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IMMOTA MANET
Professor of Rheumatology and Chief
ImmunoRheumatology Clinical Unit,
University Hospital
University of L’Aquila, L’aquila
ITALY
Bone–Cartilage
cross-talk in
inflammatory arthritis
patients
Prof. Roberto Giacomelli MD, PhD
Alexandria March 2016
Introduction
The ostheocondral junction
Encompasses the region between the deeper layers of articular
cartilage and the underlying subchondral bone. In the normal joint it
comprises the deeper non-calcified cartilage, the tidemark, calcified
cartilage, the cement line, and subchondral bone plate.
S. Suri, D.A. Walsh / Bone 51 (2012) 204–211
Cross-talk between subchondral bone
and articular cartilage
Subchondral bone influences the overlying articular
cartilage not only through its biomechanical properties,
but also biochemically.
Osteoblasts, osteoclasts, osteocytes and bone-lining cells
may each engage in molecular interactions with the
articular cartilage.
The close physical relationship between subchondral bone
and the cartilage has introduced the concept of
biochemical and molecular cross-talk across this region.
S. Suri, D.A. Walsh / Bone 51 (2012) 204–211
Cross-talk between subchondral bone
and articular cartilage II
S. Suri, D.A. Walsh / Bone 51 (2012) 204–211
Normal articular cartilage is hostile to vascular
invasion, in part due to its matrix composition.
In normal adult cartilage, chondrocytes synthesize
matrix components very slowly.
Important products of their activity to mantein
the homeostasis are anti-angiogenic factors such
as the regulatory peptides troponin I and
thrombospondin-1, and inhibitors of matrix
degrading enzymes, including tissue inhibitors of
metalloproteinases (TIMPs), secretory leukocyte
proteinase inhibitor and plasminogen activator
inhibitor-1.
S. Suri, D.A. Walsh / Bone 51 (2012) 204–211
C-met signaling pathway
An
important
pathway
of
signalling
across
the
osteochondral junction may be illustrated by hepatocyte
growth factor (HGF) and its receptor c-Met
C-Met is expressed by articular chondrocytes, in which
HGF can promote type II collagen and proteoglycan
synthesis
D. Pfander et al.: Hepatocyte growth factor in osteoarthritis
C-met signaling pathway II
In normal human cartilage HGF proteins were found in the
territorial matrix surrounding chondrocytes of the lower
deep zone and within calcified cartilage.
Only weak or absent HGF RNA transcripts were identified
in these locations by in-situ hybridization .
The HGF receptor protein was detected in normal
cartilage in a cellular or pericellular distribution. mainly in
the chondrocytes of the deep zone and within calcified
cartilage.
D. Pfander et al.:Osteoarthritis and Cartilage (1999) 7, 548–559
Chondrocyte response to injury
The chondrocytes reaction pattern after an injury is at first
glance rather heterogeneous and they can basically be
summarized in different categories:
proteoglycan
Phenotypical
modulation
Sandell LJ, Arthritis Res 2001, 3:107–113
Human chondrocytes were isolated from OA cartilage and cultured in
alginate beads for 4 or 10 days in the absence or in the presence of
osteoblasts in monolayer. The osteoblasts were either isolated from nonsclerotic (N) or sclerotic (SC) zones of human subchondral bone. Before
co-culture, osteoblasts were incubated for 72 h with IL-1b, IL-6 or
oncostatin M
SOX9, COL1, COL2, COL10, osteoblasts-stimulating factor, ALP, PTHrP and
its receptor PTH-R mRNA levels in chondrocytes are incresed
OsteoArthritis and Cartilage (2005) 13, 988e997
OsteoArthritis and Cartilage (2005) 13, 988e997
SC osteoblasts induced a phenotypic shift in OA chondrocytes that
could lead to hypertrophic phenotype and subsequently to matrix
mineralization.
IL-1b, IL-6 or OSM-treated osteoblasts isolated from N subchondral
bone fail to reproduce the SC osteoblasts effects, suggesting that the
factor(s) involved in this process is (are) not produced or produced in
an
inactive
form
by
IL-1b,
IL-6
or
OSM
stimulated
normal
osteoblasts.
OsteoArthritis and Cartilage (2005) 13, 988e997
Crosstalk Between Chondrocytes and
Osteoblasts in OA
Chondrocytes in response to changes in their chemical and
mechanical environment are activate and after they produce
several inflammatory response proteins, such as cytokines,
including IL-1β, IL-6, and TNF, and matrix-degrading enzymes
including the metalloproteinases and a disintegrin and
metalloproteinase with thrombospondin-like motifs.
The innate immune system is activated in osteoarthritis.
Chondrocytes express many toll-like receptors, which are
activated by damage-associated molecular patterns. In
osteoarthritis, these patterns consist of extracellular matrix
molecules that include the glycosaminoglycan hyaluronan.
Calcium pyrophosphate and sodium urate crystals also bind
chondrocyte toll-like receptors and might therefore play a
part in the aetiology of osteoarthritis.
Lancet 2015; 386: 376–87
Pan J, Bone 51 (2012) 212–217
Morphology and vascularity at the osteochondral
junction
Vascular densities for OA and RA were higher in the non-calcified cartilage, and lower in the
subchondral bone.. RA cases were more likely to display proliferating ECs in vascular
channels than were PM cases .
