Pathobiology of Diabetic Gastroenteropathy

Diabetic gastroparesis is one of most common gastrointestinal complications of diabetes and is associated with significant morbidity. In previous work, we determined that hallmarks of the disease are loss of heme oxygenase 1 (HOI), increased reactive oxygen species (ROS) and subsequent loss of interstitial cells of Cajal (ICC). In preliminary experiments for this proposal, we have made the following key observations. (1) Induction of HOI in the stomach occurs primarily in M2 macrophages in the stomach wall. (2) Tissue from patients with diabetes without gastroparesis contains H01 expressing macrophages. HOI expression is very low in tissue from patients with diabetic gastroparesis. (3) Addition of advanced glycation end products (AGE) or ROS to cultures result in loss of ICC. (4) Induction of HOI reverses molecular and electrophysiological changes associated with delayed gastric emptying. (5) Tachygastria is present in diabetic mice with delayed gastric emptying and is reversed with hemin treatment. (6) Inhaled CO reverses delayed gastric emptying. (7) Flow cytometry on tissue from diabetic mice with and without delayed gastric emptying allows us to determine numbers of cell, including ICC and M1 and M2 macrophages in the stomach. (8) The pyrimidine rich region in the promoter of the hmox-1 gene predicts delayed gastric emptying. Our overall hypothesis is that, in diabetes, damage to ICC and development of delayed gastric emptying is a result of an alteration in the balance between ICC loss factors such as ROS and AGE and the cytoprotective effects of induction of HOI in M2 macrophages. Induction of HOI, or use of the products of HOI activity, after development of delayed gastric emptying will re-establish the balance between survival factors and loss factors and restore normal gastric emptying. The overall hypothesis will be tested in two specific aims. SA 1 will determine the role of HOI in preventing the development of diabetic gastroparesis and SA 2 will determine the mechanisms that regulate HOI activity in diabetes. We will utilize a 13C octanoic acid gastric emptying test, electrophysiology, immunohlstochemistry, molecular biology techniques, flow cytometry, FACS and ICC cultures to address the specific aims. Successful completion of the proposed studies has both basic significance and clinical impact. Our work will shed light on basic mechanisms that underlie the cellular and molecular events linked to the development of diabetic gastroparesis. Our proposed work also goes further towards understanding and testing strategies to reverse or prevent diabetic gastroparesis that will be directly used by Project 3 to guide clinical trials.