There is now a strong consensus that prenatal stress must be incorporated into our understanding of the genesis of age-related diseases. Osteoporosis is a classical age-related disease characterized by deterioration of bone microarchitecture indicative of bone loss. By now, compelling evidence exists suggesting that inadequate maternal nutrition during pregnancy is one of the risk factors for developing osteoporosis. We asked whether not only maternal malnutrition but also some teratogens given at a dose inducing neither structural anomalies nor growth retardation can detrimentally affect skeletal health in adulthood.
Methods ICR mice were exposed to a single injection of 5-Aza-2-Deoxycytidine (5-AZA) at a sub-threshold teratogenic dose on day 10 of pregnancy. External morphology and microarchitecture of femora of 5-month-old male offspring were evaluated by radiography and micro-computed tomography (micro-CT). In parallel, apoptosis and the expression profile of micro RNAs (miRs) were evaluated in the hind limb buds of 5-AZA-exposed embryos. Finally, cultured femoral stromal/osteoblastic cells and osteoclast precursor cells obtained from 5-month-old offspring were used to evaluate the expression of an activator of osteoclastogenesis, RANKL and its decoy protein, OPG.
Results We observed that femora of 5-month-old male offspring exposed in uterus to 5-AZA exhibited trabecular microarchitecture which is suggested to be indicative of bone loss. The expression of some miRs demonstrated as regulators of key osteoblastogenic genes was altered in hind limb buds of 5-AZA-exposed embryos, while an increased expression of RANKL in femoral stromal/osteoblastic cells of 5-month-old offspring of 5-AZA-treated females was registered.
Discussion The exposure time of 5-AZA matches the beginning of osteoblastogenesis and the teratogen has the potential to affect the process of embryonic osteoblastogenesis by modulating the expression of some miRs. Distortions in embryonic osteoblastogenesis might result in the appearance of mature osteoblasts overexpressing RANKL It is conceivable, that such osteoblasts may be capable of bringing about initial bone formation but they incapable of properly regulating osteoclastogenesis in later life, leading to its activation and, consequently, to increased bone resorption.
Conclusion Collectively, this study implies for the first time that single low-level exposure to a teratogen can induce bone loss in adult offspring.