Angiotensin I-Converting Enzyme

Description

Angiotensin I-converting enzyme (EC 3.4.15.1), or kininase II, is a dipeptidyl carboxypeptidase that plays an important role in blood pressure regulation and electrolyte balance by hydrolyzing angiotensin I into angiotensin II, a potent vasopressor, and aldosterone-stimulating peptide. The enzyme is also able to inactivate bradykinin, a potent vasodilator.

Cloning and Expression

Ehlers et al. (1989) determined the cDNA sequence for human testicular ACE. The predicted protein is identical, from residue 37 to its C terminus, to the second half or C-terminal domain of the endothelial ACE sequence. The inferred protein sequence consists of a 732-residue preprotein including a 31-residue signal peptide. The mature polypeptide has a molecular weight of 80,073.

Although angiotensin-converting enzyme has been studied primarily in the context of its role in blood pressure regulation, this widely distributed enzyme has many other physiologic functions. The ACE gene encodes 2 isozymes. The somatic ACE isozyme is expressed in many tissues, including vascular endothelial cells, renal epithelial cells, and testicular Leydig cells, whereas the testicular or germinal ACE isozyme is expressed only in sperm (Ramaraj et al., 1998).

By quantitative RT-PCR, Harmer et al. (2002) found ACE1 expressed in all 72 tissues examined. Expression was particularly high in ileum, jejunum, duodenum, testis, lung, pulmonary blood vessels, and prostate.

Gene Structure

Howard et al. (1990) found that the testis-specific form of ACE has its own promoter within intron 12, is encoded by the 3-prime region of the gene, and is found only in postmeiotic spermatogenic cells and sperm.

Biochemical Features

Brown et al. (1996) found an association between the use of certain ACE inhibitors (lisinopril or enalapril vs captopril) and emergent angioedema in the African American population of Tennessee. The adjusted relative risk of angioedema was 4.5 (95% CI, 2.9-6.8) in blacks compared to whites. The African American patients were more severely affected: 7 of the 8 patients admitted to the intensive care unit were black, as were all patients who required intubation. African American users of ACE inhibitors tended to be younger and female when compared to their white counterparts. The rate of angioedema was highest within the first 30 days of use (5.79 per 1,000 patient-years) compared to long-term use (1.04 per 1,000 patient-years).

Large-scale trials of therapy for heart failure showed improvements in outcome with ACE inhibitors and beta-blockers. These results led to the recommendation that all patients who have heart failure accompanied by a low ejection fraction and who can tolerate ACE inhibitors and beta-blockers should be treated with both agents. Exner et al. (2001) focused on the fact that black patients with heart failure have a poorer prognosis than white patients and performed a study comparing racial groups. They found that whereas therapy with enalapril is associated with significant reduction in the risk of hospitalization for heart failure among white patients with left ventricular function, it had no such effect in similar black patients. The explanation for the lesser response to the ACE inhibitor in black patients was not clear.

Use of ACE inhibitors during the second and third trimesters of pregnancy is contraindicated because of their association with an increased risk of fetopathy. In contrast, first-trimester use of ACE inhibitors had not been linked to adverse fetal outcomes. From a study of association between exposure to ACE inhibitors during the first trimester of pregnancy only and the risk of congenital malformations, Cooper et al. (2006) concluded that ACE inhibitors at that stage also cannot be considered safe and should be avoided.

Crystal Structure

Natesh et al. (2003) presented the x-ray structure of human testicular ACE and its complex with one of the most widely used inhibitors, lisinopril, at 2.0-angstrom resolution. Analysis of the 3-dimensional structure of ACE shows that it bears little similarity to that of carboxypeptidase A (see 114850), but instead resembles neurolysin (611530) and Pyrococcus furiosus carboxypeptidase, zinc metallopeptidases with no detectable sequence similarity to ACE.

