Casting a Wide Net: Role of Perineuronal Nets in Neural Plasticity

Abstract

Perineuronal nets (PNNs) are unique extracellular matrix structures that wrap around certain neurons in the CNS during development and control plasticity in the adult CNS. They appear to contribute to a wide range of diseases/disorders of the brain, are involved in recovery from spinal cord injury, and are altered during aging, learning and memory, and after exposure to drugs of abuse. Here the focus is on how a major component of PNNs, chondroitin sulfate proteoglycans, control plasticity, and on the role of PNNs in memory in normal aging, in a tauopathy model of Alzheimer's disease, and in drug addiction. Also discussed is how altered extracellular matrix/PNN formation during development may produce synaptic pathology associated with schizophrenia, bipolar disorder, major depression, and autism spectrum disorders. Understanding the molecular underpinnings of how PNNs are altered in normal physiology and disease will offer insights into new treatment approaches for these diseases.

Keywords: Alzheimer's; aging; autism; chondroitin sulfate proteoglycans; drug abuse; extracellular matrix; memory; perineuronal nets; schizophrenia.

Figure 1.

Limitation of plasticity by PNNs via three mechanisms and reinstatement of plasticity by treatment with Ch-ABC. Plasticity involving PNN-surrounded neurons is limited by the following: (a) a physical barrier by PNNs to incoming synaptic inputs; (b) binding of molecules via specific sites on CSPGs of PNNs (molecules, such as semaphorin 3A, inhibit new synaptic inputs); and (c) prevention of lateral diffusion of AMPA receptors, limiting the ability to exchange desensitized receptors in the synapse for new receptors from extrasynaptic sites. Treatment with Ch-ABC disrupts PNNs, reinstating juvenile-like states of plasticity. HA, Hyaluronic acid; HAS, hyaluronic acid synthase. Figure courtesy of J.C.F. Kwok. Modified from Wang and Fawcett (2012), with permission.