A comparative analysis of the osteogenic capacity of osteoblasts from newborn and two-week-old rats.

Aim: To compare the proliferation and osteogenic differentiation of osteoblasts between newborn rats (1d group) and two-week-old rats (14d group) and to clarify the mechanism underlying these effects.
Method: The endogenous expression of osteogenic marker genes was detected by qPCR, including ALP, OCN, Col1a1, and Runx2. The osteoblasts proliferation was evaluated by EdU assay and Western Blotting [PCNA and Cyclin D1]. ALP activities in osteoblasts were detected using a PNPP kit, ALP staining and qPCR. Mineralized nodule formation and intracellular calcium levels were assessed by Alizarin Red staining and calcium colorimetric assay respectively while OCN, Col1a1 and Runx2 levels in osteoblasts were analyzed by immunostaining. Osteogenesis-associated pathways including Wnt/β-Catenin, Akt/PPAR and Smad were analyzed via Western Blotting.
Result: Endogenous ALP, OCN, Col1a1, and Runx2 expression levels were significantly higher in osteoblasts from 14d group than those from 1d group. After treatment with osteogenic induction medium, osteoblast proliferation, ALP activity, mineralized nodule formation, and intracellular calcium levels were markedly increased in osteoblasts from 1d group, with similar results also being observed for the expression of OCN, Col1a1, and Runx2. Wnt3a, β-catenin, p-Akt, p-Smad1/5/8, and p-Smad5 protein levels were also higher in osteoblasts from 1d group relative to those from 14d group, while the expression of PPARγ was lower.
Conclusion: The superior osteogenic differentiation capacity in osteoblasts was associated with the higher activation levels of Wnt/β-Catenin, Akt/PPAR and Smad signaling pathways, and the enhanced proliferative activity in osteoblasts from 1d group.
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