Proteoglycans: Road Signs for Neurite Outgrowth

Proteoglycans in the central nervous system play integral roles as ＂traffic signals＂ for the direction of neurite outgrowth. This attribute of proteoglycans is a major factor in regeneration of the injured central nervous system. In this review, the structures of proteoglycans and the evidence suggesting their involvement in the response following spinal cord injury are presented. The review further describes the methods routinely used to determine the effect proteoglycans have on neurite outgrowth. The effects of proteoglycans on neurite outgrowth are not completely understood as there is disagreement on what component of the molecule is interacting with growing neurites and this ambiguity is chronicled in an historical context. Finally, the most recent findings suggesting possible receptors, interactions, and sulfation patterns that may be important in eliciting the effect of proteoglycans on neurite outgrowth are discussed. A greater understanding of the proteoglycan-neurite interaction is necessary for successfully promoting regeneration in the iniured central nervous system.

Commentary on:“Facilitating transparency in spinal cord injury studies using data standards and ontologies”

Commentary Most would agree that providing comprehensive detail in scientific reporting is critical for the development of mean- ingful therapies and treatments for diseases. Such stellar practices 1） allow for reproduction of experiments to con- firm results, 2） promote thorough analyses of data, and 3） foster the incremental advancement of valid approaches. Unfortunately, most would also agree we have far to go to reach this vital goal （Hackam and Redelmeier, 2006; Prinz et al., 2011; Baker et al., 2014）.

Neuronal growth cones and regeneration: gridlock within th extracellular matrix

The extracellular matrix is a diverse composition of glycoproteins and proteoglycans found in all cellular systems. The extracellular matrix, abundant in the mammalian central nervous system, is temporally and spatially regulated and is a dynamic ＂living＂ entity that is reshaped and redesigned on a continuous basis in response to changing needs. Some modifications are adaptive and some are maladaptive. It is the maladaptive responses that pose a significant threat to successful axonal regeneration and/or sprouting following traumatic and spinal cord injuries, and has been the focus of a myriad of research laboratories for many years. This review focuses largely on the extracellular matrix component, chondroitin sulfate proteoglycans, with certain comparisons to heparan sulfate proteoglycans, which tend to serve opposite functions in the central nervous system. Although about equally as well characterized as some of the other proteoglycans such as hyaluronan and dermatan sulfate proteoglycan, chondroitin sulfate proteoglycans are the most widely researched and discussed proteoglycans in the field of axonal injury and regeneration. Four laboratories discuss various aspects of chondroitin sulfate proteoglycans and proteoglycans in general with respect to their structure and function （Beller and Snow）, the recent discovery of specific chondroitin sulfate proteoglycan receptors and what this may mean the field （Shen）, extracellular for increased advancements in matrix degradation by matrix metalloproteinases, which sculpt and resculpt to provide support for outgrowth, synapse formation, and synapse stability （Phillips et al.）, and the perilesion microenvironment with respect to immune system function in response to proteoglycans and central nervous system injuries （Jakeman et al.）.