GHRH expression plasmid improves osteoporosis and skin damage in aged mice

The hormone secretion of GHRH-GH-IGF-1 axis in animals was decreased as aging. These hormones play an important role in maintaining bone mass and bone structure, and also affect the normal structure and function of the skin. We used plasmid-based technology to deliver growth hormone releasing hormone (GHRH) to elderly mice. In the current study, 80 and 120 μg/kg pVAX-GHRH plasmid expression plasmid were injected into old mice, the serum GHRH and insulin-like growth factor-1(IGF-1) content were increased within three weeks (P < 0.05). In the groups of 80 and 120 μg/kg plasmid, the content of procollagen type I N-terminal pro-peptide (PINP) in the serum was increased(P < 0.05), and the content of C-terminal telopeptides of type I collagen (CTX-1) in the serum was reduced significantly (P < 0.05). Furthermore, the expression of osteoprotegerin (OPG) and osteocalcin (OCN) in the femur also was increased(P < 0.05). The bone mineral density(BMD)、trabecular bone volume (BV/TV) and trabecular number(Tb.N) of mouse femur were increased significantly (P < 0.05) and trabecular separation(Tb.Sp) was decreased(P < 0.05). There were more trabecular bones in the bone marrow cavity and the trabecular bones are thicker in the groups of 80 and 120 μg/kg plasmid relative to control. The superoxide dismutase (SOD) content in the skin was increased(P < 0.05), and the malondialdehyde (MDA) content was reduced significantly (P < 0.05). Meanwhile, the skin moisture content also increased significantly(P < 0.05). Moreover, the expression of matrix metalloproteinase 3(MMP3) and matrix metalloproteinase 9(MMP9) was decreased in the skin(P < 0.05). The thickness of the dermis and epidermis of the skin had increased significantly(P < 0.05). Skin structure is more dense and complete in the two groups. These results indicate that 80 and 120 μg/kg plasmid-mediated GHRH supplementation can improve osteoporosis and skin aging in aged mice.