AJP - Endo Fuel your research with LabChart
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Endocrinol Metab 292: E1280-E1287, 2007. First published January 9, 2007; doi:10.1152/ajpendo.00277.2006
0193-1849/07 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/5/E1280    most recent
00277.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Lu, H.
Right arrow Articles by Cassis, L. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Lu, H.
Right arrow Articles by Cassis, L. A.

Angiotensin II increases adipose angiotensinogen expression

Hong Lu,1 Carine M. Boustany-Kari,2 Alan Daugherty,1,2 and Lisa A. Cassis1,2

1Cardiovascular Research Center, Gill Heart Institute and 2Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky

Submitted 9 June 2006 ; accepted in final form 4 January 2007


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
In addition to the well-defined contribution of the liver, adipose tissue has been recognized as an important source of angiotensinogen (AGT). The purpose of this study was to define the angiotensin II (ANG II) receptors involved in regulation of adipose AGT and the relationship of this control to systemic AGT and/or angiotensin peptide concentrations. In LDL receptor-deficient (LDLR–/–) male mice, adipose mRNA abundance of AGT was 68% of that in liver, and adipose mRNA abundance of the angiotensin type 1a (AT1a) receptor (AT1aR) was 38% of that in liver, whereas mRNA abundance of the angiotensin type 2 (AT2) receptor (AT2R) was 57% greater in adipose tissue than in liver. AGT and angiotensin peptide concentrations were decreased in plasma of AT1aR-deficient (AT1aR–/–) mice and were paralleled by reductions in AGT expression in liver. In contrast, adipose AGT mRNA abundance was unaltered in AT1aR–/– mice. AT2R–/– mice exhibited elevated plasma angiotensin peptide concentrations and marked elevations in adipose AGT and AT1aR mRNA abundance. Increases in adipose AGT mRNA abundance in AT2R–/– mice were abolished by losartan. In contrast, liver AGT and AT1aR mRNA abundance were unaltered in AT2R–/– mice. Infusion of ANG II for 28 days into LDLR–/– mice markedly increased adipose AGT and AT1aR mRNA but did not alter liver AGT and AT1aR mRNA. These results demonstrate that differential mRNA abundance of AT1a/AT2 receptors in adipose tissue vs. liver contributes to tissue-specific ANG II-mediated regulation of AGT. Chronic infusion of ANG II robustly stimulated AT1aR and AGT mRNA abundance in adipose tissue, suggesting that adipose tissue serves as a primary contributor to the activated systemic renin-angiotensin system.

angiotensin II receptors; renin-angiotensin system; cardiovascular disease; obesity-related disorders; metabolic syndrome

THE RENIN-ANGIOTENSIN SYSTEM (RAS) is well known to regulate blood pressure and fluid homeostasis. Activation of the RAS is a common feature in patients with the metabolic syndrome (47). Angiotensinogen (AGT), the only known precursor of angiotensin II (ANG II), is produced primarily by the liver (16). However, AGT mRNA is expressed by a variety of tissues. Thus, under different physiological/pathophysiological conditions, such as the metabolic syndrome, alternative tissues may contribute to the circulating AGT concentration. We previously demonstrated a high level of AGT mRNA expression in white and brown adipocytes (9, 10, 50, 56). Moreover, expression of AGT in adipose tissue is nutritionally and hormonally regulated by obesity (3, 25, 48, 61), insulin (30), fatty acids (49), and cAMP (55). Furthermore, previous studies demonstrated that transgenic overexpression of AGT in adipose tissue leads to its secretion into the circulation and rescues hypotension and leanness of AGT-deficient mice (43). These observations suggest that adipose-derived AGT can contribute to plasma AGT concentrations and may be involved in the pathogenesis of obesity-related diseases.

The RAS is considered to be a classical endocrine feedback regulatory system, exerting control over the synthesis and secretion of RAS components by end-product peptides. Well-recognized sites for endocrine feedback regulation of the RAS by ANG II include AGT in the liver and renin in the kidney. ANG II positively regulates liver AGT mRNA expression and circulating AGT concentrations (33, 44) but negatively regulates kidney renin mRNA expression and release (52). The significance of positive- and negative-feedback regulation by ANG II on RAS component expression differs across species. For example, in rats and humans, the predominant effect is to reduce further ANG II synthesis by suppression of renal synthesis and secretion of renin, the rate-limiting step in ANG II production (52). In contrast, studies in mice suggest that AGT may limit the rate of production of systemic ANG II (11, 40). Thus, in mice, ANG II may predominantly increase further peptide synthesis by increasing the concentration of circulating AGT. Feedback regulation of AGT and renin by ANG II is mediated primarily through the angiotensin type 1 (AT1) receptor (AT1R) (34, 38).

