Biomedical subjects

O Smithies

Publications and source records attributed to O Smithies.

At least 19 recordsLinked to original sources

PubMed2000

Hematopoietic stem cells with controllable tEpoR transgenes have a competitive advantage in bone marrow transplantation.

In a previous study, it was found that a truncated erythropoietin receptor transgene (tEpoR tg) enables multilineage hematopoietic progenitor amplification after treatment with erythropoietin (epo) in vitro and in vivo. This study used competitive bone marrow (BM) repopulation to show that tEpoR tg facilitates transplantation by hematopoietic stem cells (HSC). Individual multilineage colonies, committed myeloid progenitor colonies, and lymphoid colonies (pre-B colony-forming units) were grown from the marrow of animals 6 months after they received a 50/50 mixture of transgene and wild-type BM cells. In epo-treated recipients, the transgene-bearing cells significantly outcompeted the wild-type cells (84%-100% versus 16%-0%, respectively). In recipients treated with phosphate-buffered saline, the repopulation was minimally different from the donor mixture (49%-64% transgene versus 51%-36% wild-type). The epo-induced repopulation advantage is maintained in secondary transplants. In addition, neither accelerated HSC depletion nor uncontrollable proliferation occurred during epo-stimulated serial transplants of transgene-containing BM. Thus, the tEpoR tg functions in a benign fashion in HSC and allows for a significant and controllable repopulation advantage in vivo without excessive HSC depletion relative to wild-type BM. (Blood. 2000;95:3710-3715)

Actins↗

PubMed2000

Uncompensated polyuria in a mouse model of Bartter's syndrome.

We have used homologous recombination to disrupt the mouse gene coding for the NaK2Cl cotransporter (NKCC2) expressed in kidney epithelial cells of the thick ascending limb and macula densa. This gene is one of several that when mutated causes Bartter's syndrome in humans, a syndrome characterized by severe polyuria and electrolyte imbalance. Homozygous NKCC2-/- pups were born in expected numbers and appeared normal. However, by day 1 they showed signs of extracellular volume depletion (hematocrit 51%; wild type 37%). They subsequently failed to thrive. By day 7, they were small and markedly dehydrated and exhibited renal insufficiency, high plasma potassium, metabolic acidosis, hydronephrosis of varying severity, and high plasma renin concentrations. None survived to weaning. Treatment of -/- pups with indomethacin from day 1 prevented growth retardation and 10% treated for 3 weeks survived, although as adults they exhibited severe polyuria (10 ml/day), extreme hydronephrosis, low plasma potassium, high blood pH, hypercalciuria, and proteinuria. Wild-type mice treated with furosemide, an inhibitor of NaK2Cl cotransporters, have a phenotype similar to the indomethacin-rescued -/- adults except that hydronephrosis was mild. The polyuria, hypercalciuria, and proteinuria of the -/- adults and furosemide-treated wild-type mice were unresponsive to inhibitors of the renin angiotensin system, vasopressin, and further indomethacin. Thus absence of NKCC2 in the mouse causes polyuria that is not compensated elsewhere in the nephron. The NKCC2 mutant animals should be valuable for uncovering new pathophysiologic and therapeutic aspects of genetic disturbances in water and electrolyte recovery by the kidney.

Animals↗

PubMed2000

Abnormal water metabolism in mice lacking the type 1A receptor for ANG II.

Mice lacking AT(1A) receptors for ANG II have a defect in urinary concentration manifested by an inability to increase urinary osmolality to levels seen in controls after thirsting. This defect results in extreme serum hypertonicity during water deprivation. In the basal state, plasma vasopressin levels are similar in wild-type controls and Agtr1a -/- mice. Plasma vasopressin levels increase normally in the AT(1A) receptor-deficient mice after 24 h of water deprivation, suggesting that the defect in urine concentration is intrinsic to the kidney. Using magnetic resonance microscopy, we find that the absence of AT(1A) receptors is associated with a modest reduction in the distance from the kidney surface to the tip of the papilla. However, this structural abnormality seems to play little role in the urinary concentrating defect in Agtr1a -/- mice since the impairment is largely reproduced in wild-type mice by treatment with an AT(1)-receptor antagonist. These studies demonstrate a critical role for the AT(1A) receptor in maintaining inner medullary structures in the kidney and in regulating renal water excretion.

