High-throughput analysis of ANRIL circRNA isoforms in human pancreatic islets

Abstract

The antisense non-coding RNA in the INK locus (ANRIL) is a hotspot for genetic variants associated with cardiometabolic disease. We recently found increased ANRIL abundance in human pancreatic islets from donors with certain Type II Diabetes (T2D) risk-SNPs, including a T2D risk-SNP located within ANRIL exon 2 associated with beta cell proliferation. Recent studies have found that expression of circular species of ANRIL is linked to the regulation of cardiovascular phenotypes. Less is known about how the abundance of circular ANRIL may influence T2D phenotypes. Herein, we sequence circular RNA in pancreatic islets to characterize circular isoforms of ANRIL. We identify several consistently expressed circular ANRIL isoforms whose expression is correlated across dozens of individuals and characterize ANRIL splice sites that are commonly involved in back-splicing. We find that samples with the T2D risk allele in ANRIL exon 2 had higher ratios of circular to linear ANRIL compared to protective-allele carriers, and that higher circular:linear ANRIL was associated with decreased beta cell proliferation. Our study points to a combined involvement of both linear and circular ANRIL species in T2D phenotypes and opens the door for future studies of the molecular mechanisms by which ANRIL impacts cellular function in pancreatic islets.

The Long Non-Coding RNA ANRIL in Cancers

“…Although their association with cancer remains somewhat poorly assessed, it is conceivable to hypothesize that these circular forms may exert a tumor-promoting influence akin to linear isoforms. This may contrast with findings in CVD and T2D, where linear and circular forms of ANRIL have been described to exhibit opposing activities [24,92].…”

Deletion of the Murine Ortholog of the Human 9p21.3 Locus Leads to Insulin Resistance and Obesity in Hypercholesterolemic Mice

“…However, it seems the functionality of the islets was not affected as there were no differences in the insulin secretion in response to glucose. In human studies, the carriers of a T2D risk allele rs564398 (T) in ANRIL exon 2 had elevated ratios of circular to linear ANRIL, which was associated with decreased β-cell proliferation [ 21 ]. It is known that aging alone reduces β-cell proliferation in both humans and mice, and obesity and pre-diabetic conditions may also alter β-cell proliferation and volume; this would be in line with the obese and insulin-resistant phenotype in the Chr4 Δ70/Δ70 mice [ 54 ].…”

“…The VITA cohort study also revealed that elevated circulating levels of ANRIL may predict later onset of T2D [ 20 ]. In addition, a T2D risk SNP in ANRIL exon 2 was reported to associate with elevated ratios of circular to linear isoforms of ANRIL and was found to reduce pancreatic β-cell proliferation [ 21 ]. The genes neighboring ANRIL have also been reported to have a role in metabolic regulation, as CDKN2B is highly expressed in subcutaneous adipose tissue (SAT), with the levels positively correlating with obesity and hepatic steatosis in 9p21.3 risk allele carriers [ 22 ].…”