Background/Purpose: Midkine (MK) is known as a heparin-binding growth factor.  Recent studies revealed that MK has various functions such as cell proliferation, differentiation, and apoptosis in various cells. Its pathological role is noted in various diseases, especially in solid tumor, such as Wilms tumor, liver cell cancer, and neuroblastoma. High level of serum MK is reported in these cancer patients who have poor prognosis. On the other hand, we reported in the last ACR meeting that high level of serum MK is correlates poor prognosis in patients with systemic vasculitis. In this study, we measured serum level of MK in patients with RA and compared with that in healthy controls. We also analyzed relationships between MK level and several clinical parameters to clarify the pathophysiological role of MK in RA.  Moreover, expression of MK protein and mRNA were examined in RA synovial tissue and/or RA synovial fibroblasts (RSFs).

Methods: Serum samples were obtained from 146 RA patients (female: male = 121:25, average age ± SD: 61.0 ± 1.2 y.o.) and 85 healthy controls (female:male = 83:8, 63.2 ± 1.3 y.o.). MK concentration was measured by Human Midkine ELISA kit using a monoclonal antibody against MK (Cellmid, Merborne, Australia). Clinical parameters for RA, such as serum CRP, ESR, rheumatoid factor (RF), MMP-3, DAS28-ESR, patient and doctor VAS, HAQ, and Sharp score were also examined. Statistical analysis was conducted by StatFlex v6.0. Immunohistochemical analysis was performed using RA synovial tissue, which wasobtained at the total knee replacement surgery. Cultured RSFs separated from RA synovial tissue were stimulated with interleukin 1β (IL-1β), tumor necrosis factor-α (TNFα) or dexamethasone for 18 hours, then culture medium was collected for measuring MK protein and mRNA was extracted from RSFs. RT-PCR of MK was performed by standard methods.

Results: Serum MK level was significantly increased in RA patients compared with that of healthy controls (average value ± SD; 157.4±13.7 and 69.64±3.0 pg/mL, respectively) by Mann-Whitney U test (P< 0.0001). ESR, RF, MMP-3, DAS28-ESR, patient VAS, doctor VAS, and HAQ, Sharp score were correlated with MK values by univariate analysis. Multiple linear regression analysis showed that MK level was positively correlated with CRP and RF (P= 0.00012 and P< 0.000001, respectively), but not with MMP-3, DAS28-ESR, HAQ, and Sharp score. Immunohistochemical analysis showed that MK was stained in lining layer of RA synovial tissues. MK mRNA in RSFs and MK protein in the culture medium of RSFs were detectable, however, their expression levels were not changed by addition of IL-1β, TNFα or dexamethasone.

Conclusion: In this study, MK was significantly increased in serum of RA patients, and its level was correlated with several clinical markers of RA. In addition, MK protein and mRNA were detected in RA synovial lining layer and/or cultured RSFs. It might be possible that MK has a pathophysiological role in RA development.

---

« Back to 2014 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/midkine-a-growth-factor-may-play-a-pathophysiological-role-in-patients-with-rheumatoid-arthritis/