Impact of alternative splicing in pancreatic islet cells in the development of type 2 diabetes

Objective: Alternative splicing (AS) plays a crucial role in diversifying the cellular protein landscape. Previous studies identified distinct AS pattern in pancreatic islet cells of diabetes-resistant B6-ob/ob compared to diabetes-prone New Zealand Obese (NZO) mice. Our objective is to investigate specific splice events to understand their potential impact on metabolic heath in mice predisposed to diabetes [1] [2] [3].

Methods: RNA-sequencing analysis was performed in pancreatic islets of male NZO and B6-ob/ob mice. Candidate genes were characterized by AVV-mediated overexpression of specific transcript variants in the MIN6 beta-cell line. Transfected cells were evaluated for glucose-stimulated insulin secretion.

Results: RNA sequencing analysis of primary pancreatic islets revealed 894 significant alternative splicing events (∆PSI>0.1) in 730 genes in NZO mice compared to B6-ob/ob mice. Different selection criteria were applied to identify promising candidates, including a ΔPSI>0.3, expression in human islets and protein functionality with the potential to affect beta-cell function. Vps39 and Slc7a2 were selected for further investigation. Vps39 (vacuole protein sorting 39; subunit of HOPS complex) encodes a protein crucial for the fusion of the late endosome and the autophagosome with the lysosome (van der Beek et al., 2019). Since lysosomes are involved in insulin granule degradation in beta cells (Müller et al., 2017) Vps39 might play an important role in this process. The alternatively spliced form of Vps39, which skips exon 3 (∆PSI>0.7), was overexpressed in MIN6 cells and tended to reduce glucose-stimulated insulin secretion in comparison to the full-length protein. Slc7a2 (solute carrier family 7 member 2) encodes a cationic amino acid transporter predominantly expressed in alpha and beta cells. The two relevant isoforms (CAT2A and CAT2B) of this transporter, which differ in alternative exon 7 (mutually exclusive exons), are differentially expressed in the two mouse strains and demonstrate markedly different substrate affinities (Closs et al., 1997). Both mouse strains show robust expression of the low-affinity amino acid transporter CAT2A. In contrast, CAT2B, characterized by its high substrate affinity, is significantly higher expressed in B6-ob/ob mice. After arginine stimulation of primary islets from B6-ob/ob and NZO mice, significant differences in insulin secretion were observed. Notably, NZO islets exhibited markedly higher insulin secretion to arginine stimulation, suggesting a pivotal role for amino acid transporters in islet cell function.

Conclusion: Our data suggest that of the splice product of Vps39 lacking exon 3 tends to result in diminished glucose-stimulated insulin secretion. Further experiments have to be performed to elucidate the effects of alternative splicing of Vps39 and Slc7a2 also on morphological changes and their cellular localization.

Publikationsverlauf

Artikel online veröffentlicht:
28. Mai 2025

• Literatur

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