PANCREATIC EXPRESSION OF TRPA1, ITS ROLE IN INSULIN SECRETION AND ITS POSSIBLE EFFECT ON POSTPRANDIAL BLOOD GLUCOSE LEVELS

Author

Tsung-han Hsieh, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2013

Degree Name

Master of Science

Department

Pharmacology

First Advisor

Copello, Julio

Abstract

Approximately 25.8 million people, 8.3% of the population in the United States have diabetes mellitus (DM), which makes this disease one of the biggest public health problems facing this country. Type 2 diabetes (T2DM) is a heterogeneous disease characterized by variable degrees of insulin resistance, impaired insulin secretion, and increased glucose production. Currently, the insulin secretagogues known as sulfonylureas represent the major mainline drug class for long-term treatment. However, serious side effects, such as hypoglycemia and loss of potency with long-term use necessitate the development of novel insulin secretagogues. Transient receptor potential (TRP) channels have been reported to be involved in pancreatic insulin secretion. TRPA1 is a Ca2+-permeable nonselective cation channel. TRPA1 can be activated by molecules produced during oxidative glycolysis. TRPA1 may be an attractive candidate for drug development because of its involvement in the mechanism of insulin secretion. Previous studies have shown TRPA1 is expressed in rat pancreatic islets and that its activation promotes insulin release. This study was designed to determine if TRPA1 is expressed in mouse and human pancreatic β cells and whether it can promote insulin secretion. I demonstrated that TRPA1 is expressed in mouse and human pancreatic islets. I measured TRPA1-induced membrane currents using patch-clamp and used Ca2+ imaging to demonstrate that TRPA1 agonists induce Ca2+ influx in rat β cell-derived RINm5F cells. I confirmed that TRPA1 KO mice have no TRPA1 mRNA or protein in pancreatic β cells. I used isolated islet cells to demonstrate TRPA1-induced Ca2+ influx using Ca2+ imaging. By using pancreatic islets obtained from wild-type and TRPA1 KO mice, I determined that TRPA1 is important for insulin secretion. Finally, I determined that intraperitoneal administration of a TRPA1 agonist and antagonist affected blood glucose levels and plasma insulin levels in a manner consistent with the TRPA1 acting to increase insulin secretion. Furthermore, glucose tolerance was impaired in TRPA1 KO mice upon intraperitoneal glucose tolerance test (IPGTT) challenge compared to wild-type mice. In summary, I have shown TRPA1 is expressed not only in rat pancreatic islets but also in mouse and human pancreatic islets. I confirmed the localization of TRPA1 in pancreatic β cells. All of the experimental results are consistent with the concept that TRPA1 acts as to increase the insulin-secreting capacity of pancreatic β cells. According to my data, TRPA1 may play a role in promoting insulin secretion in patients with T2DM. Therefore, pharmacological activation of TRPA1 may be a novel therapeutic method for the treatment of diabetes.