Poster Presentation

Positive feedback activation of notch signal by obesity enhances colorectal tumorigenicity

Dr Chu Dake
The First Affiliated Hospital of Xi'an Jiaotong University

Abstract

Background

Colorectal cancer (CRC) is one of the most common malignancies worldwide. In recent years, the incidence rates of CRC are rapidly increasing in China, where has been experiencing a four-fold increase since the 1980s. Epidemiology investigation revealed that the steep rise of CRC incidence was significantly linked to increased obesity rates. Obese individuals are also confirmed to have increased risk for developing CRC and dying from this disease. However, the molecular interactions of obesity with CRC carcinogenesis and progression are still not well understood. The Notch signaling pathway is a fundamental and evolutionarily conserved intercellular communication pathway critical for many cellular processes including survival, proliferation and differentiation, as well as cancer carcinogenesis and development. It has also been recognized as a key player in regulating body energy metabolism. Therefore, we aimed to investigate the potential interaction and mechanism of Notch signal between obesity and CRC tumorigenesis.

Methods

In the present study, we randomly recruited 968 cases of clinical CRC specimens, 262 cases of colorectal intraepithelial neoplasia specimens and 185 cases of normal epithelium specimens from patients underwent surgery or colorectal endoscope in Xijing Hospital of Digestive Diseases, Fourth Military Medical University and the First Affiliated Hospital of Xi'an Jiaotong University. Tissue microarrays were constructed as standard procedure. Target protein expression was investigated by immunohistochemistry assay. Male and female C57BL/6J mice were randomly allocated into following groups respectively: mice fed with standard rodent chow; mice fed with high-fat diet (HFD, consisting of 60% kcal fat), mice fed with HFD treated with DBZ (a γ-secretase inhibitor pharmacologically inhibit Notch signaling), mice fed with HFD treated with DAPT (another γ-secretase inhibitor). Control mice were injected with equal volumes of DMSO. Energy intake and blood glucose of each mouse was measured. Potential differentially expressed proteins were screened by iTRAQ, and these identified proteins were then analyzed. Appropriate molecular and statistical investigations were utilized to verify the interaction mechanism.

Results

Among the recruited clinical specimens, Notch1 intracellular domain and DLL4 was up-regulated in overweight participants compared with normal-weight ones, no matter in CRC, intraepithelial neoplasia or normal epithelium specimens. In overweight participants, Notch1 was increased from normal epithelium, intraepithelial neoplasia to CRC. Whereas this trend was not significant in participants with normal weight. Obesity was identified at week 5 in mice fed with HFD, which began to lead to upregulation of DLL4 and consequent increased Notch1 activity in colorectal tissues. While mice treated with DBZ and DAPT were almost resistant to HFD-induced obesity then. After 10 weeks, Notch1 activity in mice fed with HFD was significantly up-regulated compared with those fed with standard rodent chow. And the body weight of mice treated with DBZ and DAPT was significant lower than those fed with HFD. In addition, glucose tolerance and insulin sensitivity were also ameliorated by DBZ and DAPT treatment, through a PP2A-SHIP2 dependent manner. HFD fed was found to alter colorectal morphology, enhance epithelial proliferation and activate inflammatory pathways, which can be ameliorated by DBZ or DAPT induced Notch inhibition. Notch signaling inhibition was also found to alleviate β-catenin activation in colorectal epithelial induced by HFD fed.

Conclusions

Notch signaling activation is linked to obesity in both nonmalignant participants and CRC patients. Obesity induced by HFD can increase Notch activity by DLL4-Notch1 pathway. While inhibition of Notch signaling can attenuate high fat diet-induced obesity by improving insulin resistance, suggesting an obesity-Notch positive feedback axis. In addition, Notch signaling inhibition can ameliorate morphology alternation, epithelial proliferation, inflammatory pathways and β-catenin activation induced by HFD. These results indicate that activation of Notch signaling by its positive feedback with obesity could be a molecular bridge that connecting obesity and CRC. Thus, Notch signaling would be a promising therapeutic target for obesity and CRC management.