COLLAGENPredominant Extra Cellular Matrix

Component

DR.DEBASISH MISHRA (MDS Perio & Implants)

http://www.dentalorg.com/(CEO)

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INTRODUCTION

Collagenis a family of highly developed fibrous proteins found in all multicellular animals. It is the most abundant proteins found in mammals, constituting 25 percent of the total protein mass.

Collagen is the main fibrous component of skin, bone ,tendon, cartilage and periodontium.It comprises about 90% of the organic matrix of the bone. Collagen is a natural protein that provides our bodies with structural support.It seems collagen evolved early in evolution and its composition and structure have changed relatively little suggesting its design has reached optimum efficiency.

INTRODUCTION

The intercellular substance of tissue was once considered to be relatively homogeneous, nothing more than a scaffold for cells to grow or a medium to “glue” cells together.Today, the intercellular substance of tissue, or the extracellular matrix, is recognized as a complex, interactive compilation of proteins in dynamic equilibrium that can regulate the gene expression of cells.

The predominant extracellular matrix component of the periodontium is collagen, a genetically distinct super family of extracellular macromolecules that contain one or more triple-helical domains. There are as many as 25 different genes (121) that code for at least 14 different collagen molecules (121, 179).

Six different collagen types have been detected in the periodontium (Perio 2000 Vol 3)

EXTRA CELLULAR TISSUE MATRIX(PERIODONTIUM)

FIBROUS + GROUND STR.

CollagenElasti n

Oxytal inElauin

( P R O V I D E S T E N S I L E S T R E N G T H )

Non Collagenous proteinsProteoglycans, Hyaluronan

Lipids , Water(Provides Compressive

Strength)

A few crucial Physiological Roles of Collagen

* Rigid rod like structure that resists stretching of the cell and provides a high tensile strength

*Transmits mechanical forces preventing any loss or tear of ligaments

Therefore this protein is an important structural component in tissues such as the

periodontal ligament and muscle tendons in which the mechanical forces need to be transmitted

*Influences cell shape , size & migrationCOLLAGEN:MULTIFUNCTIONAL TISSUE PROTEINS

CONTENTS ……….

2.Types of Collagen3.Synthesis of Collagen

5.Collagen in Periodontium

6.Degradation & Remodeling

Functional Adaption of collagen in periodontium

1.Structure/Chemical Comp. of collagen

10.Diseases of Periodontium related to Altered Collagen

11.Conclusion

BIBLIOGRAPHY…..

STRUCTURE

STRUCTURE OF COLLAGEN

All collagens are composed of 3 polypeptide alpha chains coiled around each other to form the tripe helix configuration. The individual polypeptide chains of collagen each contain app. 1000 amino acid residues .

As a group of proteins collagens contain a number of characteristic features that

distinguish them from other matrix molecules

ALPHA HELIX OF COLLAGENAn alpha-triple helix of collagen is shaped into a right handed helix. The Alpha chains each are shaped into a left-handed symmetry (i.e. the opposite way round), and then three of these coiled strands get together and form a right-handed triple helix of collagen.Depending upon the type of the collagen , the molecule may be made up of either 3 identical Alpha chains(homotrimers), or two or three different alpha chains(heterotrimers).

The α chains are left handed helices that wrap around each other into a right handed rope

like triple helical rod.

Each such helix is around 1.4 nanometers in diameter and 300 nanometers in length

THE TRIPLE HELIX MAY BE OF A CONTINUOUS STRETCH OR IT MAY BE INTERRUPTED BY NON COLLAGENOUS ELEMENTS.

Glycine occupies every third position in the repeating amino acid sequence

GLYCINE-X-Y

PRIMARY STRUCTURE Each polypeptide chain in type I collagen contains 1056 amino acids residues. 90% of them are in the form of repeating(Gly-X-Y pattern). These 2 imino acids together with glycine at every 3rd residue , gives the featured conformation to collagen molecules .

Sec , Tertiary & Quaternary StructureThe α chains each form an extended helix with left handed symmetry with 3.3 amino acids residues per turn.The 3 polypeptide chains are then wound around each other to form the Collagen Triple Helix in a “Rope Like fashion” (Long & Thin 300 nm x 1,5 nm) . This triple helix has a Right Handed Symmetry.The entire helical structure is further strengthened by interchain H Bonding.

