# Platelet-rich plasma-derived microRNA let-7a-5p alleviates knee osteoarthritis by regulating macrophage polarization and improving inflammatory microenvironment

## TL;DR

This study shows that a specific microRNA in platelet-rich plasma helps reduce knee osteoarthritis by changing immune cell behavior and reducing inflammation.

## Contribution

The study identifies let-7a-5p as a novel therapeutic microRNA in PRP that regulates macrophage polarization and inflammation in knee osteoarthritis.

## Key findings

- PRP inhibits M1 macrophage polarization and promotes M2 polarization, reducing inflammation and cartilage damage.
- MicroRNA let-7a-5p was identified as a key regulator of macrophage polarization and cartilage degeneration in KOA.
- MAPK8 was experimentally validated as a direct target of let-7a-5p, linking it to the therapeutic effects of PRP.

## Abstract

Knee osteoarthritis (KOA) is closely associated with an imbalance in macrophage M1/M2 polarization within its inflammatory microenvironment. Platelet-rich plasma (PRP) has demonstrated therapeutic efficacy in KOA. Moreover, microRNAs (miRNAs) also play a protective or destructive role in the pathogenesis of KOA. This study aims to elucidate the molecular mechanisms by which PRP-related miRNAs ameliorate the inflammatory microenvironment to alleviate KOA.

An in vivo KOA rat model was established via intra-articular injection with monosodium iodoacetate (MIA). Safranin O-fast green staining and hematoxylin and eosin (HE) staining were used to assess cartilage degeneration and synovial inflammation, respectively. Macrophage phenotype was analyzed by immunohistochemistry (IHC) and immunofluorescence (IF). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to examine the expression of inflammatory cytokines. Chondrocyte anabolic and catabolic status was evaluated using IF and western blotting (WB). Bioinformatics analysis was employed to screen for differentially expressed miRNAs in PRP and Dual-luciferase reporter assay was conducted to verify that mRNA is a direct target for miRNA. Furthermore, we explored the biological functions of miRNA and mRNA by transfecting mimics and siRNA.

In vitro, PRP inhibited M1-type macrophage polarization while promoting M2-type polarization, leading to suppressed pro-inflammatory cytokine release and enhanced anti-inflammatory cytokine release, collectively reducing cartilage degeneration. We identified microRNA let-7a-5p using bioinformatic approaches and subsequently investigated its molecular mechanisms. Similar to PRP, let-7a-5p was found to regulate macrophage polarization, the release of inflammatory cytokine, and cartilage degeneration. Furthermore, we identified and experimentally validated MAPK8 as a target gene of let-7a-5p.

PRP reshapes macrophage polarization by regulating the let-7a-5p/MAPK8 axis, thereby improving the inflammatory microenvironment of KOA and providing a potential new therapeutic target for KOA management.