Chondroitin sulfate proteoglycan
Chondroitin sulfate proteoglycans (CSPGs) are
Importantly, CSPGs are known to inhibit axon regeneration after spinal cord injury. CSPGs contribute to glial scar formation post injury, acting as a barrier against new axons growing into the injury site.[2] CSPGs play a crucial role in explaining why the spinal cord doesn't self-regenerate after an injury.
General structure
Chondroitin sulfate proteoglycans are composed of a core protein and a sugar side chain. The core protein is generally a
Types
The following CSPGs have been identified:
- Aggrecan (CSPG1)
- Versican (CSPG2)
- Neurocan (CSPG3)
- CSPG4 (melanoma-associated chondroitin sulfate proteoglycan, NG2)
- CSPG5
- SMC3 (CSPG6, structural maintenance of chromosomes 3)
- Brevican (CSPG7)
- CD44 (CSPG8, cluster of differentiation 44)
- Phosphacan
Neurocan, brevican, versican, and aggrecan all share similar
Neural development
CSPGs play an active role in the neural development of postnatal babies. During development, CSPGs act as guidance cues for developing
Spinal cord injury
CSPGs have been implicated in inhibiting axonal regeneration and neurogenesis after central nervous system injury.[5] CSPGs are known to be part of the glial scar that forms post injury, acting as a barrier to prevent axon extension and regrowth.[6] Studies examining CSPG (neurocan, brevican, versican, and phosphacan) levels in rats before spinal cord injury and after spinal cord injury indicate that there is a large up-regulation of these CSPGs after injury is induced.[3] Neurocan, brevican, and versican levels are up-regulated one day post injury, and neurocan and versican remain elevated 4 weeks post injury (brevican remained elevated at 8 weeks post injury, the final time point in the study).[3] Phosphacan showed no up-regulation until 4 weeks post injury.[3] These results, along with previous results showing CSPGs inhibit axon growth, suggest that these four CSPGs work together to inhibit axon growth in spinal cord injury.
Regulation
Inhibition of EGFR inhibits CSPGs
Epidermal growth factor receptor (EGFR) has been suggested to regulate CSPG function. Inhibiting EGFR has been shown to block the activities of certain CSPGs, including neurocan, phosphacan, versican, and aggrecan.[7] When EGFR was inactive, CSPGs had little effect on neurons.[7] As a result, neurogenesis occurred, with significantly longer and many more neurons forming than seen with EGFR active.[7] When EGFR is active, CSPG functioned normally, restricting neurogenesis.[7] Drugs manipulating EGFR may be helpful in preventing the adverse effects CSPGs have during spinal cord injury.
PTP-sigma is a CSPG receptor
Interferon-gamma
Rho/ROCK pathway mediates CSPGs
The CSPG inhibition of axon regrowth and neurogenesis post spinal cord injury has been shown to be associated with the
In disease
Chondroitin sulfate proteoglycans have been implicated in Alzheimer's disease, stroke, and epilepsy.
Alzheimer's
The two primary markers of Alzheimer's disease are
Stroke
A stroke is a sudden loss of brain function due to either a blood clot or blood leakage in the brain. Often, a stroke seriously debilitates the patient. However, in those patients that do regain some brain function in affected areas, down-regulations of CSPGs are shown to occur. After stroke, plasticity occurs in some regions of the brain and is associated with some return of brain function.[11] Rats that were able to recover from induced stroke had down-regulations of several CSPGs, including aggrecan, versican, and phosphacan [11] Rats that did not return any brain function did not have significant down-regulation of CSPGs. The reduction of CSPGs in rats that returned some brain function after stroke suggest that more neurological connections could be made with less CSPGs present. Medications that are able to down-regulate CSPGs may help return more brain function to stroke patients.[clarification needed][citation needed]
Epilepsy
Epilepsy is a