Huntingtin-Associated Protein 1 (Hap1) is Involved in Insulin Secretion From Pancreatic Beta Cells Pubblico
Cape, Austin David (2010)
Abstract
Abstract
Huntingtin-Associated Protein 1 (Hap1) is Involved in Insulin
Secretion From
Pancreatic Beta Cells
Hap1 was identified as the first binding partner with huntingtin,
the Huntington disease
(HD) protein. Studies have revealed Hap1 participates in
intracellular trafficking in
neuronal cells, which is adversely affected by the mutant version
of huntingtin (mHtt).
Recently, Hap1 was found in pancreatic beta (β) cells and
other endocrine cells that
secrete hormones via similar exocytic mechanisms. However, the role
of Hap1 in these
endocrine cells is unknown. We generated a mouse model selectively
depleted of Hap1 in
pancreatic β cells using the Cre-loxP genetic manipulation
system. These Hap1 knockout
(KO) mice displayed impairment of glucose tolerance without
affecting insulin
sensitivity. We validated that decreased Hap1, via its shRNA,
reduced glucose-stimulated
insulin release in Min6 cells, a well-studied pancreatic β
cell line. In addition, ELISA
measurement of insulin levels in blood confirmed Hap1 KO mice are
defective for insulin
release in response to glucose treatment. Electron microscopy
revealed decreased
numbers of insulin-containing vesicles at the docking sites in
β cell membranes of Hap1
KO mice. Glucose-stimulated insulin release also reduced the
phosphorylation of
pHap1A in both cell and mouse models. Moreover, this
glucose-induced
dephosphorylation caused more Hap1 to associate with kinesin light
chain and dynactin
p150, both of which are involved in microtubule-dependent
trafficking. These results
suggest Hap1-associated intracellular trafficking is important for
vesicular release of
insulin from pancreatic β cells, providing a potential target
for treating the impairment of
β cell insulin release seen in HD and other metabolic
disorders.
Table of Contents
Table of Contents
Chapter1: General Introduction
1.1 Huntingtin Associated Protein 1 (Hap1) 2
1.2 Hap1 Function In Molecular Trafficking 4
1.3 Neuroendocrine System 9
1.4 The Pancreas 10
1.5 b Cell Dysfunction in HD 14
1.6 Dissertation Goals 14
Chapter 2: Creation of Hap1 Conditional b Cell Knockout Mice
Introduction 21
Results 23
Discussion 26
Materials and Methods 28
Chapter 3: Hap1 Depletion Reduces Insulin Secretion From Pancreas
Introduction 40
Results 43
Discussion 45
Materials and Methods 48
Chapter 4: Biochemical and Mechanistic Studies of Hap1 in b Cells
Introduction 58
Results 60
Discussion 63
Materials and Methods 66
Chapter 5: Summary and Discussion
Summary of Results 78
Future Directions 79
References 85
About this Dissertation
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