Date of Award

8-2012

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Dr. Naima Moustaid-Moussa

Committee Members

Dr. Arnold M. Saxton, Dr. Brynn H. Voy, Dr. Guoxun Chen, Dr. Cheryl J. Kojima, Dr. Gina M. Pighetti

Abstract

Obesity is characterized by metabolic complications which are related to several life-threatening diseases. Dysregulated inflammatory adipokines secretion from adipose tissue is believed as the major contributor to obesity-associated local and systemic inflammation, insulin resistance, and other metabolic dysfunctions.

Numerous studies in our lab and others pointed to the role of local adipose tissue renin-angiotensin system (RAS) in the pathogenesis of obesity, inflammation and insulin resistance. We hypothesized that adipocytes-derived angiotensinogen (Agt) played a critical role in adipogenesis and/or lipogenesis as well as adipose inflammation. To test, we established 3T3-L1 preadipocytes stably transfected with Agt-shRNA or scrambled sequence (Sc-shRNA). Transfected preadipocytes were differentiated and used to investigate the role of adipocytes-derived Agt using microarray and PCR analyses, as well as cytokine/adipokine profiling.

As expected, results confirmed that Agt gene silencing significantly reduced the expression of Agt and its hormone product angiotensin II (Ang II), as well as lipid accumulation in 3T3-L1 adipocytes compared to cells transfected with Sc-shRNA. Silencing of Agt gene also suppressed the production of pro-inflammatory adipokines, including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α [alpha]), and monocyte chemotactic protein-1 (MCP-1), in 3T3-L1 adipocytes.

Microarray studies identified several genes involved in lipid metabolism and inflammatory pathways which were down-regulated by Agt gene inactivation, such as glycerol-3-phosphate dehydrogenase 1 (Gpd1), carboxylesterase 3 (Ces3), retinol saturase (Retsat), serum amyloid A 3 (Saa3), nucleotide-binding oligomerization domain containing 1 (Nod1), signal transducer and activator of transcription 1 (Stat1) and chemokine (C-X-C motif) ligand 12 (Cxcl12). Additional analysis using mouse adipogenesis PCR arrays detected lower expression levels of adipogenic/lipogenic genes, such as peroxisome proliferator activated receptor gamma (Pparg), sterol regulatory element binding transcription factor 1 (Srebf1), adipogenin (Adig), and fatty acid binding protein 4 (Fabp4).

In conclusion, this study directly demonstrates the critical effects of Agt in preadipocytes differentiation, adipocytes lipid metabolism and inflammation. These results further support a potential role for adipose tissue-derived Agt in the pathogenesis of adiposity and obesity-associated metabolic complications.

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