Osteoblastic and osteoclastic activation in coronal sutures undergoing fusion ex vivo

Numerous studies have demonstrated the importance of dura mater in the normal development and regeneration of the cranium and its sutures. The purpose of this study was to analyze the effect of dura mater on the metabolism of bone during the process of premature suture fusion. Previously, coronal sutures of fetal rats have been shown to fuse in serum-free culture after removal of their dura mater, whereas sutures of neonatal rats resist fusion even without their dura mater present. Sutures from these two distinct developmental stages were evaluated by assaying alkaline phosphatase and tartrate-resistant acid phosphatase (TRAP), marker enzymes of bone synthesis and catabolism, respectively. Coronal sutures with adjacent calvaria were dissected from fetal day 19.5 (F19) rats (n = 142) and neonatal day 1 (N1) rats (n = 42) and randomly divided into two groups each: F19 sutures with dura mater intact; F19 sutures with dura mater removed; N1 sutures with dura mater intact; and N1 sutures with dura mater removed. Calvaria were grown in serum-free medium for up to 21 days, and enzyme activities in suture regions were assayed by microanalytical techniques at different time intervals of culture. F19 sutures without dura mater exhibited significant increases in enzyme activities during days 7 to 21 of culture, whereas those without dura mater did not. N1 sutures with or without dura mater exhibited no significant changes in enzyme activities during the 14-day period of culture. The process of F19 suture fusion, occurring in the absence of dura mater, coincided with the increased activities of both alkaline phosphatase and TRAP. These cellular, enzymatic changes may have implications for the cellular events comprising craniosynostosis in vivo.