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1. INDIAN DENTAL ACADEMY
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2. Contents
• Introduction
• Structural features
• Sequence of amino acids in chain
• Basic events in synthesis
• Some mediators that affect collagen synthesis
• Degradation & remodelling
• Disease associated with collagen alteration
• Collagen metabolism & periodontal disease
• Applied aspect of collagen
• Conclusion
• References

3. INTRODUCTION
•Collagens are the most abundant proteins in the human
body & they are found in species ranging from insects to
man.
•The word collagen is derived from Greek roots kolla
(glue) and gene, and in French, the word collagene
designates glue-producing constituents because
collagenous tissues are used as the sources of glue &
gelatin.

4. •It is the most abundant protein comprising of a large
family of related but genetically distinct proteins. It is
often presumed to be most important in terms of tooth
support.
•The collagen molecule is a rigid, rod-like structure that
resists stretching; the fibers made up of collagen have high
tensile strength. Therefore, this protein is an important
structural component in tissues such as PDL & tendon in
which mechanical forces need to be transmitted without
loss.

5. •Apart from their structural role, collagens can also
influence cell shape, differentiation, & many other
cellular activities, thus forming an important group of
multifunctional connective tissue proteins that
participate in many biologic functions.
•The collagen family consists of 30 different genes
which produce 19 known types of collagen
(Prockop & Kivirikko 1995). As a group of proteins,
the collagens contain a number of characteristic
features that distinguish them from other matrix
molecules.

6. STRUCTURAL FEATURES
All collagens are composed of three polypeptide alpha
chains coiled around each other to form the typical
collagen triple helix configuration.
Common features include the presence of amino acid
glycine in every third position, a high proportion of proline
residues, and the presence of hydroxyproline &
hydroxylysine

7. SEQUENCE OF AMINOACIDS IN COLLAGEN CHAIN
The sequence consists of repeating tripeptides of glycine-
X-Y where X & Y represent amino acids other than glycine.
X is often proline & Y residue is often the aminoacids
derived from it (hydroxyproline).
HYDROGEN BONDS

8. Collagens frequently are categorized as belonging to one
of several groups based on the structure of collagen
molecule, how the molecules are assembled, & their tissue,
cellular & sub cellular distributions.
Mesenchymal cells & their derivatives (fibroblasts,
chondrocytes, osteoblasts, odontoblasts, & cementoblasts)
are major producers of collagens. Many other cell types
(epithelial, endothelial, muscle & Schwann cells) also
synthesize collagens although on a more limited basis in
terms of amount & variety of collagen types

9. The collagen fibers have a transverse striation with a
chronic periodicity of 64nm which is caused by
overlapping arrangement of tropocollagen molecules.
The molecular configuration confers to them a tensile
strength greater than that of steel.
Therefore collagen imparts a unique combination of
flexibility & strength to tissues where it lies.

10. BASIC STEPS IN COLLAGEN SYNTHESIS
The collagen molecule is insoluble under physiological
conditions
 It contains hydroxyproline & hydroxylysine, two amino
acids that are post-translationally modified from peptidyl
prolines & lysines.
 These modifications can occur only on nascent alpha chains
because the triple helical design is not accessible to
modification enzymes.
The collagen molecule is first synthesized as a large
precursor containing extra aminoacids at both N-terminal & C-
terminal ends.

11. •Synthesis of these pro alpha chains, their assembly
into procollagen & their conversion to collagen fibers
involve several well coordinated biosynthetic reactions
occurring in nucleus, cytoplasm & extra cellular space.
STEPS 1. Nuclear events
2. Intracellular events
3. Extra cellular events

12. NUCLEAR EVENTS
Gene expression
Collagen genes are large & range from 5 kb – 130 kb
More than 30 genes have been described for collagen type I to XIX.
Fibril forming collagen genes contain 42 exons for major triple helical
region, separated by introns 80 – 2000 nucleotides long.
Most of these exons are composed of 54bp & start with an intact codon
for glycine.
In type IX collagen, the sizes of exons range from 21 to 400 bp
For type IV & VI 34 exons of size 9bp.

