7971 The Role of PDX1 In Beta Cell Response To GLP1

Abstract

Abstract Disclosure: C. Bheeman: None. K. Vann: None. O. Astapova: None. Mature Onset of Diabetes of the Young Type 4 is a rare form of diabetes mellitus caused by a defect in the Pancreatic and Duodenal homeobox 1 (PDX-1) gene, which is predominantly expressed in β-cells and is an important factor in insulin gene transcription. We aim to study the impact that a PDX1 mutation (modeled after a patient) has on the beta cell response to GLP1. This was a 33-year-old nonobese man who presented to the clinic with new onset diabetes without ketosis. He was treated with insulin and metformin and his hemoglobin A1c decreased from 16% to 6.1% in six months. Other labs showed c-peptide of 8.9 ng/mL in setting of a blood glucose of 231 mg/dL, negative islet cell antibodies and glutamic acid antibodies. Of note, patient also had significant family history of diabetes. Due to high probability of MODY, genetic testing was obtained. He was found to have a heterozygous frameshift mutation in codons 228 -233 leading to a 17 base pair deletion in the PDX1 gene causing replacement of the 56 C- terminal amino acids with a shorter, missense C-terminal tail. Patient was started on dulaglutide 0.75 mg weekly but was hypoglycemic on the smallest dose so he was then switched to Semaglutide and has been maintained on less than 0.25 mg weekly. The clinical question we aim to answer was why was this patient so sensitive to GLP1 agonist activity. To study how the mutation affects response to GLP1 we are using mouse beta-TC-6 cell as they are insulin secreting, and regulated by glucose. The PDX-1 gene is highly conserved among species and the mouse PDX gene is comparable to the human gene. We used CRISPR-Cas9 to introduce the same 17 base-pair deletion into the mouse PDX-1 gene in beta-TC-6 cells. We first measured the glucose stimulated insulin secretion in control cells to examine first and second phases of insulin secretion, determining that the first phase of insulin occurs in twenty minutes and the second phase starts at about two hours. We also evaluated if these cells responded GLP-1 by increasing insulin secretion. We found that these cells respond to glucose and GLP1 in an additive manner. Insulin was measured by enzyme-linked immunosorbent assay (ELIZA). In the next phase of the experiment we aim to determine the effect of the GLP-1 in cell lines with the PDX1 deletion mutation as compared to control cell line. We will measure insulin secretion by ELISA in both mutant and the control cells treated with and without glucose and GLP1. We will measure insulin at 0 minutes and 30 minutes and insulin mRNA at 0 minutes and 6 hours to determine the first and second phases of insulin production. Our results will help guide personalized treatment for patients with MODY type 4 and improve our understanding of beta cell response to GLP1. Presentation: 6/2/2024