3. • MSC (pluripotent) osteoblast, chondrocyte,
adipose cell, fibroblast and myocyte
• Osteoclast is derived from hematopoietic stem cells
• Wnt/β-catenin pathway : the most important signaling
to lead MSCs toward osteoblastic differentiation and
suppressing adipose development
• Transcription factor facilitate the stem cell
differentiation (migration / ossification)
Runx2 and osterix are essential for differentiation of
the osteoblast lineage.
Sox5, 6, and 9 are markers of chondrocyte
development, with Sox9 having been identified as an
essential regulator
4. SOX9 and the many facets of its regulation of the
chondrocyte lineage(Ref 2).
5. SOX9 and the many facets of its regulation of the
chondrocyte lineage(Ref 2).
6. Endochondral (at physis)：
• Mesenchymal tissue cartilage
template chondrocyte
(hypertrophy / apoptosis /
mineralization) bone formation
• GH, TH , Indian hedgehog and
parathyroid hormone related peptide
(PTHrP)
Primary ossifications
• Start in embryonic adolescence stage
Intramembranous :
• Mesenchymal stem cell contact with epithelial cell
then transfer into periosteum and osteoblast
7. Secondary ossifications
• Only in post-natal stage, widen the bone from
periphery of apophysis
• Classic, step-wise paradigm of mesenchymal
differentiation (major)
Trans-differentiation (Ref. 4)
• Osteocytes chondrocytes
( either direct / intermediate
form )
• Macrophages and B
lymphocytes osteoclast
• Potential therapy for OA and
non-union
10. Cellular biology
Osteoblast
• Abundant rough endoplasmic reticulum and
extensive Golgi apparatus
• Responsible for collagen I and osteoid synthesis
• Pre-osteoblast stage : RUNX2 / PTH expression
of alkaline phosphatase, collagen I and bone
sialoprotein II
• Create a basic environment that helps catalyze
calcium-phosphate crystal deposition
11. Cellular biology
Osteocyte
• Comprise over 90% of all bone cells in adults
• Osteoblast embedded in bone lacunae induce
osteocyte differentiation and dendritic formation
• Through MMP-1 stimulation, lacunar-canalicular
system provide gap junction to communicate
Oxygen and nutrient
To sense acute deformation of bone
• Produce sclerostin and Dkk1 (Wnt inhibitor) to
negatively regulate osteoblastogenesis
12. Cellular biology
Osteoclast
• From hematopoietic stem cells, as multinucleated
cells housed in Howship lacunae
• Creating a closed microenvironment fill with acid and
cathepsin K to degrade bone matrix
13. Resorptive activity of Osteoclast
• (+) : VitD, PTH, PTHrP, prolactin, IL-6 and TNF-
alpha
• (-) : estrogen, calcitonin, TGF-beta and IL-17
14. Cellular biology
Marrow adipocyte
• Marrow adipocytes increase with age and are tightly
correlated with reduced bone mass. (2017)
• Regulation of bone mass modulated by PPARγ and
RUNx2 proteins
• Not only influence the bone metabolism but
negatively affect hematopoiesis
15. Matrix composition
• Calcium hydroxyapatite, the most abundant
substance in bone, 60% to 70% of its mineral
composition
• Type I collagen is the dominant organic substance of
bone, comprising 90% of total protein
• Glycine-X-Y repeating
• Triple helix
• Elasticity
• Fibronectin, another important structural protein of
the bony matrix, helps develop and maintain the
structure of the collagen network
• Non-collagenous proteins : proteoglycans and
osteocalcin
16. Bone metabolism
• Remodeling is ongoing in our daily activity and
replace ~10% of our skeleton every year
• Systemic and hormonal factors : PTH, 1,25-OH Vit
D
• Local factor : TGF-beta, PDGF
• Micro-RNA modulation has also been identified as
a significant regulator of bone remodeling (Ref. 17)
19. Cartilage
• Chondrocyte, the cellular component but only
comprise 5% of dried mass
• Primary substance : Collagen II and water
• SOX5 and SOX6 , interactions with CEBP/p300
increased production of Col II and proteoglycan
• Collagen XI (2017, Ref 20)
• Component of cartilage extracellular matrix
• Chondrogenic properties and supports matrix
production and maintenance
20. Terminal differentiation
• Hypertrophy decreased proliferation apoptosis
bone formation
• Hypertrophy : essential step in pathogenesis of OA,
an irreversible degradation of matrix (2019, Ref. 19)
21. Articular cartilage layer
• Superficial : horizontal fiber, highest collagen conc.
