This document provides an overview of molecular and cell biology concepts relevant to orthopaedics. It discusses the cell cycle and DNA transcription/translation. It also covers topics like cell biology of aging, bone healing, growth factors/cytokines, and the coupling of osteoblasts and osteoclasts. The document aims to explain these concepts in 3 pages through defining key terms and processes.

1. MOLECULAR AND CELL
BIOLOGY IN ORTHOPAEDICS
PRESENTER; DR DENNIS MWENDWA
SUPERVISOR;DR GAKUYA
12th JAN 2021

2. OBJECTIVES
• The cell
• DNA transcription/translation
• Cell biology of aging
• Bone healing
• Growth factors/cytokines
• Orthobiologics
• Musculoskeletal developmental biology
• Expression of cellular phenotype
• Molecular testing
• Tissue engineering
• Gene Therapy
• Molecular basis of disease

3. The cell

7. Cell cycle

8. Cell cycle
• Begins after mitosis
• G1;make more organelles, synthesize proteins and enzymes.
• Labile, stable and permanent cells
• S; Dna replication regulated by dna polymerases
• G2; cell growth
• G0;quiescent phase

10. DNA TRANSCRIPTION/TRANSLATION
• Double-stranded helix structure
• Adenine-thymine,guanine- cytosine.
• Nucleotide;DNA sugar, phosphate group,one nitrogenous base.
• Nucleotide sequence in one strand determines the complementary
sequence in the other
• Codons;sequences of three nucleotides.
• Genetic code in codons, templates for messenger (m)RNA generation
then translation into proteins

11. ct
• 1 codon;one amino acid
Gene; Portion of DNA that codes for
a specific protein
• Unwinding of DNA for
transcription;DNA topoisomerase.
• Exons;regions of DNA that code for
mRNA.
• Introns; regions of DNA between
exons; 97% of the human genome
noncoding.
• Splicing;processing ,removal of
introns, combining of exons.

12. ct
RNA; Important differences from
DNA:
• RNA;single stranded ribose sugar
• Hydroxyl group attached to
pentose ring in 2′ position;less
stable.
• Found in both nucleus and
cytoplasm
• No thymine,Adenine -uracil.
• mrna;strand of RNA transcribed by
exons.
• Translation;Building of a protein
from mRNA through amino acids
• (t)RNA carries a specific aa to the
site of protein synthesis, based on
the mRNA codon.

13. Cell biology of aging
Crucial processes responsible for regulating cellular health in aging include;
1.Chromosome/telomere regulation; telomeres cap chromosomes and protect them from damage.Shortening associated with decline
in innate immunity and cellular sensescence.
2.Transcriptional regulation is key in coordinating activation of many genes to extend lifespan.
3. Nuclear trafficking and organization; eukaryotic nuclear pore complex[npc]; exporting messages and proteins across the
cell,cellular regulation and health,tumour suppression.
4. Protein translation; Down regulation of translation upon reduced nutrient availability extends lifespan in many organisms.
5. proteostasis; maintenance of protein quality by culling of misfolded and damaged proteins and replacement with newly formed
proteins.
6. Unfolded protein response; monitors quality of unfolded aa chains in ER. UPR dysregulation linked to many age related diseases.
7.Autophagy; organelle consumption by the cell. Inhibition;accelerated aging. Downregulation/dysregulation linked to dx eg
parkinsons,alzheimers
8. Cytoskeletal integrity; dysregulation an indicator of cellular aging. Cytoskeletal disruptions can cause degenerative neural dx.
Hyperphosphorylation of microtub ass. tau protein leads to formation of neurofibrillary tangles

