In both physiological and pathological processes, periosteum plays a determinant role in both bone formation and fracture healing. However, no specific reports are available so far focusing on the detailed structural and major cellular differences between the periostea covering different bone surface areas in relation to ageing. The aim of this study is to compare the structural and cellular differences in diaphyseal and epiphyseal periostea in different-aged rats using histological and immunohistochemical methods.

Four female Lewis rats from each group of juvenile (7-week old), mature (7-month old) and aged groups (2-year old) were sacrificed and the right femur of each rat was retrieved, fixed, decalcified and embedded. 5μm thick serial sagittal sections were cut and stained with Hematoxylin and Eosin, Stro-1 (stem cell marker), F4/80 (macrophage marker), TRAP (osteoclast marker) and vWF (endothelial cell marker). 1mm length of middle diaphyseal and epiphyseal periosteum were selected for observation. The thickness, total cell number and positive cell number for each antibody in each periosteal area and different-aged groups were measured and compared. The results were subjected to ANOVA and SNK-q tests.

The results showed that the thickness and cell number in diaphyseal periosteum decreased with age (p< 0.001). In comparison with diaphyseal area, the thickness and cell number in epiphyseal periosteum were much higher (p< 0.001). There were no significant differences between the juvenile and aged groups in the thickness and cell number in cambial layer of epiphyseal periosteum (p> 0.05). However, the juvenile rats had more Stro1+, F4/80+ cells and blood vessels and few TRAP+ cells in different periosteal areas compared with other groups(p< 0.001). The aged rats showed much less Stro1+ cells, but more F4/80+,TRAP+ cells and blood vessels in the cambial layer of epiphyseal periosteum (p< 0.001).

In conclusion, the age-related structure and cell population in diaphyseal and epiphyseal periostea are different, especially in aged rats. The epiphyseal periosteum of aged rats seems more destructive than diaphyseal part and other age groups. Macrophages in the periosteum play a dual important role in osteogenesis and osteoclastogenesis.