ABSTRACT
To address the role of angiotensinogen (agt) in lipid metabolism and its potential endocrine effects in vivo, we studied the effects of high-fat diet (HFD) on adult, 28-week-old agt knockout (KO) mice compared to wild type (WT) mice. Recent studies (Massiera et al., 2001) have demonstrated that reexpression of agt in adipose tissue of KO mice normalized adiposity, blood pressure, and kidney abnormalities. We therefore used microarray analysis to investigate changes in gene expression profile in kidneys of KO vs. Tg-KO mice, where agt expression is restricted to adipose tissue. Body weight, adiposity and insulin levels were significantly decreased (p < 0.05) in KO mice on a chow diet (CD) compared to WT mice, while circulating leptin levels were similar. On a high-fat diet, KO mice exhibited significantly lower bodyweight (p < 0.05), adiposity (p < 0.05), leptin, and insulin levels (p < 0.05) compared to WT mice. In agreement with previously reported changes in kidney histology, agt KO mice displayed altered expressions of genes involved in blood pressure regulation and renal function, but these levels were corrected by reexpression of agt in adipose tissue. Collectively, these findings further document important endocrine roles of adipocyte agt, in part via regulation of lipid metabolism and kidney homeostasis.
Subject(s)
Adipose Tissue/metabolism , Angiotensinogen/genetics , Angiotensinogen/metabolism , Dietary Fats/metabolism , Kidney/physiology , Lipid Metabolism , Angiotensinogen/deficiency , Animals , Blood Pressure/physiology , Body Composition/genetics , Body Weight/genetics , Gene Expression Profiling , Insulin/blood , Leptin/blood , Male , Mice , Mice, Knockout , Mice, Transgenic , Oligonucleotide Array Sequence AnalysisABSTRACT
White adipose tissue is known to contain the components of the renin-angiotensin system, which gives rise to angiotensin II from angiotensinogen (AGT). Recent evidence obtained in vitro and ex vivo is in favor of angiotensin II acting as a trophic factor of adipose tissue development. To determine whether AGT plays a role in vivo in this process, comparative studies were performed in AGT-deficient (agt(-/-)) mice and control wild-type mice. The results showed that agt(-/-) mice gain less weight than wild-type mice in response to a chow or high fat diet. Adipose tissue mass from weaning to adulthood appeared altered rather specifically, as both the size and the weight of other organs were almost unchanged. Food intake was similar for both genotypes, suggesting a decreased metabolic efficiency in agt(-/-) mice. Consistent with this hypothesis, cellularity measurement indicated hypotrophy of adipocytes in agt(-/-) mice with a parallel decrease in the fatty acid synthase activity. Moreover, AGT-deficient mice exhibited a significantly increased locomotor activity, whereas metabolic rate and mRNA levels of uncoupling proteins remained similar in both genotypes. Thus, AGT appears to be involved in the regulation of fat mass through a combination of decreased lipogenesis and increased locomotor activity that may be centrally mediated.
Subject(s)
Adipose Tissue/growth & development , Angiotensinogen/deficiency , Diet , Motor Activity/physiology , Weight Gain , Adipose Tissue/pathology , Adipose Tissue, Brown/growth & development , Adipose Tissue, Brown/pathology , Angiotensinogen/genetics , Animals , Mice , Mice, Inbred ICR , Mice, Knockout/genetics , Reference Values , ThermogenesisABSTRACT
The essential role of CCAAT/enhancer binding proteins (C/EBPs) beta and delta for adipocyte differentiation has been clearly established. In preadipocytes, their expression is up-regulated by the activation of leukemia inhibitory factor receptor (LIF-R) and prostacyclin receptor (IP-R) via the extracellular signal-regulated kinase (ERK) pathway and cAMP production, respectively. However, the molecular mechanisms by which LIF and prostacyclin-induced signals are propagated to the nucleus and the transcription factors mediating ERK and cAMP-induced C/EBP gene expression were unknown. Here we report that both pathways share cAMP responsive element binding protein/activation transcription factor 1 (CREB/ATF-1) as common downstream effectors. LIF-R and IP-R activation induced binding of CREB and/or ATF-1 to C/EBP promoters and CREB-dependent transcription. Expression of dominant negative forms of CREB dramatically reduced the LIF- and prostacyclin-stimulated C/EBP beta and C/EBP delta expression. Upon stimulation of the IP-R, the ERK pathway was activated in a PKA-dependent manner. ERK activation by the PKA pathway was not required for CREB/ATF-1 phosphorylation but rather was necessary for CREB-dependent up-regulation of C/EBPs expression. Our findings suggest that ERK activation is required for CREB transcriptional activity, possibly by recruitment of a coactivator.
