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Pancreatic β-cell Biology

The long-term goal of this research program is to determine the signaling pathways and molecular mechanisms involved in the regulation of β-cell mass. The objective of the research in this area is to delineate the molecular mechanisms, downstream signaling pathways and critical components involved in PI3K/Akt–dependent regulation of G1-S transition, proliferation and mass of β-cells.  Our central hypothesis is that the PI3K/Akt pathway regulates β-cell proliferation and mass by regulating protein levels, expression, cellular localization and activity of cell cycle components involved in G1 to S transition.  The rationale for the proposed research is that, once the understanding of downstream elements involved in PI3K/Akt induced β-cell proliferation is obtained, it is expected that it may become possible to identify new pharmacologic targets to treat and prevent type 2 diabetes, and increase the number and survival of β-cells for transplantation. The use of  transgenic mice expressing a constitutively active Akt in islet β-cells under the control of the insulin promoter (caAktTg) will allow us to make a very careful dissection of downstream events in vivo. To study  β-cell proliferation, we will examine the mechanisms involved in regulation of the cell cycle in pancreatic β-cells focusing in the role of cdk4 and its major regulators, p27, p21 and cyclin D. These studies will be performed in animal models and complemented with in vitro experiments in insulinoma cell lines. Another important area of investigation is the role of nutrient signaling pathways downstream of mTOR in β-cell growth. These experiments will be performed in animal models with gain and loss of function of the ribosomal S6 protein kinase (S6K). The role of these genes in apoptosis and in stress conditions such as fat feeding and transplantation will be also evaluated.

Pancreas Development

The overall goal of this area is to study the signaling pathways that regulate the differentiation program of pancreas. This work will attempt to increase the pool of pancreatic and endocrine progenitors by activating self-renewal and proliferation of progenitor cells. These studies could lead to identification of potential targets for novel therapeutic approaches that could increase the generation of β-cells in vivo and in vitro. These experiments will potentially produce cells that could be used in the transplantation model.

Islet Transplantation

One potential approach to improve the success and overcome the limited source of islets for transplantation is to increase the capacity of islets to proliferate and resist injury. The main goal in this area will be to study the mechanisms involved in regulation of transplanted β-cell mass and to generate β-cells that could be maintained in culture and will be resistant to injury after transplantation. To achieve this, we have generated tetracycline inducible transgenic animals with regulatable Akt activity. The response of islets from these mice to transplantation using different temporal patterns of Akt induction will be studied. This model will also be used as a phenotyping tool to evaluate the role of specific genes in the regulation of -cell mass, proliferation and apoptosis. The proposed studies will generate the information to develop therapeutic strategies aimed to protect the transplant and decrease the amount of tissue used for transplantation.

Novel Akt targets in pancreatic  β-cells

Identification of novel Akt targets in β-cells is significant because it will delineate potential downstream signaling events and components mediating proliferative responses that lack oncogenic potential. This is expected to have a positive impact for the design of pharmaceutical agents that will induce selectively β-cell proliferation without altering the risk of oncogenic transformation. To identify novel Akt targets, we are performing microarray experiments in islets and cell line with gain of Akt function.

Akt activating peptides

The Edmonton protocol for islet transplantation can successfully be used as therapeutic option for type 1 diabetics (2). Thus, a potential cure for diabetes is possible, given a sufficient supply of pancreas. Despite this remarkable success rate, the severe shortage of islets and post transplant functional islet graft failure limit islet transplantation for the vast majority of patients with diabetes. In spite of the widely appreciated magnitude of a shortage of transplantable islets and the vulnerability of islets during the isolation procedure, transport and transplant, there is a lack in the knowledge base that centers on how to protect and expand β-cells during this critical period. Developing pharmacological agents that expand β-cells in vivo and in vitro and resist injury could have major implications to improve the success and widespread use of islet transplantation as a cure for diabetes. The serine threonine kinase Akt is one of the promising molecules that have been identified as a potential target to induce proliferation and survival of β-cells. In addition, Akt has been shown to promote neovascularization, angiogenesis and induce resistance to oxidative stress and hypoxia, (3-11) critical regulators of islet engraftment. Moreover, exending-4 and HGF treatment, weak inducers of Akt signaling, have shown beneficial effects on rodent models of transplantation (12; 13). Similarly, adenoviral transfer of constitutively active Akt results in superior islet graft function requiring decreased number of transplanted islets, survival and prolonged remission (1). A major limitation of this approach for therapeutic benefit is the potential of oncogenic transformation when expressed constitutively. Pharmacological agents that activate Akt signaling will circumvent the limitations of constitutive activation of this signaling pathway by gene therapy and the weak induction of Akt signaling by growth factors and incretins. This is expected to have a positive impact for islet transplantation by: 1. Expansion of β-cells in vitro to potentially generate replenishable glucose responsive β-cells, 2. increase the yield and functionality of isolated islets 3. Protect islets during transport before transplantation 4. Enhance the probability to achieve euglycemia by improving islet engraftment and ameliorate failure of the graft. This is expected to positively affect treatment of human diabetes, because it would allow to overcome some of the obstacles for the widespread application of islet transplantation.