Proteoglycans

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Tolulope Adeniji  

Introduction

GAGs, proteoglycan, glycoproteins, cartilage matrix

Proteoglycan are of a class of glycoproteins of high molecular weight that are found especially in the extracellular matrix of connective tissue (the fibrous tissue that gives support to the body structure). Proteoglycans make up a major part of the extracellular matrix, filling the spaces that occur between cells. Different from other body tissues, the extracellular matrix (ECM)is the most significant part of connective tissue.

Classification

GAGs, proteoglycan, glycoprotein, keratan sulfate, cartilage matrix

Ways to classify

1. Nature of their GAGs chains: Proteoglycans can be classified according to the glycosaminoglycans (GAGs) attached to them. The types are chondroitin sulfate, dermatan sulfate, heparin sulfate, heparan sulfate, or keratan sulfate.
2. Proteoglycans are categorized by their relative size (large and small): Large molecules e.g. aggrecan, an important part of cartilage, versican, which is found in the blood vessels and skin. Small molecules eg decorin, biglycan, fibromodulin, and lumican.

Synthesis

Proteoglycans are synthesized in the rough endoplasmic reticulum, then reshaped in the golgi body, and are ultimately transported to the extracellular matrix by vesicles.

Diverse Functions

Extracellular Matrix Components of Cartilage

Aggrecan, AKA cartilage-specific proteoglycan core protein

Proteoglycans are a major component of the animal ECM, being the filler between cells in an organism. Proteoglycans have an important role in the physiology and biomechanical function of tendons, ligaments and cardiovascular system via their involvement in regulation of assembly and maintenance of ECM, and as they participate in cell proliferation through their interactions with growth factors. Eg

• Cartilage contains a variety of proteoglycans, being essential for its normal function. These include aggrecan, decorin, biglycan, fibromodulin and lumican. Each proteoglycan serves several functions that are determinedby both its core protein and its glycosaminoglycan chains. eg Aggrecan provides cartilage with the property to bind with water to form hydrated matrices. These molecules act as fillers between the cell spaces.
• Proteoglycans play important roles in organizing the bone ECM, taking part in the structuring of the tissue itself as active regulators of collagen fibrillogenesis.The bone matrix has a lower proteoglycan content than those in the cartilage and hence takes up less water as is more brittle.

Dysfunction

An inability to break down the proteoglycans (due to absent or malfunctioning lysosomal enzymes) is characteristic of a group of genetic disorders, called mucopolysaccharidoses. Over time, these GAGs collect in the cells, blood and connective tissues. The result is permanent, progressive cellular damage which affects appearance, physical abilities, organ and system functioning.

Older Persons ECM (proteoglycan)

Forever we want to be young! but our physiological systems do not allow it. The integumentary system that plays a vital role in outward appearance. Glycosaminoglycans production (named proteoglycans when attached to a protein core are part of the extracellular matrix) decrease as we age and this contributes to human skin ageing. Some of the reasons for this include:

• Reduction or absence of sexual hormonals, such as oestrogen, has been noted to contribute to a reduction in Glycosaminoglycans and proteoglycans among older adults.
• Several GAGs and PGs in the skin may explain ageing skin. In aged skin as well as photoaging skin, a reduction in ECM components such as epidermal hyaluronan, versican, elastotic materials and dermal biglycan are related to why we have ageing skin.

It is of expert opinion that analyzing the involvement of proteoglycans and glycosaminoglycans in addition to hormonal deficiency such as a drop in the level of oestrogen or complete absence in postmenopausal women may lead us to anti-ageing skin remedies.