14. BONE HEALING

16. DIAMOND CONCEPT OF FRACTURE HEALING

17. OSTEOINDUCTIVE MEDIATORS
Bleeding, coagulation cascade, fracture haematoma[platelets and
macrophages], release of cytokines
stimulating a cascade of events to initiate healing.
Proinflammatory ILs 1, 6, 8, 10 and 12, (TNFa), activated protein C
(APC), monocyte chemoattractive protein (MCP[, (M-CSF),(RANKL)
,(OPG).
Mediators with direct effect on progenitor cells to undergo the
process of mitogenesis and osteoblastic differentiation
 include; PDGF,VEGF,FGF,IGF ,TGFβ,BMPs

18. OSTEOGENIC CELLS
• Committed osteoprogenitor cells[periosteum] ,undifferentiated multipotent stem
cells (MSCs) [bone marrow],endothelial progenitor cells
• activated according to the local fracture environment in the haematoma
• cytokine release , inflammation, increased blood flow,vascular permeability,
chemotaxis,activation of the complement cascade.
• Osteoclasts/fibroblasts initiate conversion of haematoma into granulation tissue,
laying down a fibrin meshwork which is then invaded by a new capillary network
allowing further MSC migration.
• Then proliferation and differentiation of MSCs, hard and soft callus formation
• Influenced by the mechanical micro-environment and fracture biology.
• Higher oxygen tension;preferential MSC differentiation into osteoblasts
• Peripheral (cortical) zone, osteocalcin initiates periosteal osteoblasts to produce
type 1 collagen, leading to intramembranous ossification (hard callus).

19. ct
• Central (medullary) zones;MSCs develop into chondrocytes, laying down
type 2 collagen (soft callus) … endochondral ossification
• By week 3;osteocalcin induces calcification and hard callus formation.
• Mineralisation of callus into an osteoid-type matrix and type 1 col fibrils
leads to bridging of the fracture site,woven bone formation
• BMPs;induce osteogenic activity in mesenchymal stem cells and
maturation of lamellar bone, coordinate osteoclastic activity.
• Bone remodelling by bone multicellular units (BMUs) in a process of
activation, resorption, reversal and formation, taking at least 6 months to
complete.
• Disordered woven bone[weak]develops into stronger, organised lamellar
bone following Wolff’s law[ trabecular pattern of bone corresponds to the
mechanical stresses placed upon it]

20. Extracellular osteoconductive matrix
• Acts as a scaffold
• promotes migration and adhesion of osteoinductive and osteogenic cells to
the fracture site.
• Good apposition; necrotic bone at the fracture site serves this purpose.
• Insufficient ‘natural’ scaffold;autograft,allograft, (DBM)
• MECHANICAL ENVIR; In the presence of appropriate growth factors,
tension encourages fibroblasts,
shear…chondroblasts,compression/distraction… osteoblasts.
• VASCULAR SUPPLY; if compromised higher risk of non-union;insufficient
osteoinductive/osteogenic cells

21. Relevant growth factors and cytokines
Cytokines;Low-molecular-weight proteins that bind to receptors and elicit cellular responses.
Growth factors; proteins with diverse effects on cellular differentiation, proliferation, and function.
INTERLEUKINS;
1. IL-1—proinflammatory, initiates acute phase response, induces bone loss [osteoclast
activation].osteoporosis and inflammatory joint diseases
2. IL-6;- proinflammatory,B cell maturation,
produced by osteoblastic cells, bone marrow stromal cells, and synovial cells
Activates osteoclasts
Reduce RANKL-induced osteoclast formation and bone resorption
Paget disease, GCT
IL-6 receptor blocking antibody is currently being tried for the treatment of rheumatoid arthritis

22. ILs ct
• IL-7;dvlp of memory T cells after an infection,bone
homeostasis,osteoclastogenic activity, inhibition of osteoclastogenesis.
• IL-10;anti-inflammatory[ producedT cells, B lymphocytes, mast cells]
stimulates humoral and cytotoxic immune responses, attenuate localized
inflammation[RA, osteomyelitis]
• IL-17;inducing and mediating proinflammatory responses, influence
production of IL-6, M-CSF, IL-1β, TGF-β, TNF-α ,IL-8.
• Interacts with fibroblasts, endothelial cells, keratinocytes, and
macrophages.
• Function is crucial for CD4+ (T helper or Th17) cells, which play a role in
many autoimmune diseases eg RA
• IL-17 inhibitors being tested as treatment for RA

23. Interferon-γ
• Produced by T cells and natural killer cells
• Responsible for cell-mediated immunity.
• Regulate osteoclast function/formation in human and mouse studies
• Inhibits osteoclastogenesis in vitro,
• in vivo experiments revealed an opposite effect.