13. Transcription of m RNA:
•The first step involves the formation of transcription
initiation complex by RNA polymerase II.
•This begins at an adenine base +1 location preceded by
cytosine at -1
•The consensus sequence for transcription initiation is
pyridine (ANT).
•After synthesis of about 30 nucleotides, the transcript is
modified at 5’ end by capping.

14. Capping:
•It involves 5’-5’linkage of 7-methylguanine by the
enzyme guanyl transferase.
•Capping appears to be necessary for recognition of
mRNA by the nuclear transport to the cytoplasm, & it
also renders the mRNAs resistant to nucleases.
Polyadenylation:
•Pre mRNA undergoes additional tailoring reactions
before it is converted into mature transferable form.
•This pre mRNA is longer by 1000 bases at 3’end, this is
removed by endonuclease.

15. •After this endonuclease action mRNAs are rapidly
polyadenylated by the addition of about 200 adenines.
Splicing:
•It is a process by which intron sequences are removed
from the pre-mRNA.
•It involves two transesterification reaction in which
ester group are exchanged & exon ends combined
together.

16. Intracellular events
Messenger RNA directs the assembly of specific
aminoacids into polypeptide chains on ribosomes of rough
endoplasmic reticulum.
These chains are 1-1/2 times longer than those of
collagen molecules as they have N&C terminal extensions
that are necessary for the assembly of triple helix molecule.
As these chains are synthesized they are translocated in
the lumen of rough endoplasmic reticulum where post-
translational modifications occur.

17. .Firstmodification being hydroxylation of proline & lysine
which permits H+ bonding as triple helix is assembled. The
vitamin C dependant enzyme polyhydroxylase & lysyl
hydroxylase are required for this step.
3 polypeptide chains then are assembled the triple helix.
Proper alignment of the chains achieved by disulfide
bonding at the C-terminal extension, & then the three chains
twist around themselves to “ zip up” the helix.
The assembled helix then is transported to the golgicomplex,
where glycosylation is completed by the addition of glucose to
the galactose residues.

18. Exocytosis : Secretory granules containing the procollagen
molecules are formed at the transface of the golgicomplex &
are released subsequently by exocytosis at the cell surface.
The formation & secretion of the collagen molecule takes
approximately 35-60 minutes.
Extracellular events
Removal of C & N terminals by procollagen peptidases.
Alignmant of molecules to form fibrils
They aggregate each other
Undergo crosslinking which helps in further stabilization of
the fibrils.

20. Mineralization of collagen:
During the formation
of collagen based
calcified tissues,
deposition of apatite
crystals is catalyzed
by specific atomic
groups associated
with the surface,
holes & pores of
collagen fibrils.

21. Although a direct role by collagen is excluded,
regulation of this process is believed to be achieved
by non collagenous proteins.
In bone 70-80% of mineral is located within the
collagen fibril; the rest is located in the spaces
between fibrils.
Sharpey’s fibres seen in bone & cementum are
effectively mineralized.

22. Previous work(Selvig,1965) has suggested that
Sharpey’s fibres represent an embedding of the PDL
fibres by entrapment in the advancing mineral front.
This well defined interface between mineralized & non
mineralized collagen in the PDL implies some form of
strict control mechanism which retains the width
(approximately 200µm in the case of human PDL) of
unmineralized fibres.
Some authors suggested that alkaline phosphatase
activity could play a key role in collagen calcification in
vivo.

23. Regulation of collagen synthesis:
• The quantity & proportion of collagens within each
tissue need to be precisely regulated
1. to maintain tissue integrity
2. to control the amount of collagen produced
3. to control the fiber architecture.
• During development, inflammation & wound repair,
the synthesis of collagen is influenced by various
factors.

24. SOME MEDIATORS THAT AFFECT COLLAGEN SYNTHESIS
Mediator Major source Collagen synthesis
GROWTH FACTORS
PDGF platelets, macrophages, increases
smooth muscle cells,
epithelium
TGF-β Platelets, macrophages. increases
FGF platelets, macrophages, matrix increases
IGF serum matrix increases
CYTOKINES/LYMPHOKI
NES
IL-1αβ macrophages, most cells decreases
IFN-γ lymphocytes decreased
TNF-α monocytes,macrophages decreased
HORMONES
GLUCOCORTICOIDS decreased
OTHERS
PGE2 monocytes &macrophages decreased

25. •During initial stages of healing, after 1 day, type III
collagen is the major species produced, & type I collagen
synthesis becomes prominent later.
•The synthesis of collagen becomes maximal at 7-14 days
after injury, & continues for weeks & months until tensile
strength of the wound is restored to normal levels.

