Methods and compositions for treating and diagnosing diabetes and related diseases involving beta-TRP
Expression of beta-TRP is enriched in islet cells. Introduction of expression cassettes encoding beta-TRP into diabetic islet cells improved glucose-stimulated insulin production. Therefore, the invention provides methods of identifying beta-TRP modulators for treating diabetic individuals and introducing beta-TRP into islet cells
1. A method of identifying an agent that induces glucose-stimulated insulin production in an animal, the method comprising the steps of:
(i) contacting an agent to a functional cation channel polypeptide comprising an amino acid sequence at least 80% identical to SEQ ID NO:2, and wherein the polypeptide is expressed in a cell and the contacting step comprises contacting the agent to the cell;
(ii) selecting an agent that induces a differential change in electrical potential of the plasma membrane of the cell compared to the change in electrical potential of the plasma membrane of a cell contacted to the agent when:
the activity of the functional cation channel polypeptide is inhibited; or
the functional cation channel polypeptide is not expressed,
thereby indicating that the differential change is a result of contacting the agent to the polypeptide, and
(iii) determining if the agent selected in step (ii) enhances glucose-stimulated insulin secretion, thereby identifying an agent that induces glucose-stimulated insulin production in an animal.
2. The method of claim 1 , wherein the polypeptide comprises SEQ ID NO:2.
3. The method of claim 1 , wherein an agent is selected that enhances polypeptide activity and the activity of the polypeptide is determined by a step comprising measuring a change in calcium flux in the cell.
4. The method of claim 1 , wherein the membrane potential of the cell is measured be detecting a change in fluorescence of a dye whose fluorescence is dependent on cell depolarization and wherein the change in fluorescence is detected with a device sufficient for high throughput screening.
5. The method of claim 1 , wherein the cell is a pancreatic β cell.
6. The method of claim 1 , wherein the polypeptide is recombinantly expressed in the cell.
7. The method of claim 1 , wherein the polypeptide comprises an amino acid sequence at least 90% identical to SEQ ID NO:2.
8. The method of claim 1 , wherein the determining step is carried out in vitro.
9. The method of claim 1 , wherein the determining step is carried out in vivo.