In contrast to endocrine feedback regulation by ANG II in tissues with well-documented roles in the synthesis of individual RAS components, less is understood regarding endocrine feedback regulation in alternative sites of expression that are recognized as important for local production of this peptide. Given that AT1aRs are expressed in mouse adipose tissue (5, 42), we propose that ANG II exerts endocrine feedback regulation of AGT synthesis in adipocytes. Previously, we showed that the RAS is increased in hypercholesterolemic LDL receptor (LDLR)-deficient (LDLR–/–) mice (13). Therefore, in this study, we used LDLR–/– mice to attain a lipoprotein-cholesterol distribution that was more similar to that of humans. In addition, since our previous studies suggest that AGT may limit the rate of synthesis of ANG II in C57BL/6 mice (15), we used LDLR–/– mice with elevated systemic AGT to more closely mimic humans. We first compared RAS component expression of AGT, AT1aR, and angiotensin type 2 (AT2) receptors (AT2Rs) between adipose tissue and liver. We then determined the regulation of liver vs. adipose AGT and AT1aR mRNA abundance in AT1aR- and AT2R-deficient (AT1aR–/– and AT2R–/–) mice. Regulation of RAS expression in tissues was paralleled by measurement of plasma AGT and angiotensin peptide concentrations in mice with specific ANG II receptor deficiencies. Finally, we examined the effect of chronic ANG II infusion on adipose vs. liver AGT and AT1aR expression.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Mice and diet. LDLR–/– male mice (B6.129S7-Ldlrtm1Her; stock no. 002207) and AT1aR–/– male mice (B6.129P2-Agtr1atm1Unc; stock no. 002682) were obtained from the Jackson Laboratory. AT2R–/y mice were a kind gift of Dr. T. Inagami (Vanderbilt University). All genotypes had been backcrossed 10 times into a C57BL/6 background. Littermates (LDLR–/–, AT1a x LDLR–/–, and AT2 x LDLR–/–) were used for the present study. All mice were maintained in a barrier facility and fed normal mouse laboratory diet containing 5% fat, 20% protein, and 3.75 kcal/g digestible energy (diet no. 7012, Harlan Teklad, Madison, WI). All studies using animals were performed in accordance with American Association for Accreditation of Laboratory Animal Care "Guidelines for the Care and Use of Experimental Animals" and were approved by the Institutional Animal Care and Use Committee at the University of Kentucky.

Genotyping by PCR. For AT1aR genotyping, the following primers were used: 5'-AAATGGCCCTTAACTCTTCTACTG-3' (antisense) and 5'-ATTAGGAAAGGGAACAGGAAGC-3' (sense). Resultant wild-type and deficient allele bands were 650 bp and 1.1 kb, respectively. For AT2R genotyping, the following primers were used: 5'-GTAAGAATTTGGAGTTGCTG-3'(sense) and 5'-GGGATTCCTTCTTTGAGAC-3' (antisense). Resultant wild-type and deficient allele bands were 500 bp and 1.1 kb, respectively. For LDLR genotyping, the following primers were used: 5'-AGGTGAGATGACAGGAGATC-3', 5'-AGGATGACTTCCGATGCCAG-3', and 5'-GCAGTGCTCCTCATCTGACTTG-3'. Resultant wild-type and deficient allele bands were 383 and 800 bp, respectively.

Total RNA isolation and reverse transcriptase PCR. Total RNA was extracted from mouse epididymal adipose tissue and liver using the SV total RNA isolation system (Promega, Madison, WI) according to the protocol provided by the manufacturer. Extracted RNAs were suspended in ribonuclease-free water and quantified by measurement of absorbance at 260 nm.

The abundance of mRNA in mouse adipose tissue and liver was estimated by real-time PCR using an iCycler (Bio-Rad), and the threshold cycle number was determined using iCycler software version 3.0. Real-time PCR product accumulation was monitored using the intercalating dye SYBR Green I, which exhibits a higher fluorescence on the binding of double-stranded DNA. The relative abundance of each mRNA was estimated using a standard curve constructed from serial dilutions of control cDNA. The mRNA abundance was calculated as the ratio of the gene of interest to 18S rRNA. Nontemplate control and non-RT control were used as a negative control. The real-time PCR was performed using the primers shown in Table 1.


View this table:
[in this window]
[in a new window]

  		Table 1. Oligonucleotides, cDNA sequences, amplicon length, and annealing temperature

 
Administration of losartan or ANG II. Osmotic minipumps (model 2001 Alzet, Durect, Cupertino, CA) were implanted into 6- to 8-wk-old LDLR–/– male mice (5 mice/group). Pumps were filled with saline vehicle or solutions of losartan (catalog no. L-158086-005H067, Merck) that delivered 30 mg·kg–1·day–1 for 7 days. Losartan, an AT1R-specific antagonist (58), was used at a dose that previously afforded AT1R blockade (14). For ANG II infusion studies, saline or ANG II (500 ng·kg–1·min–1) was infused by osmotic minipump (model 2004) for 28 days. Pumps were placed in the subcutaneous space of ketamine-xylazine (50 and 5 mg/kg, respectively, ip)-anesthetized mice through a small incision in the flank of the neck, which was closed with surgical glue.

Western blotting analysis of AGT. As described previously (15), a chicken antibody was developed against mouse AGT. The sequence (EEEQPTTSVQPGSPE) used to generate the antibody was from the carboxyl terminus of AGT and did not react with other angiotensin peptides.

Mouse plasma samples were resolved electrophoretically, transferred to polyvinylidene difluoride membranes, and analyzed by Western blot as described elsewhere (37). Polyvinylidene difluoride membranes were incubated with chicken anti-mouse AGT IgY (1:500–1:1,000 dilution in Tris-buffered saline with 5% nonfat dry milk and 0.1% Tween 20) and then with a peroxidase-conjugated rabbit anti-chicken IgY (1:5,000–1:10,000 dilution; Jackson Immuno-Research). The immunoreactivity was visualized with an enhanced chemiluminescence Western blotting detection kit (Pierce, Rockford, IL). Kodak Image (Image Station, 440CF) was used for quantitative assessment of band densities.

Measurement of angiotensin peptides. Angiotensin peptides were resolved by HPLC as described previously (15). HPLC fractions were assayed using an anti-ANG II antibody that exhibited 100% cross-reactivity to ANG III and ANG-(3–8) (ANG IV) and 80% reactivity to ANG-(4–8).

