Modulatory effects of a retinoid-related protein on intestinal endocrine cells

PROJECT SUMMARY The gastrointestinal tract is the largest endocrine organ in the human body. This is due to the presence of intestinal endocrine cells, a scarce yet important cell lineage within the intestinal epithelium. The hormones produced by these enteroendocrine cells (EECs) exert important metabolic actions including insulin secretion and appetite regulation among many others. Important examples are the insulinotropic incretin hormones glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1). EECs undergo differentiation and subspecialize into sub-types characterized by a main hormonal product. However, several factors have been reported to induce changes in EEC sub-types/hormonal profile, a phenomenon known as plasticity. In this context, retinol-binding protein 2 (RBP2) is an important protein for intracellular retinoid trafficking and metabolism. Although it has been described as circumscribed to the enterocytes in the small intestine, the candidate in this proposal has reported that RBP2 along with other retinoid related proteins are also present in EECs. Furthermore, ablation of RBP2 results in higher GIP expression and levels in mouse studies. Gene expression of other EEC hormones is also altered. The hypothesis underlying this proposal is that the absence of RBP2 affects EEC homeostasis and hormone expression/secretion by unique cellular pathways. To further understand RBP2 modulatory effects in these cells, the specific aims in this research proposal will: 1) determine the effects of RBP2 in the modulation of EEC proliferation, migration and survival and the mechanisms involved and 2) investigate RBP2 and retinoid actions in modulating EEC populations/sub-types and hormone secretion. These specific aims will be achieved by using specialized transgenic mouse models expressing Cre recombinase that will allow direct EEC characterizations in global and conditional Rbp2 knockout mice. Studies on specialized cell and organoid lines where the Rbp2 gene has been manipulated will be performed. Changes to EEC type, distribution, proliferation, and death will be measured using immunolabeling and qPCR. Besides unraveling the modulatory effects of RBP2 and retinoids on EECs, the proposed in vivo and in vitro experiments will provide novel physiological insights essential to better harness the therapeutic potential of these cells. The applicant, Dr Rossana Calderon, has designed a comprehensive 5-year training program for her career development into an independent translational researcher. Dr Calderon is an endocrinologist by training who will expand her knowledge in several areas including metabolic physiology, advanced cellular and molecular biology as well as acquire technical skills in functional genomics and 3D cell culture generation and manipulations. She will further refine her skills in scientific writing and research dissemination. This proposal will be carried out at Columbia University, an ideal environment with vast availability of resources to support her. Dr Calderon will count with the guidance of a multi-disciplinary mentorship team that will help her with their expertise to accomplish her goals during the development of her project and her career towards independence.