis and diuresis compared with salt-loaded 18-mo-old wild-type mice. Kidney aquaporin-2 expression was decreased by 50%, whereas renin, ANG type 1 receptor, and Na+-K+-ATPase levels were not different in B2R(-/-)CRD mice compared with controls. In conclusion, this study demonstrates that B2R(-/-)CRD mice exhibit permanent phenotypic and functional abnormalities in renal growth and differentiation. This novel model of human disease links gene-environment interactions with renal development and blood pressure homeostasis.

Two functionally divergent p53-responsive elements in the rat bradykinin B2 receptor promoter

Although p53 is known to have dual functions as a transcriptional activator and repressor, there has not been an example where both p53-activating and -repressing elements reside within one target promoter. Previous work from this laboratory defined two different p53 response elements, termed P1 and P2, located at nucleotide positions -70 and -707, respectively, in the rat bradykinin B2 receptor promoter. In this study, through manipulation of the DNA sequence and context, we demonstrate opposing roles for P1 and P2 as transcriptional activator and repressor, respectively. Deletion of P1 abrogates p53-mediated activation. P1 maintains its role as an activator upon relocation to the P2 site and activates transcription from a heterologous promoter construct. Thus, P1 is a bona fide positive p53-response element. In contrast, deletion of P2 enhances P1-induced activation. P2 represses transcription when substituted for P1 or when relocated midway between P1 and P2. P2-mediated repression is sequence-dependent, because it is reversed to activation when P2 is substituted by the P1 or p53 consensus sequences. Moreover, site-directed mutagenesis that converts P2 to a higher affinity p53-binding site results in transcriptional activation rather than repression. Surprisingly, P2 strongly activates a heterologous promoter. Thus, P2-mediated transcriptional repression is both sequence- and context-dependent. Investigations into the mechanisms of P2-mediated repression indicate that it is trichostatin-insensitive and unaffected by CBP or mutation of the minimal repression C-terminal domain of p53. However, gel shift assays suggest that p53 competes with other transcriptional activators for binding to overlapping binding sequences within the P2 element. In conclusion, this study provides a rare example of a transcription factor having two divergent functional effects that are sequence- and context-dependent. The interplay of P1 and P2 may be important in the regulation of bradykinin B2 receptor gene expression in response to inflammatory stress and during development.

The Bradykinin B2 receptor is required for full expression of renal COX-2 and renin

Angiotensin converting enzyme (ACE) inhibition leads to increased levels of bradykinin, cyclooxygenase-2 (COX-2), and renin. Since bradykinin stimulates prostaglandin release, renin synthesis may be regulated through a kinin-COX-2 pathway. To test this hypothesis, we examined the impact of bradykinin B2 receptor (B2R) gene disruption in mice on kidney COX-2 and renin gene expression. Kidney COX-2 mRNA and protein levels were significantly lower in B2R-/- mice by 40-50%. On the other hand, renal COX-1 levels were similar in B2R-/- and +/+ mice. Renal renin protein was 61% lower in B2R-/- compared to B2R+/+ mice. This was accompanied by a significant reduction in renin mRNA levels in B2R-/- mice. Likewise, intrarenal angiotensin I levels were significantly lower in B2R-/- mice compared to B2R+/+ mice. In contrast, kidney angiotensin II levels were not different and averaged 261+/-16 and 266+/-15fmol/g in B2R+/+ and B2R-/- mice, respectively. Kidney angiotensinogen, AT1 receptor and ACE activity were not different between B2R+/+ and B2R-/- mice. The results of these studies demonstrate suppression of renal renin synthesis in mice lacking the bradykinin B2R and support the notion that B2R regulation of COX-2 participates in the steady-state control of renin gene expression.

A role for p53 in terminal epithelial cell differentiation

Terminal epithelial cell differentiation is a crucial step in development. In the kidney, failure of terminal differentiation causes dysplasia, cystogenesis, and cancer. The present study provides multiple lines of evidence implicating the tumor suppressor protein p53 in terminal differentiation of the renal epithelium. In the developing kidney, p53 is highly enriched in epithelial cells expressing renal function genes (RFGs), such as receptors for vasoactive hormones, the sodium pump, and epithelial sodium and water channels. In comparison, proliferating renal progenitors express little if any p53 or RFGs. p53 binds to and transactivates the promoters of RFGs. In contrast, expression of a dominant negative mutant form of p53 inhibits endogenous RFG expression. Moreover, binding of endogenous p53 to the promoters of RFGs coincides with the differentiation process and is attenuated once renal epithelial cells are fully differentiated. Finally, p53-null pups exhibit a previously unrecognized aberrant renal phenotype and spatial disorganization of RFGs. Interestingly, the p53-related protein p73 is unable to functionally compensate for the loss of p53 and fails to efficiently activate RFG transcription. We conclude that p53 promotes the biochemical and morphological differentiation of the renal epithelium. Aberrations in p53-mediated terminal differentiation may therefore play a role in the pathogenesis of nephron dysgenesis and dysfunction.