Statistical analysis. Values are means ± SE. Statistical significance between groups was assessed by an unpaired t-test (Bonferroni/Dunn) or by ANOVA using SigmaStat version 3.0. Data sets were tested to ensure that they complied with the constraints of parametric tests. P < 0.05 was considered statistically significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Differential expression of components of the RAS in adipose tissue vs. liver. We initially determined AGT, AT1aR, angiotensin type 1b (AT1b) receptor (AT1bR), and AT2R mRNA abundance in epididymal adipose tissue compared with liver of LDLR–/– mice. Adipose mRNA abundance of AGT was 68% of that in liver (Fig. 1A). In mouse adipose tissue and liver, we detected AT1aR and AT2R, but not AT1bR mRNA (data not shown). AT1aR mRNA expression was lower (2-fold) in adipose tissue than in liver (Fig. 1B), whereas AT2R mRNA expression was 57% greater in adipose tissue than in liver (Fig. 1C).


Figure 1
View larger version (7K):
[in this window]
[in a new window]

  		Fig. 1. Relative mRNA abundance of angiotensinogen (AGT, A), angiotensin type 1a (AT1a) receptor (AT1aR, B), and angiotensin type 2 (AT2) receptor (AT2R, C) in mouse liver and epididymal adipose tissue. AGT mRNA expression was higher in liver than in adipose tissue. Abundance of the AT1aR was ~2-fold greater in liver than in adipose tissue. AT2R mRNA abundance was 57% greater in adipose tissue than in liver. Data are expressed as ratio of 18S rRNA abundance for each sample. Values are means ± SE (n = 4–5 mice/group). *P < 0.001. #P = 0.001.

 
Effects of AT1aR deficiency on adipose tissue, liver, and systemic RAS. To evaluate the effects of endocrine feedback regulation by ANG II on the RAS, we determined the effects of AT1aR deficiency on the mRNA abundance of the AT2R and AGT in adipose tissue and liver. AT2R mRNA abundance was not altered in adipose tissue from AT1aR–/– mice (AT2R-to-18S rRNA ratio = 0.29 ± 0.13 and 0.27 ± 0.11 in AT1aR+/+ and AT1aR–/– mice, respectively, P = 0.929). Similarly, adipose mRNA abundance of AGT was unaltered in AT1aR–/– mice (Fig. 2A). In contrast, liver AGT mRNA abundance was decreased (by 38%) in AT1aR–/– mice (Fig. 2B). Plasma AGT exhibited two protein bands (52 and 64 kDa), both of which were decreased (2-fold) in AT1aR–/– mice (Fig. 3A). To determine whether differential glycosylation gave rise to the two AGT protein bands (37, 41), we incubated plasma with peptide N-glycosidase F, which resulted in a single ~50-kDa protein AGT band (data not shown). Reductions in plasma AGT concentrations were accompanied by a decrease in angiotensin peptide concentrations in plasma of AT1aR–/– mice (Fig. 3B).


Figure 2
View larger version (7K):
[in this window]
[in a new window]

  		Fig. 2. Effect of AT1aR deficiency on AGT mRNA abundance in adipose tissue (A) and liver (B). Adipose AGT mRNA abundance was not altered in AT1aR-deficient (AT1aR–/–) mice. Liver AGT abundance was decreased in AT1aR–/– compared with wild-type mice. Data are expressed as ratio of 18S rRNA abundance for each sample. Values are means ± SE (n = 4 mice/group). *P < 0.01.

 

Figure 3
View larger version (23K):
[in this window]
[in a new window]

  		Fig. 3. Effect of AT1aR deficiency on plasma AGT (A) and angiotensin peptide (B) concentrations. Densitometric analysis of plasma AGT protein bands demonstrates a significant decrease in levels of 52- and 64-kDa AGT protein bands in AT1aR–/– mice. Plasma concentrations of angiotensin peptides were significantly decreased in AT1aR–/– mice, resulting in a marked reduction in the sum concentration of plasma angiotensins. Values are means ± SE (n = 4–6 mice/group). *P < 0.05.

 
Effects of AT2R deficiency on adipose and systemic RAS. Adipose tissue from AT2R–/– mice exhibited increased AGT (by 63%; Fig. 4A) and AT1aR (by 83%; Fig. 4B) mRNA abundance. In contrast, liver AGT mRNA abundance was unaltered by AT2R deficiency (data not shown). Elevations in adipose expression of these RAS components were accompanied by an increase in plasma concentrations of angiotensin peptides (Fig. 4C). To determine whether these elevated angiotensin peptide concentrations contributed to enhanced RAS expression in adipose tissue through the AT1aR, we administered losartan to AT2R+/y and AT2R–/y mice. Elevations in the mRNA abundance of AGT and AT1aR in adipose tissue were totally ablated in losartan-infused mice (Fig. 4, A and B). Similar to results obtained in AT1aR–/– mice, losartan administration decreased AGT mRNA abundance (by 53%) in the liver of AT2R–/y and AT2R+/y mice.


Figure 4
View larger version (13K):
[in this window]
[in a new window]

  		Fig. 4. Effect of AT2R deficiency on adipose expression of AGT (A), AT1aR (B), and plasma angiotensin peptide (C) concentrations. A and B: AGT and AT1aR mRNA abundance in adipose tissue were increased in AT2R–/y compared with wild-type mice. Elevations in AT1aR and AGT mRNA abundance were ablated in losartan-treated AT2R–/y mice. C: angiotensin peptide concentrations in plasma of AT2R+/y and AT2R–/y mice. Values are means ± SE (n = 4–6 mice/group). *P < 0.001. #P < 0.01.

