The China Medical University team develops a new type of "cell-free" cartilage to repair cartilage damage

The Li Xu research team of the First Affiliated Hospital of China Medical University recently discovered that exosomes of human umbilical cord mesenchymal stem cells can enhance the repairing effect of the acellular cartilage extracellular matrix (ACECM) scaffold and promote cartilage regeneration
.

The results of this research were published in the journal Bioactive Materials

Once the articular cartilage is damaged, its self-healing ability is very limited
.

If it is not treated in time, it is easy to cause osteoarthritis and seriously affect people's quality of life

It has recently been discovered that a tissue engineering strategy based on mesenchymal stem cells (MSC) is a promising method for articular cartilage regeneration
.

Wharton's glial mesenchymal stem cells (hWJMSC) derived from human umbilical cord are considered to be the seed cells of articular cartilage and have broad application prospects

The exosomes derived from mesenchymal stem cells (MSC-Exo) are considered to be ideal alternatives because they have similar biological functions to MSCs and play an important role in MSC-mediated tissue repair and regeneration
.

Exosomes are not tumorigenic or immunogenic, avoid the risk of MSC transplantation, and are relatively easy to store and transport

In addition, the research team has previously prepared an acellular cartilage extracellular matrix (ACECM) scaffold, which is a bionic structure that can provide a microenvironment for stem cell adhesion, proliferation and differentiation
.

Then, using the exosomes derived from hWJMSC in combination with the ACECM scaffold, can this "cell-free" tissue engineering promote cartilage regeneration? With this question in mind, they carried out an in-depth analysis (Figure 1)

Figure 1.

Research schematic

In vitro experiments

The researchers first isolated hWJMSC from the umbilical cord and cultured it
.

Flow cytometry analysis showed that hWJMSC expressed mesenchymal stem cell-specific markers

Afterwards, they extracted exosomes (hWJMSC-Exo) from the culture supernatant by differential ultracentrifugation
.

In vitro experiments show that hWJMSC-Exo can promote the migration of bone marrow mesenchymal stem cells (BMSC) and significantly promote the proliferation of BMSC and chondrocytes

Animal model

The researchers then evaluated the effects of hWJMSC-Exo and ACECM scaffolds on animal models
.

They drilled a hole with a diameter of 3.
5 mm and a depth of 1.
5 mm in the rabbit femoral pulley to prepare a rabbit cartilage defect model
.
After that, an ACECM stent was implanted in the defect site and hWJMSC-Exo was injected as the experimental group (Exo + S group)
.
The remaining rabbits were divided into different control groups, including PBS group, PBS + S group (with stent), Exo group (with exosomes) and sham operation group (PBS + sham operation)
.

At 3 and 6 months after the operation, they found that the cartilage repair effect of the Exo + S group was significantly better than that of the other groups (Figure 2)
.
The micro-MRI results showed that at 6 months after the operation, the cartilage defects in each group had been filled with repaired tissue, but only the Exo + S group showed signals close to normal cartilage
.
The micro-CT results showed that the surface of the subchondral bone in the Exo + S group was smooth 6 months after the operation, which was similar to the sham operation group
.
These results indicate that hWJMSC-Exo can enhance the effect of the ACECM scaffold and promote cartilage regeneration
.
Tissue morphology analysis also illustrates this point
.

Figure 2.
Cartilage repair effect

Mechanism analysis

Considering that the microenvironment of the joint cavity plays an important role in cartilage regeneration, the researchers then explored whether hWJMSC-Exo can regulate the inflammatory response of the microenvironment
.
They injected hWJMSC-Exo into the knee joint cavity of a rat cartilage defect model
.
Compared with the control group, there was no significant difference in the expression levels of pro-inflammatory cytokines (IL-1 and TNF-α) in the exosomal group, but the expression levels of anti-inflammatory cytokines (IL-10) were significantly increased, indicating the level of inflammation Lower
.

To further explore the mechanism by which exosomes regulate inflammation, they stained macrophage markers
.
The results showed that the ratio of M2 type macrophages to all macrophages in the exosomal group increased significantly, while the ratio of M1 type macrophages decreased, which confirmed that hWJMSC-Exo promotes macrophage infiltration in vivo and promotes macrophages.
The phages are polarized towards the M2 phenotype
.

Finally, the researchers also sequenced the miRNA in hWJMSC-Exo and found that it is rich in miRNAs that can promote cartilage regeneration, including miR148a and miR29b
.
miR148a can promote cartilage regeneration by inhibiting the differentiation of chondrocytes into a hypertrophic phenotype and promoting the secretion of proteoglycans and collagen; miR29b plays an important regulatory role in the differentiation of BMSCs into chondrocytes
.

Concluding remarks

This study confirmed that hWJMSC-Exo can promote cartilage regeneration
.
This effect may be attributed to the fact that exosomes can promote the proliferation of endogenous BMSCs and chondrocytes, and inhibit the inflammation in the joint cavity, while exosomal miRNA can promote the synthesis of extracellular matrix of chondrocytes
.
The author believes that, considering that the ACECM scaffold has been successfully applied to the clinic, this new type of "cell-free" tissue engineered cartilage has broad prospects for clinical transformation
.

Original Search

Jiang S, Tian G, Yang Z, Gao X, Wang F, Li J, Tian Z, Huang B, Wei F, Sang X, Shao L, Zhou J, Wang Z, Liu S, Sui X, Guo Q, Guo W , Li X.
Enhancement of acellular cartilage matrix scaffold by Wharton's jelly mesenchymal stem cell-derived exosomes to promote osteochondral regeneration.
Bioact Mater.
2021 Feb 13;6(9):2711-2728.
doi: 10.
1016/j.
bioactmat.
2021.
01.
031.