26. CLASSIFICATION OF COLLAGENS
Collagens are basically classified based on their chains,
molecular distribution, length, tissue distribution &major
function.
FIBRILLAR COLLAGENS [types I, II, III, V, & XI]
Collagens I, II, III, V, & XI aggregate in a highly
organized manner in the extra cellular compartment to
form fibrils with a typical 64-nm banding pattern .

27. •In most connective tissues, type I collagen is the most
abundant collagen; type III collagen (reticular fibers) &
type V collagen are usually present.
•Type V collagen is found within fibrils of type I & III
collagen & is thought to regulate fibril diameter .
•Type II collagen is abundant in cartilage;
•type XI collagen is less abundant but heterotypic fibrils
with type II collagen.

28. BASEMENT MEMBRANE COLLAGEN [type IV]
•Collagen IV is similar in size to type I collagen but
does not assemble as fibers in the extracellular
compartment.
•It contains frequent nonhelical sequences & aggregates
in a sheetlike, chicken wire configuration.
•Type IV collagen is a major component of the basal
lamina & is a product of epithelial cells.

29. FACIT COLLAGENS [types IX, XII, and XIV]
•Fibril associated collagen with interrupted helices
[FACIT]
•Consists of chains that have different lengths &
contain a variety of noncollagenous domains.
•They exhibit several interruptions in triple helix & are
found in various locations in different tissues

30. This collagen forms heterotypic fibrils with type II
collagen in cartilage & vitreous humor.
Type XII & XIV are believed to modulate interactions
between adjacent fibrils
MESHWORK- FORMING COLLAGENS [types VIII &X]
Type VIII is associated with the basal laminae of
endothelial cells & smooth muscle cells & is present ion
Descemet’s membrane of cornea. It imparts strength while
providing an open porous meshwork.

31. Type X collagen is found almost exclusively in the
hypertropic zone of the epiphyseal cartilage growth plate

32. ANCHORING-FIBIRL COLLAGEN [type VII]
Collagen VII has unusually large non helical ends comprising two
third of the size of the molecule.
The C-terminal ends associate to form the dimers that subsequently
are assembled into the anchoring fibrils that extend from the basal
lamina into the underlying connective tissue.

33. MICROFIBRIL-FORMING COLLAGEN [type VI]
Type VI collagen, which has large N & C terminal
globular domains associate in an end to end fashion
forming beaded filaments.
It is present in epimysium & most connective tissues.
This collagen has binding properties for cells,
proteoglycans, & type I collagen & may serve as a bridge
between the cells & the matrix.

34. TRANSMEMBRANE COLLAGENS [type XIII & XVII]
These collagens function in cell matrix adhesions.
Type XVII is found in hemidesmosomes of basal
epidermal cells & attaches the cells to the basal lamina.
 Type XIII is present in focal adhesion sites of
fibroblasts & at cell matrix interfaces in some epithelia,
muscle, & nerves.
It is also present in cell to cell adhesive specializations
of cardiac muscle, intercalated disks.

35. ENDOSTATIN FORMING COLLAGENS [types XV & XVIII]
•Type XVIII is a component of basement membrane of
epithelial cells & endothelial cells, has multiple
interruptions in the central helical domain
•It has a large unique C -terminal non-helical domain
which can be cleaved by extra cellular proteases to form
endostatin,a potent inhibitor of endothelial cell migration
& angiogenesis.
•Type XV type of collagen is present in papillary
epidermis as less potent angiogenic activity.

36. OTHERCOLLAGENS[typeXVI&XIX]
Type XVI & XIX collagens have multiple
interruptions in their triple helical domain & an N-
terminal globular domain.
Their function & tissue distribution are incompletely
characterized, but they have been shown to be associated
with vascular, neural, muscular & certain epithelial
basement membranes.

