Review Question - QID 213905

Aggrecan is a proteoglycan that is found in areas of tendon compression. It contributes to the binding of the collagen fibers to specific locations.

Tendons are a group of collagen bundles separated by endotenon and surrounded by epitenon. The composition of tendons is primarily water, collagen, and proteoglycans. Types I and III collagen are the primary collagens that make up the dry weight of tendons, 85%, and 5%, respectively. Proteoglycans comprise up to 5% of the dry weight of tendons but serve important functions. Decorin is the predominant proteoglycan and regulates fiber diameter and forms cross-linking between collagen fibers and load transfers between collagen fibers. Aggrecan is another proteoglycan in tendons that is important in tendon compression contributing to the binding of the collagen fibers to specific locations.

Franchi et al. review collagen fibers in tendons and ligaments. They report that crimps within stretched tendons allow for the absorption of tension forces during fibril strengthening and recoiling of the collagen fibers when stretching is removed. They conclude that fibrillar crimps allow for the increased flexibility of the thick rigid fibrils as a consequence of a local helical arrangement of microfibrils.

Hope et al. reviewed the processes of tendon healing. They report that tendons and ligaments are primarily composed of type I collagen. However, following tendon and ligament injury, type III collagen production predominates during the inflammatory and early regenerative phases of healing. They conclude that during the later regenerative phase, type I collagen production is initiated and predominates.

Illustration A shows aggrecan molecules.

Incorrect Answers:
Answer A: Type I collagen makes up 85% of the dry weight of tendons; however, aggrecan is a proteoglycan that is found in areas of tendon compression
Answer B: Type II collagen predominates in articular (hyaline) cartilage, elastic cartilage, and the nucleus pulposus. Tendons are composed primarily of type I collagen
Answer C: Type III collagen makes up 5% of the dry weight of tendon; however, aggrecan is a proteoglycan that is found in areas of tendon compression
Answer D: Decorin is the most predominant proteoglycan in tendons and regulates collagen fiber diameter. It contributes to the cross-linking between collagen fibers and transfers loads between fibers