Gene Function

ACE is an integral membrane protein that is proteolytically shed from the cell surface by a zinc metallosecretase. Alfalah et al. (2001) found that mutagenesis of asn631 to gln in the juxtamembrane stalk region of ACE did not affect the enzymatic activity of the protein, but it was more efficiently cleaved and secreted into the medium of transfected cells than wildtype ACE. In contrast to wildtype ACE, which is cleaved between asn638 and ser639 at the cell surface by a metalloprotease, the mutant protein was cleaved between asn635 and ser636 by a serine proteinase within the endoplasmic reticulum.

Hu et al. (1999) demonstrated an association between the ACE I/D polymorphism (106180.0001) and Alzheimer disease (AD; 104300) in the Japanese population. Hu et al. (2001) found that purified ACE inhibited aggregation of amyloid-beta peptide (A-beta) in a dose-dependent manner. Inhibition of A-beta aggregation was specifically blocked by an ACE inhibitor. ACE also significantly inhibited A-beta cytotoxicity in a rat neural precursor cell line. ACE degraded A-beta by cleaving the 40-amino acid peptide between asp7 and ser8. Compared with the 40-amino acid A-beta peptide, the degradation products, A-beta(1-7) and A-beta(8-40), showed reduced aggregation and cytotoxic effects. Hu et al. (2001) concluded that ACE alters susceptibility to AD by degrading A-beta and preventing accumulation of amyloid plaques in vivo.

In testicular germ cells, Kondoh et al. (2005) identified ACE as the glycosylphosphatidylinositol (GPI)-anchored protein-releasing (GPIase) factor. ACE GPIase activity was not inactivated by substitutions of core amino acid residues for peptidase activity, suggesting that the active site elements for GPIase differ from those for peptidase activity; analysis of the released products predicted the cleavage site at the mannose-mannose linkage within the GPI moiety. GPI-anchored proteins were released from the sperm membrane of wildtype mice but not in Ace-knockout sperm in vivo; peptidase-inactivated mutant ACE and bacterial phosphatidylinositol-specific phospholipase rescued the egg-binding deficiency of Ace-knockout sperm. Kondoh et al. (2005) concluded that ACE plays a crucial role in fertilization through its GPIase activity.

Mapping

Mattei et al. (1989) assigned the ACE gene to 17q23 by in situ hybridization. Using a DNA marker at the growth hormone gene locus (139250), which they characterized as 'extremely polymorphic' and which showed no recombination with ACE, Jeunemaitre et al. (1992) mapped ACE to 17q22-q24, consistent with the in situ hybridization mapping to 17q23. A demonstration of linkage between the ACE locus and elevated blood pressure in a rat model of hypertension (see 145500) pointed to ACE as a candidate gene in human hypertension. In studies of hypertensive families, they found no evidence to support linkage between the ACE locus and the disease, however. Using affected sib-pair analysis and parametric analysis with ascertainment correction, Julier et al. (1997) found evidence of linkage of familial essential hypertension to 2 closely linked microsatellite markers, D17S183 and D17S934, located on 17q; these markers are, however, 18 cM proximal to the ACE locus.

Molecular Genetics

Benign Serum Increase of ACE

In affected members of 8 families with a 5-fold increase in serum ACE, Kramers et al. (2001) identified a heterozygous pro1199-to-leu mutation in the ACE gene (P1199L; 106180.0002). There were no other clinical abnormalities in any of the affected patients, indicating a benign phenotype. Functional analysis showed that the mutation resulted in increased shedding of the protein from the cell surface.

Renal Tubular Dysgenesis

Gribouval et al. (2005) studied 11 individuals with renal tubular dysgenesis (267430) belonging to 9 families and found that they had homozygous or compound heterozygous mutations in the genes encoding renin (REN; 179820), angiotensinogen (AGT; 106150), ACE, or angiotensin II receptor type 1 (AGTR1; 106165). They proposed that renal lesions and early anuria result from chronic low perfusion pressure of the fetal kidney, a consequence of renin-angiotensin system inactivity. This appeared to be the first identification of a renal mendelian disorder linked to genetic defects in the renin-angiotensin system, highlighting the crucial role of the renin-angiotensin system in human kidney development.