24. Tumor necrosis factor
• Proinflammatory in response to viral infections and cancer.
• Regulates osteoclast differentiation and bone resorption.
• Marked increase ;inflammatory joint diseases and osteolytic
disorders.
• Works synergistically with RANKL to stimulate osteoclastogenesis.
• Stimulate RANKL independent osteoclast differentiation in presence
of M-CSF.
• TNF-signaling targeting is used to modify inflammatory arthritis

25. BMPs
• subfamily of the TGF-β superfamily of growth factors.
• Regulation of tooth, limb development, dorsal patterning of the spinal
cord
• Induce bone and cartilage formation.
• BMP-1,metalloprotease,functions as a C-propeptidase for types I, II,
and III collagen.
• BMP-2;induces chondrogenic differentiation of mesenchymal cells.
• BMPs -5, -6, and -7;osteoinductive agents.

26. bmps
• BMP-6 and BMP-7;promote the endochondral calcification pathway.
• Induction of apoptosis in the interdigital web spaces
• BMP receptors;type I receptors, A and B, and one type II receptor.
• Activation of BMP rcptrs leads to nuclear transport of Smad
transcription factors for gene expression.
• Abnormal function of type I receptor;fibrodysplasia ossificans
progressiva; excessive ectopic bone formation in the soft tissues

27. Transforming growth factor beta
Produced by osteoblasts, chondrocytes, and cancer cells.
• Stimulates proliferation of cells of mesenchymal origin
• Activation achieved by acidic, heat, or enzymatic cleavage.
• TGF-β signaling ;metastatic bone cancers, carpal tunnel syndrome,
and arthritis.
• Stored in bone matrix in a latent form.
• During bone resorption its released and activated by acidic ph

28. TGFB
• Metastatic breast cancer;breast cancer cells stimulate osteoclastic
bone resorption, TGF-β promotes cancer cell growth, increases
angiogenesis, and inhibits host immune cells.
• Stimulates proteoglycan synthesis in chondrocytes,osteoblast
proliferation,matrix synthesis.
• Marfan syndrome;excessive TGF signaling…. aortic dilatation
• PRP also contains TGF-β.

29. PTH/PTHrP
• Regulates serum calcium.. bone, kidney, and intestine.
• Osteoblasts have PTH receptors and promote osteoclast formation by
producing RANKL in response to PTH.
• PTH stimulates kidney calcium reabsorption and calcitriol ;small intestine.
• PTH;anabolic effects on bone. formation>resorption
• Daily injection of PTH1-34;tX of osteoporosis .
• PTHrP;regulates endochondral bone formation, growth plate development,
oncogenesis.
• PTHrP stimulates the proliferation of chondrocytes and the suppression of
genes involved in chondrocyte maturation.

30. Indian hedgehog,sonic hedgehog,WNT
• Ihh; chondrocyte and osteoblast differentiation during prenatal bone
formation.
• Maintenance of the growth plate and postnatal skeletal growth.
• Present in the prehypertrophic chondrocytes; promotes chondrocyte
proliferation and differentiation into hypertrophic chondrocytes.
• Ihh induces perichondrial cells to produce PTHrP.
• PTHrP ;negative feedback signal to prehypertrophic chondrocytes,maintain
a pool of proliferating chondrocytes in the growth plate during skeletal
immaturity
• Shh a major morphogen in patterning of limb buds.
• Hh mutations;abnormal digit number

