Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Wang, Rennian

Abstract

Diabetes is a prevalent metabolic disease characterized by impaired insulin secretion, action, or both. β1-integrin is a key receptor that regulates cell-ECM interactions and is important in maintaining beta-cell functions, including insulin secretion. However, little is reported about the relationship between β1-integrin and the exocytotic proteins involved in insulin secretion. This study examined the influence of ECM-mediated β1-integrin activation on exocytotic machinery involved in insulin secretion using rat insulinoma (INS-1) cells. Collagen IV (COL IV) promoted INS-1 cell adhesion, spreading, and insulin secretion. Additionally, these cells displayed changes in levels and localization of exocytotic proteins involved in insulin secretion. β1-integrin antibody blocking on cells cultured on COL IV showed significantly reduced adhesion, spreading, and insulin secretion along with reduced exocytotic protein levels. Additionally, b1-integrin blocking influenced the localization of exocytotic proteins at varied time points of glucose stimulation. These results indicate that specific ECM-integrin interactions are critical for proper beta-cell function.

Summary for Lay Audience

Diabetes is defined as chronic high blood sugar resulting from impaired insulin release, action, or both. Insulin is a hormone produced by beta-cells, a pancreatic cell type, which functions to decrease blood sugar. Islet transplants and bioartificial pancreas replacements are techniques under investigation for the treatment of diabetics. However, there are many shortcomings with these technologies which have been suggested to be, in part, due to the loss of the normal external cellular environment. The environment of a cell plays a major role in its function. Integrins are a family of proteins found on the outside of cells which communicate information about the environment to the cell and vice versa. β1-integrins comprise a major family of integrin receptors, and β1-integrin signalling in beta-cells is well known to be important for insulin secretion. However, it is not known how β1-integrin influences the machinery required for insulin secretion. This study aimed to determine how β1-integrin signaling influences the machinery involved in insulin secretion to enhance insulin secretion. The INS-1 rat beta-cell line was used as it expresses β1-integrin and secretes insulin similar to normal physiology.

INS-1 cells were examined following culture on different protein ligands of β1-integrin. Of the different proteins, collagen IV was found to provide the greatest enhancement of glucose stimulated insulin secretion (GSIS). We then looked specifically at the machinery involved in insulin secretion and found increases in both overall protein amounts and where they were located within cells. To validate that the changes we were observing were due to interactions between collagen IV and β1-integrin, β1-integrin was blocked prior to culturing on collagen IV. Cells that had β1-integrin blocked had decreased GSIS. Furthermore, these cells have alterations in the machinery involved in insulin secretion. Overall, this adds a novel method by which β1-integrin influences insulin secretion and underscores the importance of collagen IV-β1-integrin interactions in the proper functioning of beta-cells.

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