Targeted disruption of the bradykinin B(2) receptor gene in mice alters the ontogeny of the renin-angiotensin system

Angiotensin II type 1 (AT(1)) receptor knockout (KO) mice exhibit an activated kallikrein-kinin system (KKS) that serves to attenuate the severity of the renal vascular phenotype in these mice (Tsuchida S, Miyazaki Y, Matsusaka T, Hunley TE, Inagami T, Fogo A, and Ichikawa I, Kidney Int 56: 509-516, 1999). Conversely, gestational high salt suppresses the fetal renin-angiotensin system (RAS) and provokes aberrant renal development in bradykinin B(2)-KO mice (El-Dahr SS, Harrison-Bernard LM, Dipp S, Yosipiv IV, and Meleg-Smith S, Physiol Genomics 3: 121-131, 2000). Thus the cross talk between the RAS and KKS may be critical for normal renal maturation. To further define the developmental interactions between the KKS and RAS, we examined the consequences of B(2) receptor gene ablation on the expression of RAS components. Renal renin mRNA levels are 50% lower in newborn B(2)-KO than wild-type (WT) mice. Also, the age-related decline in renin mRNA is greater in B(2)-KO than WT mice (3.5- vs. 2-fold, P < 0.05). Although renal angiotensinogen (Ao) protein levels are higher in newborn B(2)-KO than WT mice, Ao mRNA levels are not, suggesting accumulation of Ao as a result of decreased renin-mediated cleavage. Similar age-related increases (8-fold) in angiotensin I-converting enzyme (ACE) activity are observed in B(2)-KO and WT mice. Renal AT(1) protein levels are not different in B(2)-KO and WT mice. Furthermore, the developmental increases in renal kallikrein mRNA and enzymatic activity are more pronounced in B(2)-KO compared with WT mice (mRNA: 8- vs. 3-fold; activity: 13- vs. 6-fold, P < 0.05). We conclude that 1) bradykinin stimulates renin gene expression, 2) renal kallikrein is regulated via a negative feedback loop involving the B(2) receptor, and 3) Ao, ACE, and AT(1) are not bradykinin-target genes.

Targeted disruption of the bradykinin B2 receptor gene in mice alters the ontogeny of the renin-angiotensin system

First published July 12, 2001; 10.1152/ajprenal.0020.2001.—Angiotensin II type 1 (AT1) receptor knockout (KO) mice exhibit an activated kallikrein-kinin system (KKS) that serves to attenuate the severity of the renal vascular phenotype in these mice (Tsuchida S, Miyazaki Y, Matsusaka T, Hunley TE, Inagami T, Fogo A, and Ichikawa I, Kidney Int 56: 509–516, 1999). Conversely, gestational high salt suppresses the fetal renin-angiotensin system (RAS) and provokes aberrant renal development in bradykinin B2-KO mice (El-Dahr SS, Harrison-Bernard LM, Dipp S, Yosipiv IV, and Meleg-Smith S, Physiol Genomics 3: 121–131, 2000). Thus the cross talk between the RAS and KKS may be critical for normal renal maturation. To further define the developmental interactions between the KKS and RAS, we examined the consequences of B2 receptor gene ablation on the expression of RAS components. Renal renin mRNA levels are 50% lower in newborn B2-KO than wild-type (WT) mice. Also, the age-related decline in renin mRNA is greater in B2-KO than WT mice (3.5- vs. 2-fold, P < 0.05). Although renal angiotensinogen (Ao) protein levels are higher in newborn B2-KO than WT mice, Ao mRNA levels are not, suggesting accumulation of Ao as a result of decreased renin-mediated cleavage. Similar age-related increases (8-fold) in angiotensin I-converting enzyme (ACE) activity are observed in B2-KO and WT mice. Renal AT1 protein levels are not different in B2-KO and WT mice. Furthermore, the developmental increases in renal kallikrein mRNA and enzymatic activity are more pronounced in B2-KO compared with WT mice (mRNA: 8- vs. 3-fold; activity: 13- vs. 6-fold, P < 0.05). We conclude that 1) bradykinin stimulates renin gene expression, 2) renal kallikrein is regulated via a negative feedback loop involving the B2 receptor, and 3) Ao, ACE, and AT1 are not bradykinin-target genes.