AMINO ACID SEQUENCE ( STRUCTURE CONTINUED )

•Collagen is rich in PROLINE,HYDROXYPROLINE& GLYCINE

Helps in the formation of helical orientation of each α chain

PROLINE :

GLYCINE : The smallest amino acid found

in every 3rd position in the polypeptide chain

--(--GLY---X---Y---GLY---X---Y--)--

X= PROLINE

Y= Hydroxy Proline Hydroxy Lysine

Proline frequently occupies the X position.

Hydroxyproline and hydroxylysine are two unique amino acids. Vertebrate collagens exhibit the two of them in the Y positions

Each collagen molecule is stabilized through lysine derived intra and intermolecular cross links.

Each α chain comprises of around 1056 amino acids.

There are around 3 amino acids per turn.

Hydroxy Proline & Hydroxy Lysine*Collagen has Hydroxy Proline & Lysine that are not

Present in many other proteins .These residues result

due to Hydroxylation of Proline &

Lysine residues after their incorporation in to polypeptide chains

(POST TRANSLATION MODIFICATION)Hydroxy Proline :

Stabilizes Triple Helical StructureExtra Capacity for Hydrogen Bonding. Prevents denaturation of collagen fibers in temperature changes. Non hydroxylated triple helices have been shown to undergo denaturation at temperatures below 37*C.

GLYCINE SIGNIFICANCESymbol: Gly GMolecular Weight: 75.07Isolectric point (pH) 6.06Molecular Formula: C2H5NO2

Glycine is a nonpolar amino acid. It is the simplest of the 20 natural amino acids; its side chain is a hydrogen atom. Because there is a second hydrogen atom at the carbon, glycine is not optically active.Since glycine has such a small side chain, it can fit into many places where no other amino acid can. For example, only glycine can be the internal amino acid of a collagen helix.

In type I collagen there are 338 [Gly–X– Y] triplets repeated in a sequence per α chain accounting for 95% of the total structure in the form of uninterrupted triple helix. However the N- &C- termini of the α chains do not have the [Gly-X-Y] motif. This produces a non helical conformation at the ends of the molecule. These regions are referred to as TELOPEPETIDES . In comparison to the triple helical central domain , the telopeptides are particularly prone to proteolytic attack.

There is both an amino terminal ( -NH2 ) and a carboxy terminal (-COOH ) telopeptide.

TYPES OF COLLAGEN

Types of Collagen Collagens represent a large family of proteins and 19 different collagen types have been described so far.

Many genetically, chemically, and immunologically distinct types of collagen have been identified

VARIATIONS ARE DUE TO …..

1. Differences in the assembly of basic polypeptide chains

2. Different lengths of the helix 3. Various interruptions in the helix

and 4. Differences in the terminations of

the helical domains

Collagens are divided roughly into 3 groups based on their abilities to form fibrils. They are as follows….

1)FIBRIL FORMING COLLAGENS: FORM BANDED FIBRILS.TYPE ITYPE IITYPE IIITYPE VTYPE XI

The triple helical domain contains an uninterrupted stretch of 338 to 343 Gly – X – Y triplets in each α chain and the molecule measures 15 x 3000 Ao

2)Fibril associated collagens with interrupted triple helices ( FACIT )

This group of collagens consists of proteins in which collagenous domains are interrupted by non collagenous sequences. These are associated with the surface of fibril forming collagens.

Includes type IX, type XII, type XIV and perhaps type XVI also. The former three are unique in containing glycosaminoglycan components covalently linked to the protein molecule.

3)All other non fibrillar collagens form the third group which includes

*Type IV, type VIII and type X ( network forming collagens)*Type VI ( beaded fibril forming collagen)*Type VII ( anchoring fibrils and invertebrate cuticle

collagen)*In addition to the above collagen groups atleast 10 non

collagenous proteins incorporating short triple helical collagen domains have been described

4)This group of collagen domain containing non matrix protein molecules includes (10 Non Collagenous Proteins)

*C1q component of C1 complement*Lung surfactant protein*Acetylcholine esterase*Conglutinin*Mannose binding protein****These proteins are not considered true collagens because they do not form a part of the extracellular matrix.