Angiotensin Receptor Antagonists↗

PubMed2000

Regulation of sodium balance and blood pressure by the AT(1A) receptor for angiotensin II.

To examine the role of the angiotensin II (AT)(1A) receptor in the regulation of blood pressure and sodium balance, we measured systolic blood pressure responses in AT(1A) receptor-deficient (Agtr1a-/-) and wild-type (Agtr1a+/+) mice while dietary sodium content was systematically altered. On a 0.4% sodium diet, systolic blood pressures were significantly lower in Agtr1a-/- than in +/+ mice. In Agtr1a+/+ mice, changing dietary sodium content did not affect blood pressure. In contrast, when Agtr1a-/- mice were fed a high-salt diet (6% NaCl), their systolic blood pressures increased significantly from 79+/-4 to 94+/-4 mm Hg (P<0.006). The low blood pressures of Agtr1a-/- mice decreased further while on a low-salt diet from 82+/-3 to 69+/-3 mm Hg (P<0.03). On the high-salt diet, urinary sodium excretion increased to similar levels in Agtr1a+/+ and -/- mice. Although urinary sodium excretion was substantially reduced in both groups during the low-salt diet, cumulative sodium balances became negative in Agtr1a-/- mice despite a 6-fold increase in urinary aldosterone. We infer, therefore, that the reduced blood pressures in Agtr1a-/- mice on a normal diet are caused by depletion of sodium and extracellular volume. Their "sodium sensitivity" suggests a critical role for renal AT(1A) receptors to modulate sodium handling.

Aldosterone↗

PubMed2000

Impaired mucosal defense to acute colonic injury in mice lacking cyclooxygenase-1 or cyclooxygenase-2.

To investigate roles in intestinal inflammation for the 2 cyclooxygenase (COX) isoforms, we determined susceptibility to spontaneous and induced acute colitis in mice lacking either the COX-1 or COX-2 isoform. We treated wild-type, COX-1(-/-), COX-2(-/-), and heterozygous mice with dextran sodium sulfate (DSS) to provoke acute colonic inflammation, and we quantified tissue damage, prostaglandin (PG) E(2), and interleukin-1beta. No spontaneous gastrointestinal inflammation was detected in mice homozygous for either mutation, despite almost undetectable basal intestinal PGE(2) production in COX-1(-/-) mice. Both COX-1(-/-) and COX-2(-/-) mice showed increased susceptibility to a low-dose of DSS that caused mild colonic epithelial injury in wild-type mice. COX-2(-/-) mice were more susceptible than COX-1(-/-) mice, and selective pharmacologic blockade of COX-2 potentiated injury in COX-1(-/-) mice. At a high dose, DSS treatment was fatal to 50% of the animals in each mutant group, but all wild-type mice survived. DSS treatment increased PGE(2) intestinal secretion in all groups except COX-2(-/-) mice. These results demonstrate that COX-1 and COX-2 share a crucial role in the defense of the intestinal mucosa (with inducible COX-2 being perhaps more active during inflammation) and that neither isoform is essential in maintaining mucosal homeostasis in the absence of injurious stimuli.

Animals↗

PubMed2000

Enhanced atherosclerosis and kidney dysfunction in eNOS(-/-)Apoe(-/-) mice are ameliorated by enalapril treatment.