37. TYPE I COLLAGEN MOLECULE
 In the α-chain of type I collagen, there are 338 Gly-X-Y
triplets repeated in a sequence, the additional 32 amino
acids flank the long triplet sequence at each end, which are
known as telopeptides. (Amino terminal & a carboxy
terminal telopeptide.)
Type I collagen molecule is a heterotrimer, that is two α
chains are identical & third is distinct. Molecular
composition can be written as (α1)2(α2). And type I
collagen composition is given as [α1 (I) 2[α2 (I)].

38. The three α-chains in each collagen molecule are
wrapped around each other to form a long rigid triple
helical molecule & telopeptides remain free.
Glycine is the smallest aminoacids & its replacement
inhibits triple helix formation
The structure of collagen depends critically on the
presence of high amounts of proline & hydroxyproline;
these aminoacids differ from other aminoacids as these are
imino acids with a rigid cyclical structure, which is
essential for stability.
Type I collagen that lack hydroxyproline can form a
triple helix at low temp, but triple helix falls apart at body
temp.

39. COLLAGEN DEGRADATION & REMODELLING
Collagen degradation is a precisely controlled complex
process.
It is an essential concomitant of tissue development during
growth & of tissue maintenance in the adult.
It also occurs during wound healing & inflammatory
responses of tissues
Since collagen in connective tissue is in intimate contact
with glycoproteins, Proteoglycans & other components,
these will influence susceptibility of collagen tissue to
degradation extracellularly.

40. Intracellular degradation, considered as an important
mechanism for physiologic turnover & remodeling wherein
phagocytosis of collagen fragments takes place by
lysosomal enzymes [cathepsins]
Problems in collagen destruction
Bulk of collagen is inaccessible within fibers & even the
outer collagen molecules in these fibers are chemically
cross linked to each other & to those within fibers.
The triple helical structure of collagen molecule cannot
be cleaved by proteases, trypsin, and pepsin except under
extreme, essentially non physiological conditions.

42. DISEASES ASSOCIATED WITH COLLAGEN ALTERATIONS
Because most tissues contain a mixture of collagen types,
any change in the structure, content, & proportion of
collagen types can be expected to lead to functional
abnormalities of these tissues containing these collagens
Three types of alterations can affect collagens
A molecular defect in the processing enzymes - inherited
A defect in the structure of collagen genes – due to point mutations
Mechanism affecting the expression of collagen genes due to
pathologies of acquired diseases – due to physiologic & environmental
factors.

43. .Ex—
1. Osteogenesis Imperfecta [Type I, II, III, IV]
2. Ehler danlos syndrome [Type IV, VI, VII, VIII, & IX].
3. Chondrodysplasias
Ex—achondrogenesis, spondyloepiphyseal dysplasia,
Stickler syndrome(type II &XI)
4. Alport syndrome.(type IV)
5. Dystrophic epidermolysis bullosa (type VII &XVII

44. COLLAGEN IN PERIODONTAL CONNECTIVE TISSUE:
1)GINGIVA:
• The various cell fibers of the gingival connective tissue
provide a rigid structural framework in the gingiva.
• These provide 60% of the total tissue protein
• Ratio of type I collagen to type III is 7:1

45. •Type I is organized into denser fibrils, seen in deeper
part
•Type III is localized mostly as thinner fibers &
distributed in a reticular pattern, seen in superficial
part.
•Type IV is synthesized by endothelial cells & the
ectodermal cells of the basement membrane of the
overlying epithelium

46. There are 11 types gingival fibers :
1. Dentogingival
2. Dento periosteal
3. Alveologingival
4. Cicrular
5. Semicircular
6. Transgingival
7. Intergingival
8. Transseptal
9. Interpapillary
10.Intercircular
11.Periosteogingival

47. 2) PERIODONTAL LIGAMENT:
•Major collagen types: type I & type III
•Type III fibers when formed are of smaller diameter than type
I & appear to be more suited to withstanding deformation than
are type I fibers, thus it shows more elasticity.
•Other collagens in less proportions are type IV & V