COLLAGEN IN PERIODONTIUM&

TOOTH STRUCTURES

COLLAGEN IN PERIODONTIUMThe collagen of PDL is largely Type I , with lesser amounts of type III , IV , VI and XII .

Fibril Collagens include type I , III , V that generally co distributes with collagen type I. Higher portion of collagen III usually seen in foetal tissues.

Collagen Type IV does not form fibrils and is found in basement membranes of neurovascular bundles and other PDL cells. Though this collagen is specifically associated with basement membranes , it also plays role in maintaining the elastic system of the vasculature of the gums.

Collagen fibers of the periodontium ( particularly Type I ) provide the structural requirements to withstand intrusive forces of mastication ( tooth support ) and also to accommodate growing tooth in mammals.

COLLAGEN TYPE ISynthesized by the fibroblast, procollagen is secreted and converted to collagen

One molecule of collagen consists of two 1 and one 2 polypeptide chains each coiled individually in a left handed helix .

The three chains coil together in a right handed triple helix to form a molecule of collagen

2/3 of the molecule consist of the following amino acids- glycine , proline, Hydroxyproline. Every third aa is glycine, essential for the formation of the triple helix Crosslinks between the chains and the molecules of collagen which give collagen its strength As collagen matures the crosslinks become more stable

MINERALIZATION OF COLLAGEN

DENTINE COLLAGENIt has been found that type I collagen with the structure [α1 (I) α2 (I) ] was the most exclusive collagen in dentine and predentine

Demineralized dentine and predentine show closely packed collagen fibers of 20-50nm

Dentinal collagen contains 2-3 fold increase of hydroxylysine compared to that of soft tissues.

Dentinal collagen is relatively insoluble in acid and neutral solutions

The only other collagen synthesized in culture by odontoblasts is type V collagen which is secreted into predentine( only 3%).

PULPAL COLLAGENApproximately 34% dry weight of pulp is collagen

There is higher content of collagen in the radicular areas compared to the pulp chambers and higher concentration in the middle and apical portion of the root compared to the rest of the tooth

After a small increase in collagen synthesis which occurs at the time of eruption and root closure, there is no change in collagen content of the tooth for rest of the life

BONE COLLAGENIt contains type I collagen predominantly with the molecular configuration of [α1 (I) α2 (I)].

During its formation in the osteoblast the large procollagen precursor undergoes important post translational modifications. Suitably located proline and lysine residues are hydroxylated to hydroxyproline and hydroxylysine respectively

The collagen of bone has less diglycosylated hydroxylysine than that of skin.

The ratio of glycosyl-galactosyl hydroxylysine to galactosyl hydroxylysine is 0.47 in bone compared to 2.06 in skin

CEMENTAL COLLAGENThe amino acid composition of human cemental collagen resembles that of type I collagen.

5% of type III collagen is accounted for the Sharpey’s fibers that are a part of the periodontal ligament.

Major cross link is dehydrodihydroxylysinonorleucine (DHLNL

The other cross link is dehydrohydroxylysinonorleucine (HLNL).

GINGIVAL COLLAGENCollagens are the most abundant biochemical constituents of gingival CT. (90%)

The collagen matrix of gingival CT is well organized into fiber bundles, which constitute the gingival supra alveolar fiber apparatus.

Based on their preferential orientation, architectural arrangement and sites of insertion they are classified as :

1.Dentogingival2.Dentoperiosteal3.Alveologingival4.Periosteogingiva5.Circular and semicircular6.Transgingival7.Transseptal8.Interpapillary9.Intercircular10.Intergingival

PERIODONTAL FIBERSIt contains type I and type III

collagen.Relative proportion of type III to type

I varies from 10-25%

Type III collagen fibers are smaller in diameter and appear to withstand deformation better than type I. It also helps reduce fibril diameter with type I.

Type IV is found in the basement membranes and type V with cell surfaces(0.1-0.2%).

Major crosslink is of dihydroxylysinonorleucine while hydroxylysinonorleucine is a minor component

The presence of covalent cross-links between collagen molecules stabilizes the ligament fibres and increases the tensile strength

In contrast to other tissues, the proportion of reducible cross-links in PDL does not decrease with age

The constantly high level of reducible cross-links may reflect a high collagen turn-over with an incomplete maturation process. High levels of DHLNL and type III collagen possibly result from rapid collagen turnover as a consequence of repeated microtrauma induced by mechanical stresses during normal occlusal function.