Hypertension and atherosclerosis are each important causes of morbidity and mortality in the developed world. We have investigated the interaction between these conditions by breeding mice that are atherosclerotic due to lack of apolipoprotein (apo) E with mice that are hypertensive due to lack of endothelial nitric oxide synthase (eNOS). The doubly deficient mice (nnee) have higher blood pressure (BP) and increased atherosclerotic lesion size but no change in plasma lipoprotein profiles compared with normotensive but atherosclerotic (NNee) mice. The nnee mice also develop kidney damage, evidenced by increased plasma creatinine, decreased kidney weight/body weight ratio, and glomerular lipid deposition and calcification. Enalapril treatment abolishes the deleterious effects of eNOS deficiency on BP, atherosclerosis, and kidney dysfunction in nnee mice. In striking contrast, a genetic lack of inducible NOS, which does not affect BP, has no effect on the development of atherosclerotic lesions in Apoe(-/-) mice. We also observed a positive relationship between BP and size of atherosclerotic lesions These results suggest that the atherogenic effects of eNOS deficiency can be partially explained by an increase in BP and reemphasize the importance of controlling hypertension in preventing atherosclerosis.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1999

Estrogen inhibits the vascular injury response in estrogen receptor beta-deficient female mice.

The protective effects of estrogen in the cardiovascular system result from both systemic effects and direct actions of the hormone on the vasculature. Two estrogen receptors have been identified, ERalpha and ERbeta. We demonstrated previously that estrogen inhibits the response to vascular injury in both wild-type and ERalpha-deficient mice, and that ERbeta is expressed in the blood vessels of each, suggesting a role for ERbeta in the vascular protective effects of estrogen. In the present study, we examined the effect of estrogen administration on mouse carotid arterial injury in ERbeta-deficient mice. Surprisingly, in ovariectomized female wild-type and ERbeta knockout mice, 17beta-estradiol markedly and equally inhibited the increase in vascular medial area and the proliferation of vascular smooth muscle cells after vascular injury. These data demonstrate that ERbeta is not required for estrogen-mediated inhibition of the response to vascular injury, and suggest that either of the two known estrogen receptors is sufficient to protect against vascular injury, or that another unidentified estrogen receptor mediates the vascular protective effects of estrogen.

Animals↗

PubMed1999

The natriuretic peptide clearance receptor locally modulates the physiological effects of the natriuretic peptide system.

Natriuretic peptides (NPs), mainly produced in heart [atrial (ANP) and B-type (BNP)], brain (CNP), and kidney (urodilatin), decrease blood pressure and increase salt excretion. These functions are mediated by natriuretic peptide receptors A and B (NPRA and NPRB) having cytoplasmic guanylyl cyclase domains that are stimulated when the receptors bind ligand. A more abundantly expressed receptor (NPRC or C-type) has a short cytoplasmic domain without guanylyl cyclase activity. NPRC is thought to act as a clearance receptor, although it may have additional functions. To test how NPRC affects the cardiovascular and renal systems, we inactivated its gene (Npr3) in mice by homologous recombination. The half life of [125I]ANP in the circulation of homozygotes lacking NPRC is two-thirds longer than in the wild type, although plasma levels of ANP and BNP in heterozygotes and homozygotes are close to the wild type. Heterozygotes and homozygotes have a progressively reduced ability to concentrate urine, exhibit mild diuresis, and tend to be blood volume depleted. Blood pressure in the homozygotes is 8 mmHg (1 mmHg = 133 Pa) below normal. These results are consistent with the sole cardiovascular/renal function of NPRC being to clear natriuretic peptides, thereby modulating local effects of the natriuretic peptide system. Unexpectedly, Npr3 -/- homozygotes have skeletal deformities associated with a considerable increase in bone turnover. The phenotype is consistent with the bone function of NPRC being to clear locally synthesized CNP and modulate its effects. We conclude that NPRC modulates the availability of the natriuretic peptides at their target organs, thereby allowing the activity of the natriuretic peptide system to be tailored to specific local needs.

Animals↗

PubMed1999

Homeostasis in mice with genetically decreased angiotensinogen is primarily by an increased number of renin-producing cells.