31. CT
• IM ossification; Ihh promotes bone formation by regulating osteogenic
differentiation rather than proliferation.
• Mice studies showed the importance of Ihh signaling in endochondral bone
formation.
• Mutation of the Ihh gene; brachydactyly.
• OsteophyteS[OA] are formed during pathologic endochondral ossification of
quiescent articular chondrocytes.
• Ihh;diagnostic marker,blockers; potential targeted therapy for OA
• Multiple osteochondromatosis ;increase in Ihh signaling and enhanced cell
proliferation by mutations of PTH type I receptor and subequent loss of
Ihh/PTHrP negative feedback.

32. Signalling ct
• Hh and Wnt signalling regulate cartilage development, endochondral bone
formation and synovial joint formation.
• Ectopic Hh signaling/overexpression of shh in the cartilage;joint fusion.
• synovial joint formation;upregulating Ihh signalling and inactivating Wnt
signaling.
• Ihh kept at a low level to prevent joint fusion.
• Hh role bone homeostasis, and reducing Hh signalling protects against age-
related bone loss.
• Activated Hh signalling in mature osteoblasts in adult mice leads
osteoporosis

33. IGF[1 and 2]
• Insulin-like growth factors [somatomedin C];anabolic hormone-like
proteins,structure is similar to that of insulin.
• Regulate growth, differentiation, and homeostasis of adult tissues.
• Activation of receptors leads to myoblast differentiation.
• Hypoxic microenvironment; myoblast differentiation inhibited
,cellular proliferation stimulated
• IGF-1 deficiency;dwarfism due to ineffective relaying of signals
between growth hormone and growth plates.
• Aberrant activation of IGF signaling seen in osteosarcomas

34. Fibroblast growth factors
• In the cartilage matrix and bone.
• FGF-1 and FGF-2 are the most common
• With heparin/heparan sulfate, FGFs activate FGF receptors, activation of
signaling cascades and genes involved in cellular processes;migration,
proliferation, apoptosis, angiogenesis, and wound healing.
• FGFR types 1 and 2 mutation; craniosynostosis.
• FGFR3 signaling suppresses chondrocyte proliferation.
• FGF23 a causative factor in tumor-induced osteomalacia.
• FGF-23 inhibits phosphate reabsorption in the prt,inhibits 1α-hydroxylase,
…decreased 1,25- dihydroxyvitamin D3 levels.

35. VEGF
• Stimulates angiogenesis
• endochondral bone formation and bone regeneration.
• Produced by; endothelial cells,bone marrow stromal cells, osteoblasts
• in response to bone injury and a bone repair process is necessary
• Cancers are associated with autonomous and increased angiogenesis.
• VEGF-targeting agents are undergoing clinical trials.

36. Osteoblast osteoclast coupling
• Remodelling of bone throughout life .
• Cycle commences with osteoclast recruitment by cytokines (IL-6)
• osteoclasts adhere to areas of trabecular bone and dig pits by secreting hydrogen
ions and proteolytic enzymes
• leads to liberation of factors that are embedded in bone
• Recruit and activate osteoblasts, which have been primed to develop from
precursor cells by PTH and calcitriol
• Osteoblasts invade the pits and synthesize osteoid[organic matrix of bone]
• The osteoid is then mineralized
• Osteoblasts and their precursors secrete IGF-1 and IL-6, which in turn recruit
osteoclasts (a return to the start of the cycle).

37. Coupling ct
• Resorption by osteoclasts and formation by osteoblasts.
• Imbalance…..osteoporosis.
• Osteoblasts and osteoclasts communicate;direct cell-cell contact,
cytokines and extracellular matrix interaction.
• Osteoblasts can affect osteoclast formation, differentiation or
apoptosis through several pathways eg OPG/RANKL/RANK
• Cytokine released from resorbed bone matrix,TGF-β, IGF affect
activity of osteoblasts.

