Using exosomes to treat osteoporosis, the Naval Medical University team made new progress

Osteoporosis is a common chronic disease among the elderly
.

According to statistics, more than 200 million people worldwide suffer from osteoporosis, and an osteoporotic fracture occurs every 3 seconds

Recently, the Su Jiacan/Chen Xiao research team of the Naval Military Medical University published their research results in the journal Bioactive Materials
.

They proposed a new method to obtain bone-targeted exosomes by displaying CXCR4 on the surface, which is expected to reverse age-related bone loss

Research Background

Bone marrow mesenchymal stem cells (BMSC) are the progenitor cells of bone marrow adipocytes and osteoblasts
.

BMSC changes from osteogenic differentiation to adipogenic differentiation, and bone formation is impaired, which is the characteristic of many pathological bone loss

Previous studies have found that miR-188 increases significantly with age
.

This miRNA can regulate the differentiation fate of BMSCs, promote adipogenesis and inhibit bone formation

Exosomes show amazing potential in drug delivery
.

At the same time, considering that the SDF-1/CXCR4 axis plays an important role in the homing of hematopoietic stem cells, the researchers hypothesized that CXCR4-positive exosomes can be recruited to the bone marrow

Distribution of CXCR4+ exosomes in vivo

To verify this hypothesis, the researchers introduced the CXCR4 gene into NIH-3T3 cell line through a lentiviral packaging system, and proved that CXCR4 was successfully expressed on NIH-3T3 cells through RT-qPCR and immunofluorescence
.

Afterwards, they isolated exosomes from the culture supernatant and confirmed that CXCR4 was expressed on the surface of exosomes

Next, in order to verify the bone-targeting properties of CXCR4+ exosomes, they carried out in vivo tracking experiments
.

They used Cy5 fluorescent dye to label the exosomes of NIH-3T3 cells and CXCR4+ NIH-3T3 cells, and injected them into mice through the tail vein

Figure 1.

Distribution of CXCR4+ exosomes in vivo

Bone targeting properties of hybrid nanoparticles

Afterwards, the researchers fused CXCR4+ exosomes with liposomes carrying antagomir-188 (miR-188 antagonist, Cy5 label) to form hybrid NPs, and injected them into mice
.

As shown in follow-up studies, hybrid nanoparticles with exosomes/liposomes ratios of 1:1 and 4:1 can accumulate in bone marrow
.
In addition, the intensity of fluorescence in mouse femurs gradually increased, indicating that the fluorescently labeled cargo was trapped in the bone marrow (Figure 2)
.
48 hours after the injection, the liver and kidney functions of the mice remained stable, proving that the nanoparticles were not cytotoxic in vivo
.
These results indicate that CXCR4+ hybrid nanoparticles with bone targeting properties were successfully constructed
.

Figure 2.
Distribution of CXCR4+ hybrid nanoparticles in vivo

Hybrid nanoparticles promote osteogenic differentiation and inhibit adipogenic differentiation

To further study the efficacy of hybrid nanoparticles carrying antagomir-188, the researchers tested its effect on a mouse model of age-related osteoporosis
.
They injected hybrid nanoparticles into 18-month-old male mice intravenously once a week for a total of 8 weeks
.
Compared with the control, the mice treated with antagomir-188 NP showed significantly higher bone retention
.

Next, they used hematoxylin/eosin (H&E) staining and fatty acid binding protein 4 (FABP4) immunohistochemistry to explore osteogenesis and adipogenesis
.
They found that the hybrid nanoparticles carrying antagomir-188 reduced the number of bone marrow fat cells around the trabecular bone and increased the number of bone lining cells (Figure 3)
.

In an in vitro study, they also found that hybrid nanoparticles carrying antagomir-188 can increase the synthesis of ALP-positive osteoblasts
.
Oil red O staining also proved that antagomir-188 NP inhibited the formation of lipid droplets in BMSCs after adipogenesis
.
Here, the researchers used Saiye's osteogenic differentiation medium and adipogenic differentiation medium
.
These results indicate that the bone-targeted nanotherapeutic agent delivered antagomir-188 reverses age-related bone loss by promoting osteogenic differentiation and inhibiting adipogenic differentiation of BMSCs
.

Figure 3.
Hybrid nanoparticles reverse age-related bone loss

Concluding remarks

This study displayed CXCR4 on the surface of exosomes and fused it with liposomes carrying antagomir-188
.
CXCR4+ exosomal-liposome hybrid nanoparticles tend to accumulate in the bone marrow and release antagomir-188, which can promote osteogenic differentiation and inhibit adipogenic differentiation, thereby reversing age-related bone loss
.
It provides a bone-targeted RNAi delivery strategy based on exosomes, which is expected to be used as a therapy for pathological bone loss
.

Original Search

Exosome-guided bone targeted delivery of Antagomir-188 as an anabolic therapy for bone loss

Bioactive Materials

Volume 6, Issue 9, September 2021, Pages 2905-2913