SAT-159 Hltf-Deletion Causes Immune Destruction of Pancreatic Beta Cells during Development

Abstract

Immune destruction that causes the failure of β cell insulin secretion in type I diabetes (T1D) results from an imbalance in genetic, epigenetic and environmental factors that can begin in utero. A key unanswered question is how and why immune cells are targeted to specifically destroy insulin-producing pancreatic β cells while selectively excluding other islet-resident cells. One possibility is an epigenetic alteration in the transcriptome of developing β cells that causes activation/homing of immune cells. The helicase-like transcription factor (HLTF), a known target for epigenetic silencing in colorectal cancer and autoimmune diseases, is a likely candidate in this initiating event. The methylation status of HLTF DNA in serum and stools is a prognostic biomarker in colorectal cancer patients mainly because HLTF is a bona fide tumor suppressor in intestinal epithelium. The methylation status of HLTF DNA is a putative biomarker of pre-diabetes and undiagnosed diabetes. However, in order to authenticate the prognostic value of the methylation status of HLTF in diabetes, it is necessary to define the regulatory role of HLTF in pancreatic β cells. To this end we developed a global Hltf-deleted mouse model to recapitulate the effects of HLTF inactivation. Newborn Hltf-deleted mice and their littermate controls are bright pink in color and breathe freely suggesting normal lung and diaphragm function. Collectively, they display a sucking reflex immediately after birth, and milk is visible in their stomachs. However, after 6-8 hours, three of four Hltf-deleted pups are postprandial hypoglycemic. Seventy-five percent succumb to severe hypoglycemia not caused by elevated insulin. Serum insulin levels of these mice are negligible and their pancreatic β cells are devoid of insulin. We next developed β cell-specific Hltf-deleted mice to eliminate the potential effects of Hltf-deletion on other aspects of glucose homeostasis. These mice have the same phenotype as the global Hltf-deleted mice suggesting the phenotype is solely attributable to alterations in islet β cells. When the Hltf-deletion was bred into an immunodeficient background (no T, B and NK cells) to evaluate the potential involvement of the immune system, newborn Hltf-deleted mice are euglycemic and normoinsulinemic with survival rates equivalent to controls. RNA-seq differential expression analysis was used to test the hypothesis that Hltf deletion-induced alterations in the transcriptome of pancreatic β cells triggered an immune response that compromised glucose homeostasis and postpartum survival. Bioinformatics analysis showed Hltf-deletion activated the interleukin-33 (IL-33, pro-inflammatory cytokine) receptor (ST2) signaling pathway via increased IL33 transcription in β cells. Increased IL33 protein in β cells was confirmed by immunolabeling. Aspects of this mouse model phenocopy early-onset T1D in children.