38. OPG/RANKL/RANK
• RANKL[receptor activator of nuclear kappa B ligand] ; membrane-bound on
osteoblasts.
• Binds with its receptor RANK[ osteoclastic progenitor cells]and activates
the down signaling pathways related with cell growth and differentiation.
• Activates TNF receptor-associated factors (TRAFs 2,5 and 6.
• TRAF6 alone can induce osteoclastogenesis and is essential for the
activation of intracellular signal transduction pathways.
• cytokines, hormones and growth factors regulate RANKL expression; PTH,
estrogen, and inflammatory cytokines
• RANK; transmembrane protein member of the TNF receptor superfamily.

39. OPG/RANK/RANKL
• Highly expressed on membrane of osteoclast progenitor, mature osteoclasts and
dendritic cells.
• The cancers with high bone metastatic potential also express RANK, such as breast and
prostate cancer.
• RANK/TRAF regulates osteoclast formation, activation and survival via different signaling
pathways, including JNK/AP-1, IκK/NF-κB, c-myc and calcineurin/NFATc1 for osteoclast
formation; src and MKK6/p38/MITF for activation.
• OPG [osteoclastogenesis inhibitory factor (OCIF)];produced by osteoblasts, heart, liver
and spleen cells
• OPG,decoy receptor, can bind with RANKL and block its binding and activation with RANK
blocking the main signaling pathway of osteoclast differentiation and activation
• OPG regulated by hormones, cytokines and growth factors such as estrogen, 1,
25(OH)2D3 and TNF.

41. Rank/rankl/opg
• Osteopetrosis is observed in transgenic mice over-expressing OPG
• OPG knock-out mice;osteoporosis due to unregulated osteoclasts
• OPG protects against bone loss
• RANKL;drug target for osteoporosis as decreased RANKL expression
results in inhibited bone loss in osteoporotic patients.
• The use of antiRANKL therapy for GCT is underway

42. Coupling[others]
1.Cell-cell contact; osteoblast can communicate with osteoclast via gap
junctions and small water-soluble molecules can pass between the two cell
types.
2. Ephrin2/ephB4; ephrin2 on osteoclast, ephB4 on osteoblast and
osteocytes. Osteoblast can inhibit osteoclast formation via ephb4 and
osteoclast could stimulate osteoblast differentiation via ephrin2.
3. M-CSF/MCP-1;
M-CSF[osteoblasts] important cytokine for survival, differentiation, cell
migration and activity in macrophages and osteoclasts.
Monocyte chemoattractant protein-1 (osteoblasts]; candidate recruiter of
osteoclast precursors.

43. ct
4.Sema3A/Nrp; Semaphorins are axonal growth cone guidance
molecules, which are involved in the interaction between
osteoblasts and osteoclasts
Sema3A inhibits osteoclast differentiation.
5.Lysophosphatidic acid ;
potent bioactive phospholipid produced by osteoblasts.
Osteoblast-derived LPA;regulate the activity of tumor cells in
the skeletal microenviroment and osteoclasts.

44. Macrophage colony stimulating factor
• Necessary for proper osteoclast formation.
• Mutation in mice resulting in a severe osteopetrotic phenotype
• Found to be osteopetrotic due to the absence of M-CSF production.
• M-CSF;regulates macrophage survival and osteoclast formation

45. orthobiologics
Use of biological substances to help musculoskeletal injuries heal
quicker.
Bone grafts,autologous blood,platelet rich plasma,autologous
conditioned serum and stem cells.
Act by delivering growth factors,replenishing dead or dying cells
PRP is a mixture of plasma and platelets in the buffy coat,autologous
growth factors and cytokines; (PDGF), TGF, IGF, VEGF, and IL-8.
Applications of PRP;
Achilles tendinopathy,patella tendinopathy,Lateral epicondylar
tendinopathy,rotator cuff injuries,OA knee,plantar fasciitis

