Dynamic changes in circulating microRNAs during oral glucose tolerance testing support their potential as diagnostic and monitoring biomarkers in cystic fibrosis-related diabetes

MicroRNAs are potential predictors and mediators of metabolic disease. Cystic fibrosis-related diabetes (CFRD) is the most common comorbidity in cystic fibrosis (CF). Here we aimed to investigate serum microRNAs in individuals with CF and differing glucose tolerance status. Specifically, we hypothesised that the circulating microRNA profile varies depending on glucose tolerance status and can change rapidly in response to a glucose challenge in individuals with CF.

We studied a cohort of 93 adult Danish participants with CF from four glucose tolerance categories: normal glucose tolerance, indeterminate glucose tolerance, impaired glucose tolerance and CFRD. In a cross-sectional design we sampled during an OGTT at baseline, 10 min, 30 min, 60 min and 180 min. A total serum microRNA sequencing was performed using baseline and 60 min samples from 12 selected individuals, three from each category. We identified 16 candidate microRNAs, and these were further investigated in the full cohort at all OGTT timepoints using a locked nucleic acid reverse transcription quantitative PCR assay. Three microRNAs were selected for in-depth assessment including impact on insulin secretion.

We identified four microRNAs differentially expressed at baseline (miR-34a-5p, miR-122-5p, miR-885-3 and miR-885-5p) and 12 with differential expression changes in response to glucose ingestion. Locked nucleic acid reverse transcription quantitative PCR assay validated the results of eight of these microRNAs and miR-34a-5p, miR-122-5p and miR-223-3p were selected for in-depth assessment. MiR-34a-5p and miR-122-5p were elevated at baseline in indeterminate glucose tolerance and CFRD and were associated with elevated liver damage markers. MiR-223-3p was differentially expressed during the OGTT, with different patterns depending on glucose tolerance state. Glucose-stimulated insulin secretion was increased after overexpression of miR-122-5p or miR-223-3p and cell viability was decreased after overexpression of miR-34a-5p in insulin-secreting cells.

MiR-34a-5p and miR-122-5p show potential as biomarkers for CFRD development and liver damage. MiR-122-5p and miR-223-3p could mitigate CFRD development by increasing the secretory capacity of the beta cells while miR-34a-5p might propagate CFRD development by reducing cell viability. We propose that circulating microRNAs can serve as biomarkers for CF complications. We further advocate that circulating microRNAs can play a part in the intricate crosstalk between metabolic organs and the endocrine pancreas in health and disease.

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