 
Adipose AGT and AT1aR mRNA are increased by infusion of ANG II and paralleled by an increase in systemic AGT protein. Results described above suggest that elevated systemic angiotensin peptide concentrations stimulate the adipose RAS. We infused LDLR–/– mice with ANG II at a dose that has been demonstrated to increase blood pressure (32). Infusion of ANG II did not change AT2R mRNA expression in epididymal adipose tissue (AT2R-to-18S rRNA ratio = 0.14 ± 0.01 and 0.18 ± 0.02 in saline- and ANG II-infused animals, respectively, P = 0.07). However, infusion of ANG II resulted in a striking increase in the abundance of AT1aR (7.3-fold) and AGT (2.8-fold) mRNA in adipose tissue (Fig. 5). In contrast, there was no effect of ANG II infusion on liver AGT and AT1aR mRNA expression (Fig. 5). Plasma AGT concentrations (64-kDa band) were increased (2-fold) by ANG II infusion (Fig. 6).


Figure 5
View larger version (10K):
[in this window]
[in a new window]

  		Fig. 5. Effect of chronic infusion of ANG II on AT1aR (A) and AGT (B) mRNA abundances in adipose tissue and liver. Saline or ANG II (500 ng·kg–1·min–1) was infused by osmotic minipump for 28 days. AT1aR and AGT mRNA abundances were significantly increased in adipose tissue from ANG II-infused mice. AT1aR and AGT mRNA abundances were unaltered in livers of ANG II-infused mice. Values are means ± SE (n = 4–5 mice/group). *P < 0.001.

 

Figure 6
View larger version (27K):
[in this window]
[in a new window]

  		Fig. 6. Effect of chronic infusion of ANG II on plasma AGT. Saline or ANG II (500 ng·kg–1·min–1) was infused by osmotic minipump for 28 days. The 64-kDa protein band of immunoreactive AGT was markedly increased by ANG II infusion. Values are means ± SE (n = 4 mice/group). * P < 0.001.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
Our results demonstrate differential endocrine feedback regulation of the RAS in adipose tissue vs. liver. Mechanisms contributing to these effects include differences in AT1aR vs. AT2R expression between adipose tissue and liver and differences in the ability of systemic ANG II to regulate AT1aR expression in adipose tissue compared with liver. In AT1aR–/– mice, we found that AGT protein concentrations in plasma parallel the mRNA abundance in liver. This suggests that AT1aR-mediated regulation of AGT in mouse liver serves a primary role in determining the circulating AGT and ANG II concentrations. Results from AT2R–/– mice demonstrate that a primary mediator of differential regulation of AGT by ANG II in liver vs. adipose tissue relates to expression of the AT2R in adipose tissue. In AT2R–/– mice, adipose expression of the AT1aR and AGT paralleled plasma angiotensin peptide concentrations. Interestingly, in states of elevated systemic ANG II, marked elevations in AT1aR expression in adipose tissue resulted in pronounced regulation of AGT in adipose tissue, but not in liver. These results suggest that adipose tissue contributes to the concentration of plasma AGT and/or ANG II under conditions of high systemic ANG II.

Tissue-specific regulation of the AT1aR by ANG II. Previous studies have reported elevations in AT1aR mRNA expression in a tissue-specific manner in states of elevated systemic ANG II, such as low salt, chronic ANG II infusion, and renovascular hypertension (17, 18, 29, 45, 53). However, regulation of AT1aR expression by ANG II has not been examined in adipose tissue. Our results extend previous findings by demonstrating a robust effect of ANG II to increase AT1aR mRNA abundance in adipose tissue. In this study, a physiological consequence of ANG II regulation of AT1aR expression in adipose tissue was the promotion of AGT expression. However, ANG II has been demonstrated to exert a variety of AT1R-mediated effects at adipocytes (8, 57, 59, 60). Thus upregulation of AT1aR mRNA in adipose tissue in states associated with high plasma ANG II concentrations could result in changes in a variety of adipocyte functions. In contrast to findings in adipose tissue, our results do not support regulation of liver AT1aR expression after chronic ANG II infusion. These results are in agreement with previous data demonstrating no change in liver AT1aR gene expression with ANG II infusion (29). The relatively high mRNA abundance of the AT1aR in liver vs. adipose tissue may have contributed to differences in the ability of ANG II to upregulate AT1aR expression between these tissues.

No studies have examined differential expression of upstream transcriptional binding partners in adipose tissue vs. liver. The AT1a promoter exhibits a high degree of complexity in its regulation, and certain polymorphisms are thought to be associated with differential regulation of this receptor (12). The transcription factor Sp1 associates with a –98/–79 and –58/–34 region sequence (GC-rich) of the AT1aR promoter in A10 smooth muscle cells and a human trophoblast cell line (19, 36). Expression of the AT1aR is induced by ANG II in vascular smooth muscle cells but is inhibited in the adrenal gland (12). However, no studies have specifically examined whether liver and/or adipose tissue AT1aR is associated with regulation by Sp1. Furthermore, a negative cis-regulatory element between –489 and –331 on the AT1aR promoter was identified in PC-12 cells and rat brain, but not in liver (46). These results suggest possible tissue-specific regulation of the AT1aR via different transcription factors. Alternatively, cross talk between the AT1aR and the AT2R in adipose tissue, but not in liver, may have influenced differential ANG II regulation of AT1aR expression between these tissues.

