bone formation and resorption

bone formation and resorption

1. BONE FORMATION AND RESORPTION PRESENTED BY, Dr. Dandu Sivasai Prasad Reddy 1 st yr PG Mamata dental college

2. CONTENTS: Introduction Classification of bones Shape Development: Intramembranous ossification Immature and mature bone Intracarilaginous bone formation Microscopic structure Composition of bone Bone cells Osteoblasts Bone lining cells Osteocytes Osteoclast

3. Bone formation and factors affecting bone formation Bone resorption Differences between resorbed and unresorbed surfaces Role of TRAP in bone resorption Factors affecting bone resorption Bone remodelling Sequence of events Mediators Markers of bone turn over Conclusion References

4. introduction

5. CLASSIFICATION OF BONES : Shape development histology Long flat irregular endochondral Intramembranous sutural mature immature compact cancellous short

6. Classification… Based on shape: Long bones Short bones Flat bones Irregular bones

7. Based on shape Limbs Carpals Tarsals Vertebrae Skull bones, Ribs Sternum, Scapula

8. Classification… BASED ON DEVELOPMENT : ENDOCHONDRAL BONES: Intra cartilaginous or endochondral bone formation or indirect bone formation :

9. Classification… INTRAMEMBRANOUS BONES : Intramembranous ossification/direct bone formation SUTURAL BONES: Growing face and skull.

10. Classification… BASED ON MICROSCOPIC STRUCTURE :

11. COMPOSITION OF BONE :

12. Composition of Bone … Inorganic component: Hydroxyapatite crystals with carbonate content Organic component: - Osteoid Type I collagen (95%) type V collagen (<5%) Non collagenous proteins Osteocalcin , Osteopontin , Bone sialoprotein , Osteonectin .(SPARC)- Cell adhesion ,proliferation, modulation of cytokine activity.

13. Osteoblasts : Derived from osteoprogenitor cells Periosteum serves as important reservoir . Morphology : basophilic cuboidal or slightly elongated cells contain prominent bundles of actin, myosin BONE CELLS:

14. Formation : Pleuripotent stem cells IOPC’S DOPC’S BMP’s ,GF’s Osteoblasts

15. Functions New bone formation Controls bone mineralization at 3 levels- In its initial phase, by production of matrix vesicle. At a later stage, by controlling the ongoing process of mineralization. By regulating the number of ions available. Regulation of bone remodeling and mineral metabolism.

16. Functions Osteoblasts secrete type I collagen, small amount of type V collagen, osteonectin , osteopontin , RANKL, osteoprotegerin , Proteoglycans , latent proteases and growth factors including bone morphogenic proteins. Osteoblasts exhibit high levels of alkaline phosphatase - cytochemical marker.

17. Bone resorbing factors that act via the osteoblast are parathyroid hormone, vitamin D 3, interlukin -1 and tumor necrosis factor . RANKL - osteoclast differentiation Cbfa1 - regulates the expression of OPG (osteoprotegerin).

18. Regulation of osteoblast activity : Hypocalcemia PTH activates PTH receptors on osteoblasts Role of parathormone (PTH ): Resorption

19. Osteoblasts -PTHrP (parathyroid hormone related protein) differentiation. PTHR1(type 1 PTH receptor) -later stage in differentiation-pre osteoblasts Increased - local PTHrP favor- increased osteoclast formation -stimulation of RANKL production . PTHrP - bone cytokine .

20. Vitamin D 3 : Stimulates bone resorption. essential for normal bone growth and mineralization Stimulates osteopontin and osteocalcin – suppresses collagen production Growth hormone: required for attaining normal bone mass - mediated by local production of IGF-1 . Insulin: stimulates bone matrix formation and mineralization

21. Bone morphogenic proteins : TGF-β family migration, aggregation and proliferation of mesenchymal type cells and their differentiation in to osteogenic cells Insulin growth factor I and II (IGF): Effects similar to TGF- β T hey also stimulate proliferation of osteoblast precursors Fibroblast growth factor (FGF) : increases proliferation of osteoprogenitor cells. promotes osteogenic differentiation

22. BONE LINING CELLS: Osteoblasts flatten, when bone is not forming and extend along the bone surface and hence the name. They are present on periosteal as well as endosteal surfaces.