48. •One of the novel collagen components of the PDL is type
XII collagen, which is believed to be involved in the 3-
dimensional organization of the extra cellular matrix.
•This collagen is restricted to mature tissues & is not
expressed during development.
The principle fibers of PDL:
• Alveolar crest group
• Horizontal group
• Oblique group
• Apical group
• Interradicular group

49. Collagen fibers & tooth eruption:
• It is known that collagen turn over is inversely
proportional to the tensile strength & directly
proportional to the remodeling activity.
• The dual function of support & eruption of teeth appear
to demand conflicting roles for PDL.
• During eruption fibroblasts move from a basal position in
an occlusal direction & PDL fibroblasts possess a system
of microfilaments & microtubules which make their
movement active process.

50. •Hence they move by means of collagenous attachment,
pull the teeth with them as they migrate.
•During hypo function, the collagen may be replaced by
less aggregated forms of collagen, those that are newly
formed are also degrade into collagen fibrils & hence thin
PDL in such cases.
•The increased turnover of prefibrillar forms of collagen in
association with a net loss of the extracellular fibrillar
collagen may also be an important factor in the mechanism
of tooth eruption.

51. 3) CEMENTUM:
•Composed of type I & type III – predominantly
seen
•Type V in minute amount seen in Sharpey’s
fibers.
4) ALVEOLAR BONE:
•Predominantly type I, expressed by osteoblasts
•Type III also seen

52. COLLAGEN METABOLISM & PERIODONTAL DISEASES
CIPD [chronic inflammatory periodontal disease] involves
the net destruction of collagen in the extracellular matrix.
Though etiology remains obscure, the unusual rapid rate of
turnover raises the possibility that the pathology is related to
disturbances in the host synthesis/degradation pathway.
Low level persistent bacterial infection could conceivably
result in chronic inflammation leading to cytokine production
& induction of MMPS by host cells.

53. Collagenase activity has been shown to be greater in the
presence of inflammatory periodontal disease.
Christener in 1980 reported collagenase activity in human
periodontal tissue only in periodontal ligaments from teeth
that had suffered loss of attachment.
Levels of tissue-derived collagenase were found to be higher
in GCF of patients with CIPD, which were reduced after
treatment

54. •MMPase activity was seen to increase at specific sites in
diseased periodontium. [Heath &coworkers 1982]
•Intracellular lysosomal digestion of collagen turnover
pathway could be abnormal during CIPD & this was
supported by findings of Morris & Harper [1987] who
reported decreased amounts of TIMP in CIPD

55. APPLIED ASPECTS OF
COLLAGEN
• During the course of periodontal disease morphological
changes occur in the collagen fibers, the connective
tissues of chronically inflamed gingival tissue contain
types I,III,V,IV,VI
• Type I synthesized in normal amounts
• Type III less than normal

56. Reasons for this are:
•Altered synthetic ability of fibroblasts
•Toxic substanced inflamed tissues may alter all
populations
•Alteration in tissue serum levels; it has been found that
serum levels affect the synthesis rate of each type of
collagen with type I, being formed faster than type III

57. •Along with collagen type I & III, a new collagen species,
type I trimer, can be detected in inflamed gingiva.
•This collagen is a homotrimer of the α1(I) chain, which
accumulates in the absence of functional α2(I) chains in
certain collagen molecular diseases, tumours.
•Cementum may become altered due to its exposure to
oral or pocket environment in which there is a loss of
collagenous attachment & both its organic & inorganic
content are changed.

58. • Early studies on the turnover of periodontal collagens
focused on measuring the hydroxyproline levels in
gingival tissue extracts & GCF in an attempt to monitor
periodontal breakdown.( Hara & Takahashi 1975 )
• The hydroxyproline content of GCF & serum has been
reduced significantly following periodontal surgery.

59. Gingival overgrowth:
• Collagen content increases
• Type I/III ratio becomes different with some loss of type I
& elevated levels of type III collagen.
( Narayanan & Hassell 1985).
• 2 mechanisms for accumulation:
1. Decreased levels of matrix degrading enzymes in these
lesions,
2. Induction of collagen production.

