Thesis Format
Monograph
Degree
Master of Science
Program
Pathology and Laboratory Medicine
Supervisor
Dhanvantari, Savita
Abstract
In diabetes, excess glucagon secretion and insulin deficiency contribute to disease progression and hyperglycemia. Understanding the intracellular trafficking of glucagon in alpha cells can reveal potential therapeutic targets to alleviate hyperglycemia. Stathmin-2 (Stmn2) was previously found in the secretory granules of αTC1-6 cells and was hypothesized to direct glucagon to lysosomes for degradation. My work aims to investigate whether paracrine inhibition of glucagon secretion operates through the Stmn2-mediated lysosomal pathway.
I manipulated Stmn2 levels and applied paracrine treatment to observe glucagon and lysosome distribution using microscopy. I found that Stmn2 was essential in mediating paracrine redistribution of glucagon and lysosomes. Microscopy also showed strong colocalization and similar distribution of Stmn2 and lysosomes in both mouse and human alpha cells, while qPCR analysis showed that Stmn2 upregulated autophagy genes.
In summary, my thesis describes a potential regulator of glucagon secretion with therapeutic potential for hyperglucagonemia and hyperglycemia of diabetes.
Summary for Lay Audience
Diabetes is a condition of high blood sugar caused by abnormally high levels of a hormone called “glucagon”, vital in regulating physiological processes, such as sugar and fat metabolism. Cells that secrete hormones are called endocrine cells, and we wish to study the cellular mechanisms of how endocrine cells secrete hormones to maintain body balance and how this process can go wrong. Our research focuses on glucagon, secreted from endocrine alpha cells in the pancreas, to increase blood sugar levels. Inside the alpha cell, glucagon is contained in tiny specialized packages called “granules” which move to different destinations. Within these granules are important molecules that may affect whether glucagon is released or degraded for an optimal level, with one candidate being stathmin-2. We know these granules must be in particular locations within the cell for glucagon to be released or degraded in response to signals like other pancreatic hormones (insulin and somatostatin). However, how they get to these locations is unclear. This is an important question because it explains how abnormally high glucagon secretion can be controlled in diabetes. To find out how other pancreatic hormones can potentially direct glucagon towards sites of degradation(lysosomes) via stathmin-2, we used state-of-the-art technologies in advanced microscopy to visualize the movement of glucagon in mouse alpha cells. We found that insulin and somatostatin both moved glucagon towards degradation. In addition, Stmn2 and lysosomes overlapped strongly in their locations, suggesting a link between them. So, I followed up with a genetic analysis and found that stathmin-2 increased genes that produce more lysosomes. To determine stathmin-2’s role in trafficking glucagon, I removed Stmn2 from alpha cells and found that glucagon no longer moved towards lysosomes even in the presence of insulin and somatostatin, which confirms that trafficking of glucagon by other endocrine hormones requires Stmn2. Therefore, Stmn2 is a molecule that can control glucagon secretion and can be used to decrease high blood sugar in people with diabetes.
Recommended Citation
Chang, Nelson, "Paracrine factors regulate glucagon trafficking through the Stmn2-mediated lysosomal network" (2024). Electronic Thesis and Dissertation Repository. 10226.
https://ir.lib.uwo.ca/etd/10226
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License