Hyaluronan in articular cartilage: Analysis of hip osteoarthritis and osteonecrosis of femoral head

概要

主論文の要旨

Hyaluronan in articular cartilage: Analysis of hip
osteoarthritis and osteonecrosis of femoral head
関節軟骨中のヒアルロン酸分析：変形性股関節症と
大腿骨頭壊死症の比較

名古屋大学大学院医学系研究科
運動・形態外科学講座

総合医学専攻

整形外科学分野

（指導：今釜 史郎 教授）
张 佳瑞

【Introduction】
Osteoarthritis（OA）is a degenerative disease causing joint pain, stiffness, and swelling as
the main symptoms. The most common pathological changes in OA joints include loss and
destruction of articular cartilage, formation of osteophytes, synovial inflammation, and
degeneration of ligaments.
In human articular cartilage, hyaluronan (HA) plays important roles as one of the main
components of extracellular matrix (ECM) molecules. Many aggrecans bound to HA maintain
the required compressive resilience.
HA is synthesized by hyaluronan synthase (HAS), of which there are three isoforms. HAS2
is considered to be most important enzyme among the three of them in articular cartilage.
HAS2 is known to produce high molecular weight (MW) HA. Previous reports indicated that
HA degradation mainly relied on hyaluronidase (HYAL) 1,2; however, research results on
HYAL1 and HYAL2 do not support their being central HYALs.
Recently, KIAA1199 has been reported to be an enzyme that powerf ully degrades HA
independently of CD44 and HYAL1,2. The discovery of this new HYAL, KIAA1199, has led
to several studies on the involvement of KIAA1199 in OA cartilage and synovium, and the
results have been reported. KIAA1199 is upregulated in OA chondroc ytes and leads to the
degradation of high MW HA in OA cartilage. KIAA1199 expression is significantly higher in
OA synovium than in normal control synovium. However, no studies have reported KIAA1199
involvement in osteonecrosis of femoral head (ONFH) in comparison to hip OA.
ONFH is a disease characterized by the death of osteocytes and bone marrow mostly caused
by ischemia of the femoral head. Bone necrosis eventually causes collapse of the femoral head.
Due to lack of cartilage nutrition, the collapsed area will become degraded and softened.
Several studies performed gene expression analysis on ONFH, and reported high expression
of some chondrogenesis- or ECM-related genes. However, these studies could not identify any
HA-related genes including KIAA1199. In the present study, HA status and metabolism in
articular cartilage of human ONFH were investigated focusing on KIAA1199 in comparison to
OA and control cartilage.
【Material and Methods】
Human articular cartilage tissues of ONFH, OA, and control were o btained from femoral
head (n = 27, mean ± SD age: 59.4 ± 14.03) (Table 1). Tissues of ONFH and OA were retrieved
during total hip arthroplasty. Control cartilage tissues were obtained during artificial head
replacement for femoral neck fracture or hip disarticulation surgery for mali gnant bone and
soft tissue tumors at our institution. OA cartilage specimens were taken from the
macroscopically damaged part of the femoral head. ONFH cartilage specimens were taken
from the cartilage in collapsed areas of the femoral head. Control group cartilage specimens
were taken from femoral head cartilage was macroscopically normal and without any

-1-

osteoarthritic changes on preoperative X-ray.
During the process of extracting HA from cartilage, we use deferoxamine to inhibit the
depolymerization of high molecular weight (MW) HA. The amount of HA and the MW in the
cartilage tissue were analyzed by competing HA ELISA and chromatography, respectively. The
mRNA expression of HAS1, HAS2, HAS3, HYAL1, HYAL2, and KIAA1199 was evaluated
using quantitative RT-PCR, and the tissue distribution of KIAA1199 and HA was analyzed by
immunohistochemical staining for KIAA1199 and staining with HA -binding protein (HABP).
All data are expressed as mean ± SD. The Mann–Whitney U-test followed by Bonferroni
corrections was used to assess two independent groups, with values of <0.05 considered
significant.
【Results】
According to the immunostaining results. Overexpression of KIAA1199 was observed in the
region of fibrillation and cracks in OA cartilage and positivity of HABP staining was reduced.
There was remarkably decreased expression of KIAA1199 in the cartilage of the ONFH
collapsed part, and a slight decrease in HABP staining was observed.
The MW distribution results show that MW of HA in OA cartilage was increased, while in
ONFH it was decreased.
The HA content in OA cartilage (0.33 ± 0.23 μg/mg) was lower than control cartilage
(0.80 ± 0.40 μg/mg); however, it was not significant (p = 0.154). The HA content in the ONFH
cartilage varied widely, and no particular tendency was observed.
Results of RT-PCR showed that mRNA expression of HAS2 and KIAA1199 was increased
in OA cartilage, and the mRNA expression of genes related to HA catabolism was decreased
in ONFH cartilage.
【Discussion】
HAS2 is considered to be the key HA synthase in cartilage and produces high MW HA.
Overexpression of HAS2 in OA cartilage in the present study might be the main ca use of the
increase of HA MW, whereas, inactivated HA metabolism may result in the lowered HA MW
distribution of ONFH.
Regarding the pathogenesis of ONFH, ischemia is considered the main cause of femoral
head necrosis, cartilage in ONFH was considered to be in a nutrient deficiency environment.
Meanwhile, the synthetic process of HA requires sufficient energy supply. We speculate the
nutrient deficient environment cause the inactivation of molecules which related to the HA
metabolism, resulting in the reduction of HA molecular weight in ONFH cartilage.
The amount of HA in OA cartilage showed a downward trend but was not statistically
significant, and it is speculated that it might be caused by the imbalance of HA catabolism and
anabolism. Although the lytic enzyme of HA, KIAA1199, shows very active, overexpression

-2-

of HAS2 may compensate for part of the HA loss in OA cartilage. Considering that KIAA1199
was found to play a key role in HA catabolism in arthritic synovium, we guess that excess HA
in OA synovial fluid may partially originate from degenerated cartilage and be depolymerized
into small molecules by KIAA1199 in synovium.
According to the previous report, cartilage above necrotic zone in ONFH may not have
progressed to identical pathological state, it might be responsible for the large variance of HA
content and size in ONFH cartilage.
KIAA1199 was found to be overexpressed in OA knee cartilage and synovial tissue and play
a key role in the process of HA degradation. The expression of KIAA1199 was also increased
in hip OA cartilage, but not in ONFH. These results help to make a clear distinction between
the pathophysiology of articular cartilage in OA and ONFH.
【Conclusions】
HA metabolism in ONFH cartilage was suggested to be slow and was activated in O A with
high expression of KIAA1199. The fact that the MW of HA in OA cartilage did not decrease
may be related to the increase in the synthetic system, HAS expression.

-3-

Table 1
Age
Classification

Case

mean± SD
Control

OA

ONFH

59.6±11.95

7
K-L Grade

Case

2

1

3

4

4

5

Ficat stage

Case

III A

5

III B

2

IV

3

63.8±11.64

54.8±17.12

-4-