46. Stem cells in orthopaedics
TYPES; induced pluripotent stem cells,embryonic sc,adult somatic sc,protein
induced pluripotent sc,somatic cell nuclear transfer.
Can be used in;
• Spinal cord injury
• AVN
• IV disc degeneration
• Cartilage repair
• Defects and non unions
• Muscular dystrophy
• Inflammatory autoimmune disorders
• O.I

47. Musculoskeletal developmental biology
• Transcription Factors; Proteins Affecting Musculoskeletal Cell
Differentiation, Function, and Phenotypes
• Correct biologic functioning requires tight gene expression regulation
• DNA-binding proteins known as transcription factors control the
transcription of a gene by binding to the regulatory elements found
on the DNA.
• TFs classified into families based on the structural characteristics of
their DNA binding domains.
• Some essential in the cells of the musculoskeletal system (bone,
cartilage, tendon, and muscle).

48. INCLUDE
• Runt related transcription factor
• Osterix
• Twist 1
• Muscle segment homeobox
• Distal less homeobox
• C-fos
• Nascent polypeptide associated
complex and coactivator
• Myogenic regulatory factor
• Myocyte enhancer factor 2
• Nuclear factor of activated t cells
c1
• Nuclear factor kappa light
chainenhancer of activated b
cells
• c/ebp
• scleraxis

50. Expression of cellular phenotype
• Genotype of an organism or a cell refers to the genes present in its
genome.
• only a fraction of the genes are expressed
• regulated by specific interactions with the matrix and various factors
• Phenotype; array of genes that are expressed and their relative levels
of expression.
• Cell Differentiation; acquisition of a specific profile of gene expression
that sets the cell apart from other types of cells, and determines its
structure and function.

51. • Cell proliferation and differentiation inversely regulated.
• Proliferation of normal cells is prevented by cell-cell contacts; contact
inhibition.
• Low densities in culture;no contact inhibition, enter the cell cycle and
proliferate.
• Confluency ;contact inhibition triggers mechanisms that inhibit the
cell cycle, and cells tend to differentiate, expressing specific
characteristics of the tissue from which they were derived.
• This paradigm has been well established in several skeletally relevant
tissues, including in the culture of osteoblasts.

52. CT
Osteoblasts express proteins characteristic of differentiation at confluency such as alkaline
phosphatase, osteocalcin, and osteopontin, and ultimately produce a mineralized osteoid matrix
Cells of most skeletal tissues derived from mesenchymal stem cells
• MSCs give rise to all the skeletal elements during development, and remain present in low
numbers in sites such as periosteum and bone marrow throughout life.
• Can differentiate into bone, cartilage, and fibrous tissue following a fracture and generate a
reparative callus.
• MSCs can be isolated from bone marrow, and under the correct culture conditions can be
induced to differentiate into osteoblasts, chondrocytes, lipoblasts, myoblasts, fibroblasts, and
tenoblasts
• MSCs number/responsiveness to growth factors declines with age; hence, the ability to
regenerate various mesenchymal tissues declines as a function of aging.
• The use of MSCs for regenerating bone and repairing osteochondral defects is well under way and
feasibility has been demonstrated in several animal models.

53. Molecular testing
• Genomics;a branch of molecular biology concerned with the
structure,function,evolution and mapping of genomes.
• Proteomics;study of proteins
• Testing;predisposition,diagnosis,response to therapy,progression.
• Genetic diseases;achondroplasia,OI,Ehlers Danlos,osteopetrosis
• Polymorphism; single nucleotide polymorphism. Profiling allows
prediction,early dx,progression; OA, non
unions,RA,pharmacogenomics

57. Tissue engineering
• Practice of combining
scaffolds,cells,and biologically
active molecules into functional
tissues.
• Science of generating living
tissues.
• Goal is to assemble functional
constructs that restore maintain or
improve damaged tissues or whole
organs.
• Appl; non
union,osteonecrosis,osteochondral
defects