ACE Insertion/Deletion Polymorphism

The importance of ACE in circulatory homeostasis is well documented. Besides being present as a membrane-bound enzyme on the surface of vascular endothelial cells, ACE also circulates in plasma. The plasma enzyme may be synthesized in vascular endothelium. In normal individuals, plasma ACE levels can show as much as a 5-fold interindividual variation; on the other hand, intra-individual variation is small. Cambien et al. (1988) studied familial resemblance for plasma ACE activity in 87 healthy families. The mean levels were 34.1, 30.7, and 43.1 in fathers, mothers, and offspring, respectively. Plasma ACE was uncorrelated with age, height, weight, or blood pressure in the parents, but a negative correlation with age was observed in offspring. Results of genetic analysis suggested that a major gene may affect the interindividual variability of plasma ACE. Okabe et al. (1985) described a family in which an abnormal elevation in plasma ACE levels was transmitted apparently as an autosomal dominant trait. Plasma ACE levels in affected individuals in this kindred were much higher than the values observed in the 87 families studied by Cambien et al. (1988). Tiret et al. (1992) demonstrated that the interindividual variability of plasma ACE was associated with an insertion (I)/deletion (D) polymorphism involving about 250 bp situated in intron 16 of the ACE gene, the so-called ACE/ID polymorphism (106180.0001). Rigat et al. (1990) found that the ACE/ID polymorphism was strongly associated with the level of circulating enzyme. The mean plasma ACE level of DD subjects was about twice that of II subjects, with ID subjects having intermediate levels. Rigat et al. (1992) determined that the ACE insertion corresponds to an Alu repetitive sequence and is 287 bp long.

Berge and Berg (1994) found no evidence of association between genotypes in the insertion/deletion polymorphism and level of systolic or diastolic blood pressure. In 2 series of monozygotic twin pairs, there was no difference between genotypes in within-pair variation in systolic or diastolic blood pressure. On the other hand, Schunkert et al. (1994) found an association between left ventricular hypertrophy, as assessed by electrocardiographic criteria, and the DD genotype of ACE. Epidemiologic studies had shown that left ventricular hypertrophy is often found in the absence of an elevated cardiac workload. The association with the D/D genotype was stronger in men than in women and was more prominent when blood pressure measurements were normal. The findings suggest that the D/D genotype is a genetic marker associated with an elevated risk of left ventricular hypertrophy in middle-aged men.

Lindpaintner et al. (1996) were unable to confirm an association between ACE genotype and electrocardiographically determined left ventricular mass (determined by echocardiography) and left ventricular hypertrophy (adjusted for clinical covariates) in an analysis of 2,439 subjects from the Framingham Heart Study. Montgomery et al. (1997) reported a prospective study of 460 normotensive Caucasian male military recruits undergoing an intensive 10-week physical training course. Echocardiographic indices of left ventricular mass increased by 18% during training (p less than 0.0001); those individuals with the D ACE allele showed a significantly greater response. In addition, Montgomery et al. (1997) found that electrocardiographic evidence of left ventricular hypertrophy occurred only in individuals with the DD genotype. The authors concluded that exercise-induced left ventricular growth in young males is strongly associated with the ACE I/D polymorphism.

Yoshida et al. (1995) presented evidence suggesting that the deletion polymorphism in the ACE gene, particularly the homozygote DD, is a risk factor for progression to chronic renal failure in IgA nephropathy (161950). Moreover, this deletion polymorphism appeared to predict the therapeutic efficacy of ACE inhibition on proteinuria and, potentially, on progressive deterioration of renal function in that disorder.

Marre et al. (1994) and Doria et al. (1994) reported that the I/D polymorphism of the ACE gene is associated with diabetic nephropathy (see 612624), but this association was disputed by others, e.g., Tarnow et al. (1995) and Schmidt et al. (1995). Marre et al. (1997) performed a large-scale, multicenter study on individuals with insulin-dependent diabetes mellitus (IDDM; 222100) at risk of kidney complications due to long-term exposure to hyperglycemia, i.e., those who had developed proliferative diabetic retinopathy, to test the relationship between genetic factors and renal involvement in IDDM. The study, called GENEDIAB (GEnetique de la NEphropathie DIABetique), was conducted prospectively over 1 year. The degree of renal involvement of the patients was classified according to the genetic polymorphism of ACE and 2 other elements of the renin-angiotensin system, AGT (106150) and AT2R1 (106165). The study concluded that the ACE gene is involved in both the susceptibility to diabetic nephropathy and its progression toward renal failure. The other 2 polymorphisms were found not to be contributive alone, but an interaction between the ACE I/D and AGT M235T (106150.0001) polymorphisms was found that could account for the degree of renal involvement in the patients studied.