Ureteric bud derivatives express angiotensinogen and AT1 receptors

Inactivation of the renin-angiotensin system interferes with the morphogenesis of the renal medulla. Thus ureteric bud (UB) derivatives may be a target for angiotensin production and action. To begin to test this hypothesis, we examined the cellular expression of angiotensinogen (Ao) and AT(1) receptor proteins during rat metanephrogenesis by immunohistochemistry. In addition, we tested whether UB-derived cells in culture express the Ao and AT(1) proteins. On embryonic day E15, Ao and AT(1) are expressed in the UB branches and stromal mesenchyme. S-shaped bodies, including the vascular cleft, express AT(1) but not Ao. The metanephric mesenchyme and pretubular aggregates are Ao negative and AT(1) negative. Expression of Ao and AT(1) in UB branches and ampullae is also observed on E16. However, UB expression of Ao is transient and is no longer detectable in the developing distal nephron beyond E17. On E17, both Ao and AT(1) are expressed in capillary loop glomeruli and proximal tubules, whereas UB branches express AT(1) only. By E18, the majority of Ao immunoreactivity is clustered in terminally differentiated proximal tubules, whereas AT(1) receptors are expressed in both proximal and distal nephron segments. The specificity of Ao and AT(1) staining was documented by the elimination/attenuation of immunoreactivity after preadsorption of the primary antibodies with their respective antigens. Consistent with the in vivo findings, the AT(1) protein is abundantly expressed in cellular lysates of mouse UB (E11.5) and IMCD3 (adult) cells. Moreover, AT(1) receptors in UB and IMCD3 cells are functional, since angiotensin II treatment elicits the tyrosine phosphorylation of the mitogen-activated protein kinases, ERK1/2. To our knowledge, this is the first demonstration of Ao and AT(1) protein expression in the developing distal nephron. Angiotensin II may have a paracrine role in the ontogeny of the collecting system.

Bradykinin B2 null mice are prone to renal dysplasia: gene-environment interactions in kidney development

Congenital abnormalities of the kidney and urinary tract are a common cause of end-stage renal disease in children. Host and environment factors are implicated in the pathogenesis of aberrant renal development. However, direct evidence linking gene-environment interactions with congenital renal disease is lacking. We report an animal model of renal dysgenesis that is dependent on a defined genetic defect and specific embryonic stressor. Specifically, mice that are deficient in the bradykinin type 2 receptor gene (B(2)) and salt loaded during embryogenesis acquire an aberrant kidney phenotype and die shortly after birth. In contrast, B(2) mutant mice maintained on normal sodium intake or salt-loaded wild-type mice do not develop kidney abnormalities. The kidney abnormality is evident histologically on embryonic day 16, shortly after the onset of metanephric B(2) gene expression, and consists of distorted renal architecture, foci of tubular dysgenesis, and cyst formation. The dysplastic tubules are of distal nephron origin [Dolichos biflorus agglutinin (DBA)- and aquaporin-2 (AQP2) positive, and angiotensinogen negative]. Neonatal antihypertensive therapy fails to ameliorate the renal abnormalities, arguing against the possibility that the nephropathy is a consequence of early hypertension. Moreover, the nephropathy is intrinsic to the embryo, because B(2) homozygous offspring from heterozygous parents exhibit the same renal phenotype as offspring from homozygous null parents. Further characterization of the renal phenotype revealed an important genetic background effect since the penetrance of the congenital nephropathy is increased substantially upon backcrossing of 129/BL6 B(2) mutants to a uniform C57BL/6J. We conclude that the type 2 bradykinin receptor is required for the maintenance of metanephric structure and epithelial integrity in the presence of fetal stress. This study provides a "proof-of-principle" that defined gene-environment interactions are a cause of congenital renal disease.

