„Interaktion und Einwachsverhalten von Sehnen- und Knochenzellen: quantitative und qualitative Änderungen der Genexpression sehnenspezifischer Gene im Ko-Kulturmodell nach Gabe von BMP2 bzw. BMP7“

Ruptures of the anterior cruciate ligament are very common knee injuries, especially among young and athletic persons. Arthroscopic reconstructions of the anterior cruciate ligament have been performed more frequently over the last decades. In about 11.6 percent of the cases the surgical therapy fails. This is caused by either surgical failure, another traumatic experience or biological failure. The pathophysiology of the biological failure is very complex. The process of developing a stable link between the tendon graft and the bone during the healing period is also complex and passes several stages. This newly formed artificial tendon-bone link is biomechanically inferior to native tendon-bone or ligament-bone links. Increasing the stability of these links is the focus of several research groups. BMP2 and BMP7 are growth factors which have shown a positive effect on tendon-bone healing in several non-clinical trials. There have already been clinical trials using BMP2 and BMP7 to improve bone healing. Until now time and dose dependent molecular biological effects of these growth factors regarding the expression of tendon specific genes have not been described. Within this trial we examined the expression of those genes. Therefore, we used a highly standardized co-culture model as well as real-time PCR. The expression of COL1A2, COL1A2, COL5A1, DCN, FMOD and MKX by murine preosteoblasts (MC3T3-E1), fibroblasts (3T6 or 3T3) and in an interface region, after singular and multiple stimulation with BMP2 and BMP7 has been analyzed. We got an insight in cellular and molecular biological changes and interactions of gene expression. There have been cellular differences between singular and multiple stimulation using the same growth factor. That means multiple stimulation does not necessarily increase the biological effect of those grows factors. In addition to that, the different growth factors caused different results in gene expression. The singular stimulation with BMP2 increased the expression of the examined genes in fibroblast. After multiple stimulation with BMP7 we found an increased expression of the examined genes except COL1A1 in preosteoblasts. Furthermore, equal stimulation often led to similar patterns of expression in several genes. Another interesting result was found regarding the interface region. This area usually showed different patterns of gene expression compared to those of the fibroblasts or osteoblasts region. After multiple stimulation with BMP7 we found an increased expression of COL5A1 in this area whereas singular stimulation with BMP2 increased the expression of COL1A1 and COL1A2. From former projects we know that preosteoblasts as well as fibroblasts migrate into the interface region. This may lead to the conclusion that both types of cells influence each other by auto-, paracrine or cellular mediators. In order to understand these effects and method of regulation further trials are needed. With regard to the clinical use of BMP2 and BMP7 in tendon-bone healing it is necessary to expedite further research regarding indication, side effects, long term results and safety.