Wnt signaling regulates pancreatic beta cell proliferation.
There is widespread interest in defining factors and mechanisms that stimulate proliferation of pancreatic islet cells. Wnt signaling is an important regulator of organ growth and cell fates, and genes encoding Wnt-signaling factors are expressed in the pancreas. However, it is unclear whether Wnt signaling regulates pancreatic islet proliferation and differentiation. Here we provide evidence that Wnt signaling stimulates islet beta cell proliferation. The addition of purified Wnt3a protein to cultured beta cells or islets promoted expression of Pitx2, a direct target of Wnt signaling, and Cyclin D2, an essential regulator of beta cell cycle progression, and led to increased beta cell proliferation in vitro. Conditional pancreatic beta cell expression of activated beta-catenin, a crucial Wnt signal transduction protein, produced similar phenotypes in vivo, leading to beta cell expansion, increased insulin production and serum levels, and enhanced glucose handling. Conditional beta cell expression of Axin, a potent negative regulator of Wnt signaling, led to reduced Pitx2 and Cyclin D2 expression by beta cells, resulting in reduced neonatal beta cell expansion and mass and impaired glucose tolerance. Thus, Wnt signaling is both necessary and sufficient for islet beta cell proliferation, and our study provides previously unrecognized evidence of a mechanism governing endocrine pancreas growth and function.
Rulifson
Ingrid C
IC
Department of Developmental Biology, Oncology Division, Stanford University, Stanford, CA 94305-5329, USA.
Karnik
Satyajit K
SK
Heiser
Patrick W
PW
ten Berge
Derk
D
Chen
Hainan
H
Gu
Xueying
X
Taketo
Makoto M
MM
Nusse
Roel
R
Hebrok
Matthias
M
Kim
Seung K
SK
D000818:Animals; D049109:Cell Proliferation; D056742:Cyclin D2; D016213:Cyclins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D050417:Insulin-Secreting Cells / Q000502:physiology*; D051379:Mice; D008817:Mice, Mutant Strains; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism*; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D000097577:Homeobox Protein PITX2
D056742:Cyclin D2; D016213:Cyclins; D018398:Homeodomain Proteins; D014157:Transcription Factors; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D000097577:Homeobox Protein PITX2; C486196:Ccnd2 protein, mouse; C555511:Wnt3a protein, mouse