The bradykinin type 2 receptor is a target for p53-mediated transcriptional activation

The bradykinin type 2 receptor (BK2) is a developmentally regulated G protein-coupled receptor that mediates diverse actions such as vascular reactivity, salt and water excretion, inflammatory responses, and cell growth. However, little is known regarding regulation of the BK2 gene. We report here that the rat BK2 receptor is transcriptionally regulated by the tumor suppressor protein p53. The 5'-flanking region of the rat BK2 gene contains two p53-like binding sites: a sequence at -70 base pairs (P1 site) that is conserved in the murine and human BK2 genes; and a sequence at -707 (P2) that is not. The P1 and P2 motifs bind specifically to p53, as assessed by gel mobility shift assays. Transient transfection into HeLa cells of a CAT reporter construct driven by 1.2-kilobases of the BK2 gene 5'-flanking region demonstrated that the BK2 promoter is dose dependently activated by co-expression of wild-type p53. Co-expression of a dominant negative mutant p53 suppresses the activation of BK2 by wild-type p53. Promoter truncation localized the p53-responsive element to the region between -38 and -94 base pairs encompassing the p53-binding P1 sequence. Furthermore, p53-mediated activation of the BK2 promoter is augmented by the transcriptional co-activators, CBP/p300. Interestingly, removal of the P2 site by truncation or site-directed deletion amplifies p53-mediated activation of the BK2 promoter. These results demonstrate that the rat BK2 promoter is a target for p53-mediated activation and suggest a new physiological role for p53 in the regulation of G protein-coupled receptor gene expression.

Fetal ontogeny and role of metanephric bradykinin B2 receptors

Previous studies in rats have shown that blockade of bradykinin B2 receptors (B2R) in combination with a high-salt intake during gestation result in poor postnatal survival and long-term hypertension in the offspring. In this study, we examined the fetal ontogeny of B2R and determined the consequences of gestational B2R blockade and high salt on kidney development. B2R gene expression is induced on embryonic day (E16) of fetal metanephrogenesis and remains sustained until term. The earliest expression of the B2R protein is observed on apical membranes of ureteric bud branches and in capillary loop stage glomeruli. By the end of gestation, B2R becomes restricted to more-differentiated tubules in the deep cortex and medulla. Pairs of rats on normal (0.12 mmol/g) or high (0.84 mmol/g) salt diets were mated at 14 weeks of age. The B2R antagonist, Icatibant (previously known as Hoe-140) (300 nmol/kg per day) or saline (vehicle) was infused intraperitoneally during gestation via osmotic minipumps. Fetuses were examined on E20 (n=27-36 per group). No significant differences in litter size or body weight were observed among the groups. Combined high-salt and Icatibant treatment caused aberrant fetal renal development characterized by tubular dysgenesis, widened stromal mesenchyme, and glomerular cysts. The dysgenetic tubules stained positively for the distal nephron lectin, Dolichos biflorus, and exhibited enhanced Bax expression and apoptosis. Renal microvascular development, the number of mature glomeruli, and percentage of proliferating glomerular cells were not affected. Gestational Icatibant or high salt alone had no deleterious effects on fetal nephrogenesis. We conclude that gestational blockade of the kallikrein-kinin system impairs fetal nephrogenesis if combined with an intrauterine stressor such as high-salt intake. B2R may play a protective role during segmental nephron differentiation.

Inhibition of Na-K-ATPase activity and gene expression by a myeloma light chain in proximal tubule cells

BACKGROUND

Light chain nephrotoxicity is frequently associated with Fanconi syndrome characterized by amino-aciduria, glycosuria, phosphaturia, and bicarbonaturia. The mechanisms of these transport abnormalities are unknown. To determine the role of Na-K-ATPase, we examined the effects of a lambda-light chain on both the activity and gene expression of Na-K-ATPase in primary cultures of rat proximal tubule cells.

METHODS

The lambda-light chain used here was isolated from urine of a patient with multiple myeloma and previously shown to inhibit sodium-dependent phosphate and glucose transport in proximal tubule cells. Na-K-ATPase was determined spectrophotometrically and the gene expression by Northern analysis in cells exposed to light chain.

RESULTS

In cells exposed to 200 mumol/L light chain Na-K-ATPase activity was reduced significantly, up to 73%, at 2, 24, and 48 hours compared with control cells (N = 12, P < 0.001). Northern analysis showed that in cells exposed to light chain for 24 and 48 hours the message for the alpha-1 isoform of Na-K-ATPase was suppressed significantly compared with control cells. The messages for GAPDH, beta-actin, and 28 S RNA in light chain exposed cells were also depressed in comparison with control cells. This light chain also significantly inhibited thymidine incorporation by proximal tubule cells in a dose-dependent manner.

CONCLUSIONS

These data suggest a general toxicity to cells by this light chain and indicate that inhibitory effects on both the activity and gene expression of Na-K-ATPase may be an important mechanism of light chain cytotoxicity on proximal tubule cells.

