Age-related changes in bone morphology, function, and cell populations in inbred C57BL/6N mice

Bones play crucial roles in controlling motility, regulating electrolyte metabolism, and hematopoiesis. We examined age-related changes in bone morphofunction using 3-, 6-, and 13-month-old male C57BL/6N mice. Tibia weight and length generally increased with age. Phosphorus, hemoglobin, and hematocrit measurements in blood, indices of electrolyte metabolism and hematopoiesis, significantly decreased with age. Bone histology showed that osteocyte and osteoblast numbers in the tibia were significantly correlated with decreases in hemoglobin levels and hematocrit values. Furthermore, platelet levels in blood increased with age, negatively correlating with osteoblast and osteoclast number. Thus, we have demonstrated age-related changes in bone morphofunction in healthy mice, particularly quantitative alternations of bone-composing cells and hematopoietic activities.