FUNCTIONAL ADAPTATIONS OF

COLLAGEN IN PERIODONTIUM

Functional Adaptations of Collagen in PDL

Tooth support system is a multiphasic system comprising of fibres , ground substances,blood vessels,fluids acting together to resist mechanical forces.

MECHANICAL FORCES

TENSION & COMPRESSION

Axially & Laterally directed

Majority of PDL collagen fibers are arranged in to Horizontal & Oblique directed groups to adapt to axial forces.

OVERLAPPING ARRANGEMENT : Its visible in Electron Microscope. Just like the spokes of a cycle wheel. This overlapping arrangement is very crucial in withstanding Rotational & Intrusive Forces. This overlapping arrangement helps in spreading the load uniformly and reduce the strain on PDL.

Mechanical Advantage

Internal Orientation of collagen fibers influences the mechanical properties of the tissue . Collagen fibers best resist axially directed force.

The complex 3D arrangement of fibers also means that some bundles would always be placed in Tension, irrespective of the direction of an applied force. This enables local areas of the PDL to resist compressive forces.

COLLAGEN CRIMPINGCollagenous tissues exhibit a quantifiable periodicity of structure of variable scale, the waveform that describes this periodicity has been referred to as crimp. In the polarizing microscope crimping can be seen by regular banding of dark lines across the bundles.

Causes Of Collagen Crimping:Sharp Zig Zag arrangement of collagen fibers with quantifiable periodicity angular deflection frm axis.

Microanatomical organization of collagenous sheets and bundles in sinusoidal wave forms.

Significance of Crimping :It is an early ,easily extensible , non linear region that causes the straightening out of the crimp. This enables the ligament to absorb impact tensile loads without extending collagen fibrils and without producing heat .

Fibroblast processes in the developing collagenous tissues play a role in fabricating the crimped arrangement and consequently that crimping may be an important feature in tooth eruption.

It also has been proposed that crimp some times can generate contractile forces in collagen molecules .

SHARPEY FIBERS

At their insertion the collagen bundles of PDL are embed in to cementum and alveolar bone in a manner similar to tendon inserting in to the bone . They usually tend to be concentrated in the crestal region.

Some Sharpey fibers pass right through alveolar bone , which implies that there may be continuity between the collagen fibers of the PDL of adjacent teeth . ( Transalveolar Fibers )

Sharpey Fibers are enclosed within a sheath of collagen Type III and it not only confers elasticity on the fibers but it also maintains the elasticity of the fibers when they are inserted in to the bone by preventing their mineralization.

Collagen are arranged in bundles and they form the Principal Fibers . The terminal ends of the collagenous principal fibers are inserted in to bones to form SharpeyFibers.

The periodontal ligament is very important to the maintenance of the periodontal apparatus. This is proved by the atrophy of the alveolar bone that often follows the removal of the teeth and associated PDL.

Under the scanning electron microscope it is revealed that the point where the fibers insert obliquely , the bone surface exhibits a stepped appearance that indicates mineralization occurs approximately at right angles to the axis of the fiber. These mineralized points provide mechanical advantages for transmitting axially directed forces.

The mineral interface also appears concave and this maximum strength to the mineral-collagen interface.

In case of periodontal diseases there is destruction of PDL , sharpey fibers . Due to this teeth is not able to withstand the varying types of mechanical forces that ultimately leads to tooth mobility .

ELASTIC FIBERS OF PDLIn PDL the collagen fibers are associated with elastic mesh work which may function either as a static elastic element or as a resilient material.

The 3 fibrous components are OXYTALAN , ELAUNIN & ELASTIN.

Oxytalan fibers form a 3D meshwork that extends from the cementum to the periodontal blood vessels. The size of the fibers vary depending on the site.

It is oriented in the Apico Occlusal plane .

Oxytalan & Elaunin Fibers are precursors of the elastin fibres.

Oxytalan fibers are composed of microfilaments surrounded by amorphous material.

Elastin fibers are composed of microfibrillar glycoprotein and amorphous elastin.

Elementary units of elastin are Rod-Like in shape .

Elastin fibers are found only in the PDL of some species.

