Sustained epidermal growth factor receptor levels and activation by tethered ligand binding enhances osteogenic differentiation of multi-potent marrow stromal cells

Epidermal growth factor receptor (EGFR)-mediated signaling helps regulate bone development and healing through its effects on osteogenic cells. Here, we show how EGFR activity and osteogenic differentiation responses in primary human bone marrow-derived multipotent stromal cells (MSCs) are influenced by presenting covalently tethered epidermal growth factor (tEGF) on the culture substratum, a presentation mode that reduces EGFR internalization and restricts signaling to the cell surface. In both absence and presence of tEGF, MSCs increase expression levels of EGFR and its heterodimerization partner HER2 during the course of osteogenic differentiation. tEGF substrata increased levels of phosphorylated EGFR and phosphorylated extracellular regulated kinase (ERK) compared to control substrata, and these elevations were associated with a twofold enhancement of MSC alkaline phosphatase activity at day 7 and matrix mineralization at day 21. Surprisingly, addition of soluble EGF (sEGF) to cells cultured on tEGF substrata reduces osteogenic differentiation, even though EGFR signaling is more strongly activated in acute, short-term manner by sEGF treatment than by tEGF treatment. A striking concomitant result of the sEGF effects is near-complete downregulation of EGFR and HER2, demonstrating that the tEGF/EGFR interaction is dynamically reversible even though temporally sustained. Taken together, our results show that enhanced MSC osteogenic differentiation corresponds to a sustained combination of receptor expression and ligand presentation, both of which are maintained by tEGF. J. Cell. Physiol. 221: 306–317, 2009. © 2009 Wiley-Liss, Inc.     

In Vivo Assessment of Bone Regeneration in Alginate/Bone ECM Hydrogels with Incorporated Skeletal Stem Cells and Single Growth Factors

The current study has investigated the use of decellularised, demineralised bone extracellular matrix (ECM) hydrogel constructs for in vivo tissue mineralisation and bone formation. Stro-1-enriched human bone marrow stromal cells were incorporated together with select growth factors including VEGF, TGF-β3, BMP-2, PTHrP and VitD3, to augment bone formation, and mixed with alginate for structural support. Growth factors were delivered through fast (non-osteogenic factors) and slow (osteogenic factors) release PLGA microparticles. Constructs of 5 mm length were implanted in vivo for 28 days within mice. Dense tissue assessed by micro-CT correlated with histologically assessed mineralised bone formation in all constructs. Exogenous growth factor addition did not enhance bone formation further compared to alginate/bone ECM (ALG/ECM) hydrogels alone. UV irradiation reduced bone formation through degradation of intrinsic growth factors within the bone ECM component and possibly also ECM cross-linking. BMP-2 and VitD3 rescued osteogenic induction. ALG/ECM hydrogels appeared highly osteoinductive and delivery of angiogenic or chondrogenic growth factors led to altered bone formation. All constructs demonstrated extensive host tissue invasion and vascularisation aiding integration and implant longevity. The proposed hydrogel system functioned without the need for growth factor incorporation or an exogenous inducible cell source. Optimal growth factor concentrations and spatiotemporal release profiles require further assessment, as the bone ECM component may suffer batch variability between donor materials. In summary, ALG/ECM hydrogels provide a versatile biomaterial scaffold for utilisation within regenerative medicine which may be tailored, ultimately, to form the tissue of choice through incorporation of select growth factors.     

Validation and implementation of a liquid chromatography/tandem mass spectrometry assay to quantitate dimethyl benzoylphenylurea (BPU) and its five metabolites in human plasma and urine for clinical pharmacology studies

A method has been developed for the quantitation of N-[4-(5-bromo-2-pyrimidinyloxy)-3-methylphenyl]-N'-(2-dimethylamino-benzoyl)urea (BPU) and its metabolites in human plasma and urine. BPU and metabolites were separated on a C18 column with acetonitrile-water mobile phase containing 0.1% formic acid using isocratic flow for 5 min. The analytes were monitored by tandem mass spectrometry. Calibration curves were generated over the range of 2.5-500 ng/mL for BPU, mmBPU, and aminoBPU in plasma; and 0.1-20, 0.1-20, 0.5-100, 10-2000, 1-200, and 3-600 ng/mL for BPU, mmBPU, aminoBPU, G280, G308, and G322 in urine, respectively. The method has been successfully applied to study the pharmacokinetics of BPU.     

Histological evidence for the role of mechanical stress in modulating thermal denaturation of collagen

The hyperthermia and thermal denaturation literatures reveal a time-temperature equivalency when heating cells or connective tissues: thermal damage increases with increasing temperature (for the same duration) and increases with increasing duration (for the same temperature). Recent findings conversely suggest that increasing the mechanical loading on a tissue during heating decreases the thermal damage (for a given temperature and duration of heating). Surprisingly, however, there are few histological correlates of such damage. In this paper, we show that progressive light microscopic changes – swelling of collagen bands, thickening of collagen-rich layers, hyalinization, and loss of birefringence~– correlate very well with both increased heating times and decreased mechanical loading. Increased mechanical stress is thus thermally protective and should be considered in the design of clinical procedures that use heating to treat diseases or injuries. P. B. Wells and S. Thomsen contributed equally to this work.