Altering β-cell number through stable alteration of miR-21 and miR-34a expression

Aim: An insufficient functional beta-cell mass is a prerequisite to develop diabetes. Thus, means to protect or restore beta-cell mass are important goals in diabetes research. Inflammation and proinflammatory cytokines play important roles in beta-cell dysfunction and death, and recent data show that 2 miRNAs, miR-21 and miR-34a, may be involved in mediating cytokine-induced beta-cell dysfunction. Therefore, manipulation of miR-21 and miR-34a levels may potentially be beneficial to b cells. To study the effect of long-term alterations of miR-21 or miR-34a levels upon net beta-cell number, we stably over-expressed miR-21 and knocked down miR-34a, and investigated essential cellular processes. Materials and Methods: miRNA expression was manipulated using Lentiviral transduction of the beta-cell line INS-1. Stable cell lines were generated, and cell death, NO synthesis, proliferation, and total cell number were monitored in the absence or presence of cytokines. Results: Overexpression of miR-21 decreased net beta-cell number in the absence of cytokines, and increased apoptosis and NO synthesis in the absence and presence of cytokines. Proliferation was increased upon miR-21 overexpression. Knockdown of miR-34a increased net beta-cell number in the absence of cytokines, and reduced apoptosis and NO synthesis in the absence and presence of cytokines. Proliferation was decreased upon miR-34a knockdown. Conclusion: As overexpression of miR-21 increased proliferation, but also apoptosis and NO synthesis, the potential of miR-21 as a therapeutic agent to increase beta-cell survival is doubtful. Knockdown of miR-34a slightly decreased proliferation, but as apoptosis and NO synthesis were highly reduced, miR-34a may be further investigated as a therapeutic target to reduce beta-cell death and dysfunction.