Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Pathology and Laboratory Medicine

Supervisor

Wang, Rennian

Abstract

The receptor tyrosine kinases (RTKs) c-Kit and insulin receptor (IR) initiate similar intracellular signalling pathways in pancreatic beta cells to regulate beta cell proliferation, survival, and insulin secretion. Mice with a c-Kit overexpression specifically in beta cells (c-KitβTg) demonstrated improved beta cell proliferation and insulin secretion compared to control mice, and islets from c-KitβTg mice also demonstrated increased IR expression. The potential interplay between c-Kit and IR and their roles during ageing and metabolic stress are not currently known. This work reports the examination of c-Kit and IR signalling using in vitro and in vivo models to determine their effects on beta cell proliferation and insulin secretion.

To examine the effects of prolonged c-Kit signalling, c-KitβTg mice were analyzed at 60 weeks of age. The results from this section demonstrated that c-KitβTg mice developed impaired insulin release due to reduced soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) expression. Increased IR and phosphorylated IRS-1S612 and reduced insulin-induced Akt signalling were observed in islets from 60-week c-KitβTg mice. The effect of IR deficiency was examined by knocking down beta cell IR at 40 weeks in c-KitβTg mice and resulted in partial restoration of glucose tolerance. To determine the role of postnatal IR function on insulin secretion, a mouse model with beta cell-specific IR knockout (MIP-βIRKO) was generated and exposed to high-fat diet (HFD). MIP-βIRKO mice on HFD developed glucose intolerance due to reduced insulin secretion and SNARE expression. Islets from MIP-βIRKO HFD mice also demonstrated reduced Akt phosphorylation and GLUT2 levels. In vitro examination of INS-1 832/13 cells showed that co-stimulation of c-Kit and IR with ligands stem cell factor (SCF) and insulin, respectively, did not lead to synergistic intracellular signalling or proliferation when compared to single ligand treatments. This may be due to negative feedback from IRS-1S612 phosphorylation, which can be inhibited with rapamycin.

In summary, this work presents a regulatory role for altered c-Kit and IR activity in maintaining beta cell intracellular signalling and insulin release. Results from these studies may be useful when considering RTK-based treatments to optimize islet function.

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