Background/Purpose: Bone destruction
is one of the main pathological features in ankylosing spondylitis (AS). This research
aims to explore the role of nuclear factor kappa-B ligand (RANKL), monocyte-macrophages and RANKL/RANK
pathway in AS bone destruction.

Methods: 60 AS patients (age
18-55years, BASDAI>4.0) and 30 healthy volunteers (age 18-50years) were
included in the first part of the study. Use ELISA to detect the serum RANKL. The
second part, hip joint synovium was used to separate monocyte-macrophages. Specimens were obtained from 10 male
AS (age 25-50years) patients who underwent hip joint replacement operation and
another 5 male patients (age 30-60years) who had fracture at hip joint and underwent
hip joint replacement operation. Digestion and adherent culture was adopted for
the primary culture of monocyte-macrophages. Identified the cells with flow cytometry. Detected
the expression of protein by Western blot. Immunohistochemical
methods were used to test the protein expression in the tissues.

Results: The
expression of serum RANKL in the two groups were 103.74±51.09
pg/mL (normal group, n=30) and 228.16±139.15 pg/mL(AS group,
n=60).
Comparing with normal group, serum RANKL in AS group increased significantly, P
<0.05. The correlation test showed that RANKL had no significant correlation
with the clinical observation indexes (BASDAI, BASDFI, BASMI, PGA, HAQ) (P
>0.05).
(Table 1)
In
vitro, the
Western
blot
results showed that, in AS monocyte-macrophages, the expressions of RANK,
TRAF6, NF-kB, JNK, ERK, p38, NFATc1,TRAP, CATK, MMP3 were significantly
higher than normal control group, P<0.05.(Table 3) Immunohistochemical
results showed that TRAP positive cells in AS synovium was
much more than the control group, P <0.05.

Table 1 the correlation
between RANKL
and
BASDAI, BASDFI, BASMI, HYPNALGIA, PGA,
HAQ

Table 2 relative
intensity of ratio of signaling molecules to b-actin

N:
normal group, AS: AS group, *
P<0.05.

Conclusion: RANKL
was highly expressed in active AS patients’ serum. Furthermore, experimental results
suggested that
the
mechanism of bone destruction in AS could be: much RANKL
combined with RANK, and activated RANKL/RANK pathways, then induced
differentiation of monocyte – macrophages into a large number of mature
osteoclasts, and eventually caused bone destruction. Serum RNAKL level could
indicate the possibility of bone destruction in active AS patients, but could
not reflect the progression of AS. Blocking the RANKL/RANK pathway would be an
important method for treating bone destruction of AS.