Tissue-specific regulation of AGT by ANG II. Adipose tissue has been demonstrated to express the majority of components required for the synthesis of ANG II (7, 22). Of these, AGT has been consistently demonstrated at a high level of expression in mouse (23, 35, 39, 50), rat (3, 27), and human (25, 26, 61) adipocytes. Previous investigators have demonstrated a variety of factors that regulate adipose AGT expression (1–3, 6, 10, 23, 24, 31, 35, 39, 49, 54, 55). In contrast, relatively few studies have examined endocrine feedback regulation of adipose-derived AGT by angiotensin peptides. ANG II was reported to decrease AGT expression in differentiating human preadipocytes (51) but had no effect when incubated with primary mammary adipocytes (28). Similar to responses observed in primary mammary adipocytes, we did not observe alterations in AGT mRNA expression in adipose tissue of AT1aR–/– mice. In contrast, our results demonstrate robust regulation of AGT expression in adipose tissue of AT2R–/– mice. It is conceivable that the AT2R, by providing a competing site for ANG II binding in adipocytes, may have reduced the availability of ANG II to occupy the AT1aR and, subsequently, regulate AGT expression. In support of this conclusion, the infusion of ANG II, which would elevate systemic ANG II concentrations at adipocytes and afford greater AT1aR occupation, resulted in an upregulation of AT1aR and AGT mRNA expression in adipocytes.

Taken together, our results demonstrate that in the presence of low or normal concentrations of plasma ANG II, the AT1aR is not a primary mediator of AGT regulation in adipose tissue. In contrast, the AT1aR is a primary regulator of AGT by ANG II in liver under these circumstances. In contrast, when AT2R expression is reduced in adipose tissue or in a situation of elevated systemic ANG II, our results support a primary role for AT1aRs in the regulation of adipose AGT expression.

Relationship between adipose and liver AGT regulation and systemic ANG II. Under most physiological conditions, ANG II generation is largely dependent on ANG I cleavage by renin, the rate-limiting enzyme in the generation of systemic ANG II. However, in most species, the Michaelis-Menten constant for renin approximates the plasma AGT concentration, suggesting that alterations in circulating AGT can influence ANG II synthesis (20). In mice, several lines of evidence suggest that AGT may limit the rate of ANG II synthesis. Graded doses of sheep AGT resulted in a dose-dependent increase in blood pressure in mice, but not in rats, suggesting that AGT was limiting in mouse plasma (40). Similarly, a dose-dependent increase in blood pressure was observed in mice treated with increasing doses of intravenously infused AGT, coincident with an elevation in systemic ANG II concentrations (11). Collectively, these results suggest that regulation of AGT may serve as a primary mechanism for control of angiotensin peptide concentrations in mice.

Our findings demonstrate that liver AGT mRNA expression paralleled angiotensin peptide concentrations in AT1aR–/– mice, supporting an important role of liver-derived AGT in the production of systemic ANG II. Interestingly, in AT2R–/– mice, the plasma concentrations of angiotensin peptides began to parallel AGT expression in adipose tissue, but not in liver. A primary mechanism for this effect was a striking increase in AT1aR mRNA expression in adipose tissue of AT2R–/– mice. The ability of adipose tissue to contribute to AGT in plasma has been suggested from studies in transgenic mice overexpressing AGT in adipose tissue. These mice exhibit elevations in circulating concentrations of AGT and blood pressure (43). Results from our studies extend these findings by demonstrating that marked upregulation of AT1aR mRNA expression by ANG II makes adipose tissue a more prominent contributor to circulating AGT concentrations and, thereby, ANG II concentrations. In addition, these results demonstrate that ANG II can modulate adipose-derived AGT in a positive endocrine feedback loop through effects at the AT1aR. Thus, under conditions of elevated systemic ANG II, our results would suggest that adipose tissue becomes a prominent source of AGT. We previously reported that diet-induced obesity in rats was associated with increased adipose AGT mRNA expression that correlated positively to plasma angiotensin peptide concentrations and blood pressure (3). Interestingly, liver AGT expression was not altered in obese rats, suggesting that adipose tissue contributed significantly to systemic AGT/angiotensin concentrations. Recent studies suggest that reductions in body weight in obese patients were associated with decreased plasma AGT concentration, which correlated to waist circumference (21). The positive-feedback endocrine regulation of adipose-derived AGT by ANG II demonstrated in this study may contribute to overactivity of the RAS in obesity-associated disorders.

In conclusion, results from this study demonstrate that adipose tissue differs from liver in the regulation of AGT by ANG II because of differences in the AT1aR/AT2R populations of these tissues. Expression of the AT2R in mouse adipose tissue masks the effects of ANG II to increase AGT expression through the AT1aR. When AT2Rs are ablated, plasma concentrations of ANG II begin to parallel AGT expression in adipose tissue, and not in liver. In addition, chronic infusion of ANG II resulted in marked upregulation of AT1aR and AGT mRNA expression in adipose tissue, but not in liver. In ANG II-infused mice, plasma AGT concentrations paralleled adipose AGT mRNA expression. These results demonstrate that ANG II regulates adipose AGT via activation of the AT1aR and that this positive-feedback loop may play an important role in the pathogenesis of ANG II-related cardiovascular diseases.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
These studies were supported by National Heart, Lung, and Blood Institute Grants HL-73085 (L. A. Cassis) and HL-62846 (A. Daugherty).