58. Gene therapy
• genetic modification of cells to
produce a therapeutic effect or the
treatment of disease by repairing
or reconstructing defective genetic
material.
• Absent or faulty gene is replaced
by a functional gene in order to
make the correct protein and
eliminate disease.
• appl;impared bone
healing,cartilage repair,metabolic
dx,induction of tumour necrosis

59. Molecular basis of dx
• Achondroplasia— mutation in the FGF-R3, affecting the proliferative
growth plate zone….dwarfism
•Diastrophic dysplasia; Mutation in the DTDST gene on chromosome 5
that encodes for a sulfate transport protein—undersulfation of
cartilage proteoglycans.cccd by hitchhiker thumb, cauliflower ear,
scoliosis, hip dysplasia, cleft palate, foot deformities/club foot.
•Hypophosphatemic rickets; PHEX gene mutation. PHEX regulates FGF-
23, which normally prevents the kidney’s reabsorption of phosphate.
mutation therefore reduces phosphate reabsorption.

60. ct
• Collagen type I (bone) defects:
1. Osteogenesis imperfecta (types I-IV)—COL1A1 and COL1A2
2. Ehlers-Danlos—COL5A1 and COL5A2
• Collagen type II (cartilage) defects:
1.Spondyloepiphyseal dysplasia (SED)—COL2A1, usually random mutations
• Others:
• Multiple epiphyseal dysplasia—COMP (cartilage oligomeric matrix protein
gene also associated with pseudoachondroplasia)
• Marfan syndrome—FBN1 with superior lens dislocation
• Achondroplasia—FGFR3
• Spinal muscular atrophy—SMN1 (survival motor neuron-1]

61. ct
1. VATER/VACTERL—spinal deformity, radius defects
2. Neurofibromatosis (NF)1 (AD)—scoliosis and congenital tibial
pseudarthrosis
3.McCune-Albright—mutation in GNAS gene; fibrous dysplasia
4.Trisomy 21—ligamentous laxity, atlanto-axial instability, patellar and
hip dislocations, severe flatfoot and bunion

62. Hh signaling and bone disease
• Abnormalities of the Hh pathway result in various bone diseases;
1.IHH mutation-brachydactyly type A1 (BDA1)[shortened or missing
middle phalanges]
2. A GLI3 mutation;Pallister–Hall syndrome;syndactyly, polydactyly,
abnormality of limbs or skull or hip dislocations.
3.VACTERL Syndrome;vertebral defects and limb abnormalities, related
to Gli2 or Gli3 mutations.
4.Shh mutations;Smith–Lemli–Opitz syndrome (SLOS);syndactyly and
polydactyly

63. 5.PTCH1 mutations;Gorlin syndrome[ nevoid basal cell carcinoma
syndrome]; polydactyly, rib anomalies, ectopic ossification, spina bifida
6.Genome-wide association studies (GWAS) shown Hh signaling;
regulation of human height
7. Hh signalling upregulated in patients with progressive osseous
heteroplasia (POH);progressive ankylosis and growth retardation
8.Disruption of the Ihh-PTHrP feedback loop; enchondromas and
osteochondromas during childhood.

64. referrences
• The cell biology of aging ;Race DiLoreto and Coleen T. Murphy1
• Osteoblast-Osteoclast InteractionsXiao Chen,1 Zhongqiu Wang,1 Na Duan,1 Guoying Zhu,2 Edward
M. Schwarz,3 and Chao Xie
• The Hedgehog signalling pathway in bone formation;Jing Yang,1,2 Philipp Andre,2 Ling Ye,1 and Ying-Zi Yang2,3
• Orthobiologics and platelet rich plasmaMandeep S Dhillon, Prateek Behera, Sandeep Patel, and Vijay Shetty
• Tissue engineering in orthopaedics; Alexander M Tatara
• ORTHOPAEDIC BASIC SCIENCE
• GANONG;PHYSIOLOGY
• MILLERS REVIEW OF ORTHOPAEDICS