MicroRNA-411 and Its 5′-IsomiR Have Distinct Targets and Functions and Are Differentially Regulated in the Vasculature under Ischemia

Abstract

MicroRNAs are posttranscriptional regulators of gene expression. As microRNAs can target many genes simultaneously, microRNAs can regulate complex multifactorial processes, including post-ischemic neovascularization, a major recovery pathway in cardiovascular disease. MicroRNAs select their target mRNAs via full complementary binding with their seed sequence, i.e., nucleotides 2-8 from the 5 0 end of a microRNA. The exact sequence of a mature microRNA, and thus of its 5 0 and 3 0 ends, is determined by two sequential cleavage steps of microRNA precursors, Drosha/DGCR8 and Dicer. When these cleavage steps result in nucleotide switches at the 5 0 end, forming a so-called 5 0 -isomiR, this results in a shift in the mature microRNA's seed sequence. The role of 5 0 -isomiRs in cardiovascular diseases is still unknown. Here, we characterize the expression and function of the 5 0 -isomiR of miR-411 (ISO-miR-411). ISO-miR-411 is abundantly expressed in human primary vascular cells. ISO-miR-411 has a different "targetome" from WT-miR-411, with only minor overlap. The ISO-miR-411/WT-miR-411 ratio is downregulated under acute ischemia, both in cells and a murine ischemia model, but is upregulated instead in chronically ischemic human blood vessels. ISO-miR-411 negatively influences vascular cell migration, whereas WT-miR-411 does not. Our data demonstrate that isomiR formation is a functional pathway that is actively regulated during ischemia.

An Emerging Role for isomiRs and the microRNA Epitranscriptome in Neovascularization

“…We demonstrated that the 5 -isomiR has a different targetome than the canonical miR-411-5p and inhibits translation of, among others, the pro-angiogenic Angiopoietin-1. Finally, we showed that the 5 -isomiR decreases vascular cell migration while the canonical miR-411-5p does not [99]. Combined these data show that isomiR formation is indeed a functional pathway, which is actively regulated during ischemia, with direct implications for neovascularization.…”

“…MicroRNAs have already been established as multifactorial regulators of both angiogenesis and arteriogenesis [7][8][9], and therefore this additional regulatory layer may provide new options for therapeutic neovascularization. The therapeutic potential of both isomiRs and the microRNA epitranscriptome is highlighted by the findings that 5 -isomiR formation of miR-411-5p and A-to-I editing of miR-487b-3p are actively regulated in response to ischemia in vivo, resulting in novel microRNAs with anti-or pro-angiogenic properties, respectively [99,123]. Therefore, altered microRNAs could provide novel targets for therapeutic inhibition or overexpression to stimulate neovascularization after ischemic CVD.…”

“…We have recently performed a focused study on the 5 -isomiR of miR-411-5p from the vasoactive 14q32 microRNA cluster in order to collect direct evidence that isomiRs are actively regulated during ischemia-induced neovascularization [99]. We found that miR-411 s isomiR expression profile was tissue-specific and that canonical miR-411-5p was less abundant than its 5 -isomiR in human vascular ECs, fibroblasts and in whole human venous tissue.…”

“…We found that miR-411 s isomiR expression profile was tissue-specific and that canonical miR-411-5p was less abundant than its 5 -isomiR in human vascular ECs, fibroblasts and in whole human venous tissue. We discovered that the expression of the 5 -isomiR is decreased relative to canonical miR-411-5p expression in response to acute ischemia, both in cells and in a murine model for effective neovascularization after ischemia [99]. Strikingly, the relative 5 -isomiR expression was upregulated instead in ischemic veins from patients with critical limb ischemia due to peripheral artery disease (PAD).…”

“…Table 1 presents a summary of the key studies that demonstrate the prevalence and importance of isomiRs. • Independent regulation of miR-411-5p and its 5 -isomiR in response to ischemia [99] HUVECs: human umbilical vein endothelial cells.…”