Early onset salt-sensitive hypertension in bradykinin B(2) receptor null mice

Kinins have been implicated in the hemodynamic adaptation to postnatal life. The present study examined the impact of bradykinin B(2) receptor (B(2)R) gene disruption on the postnatal changes in blood pressure (BP) and the susceptibility to early onset salt-sensitive hypertension in mice. B(2)R null (-/-) and wild-type (+/+) mice were fed normal (NS, 1% NaCl) or high (HS, 5% NaCl) salt diets during pregnancy. After birth, the pups remained with their mothers until they were weaned and were subsequently continued on the respective maternal salt intake until 4 months of age. The age-related changes at 3 and 4 months in tail-cuff BP and anesthetized mean arterial pressure at 4 months were not different in NS/B(2)R(-/-) and NS/B(2)R(+/+) mice. However, there was a mild increase in BP in NS/B(2)R(-/-) at 2 months versus NS/B(2)R(+/+). In contrast, HS/B(2)R(-/-) mice manifested early onset and persistent elevations of tail-cuff BP (P<0.05) at 2, 3, and 4 months versus other groups. MAP was also higher in HS/B(2)R(-/-) than HS/B(2)R(+/+), NS/B(2)R(-/-), and NS/B(2)R(+/+) (91+/-3 versus 75+/-5, 74+/-2, and 70+/-2 mm Hg, respectively; P<0.05). Kidney renin and angiotensin type 1 receptor mRNA levels were not different. Additional studies showed that a delay in the initiation of HS until after birth was accompanied by later development of hypertension, although postnatal discontinuation of HS resulted in a gradual return of BP to normal values by 4 months of age. The results demonstrate that (1) kinins protect the developing animal from salt-sensitive hypertension, (2) lack of B(2)R from early development does not alter the maturation of BP under conditions of normal sodium intake, and (3) exposure to a HS diet during fetal life is not sufficient in itself to induce long-term hypertension in either wild-type or B(2)R null mice.

Bradykinin stimulates the ERK-->Elk-1-->Fos/AP-1 pathway in mesangial cells

Among its diverse biological actions, the vasoactive peptide bradykinin (BK) induces the transcription factor AP-1 and proliferation of mesangial cells (S. S. El-Dahr, S. Dipp, I. V. Yosipiv, and W. H. Baricos. Kidney Int. 50: 1850-1855, 1996). In the present study, we examined the role of protein tyrosine phosphorylation and the mitogen-activated protein kinases, ERK1/2,in mediating BK-induced AP-1 and DNA replication in cultured rat mesangial cells. BK (10(-9) to 10(-7) M) stimulated a rapid increase in tyrosine phosphorylation of multiple proteins with an estimated molecular mass of 120-130, 90-95, and 44-42 kDa. Immunoblots using antibodies specific for ERK or tyrosine-phosphorylated ERK revealed a shifting of p42 ERK2 to a higher molecular weight that correlated temporally with an increase in tyrosine-phosphorylated ERK2. Genistein, a specific tyrosine kinase inhibitor, prevented the phosphorylation of ERK2 by BK. In-gel kinase assays indicated that BK-induced tyrosine phosphorylation of ERK2 is accompanied by fourfold activation of its phosphotransferase activity toward the substrate PHAS-I (P < 0.05). Furthermore, BK stimulated a 2.5-fold increase (P < 0.05) in phosphorylation of Elk-1, a transcription factor required for growth factor-induced c-fos transcription. In accord with the stimulation of Elk-1 phosphorylation, BK induced c-fos gene expression and the production of Fos/AP-1 complexes. In addition, thymidine incorporation into DNA increased twofold (P < 0. 05) following BK stimulation. Each of these effects was blocked by tyrosine kinase inhibition with genistein or herbimycin A. Similarly, antisense oligodeoxynucleotide targeting of ERK1/2 mRNA inhibited BK-stimulated DNA synthesis. In contrast, protein kinase C inhibition or depletion had no effect on BK-induced c-fos mRNA, AP-1-DNA binding activity, or DNA synthesis. Collectively, these data demonstrate that BK activates the ERK-->Elk-1-->AP-1 pathway and that BK mitogenic signaling is critically dependent on protein tyrosine phosphorylation.