   FOOTNOTES
 

Address for reprint requests and other correspondence: L. A. Cassis, Graduate Center for Nutritional Sciences, Rm. 521b, Wethington Bldg., 900 S. Limestone, Univ. of Kentucky, Lexington, KY 4053-0200 (e-mail: lcassis{at}uky.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Aubert J, Darimont C, Safonova I, Ailhaud G, Negrel R. Regulation by glucocorticoids of angiotensinogen gene expression and secretion in adipose cells. Biochem J 328: 701–716, 1997.[ISI][Medline]
  2. Aubert J, Safonova I, Negrel R, Ailhaud G. Insulin down-regulates angiotensinogen gene expression and angiotensinogen secretion in cultured adipose cells. Biochem Biophys Res Commun 250: 77–82, 1998.[CrossRef][ISI][Medline]
  3. Boustany CM, Bharadwaj K, Daugherty A, Brown DR, Randall DC, Cassis LA. Activation of the systemic and adipose renin-angiotensin system in rats with diet-induced obesity and hypertension. Am J Physiol Regul Integr Comp Physiol 287: R943–R949, 2004.[Abstract/Free Full Text]
  4. Burson JM, Aguilera G, Gross KW, Sigmund CD. Differential expression of angiotensin receptor 1A and 1B in mouse. Am J Physiol Endocrinol Metab 267: E260–E267, 1994.[Abstract/Free Full Text]
  5. Cassis LA. Downregulation of the renin-angiotensin system in streptozotocin-diabetic rats. Am J Physiol Endocrinol Metab 262: E105–E109, 1992.[Abstract/Free Full Text]
  6. Cassis LA. Fat cell metabolism: insulin, fatty acids, and renin. Curr Hypertens Rep 2: 132–138, 2000.[Medline]
  7. Cassis LA, English VL, Bharadwaj K, Boustany CM. Differential effects of local versus systemic angiotensin II in the regulation of leptin release from adipocytes. Endocrinology 145: 169–174, 2004.[Abstract/Free Full Text]
  8. Cassis LA, Lynch KR, Peach MJ. Localization of angiotensinogen messenger RNA in rat aorta. Circ Res 62: 1259–1262, 1988.[Abstract/Free Full Text]
  9. Cassis LA, Saye J, Peach MJ. Location and regulation of rat angiotensinogen messenger RNA. Hypertension 11: 591–596, 1988.[Abstract/Free Full Text]
  10. Cholewa BC, Mattson DL. Influence of elevated renin substrate on angiotensin II and arterial blood pressure in conscious mice. Exp Physiol 90: 607–612, 2005.[Abstract/Free Full Text]
  11. Clauser E, Curnow KM, Davies E, Conchon S, Teutsch B, Vianello B, Monnot C, Corvol P. Angiotensin II receptors: protein and gene structures, expression and potential pathological involvements. Eur J Endocrinol 134: 403–11, 1996.[Abstract]
  12. Daugherty A, Manning MW, Cassis LA. Angiotensin II promotes atherosclerotic lesions and aneurysms in apolipoprotein E-deficient mice. J Clin Invest 105: 1605–1612, 2000.[ISI][Medline]
  13. Daugherty A, Manning MW, Cassis LA. Antagonism of AT2 receptors augments angiotensin II-induced abdominal aortic aneurysms and atherosclerosis. Br J Pharmacol 134: 865–870, 2001.[CrossRef][ISI][Medline]
  14. Daugherty A, Rateri DL, Lu H, Inagami T, Cassis LA. Hypercholesterolemia stimulates angiotensin peptide synthesis and contributes to atherosclerosis through the AT1A receptor. Circulation 110: 3849–3857, 2004.[Abstract/Free Full Text]
  15. Devenyi I, Dauda G, Nemes Z. The role of the liver in angiotensinogen production. Acta Physiol Acad Sci Hung 34: 43–46, 1968.[ISI][Medline]
  16. Douglas JG. Subpressor infusions of angiotensin II alter glomerular binding, prostaglandin E2, and cyclic AMP production. Hypertension 9: III49–III56, 1987.[Medline]
  17. Du Y, Guo DF, Inagami T, Speth RC, Wang DH. Regulation of ANG II-receptor subtype and its gene expression in adrenal gland. Am J Physiol Heart Circ Physiol 271: H440–H446, 1996.[Abstract/Free Full Text]
  18. Duffy AA, Martin MM, Elton TS. Transcriptional regulation of the AT1 receptor gene in immortalized human trophoblast cells. Biochim Biophys Acta 1680: 158–170, 2004.[Medline]
  19. Dzau VJ, Herrmann HC. Hormonal control of angiotensinogen production. Life Sci 30: 577–584, 1982.[CrossRef][ISI][Medline]
  20. Engeli S, Bohnke J, Gorzelniak K, Janke J, Schling P, Bader M, Luft FC, Sharma AM. Weight loss and the renin-angiotensin-aldosterone system. Hypertension 45: 356–362, 2005.[Abstract/Free Full Text]
  21. Engeli S, Negrel R, Sharma AM. Physiology and pathophysiology of the adipose tissue renin-angiotensin system. Hypertension 35: 1270–1277, 2000.[Abstract/Free Full Text]
  22. Frederich RC Jr, Kahn BB, Peach MJ, Flier JS. Tissue-specific nutritional regulation of angiotensinogen in adipose tissue. Hypertension 19: 339–344, 1992.[Abstract/Free Full Text]
  23. Gabriely I, Yang XM, Cases JA, Ma XH, Rossetti L, Barzilai N. Hyperglycemia modulates angiotensinogen gene expression. Am J Physiol Regul Integr Comp Physiol 281: R795–R802, 2001.[Abstract/Free Full Text]