Yoshioka et al. (1998) studied the influence of the I/D polymorphism in intron 16 of the ACE gene on the clinical manifestations of childhood Henoch-Schonlein purpura nephritis (HSPN). One-fifth of patients with HSPN had the DD genotype. The incidence of persisting proteinuria in this group was significantly greater in DD homozygotes than in II homozygotes, with an intermediate incidence in heterozygotes. This effect was not seen in a control group of patients with IgA nephropathy. The authors suggested that persisting proteinuria may be related to a defective angiotensin system genetically determined by the I/D polymorphism.

Singer et al. (1996) provided a review of the clinical literature.

There is evidence for a skeletal muscle renin-angiotensin system, suggesting that muscle growth, and thus physical performance, might be possibly associated with the D allele of the ACE insertion/deletion polymorphism. However, in initial studies, Montgomery et al. (1998) found that the ACE I allele was associated with improved endurance performance. This association was investigated in 2 parallel experiments. A relative excess of II genotype and a deficiency of DD genotype was found in 25 elite unrelated male British mountaineers, with a history of ascending beyond 7,000 meters without using supplementary oxygen, as compared with 1,906 British males free from clinical cardiovascular disease. Among 15 climbers who had ascended beyond 8,000 meters without oxygen, none was homozygous for the D allele.

In a second study, Montgomery et al. (1998) determined ACE genotype in 123 Caucasian males recruited to the U.K. Army consecutively. The maximum duration (in seconds) for which they could perform repetitive elbow flexion while holding a 15-kg barbell was assessed both before and after the training period. Pre-training performance was independent of insertion/deletion genotype. Duration of exercise improved significantly for the 66 individuals of II and ID genotypes but not for the 12 of D/D genotype. Improvement was 11-fold greater for those of II than for those of DD genotype. The mechanism of the association of the I allele with improved endurance was discussed.

Williams et al. (2000) examined training-related changes in the mechanical efficiency of human skeletal muscle and found that the presence of the II genotype confers an enhanced mechanical efficiency in trained muscle over the DD genotype. Williams et al. (2000) concluded that such benefits could be associated with the lower ACE activity of the I allele, an idea that may partly explain the beneficial effects of ACE inhibitors on myocardial cell survival during ischemia and on the survival of patients with cardiac dysfunction.

Zhang et al. (2003) demonstrated that the ACE I allele was associated with increased type I skeletal muscle fibers and suggested that this may be a mechanism for the association between the ACE genotype and endurance performance.

Winnicki et al. (2004) studied the relationship between the ACE I/D polymorphism and physical activity status in 355 mild hypertensives in whom power exercise was contraindicated. They found that a sedentary lifestyle was more common among DD than II hypertensives, with ID subjects having intermediate values (chi square = 13.9, p = 0.001). Winnicki et al. (2004) suggested that the increased risk for the development of cardiovascular complications associated with a deletion polymorphism of the ACE gene could be partially explained by the sedentary lifestyle of these subjects.

Keramatipour et al. (2000) provided genotype data on 258 subjects with ruptured intracranial aneurysm and 299 controls from the same geographic region. ACE allele frequencies were significantly different between the cases and controls (chi square = 4.67, p = 0.03)(odds ratio for I allele vs D allele = 1.3; odds ratio for II vs DD genotype = 1.67).