Here we investigate the biochemical, molecular, and cellular changes directed toward blood pressure homeostasis that occur in the endocrine branch of the renin-angiotensin system of mice having one angiotensinogen gene inactivated. No compensatory up-regulation of the remaining normal allele occurs in the liver, the main tissue of angiotensinogen synthesis. No significant changes occur in expression of the genes coding for the angiotensin converting enzyme or the major pressor-mediating receptor for angiotensin, but plasma renin concentration in the mice having only one copy of the angiotensinogen gene is greater than twice wild-type. This increase is mediated primarily by a modest increase in the proportion of renal glomeruli producing renin in their juxtaglomerular apparatus and by four times wild-type numbers of renin-producing cells along afferent arterioles of the glomeruli rather than by up-regulating renin production in cells already committed to its synthesis.

Alleles↗

PubMed1999

CD8+ T cells are a biologically relevant source of macrophage inflammatory protein-1 alpha in vivo.

Chemokines are small proteins that direct the migration of leukocytes to inflammatory foci. Many cell types, including macrophages, fibroblasts, endothelial cells, and lymphocytes, produce chemokines in vitro, but biologically relevant sources of chemokines in vivo have not been well characterized. To investigate the pertinent sources of macrophage inflammatory protein-1 alpha (MIP-1 alpha) in vivo, we used MIP-1 alpha-deficient (MIP-1 alpha-/-) mice as donors and as recipients in adoptive transfer experiments after a lethal infection with Listeria monocytogenes (LM). Unexpectedly, we found that the production of MIP-1 alpha by CD8+ T cells was critical in this system, as the cells from MIP-1 alpha-/- mice primed with LM were significantly less effective in protecting naive mice against a lethal infection by LM than were the CD8+ T cells from wild-type (wt) mice. This requirement for donor T cell production of MIP-1 alpha was confirmed by the observation that wt donor T cells do not mediate protection when coadministered with an anti-MIP-1 alpha polyclonal antiserum. Production of MIP-1 alpha by the recipient mice was not required for protection, because wt and MIP-1 alpha-/- recipients were equally well protected by wt T cells. A 2- to 3-fold decrease in the number of transferred lymphocytes was seen in the spleens of mice receiving T cells from MIP-1 alpha-/- mice compared with those receiving wt T cells. In addition, CD8+ T cells from MIP-1 alpha-/- mice had a reduced ability to kill LM-infected target cells in vitro. These findings demonstrate that T cell production of MIP-1 alpha is required for clearance of an intracellular pathogen in vivo.

Adoptive Transfer↗

PubMed1999

The influence of chromosomal location on the expression of two transgenes in mice.

We have generated mice having a single copy of the human haptoglobin gene (Hp2), driven by its natural promoter, and a neomycin resistance gene (Neo), driven by a herpes simplex thymidine kinase promoter with polyoma enhancers, inserted into two defined chromosomal locations, the Hprt locus on the X-chromosome and the apolipoprotein (apo) AI-CIII gene cluster on chromosome 9. The haptoglobin promoter is highly specialized in its tissue of action; the viral promoter has few restrictions. The apoAI-CIII gene is naturally active in only two tissues, whereas the Hprt gene region is ubiquitously active. Expression of both transgenes at substantial levels was achieved only (a) when the transgenes were inserted into the genome close to a known tissue-specific enhancer/locus control region in the apoAI-CIII gene cluster, and (b) when known conditions for function of their promoters were met. The specificities of the two chromosomal regions and of the two promoters are preserved, but their interactions are not specific. We conclude that transgenes are affected by locus-related enhancers in the same manner as nearby endogenous genes. Our experiments reinforce the usefulness of using gene targeting to direct single-copy transgenes to appropriate chromosomal locations.

Animals↗

PubMed1999

Genetic disruption of atrial natriuretic peptide causes pulmonary hypertension in normoxic and hypoxic mice.

