Loss of insulin-producing β-cells is central to the development of Type 1 diabetes (T1D). Currently, we lack diagnostic tools to quantitate this β-cell loss.
Non-protein coding RNAs called microRNAs (miRNAs/miRs) play an important role in islet development and function. Recent detection of miRNAs in peripheral circulation, has renewed interest in microRNA biomarkers of diabetes. Comparably, circulating insulin cell-free (cf)DNA has been proposed as a direct biomarker of β-cell death. DNA methylation studies have identified specific sites within DNA that are unmethylated in β-cells but methylated in other cell types, thus providing a handle to discriminate between cfDNA from β-/non-β-cells.
Previous research carried out in the Hardikar lab identified a signature of 20 miRNAs (the ‘RAPID’ signature) with potential as a biomarker of β-cell death. The RAPID signature was revised to accommodate other microRNAs finally constituting a panel of 50 microRNAs (PREDICT T1D panel). An analysis of these 50 miRNAs, as well as insulin cfDNA in serum/plasma from individuals before, during and after clinical diagnosis of T1D is presented.
Human islet cell death assays using sodium nitroprusside exposure identified a subset of 27 miRNAs and insulin cfDNA associated with islet cell stress/death. Non-obese diabetic mice (N=32) were found to have elevated candidate miRNAs prior to immune infiltration and glycaemic dysfunction. This trend was also noted in the human progression to T1D; 26 miRNAs were elevated in (N=19) high-risk individuals and those at diagnosis (N=199) but decreased within 6-weeks after diagnosis. Furthermore, candidate miRNAs exhibited differential abundance with disease duration, residual C-peptide, and microvascular complications in 180 subjects with prolonged T1D. At diagnosis, miRNAs and cfDNA associated with GAD
autoantibody titres (N=167 P-values range from 0.044 to <0.0001) and HbA1c levels (N=187, P-values range from 0.047 to 0.00095).
Such biomarkers may inform medical researchers as to how to predict the development of T1D, monitor response to interventions such as islet transplantation, vaccines & drugs aiming to retard β-cell loss. In basic research, such an assay may help to select treatments to block β-cell death and guide the development of new treatments to lessen the burden of diabetes.