Prøveforelesning
Bedømmelseskomité
Professor Vidar Bakken, UiB
Postdoc Therese Standal, NTNU
Professor Harald Osmundsen, UiO
Leder av disputas: Instituttleder professor Pål Barkvoll
Veileder: Ståle Petter Lyngstadaas og Janne Elin Reseland
Sammendrag
Ameloblastin in mesenchymal cells; A study on expression, regulation and putative function of ameloblastin in bone related cells
Previously, ameloblastin was regarded as specifically expressed in tooth buds. Recently, ameloblastin was also found in embryonic bone tissues in rats. This thesis further elucidates the distribution and regulation nature of ameloblastin expression in bone related mesenchymal cells.
The main objective of the study was to investigate ameloblastin expression, distribution and putative effect in bone formation and repair, including characterization of the promoter for potential regulatory elements.
The results show that ameloblastin mRNA is expressed in primary human mesenchymal stem cells, osteoblasts, chondrocytes, and in cells of haematopoietic origin. The ameloblastin protein was also detected in various cell lysates and found to be secreted into the cell culture media. The expression of ameloblastin in bone defects in adult rats confirmed ameloblastin expression in vivo. Moreover, 50 potential regulatory elements in the upstream promoter region were detected, whereof at least 29 are previously reported to be involved in bone metabolism. It was found ameloblastin promoter activity in transfected stromal cells that was strongly enhanced after recombinant ameloblastin (rAmbn) treatment. It was also found that rAmbn stimulation enhanced proliferation of cells of mesenchymal origin, and significantly increased the number of differentiated osteoclasts. rAmbn stimulation also had a profound effect on cytokines related to immune response and tissue repair. These cytokines are also known to play crucial roles during chemoattraction, proliferation and differentiation of bone progenitor cells. In vivo experiments in rats further confirmed that application of rAmbn could be used for stimulating healing of mandibular bone.
To conclude; in skeletal tissues ameloblastin seems to act as a signaling molecule for attraction, proliferation and differentiation of cells needed during hard tissue formation and repair.