To determine whether atrial natriuretic peptide (ANP) plays a physiological role in modulating pulmonary hypertensive responses, we studied mice with gene-targeted disruption of the ANP gene under normoxic and chronically hypoxic conditions. Right ventricular peak pressure (RVPP), right ventricle weight- and left ventricle plus septum weight-to-body weight ratios [RV/BW and (LV+S)/BW, respectively], and muscularization of pulmonary vessels were measured in wild-type mice (+/+) and in mice heterozygous (+/-) and homozygous (-/-) for a disrupted proANP gene after 3 wk of normoxia or hypobaric hypoxia (0.5 atm). Under normoxic conditions, homozygous mutants had higher RVPP (22 +/- 2 vs. 15 +/- 1 mmHg; P < 0.05) than wild-type mice and greater RV/BW (1.22 +/- 0.08 vs. 0.94 +/- 0.07 and 0.76 +/- 0.04 mg/g; P < 0.05) and (LV+S)/BW (4.74 +/- 0. 42 vs. 3.53 +/- 0.14 and 3.18 +/- 0.18 mg/g; P < 0.05) than heterozygous or wild-type mice, respectively. Three weeks of hypoxia increased RVPP in heterozygous and wild-type mice and increased RV/BW and RV/(LV+S) in all genotypes compared with their normoxic control animals but had no effect on (LV+S)/BW. After 3 wk of hypoxia, homozygous mutants had higher RVPP (29 +/- 3 vs. 23 +/- 1 and 22 +/- 2 mmHg; P < 0.05), RV/BW (2.03 +/- 0.14 vs. 1.46 +/- 0.04 and 1.33 +/- 0.08 mg/g; P < 0.05), and (LV+S)/BW (4.76 +/- 0.23 vs. 3.82 +/- 0.09 and 3.44 +/- 0.14 mg/g; P < 0.05) than heterozygous or wild-type mice, respectively. The percent muscularization of peripheral pulmonary vessels was greater in homozygous mutants than that in heterozygous or wild-type mice under both normoxic and hypoxic conditions. We conclude that endogenous ANP plays a physiological role in modulating pulmonary arterial pressure, cardiac hypertrophy, and pulmonary vascular remodeling under normoxic and hypoxic conditions.

Animals↗

PubMed1999

Tubuloglomerular feedback in ACE-deficient mice.

In these experiments, we used a strain of angiotensin converting enzyme (ACE) germline null mutant mice, generated by J. H. Krege and co-workers (J. H. Krege, S. W. M. John, L. L. Langenbach, J. B. Hodgin, J. R. Hagaman, E. S. Bachman, J. C. Jennette, D. A. O'Brien, and O. Smithies. Nature 375: 146-148, 1995), to examine the effect of chronic ACE deficiency on the magnitude of tubuloglomerular feedback (TGF) responses. The genotype was determined by PCR on DNA extracted from the tail and was verified after each experiment by assessment of the blood pressure response to an injection of ANG I. To assess TGF responsiveness, we determined the change in stop-flow pressure (PSF) caused by increasing NaCl concentration at the macula densa by using micropuncture techniques. When loop of Henle flow rate was increased from 0 to 40 nl/min, PSF fell from a mean of 42.3 +/- 1.95 to 33.6 +/- 2.09 mmHg (n = 6, P = 0.005) in wild-type mice (+/+), fell from 40.6 +/- 2.35 to 38.6 +/- 1.93 mmHg in heterozygous (+/-) mice (n = 7, P = 0.014), and did not change in homozygous ACE (-/-) mice [36.7 +/- 2.02 mmHg vs. 36.4 +/- 2.01 mmHg; n = 4, P = not significant (NS)]. During an infusion of ANG II at a dose that did not significantly elevate blood pressure (70 ng. kg-1. min-1), TGF response magnitude (PSF 0 - PSF 40) increased from 6.5 +/- 1.4 to 9.8 +/- 1.19 mmHg in +/+ (P = 0.006), from 1.14 +/- 0.42 to 4.6 +/- 1.3 mmHg in +/- (P = 0.016), and from 0.42 +/- 0.25 to 4.02 +/- 1.06 in -/- mice (P = 0.05). Absence of TGF responses in ACE null mutant mice and restoration of near-normal responses during an acute infusion of ANG II supports previous conclusions that ANG II is an essential component in the signal transmission pathway that links the macula densa with the glomerular vascular pole.

