Enriched Alternative Splicing in Islets of Diabetes-Susceptible Mice

Abstract

Dysfunctional islets of Langerhans are a hallmark of type 2 diabetes (T2D). We hypothesize that differences in islet gene expression alternative splicing which can contribute to altered protein function also participate in islet dysfunction. RNA sequencing (RNAseq) data from islets of obese diabetes-resistant and diabetes-susceptible mice were analyzed for alternative splicing and its putative genetic and epigenetic modulators. We focused on the expression levels of chromatin modifiers and SNPs in regulatory sequences. We identified alternative splicing events in islets of diabetes-susceptible mice amongst others in genes linked to insulin secretion, endocytosis or ubiquitin-mediated proteolysis pathways. The expression pattern of 54 histones and chromatin modifiers, which may modulate splicing, were markedly downregulated in islets of diabetic animals. Furthermore, diabetes-susceptible mice carry SNPs in RNA-binding protein motifs and in splice sites potentially responsible for alternative splicing events. They also exhibit a larger exon skipping rate, e.g., in the diabetes gene Abcc8, which might affect protein function. Expression of the neuronal splicing factor Srrm4 which mediates inclusion of microexons in mRNA transcripts was markedly lower in islets of diabetes-prone compared to diabetes-resistant mice, correlating with a preferential skipping of SRRM4 target exons. The repression of Srrm4 expression is presumably mediated via a higher expression of miR-326-3p and miR-3547-3p in islets of diabetic mice. Thus, our study suggests that an altered splicing pattern in islets of diabetes-susceptible mice may contribute to an elevated T2D risk.

Control of pancreatic islet function and glucose homeostasis by a novel microexon program misregulated in type 2 diabetes

“…Secondly, exposure of human islets to mildly elevated glucose concentrations led to increased SRRM3 expression and IsletMIC inclusion, suggesting an adaptive mechanism to modulate insulin secretion in a setting that has the potential to enhance secretion. Finally, we also observed that IsletMICs are broadly down-regulated in islets from T2D patients, an effect also recently reported in a diabetic mouse model 27 . Altogether, these data suggest that changes in the activity of SRRM3 and its microexon targets affect islet function and glucose homeostasis, potentially contributing to T2D predisposition.…”

“…A similar pattern was also found in islets from diabetes-susceptible NZO mice following a diabetogenic stimulus (Extended Data Fig. 6E) 27 . Importantly, down-regulation of IsletMICs was unlikely to be due to beta cell loss, as we also observed it in individuals with impaired glucose tolerance (Extended Data Fig.…”

“…E) SRRM3 expression and IsletMIC inclusion in human islets from non-diabetic (ND) and type 2 diabetes (T2D) individuals from 30 ( n = 16-28). F) Srrm3 expression and IsletMIC inclusion in islets from B6-ob/ob (OBOB) and New Zealand Obese (NZO) mice from 31 ( n = 5). G) SRRM3 expression and IsletMIC inclusion in human islets from non-diabetic (ND) and impaired glucose tolerant (IGT) individuals from 28 ( n = 14-34).…”

RNA‐binding proteins in diabetic microangiopathy

“… 34 Associations have been observed between three RNA‐binding proteins and insulin resistance; therefore, increased type 2 diabetes risk. 35 , 36 Hence, the authors hypothesized an association between elevated RNA‐binding protein subunit (#38) levels and diabetic renal complications in T1DM patients with DN. 37 …”

“…RNA‐binding protein regulatory subunit 38, also known as Protein DJ‐1, is likely to be significantly more abundant in T1DM patients with DN due to specific mRNAs stabilization, a process by which cells may control protein expression levels 34 . Associations have been observed between three RNA‐binding proteins and insulin resistance; therefore, increased type 2 diabetes risk 35,36 . Hence, the authors hypothesized an association between elevated RNA‐binding protein subunit (#38) levels and diabetic renal complications in T1DM patients with DN 37 …”