Perineuronal nets protect against amyloid β-protein neurotoxicity in cultured cortical neurons

Perineuronal nets (PNs) consisting of chondroitin sulfate proteoglycans (CSPGs) and hyaluronic acid are associated with distinct neuronal populations in mammalian brain. Cortical areas abundant in PNs have been known to be less affected by neurotoxicity in human Alzheimer's disease. In the present study, we examined whether PNs protect the neurotoxicity caused by amyloid β-protein (Aβ), a major constituent of senile plaques in Alzheimer's disease using cortical neurons of dissociated culture. Double labeling experiments using confocal microscopy showed that the neurons associated with PNs were visualized with the anti-CSPG antibody in dissociated cortical culture. The analysis of reverse transcription-polymerase chain reaction revealed that mRNA expression of chondroitin sulfotransferases, CSPG-specific enzymes, was detected in neuronal culture, indicating that cultured cortical neurons are able to synthesize CSPGs and construct PNs structure. The treatment of Aβ1–42 showed significant neurotoxicity on PNs-free cortical neurons, however, it did not reveal neurotoxicity on PNs-associated neurons. Moreover, it was shown that the treatment of Aβ1–42 was able to kill PNs-associated neurons after the removal of chondroitin sulfate (CS) glycosaminoglycans with chondroitinase ABC. The treatment of glutamate killed not only PNs-free cortical neurons but also PNs-associated neurons. These results suggest that CS glycosaminoglycans on PNs are responsible for protecting neurons from Aβ1–42 neurotoxicity.