Subject(s)
Adipocytes/physiology , CCAAT-Enhancer-Binding Protein-beta/metabolism , CCAAT-Enhancer-Binding Proteins/metabolism , DNA-Binding Proteins , Mitogen-Activated Protein Kinases/metabolism , Transcription Factors/metabolism , Activating Transcription Factor 1 , Animals , CCAAT-Enhancer-Binding Protein-beta/drug effects , CCAAT-Enhancer-Binding Protein-beta/genetics , CCAAT-Enhancer-Binding Protein-delta , CCAAT-Enhancer-Binding Proteins/drug effects , CCAAT-Enhancer-Binding Proteins/genetics , Cells, Cultured , Cyclic AMP Response Element-Binding Protein/metabolism , Cyclic AMP-Dependent Protein Kinases/drug effects , Cyclic AMP-Dependent Protein Kinases/metabolism , Enzyme Activation , Epoprostenol/pharmacology , Gene Expression Regulation/drug effects , Leukemia Inhibitory Factor Receptor alpha Subunit , Mice , Mice, Inbred Strains , Mice, Mutant Strains , Mitogen-Activated Protein Kinases/genetics , Phosphorylation , Receptors, Cytokine/metabolism , Receptors, Epoprostenol , Receptors, OSM-LIF , Receptors, Prostaglandin/agonists , Transcription Factors/genetics , Transcription Factors/immunology , TransfectionABSTRACT
White adipose tissue and liver are important angiotensinogen (AGT) production sites. Until now, plasma AGT was considered to be a reflection of hepatic production. Because plasma AGT concentration has been reported to correlate with blood pressure, and to be associated with body mass index, we investigated whether adipose AGT is released locally and into the blood stream. For this purpose, we have generated transgenic mice either in which adipose AGT is overexpressed or in which AGT expression is restricted to adipose tissue. This was achieved by the use of the aP2 adipocyte-specific promoter driving the expression of rat agt cDNA in both wild-type and hypotensive AGT-deficient mice. Our results show that in both genotypes, targeted expression of AGT in adipose tissue increases fat mass. Mice whose AGT expression is restricted to adipose tissue have AGT circulating in the blood stream, are normotensive, and exhibit restored renal function compared with AGT-deficient mice. Moreover, mice that overexpress adipose AGT have increased levels of circulating AGT, compared with wild-type mice, and are hypertensive. These animal models demonstrate that AGT produced by adipose tissue plays a role in both local adipose tissue development and in the endocrine system, which supports a role of adipose AGT in hypertensive obese patients.
Subject(s)
Adipose Tissue/growth & development , Angiotensinogen/physiology , Blood Pressure/physiology , Adipocytes/pathology , Adipose Tissue/cytology , Angiotensinogen/blood , Angiotensinogen/genetics , Animals , Drinking , Gene Expression Regulation , Kidney/metabolism , Kidney/pathology , Kidney/physiopathology , Mice , Mice, Knockout , Mice, Transgenic , RNA, Messenger/genetics , RNA, Messenger/metabolism , Renin/genetics , Renin/metabolism , UrinationABSTRACT
Adipose tissue is an important source of angiotensinogen (AGT). Recent evidence shows that a local renin-angiotensinogen system (RAS) is present in human adipose tissue and may act as a distinct system from plasma RAS. In obese patients, the involvement of angiotensin II (angII) as a consequence of increased plasma AGT secreted from adipose tissue has been proposed in the development of hypertension. Another role of AGT via angII in the development of adipose tissue is supported by the following: (i) in vitro, angII stimulates the production and release of prostacyclin from adipocytes, which in turn promotes the differentiation of precursor cells into adipocytes; (ii) ex vivo and in vivo, both angII and (carba)prostacyclin promote the formation of new fat cells; and (iii) AGT -/- mice exhibit a slowing down of adipose tissue development, as compared to wild-type mice. Altogether the data are consistent with an autocrine/paracrine mechanism implicating AGT, angII and prostacyclin in adipose tissue development.