23. OSTEOCYTES: Nerve cells Sense the change in environment and send signals that affect response of other cells involved in bone remodelling Maintains balance between resorption and remodelling Bone that forms more rapidly shows more osteocytes.

24. Osteocytic lacunae Canaliculi- narrow extension of lacunae, permits diffusion of gases and nutrients Maintains bone integrity and vitality Failure of inter connecting system between osteocytes and osteoblasts leads to sclerosis and death of bone

25. OSTEOCLAST: In Greek it means “ bone and broken ’’ Morphology Howship’s lacunae Diameter – 50-100 um 15 to 20 nuclei ( more nuclei more resorption) TRAP – distinguishes from other multinucleated giant cells

26. morphology Extensive mitochondria except below the ruffled border Ruffled border – deep folds Cathepsin containing vesicles and vacuoles are present close to ruffled border – resorptive capacity Clear or sealing zone

27. Formation of osteoclasts

28. Cells of monocyte macrophage lineage differentiate into osteoclast by cell to cell interaction RANKL and M-CSF are produced by osteoblasts. These are required for formation of osteoclasts M-CSF – proliferation and differentiation. It acts through c-fms present on osteoclasts RANKL- differentiation in to matured osteoclast and their activity. RANKL/ ODF / TRANCE( TNF related induced cytokine) / OPGL Formation of osteoclast

29. Stimulatory factors Inhibitory factors Vitamin D3 and PTH OPG TNF-β Calcitonin PGE-2 OCIL IL-1,6,8,11 IL-4,10,12,13,18 TGF- β & Interferon-ϒ Bisphosphonates

30. BONE FORMATION AND FACTORS AFFECTING BONE FORMATION Two theories have been put forward for how the bone is formed and calcified . 1st theory: Matrix vacuoles, which are produced as an outgrowth of osteoblasts or chondroblasts or odontoblasts are responsible for calcification. 2nd theory Macromolecular constituents of bone and cartilage matrix directly implicates in calcification

31. Factors regulating bone formation: Platelet derived growth factor Cationic heparin binding polypeptide Collagen synthesis and rate of bone apposition Acidic fibroblast growth factors and basic fibroblast growth factor Increases collagen synthesis

32. Insulin like growth factor Increase preosteoblasts replication and stimulates collagen synthesis Transforming growth factor TGF- α – resorption TGF- β – formation Bone morphogenetic proteins (BMPs) during repair they are released and are required for healing

33. BONE RESORPTION : Sequence of events of bone resorption: Involves 3 phases First phase - formation of osteoclast Second phase- activation of osteoclast Third phase - resorption of bone

34. Alterations in the osteoclast Removal of hydroxyapatite acidic environment by proton pump Degradation of organic matrix acid phosphatase, cathepsin B Removal of degradation products from lacunae endocytosis Translocation of degraded products and extracellular release

35. Alterations in the osteoclast: The osteoclasts create - Howship ’ s lacunae. assumes polarity of structure and function. The two distinct alterations are the development of a ruffled border sealing zone at the plasma membrane. The cytoplasm adjacent to ruffled border is devoid of cell organelles, contains actin microfilaments surrounded by vinculin rings- clear zone. When osteoclasts arrive at resorption site, they use the sealing zone to attach themselves to the bone surface.

36. Removal of hydroxyapatite : The initial phase involves the dissolution of the mineral phase – HCl The protons for the acid arise from the activity of cytoplasmic carbonic anhydrase II, which is synthesized in osteoclast. The protons are then released across the ruffled border into the resorption zone by an ATP consuming proton pump. This leads to a fall in pH to 2.5 to 3.0 in the osteoclast resorption space.

37. Degradation of organic matrix : Proteolytic enzymes are synthesized by osteoclasts- cathepsin k and MMP-9. cathepsin k is the most important enzyme in bone. It degrades major amount of type I collagen and other non collagen proteins MMP-9(collagenase B) - osteoclast migration. MMP-13 -bone resorption and osteoclast differentiation.

38. Removal of degradation products from lacunae : Once liberated from bone, the free organic and non organic particles of bone matrix are taken in or endocytosed from resorption lacunae, across the ruffled border, into the osteoclast. These are then packed into membrane bound vesicles within cytoplasm of osteoclast. These vesicles and their contents pass across the cell and fuse with functional secretory domain (FSD) a specialized region of the basement membrane. Then the vesicles are released by exocytosis .