Angiotensin II↗

PubMed1999

Reduced angiotensinogen expression attenuates renal interstitial fibrosis in obstructive nephropathy in mice.

A novel approach was employed to assess the contribution of the renin-angiotensin system (RAS) to obstructive nephropathy in neonatal mice having zero to four functional copies of the angiotensinogen gene (Agt). Two-day-old mice underwent unilateral ureteral obstruction (UUO) or sham operation; 28 days later, renal interstitial fibrosis and tubular atrophy were quantitated. In all Agt genotypes, UUO reduced ipsilateral renal mass and increased that of the opposite kidney. Renal interstitial collagen increased after UUO linearly with Agt expression, from a fractional area of 25% in zero-copy mice to 54% in two-copy mice. Renal expression of transforming growth factor-beta1 was increased by ipsilateral UUO in mice expressing Agt, but not in zero-copy mice. However, the prevalence of atrophic tubules due to UUO did not vary with Agt expression. Blood pressure was not different in all groups, except for a reduction in sham zero-copy mice. We conclude that a functional RAS is not necessary for compensatory renal growth. This study demonstrates conclusively that angiotensin regulates at least 50% of the renal interstitial fibrotic response in obstructive nephropathy, an effect independent of systemic hemodynamic changes. Angiotensin-induced fibrosis likely is a mechanism common to the progression of many forms of renal disease.

Angiotensinogen↗

PubMed1999

Angiotensin II regulates cellular immune responses through a calcineurin-dependent pathway.

The renin-angiotensin system (RAS) is a key regulator of vascular tone and blood pressure. In addition, angiotensin II also has a number of cellular effects that may contribute to disease pathogenesis. Using Agtr1a(-/-) mice, which lack AT(1A) receptors for angiotensin II, we have identified a novel function of the RAS to modulate the immune system. We find that angiotensin II, acting through type 1 (AT(1)) receptors on immune cells, triggers the proliferation of splenic lymphocytes. These actions contribute to the vigor of cellular alloimmune responses. Within lymphoid organs, sufficient components of the RAS are present to activate AT(1) receptors during an immune response, promoting cell growth. These actions require activation of calcineurin phosphatase. In an in vivo model of cardiac transplantation, the absence of AT(1) signaling accentuates the immunosuppressive effects of the calcineurin inhibitor cyclosporine. We conclude that inhibition of AT(1) receptor signaling should be useful as an anti-inflammatory and immunosuppressive therapy. Furthermore, the actions of the RAS to promote lymphocyte activation may contribute to inflammation that characterizes a number of diseases of the heart and the vascular system.

Angiotensin II↗

PubMed1999

Hypertension associated with decreased testosterone levels in natriuretic peptide receptor-A gene-knockout and gene-duplicated mutant mouse models.

Mice lacking the gene (Npr1) encoding the natriuretic peptide receptor A (NPRA) have hypertension with elevated blood pressure and cardiac hypertrophy. In particular, Npr1 gene-deficient male mice exhibit lethal vascular events similar to those seen in untreated human hypertensive patients. Serum testosterone levels tend to be lower in hypertensive male humans than in normal males without hypertension, but the genetic basis for this tendency remains unknown. To determine whether Npr1 gene function affects the testosterone level, we measured serum testosterone in male hypertensive mice lacking a functional Npr1 gene, wild-type animals with two copies, and the gene-duplicated littermates expressing four copies of the gene. In the Npr1 gene-knockout (zero-copy) mice, the serum testosterone level was 62% lower than that in the two-copy control mice (80+/-10 ts. 120+/-14 ng/ml, respectively; P < 0.005). Serum testosterone in the four-copy mice was 144% (P < 0.005) of that in the two-copy wild-type control mice. To investigate the role of NPRA in testicular steroidogenesis, we analyzed atrial natriuretic peptide (ANP)-dependent guanylyl cyclase activation, accumulation of intracellular cGMP, and testosterone production in purified primary Leydig cells from animals with zero, two, or four copies of the Npr1 gene. Leydig cells lacking the Npr1 gene did not show ANP-stimulated guanylyl cyclase activation or cGMP accumulation and had no ANP-dependent testosterone production. ANP stimulation of Leydig cells from the four-copy males elicited a 2-fold greater production of cGMP compared to that in the two-copy wild-type counterparts (260+/-12 vs. 126+/-7 pmol/l x 10(6) cells; P < 0.001). Similarly, ANP-dependent testosterone production in Leydig cells was nearly twice as high in four-copy mice as in two-copy wild-type controls (561+/-18 vs. 325+/-11 ng/l x 10(6) cells; P < 0.001). ANP-dependent guanylyl cyclase activation and production of cGMP in Leydig cells increased progressively with the number of Npr1 gene copies. Our results establish the existence of an alternate mechanism for testicular steroidogenesis that is stimulated by NPRA-dependent cGMP signaling, in addition to that mediated by gonadotropins, via a cAMP pathway. These findings demonstrate the role of Npr1 gene function in the maintenance of serum testosterone levels and testicular steroidogenesis and provide a genetic link between hypertension associated with decreased NPRA and low testosterone levels.