A CEMENTUM

B PRINCIPAL OXYTALAN FIBER

C Oxytalan Tract

D Periodontal Vessel

AGE CHANGES IN COLLAGENAs age advances qualitative and quantitative changes of collagen are seen -Higher conversion of soluble to insoluble collagen -Increased mechanical strength. - More organized and thicker. - Areas of hyalinization. -Increased denaturing temperature -Apparent decrease in the number of collagen & PDF fibers due to Increased Fibrosis+ decreased cellularity. - Gradual decrease in the number of synthesizing connective tissue cells - A gradual recession of alveolar bone. Irregular Alveolar Bone & cementum surface.These changes are due to higher cross linking and stabilized forms of collagen

BIOSYNTHESIS OF COLLAGEN

BIOSYNTHESIS OF COLLAGENSites For The Synthesis of Collagen :

1.Mesenchymal Cells & Their Derivatives

FIBROBLASTS ( major cells )

ChondrocytesOsteoblasts

OdontoblastsCEMENTOBLASTS

2.Other Cells : Epithelial cells. Endothelial cells. Muscle cells. Schwann cells.

Fibro Blasts Fibroblasts are responsible for the production of the extracellular matrix components.They reside in close proximity to the collagen fibers.The nucleus appears as an elongated or disk like structure in H & E preparations. The thin, pale staining, flattened processes that form the bulk of the cytoplasm are usually not visible.

Myofibroblast is an elongate, spindle connective tissue cell that displays typical characteristics of the fibroblast along with characteristics of smooth muscle cells

FIBROBLASTS IN PERIODONTIUM

They are usually identified by cigar shaped or stellate morphology, presence of vimentin intermediate filaments and synthesis of matrix collagens and fibronectin.

Fibroblasts of healthy and diseased periodontal tissues are heterogeneous and show diversity of synthetic products, rates of product synthesis, responses to regulatory molecules, cellular turnover rates and morphologic features

SYNTHESIS OF COLLAGEN

Gene Expression

Translational and post translational events or intracellular steps in collagen synthesis procollagen formation .

THE ENTIRE PROCESS OF COLLAGEN SYNTHESIS CAN BE BEST UNDERSTOOD UNDER THE FOLLOWING STAGES …

Extracellular collagen biosynthetic events

Regulation of Synthesis

(Nucleus)

(Cytoplasm)

( Extracellular)

A. Sequence of intracellular collagen biosynthesis Assembly pro-alfa chains (directed by specific mRNAs)

Proline hydroxylation

Lysine hydroxylation

Hydroxylysine glycosylation

Disulphide bond formation/incorporation of C Terminal Propeptides. Secretion

B. Sequence of extracellular collagen biosynthesis Amino terminal extension cleavage

Carboxyl terminal extension cleavage

Microfibril formation Lysine hydroxylysine terminal NH2 oxidation (Cu-containing lysyl oxidase)

Fibril formation Reducible cross-link formation Maturation of cross-links. Growth and reorganization of fibers.

SEQUENCE OF EVENTS

Gene ExpressionCollagen genes are large and range in size from 5kb for (COL1A1) TO 130 kb for COL1A31. More than 30 genes have been described for collagen types I to type XIX.

Although differences exists among various collagen genes , those coding for “Fibril forming collagens” have similar exon arrangement. These genes have 42 exons for the major triple helical region .Most of these exons are composed of 54 bp(or multiple) & start with an intact codon for glycine.

TYPE 1

TYPE 2

TYPE 3

TYPE 5

COL1A1

COL2A1

COL3A1

COL4A1-COL4A6

Central Dogma of Molecular BiologyProtein synthesis requires two steps: transcription and translation.

INTRA NUCLEAR STEPS

The 3 polypeptide chains of collagen molecule are formed separately under the direction of their respective genes. The initial RNA transcript is processed to mRNA.

CYTOPLASMIC STEPS

Pre Pro collagen Cleavage of Signal Peptide

PROCOLLAGEN α CHAIN Hydroxylation Glycosylation Association C terminal Peptides Disulphide Bond Formation PROCOLAGEN MOLECULE Passes in to golgoi complex combines with Secretory Vacuoles to move outside cell .

After Nuclear steps the mRNA translocates to cytoplasm where it binds to ribosome to get translated & codes for PreProCollagen.

