(726a) Cyclic Strain Versus Endothelial Cell Presence On MSC Osteogenesis

      Mesenchymal stem cells (MSCs) are increasingly
recognized as a viable cell source for bone regeneration applications. In
addition to soluble factors, cyclic stretch has been shown to have a profound
effect on mesenchymal stem cell (MSC) osteogenesis. Similarly, endothelial cell
(EC) presence has been demonstrated to enhance MSC osteogenic differentiation. However,
potential synergistic interactions between mechanical stimulation and EC presence
remain to be elucidated.  The aim of the present manuscript was therefore to
examine the simultaneous influence of cyclic stretch and EC paracrine signaling
on MSC osteogenesis in the context of scaffolds with ?osteogenic? moduli.

            To accomplish this, 10T½ multipotent stem cells were
encapsulated in poly(ethylene glycol) diacrylate [PEGDA] hydrogels with moduli
within the ?osteogenic? range. Half of the constructs were fabricated with a
luminal EC layer. EC⁺ and EC^-
constructs were then subjected to continuous cyclic stretch. Following 10 days
of culture, both EC⁺ and EC^- constructs were associated
with significantly elevated levels of chondrogenic transcription factor sox9
relative to initial (day 0) expression levels. By day 22 of culture, however,
sox9 levels in both the EC⁺ and EC^- constructs had
returned to or fallen below day 0 levels. In contrast, osteocalcin expression
was significantly higher in Day 22 EC⁺ constructs relative to EC^-
constructs and relative to day 0. Similarly, osteopontin and alkaline phosphatase
levels were elevated in Day 22 EC⁺ constructs relative to EC^-
constructs. Cumulatively, the present results suggest that EC paracrine
signaling enhances MSC osteogenesis in the presence of cyclic stretch. In
addition, the observed transition from chondrogenic to osteogenic protein
expression associated with the EC⁺ constructs would be consistent
with the neovascularization-dependent transition from cartilage matrix to
osteoid matrix associated with endochondral bone formation.