Smooth muscle a-actin
positive cells
Vascular channels stained
for CD34-positive ECs
Walsh D, Rheumatology 2010;49:1852–1861
Vascular growth factor expression in
articular cartilage and bone
VEGF-positive cells
VEGF-positive
Chondrocytes
were predominantly localized to
the superficial zone of articular
cartilage of OA cases.
PDGF-positive cells
PDGF-positive cells in
vascular channels were
most abundant in RA
Chondrocytes displaying VEGF
immunoreactivity in deep (RA)
and superficial (OA) articular
cartilage
Walsh D, Rheumatology 2010;49:1852–1861
Comparison of OA and RA
Cartilage damage and chondrocyte response secondary to bone/cartilage cross-talk
is a key feature in inflammatory joint diseases, such as rheumatoid arthritis and in
degenerative joint disorders- osteoarthritis.
Joint damage in OA and RA proceeds via different pathways that nonetheless
share certain mechanistic similarities.
Nature Reviews Rheumatology 11, 606–615 (2015)
Interaction of cartilage matrix and
chondrocytes in OA
In OA, cartilage loss occurs as part of a complex programme that resembles
aspects of embryonic bone formation through endochondral ossification.
Nature Reviews Rheumatology 11, 606–615 (2015)
Inflammatory cells in subchondral bone
spaces are associated vascular channels
CD3-positive lymphocytes within fibrovascular tissue occupying subchondral
bone spaces in RA and OA
Mononuclear CD68-positive cells
Walsh D, Rheumatology 2010;49:1852–1861
Cartilage damage in RA triggers the
tissue response and FLS activation
In RA, early cartilage damage is a key trigger of cellular reactions
in the synovium. In a proposed model of RA as a site-specific
manifestation of a systemic autoimmune disorder, early cartilage
damage in the context of immune activation leads to a specific
cellular response within articular joints that could explain not only
the organ specificity of RA, but also the chronic nature and
perpetuation of the disease
Nature Reviews Rheumatology 11, 606–615 (2015)
Lymphoid aggregates with lymphoid neogenetic
subchondral side of the joint in established RA.
features
are
detectable
on
the
The local inflammation/aggregation process appears to be related to osteoclast
differentiation on the marrow side of subchondral bone, supporting a functional role of
the bone compartment in local carthilage damage.
Cross-talk between synovial fibroblasts and immune cells is suggested to
play a crucial role in inflammation and chronification of RA.
In B cells-SF cocultures the concentrations of IL-6 and IL-8 increased
manifold compared with single cultures and remained stable for several
days after B-cell removal.
Intracellular staining confirmed SF as key producers of IL-6 and IL-8, and
B cells as main producers of TNFα and IL-1ß.
Blocking experiments with a combination of anti-TNFα-antibodies and rIL-
1RA significantly reduced SF cytokine production by up to 90%, suggesting
that B-cell-derived TNFα and IL-1ß were crucial mediators of SF
activation.
Besides cytokines, B-cell-activated SF also upregulated secretion of matrix
metalloproteases such as MMP-3, thereby acquiring potential tissue
destructive properties.
Storch H, Ann Rheum Dis. 2015 May 18
Histologic features of femoral heads obtained
from patients with ankylosing spondylitis
In areas without cartilage the
density of mononuclear cell
infiltrates in the subchondral
bone marrow was clearly lower
or absent
Dense rims of osteoblasts along
the bone trabeculae were
present in areas without
cartilage
CD3 T cell aggregates
The number of CD3 T cell follicles in
AS patients was significantly higher
than in OA patients, but was similar
to that in RA patients.
In AS patients, the number of
lymphocytic
infiltrates
was
significantly reduced in areas of
complete cartilage destruction as
compared with areas with remaining.
This clearly differed from the findings
in RA patients, where T cell follicles
persisted even in the absence of
surface cartilage.
In RA patients, the number of CD3 T
cell follicles was slightly increased in
areas without cartilage as compared
with areas with remaining cartilage
Interstitial T cells positive for CD4 and CD8
In femoral heads with
cartilage on the surface,
CD4 T cells and
CD8
T
cells
were
significantly increased in
AS patients as compared
with OA patients.
In
RA
patients,
in
contrast, the number of
CD4 T cells at sites with
cartilage on the surface
was similar to that in AS
patients.
The number of CD8 T
cells in AS patients was
significantly higher than
that in RA patients.
CD68 osteoclastic foci at the bone–cartilage
interface
These findings suggest that the subchondral bone
marrow and bone–cartilage interface are primary
sites of inflammation in AS and that cartilage
might
be
necessary
for
the
induction
of
inflammation, and cross-talk between cartilage
and subchondral bone may be different from RA
and OA
Conclusions
The crosstalk at the bone/cartilage interface may be elevated in inflammatory
arthritis patients in vivo and in vitro.
Increased
vascularisation
and
formation
of
microcracks
associated
with
abnormal bone remodelling in joints facilitate molecular transport from cartilage
to bone and vice versa.
Recent reports suggest that several critical signalling pathways and biological
factors are key regulators and activate cellular and molecular processes in
crosstalk among joint compartments.
Therapeutic interventions including angiogenesis inhibitors, agonists/antagonists
of molecules and drugs targeting bone remodelling are potential candidates for
this interaction.
A better understanding of crosstalk in bone/cartilage interface may lead to
development of more effective strategies for treating these patients.