Glial cell line-derived neurotrophic factor increases beta-cell mass and improves glucose tolerance.
OBJECTIVE
Pancreatic beta-cell mass increases in response to increased demand for insulin, but the factors involved are largely unknown. Glial cell line-derived neurotrophic factor (GDNF) is a growth factor that plays a role in the development and survival of the enteric nervous system. We investigated the role of GDNF in regulating beta-cell survival.


METHODS
Studies were performed using the beta-TC-6 pancreatic beta-cell line, isolated mouse pancreatic beta cells, and in vivo in transgenic mice that overexpress GDNF in pancreatic glia. GDNF receptor family alpha1 and c-Ret receptor expression were assessed by reverse-transcription polymerase chain reaction and immunofluorescence microscopy. Apoptosis was evaluated by assessing caspase-3 cleavage. Phosphoinositol-3-kinase signaling pathway was analyzed by Akt phosphorylation. Glucose homeostasis was assessed by performing intraperitoneal glucose tolerance tests. Insulin sensitivity was assessed using intraperitoneal injection of insulin.


RESULTS
We demonstrate the presence of receptors for GDNF, GFRalpha1, and c-Ret on beta cells. GDNF promoted beta-cell survival and proliferation and protected them from thapsigargin-induced apoptosis (P<.0001) in vitro. Exposure of beta-cells to GDNF also resulted in phosphorylation of Akt and GSK3beta. Transgenic mice that overexpress GDNF in glia exhibit increased beta-cell mass, proliferation, and insulin content. No differences in insulin sensitivity and c-peptide levels were noted. Compared with wild-type mice, GDNF-transgenic mice have significantly lower blood glucose levels and improved glucose tolerance (P<.01). GDNF-transgenic mice are resistant to streptozotocin-induced beta-cell loss (P<.001) and subsequent hyperglycemia.


CONCLUSIONS
We demonstrate that over expression of GDNF in pancreatic glia improves glucose tolerance and that GDNF may be a therapeutic target for improving beta-cell mass.
Mwangi
Simon
S
Division of Digestive Diseases, Emory University, Atlanta, Georgia, USA.
Anitha
Mallappa
M
Mallikarjun
Chaithanya
C
Ding
Xiaokun
X
Hara
Manami
M
Parsadanian
Alexander
A
Larsen
Christian P
CP
Thule
Peter
P
Sitaraman
Shanthi V
SV
Anania
Frank
F
Srinivasan
Shanthi
S
D000818:Animals; D017209:Apoptosis; D001786:Blood Glucose / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism*; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors / Q000235:genetics / Q000378:metabolism; D018149:Glucose Intolerance / Q000378:metabolism* / Q000473:pathology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007328:Insulin / Q000097:blood; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D015854:Up-Regulation
D001786:Blood Glucose; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D007328:Insulin; D019284:Thapsigargin; D051096:Proto-Oncogene Proteins c-ret; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3