A microRNA-24-to-secretagogin regulatory pathway mediates cholesterol-induced inhibition of insulin secretion

Hypercholesterolemia is a key factor leading to β-cell dysfunction, but its underlying mechanisms remain unclear. Secretagogin (Scgn), a Ca(2+) sensor protein that is expressed at high levels in the islets, has been shown to play a key role in regulating insulin secretion through effects on the soluble N-ethylmaleimide-sensitive factor attachment receptor protein complexes. However, further studies are required to determine whether Scgn plays a role in hypercholesterolemia-associated β-cell dysfunction. The present study investigated the involvement of a microRNA-24 (miR-24)-to-Scgn regulatory pathway in cholesterol-induced β-cell dysfunction. In the present study, MIN6 cells were treated with increasing concentrations of cholesterol and then, the cellular functions and changes in the miR-24-to-Scgn signal pathway were observed. Excessive uptake of cholesterol in MIN6 cells increased the expression of miR-24, resulting in a reduction in Sp1 expression by directly targeting its 3′ untranslated region. As a transcriptional activator of Scgn, downregulation of Sp1 decreased Scgn levels and subsequently decreased the phosphorylation of focal adhesion kinase and paxillin, which is regulated by Scgn. Therefore, the focal adhesions in insulin granules were impaired and insulin exocytosis was reduced. The present study concluded that a miR-24-to-Scgn pathway participates in the mechanism regulating cholesterol accumulation-induced β-cell dysfunction.