Activation of kininogen expression during distal nephron differentiation

Previous studies have shown that the epithelial precursors of the connecting tubule and collecting duct express tissue kallikrein and bradykinin B2 receptors, respectively, suggesting the presence of a local kinin-producing/responsive system in the maturing distal nephron. However, evidence for the existence of kininogen in the developing nephron is still lacking. This study examined the spatiotemporal relationships between segmental nephron differentiation and the ontogeny of kininogen and kinins in the rat. Kininogen immunoreactivity is detectable in the metanephros as early as embryonic day 15. In the nephrogenic zone, the terminal ureteric bud branches are the main kinin-expressing segments. Kininogen is also observed in the stromal mesenchyme. In contrast, proximal ureteric bud branches, metanephrogenic mesenchyme, and pretubular aggregates express little or no kininogen. After completion of nephrogenesis, kininogen distribution assumes its classic "adult" pattern in the collecting ducts. Peak kininogen mRNA and protein expression occur perinatally, corresponding to the period of active nephrogenesis in the rat, and declines gradually thereafter. Estimations made by RT-PCR, Western blotting, and radioimmunoassays indicate that renal kininogen mRNA and protein levels are at least 20-fold higher in newborn than adult rats. Likewise, immunoreactive tissue kinin levels are 2.3-fold higher in newborn than adult kidneys (P < 0.05). In summary, the present study demonstrates the activation of kininogen gene expression and kinin production in the developing kidney. The terminal ureteric bud branches and their epithelial derivatives are the principal kinin-producing segments in the maturing nephron. The results suggest an autocrine/paracrine role for the kallikrein-kinin system in distal nephron maturation.

Role of bradykinin B2 receptors in neonatal kidney growth

The kallikrein-kinin system is developmentally expressed in newborn kidneys. In addition, bradykinin (BK) is mitogenic in cultured glomerular mesangial cells. However, the role of endogenous BK in postnatal renal development has not been defined. In this study, the role of the BK-B2 receptor in neonatal kidney growth in the rat was examined. RNA blot analysis and semiquantitative reverse transcription-polymerase chain reaction showed that BK-B2 mRNA levels were approximately 30- to 40-fold higher in newborn than adult kidneys. Treatment of newborn rats with the selective BK-B2 antagonist, Hoe 140 (600 micrograms/kg per day, sc), from days 1 through 14 of life significantly reduced body weight, kidney-to-body weight ratios, and kidney DNA content, compared with saline-treated controls. Hoe 140 treatment had no effect on kidney protein or RNA content or the expression of transforming growth factor-beta mRNA. The growth retardation induced by BK-B2 blockade was observed only in the kidney and, to a lesser extent, in the heart. BK-B2 blockade had no effect on renal growth in adult rats, suggesting that these effects are developmentally regulated. In contrast to Hoe 140 treatment, neonatal protein undernutrition resulted in a generalized reduction in kidney DNA, RNA, and protein contents; increased renal transforming growth factor-beta gene expression; and decreased renal kallikrein expression and enzymatic activity. The results suggest that activation of BK-B2 receptor expression in the neonatal kidney plays an important role in the regulation of DNA synthesis during the latter stages of nephrogenesis.

Bradykinin stimulates c-fos expression, AP-1-DNA binding activity and proliferation of rat glomerular mesangial cells

An important role for bradykinin (BK) in nephrogenesis has been suggested based on impairment of renal growth in developing rats treated with a kinin antagonist. However, direct effects of BK on renal cell mitogenesis have not been reported. In the present study, we examined the mitogenic effects of BK on cultured rat mesangial cells. Transcripts encoding BK-B2 receptors were detected in quiescent and proliferating mesangial cells by reverse transcription-coupled polymerase chain reaction. In quiescent mesangial cell cultures (0.5% FCS for 48 hr), BK (10(-9) to 10 (-7)M) caused a significant increase in DNA synthesis (3H-thymidine incorporation into DNA) and cell number. BK-induced DNA synthesis was preceded by activation of c-fos gene expression and both of these effects were inhibited by Hoe-140, a specific BK-B2 antagonist. Electrophoretic gel mobility shift assays revealed enhanced binding of AP-1 complexes to a consensus AP-1 DNA sequence in BK-stimulated cells. Gel supershift assays confirmed that the AP-1 complexes contained the fos protein. These data document a direct mitogenic effect of BK, acting on B2 receptors, on mesangial cells.

