Organogenesis and replication phenoypes in vivo suggest distinct effects of hypusinated and unhypusinated eIF5A

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: transgenic zebrafish and inducible, β cell-specific knockout mice fed a high fat diet. 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. 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. Taken together, our data provide evidence that DHPS deficiency and obesity conditions impair β cell function, inpart, 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. Zebrafish embryos were injected with control, dhps, or eif5a1/2 morpholinos; 24 hours post fertilization embryoes were processed for RNA and sent to sequencing.