Protection of beta cells against pro-inflammatory cytokine stress by the GDF15-ERBB2 signaling

Aim/hypothesis Growth/differentiation factor 15 (GDF15) is a therapeutic target for a variety of metabolic diseases, including type 1 diabetes (T1D). However, the nausea caused by GDF15 is a challenging point for therapeutic development. In addition, it is unknown why the endogenous GDF15 fails to protect from T1D development. Here, we investigate the GDF15 signaling in pancreatic islets towards opening possibilities for therapeutic targeting in beta cells and to understand why this protection fails to occur naturally. Methods GDF15 signaling in islets was determined by proximity-ligation assay, untargeted proteomics, pathway analysis, and treatment of cells with specific inhibitors. To determine if GDF15 levels would increase prior to disease onset, plasma levels of GDF15 were measured in a longitudinal prospective study of children during T1D development (n=132 cases vs. n=40 controls) and in children with islet autoimmunity but normoglycemia (n=47 cases vs. n=40 controls) using targeted mass spectrometry. We also investigated the regulation of GDF15 production in islets by fluorescence microscopy and western blot analysis. Results The proximity-ligation assay identified ERBB2 as the GDF15 receptor in islets, which was confirmed using its specific antagonist, tucatinib. The untargeted proteomics analysis and caspase assay showed that ERBB2 activation by GDF15 reduces beta cell apoptosis by downregulating caspase 8. In plasma, GDF15 levels were higher (p=0.0024) during T1D development compared to controls, but not in islet autoimmunity with normoglycemia. However, in the pancreatic islets GDF15 was depleted via sequestration of its mRNA into stress granules, resulting in translation halting. Conclusions/interpretation GDF15 protects against T1D via ERBB2-mediated decrease of caspase 8 expression in pancreatic islets. Circulating levels of GDF15 increases pre-T1D onset, which is insufficient to promote protection due to its localized depletion in the islets. These findings open opportunities for targeting GDF15 downstream signaling for pancreatic beta-cell protection in T1D and help to explain the lack of natural protection by the endogenous protein. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by the National Institutes of Health, the National Institute of Diabetes and Digestive and Kidney Diseases grants U01 DK127505 (to E.S.N.), U01 DK127786 (to R.G.M, C.E.M., D.L.E, B.J.M.W.R and T.O.M.), R01 DK105588 (to R.G.M.) R01 DK126444 (to D.L.E.), R01 DK32493 (to M.R.), and R01 DK093954 (to C.E.M); VA Merit Award I01BX001733 (to C.E.M.). E.S.N. was also supported by the Human Islet Research Network Catalyst Award. F.S. was supported by JDRF (3-PDF-20016-199-A-N and JDRF 5-CDA-2022-1176-A-N). F.S. and J.L. were supported by NIH/NIDDK dkNET (U24 DK097771). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Protocols approved by the Colorado Multiple Institutional Review Board and written informed consent was obtained from donors or their parents. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data is available at Open Science Framework and Massive databases.