But with limited regenerative capacity
• Intermediate : random fiber
• Deep : radial fiber
• Tidemark :
Injury in this region may cause healing
Replaced by weaker fibrocartilage
22. Synovial membrane
• Synoviocyte
Macrophage-like (type A) : phagocytic, antigen
presenting cell
Fibroblast-like (type B ) : most predominant,
secret HA, fibronectin, collagen and lubricin
Intermediate type (type C) : precursor to other
cells
• Lubricin (2018, Ref. 26)
• Role in maintenance of cartilage and ECM
• Proteoglycan-4 gene expression
28. Meniscus
• Meshwork structure of fibrocartilage with
circumferential (outer) and radial (inner)
• Red-red zone : highly vascular, allow heal after injury
• White-white zone : poor healing potential
29. Cell type
• Outer region : similar to fibroblast and produce
fibrous region containing type I collagen
• Inner region : similar to chondrocyte secret aggrecan
and type II collagen
• Third type cell : progenitor cells
33. Tendons
• Positional tendons
• Extensor, carry little load to keep position
• Greater strength and stiffness
• Energy-storing tendons
• Flexor, drive motion
• Greater sliding and superior fatigue resistance
• Cell component :
• Tenoblast - abundant, one kind of fibroblast
• Tenocyte – similar to tenoblast but lower metabolic
activity
• Chondrocyte (<10%) and synovial cells
34. Ligaments
• Insertion
• Direct : fibers bone
• Indirect : superficial periosteum , deep
bone
• Immobilization will result in precipitous
reduction of tissue strength and mass
• Exercise only increase slightly ligament
strength but not increase size
39. DM medication related fracture risk
• Thiazolidinediones (Avandia, Actos)
• Induce MSC differentiation into adipocyte via PPAR-γ
modulation
40. Malignancy
• Radiation therapy
• Bone necrosis (hypoxic / hypovascular / tissue
breakdown / disrupted wound healing)
• Bone metastasis
• Osteolytic – lung, breast, renal and MM
• Over expression of RANK-L, MMP and PTHrP
• Tumor cell mimicry osteoclast
• Osteoblastic – prostate CA
• Production of immature woven bone
• Major pathway : Tumor cell epithelial – to – mesenchymal
transdifferentiation and osteomimicry
41. Smoking
• Reactive oxygen species (ROS)
• Impair mitochondrial activity / fibroblast migration /
blood flow to injury site
• Risk of infection and osteomyelitis after trauma
• Increased osteoclast number and impaired bone growth
• Greater time to union and impaired chondrogenesis
• Higher rates of spinal fusion failure and pseudarthrosis
Good morning superintendent , dear mentors and my colleagues
Today , my topic is about orthopedic tissue of which the content is from OKU
I hope the is presentation can assist our chief resident to prepare this chapter more easily
The first part is cell origination
As we know, our body cells are from stem cells.
And for orthopedic tissue which are derived from mesenchymal stem cell, one kind of pluripotent stem cells then differentiated into osteoblast, chondrocyte, adipose cell, m fibroblast and myocyte
During this process, the most important pathway is wnt/b-catenin pathway which induce osteoblast differentiation and suppress adipose formation.
And all these expressions are regulated by certain transcription factor, for example,
Runx2 and osterix are critical for …
Sox5/6/9 are markers for chondrocyte development
just like in this picture show, the sox 9 is a homodimer structure which can bind to the super-enhancer region and increase more cartilage gene expression
Sox 9 also play critical role in several stages of chondrocyte maturation
For primary ossifications which start from the beginning of embryonic stage to the adolescent stage.
And there are 2 types, and in intramembranous type, the mesenchymal stem cell contact wit surrounding epithelial cell then …
The other type is endochondral which occur at physis, the MSC developed into cartilage template, then following the infiltration of chondrocyte which go through stage of hypertrophy, apoptosis and finally the bone formation
Several systemic and local factors regulate this process, such as GH, TH , PTHrp and Indian hedgehog
In contrast to primary ossification, the secondary ossifications occur only in post-natal stage with widening of bone from apophysis
And the majority of bone formation is through step-wised MSC differentiation
However, more recent studies have identify the effect of trans-differentiation that is
It has become an issue for the treatment of OA and non-union
this table is from OKU, it show the important transcription factors in different cell line
For example
Here we will talk about the bone, the basic orthopedic tissue
About cellular biology, the first is osteoclast , which has abundant Rough ER and golgi apparatus to synthesize and secret collagen I and osteoid.
And in early stage, after stimulation of runx2 and PTH, the osteoblast can increase expression of alkaline phosphatase, collagen I and bone sialoprotein ii to create a basic environment beneficial for deposition of calcium phosphate
The second is osteocyte which is the major part of bone tissue.
After the osteoblast start to embed in lacunae
After the stimulation of MMP-1, the canalicular system developed and provide the gap junction to transmit oxygen or nutrition and to sense acute deformation of bone
The osteocyte also produce sclerostin and DKK1 both are wnt pathway inhibitor to negatively control osteoblastogenesis
The third is osteoclast which comes from hematopoietic stem cell, it is multinucleated and live in howship lacunqe.
When contact with bone surface, the osteoclast can create a closed ……
In this picture, we can see osteoblast and osteocyte can secret OPG and RANK-L to regulate osteoclastogenesis
Besides the effect of osteocyte, the resorption can also be affected by several hormones and factor, it can be triggered by….. And inhibited by…..