60. Collagen induction occur
•Directly by the action of drugs on collagen.
•Indirectly, by decreasing the production of collagenase.
(McCulloch & Knowles 1993)

61. AGE
♦Increasing age results in coarser & denser gingival
connective tissues.
♦Qualitative & quantitative changes include an increased
rate of conversion of soluble to insoluble collagen, increased
mechanical strength, & increased denaturing temperature.
♦Greater collagen content has been found in gingiva of older
animals, despite lower rate of collagen synthesis decreasing
with age.

62. ALTERED COLLAGEN METABOLISM
♦Increased collagen activity & decreased collagen synthesis is found in
individuals with diabetes & in chronic hyperglycemia.
♦Gingival infllammation, bone destruction associated with local
factors are more severe in diabetics.
♦In hyperglycemic state, numerous proteins & matrix molecules
undergo a nonenzymatic glycosylation, resulting in advanced glycation
end products. [AGEs] The formation of AGEs can occur at normal
glucose levels, but in hyperglycemic environment, AGEs formation is
excessive. AGE s formation cross links collagen , making it more
soluble, & less likely to be normally replaced or repaired ,as a result of
which poorly controlled diabetics is AGED & more susceptible to
breakdown.

63. GINGIVAL CHANGES
♦Upto 70% of collagen is destroyed in the early lesion of gingivitis
♦.In patients with periodontal pocket formation, the fibroblasts show
cytotoxic alterations with decreased capacity for collagen production.
♦P.gingivalis & Actinobacillus actinomycetemcomitans are the species
of bacteriae producing collagenase.
♦P. gingivalis possesses the proteolytic activity to degrade collagen
into peptide components .The bacterial collagenase & the host
collagenase, both contribute to collagen degradation.
♦P. gingivalis produces gingipains [specific peptidases that cleave
proteins at peptide bond following arginine residues ]

64. ♦In LAP, predominant collagenase found in tissues & GCF is MMP-
1 & increased TIMP-1 is present.
♦Collagen fibers are non attached & run parallel to implant surface,
owing to lack of cementum, an important difference between peri
implant & periodontal tissues.
♦Fibro-osseous system of implant retention suggests that the
presence of a dense collagenous tissue between implant & bone may
act as an osteogenic membrane
♦Tetracycline impregnated collagen membrane delays degradation
when 50 mg/ml of TCN solution concentration presented the highest
degree of MMP inhibition &TCN high concentration may affect the
collagen membrane integrity & enhance degradation. [J Periodontol
2OO4]

65. ♦Expression of MMPS & TIMPS showed that in stage II gingivitis and
stage III GINGIVITIS MMP-1, MMP-13, MMP-9 & TIMP-1 were
raised. [J Periodontol 2OO3]
♦Cytokines linked to collagen breakdown during periodontal disease
progression from ELISA study showed that IL-Iβ stimulates bone
resorption & decreased bone formation & IL-Iβ is considered as a
marker of clinical severity of periodontitis [JPR 1996]

66. Changes in the regulation of collagen post-translational
modification in transformed cells were studied in three established
human sarcoma cell lines.
 The collagens synthesized by all but one of these and by all the
control human cell lines were almost exclusively of types I
and/orIII.
The relative rate of collagen synthesis and the amounts of prolyl
hydroxylase activity and immunoreactive protein were markedly low
in all the transformed human cell lines.
 The other enzymes studied, lysyl hydroxylase, hydroxylysyl
galactosyltransferase and galactosylhydroxylysyl
glucosyltransferase, never showed as large a decrease in activity as
did prolyl hydroxylase
(Biochem J. 1981 Jun 15;196(3):683-92 )

67. Conclusion
They are synthesized in a series of biochemical events &their
syntheses are highly regulated.
Synthesis & turnover of collagens are prominent activities
associated with wound healing.
Mechanism regulating collagen synthesis has a direct bearing on
periodontal structures in which collagens undergo dramatic changes
during periodontitis & drug induced gingival hyperplasia.
Periodontal regeneration is also intertwined with events
associated with collagen production & degradation.

68. RefeRences
• Oral histology – Tencates
• Biology of the periodontal connective tissues –
Bartold & Sampath Narayan
• The periodontal ligament in health & disease –
Berkovitz
• Collagen & dental mattrices – J.P.Gage

69. Thank
you