Methods and compositions for treating and diagnosing diabetes and related diseases involving beta-TRP

Abstract

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 polypeptide comprising at least 20 contiguous amino acids of SEQ ID NO:2;    (ii) selecting an agent that binds to the polypeptide or enhances the expression or activity of the polypeptide, and    (iii) determining the effect of the selected agent on glucose-stimulated insulin secretion, thereby identifying an agent that induces glucose-stimulated insulin production in an animal.    
     
     
         2 . The method of  claim 1 , wherein step (ii) comprises selecting an agent that enhances the expression of the polypeptide.  
     
     
         3 . The method of claim I, wherein step (ii) comprises selecting an agent that enhances the activity of the polypeptide.  
     
     
         4 . The method of  claim 1 , wherein step (ii) comprises selecting an agent that binds to the polypeptide.  
     
     
         5 . The method of  claim 1 , wherein the polypeptide comprises SEQ ID NO:2.  
     
     
         6 . The method of  claim 1 , wherein the polypeptide is expressed in a cell and the contacting step comprises contacting the agent to the cell.  
     
     
         7 . The method of  claim 6 , 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.  
     
     
         8 . The method of  claim 6 , 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 membrane potential of the cell.  
     
     
         9 . The method of  claim 8 , 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.  
     
     
         10 . The method of  claim 6 , wherein the cell is an insulin-secreting cell.  
     
     
         11 . The method of  claim 6 , wherein the cell is a pancreatic β cell.  
     
     
         12 . The method of  claim 6 , wherein the polypeptide is recombinantly expressed in the cell.  
     
     
         13 . The method of  claim 6 , wherein the cell is a Chinese hamster ovary (CHO) cell.  
     
     
         14 . The method of  claim 1 , the method further comprising administering the agent to a diabetic animal and testing the animal for increased glucose-stimulated insulin secretion.  
     
     
         15 . The method of  claim 14 , wherein the animal is selected from a ZDF rat and a db/db mouse.  
     
     
         16 . The method of  claim 1 , wherein the polypeptide comprises at least 100 amino acids.  
     
     
         17 . The method of  claim 1 , wherein the polypeptide is at least 80% identical to SEQ ID NO:2.  
     
     
         18 . A method of inducing glucose-stimulated insulin production in an animal, the method comprising administering a therapeutically effective amount of the agent selected in  claim 1 .  
     
     
         19 . The method of  claim 18 , wherein the animal is a human.  
     
     
         20 . The method of  claim 19 , wherein the human has Type 2 diabetes.  
     
     
         21 . The method of  claim 19 , wherein the human is predisposed for Type 2 diabetes.  
     
     
         22 . A method of expressing βTRP in a pancreatic islet cell, the method comprising introducing into an islet cell a polynucleotide encoding a polypeptide comprising at least 20 contiguous amino acids of SEQ ID NO:2.  
     
     
         23 . The method of  claim 22 , wherein the islet cell is defective for glucose-stimulated insulin secretion.  
     
     
         24 . The method of  claim 22 , wherein the polynucleotide is introduced in vitro.  
     
     
         25 . The method of  claim 22 , wherein the polynucleotide is introduced in vivo.  
     
     
         26 . The method of  claim 22 , wherein the polypeptide comprises at least 100 amino acids.  
     
     
         27 . The method of  claim 22 , wherein the polypeptide is at least 80% identical to SEQ ID NO:2.  
     
     
         28 . The method of  claim 22 , wherein the polypeptide comprises SEQ ID NO:2.  
     
     
         29 . The method of  claim 22 , wherein the polynucleotide comprises SEQ ID NO:1.  
     
     
         30 . The method of  claim 22 , wherein the islet cell is a β cell.