Osteogenic and adipogenic cell fractions isolated from postnatal mouse calvaria.

The use of stem/progenitor cells represents a promising approach to treat craniofacial bone defects, but successful treatments will rely on the availability of cells that can be expanded in vitro and which will differentiate appropriately in vivo. The calvaria may represent a source of autologous cells for such purposes. We demonstrate expression of stem cell antigen-1 (Sca-1) in mouse calvaria. We isolated Sca-1(+) and Sca-1(-) cells at high purity and tested the ability of these cells to differentiate into adipose and bone. We show that the Sca-1(+) cell fraction has adipogenic differentiation potential and that the cell Sca-1(-) fraction has osteogenic differentiation potential. The Sca-1(+) cell fraction partially retains its adipogenic differentiation potential and the Sca-1(-) cell fraction partially retains its osteogenic differentiation potential after in vitro expansion. These data suggest that the calvaria may be used as a source of stem/progenitor cells that can be expanded in vitro and transplanted in vivo for craniofacial tissue regeneration.

JunB as a potential mediator of PTHrP actions: new gene targets Ephrin B1 and VCAM-1.

Parathyroid hormone-related protein (PTHrP) is an integral mediator of physiologic and pathologic processes and has demonstrated actions in the periodontium. PTHrP functions via AP-1, and specifically through JunB. This study identified JunB-dependent downstream mediators of PTHrP using OCCM cementoblastic transfectants with JunB over- or reduced expression. Over-expressing cells showed an increase in proliferation, while the opposite was seen in siRNA transfected cells. Microarray analysis of over-expressing cells revealed more than 1000 regulated genes. Three genes were investigated in more detail. The PTH/PTHrP receptor (PTHR1) and ephrin B1 (EfnB1) were down-regulated, and vascular cell adhesion molecule-1 (VCAM-1) was up-regulated with JunB over-expression. JunB siRNA transfectants had increased PTHR1, but reduced ephrin B1 and unaltered VCAM-1 in vitro. To validate these targets, parental OCCM cells and primary osteoblasts were treated with PTHrP, resulting in reduced PTHR1 and ephrin B1, and increased VCAM-1. Cell transfectants were implanted subcutaneously in vivo, and microarray analysis and RT-PCR performed. Over-expression of JunB down-regulated PTHR1 and ephrin B1, and increased VCAM-1. JunB siRNA transfectant implants had increased PTHR1 and ephrin B1, but no altered VCAM-1. These data highlight new gene targets for PTHrP and indicate JunB is a critical mediator of PTHrP actions.