mir-124-5p Regulates Phagocytosis of Human Macrophages by Targeting the Actin Cytoskeleton via the ARP2/3 Complex

Abstract

Phagocytosis is a cellular process crucial for recognition and removal of apoptotic cells and foreign particles, subsequently initiating appropriate immune responses. The process of phagocytosis is highly complex and involves major rearrangements of the cytoskeleton. Due to its complexity and importance for tissue homoeostasis and immune responses, it is tightly regulated. Over the last decade, microRNAs (miRNAs) have emerged as important regulators of biological pathways including the immune response by fine-tuning expression of gene regulatory networks. In order to identify miRNAs implicated in the regulation of phagocytosis, a systematic screening of all currently known, human miRNAs was performed using THP-1 macrophage-like cells and serum-opsonized latex beads. Of the total of 2,566 miRNAs analyzed, several led to significant changes in phagocytosis. Among these, we validated miR-124-5p as a novel regulator of phagocytosis. Transfection with miR-124-5p mimics reduced the number of phagocytic cells as well as the phagocytic activity of phorbol-12-myristate-13-acetate (PMA)-activated THP-1 cells and ex vivo differentiated primary human macrophages. In silico analysis suggested that miR-124-5p targets genes involved in regulation of the actin cytoskeleton. Transcriptional analyses revealed that expression of genes encoding for several subunits of the ARP2/3 complex, a crucial regulator of actin polymerization, is reduced upon transfection of cells with miR-124-5p. Further in silico analyses identified potential binding motifs for miR-124-5p in the mRNAs of these genes. Luciferase reporter assays using these binding motifs indicate that at least two of the genes (ARPC3 and ARPC4) are direct targets of miR-124-5p. Moreover, ARPC3 and ARPC4 protein levels were significantly reduced following miR-124-5p transfection. Collectively, the presented results suggest that miR-124-5p regulates phagocytosis in human macrophages by directly targeting expression of components of the ARP2/3 complex.

Essential omega-3 fatty acids tune microglial phagocytosis of synaptic elements in the mouse developing brain

“…Additionally, recent work found that DHA decreases microglia phagocytic activity of myelin debris in the spinal cord after injury through mir-124 68 , a non-coding nucleotide involved in synaptic plasticity. In macrophages, mir-124 has been shown to regulate actin-related protein 2/3 (ARP2/3), which is involved in the formation of the phagocytic cup 74 . This is in line with results showing that DHA reduced LPS-induced phagocytic activity of microglia, through a reduction of filopodia 75 .…”

Development of a Phagocytosis-Dependent Gene Signature to Predict Prognosis and Response to Checkpoint Inhibition in Clear-Cell Renal Cell Carcinoma

“…Padilla et al. reported that mir-124-5p regulates phagocytosis of human macrophages by targeting the actin cytoskeleton via the Arp2/3 complex ( 39 ). Silencing of the ARP2/3 complex has also been shown to disturb pancreatic cancer cell migration ( 40 ).…”

The Role of miRNA in Regulating the Fate of Monocytes in Health and Cancer

“…The role of miRNAs in the regulation of phagocytosis is poorly understood. To date, four miRs have been described as negative regulators of phagocytosis, e.g., miR-24, miR-30b, miR-124-5p and miR-142-3p [ 46 , 47 ]. miR-142-3p directly regulates protein kinase C alpha (PKCα), a key gene involved in phagocytosis.…”

“…miR-124-5p is involved in the regulation of the activity of the actin cytoskeleton. The direct targets of miR-124-5p are ARPC3 and ARPC4 transcripts, which result in reduced expression of the ARP2/3 complex, a crucial regulator of actin polymerization [ 47 ]. miR-21 was described as directly implicated in switching wound-associated macrophages to an anti-inflammatory status after the engulfment of apoptotic cells or efferocytosis [ 28 ].…”