EXTRA CELLULAR STEP ( ASSEMBLY OF COLLAGEN )

REMOVAL OF TERMINAL PRO PEPTIDES Cleavage of C & N Pro peptides by C & N Proteinase .

ASSEMBLY OF COLLAGEN The collagen molecules then align themselves laterally to each other , having a quarter over-lap such that there is typical 64nm banded appearance. These fibrils are immature and lack strength

CROSS LINK OF FIBRILS TO FORM FIBRESCross-linkage is a slow process and the tensile strength of collagen steadily increases over a long period

Type I Procollagen with N- & C- Terminal propeptide. The C-Terminal is bigger in size than N-terminal.Cysteine residues at the propeptides forms intrachain disulphide bonds.Both the propeptides under go cleavage in the extracellular space before collagen molecules can combine to form fibrils. Failure to remove the terminal ends results in defective production of collagen fibers.

Hydroxylation & Glycosylation (in cytoplasm RER)

Both hydroxyproline and hydroxylysine are formed in the RER by the hydroxylation of prolyl and lysyl residues. This is an essential step in biosynthesis of collagen for it stabilizes the molecules.Requirements for hydroxylation are:

1. Specific enzymes :2. prolyl hydroxylase and

lysyl hydroxylase 3. α-ketoglutarate 4. Ferrous ions 5. Molecular oxygen6. Ascorbic acid (Vitamin

C)Following hydroxylation and glycosylation, three polypeptide chains form a triple helix = PROCOLLAGEN

Significance of Hydroxylation & GlycosylationTriple Helical Type 1 collagen, with complete hydroxylation of Prolyl has a Tm of 39*C. However underhydroxylated molecules melt at lower temperatures i.e the Tm is around 25*C.

Therefore Prolyl hydroxylation is essential for collagen thermal stability at physiologic temperature. While underhydroxylated molecules are denatured and degraded.

Hydroxylysine residues on the other hand , serve as specific glycosylation sites and form more stable cross links than lysine.

Cross Linkage Formation(EXTRA CELLULAR)

LYSYL OXIDASE(EXTRA CELLULAR ENZYME)

Oxidative Deamination

Lysyl Oxidase Acts on

LYSYL & HYDROXY LYSYL RESIDUES IN COLLAGEN

Reactive Aldehydes(Allysine + Hydroxy Allysine)

Combines with collagen residues to form Cross Links

REGULATION OF COLLAGEN SYNTHESIS

Regulation of Collagen BiosynthesisCollagen biosynthesis is tightly regulated during normal development & homeostasis in a cell & tissue specific manner .

GENE TRANSCRIPTION

POST TRANSLATIONAL MODIFICATION

The changes at the gene transcription stage are reflected by dec in the mRNA levels and unstable mRNA.

Collagen genes contain CIS-regulatory sequences , promoters and enhancers.

Gene transcription is regulated by binding of protein transcription factors to the sequences.Eg. TGF-β activates collagenase gene transcription through regulatory DNA sequence that binds to NF-1.

Post Translationally Col synthesis is regulated by the extent of prolyl hydroxylation .

Under Hydroxylation results in dec stability of the collagen molecule which is then degraded .

Correct amount of hydroxylation results in the production of stable and strong collagen fibers .

The manner in which collagen genes are regulated differs from collagen to collagen.

In type I collagen , short enhancer and promoter gene are present in the 1st Intron of the COL1A2 gene.

In Type IV collagen the pair of genes for COL4A1 and COL4A2 are each arranged in a unique head to head arrangement separated by a short 130 bp segment with a binding site at the center . This site interacts with enhancer or negative regulatory elements which regulates the gene transcription.

The magnitude of collagen synthesis is dependant upon the levels of mRNA for its α Chains

A variety of growth factors and cytokines regulate collagen production during development , inflammation and wound repair .

TGF-β is an important mediator as it enhances the synthesis of collagen . This polypeptide is believed to play a major role in the wound repair and fibrosis. In contrast TNF-α suppress collagen gene expression .

These mediators affecting collagen synthesis are secreted by platelets, macrophages , keratino cytes , lymphocytes , monocytes during imflamation and their presence at the foci of inflammation and wound sites generally co relates with change in collagen synthesis.

