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OBJECTIVES - To comprehensively inventory the proteins that control the Gl/S cell cycle checkpoint in the human islet and compare them with those in the murine islet, to determine whether these might therapeutically enhance human β-cell replication, to determine whether human β-cell replication can be demonstrated in an in vivo model, and to enhance human β-cell function in vivo.
RESEARCH DESIGN AND METHODS- Thirty-four Gl/S regulatory proteins were examined in human islets. Effects of adenoviruses expressing cdk-6, cdk-4, and cyclin D1 on proliferation in human ß-cells were studied in both invitro and in vivo models.
RESULTS - Multiple differences between murine and human islets occur, most strikingly the presence of cdk-6 in human β-cells versus its low abundance in the murine islet. Cdk-6 and cyclin D^sub 1^ in vitro led to marked activation of retinoblastoma protein phosphorylation and cell cycle progression with no induction of cell death. Human islets transduced with cdk-6 and cyclin D^sub 1^ were transplanted into diabetic NOD-SCID mice and markedly outperformed native human islets in vivo, maintaining glucose control for the entire 6 weeks of the study.
CONCLUSIONS- The human G1/S proteome is described for the first time. Human islets are unlike their rodent counterparts in that they contain easily measurable cdk-6. Cdk-6 overexpression, alone or in combination with cyclin D^sub 1^, strikingly stimulates human β-cell replication, both in vitro as well as in vivo, without inducing cell death or loss of function. Using this model, human β-cell replication can be induced and studied in vivo. Diabetes 58:882-893, 2009
Recent reports demonstrate that human islet transplantation is technically feasible (1,2), that replication is a major means of maintaining β-cell numbers in rodents, and that all rodent β-cells are capable of replicating (3-5). In addition, in understanding the signaling pathways and growth factors that can induce β-cell replication continue to accrue (6-13). It is now clear that both type 1 and type 2 diabetes result from a decline in β-cell mass (14-16). Collectively, these observations underscore a need to understand, and to therapeutically exploit the molecular mechanisms underlying β-cell replication and regeneration. Abundant data in mice have demonstrated that the "Gl/S checkpoint," or the "Gl/S pathway" (supplemental Fig. 1, available in an online appendix at http://diabetes. diabetesjoumals.org/cgi/content/nill/db0cM)631/DCl), in the cell cycle...