Pathway 13-5 Connective Tissue Fibers of the Pulp

Study Notes

The pulp contains two primary structural proteins: collagen and elastin.
Elastin is primarily found in the walls of arterioles and is not part of the extracellular matrix (ECM).
Collagen is a major component of the pulp, making up 26% to 32% of the dry weight in premolars and molars.
Collagen is composed of three polypeptide chains, designated as α-1 or α-2, forming a single molecule called tropocollagen.
Type I and Type III collagen are the main types found in the pulp, with Type I present in thick striated fibrils throughout the tissue.

Type I collagen is found in various tissues, including skin, tendon, bone, dentin, and pulp.
Type II collagen is present in cartilage.
Type III collagen is found in most unmineralized connective tissues, including the dental papilla and mature pulp.
Type IV and VII collagen are components of basement membranes.
Type V collagen is a part of interstitial tissues.
Type VI collagen is widely distributed in low concentrations in soft tissues and is involved in interfibrillar filaments.

Odontoblasts and osteoblasts synthesize Type I collagen.
Fibroblasts synthesize Types I, III, V, and VII collagen.
Collagen synthesis begins with the formation of the protein portion of the molecule by polyribosomes in the rough endoplasmic reticulum (RER) of connective tissue cells.
Proline and lysine residues in the polypeptide chains are hydroxylated in the RER cisternae.
The chains assemble into a triple-helix configuration in the smooth endoplasmic reticulum, forming procollagen.
Procollagen molecules are glycosylated and packaged in secretory vesicles within the Golgi complex.
These vesicles are transported to the plasma membrane and released by exocytosis into the extracellular space.
The terminal telopeptide of procollagen is cleaved by a hydrolytic enzyme, allowing tropocollagen molecules to aggregate and form collagen fibrils.
Glycosaminoglycans (GAGs) are believed to play a role in mediating the aggregation of tropocollagen.
Cross-linking of tropocollagen molecules leads to the conversion of soluble collagen into insoluble fibers.

SOX9, a transcription factor, is strongly expressed in normal pulp tissue and promotes collagen synthesis and ECM balance.
Collagen fibers extend from the dentin matrix between odontoblasts into the dental pulp, particularly in fully erupted teeth.
Larger collagen fiber bundles are more abundant in the radicular pulp than in the coronal pulp.
The highest concentration of these larger bundles is typically found near the apex of the tooth.

SOX9 is a transcription factor, which means it controls the expression of other genes.
SOX9 is abundant in healthy dental pulp tissue.
SOX9 expression is reduced in inflamed dental pulp.
SOX9 appears to stimulate collagen production.
SOX9 likely contributes to maintaining the balance of the extracellular matrix (ECM) in dental pulp.