Current therapies aimed at the treatment of diabetes primarily consist of administration of exogenous insulin to maintain euglycemia, which is not nearly as effective as endogenous beta cells in controlling glucose homeostasis. Therefore therapies aimed at replacing (via islet transplantation) or maintaining beta cell function (immunotherapies) are currently being explored as alternative treatment strategies. The transcription factor Pdx-1 has been implicated as being central in pancreatic formation and adult beta cell function. Mutations of Pdx-1 and/or decreased Pdx-1 protein levels have been associated with defective pancreatic development and diabetes. As a result a concerted effort has been made to fully understand Pdx-1 function and identify Pdx-1 binding partners. Recently, the MATH-BTB protein, Pcif1 (or SPOP) has been identified as a Pdx-1 interacting protein and subsequently shown to recruit Pdx-1 for ubiquitin-mediated degradation. Preliminary results demonstrate that decreasing Pcif1 levels (Pcif1[+/gt]) on a Pdx-1 heterozygous background increases Pdx1 protein expression and attenuates the pancreatic defects seen in Pdx1[+/-] mice. Further, Pcif1[gt/gt] animals display expanded Beta cell mass at the expense of other endocrine lineages and delayed acinar cell maturation. These results indicate Pcif1 modulates multiple targets in the pancreas. Thus we hypothesize that Pcif1 regulates the levels of key pancreatic transcription factors during development thereby allowing for the proper formation and maturation of both the exocrine and endocrine compartments.
Specific Aim 1 : To determine the role of Pcif1 in islet cell allocation and maturation. We will define the expression pattern of Pcif1 during pancreatic development and then examine the effect of loss of Pcif1 function on endocrine development by using a Pcif1 gene trap mouse. Islet cell formation will be analyzed to determine the mechanisms by which Pcif1 is affecting endocrine development. To complement the knockout studies, an inducible over-expression Pcif1 mouse model will be used to determine the impact of excess Pcif1 at the same critical time points in endocrine cell formation.
Specific Aim 2 :. To examine Pcif1 action on exocrine cell development. We wish to determine if Pcif1 is crucial in acinar formation and maturation. These studies will require the use of our Pcif1 null and Cre inducible Pcif1 mouse lines to define the contribution of Pcif1 function in the exocrine pancreas. Specifically, we will assess the role in acinar cell formation by quantifying cell numbers and the levels of proteins crucial for formation and function, including Ptf1a and amylase.
The elucidation of the role of Pcif1 in pancreas formation combined with its role in the adult can be used to better understand windows of clinical intervention to maintain beta cell mass in diabetic patients.