The goal in the present proposal is to develop a physiologically-relevant 3D tissue system for type two diabetes mellitus (T2DM), a disease state hallmarked by insulin resistance. While adipose tissue is not the primary site for glucose disposal in humans, glucose uptake, secretion of adipokines, and lipolysis are all altered in T2DM. Increased lipolysis in insulin resistant adipose tissue can directly contribute to insulin resistance in liver and skeletal muscle through secretion of free fatty acids (FFAs) that activate pathways known to disrupt insulin signaling. Animal models have given great insight to both obesity and T2DM, but there are several important differences between human and rodent adipose tissue function that necessitate the development of a relevant in vitro model derived from human cells. 3D tissues are proposed to be essential for in vitro disease models (Bin Kim 2004;Sainz 2009;Marrero 2009;Bott 2010), but these studies have not focused on adipose tissue. It is not known if a 3D culture will better represent in vivo adipose tissue than 2D, but i is hypothesized that endothelial cells will polarize better in 3D than 2D, and that 3D is necessary for subsequent organization into lumens. The 3D tissue is also hypothesized have enhanced cell-extracellular matrix (ECM) interactions from a greater amount of ECM that may be deposited around the cells.
Aim 1 will investigate 2D and 3D co-cultures of human adipocytes with endothelial cells to establish baseline differences in structure and function of the co- cultures in the different geometries.
Aim 2 will add complexity to the model by incorporating human fibroblasts and monocytes, which may activate to M1 macrophages to create a pro-inflammatory environment like that found in obese adipose tissue. The cultures will be characterized by quantifying DNA, relative gene expression by qRT-PCR, secreted proteins by ELISAs, triglyceride accumulation and lipolysis using colorimetric assays, relative protein expression by Western blot, and energy use by glucose and lactate assays. Microscopy (light, fluorescence, confocal) will be used to examine cellular organization and adipocyte size and lipid accumulation. Functional responses to hormones will assess physiological responses.
Aim 3 will expose the 2D and 3D cultures developed in Aim 2 to insulin and FFAs, two stimuli elevated in obese type 2 diabetics, and proteins that alter ECM remodeling. The tissue responses to the T2DM stimuli and the altered remodeling conditions will be compared separately first and then together. Activation of insulin signaling pathways known to be affected by FFAs and inflammatory cytokines will also be examined using Western blot to determine how pathway activation may change in response to these stimuli and with geometry. The proposed work will thus advance understanding of adipose tissue engineering by developing a new 3D in vitro model for inflamed adipose tissue, directly comparing structure and function of 2D and 3D cultures, and by understanding how insulin signaling is impaired in response to stimuli found in obese type 2 diabetics and may change in 2D and 3D models and with altered matrix remodeling.
Obesity is a known risk factor for type 2 diabetes mellitus (T2DM), the most common form of diabetes. As the prevalence of T2DM is increasing due to obesity and the underlying mechanisms of insulin resistance are not well known, the proposed work seeks to develop a 3D tissue model for obese adipose tissue in humans to understand how excess nutritional and inflammatory signals lead to insulin resistance and to provide a physiologically- relevant platform that may be used to evaluate new therapies. This 3D tissue model approach is therefore anticipated to provide improved and novel insight into disease mechanisms, and thus treatment options, particularly when compared to currently used cell culture systems or animal models.
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