Animals↗

PubMed1999

Gene targeting approaches to analyzing hypertension.

Essential hypertension probably results from combinations of small genetic variations that are partly normal variations and may not be appreciably harmful individually. Strategies to identify genes contributing to hypertension are discussed in this review. Gene targeting approaches, especially gene titration, have been used in these studies of hypertension. Gene titration experiments vary the expression of a chosen gene product by generating animals having different numbers of copies of the gene coding for the product. Gene titration is powerful for analyzing quantitative variations seen in common polygenic disorders, such as kidney diseases, diabetes mellitus, and atherosclerosis, as well as hypertension, because it allows tests of causation by determining the effects on a phenotype by changes in expression of the altered gene and because it matches normal quantitative variations more closely than is possible with classic transgenic mice. The use of zero-copy (gene "knockout") animals generated by gene disruption for studies of qualitative gene effects is also discussed. These various gene targeting experiments help identify genes regulating BP, promote a better understanding of the pathophysiology of the condition, and help identify potential targets for therapies.

Animals↗

PubMed1998

Reduced growth, abnormal kidney structure, and type 2 (AT2) angiotensin receptor-mediated blood pressure regulation in mice lacking both AT1A and AT1B receptors for angiotensin II.

The classically recognized functions of the renin-angiotensin system are mediated by type 1 (AT1) angiotensin receptors. Whereas man possesses a single AT1 receptor, there are two AT1 receptor isoforms in rodents (AT1A and AT1B) that are products of separate genes (Agtr1a and Agtr1b). We have generated mice lacking AT1B (Agtr1b -/-) and both AT1A and AT1B receptors (Agtr1a -/-Agtr1b -/-). Agtr1b -/- mice are healthy, without an abnormal phenotype. In contrast, Agtr1a -/-Agtr1b -/- mice have diminished growth, vascular thickening within the kidney, and atrophy of the inner renal medulla. This phenotype is virtually identical to that seen in angiotensinogen-deficient (Agt-/-) and angiotensin-converting enzyme-deficient (Ace -/-) mice that are unable to synthesize angiotensin II. Agtr1a -/-Agtr1b -/- mice have no systemic pressor response to infusions of angiotensin II, but they respond normally to another vasoconstrictor, epinephrine. Blood pressure is reduced substantially in the Agtr1a -/- Agtr1b -/- mice and following administration of an angiotensin converting enzyme inhibitor, their blood pressure increases paradoxically. We suggest that this is a result of interruption of AT2-receptor signaling. In summary, our studies suggest that both AT1 receptors promote somatic growth and maintenance of normal kidney structure. The absence of either of the AT1 receptor isoforms alone can be compensated in varying degrees by the other isoform. These studies reaffirm and extend the importance of AT1 receptors to mediate physiological functions of the renin-angiotensin system.

Adrenal Glands↗