Low bone mineral density and muscle weakness are major risk factors for postmenopausal osteoporotic fracture. Hormone replacement therapy reverses the menopausal decline in maximum voluntary force of the adductor pollicis and reduces serum ACE levels. The I allele of the ACE gene polymorphism is associated with lower ACE activity and improved muscle efficiency in response to physical training. Woods et al. (2001) investigated whether the presence of the I allele in postmenopausal women would affect the muscle response to hormone replacement therapy. Those taking hormone replacement therapy showed a significant gain in normalized muscle maximum voluntary force slope, the rate of which was strongly influenced by ACE genotype (16.0 +/- 1.53%, 14.3 +/- 2.67%, and 7.76 +/- 4.13%, mean +/- SEM for II, ID, and DD genotype, respectively; p = 0.017 for gene effect, p = 0.004 for I allele effect). There was also a significant ACE gene effect in the response of bone mineral density to hormone replacement therapy in the Ward triangle and a significant I allele effect in the spine, but not in the neck of femur or total hip. The authors concluded that low ACE activity associated with the I allele confers an improved muscle and bone mineral density response in postmenopausal women treated with hormone replacement therapy.

Dynamic exercise is effective in lowering resting blood pressure, in both the long- and short-term, and has been advocated as a primary treatment for mild hypertension or as an adjunct therapy for more severe hypertension, in part because of its low cost and few side effects. An inverse relationship between baseline plasma renin activity and the depressor effect of mild exercise has been observed. Furthermore, resting diastolic blood pressure after upright bicycle exercise decreased in children and young adults of normotensive parents but not in those of hypertensive parents (Seguro et al., 1995). A twin study by van den Bree et al. (1996) showed that blood pressure during dynamic exercise is regulated by genetic factors. Zhang et al. (2002) studied the association of the ACE ID polymorphism with the depressor response to exercise therapy in 64 Japanese subjects with mild to moderate essential hypertension. Each subject performed 10 weeks of mild exercise therapy on a bicycle ergometer. Systolic blood pressure, diastolic blood pressure, and mean arterial pressure were significantly decreased by exercise therapy in subjects with the homozygous II and heterozygous ID genotypes, but not in homozygous DD subjects.

Age-related macular degeneration-1 (ARMD1; 603075) is the leading cause of blindness in the elderly. Hamdi et al. (2002) reported an association between an Alu polymorphism in the ACE gene with the dry/atrophic form of ARMD1. Using PCR on genomic DNA isolated from 173 patients with ARMD1 and 189 age-matched controls, they amplified a region polymorphic for an Alu element insertion in the ACE gene. The Alu +/+ genotype (i.e., the II genotype) occurred 4.5 times more frequently in the control population than in the dry/atrophic ARMD1 patient population (p = 0.004). The predominance of the Alu +/+ genotype within the unaffected control group represented a protective insertion with respect to dry/atrophic ARMD1. This was the first demonstration of an Alu element insertion exerting protective effects against a known human disease.

Kehoe et al. (2003) performed a large-scale study involving multiple markers spanning ACE, in conjunction with a metaanalysis of previously published data on a common Alu insertion/deletion polymorphism, which supported the finding of Kehoe et al. (1999) that one or more alleles of ACE contribute to Alzheimer disease (AD; 104300).

Suehiro et al. (2004) demonstrated that the D allele of the ACE I/D polymorphism leads to higher expression of the ACE mRNA and may affect the renin-angiotensin system in local regions.

Other ACE Polymorphisms

Pedigree analyses showed that ACE levels are influenced by a quantitative trait locus (QTL) located within or close to the ACE gene and most likely residing in the 3-prime region of this locus. Zhu et al. (2000) evaluated linkage disequilibrium involving 7 polymorphisms spanning 13 kb in the 3-prime end of the ACE gene to narrow the genomic region associated with elevated ACE levels using a cladistic analysis.

In a study in 332 Nigerian families, using 13 polymorphisms in the ACE gene, Zhu et al. (2001) found strong linkage between the circulating levels of ACE and the 17q23 region (maximum lod score 7.5). Likewise, most of the polymorphisms in the ACE gene were significantly associated with ACE concentration. They also found that the 2 polymorphisms explaining the greatest variation in ACE concentration, ACE4 (A-240T) and ACE8 (A2350G), were significantly associated with blood pressure, through interaction, in this African population sample.