  24. Giacchetti G, Faloia E, Mariniello B, Sardu C, Gatti C, Camilloni MA, Guerrieri M, Mantero F. Overexpression of the renin-angiotensin system in human visceral adipose tissue in normal and overweight subjects. Am J Hypertens 15: 381–388, 2002.[CrossRef][ISI][Medline]
  25. Giacchetti G, Faloia E, Sardu C, Camilloni MA, Mariniello B, Gatti C, Garrapa GG, Guerrieri M, Mantero F. Gene expression of angiotensinogen in adipose tissue of obese patients. Int J Obes Relat Metab Disord 24 Suppl 2: S142–S143, 2000.[CrossRef][ISI]
  26. Gomez RA, Cassis L, Lynch KR, Chevalier RL, Wilfong N, Carey RM, Peach MJ. Fetal expression of the angiotensinogen gene. Endocrinology 123: 2298–2302, 1988.[Abstract]
  27. Gorzelniak K, Engeli S, Janke J, Luft FC, Sharma AM. Hormonal regulation of the human adipose-tissue renin-angiotensin system: relationship to obesity and hypertension. J Hypertens 20: 965–973, 2002.[CrossRef][ISI][Medline]
  28. Harrison-Bernard LM, El-Dahr SS, O'Leary DF, Navar LG. Regulation of angiotensin II type 1 receptor mRNA and protein in angiotensin II-induced hypertension. Hypertension 33: 340–346, 1999.[Abstract/Free Full Text]
  29. Harte A, McTernan P, Chetty R, Coppack S, Katz J, Smith S, Kumar S. Insulin-mediated upregulation of the renin angiotensin system in human subcutaneous adipocytes is reduced by rosiglitazone. Circulation 111: 1954–1961, 2005.[Abstract/Free Full Text]
  30. Harte AL, McTernan PG, McTernan CL, Crocker J, Starcynski J, Barnett AH, Matyka K, Kumar S. Insulin increases angiotensinogen expression in human abdominal subcutaneous adipocytes. Diabetes Obes Metab 5: 462–467, 2003.[CrossRef][ISI][Medline]
  31. Henriques TA, Huang J, D'Souza SS, Daugherty A, Cassis LA. Orchiectomy, but not ovariectomy, regulates angiotensin II-induced vascular diseases in apolipoprotein E-deficient mice. Endocrinology 145: 3866–3872, 2004.[Abstract/Free Full Text]
  32. Herrmann HC, Dzau VJ. The feedback regulation of angiotensinogen production by components of the renin-angiotensin system. Circ Res 52: 328–334, 1983.[Abstract/Free Full Text]
  33. Hilgenfeldt U, Schwind S. Angiotensin II is the mediator of the increase in hepatic angiotensinogen synthesis after bilateral nephrectomy. Am J Physiol Endocrinol Metab 265: E414–E418, 1993.[Abstract/Free Full Text]
  34. Jones BH, Standridge MK, Taylor JW, Moustaid N. Angiotensinogen gene expression in adipose tissue: analysis of obese models and hormonal and nutritional control. Am J Physiol Regul Integr Comp Physiol 273: R236–R242, 1997.[Abstract/Free Full Text]
  35. Kambe T, Kinjyo N, Hiruki H, Kubo T. Basal transcriptional regulation of rat AT1 angiotensin II receptor gene expression. Clin Exp Pharmacol Physiol 31: 96–100, 2004.[CrossRef][ISI][Medline]
  36. Kobori H, Harrison-Bernard LM, Navar LG. Expression of angiotensinogen mRNA and protein in angiotensin II-dependent hypertension. J Am Soc Nephrol 12: 431–439, 2001.[Abstract/Free Full Text]
  37. Kurtz A, Wagner C. Regulation of renin secretion by angiotensin II-AT1 receptors. J Am Soc Nephrol 10 Suppl 11: S162–S168, 1999.[ISI][Medline]
  38. Le Lay S, Krief S, Farnier C, Lefrere I, Le Liepvre X, Bazin R, Ferre P, Dugail I. Cholesterol, a cell size-dependent signal that regulates glucose metabolism and gene expression in adipocytes. J Biol Chem 276: 16904–16910, 2001.[Abstract/Free Full Text]
  39. Lum C, Shesely EG, Potter DL, Beierwaltes WH. Cardiovascular and renal phenotype in mice with one or two renin genes. Hypertension 43: 79–86, 2004.[Abstract/Free Full Text]
  40. Lynch KR, Peach MJ. Molecular biology of angiotensinogen. Hypertension 17: 263–269, 1991.[Free Full Text]
  41. Mallow H, Trindl A, Loffler G. Production of angiotensin II receptors type 1 (AT1) and type 2 (AT2) during the differentiation of 3T3-L1 preadipocytes. Horm Metab Res 32: 500–503, 2000.[ISI][Medline]
  42. Massiera F, Bloch-Faure M, Ceiler D, Murakami K, Fukamizu A, Gasc JM, Quignard-Boulange A, Negrel R, Ailhaud GSJ, Meneton P, Teboul M. Adipose angiotensinogen is involved in adipose tissue growth and blood pressure regulation. FASEB J 15: 2727–2729, 2001.[Free Full Text]
  43. Menard J, Bouhnik J, Clauser E, Richoux JP, Corvol P. Biochemistry and regulation of angiotensinogen. Clin Exp Hypertens 5: 1005–1019, 1983.[ISI]
  44. Modrall JG, Quinones MJ, Frankhouse JH, Hsueh WA, Weaver FA, Kedes L. Upregulation of angiotensin II type 1 receptor gene expression in chronic renovascular hypertension. J Surg Res 59: 135–140, 1995.[CrossRef][ISI][Medline]
