The Interaction Between Stromal Cell-derived Factor1Alpha(SDF-1α) And Dickkopf-1(DKK-1) Mediates Myeloma Bone Disease

Background and ObjectAbout80%patients with multiple myeloma (MM) represents destructive bone disease, which is negatively correlated with life quality and survival. The mechanism of myeloma bone disease involves the enhancement of bone absorption accompanied with inhibition of bone formation, namely, over-activated osteoclasts and suppressed osteoblasts. In our previous study, we have found that serum level of stromal cell derived factor1alpha (SDF-1a), secreted by bone marrow stromal cells (BMSC) for stem cell homing, was positively related to the serum level of Dickkopf-1(DKK-1), a soluble inhibitor of Wnt signaling pathway which plays an important role in osteoblast differentiation and proliferation. To further reveal the pathogenesis of MM bone disease, this study was to explore the relationship between SDF-1α, DKK-1and the severity of clinical bone disease, as well as the mechanism how the two factors interact to promote myeloma bone disease.Materials and MethodsForty-six previously untreated patients diagnosed as MM were included in our study. The clinical data, sera and bone marrow aspirates were collected. Serum were tested using ELISA kits. Radiographic methods including computerized tomography (CT) with three-dimension bone reconstruction and plain radiographs were used to assess myeloma bone disease. The relationship between the severity of bone disease and serum values of SDF-1α and DKK-1was analyzed. Human MM cell line RPMI8226was cultured in vitro. Under the condition of SDF-1α10ng/ml, the transcription level of DKK-1was detected at8h and36h by Realtime PCR relative quantitation SYBR technique. Myeloma cells from patients’ bone marrow were sorted by CD138immunomagnetic beads. The purity of sorted cells was detected by flowcytometry. The transcription level of DKK-1in primary myeloma cells was tested after stimulation of SDF-1α for72hours. BMSCs from MM patients were cultured in vitro. When added with Wnt-3a (200ng/ml) and/or DKK-1(20ng/ml), the transcription level of SDF-1alpha was assayed. Statistics was carried out using SPSS Statistics17.0. P value of less than0.05was considered as significance.ResultsThe serum level of SDF-1α in MM patients (n=46) was significantly higher than that of the age-matched health control (n=30)(3275.9±1093.0pg/ml vs2817.5±419.6pg/ml, P=0.015). The serum level of DKK-1in MM patients was also significantly higher than that of the health control (3275.9±1093.0pg/ml vs1494.2±918.7pg/ml, P=0.025). There was a positive relationship between serum SDF-1alpha and DKK-1in MM patients (r=0.40, P=0.001). However, such association did not show in health control group (r=0.15, P=0.428). Both CT three-dimension bone reconstruction and plain radiographs were conducted on13MM patients. CT showed higher sensitivity in determining minor fracture and osteolytic lesions compared to plain films. Patients with positive findings on CT had higher level of SDF-1α compared to patients with negative CT (2989±838pg/ml vs2460±739pg/ml,P=0.12). Serum DKK-1was also higher in patients with positive bone disease, which was5072±8032pg/ml compared to1032±720pg/ml in patients with negative CT findings(P=0.13). Both SDF-1α and DKK-1had the increasing trend according to more advanced stage of ISS, yet with no statistical difference. After stimulation of SDF-1α for8h and36h in RPMI8226cell line, the mRNA of DKK-1was increased by1.92and4.19folds respectively(P=0.099). The purity of CD138positive myeloma cells was99.5%. Primary myeloma cells from9MM patients had a wide range of DKK-1relative expression from0.06%to11.09%contrasted to the house keeping gene of glyceraldehyde3-phosphate dehydrogenase (GAPDH). Myeloma cells with higher baseline DKK-1transcription level (higher than0.2%) seemed to be more susceptible to extra SDF-la, which leads to significantly upregulated DKK-1expression (P=0.043). However, upregulation of DKK-1was not seen in cells with low baseline DKK-1expression. When BMSCs exposed to Wnt-3a, it showed that SDF-la mRNA was significantly down regulated to29%(P=0.028). However, this effect was reversed with the co-existence of DKK-1and Wnt-3a.Conclusion The serum levels of both SDF-la and DKK-1were elevated in MM patients with positive correlation. The severity of clinical bone disease has the trend to parallel to SDF-1α and DKK-1. SDF-1α enhanced mRNA transcription level of DKK-1in both myeloma cell line and primary myeloma cells, while DKK-1promoted the transcription of SDF-1α in BMSCs. SDF-1α and DKK-1interacted with each other as a vicious cycle to facilitate myeloma bone disease. It would be a new target to interrupt the communication of SDF-1α and DKK-1for treating myeloma bone disease.