Studies on obesity-related dysfunction in insulin-target tissues : insulin receptor isoforms and intraocular in vivo liver imaging

Abstract

Obesity, caused by poor dietary habits and sedentary lifestyle, has brought on a global health crisis. This condition affects over one-third of adults and largely increases the risk of developing metabolic diseases, such as type 2 diabetes and steatotic liver disease. Insulin is a central hormone in regulating metabolism and insulin receptors are ubiquitously expressed. In mammals, the insulin receptor (IR) has two isoforms, IR-A and IR-B, which differ in structure and function and trigger different signalling pathways within the cell. The first half of this thesis focuses on studying the IR isoforms and their role in metabolic dysfunction. Insulin resistance has been associated with variations in IR isoform expression, however, the mechanisms behind tissue/cell type-specific changes in metabolic disease are poorly understood. Using mouse models of obesity/diabetes we report IR isoform expression patterns in different tissues. We further investigated a shift in IR isoform ratio in perigonadal adipose tissue, and found tissue remodeling and immune cells infiltration to be responsible, rather than a change in IR isoform expression in adipocytes. We also worked to identify novel and isoform-specific IR interaction partners, to understand more about the intracellular signalling triggered by the receptors. The second half of this thesis focusses on the liver, a key player in metabolic regulation. The liver is inaccessible for optical imaging and there is a lack of high-resolution non-invasive imaging techniques. Addressing this need, we developed a novel in vivo imaging platform to monitor liver function longitudinally at cellular resolution. We use the anterior chamber of the mouse eye as a transplantation site for liver spheroids, which engraft on the iris. The cornea acts as a natural body window and allows repeated imaging of the same cells over time. We show that the liver spheroids in the eye retain hepatocyte-specific and liver-like features and perform typical hepatic functions. Importantly, we show that in feeding graft-bearing animals an obesogenic diet, the intraocular grafts developed hepatosteatosis, thereby reporting on endogenous liver function. Thus, we foresee this new technology could provide a unique tool to study steatotic liver disease in both basic and pre-clinical settings.