Osteoclast-derived exosomal let-7a-5p targets Smad2 to promote the hypertrophic differentiation of chondrocytes

Abstract

The invasion of osteoclasts into the cartilage via blood vessels advances the process of endochondral ossification, and dysregulation of dynamic intercellular interactions results in skeletal dysplasias. Although the regulation of osteoclasts by growth plate chondrocytes has been reported in detail, the effect of osteoclasts on chondrocytes remains to be determined. In this study, ATDC5 cells and bone marrow mesenchymal stem cells were differentiated into chondrocytes and treated with conditioned medium obtained from bone marrow macrophages differentiated to osteoclast precursors and osteoclasts. Exosomes were inhibited in conditioned medium or isolated directly from osteoclasts to further determine whether osteoclast-derived exosomes play an important role in chondrocyte hypertrophy. Additionally, exosomal miRNAs were detected, and let-7a-5p was selected as an miRNA with significantly increased expression in osteoclast-derived exosomes. Experiments were performed to verify the potential target Smad2 and investigate how let-7a-5p affected chondrocytes. The results suggest that both osteoclast precursors and osteoclasts promote chondrocyte hypertrophy and that the promotive effect of osteoclasts is more significant than that of osteoclast precursors. Osteoclast-derived exosomes promote the hypertrophic differentiation of chondrocytes. Moreover, osteoclast-derived exosomal let-7a-5p inhibits Smad2 to decrease the transforming growth factor-β-induced inhibition of chondrocyte hypertrophy. Our research reveals the role of osteoclasts in the regulation of chondrocytes and provides insights into the highly coordinated intercellular process of endochondral ossification.

Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis

“…Osteoclasts at distinct stages of differentiation derived from bone marrow mononuclear cells (BMMCs) may affect the normal phenotype of chondrocytes. Our group reported that exosomal let-7a-5p from preosteoclasts and mature osteoclasts targets Smad2 to promote the hypertrophic differentiation of chondrocytes, 75 providing insights into ‘OC–CC coupling’ during OA progression.…”

miRNAs in osteoclast biology

“…Similarly, exosomes derived from RANKL-induced, osteoclastic RAW 264.7 cells contain miR-23a-5p that downregulates Runx2, an essential transcription factor for bone formation [123], to inhibit osteogenic differentiation [124]. Osteoclast-derived exosomes also contain let-7a-5p, which targets the SMAD2/TGFB-induced pathway to inhibit chondrogenic differentiation and therefore promotes hypertrophic differentiation of chondrocytes [125]. Thus, it remains an exciting possibility that osteoclast-derived exosomes, which possess targeting for osteoprogenitors, may be loaded with anabolic miRNAs for therapeutic purposes to drive osteogenic responses.…”

“…Slightly more is known about systemically-derived EVs that target osteoclasts to influence the regulation of bone mass. Many of these miRNA-containing exosomes originate from tumor cells from various sources, and are often called "tumor-derived exosomes", which can influence various aspects of osteoclastic activity, depending on their particular target mRNAs [126]. These miRNA-containing exosomes arise from diverse sources including breast cancer cells [127], prostate cancer cells [77,128], multiple myeloma plasma cells [129][130][131], osteosarcoma cells [132] and lung adenocarcinoma cells [133].…”

Inflammatory osteoclasts‐derived exosomes promote bone formation by selectively transferring lncRNA LIOCE into osteoblasts to interact with and stabilize Osterix

“…The exosome sample was diluted 1:100 in PBS, and 1000 μl of diluted sample was injected into the sample tank, and the sample was pressurized to pass through the nanopore at a uniform speed and analyzed by the software. The characteristic proteins, TSG101 and CD63, were detected through western blotting 14,24 …”