Kehoe et al. (2004) explored the potential influence of ACE on age at onset (AAO) of AD. They examined 2,861 individuals from 3 European populations, including 6 independent AD samples. A strong effect upon AAO was observed for 1 marker in exon 17 and evidence was also obtained indicating a possible independent effect of a second marker located in the ACE promoter. Effects were consistent with data from previous studies suggesting that alleles that confer risk to disease also appear to reduce AAO. Equivalent effects were evident regardless of APOE4 (see 107741) carrier status and in both males and females.

In 4,000 Swedish individuals, Katzov et al. (2004) demonstrated associations in males exclusively between ACE SNPs and several metabolic traits, including fasting plasma glucose levels, insulin levels, and measures of obesity (601665). Extending cladistic models to the study of myocardial infarction (608446) and Alzheimer disease (AD; 104300), significant associations were observed with greater effect sizes than those typically obtained in large-scale metaanalyses based on the Alu indel. Population frequencies of ACE genotypes changed with age, congruent with previous data suggesting effects upon longevity. Clade models consistently outperformed those based upon single markers, reinforcing the importance of taking into consideration the possible confounding effects of allelic heterogeneity in this genomic region.

Catarsi et al. (2005) studied 227 Italian nephrotic syndrome patients in whom hypertension was the major side effect of treatment by cyclosporine A (CsA). ACE haplotypes were determined in 304 Italian blood donors and assembled in clades (A, B, C) that include 95% of observed haplotypes. The association between ACE clade combinations and serum enzymatic levels reconfirmed the role of a genetic variant in the intragenic recombination site near intron 7. Haplotyping patients revealed that ACE genotype and responsiveness to CsA were strictly associated, because homozygosity for ACE B clade was able to influence CsA sensitivity. This highlights the role of 5-prime variants that differentiate clades B and C. Catarsi et al. (2005) hypothesized that the effect of ACE polymorphisms on blood pressure may be detectable once environmental factors, like CsA treatment, overcome physiologic homeostatic mechanisms.

Meng et al. (2006) evaluated the association between 15 SNPs in the ACE gene and AD in a sample of 92 patients with AD and 166 nondemented controls from an inbred Israeli Arab community. They observed significant association with 2 adjacent SNPs and with a combination of the 2. Their haplotype 'GA' had a frequency of 0.21 in cases and 0.01 in controls. Individuals with this haplotype had a 45-fold increased risk of developing AD compared with those possessing any of the other 3 haplotypes. Longer range haplotypes including I/D were even more significant.

Animal Model

Krege et al. (1995) investigated the role of the ACE gene in blood pressure control and reproduction using mice generated to carry an insertional mutation that was designed to inactivate both forms of Ace. All homozygous female mutants were found to be fertile, but the fertility of homozygous male mutants was greatly reduced. Heterozygous males but not females had blood pressures that were 15 to 20 mm Hg less than normal, although both male and female heterozygotes had reduced serum Ace activity.

Although significant ACE activity is found in plasma, the majority of the enzyme is bound to tissue such as vascular endothelium. Esther et al. (1997) used targeted homologous recombination to create mice expressing a form of ACE that lacks the C-terminal half of the molecule. This modified ACE protein was catalytically active but entirely secreted from cells. Mice that expressed only this modified ACE had significant plasma ACE activity but no tissue-bound enzyme. These animals had low blood pressure, renal vascular thickening, and a urine-concentrating defect. The phenotype was very similar to that of completely ACE-deficient mice previously reported, except that the renal pathology was less severe. These studies strongly supported the concept that the tissue-bound ACE is essential for the control of blood pressure and the structure and function of the kidney.

ACE gene knockout mice lack both isozymes and exhibit low blood pressure, kidney dysfunctions, and male infertility. Ramaraj et al. (1998) reported the use of a sperm-specific promoter and interbreeding of transgenic and gene knockout mice for generating a mouse strain that expressed ACE only in sperm. The experimental mice maintained the kidney defects of ACE -/- mice, but unlike the knockout strain, the males were fertile. Thus, Ramaraj et al. (1998) established that the role of ACE in male fertility is completely dependent on its exclusive expression in sperm. Their study demonstrated how transgenic and knockout techniques can be combined for ascribing a specific physiologic function to the expression of a multifunctional protein in a given tissue.