39. Factors associated with mechanism of bone Resorption: Interleukin 1 – IL-1 α , IL-1 β . It stimulates production and release of prostaglandin PGE2 Interleukin-6 (IL-6) Tumor necrosis factor lymphotoxin Gamma interferon – inhibits resorption Colony stimulating factors Prostaglandins and other arachidonic acid metabolites

40. Role of trap in bone resorption: Synthesized as inactive pro enzyme Bone resorption inside and outside the cell Concentration of TRAP in serum can be assessed which indicates resorption day by day basis

41. BONE REMODELLING The process by which overall size and shape of bone is established- bone modelling . Embryo to pre-adult period. Rapidly formed on periosteal surface simultaneous destruction on endosteal surface at focal points and with in the osteon . Bone formation greater than resorption. Bone turnover or remodelling – replacement of old bone by new bone .

42. As age increases resorption exceeds Cortical bone turnover-5% per year Trabecular and endosteal surface – 15% per year Coupling The processes of bone synthesis and bone breakdown go on simultaneously and the status of the bone represents the net result of a balance between the two processes. This phenomenon is called coupling .

43. Hormones and coupling With the exception of calcitonin, all the hormones, cytokines, and growth factors that act on bone, as an organ, mediate their activity through osteoblasts. R esorbing hormones act directly on osteoblasts, which then produce other factors that regulate osteoclast activity. This results in both bone formation and bone resorption being coupled.

44. The coupling theory is based on the observation that once resorption occurs, osteoblasts respond by making bone matrix. That is, any change in resorption or formation results in change in the other. A hypothetical mechanism for explaining the coupling phenomenon is that resorbing bone produces a factor that influence the rate or extent of osteoblastic activity.

45. Functions of remodelling To prevent accumulation of damaged bone by regenerating new bone. Allowing to respond to the changes in mechanical forces. Mineral homeostasis.

46. First the osteoclasts tunnel into surface of bone, which lasts for 3 weeks- resorb the haversian lamellae, and form a resorption tunnel or cutting cone. After sometime resorption ceases and osteoclasts are replaced by osteoblasts. These osteoblasts lay down a new set of haversian lamellae, encircling a vessel upon a reversal line. This cement line is a thin layer of glycoproteins comprising bone sialoprotein and osteopontin that acts as a cohesive mineralized layer between the old bone and new bone to be secreted.

47. The entire area of osteon, where active formation occurs is termed the filling cone. The osteoblasts get entrapped in new bone and are called osteocytes. Fragments of lamellae from old bone haversian systems are left behind as interstitial lamellae

48. Sequence of events in bone remodelling:

49. MEDIATORS OF BONE REMODELLING : Parathyroid hormone Calcitonin Vitamin D metabolites i.e., 1, 25-dihydroxycholecalciferol Cytokines Prostaglandins Growth factors Mechanical factors Bacterial products .

50. MARKERS OF BONE TURNOVER: The markers of bone formation are: (serum markers) Alkaline phosphatase (total) Alkaline phosphatase (skeletal isoenzymes) Osteocalcin Procollagen I extension peptide

51. The markers of bone resorption are: (urinary markers) Urine calcium Urine hydroxy proline Collagen cross linking fragments Urine N – telopeptide Urine C- telopeptide Urine total pyridinoline Urine free deoxypyridinoline

52. Serum markers of bone resorption: Serum TRAP Serum β2 macroglobulin Pathologies caused due to improper control of remodelling are : Osteoporosis Osteopetrosis Malignant bone tumors Inflammatory joint diseases

53. CONCLUSION : The response of bone to inflammation includes bone formation as well as resorption. Thus bone loss in disease is not simply a destructive process, but results from the predominance of resorption over formation Proper understanding of changes seen in the bone in variety of diseases will help in finding new therapeutic strategies

54. REFERENCES: Carranza’s clinical periodontology-10 th edition Lindhe – Textbook of periodontology-5 th edition Orban’s oral histology & embryology-13 th edition Tencate oral histology-8 th edition Fundamentals of Periodontics.- Thomas G. Wilson, Kenneth S. Kornman -2nd Edition Biology of periodontal tissues. P. Mark Bartold and A.SampathNarayanan-1 st edition Periodontology 2000, Vol. 24, 2000, 99-126