Abstract A13: AdipoR1 overexpression and AMPK signaling in histologically normal endometrium from obese women and in endometrial tumorigenesis
Authors: McCampbell Adrienne S. , Burzawa Jennifer K. , Zhang Qian , Wei Caimiao , Walker Cheryl L. , Lu Karen H. , Broaddus Russell R. 
Published: June 2012

Background: Obesity is a significant risk factor for the development of endometrial cancer (EC). Epidemiological studies indicate that adiponectin is significantly decreased in the obese woman and in women with EC. Adiponectin is an insulin-sensitizing, anti-inflammatory cytokine produced in adipose that has pleiotropic effects on numerous physiologic processes and peripheral tissues. In normal metabolic tissues, adiponectin acts through the adiponectin receptor 1 (AdipoR1) to activate the AMPK pathway. Adiponectin stimulates AMPK by promoting the formation of AdipoR1-APPL1 complexes. APPL2 antagonizes AdipoR1 signaling by blocking the formation of these complexes. AdipoR1-APPL1 complexes activate AMPK signaling which can negatively regulate the mTOR pathway, an important contributor to the development of endometrial complex atypical hyperplasia (CAH) and EC, to inhibit protein synthesis and cell growth during times of cellular starvation. The goal of these studies was to assess adiponectin signaling pathway components (AdipoR1, APPL1 and APPL2) expression and activation of AMPK and mTOR signaling in histologically normal endometrium from lean and obese women and in endometrial CAH and EC from obese women.

Methods: We quantitated transcript levels of AdipoR1 by qRT-PCR in timed endometrial biopsies obtained from lean women (BMI &lt; 25.0kg/m2) and obese women (BMI &gt; 30.0kg/m2) that were histologically confirmed to have normal proliferative phase endometrium and compared to biopsies from obese women with endometrial CAH and grade 1 endometrioid endometrial adenocarcinoma. Protein expression of AdipoR1 and the adaptor proteins APPL1/L2 was evaluated by immunohistochemistry. We assessed functional activation of AMPK (phosphorylation of S35 of ACC) and mTOR (phosphorylation of S235 of S6 ribosomal protein) pathways by immunohistochemistry.

Results: There was a significant stepwise increase in the expression of AdipoR1 in normal obese endometrium and endometrial CAH as compared to normal lean endometrium. However, the expression of AdipoR1 was not significantly increased in EC (confirmed at the protein level). Overexpression of APPL2, but not APPL1 was evident in EC as compared to normal lean endometrium, normal obese endometrium and endometrial CAH. Consistent with normal physiology, phosphorylation of ACC was higher in normal lean endometrium as compared to normal obese endometrium. This data indicates that AMPK signaling was activated in normal lean endometrium as compared to normal obese endometrium, although there was no difference in mTOR activation. Endometrial CAH showed low expression of phosphorylated ACC and overexpression of phosphorylated S6 indicating that AMPK signaling is not activated and mTOR signaling is increased. Surprisingly, phosphorylation of ACC was significantly increased in EC with concomitant overexpression of phosphorylated S6 indicating that both AMPK and mTOR signaling were activated.

Conclusions: Under conditions of obesity and we identified overexpression of AdipoR1 which is known in metabolic tissues to signal to AMPK. Upregulation of AdipoR1 occurs despite decreased serum levels of adiponectin in obesity and may indicate that receptor overexpression is compensatory to decreased levels of ligand. However, in the setting of EC we identified upregulation of AMPK signaling with low expression of AdipoR1 and upregulation of mTOR signaling. In addition, overexpression of APPL2, which is thought to inhibit AdipoR1-APPL1 complex formation did not effect activation of AMPK signaling in EC. Overall, these studies suggest that in EC there is a defect in the ability of AMPK to engage TSC2 and inhibit mTOR.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):A13.