Differential effects of ureteral obstruction on rat kininogen gene family

The precursors of kinins, K-kininogens and T-kininogens (KG), are encoded by separate genes that display 90% nucleotide sequence homology. Despite their homology, K-KG and T-KG genes are differentially regulated. The K-KG gene is expressed constitutively and encodes high- and low-molecular-weight KG, the precursors of the vasoactive nonapeptide bradykinin. In contrast, the T-KG gene is inducible, and its protein is a potent thiol-protease inhibitor. Given their potential role in the regulation of blood pressure, renal hemodynamics, and the response to inflammation and tissue injury, K-KG and T-KG gene expression in rats subjected to chronic (1 or 5 wk) unilateral ureteral obstruction (UUO), a maneuver that suppresses renal kallikrein synthesis to 25% of controls, has been examined. Northern and slot blots of total liver and kidney RNA were probed with oligonucleotides complementary to either T-KG or K-KG mRNA under high-stringency conditions. Steady-state levels of hepatic T-KG mRNA were increased in the UUO compared with sham-operated rats--2.7-fold at 1 wk and 4.1-fold at 5 wk (P < 0.05). Western blot analysis revealed that the 68-kd T-KG protein was up-regulated 2.5- to 3-fold in the liver of UUO rats (P < 0.05). In marked contrast, the abundance of high (2.3-kb)- and low (1.6-kb)-molecular-weight splicing transcripts of hepatic pre-K-KG mRNA was not altered at either time after UUO.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of somatic angiotensin-converting enzyme

Angiotensin-converting enzyme or kininase II (ACE-KII) plays a central role in the control of circulating and tissue levels of angiotensin II and kinins. Both peptides have been implicated in the regulation of renal function and growth during normal development. We tested the hypothesis that the developing rat kidney expresses ACE-KII mRNA transcripts and the active enzyme and evaluated whether the developmental expression of the ACE-KII gene is related to changes in circulating angiotensin II and tissue kallikrein. ACE-KII mRNA and enzymatic activity were low in the newborn kidney; peak expression occurred on days 15 and 20 of postnatal life (16-fold versus day 1). In extrarenal tissues, ACE-KII activity and mRNA levels were also low during the newborn period in the following order of abundance: lung > kidney > aorta > heart. The lung showed a higher age-related increase in active ACE-KII and mRNA abundance (15-fold) than heart and aorta (activity, 3- to 4-fold; mRNA, 6- to 10-fold). The developmental profile of ACE-KII correlated temporally with changes in circulating angiotensin II and tissue kallikrein. Plasma angiotensin II levels were 2.5-fold higher in newborn than adult rats, whereas renal and extrarenal kallikrein-like activity increased twofold to fivefold from birth to adulthood. These results demonstrate that the ACE-KII gene is developmentally regulated in a tissue-specific manner. Tissue kinin generation and degradation, reflected by kallikrein and ACE-KII activities, are coordinately regulated during development, whereas circulating angiotensin II and tissue ACE-KII change in a reciprocal manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin, angiotensinogen, and kallikrein gene expression in two-kidney Goldblatt hypertensive rats

An imbalance in the activity of the vasopressor renin-angiotensin and vasodepressor kallikrein-kinin systems may play an important role in the pathogenesis of hypertension after unilateral renal artery constriction. To test this hypothesis, we examined the expression of the renin, angiotensinogen (Ao), and tissue kallikrein genes 7 and 25 days after placement of a 0.25-mm clip on the left renal artery of rats. One week after clipping, renin mRNA levels were 4.6-fold higher in the clipped and 50% lower in the nonclipped kidneys compared with kidneys from sham-operated rats. At 25 days, renin mRNA levels in the clipped kidneys were not different from sham kidneys, but were suppressed to almost undetectable levels in the nonclipped kidneys. Steady-state Ao mRNA levels in the clipped kidneys were not different from those of nonclipped or sham kidneys at either 7 or 25 days. However, at 25 days, Ao mRNA levels were lower in the liver (70%), left ventricle (55%), and aorta (45%) of clipped than sham-operated rats. The expression of the renal kallikrein gene was unchanged at 7 days and was suppressed by 50% at 25 days. These results are consistent with the notion that activation of the intrarenal renin-angiotensin system occurs during the initial phase of the two-kidney, one-clip hypertension model. The renal kallikrein gene, in marked contrast to renin, becomes downregulated in the chronic phase. The differential regulation of renin-angiotensin and kallikrein genes may be an important pathogenetic factor in renovascular hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular aspects of kallikrein and kininogen in the maturing kidney

Kinins are vasoactive paracrine peptides which participate in a wide range of functions, including the regulation of local organ blood flow, systemic blood pressure, transepithelial water and electrolyte transport, cellular growth, capillary permeability and inflammatory response, and pain. The recent introduction of specific bradykinin receptor subtype antagonists has greatly advanced our understanding of the role of the kallikrein-kinin system (KKS) in various physiological and disease states. However, a major gap remains in our knowledge of the role of kinins in early development. In this review, evidence is presented that the developing nephron expresses both tissue kallikrein and kininogen, and that the genes encoding the components of the KKS are subject to considerable developmental regulation. The activity of the intrarenal kinin-generating system is lowest in the developing kidney and increases with age. Completion of nephrogenesis is characterized by a marked surge in intrarenal kallikrein synthesis and gene transcription. Maturation is associated with redistribution of intrarenal kallikrein and its messenger RNA from the inner to outer cortical nephrons following the centrifugal pattern of nephron development. Challenges for the future include delineation of the direct role of kinins in the maturation of renal functions and elucidation of the molecular mechanisms underlying the developmental expression of the KKS.