COLLAGEN DEGRADATION

Degradation of CollagenBreak down of the collagen matrix element is a key component of any normal tissue that is undergoing morphogenesis and growth. But it is vital that this process is kept under rigid control.

Although several enzymes are involved in the destruction of matrix components collage breakdown is mediated primarily by the COLLAGENASES ( Type of MMP) These are specialized enzymes that have evolved specifically to hydrolyze collagens ,because their triple helical collagen structure is resistant to most common proteinases.

COLLAGEN DEGRADATION BY MMPS COLLAGEN DENATURED

Gene Expression

*TRANSLATION*POST TRANSLATION*EXTRACELLULAR ASSEMBLY

Collagen Synthesis

- - - - - -(EQUILIBRIUM BETWEEN DEGRADATION & SYNTHESIS)- - - -

The collagenases belong to a family of enzymes called Matrix Metallo Proteinase(MMPs) that consists of at least 13 members with closely related domain structures and discrete functions.

All have a 21-kd catalytic domain that contains a Zn++ binding site. Based on their substrate specificity they have been classified as COLLAGENASES , GELATINASES , STROMELYSINS , MATRILLYSINS.

3 interstitial collagenases capable of degrading native collagen matrix fivers have been described so far. They cleave α1(I) and α(I)2 chains at glycine-leucine bonds.

The cleavage of these susceptible peptide bonds ( located approx one quarter of the length from C Terminus ) results in the release of cleavage fragments three quarters & One quarters of the original chain size .

The released fragments have a lower Tm than the intact collagen molecule at physiologic temperatures and therefore they become denatured and subsequently are degraded by other common body proteinases.

MMPs are usually secreted by the connective tissue cells (predominantly fibroblasts ) but are also produced by some leucocytes ( PMNs , Macrophages ) .

MECHANISM OF ACTION

REGULATION OF MMP ACTIONThe destructive properties of MMPs are kept under control by 3 different mechanisms.

These enzymes are normally present in tissues as inactive precursors , and converion to an active form requires activation factors like plasmin , trypsin and proteinases.

MODULATION SYNTHESIS : MMP synthesis is induced by numerous mediators that modulate its synthesis and gene expression. Two key regulators are IL-1 and TGF-β.

The activities of MMPs are neutralized by inhibitors present in serum and tissues. A major inhibitor is Alpha-2-Macro globulin that covalently crosslinks with collagenases and other susceptible proteolytic enzymes and inactivates them. Its binds to MMP-1 and stops its action.

Tissues contain another group of inhibitors called TIMP( Tissue inhibitor of MMPs) that are distributed in the body tissues and fluids.3 such members are described till today TIMP, TIMP-1 & TIMP-2.

TIMP is highly conserved glycoprotein that forms irreversible complexes with MMPs via non covalent interactions. Its usually is secreted by Fibroblasts and macrophages .

COLLAGEN DISORDERS OR DISTURBANCES

Osteogenesis Imperfecta.Ehler Danlos syndrome.Lupus Erythematosus.

Scleroderma.Scurvy.

Polyarteritis nodosa.Epidermolysis bullosaRheumatoid arthritis

Crohn`s disease.Wegner`s granulomatosis

The diseases arise due to point mutations, deletions or insertions in the structural genes for collagens or changes in the post translational processing enzymes. Usually the type I collagen mutation that affect proα1(I) chains and C terminus can be lethal. Those affecting proα2(I) are not lethal.

• Fascinating proteins . • Most diseases in higher animals involve collagen containing

connective tissue directly/indirectly.• The collagens are a group of 20 closely related types that have

numerous functions all over body . • Mechanisms that regulate collagen synthesis have a direct

bearing on periodontal structures in which the connective tissues specially collagen undergo dynamic changes during periodontitis and drug-induced gingival hyperplasia.

• A balanced synthesis , regulation and degradation of collagen ensures a healthy periodontal health.

CONCLUSION …

*The periodontal ligament in health and disease: 2nd edition, Barry K B Berkovitz*Text Book Of Oral Histology- R. TENCATE*Clinical Periodontology: 10th edition; Carranza*Perio 2000,Vol 19,1999*Text book of Oral Pathology: 4th edition; shafers*Text Book Of Oral Histology- B.Berkovitz*PUBMED

REFERENCES ….