October 6, 2008
Chondrogenesis, HA and aggrecan
Read pages 1091-1096 Albert 4th edition,
Remember from the last lecture that HA is a non-sulfated GAG.
Proteoglycans (PGs) are
composed of GAG chains consisting of repeated disaccharides, which usually contain a
sulfated hexosamine and uronic acid, covalently linked to a central protein core.
classes of GAGs are recognized based on different monosaccharide composition,
sulfation, and epimerization of uronic acid.
See slides 25-30, lecture 8 and Alberts for
Hybrid molecules with additional structural diversity may arise due to the
attachment of N- and O-linked glycoprotein-type oligosaccharides.
You are responsible for remembering the names of sugar repeats that make up the major
GAGs, not their precise chemical composition.
It has long been known that in cartilage, the ECM exerts effects on chondrocyte cells
shape, phenotype, and metabolism.
Conversely, chondrocyte cell shape changes exert
effects on matrix organization, assembly, and retention.
The process of dynamic
reciprocity we discussed at the beginning of the course.
Structure of the growth plate
(Verbatim with minor modifications from S. Price,
B.O. Oyajobi and R.G.G. Russell Department of Human Metabolism and Clinical
Biochemistry, Sheffield University Medical School, Beech Hill Road, Sheffield S10
1RX, UK, http://www.unu.edu/Unupress/food2/UID06E/uid06e0u.htm ,references
The epiphyseal growth plate is made up of three tissue types: the cartilage component
divided into distinct zones (slides 5) , the bony tissue of the metaphysis and the fibrous
tissue that surrounds the growth plate. The vascular supplies to the growth plate are not
illustrated in slide 5, but remember that the primary and secondary ossification regions
are highly vascularized.
Growth plate chondrocytes are organized into different zones (slides 5 and 6) with each
cell population being part of a different stage of maturation in the endochondral
sequence. Traditionally studies of growth plate have described cell populations in terms
of cell size, shape and contents. Functions of these cells used to be speculated upon
depending on their morphology. However, improvements in cell and molecular biology
techniques now enable growth plate chondrocyte function to be studied where
morphology is maintained.
Reserve or resting zone
. Cells exist singly or in pairs separated by an abundant
extracellular matrix, and have low rates of proliferation. Proteoglycan synthesis and type