Upregulation of renin-angiotensin system and downregulation of kallikrein in obstructive nephropathy

The purpose of this study was to delineate the effects of prolonged (1 and 5 wk) unilateral ureteral obstruction (UUO) on the intrarenal renin-angiotensin and kallikrein-kinin systems in the rat. Systolic blood pressure (SBP) and plasma angiotensin (ANG) II levels were significantly higher at 1 and 5 wk of obstruction than in sham-operated groups. Also, plasma renin activity and ANG I levels were elevated at 1 wk (P < 0.05), and plasma angiotensin-converting enzyme (ACE)-kininase II activity was elevated at 5 wk (P < 0.05). Blockade of ANG II receptors with losartan (Dup 753) prevented the rise in SBP after UUO and normalized SBP in chronically hypertensive UUO rats. Renin mRNA levels and ANG II content were elevated in the obstructed kidneys at 1 and 5 wk compared with sham-operated kidneys (P < 0.05). ACE-kininase II activity was elevated in both the obstructed and contralateral kidneys at 5 wk compared with sham-operated kidneys (P < 0.05). In marked contrast to renin, total immunoreactive kallikrein contents and tissue kallikrein mRNA levels in the obstructed kidneys were reduced to 25% of sham-operated kidneys both at 1 and 5 wk (P < 0.001). The results indicate that urinary obstruction activates renin and suppresses kallikrein gene expression. Activation of ACE-kininase II by UUO also serves to enhance intrarenal ANG II generation and kinin degradation. The results implicate ANG II overproduction and kinin deficiency in the pathogenesis of UUO-induced hypertension and intrarenal vasoconstriction.

Differential developmental expression of the rat kininogen genes

The rat liver expresses two low molecular weight kininogens (T-KG and K-KG). Although they share 90% of the nucleotide sequence in their 5' flanking regions, T- and K-KG genes are differentially regulated. The T-KG gene is inducible, and its protein is a potent thiol-protease inhibitor. In contrast, K-KG gene is expressed constitutively and encodes the precursor of the vasoactive nonapeptide bradykinin. To further elucidate the differential regulation of T- and K-KG genes, we examined their developmental expression in the Sprague-Dawley rat. Northern blots of total liver RNA were probed with oligonucleotides complementary to T and K-KG mRNA under high-stringency conditions. A single T-KG mRNA (1.8 kb) and two K-KG mRNA species (1.6 and 2.3 kb) were consistently detected at all ages studied. Steady state T-KG mRNA levels increased 3.5-fold at birth and remained high during the 1st week of postnatal life only to decline thereafter. T-KG immunoreactivity in the liver and plasma determined by Western blot analysis paralleled T-KG mRNA expression. In marked contrast, K-KG mRNA expression was not altered during the transition from fetal to neonatal life, nor was it affected by postnatal maturation. The results demonstrate that the fetal rat liver synthesizes kininogens and that T- and K-KG genes are differentially regulated during development. Up-regulation of T-KG synthesis after birth may serve a protective function in the newborn via its antiprotease activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of rob beta-lactamase among ampicillin-resistant Haemophilus influenzae isolates in the United States

We surveyed 161 clinical isolates of ampicillin-resistant, beta-lactamase-producing isolates of Haemophilus influenzae obtained between 1975 and 1985 to determine whether they produced TEM-1 or Rob beta-lactamase. Plasmid DNA was obtained from a Rob-producing isolate, F990, and a plasmid (pBR322) known to encode TEM-1. Both plasmids were labeled with 32P and hybridized to whole cell DNA obtained from the clinical isolates. All 161 isolates hybridized with one of the plasmid probes and could be classified as TEM-1- or Rob-producing isolates. Analysis of the distinctive pH profiles of the two beta-lactamases was used to confirm the findings of the DNA hybridization assay. Overall, 13 (8%) isolates obtained from patients in California, North Carolina, Tennessee, Missouri, Louisiana, and Mississippi produced the Rob beta-lactamase. The remaining isolates elaborated the TEM-1 enzyme. We conclude that ampicillin resistance in H. influenzae may be mediated by the production of Rob beta-lactamase and that the occurrence of this enzyme is not limited to the two isolates described to date.