Rapamycin impairs in vivo proliferation of islet beta-cells.
BACKGROUND
Progressive graft dysfunction is commonly observed in recipients of islet allografts treated with high doses of rapamycin. This study aimed at evaluating the effect of rapamycin on pancreatic islet cell proliferation in vivo.


METHODS
The murine pregnancy model was utilized, since a high rate of beta-cell proliferation occurs in a well-defined time frame. Rapamycin (0.2 mg/kg/day) was given to C57BL/6 mice for 5-7 days starting on day 7.5 of pregnancy. Cell proliferation was evaluated by detection of bromodeoxyuridine incorporation by immunohistochemistry.


RESULTS
Pregnancy led to increased beta-cell proliferation and islet yield with skewing in islet size distribution as well as higher pancreatic insulin content, when compared to that of nonpregnant females. These effects of pregnancy on beta-cell proliferation and mass were significantly blunted by rapamycin treatment. Minimal effect of rapamycin was observed on islet function both in vivo and in vitro. Rapamycin treatment of islets in vitro resulted in reduced p70s6k phosphorylation, which was paralleled by increased ERK1/2 phosphorylation.


CONCLUSIONS
Rapamycin treatment reduces the rate of beta-cell proliferation in vivo. This phenomenon may contribute to impair beta-cell renewal in transplanted patients and to the progressive dysfunction observed in islet graft recipients.
Zahr
Elsie
E
Diabetes Research Institute, University of Miami Leonard Miller School of Medicine, Miami, FL 33136, USA.
Molano
R Damaris
RD
Pileggi
Antonello
A
Ichii
Hirohito
H
Jose
Sergio San
SS
Bocca
Nicola
N
An
Weijun
W
Gonzalez-Quintana
Jorge
J
Fraker
Christopher
C
Ricordi
Camillo
C
Inverardi
Luca
L
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects*; D002469:Cell Separation / Q000379:methods; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007328:Insulin / Q000032:analysis; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D010179:Pancreas / Q000166:cytology / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*
D001786:Blood Glucose; D007166:Immunosuppressive Agents; D007328:Insulin; D011494:Protein Kinases; D020123:Sirolimus