Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Pathology

Supervisor

Dr. Rennian Wang

Abstract

The pancreas is a glandular organ composed of endocrine and exocrine compartments. Integrins are cell adhesion molecules that connect cells to the extracellular matrix (ECM). Integrins modulate a variety of cellular effects, yet their mechanism of action in the developed pancreas is not well understood. Fibrin is a provisional ECM protein that contains ligands for integrin receptors. Fibrin is capable of supporting islet health, but it is unclear how fibrin exerts its effects. The objective of this thesis is to understand the role of integrin receptors on in vivo pancreatic cell function, survival, and proliferation. In addition, this thesis investigates how fibrin promotes pancreatic cell maturation, function, and survival in culture. Pancreatic tissues from transgenic adult mice lacking β1 integrin were harvested at 4 and 7 weeks post-induction. The rat insulinoma cell line, INS-1, and human fetal-islet epithelial cells were cultured on tissue culture polystyrene plates or with fibrin in two or three dimensions for up to 4 weeks, then collected for analyses.

β1 integrin knockout mice demonstrated significant glucose intolerance and reduced glucose-stimulated insulin secretion (GSIS). β1 integrin knockout mice also had reduced beta cell expression of Pdx-1 and Nkx6.1, as well as reduced acinar cell expression of amylase, lipase and Reg-II. Alternatively, to investigate the effects of supplementing pancreatic cells with ECM in culture, INS-1 cells and human fetal islet-epithelial clusters were cultured with fibrin. Culturing these cells with fibrin led to significantly increased integrin αvβ3 expression. INS-1 cells cultured with fibrin had significantly increased GSIS and significantly reduced caspase-3 cleavage, which was reversed by antibody blockade of integrin αvβ3. Human fetal islet-epithelial cells cultured with fibrin had increased PDX-1 expression, which was mediated, in part, by the mTOR/p70s6k pathway. Transplantation of fibrin-mixed human fetal-islet epithelial cells led to maintained differentiation and improved graft vascularization. Integrins are essential for maintaining glucose homeostasis and acinar cell function. Furthermore, culturing pancreatic cells with fibrin leads to increased integrin expression and improved cell maturation, function, survival and proliferation. Understanding how integrins modulate the pancreas and associated islet cells will lead to more effective protocols for the culture of isolated islets.

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