Proteoglycans are some of the major constituents of the
extracellular matrix and are composed of a core protein molecule to
which glycosaminoglycans (GAGs) are covalently linked as side
chains.
1 2 They are classified into several groups (e.g.,
chondroitin sulfate, heparan sulfate, dermatan sulfate, and keratan
sulfate proteoglycans) on the basis of their GAG side chains. Varner
and associates
3 4 have clearly demonstrated, by
histochemical and biochemical studies, the presence of chondroitin
sulfate and heparan sulfate GAGs in mammalian retinas, especially in
the interphotoreceptor matrix. In addition, recent molecular biological
studies have revealed the molecular characterization of a number of
proteoglycan core proteins. Since then, biological activities of
proteoglycans have been intensively studied, on the basis of
characterizations of their core proteins.
1 In developing
brain, a diverse set of proteoglycan core proteins is present and
precisely regulated,
5 6 which suggests an important
role in the development and maintenance of neural networks. In neural
tissues, proteoglycans have been shown to elicit an alteration in
neurite outgrowth, neural cell adhesion, and
differentiation.
5 6 Accordingly, characterization of
retinal proteoglycans is necessary to better understand both
developmental and pathologic processes. Knowledge about proteoglycan
core proteins in the retina is limited.
7 8 However, it is
known that a nervous tissue–specific proteoglycan, neurocan, is the
major proteoglycan in the brain
9 and that it regulates
neurite outgrowth and cell adhesion in neural
tissues.
10 11 It is also possible that neurocan plays a
pivotal role in formation of the neural network. However, to date,
there are no conclusive data regarding the expression of neurocan in
the retina. It has been reported that a neurocan-derived C-terminal
product (also called chondroitin sulfate proteoglycan [CSPG]-150 or
neurocan-C) is created in rat brain by proteolytic processes and that
it ultimately becomes the major form and has biological activities
similar to full-length neurocan.
12 In a previous study, a
monoclonal antibody (MAb 1G2) recognizing both a 220-kDa glycoprotein
(full-length neurocan) and a 150-kDa glycoprotein (C-terminal half
proteolytic product of neurocan) was raised.
13 Herein, we
report on the gene expression and localization of neurocan core protein
in the retina and show alterations in the distribution and amount in
the developing retina.