Bone marrow mesenchymal stem cells are the main effector cells for bone formation. With the increase of age, the regenerative ability of bone marrow mesenchymal stem cells is weakened and the differentiation function is impaired, leading to poor osteoporosis. Therefore, restoring the regenerative capacity and cellular function of aged bone marrow mesenchymal stem cells is essential for the effective treatment of osteoporosis.

To investigate the effects of passage 3 and passage 11 bone marrow mesenchymal stem cells-derived exosomes of young rats on the aging of bone marrow mesenchymal stem cells derived from elderly rats.

Bone marrow mesenchymal stem cells from 6-8-week-old female SD rats were isolated and cultured, and passaged to the passages 3 and 11, respectively. Then, exosomes from passages 3 and 11 bone marrow mesenchymal stem cells were extracted. Bone marrow mesenchymal stem cells from 18-month-old female SD rats were isolated and cultured, passaged to passage 3, and divided into 3 groups. The control group was routinely cultured, and the other two groups were intervened with exosomes from passages 3 and 11 bone marrow mesenchymal stem cells. After 48 hours of exosome intervention, the expression of β-galactosidase in the nucleus was detected by β-galactosidase staining kit. The expression of aging-related genes was detected by qRT-PCR. The expression differences of miRNA in exosomes from passages 3 and 11 bone marrow mesenchymal stem cells were compared by Small RNA sequencing.

(1) Compared with the control group and passage 11 bone marrow mesenchymal stem cell-derived exosomes group, the β-galactosidase activity of bone marrow mesenchymal stem cells of aged rats was significantly lower in the passage 3 bone marrow mesenchymal stem cell-derived exosomes group. (2) Compared with the control group, the expression of aging-related genes p21 and p16 was significantly reduced in the passage 3 bone marrow mesenchymal stem cell-derived exosome group (P < 0.05), while there was no significant difference in the expression of aging-related genes p21 and p16 in the passage 11 bone marrow mesenchymal stem cell-derived exosome group. (3) Sequencing results showed that there was a significant difference in the expression of miRNAs in the two exosomes, among which the miRNAs with the most significant expression differences were let-7c-5p, let-7b-5p, miR-320-3p, and miR-26a-5p. KEGG analysis results showed that significantly different miRNA enrichment pathways include mTOR, AMPK and other aging-related signaling pathways. The above results indicate that passage 3 bone marrow mesenchymal stem cell-derived exosomes have the ability to reverse the aging of bone marrow mesenchymal stem cells in aged rats.