SAT075 Beta Cells Adapt To Insulin Resistance Via Posttranslational Modification Of The Translation Factor eIF5A

Abstract

Abstract Disclosure: C. Anderson: None. A. Kulkarni: None. B. Maier: None. S.A. Tersey: None. R. Anderson: None. R.G. Mirmira: None. Prior to type 2 diabetes onset, β cells adapt to insulin resistance through compensation—a process that maintains insulin secretion and glucose homeostasis. Our lab has previously shown that β cell compensation requires the activity of deoxyhypusine synthase (DHPS), which post-translationally catalyzes the formation of the amino acid hypusine at Lys50 of eukaryotic initiation factor eIF5A. Although hypusinated eIF5A is required for β cell compensation, it is unclear if unhypusinated eIF5A limits this compensatory response. To identify the role of unhypusinated eIF5A, we used the following animal and cell-based models: RNAi knockdown and transgenic zebrafish; inducible, β cell-specific knockout mice fed a high fat diet; and cultured HEK-293 cells. Zebrafish embryos injected with morpholinos to reduce global DHPS (and accumulate unhypusinated eIF5A) showed stunted exocrine pancreas growth at 3 days post-fertilization. Although, those injected with anti-eIF5A morpholinos (to deplete all eIF5A) showed normal pancreas growth. Transgenic overexpression of a mutant eIF5A incapable of hypusination resulted in reduced pancreas size in zebrafish. Although a unique function of unhypusinated eIF5A has not yet been documented, these findings suggest that the presence of unhypusinated eIF5A may be the major driver of altered pancreas phenotypes. Similarly, following 4 weeks of high fat diet feeding and obesity, mice lacking total eIF5A in β cells had improved glucose tolerance compared to mice lacking DHPS in β cells, despite similar weight gain and insulin sensitivity. To clarify the molecular mechanisms behind the damaging role of unhypusinated eIF5A, we performed polyribosome profiling to measure translation in lysates from HEK-293 cells in which either DHPS or total eIF5A were depleted by RNAi. Whereas loss of total eIF5A slightly reduced mRNA translation elongation, loss of DHPS (and accumulation of unhypusinated eIF5A) reduced mRNA translation initiation. Further experiments in HEK-293 cells suggest that unhypusinated eIF5A increases levels of phosphorylated eIF2α (an inhibitor of global mRNA translation) by specifically interacting with the kinase GCN2. Taken together, our data provide evidence that DHPS deficiency and obesity conditions impair β cell function, in part, from the accumulation of the unhypusinated form of eIF5A. Our studies reveal a mechanism in which β cells respond to obesity by regulating mRNA translation through the balance between hypusinated and unhypusinated forms of eIF5A. Presentation: Saturday, June 17, 2023