  45. Murasawa S, Matsubara H, Mori Y, Kijima K, Maruyama K, Inada M. Identification of a negative cis-regulatory element and trans-acting protein that inhibit transcription of the angiotensin II type 1a receptor gene. J Biol Chem 270: 24282–24286, 1995.[Abstract/Free Full Text]
  46. Prasad A, Quyyumi AA. Renin-angiotensin system and angiotensin receptor blockers in the metabolic syndrome. Circulation 110: 1507–1512, 2004.[Free Full Text]
  47. Rahmouni K, Mark AL, Haynes WG, Sigmund CD. Adipose depot-specific modulation of angiotensinogen gene expression in diet-induced obesity. Am J Physiol Endocrinol Metab 286: E891–E895, 2004.[Abstract/Free Full Text]
  48. Safonova I, Aubert J, Negrel R, Ailhaud G. Regulation by fatty acids of angiotensinogen gene expression in preadipose cells. Biochem J 322: 235–239, 1997.[ISI][Medline]
  49. Saye JA, Cassis LA, Sturgill TW, Lynch KR, Peach MJ. Angiotensinogen gene expression in 3T3-L1 cells. Am J Physiol Cell Physiol 256: C448–C451, 1989.[Abstract/Free Full Text]
  50. Schling P, Loffler G. Effects of angiotensin II on adipose conversion and expression of genes of the renin-angiotensin system in human preadipocytes. Horm Metab Res 33: 189–195, 2001.[CrossRef][ISI][Medline]
  51. Schunkert H, Ingelfinger JR, Jacob H, Jackson B, Bouyounes B, Dzau VJ. Reciprocal feedback regulation of kidney angiotensinogen and renin mRNA expressions by angiotensin II. Am J Physiol Endocrinol Metab 263: E863–E869, 1992.[Abstract/Free Full Text]
  52. Sechi LA, Griffin CA, Giacchetti G, Valentin JP, Llorens-Cortes C, Corvol P, Schambelan M. Tissue-specific regulation of type 1 angiotensin II receptor mRNA levels in the rat. Hypertension 28: 403–408, 1996.[Abstract/Free Full Text]
  53. Serazin-Leroy V, Morot M, de Mazancourt P, Giudicelli Y. Androgen regulation and site specificity of angiotensinogen gene expression and secretion in rat adipocytes. Am J Physiol Endocrinol Metab 279: E1398–E1405, 2000.[Abstract/Free Full Text]
  54. Serazin V, Dieudonne MN, Morot M, de Mazancourt P, Giudicelli Y. cAMP-positive regulation of angiotensinogen gene expression and protein secretion in rat adipose tissue. Am J Physiol Endocrinol Metab 286: E434–E438, 2004.[Abstract/Free Full Text]
  55. Shenoy U, Cassis L. Characterization of renin activity in brown adipose tissue. Am J Physiol Cell Physiol 272: C989–C999, 1997.[Abstract/Free Full Text]
  56. Skurk T, van Harmelen V, Hauner H. Angiotensin II stimulates the release of interleukin-6 and interleukin-8 from cultured human adipocytes by activation of NF-{kappa}B. Arterioscler Thromb Vasc Biol 24: 1199–1203, 2004.[Abstract/Free Full Text]
  57. Timmermans PB. Pharmacological properties of angiotensin II receptor antagonists. Can J Cardiol 15 Suppl F: 26F–8F, 1999.[Medline]
  58. Tondu AL, Robichon C, Yvan-Charvet L, Donne N, Le Liepvre X, Hajduch E, Ferre P, Dugail I, Dagher G. Insulin and angiotensin II induce the translocation of scavenger receptor class B, type I from intracellular sites to the plasma membrane of adipocytes. J Biol Chem 280: 33536–33540, 2005.[Abstract/Free Full Text]
  59. Tsuchiya K, Yoshimoto T, Hirono Y, Tateno T, Sugiyama T, Hirata Y. Angiotensin II induces monocyte chemoattractant protein-1 expression via a nuclear factor-{kappa}B-dependent pathway in rat preadipocytes. Am J Physiol Endocrinol Metab 291: E771–E778, 2006.[Abstract/Free Full Text]
  60. Van Harmelen V, Ariapart P, Hoffstedt J, Lundkvist I, Bringman S, Arner P. Increased adipose angiotensinogen gene expression in human obesity. Obes Res 8: 337–341, 2000.[ISI][Medline]



This article has been cited by other articles:


Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
M. Gupte, C. M. Boustany-Kari, K. Bharadwaj, S. Police, S. Thatcher, M. C. Gong, V. L. English, and L. A. Cassis
ACE2 is expressed in mouse adipocytes and regulated by a high-fat diet
Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2008; 295(3): R781 - R788.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Endocrinol. Metab.Home page
C. Roberge, A. C. Carpentier, M.-F. Langlois, J.-P. Baillargeon, J.-L. Ardilouze, P. Maheux, and N. Gallo-Payet
Adrenocortical dysregulation as a major player in insulin resistance and onset of obesity
Am J Physiol Endocrinol Metab, December 1, 2007; 293(6): E1465 - E1478.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/5/E1280    most recent
00277.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Lu, H.
Right arrow Articles by Cassis, L. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Lu, H.
Right arrow Articles by Cassis, L. A.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2007 by the American Physiological Society.