Background/Purpose: MicroRNAs (miRNAs) are small noncoding RNAs which post-transcriptionally regulate gene expression. The miR-17-92 cluster is well characterized; its overexpression has been found to serve a major oncogenic role in the targeting and downregulation of tumor-suppressive pathways. Our previous work identified several members of the cluster with significantly higher levels in monocytes from patients with active Systemic Juvenile Idiopathic Arthritis (SJIA), a chronic inflammatory disease of childhood. Children with SJIA are at risk for life-threatening complications including Macrophage Activation Syndrome (MAS), an episode of overwhelming inflammation driven by IFNɤ. The objectives of this study were to characterize the regulation of the miR-17-92 cluster, define key targets, and determine the cluster’s role in inflammation and SJIA.

Methods: MiRNA levels were examined in THP-1 cells and primary human monocytes over the course of the monocyte to monocyte-derived macrophage (MDM) transition. MiR-17, miR-19a, and miR-20a were overexpressed in CD14+ monocytes for 2 days. Transcriptional profiles were performed using Ampliseq Transcriptome and the Ion Torrent S5 system and analyzed using AltAnalyze. Potential targets of the miR-17-92 cluster were then validated via dual-luciferase reporter assay.

Results: Neither blood monocytes nor fully differentiated THP-1 cells showed significant changes in miR-17-92 levels under standard polarization conditions, including M1, M2a, and M2b conditions, or IL-6 and IL-10 stimulation. The most sizable changes in miR-17-92 levels were found during monocyte to macrophage transition. Interestingly, primary monocytes showed increases in miR-17-92 levels within the first 48 hours of differentiation towards MDM similar to that seen in SJIA monocytes. In contrast, both PMA-differentiated THP1 cells and fully differentiated MDMs showed decreased miR-17-92 compared to undifferentiated monocytic cells. MiR-17-92 was overexpressed in primary monocytes to model these early transition changes. Genome-wide transcriptional profiling showed an upregulation of genes involved in Type I and II Interferon pathways, including response to interferon-alpha (adjusted p=2.71×10-12) and interferon-gamma (adjusted p=7.81×10-9). Analysis of genes significantly downregulated by miR-17, miR-19a, or miR-20a identified several putative and previously validated miR-17-92 cluster targets, including ATG5, IFRD2, JAK1, PPARG, and PTPN2 which have interferon-regulatory functions. Dual-luciferase reporter assay experiments support that these genes are direct targets of miR-17, miR-19a, and/or miR-20a.

Conclusion: MiR-17-92 demonstrates initial increase followed by subsequent decrease in human monocyte to macrophage differentiation. Overexpression of miR-17-92 upregulates Type I and II interferon pathway genes, and these miRNAs target multiple genes involved in regulating interferon signaling and/or inflammatory response. Taken together, miR-17-92 overexpression in SJIA monocytes may suggest a more differentiated phenotype, and contribute to IFNɤ sensitivity and risk for MAS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/changes-in-mir-17-92-cluster-expression-link-systemic-juvenile-idiopathic-arthritis-monocyte-to-macrophage-differentiation-and-interferon-regulation/