In condition with infection, the bacteria secret LPS to activate MAPKK pathway to increase resorption
In Metastatic cancer, tumor cell can mimic osteoblast to secret RANK-L to trigger osteoclast
In RA case, TNF can also increase the activity of resorption
The last one is marrow adipocyte
We have observed marrow adipocyte increase with age and related to reduced bone mass
And be regulated by PPAR and runx2 proteins
Not only influence the bone metabolism but also inhibit hematopoisis
About the matrix composition, the calcium hydroxyapatite occupy the most of bone and the collagen I is the most dominant organic substance which has glycine x-y repeating, triple helix contour and elastic character.
Other protein such as fibronectin which maintain the collagen framework
About the bone metaboli
Both systemic and local factor can regulate remodeling
Recent study has identify micro-RNA to be a important regulator of bone remodeling
In picture A, we can see there are binding site for different micro RNA
In picture B, runx2 showed different expression level either in osteogenesis and chondrogenesis under control of various microRNA
In terms of cartilage, chondrocyte is the major cellular component of cartilage but only comprise 5% of dried mass
Collagen II and water are primary substance
Expression of sox5/6 along with CEBP/p300 can stimulate chondrocyte to secret more collagen II and proteoglycan
The most recent research is collagen 11 which is one of component in ECM and has a critical role in chondrogenesis and matrix maintenance
Just like previous slide mentioned, chondrocyte will go through a process of terminal differentiation and turn into the bone
And among theses stages, hypertrophy is critical step, especially in OA, once the chondrocyte undergo phenotype shift, it will trigger the irreversible degradation of matrix
For articular cartilage, there are 3 zone with different fiber orientation
Horizontal fibers in superficial zone, random type in intermediate zone and radial fiber in deep zone.
For tidemark, it separate calcified cartilage from deep zone
If cartilage got injured deep to the tidemark region it can cause healing but only replaced by weaker fibrocartilage
Injuries above the tidemark are unable to heal.
In synovial membrane, there are 3 types of synoviocyte,
type-a is macrophage-like with function of phagocytosis and antigen presentation;
type b is fibroblast-like which is the most dominant and secret major component;
type c is intermediate type and it maybe the precursor of other cells
Brush-like structure can avoid the molecules’ detachment by compression and shear force
About the special joint element
Both meniscus and disc share many features
They are composed of fibrocartilage, had function of joint lubrication and sustain load bearing and compression forces
For meniscus, it is a meshwork structure of fibrocartilage with circumferential in outer layer and radial in inner region
The red-red zone with rich vessels allow healing after injury, however, the white-white zone is poor in healing potential
The cell in outer region is fibroblast like which can produce type I collagen and cell in inner region is chondrocyte-like and secret aggrecan and type ii collagen
Also, Exercise effect will change meniscus , for example
Physical loading following immobilization and dynamic compression up
to 10%, decrease degradation and inflammation and increased repair and anabolism
In Pathologic loading states, immobilization and extreme compression or strain
greater than 20%, increase catabolism and inflammation and decreased cell viability.
IVD is also fibrocartilaginous structure like meniscus
Nucleus pulposus is rich in type II collagen and proteoglycan
But for Annulus fibrosus , there are 2 layers.
the outer layer contain fibroblast and secret type I collagen while inner layer is composed with chondrocyte-like cell and secret type II collagen
As we know, disc is totally avascular, nutrient diffuse from subchondral capillary, any occlusion of capillary will increase lactate level and result in disc degeneration
Tendon and ligament share similar composition and provide bone stability and activity
There are two types of tendon, one is position tendon which is common in extensor part and carry little load to keep position, it has greater strength and stiffness
The other one is energy-storing tendon which can drive motion
About Cell component, the most abundant is tenoblast , not tenocyte.
tenocyte is similar to tenoblast but with lower metabolic activity.
There are also chondrocyte and synovial cells in tendons but less than 10%.
For ligaments, there are 2 types of insertion, direct and indirect
Prolonged immobilization will decrease tissue strength and mass, however, exercise training only increase a little strength but not increase mass
The last part is the factor that can affect the bone quality
bone mass is determined by a balance between formation and resorption. It is also affected by race , gender , age , systemic and local factor
Aging bone is due to remodeling dysregulation, that is bone formation decreased slightly but the resorption rate is still the same
The other factor is increased cross-linked collagen which can cause the bone to be more brittle and easy got fractured.
For DM patients, hyperglycemia can increase glycosylated end product to damage cell and microvascular compromise.
Hyperglycemia also lower the level of PTH and IGF-1 while increase the sclerostin and DKK1 which inhibit the new bone formation and finally increased fracture risk with poor bone healing
Medication for DM such as Actos has been studied to induce MSC turn into adipocyte and increase fracture risk
ROS is end-product of smoking which can impaired mitochondrial function and cause many complications,
