The role of the adipose tissue microenvironment in kidney cancer

Abstract

Obesity increases the risk of tumourigenesis, but paradoxically may predict better prognosis after cancer has been diagnosed. There is a general lack of understanding of interactions between cancer cells and adipose tissue. Obesity is characterised by activated endoplasmic reticulum (ER) stress and increased infiltration of macrophages in the adipose tissue. Little is known about the connection between the ER stress and infiltration of macrophages in the adipose tissue. Additionally, the impact of each characteristic on the biology of cancer cells is unclear. This PhD project attempted to define the adipose tissue microenvironment in the setting of cancer, in particular, kidney cancer. The thesis adds knowledge that helps to define the heterogeneous adipose tissue microenvironment and its functions in cancer development.The thesis is presented as a literature review (Chapter 1) followed by four original research sections (Chapters 2-5) that have, in some cases, been published (Chapter 2) or submitted (Chapters 3 and 4).The literature review (Chapter 1) will initially introduce the epidemiology, pathophysiology and prognostic factors for kidney cancer, followed by a summary of the advances in biomarker discovery in renal cell carcinoma (RCC). The literature review then introduces the structure, function and signaling pathways of the ER, followed by a discussion of the involvement of ER stress in cancer.The crosstalk between obesity, cancer and ER stress is also discussed. Finally, the role of macrophages in the tumour microenvironment is summarised.Chapter 2 is an immunohistochemistry-based retrospective cross-sectional study. Software-assisted quantification of staining intensity and proportion of positive pixels was applied to measure expression of glucose-regulated-protein-78/GRP78 (an ER stress marker) in archived specimens of renal tumour tissues (n=114), adjacent non-neoplastic renal tissues (n=68), and perinephric adipose tissues (n=60) in participants diagnosed with clear cell RCC (ccRCC), the commonest subtype of the RCC. Results demonstrated that GRP78 was not an optimal risk stratification marker for ccRCC.However, upregulated GRP78 in perinephric adipose tissue may be linked with a lower chance of metastasis.Chapter 3 introduces a liquid-overlay based method to generate reproducible and functional mature adipocyte spheroids using human perinephric adipose tissue-derived mesenchymal stem cells and the murine 3T3-L1 cell line. The established adipocyte spheroids were responsive to the ER stress activator, tunicamycin. and could secrete adiponectin, monocyte chemoattractant protein-1 (MCP-1) and interleukin/IL-8. Hence, the three-dimensional culture platform was able to serve as an adipose tissue microenvironment that could be applied in in vitro experiments.ii In Chapter 4, macrophage behaviour in the adipose tissue microenvironment was investigated using the 3D culture platform introduced in Chapter 3. Co-culture experiments were performed to measure the polarisation, migration and invasion of murine an...