Hagaman et al. (1998) used transgenic mice lacking somatic and testis ACE to investigate the male fertility defect. They demonstrated that mice lacking both somatic and testis ACE isozymes have defects in sperm transport within the oviducts and in binding to zonae pellucidae. Males generated by gene targeting experiments that lack somatic ACE but retain testis ACE are fertile. Both male and female mice lacking angiotensinogen have normal fertility. The authors found that males heterozygous for the mutation inactivating both ACE enzymes had offspring of wildtype and heterozygous genotypes at the same frequency, suggesting that sperm carrying the mutation are not at a selective disadvantage.

As indicated by the work of Marre et al. (1994), Doria et al. (1994) and others, nephropathy of type 1 diabetes (222100) is associated with the D allele of the insertion/deletion (I/D) polymorphism in intron 16 of the ACE gene. The D allele determines higher enzyme levels. To address causality underlying this association, Huang et al. (2001) induced diabetes in mice having 1, 2, or 3 copies of the Ace gene, normal blood pressure, and an enzyme level range (65-162% of wildtype) comparable to that seen in humans. Twelve weeks later, the 3-copy diabetic mice had increased blood pressures and overt proteinuria. Proteinuria was correlated to plasma ACE level in the 3-copy diabetic mice. Thus, a modest genetic increase in ACE levels was sufficient to cause nephropathy in diabetic mice.

Kessler et al. (2003) generated 2 strains of mice that express ACE in only vascular endothelial cells or renal proximal tubules. Both strains had equivalent serum ACE and angiotensin II levels and renal function, but only the group that expressed ACE in vascular endothelial cells had normal blood pressure. Kessler et al. (2003) concluded that ACE-mediated blood pressure maintenance can be dissociated from its role in maintaining renal structure and function, supporting the hypothesis that specific physiologic functions of ACE are mediated by its expression in specific tissues.

Because experiments in mice and computer simulations indicated that modest increases in ACE have minimal effects on blood pressure and angiotensin II levels but cause a significant decrease in bradykinin levels (see 113503), Kakoki et al. (2004) hypothesized that bradykinin is critical for protecting the kidney in diabetics. They confirmed this by demonstrating that Akita diabetic mice lacking the bradykinin B2 receptor (BDKRB2; 113503) developed overt albuminuria, excreting the equivalent of more than 550 mg/day of albumin in humans, which contrasted with the microalbuminuria (equivalent to less than 150 mg/day) seen in their simply diabetic littermates. The overt albuminuria was accompanied by a marked increase in glomerular mesangial sclerosis.

Tian et al. (2004) generated a transgenic rat model with selective overexpression of human ACE1 in the cardiac ventricles. The left ventricular ACE1 activity was elevated about 50-fold in transgenic rats. Angiotensin-1 perfusion of isolated hearts demonstrated a significant decrease in coronary artery flow compared with nontransgenic littermates, suggesting that the transgenic ACE1 is functional. Neither cardiac hypertrophy nor other morphologic abnormalities were observed in transgenic rats under standard living conditions. After induction of hypertension by suprarenal aortic banding, the degree of cardiac hypertrophy in transgenic rats was significantly higher than that of banded control rats. The expressions of both ANF (108780) and collagen III (see 120180), molecular markers of cardiac hypertrophy, were also increased in banded transgenic rats compared with banded control. Tian et al. (2004) concluded that increased cardiac ACE1 does not trigger but augments cardiac hypertrophy.

Jayasooriya et al. (2008) stated that Ace -/- mice have lower body weight than wildtype mice, and they found that the reduced weight was due to greater fed-state total energy expenditure and resting energy expenditure. In addition, livers of Ace -/- mice showed pronounced expression of genes related to lipolysis and fatty acid oxidation, and plasma leptin (164160) levels were reduced. Jayasooriya et al. (2008) concluded that reduced Ace activity causes increased metabolism of fatty acids in the liver, with additional effect of increased glucose tolerance.