Comparative proteomic analysis of human mesenchymal stromal cell behavior on calcium phosphate ceramics with different osteoinductive potential.

In recent years, synthetic calcium phosphate (CaP) ceramics have emerged as an alternative to bone grafts in the treatment of large critical-sized bone defects. To successfully substitute for bone grafts, materials must be osteoinductive, that is, they must induce osteogenic differentiation and subsequent bone formation in vivo. Although a set of osteoinductive CaP ceramics has been developed, the precise biological mechanism by which a material directs cells toward osteogenesis and the role of individual chemical and physical properties in this mechanism remain incompletely understood. Here, we used proteomics to compare serum protein adsorption to two CaP ceramics with different osteoinductive potential, namely an osteoinductive ß-tricalcium phosphate (TCP) and a non-osteoinductive hydroxyapatite (HA). Moreover, we analyzed the protein profiles of human mesenchymal stromal cells (hMSCs) cultured on these two ceramics. The serum protein adsorption experiments in the absence of cells highlighted the proteins that are highly abundant in the serum and/or have a high affinity to CaP. The extent of adsorption was suggested to be affected by the available surface area for binding and by the ion exchange dynamics on the surface. Several proteins were uniquely expressed by hMSCs on TCP and HA surfaces. Proteins identified as enriched on TCP were involved in processes related to wound healing, cell proliferation, and the production of extracellular matrix. On the other hand, proteins that were enriched on HA were involved in processes related to protein production, translation, localization, and secretion. In addition, we performed a separate proteomics analysis on TCP, HA, and two biphasic calcium phosphates with known osteoinductive potential and performed a clustering analysis on a combination of a set of proteins found to be enriched on osteoinductive materials with a set of proteins already known to be involved in osteogenesis. This yielded two protein networks potentially involved in the process of osteoinduction - one consisting of collagen fragments and collagen-related enzymes and a second consisting of endopeptidase inhibitors and regulatory proteins. The results of this study show that protein profiling can be a useful tool to help understand the effect of biomaterial properties on the interactions between a biomaterial and a biological system. Such understanding will contribute to the design and development of improved biomaterials for (bone) regenerative therapies.

Transplantation of human myoblasts in SCID mice as a potential muscular model for myotonic dystrophy.

Myotonic dystrophy (DM), the most frequent hereditary myopathy in adults, is characterized clinically by muscle weakness, myotonia, and systemic symptoms. Although the specific genetic basis for DM has been established, less is known about the cellular defects responsible for its pleiotropic manifestations. DM pathogenesis studies are presently limited due to the absence of animal models. In the present study, we transplanted myoblasts of DM patients into the Tibialis anterior of Severe Combined Immunodeficient (SCID) mice to determine whether this approach could reproduce the muscular characteristics of DM. One to 4 months after transplantation, a variable number of innervated human muscle fibers, recognized by an antibody specific for the human dystrophin, were found in the transplanted muscles. The CTG expansion was retained in human muscle fibers as determined by Southern blot analysis. Although the histological characteristics of DM were absent in these fibers, electromyographic recording showed typical myotonic discharges in muscles transplanted with DM myoblasts. The specificity of the myotonic runs was demonstrated by its inhibition by apamin, a drug that specifically blocks DM myotonia. We conclude that transplantation of myoblasts from DM patients into SCID mice represents a potential in vivo model for basic studies of this disease.