FUNCTIONS OF PERK eIF2-alpha KINASE IN THE MOUSE PANCREATIC Beta-CELLS

Open Access
- Author:
- Zhang, Wei
- Graduate Program:
- Genetics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 07, 2007
- Committee Members:
- Douglas Cavener, Committee Member
Richard W Ordway, Committee Chair/Co-Chair
Pamela Hankey Giblin, Committee Member
Gong Chen, Committee Member - Keywords:
- ER stress
PERK
eIF2-alpha
Beta-cell
hypoplasia - Abstract:
- PERK eIF2-alpha kinase is an ER transmembrane protein sensing ER stress and [Ca2+]ER alteration under physiological or pharmacological condition. When large scale of eIF2-alpha is phosphorylated, global translation is repressed to alleviate ER stress; while moderate eIF2-alpha level may selectively induce a subgroup of gene expression. PERK is highly expressed in secretory cells such as pancreatic Beta-cells, which have elaborate network of ER and high protein load in the ER. Thus PERK is widely speculated to alleviate ER overload or stress and preserve exquisite ER function in those cells in particular. Genetic deletion of PERK in mice causes early onset of diabetes and other disorders, mirroring Wolcott Rallison Syndrome in human. Our lab demonstrated that Beta-cell hypoplasia and dysfunction contribute to hyperglycemia in PERK null mutant mice. Immunofluorescent assay revealed that disrupted proliferation and neogenesis rather than apoptosis cause Beta-cell hypoplasia, which disproves the popular perception that excessive Beta-cell death under ER stress being the main reason. Molecular evidence indicated that Beta-cell is trapped in G2 or late G1/S phase of cell cycle, while we failed to see the reduction of cyclin D and cdk4. Cyclin D and cdk4 was stated to be dispensable for Beta-cell duplication in the early developmental stage. The Proliferation defects since fetal stage, together with neogenesis degeneration illustrate impeded Beta-cell development. We speculate that maternal factors such as glucose may regulate Beta-cell proliferation and neogenesis via PERK, which will be exploited. For Beta-cell function, glucose stimulated insulin secretion is compromised in Perk -/- islets; Beta-cell marker, such as insulin, MafA and Pdx1 are downregulated. In addition, insulin and GLUT2 are accumulated in distended ER, suggesting general ER dysfunction. ER stress markers, Bip, spliced Xbp1 and Chop are not induced. Thus, via eIF2-alpha substrate, PERK either directly or indirectly affect the development, expansion and function of Beta-cells. The mechanism is still under investigation, however it is not along ER stress induced canonical unfold protein response (UPR) pathway. Study of tissue specific knockout mice, including pcPKO, enPKO, BetaPKO, exPKO mice, and Beta-PERK:PKO mice (Perk transgenic mice) suggest deteriorated Beta-cells are cell autonomous effect.