Since the recent recommendation by the American Academy of Pediatrics that babies be kept supine during sleep, there has been an observed increase in calvarial deformation. Most of these new cases are diagnosed as positional plagiocephaly because the deformation is most likely secondary to the external mechanical compression caused by prolonged supination of the babies head. Three major model have been proposed for the mechanotransduction of extrinsic forces to cellular events that may apply to neonatal sutures, and may explain the mechanism of calvarial deformation. The first is the tensegrity model in which extrinsic tension is linked to tension-integrated cytoskeletal changes via integrins. This model suggests that the cytoskeleton is capable of registering deformation and conveying that information to cytosolic and nuclear sites. The second model is the damage sensor model. This model suggests that plasma membrane disruptions in response to extrinsic forces lead to the influx of Ca++ or the efflux of growth factors capable of altering gene expression. The third model is the stretch activated channel (SAC) model which involves the opening of Ca++-permeable channels in response to cell deformation. Our hypothesis is that cells within immature cranial sutures are capable of mechanotransduction by a mechanism involving one or more of the above models. To test this we will separate and study these three models.
In Specific Aim #1 we will apply external tension to neonatal cranial sutures in organ culture in the presence and absence of inhibitors of cytoskeleton assembly. We will measure the modulation of mRNA and protein expression of the immediate-early gene product c-fos and connexin 43 which are both upregulated in response to stretch.
Specific Aim #2 examines the relative uptake by stretched vs. unstretched sutures of fluorescent dextran (Mr approximately 10,000), a cell-impermeant marker requiring cell membrane rupture and reseal to enter living cells.
Specific Aim #3 measures Ca++ influx into cranial sutures loaded with the fluorescent Ca++-sensitive dye indo-1 and stretched in the presence of L-type Ca++-channel and SAC blockers. This study will determine if a raise in cell Ca++ occurs in response to SAC or Ca++-channel- independent event. Mechanotransduction has been minimally studied in immature cranial sutures and elucidation of this mechanism promises important insight into this new and important area of research.
