Perineuronal net complex proteins (PNNs)

Perineuronal nets (PNNs) are specialized, lattice-like extracellular matrix structures that enwrap the cell bodies and proximal dendrites of specific neurons, most notably fast-spiking parvalbumin-positive GABAergic interneurons. These structures are primarily composed of a hyaluronan backbone linked to chondroitin sulfate proteoglycans (lecticans such as aggrecan, brevican, and neurocan) and stabilized by link proteins (HAPLN1/4) and tenascins. PNNs play a critical role in brain development by signaling the end of "critical periods," during which the brain is highly plastic, and thereafter acting to stabilize mature synaptic connections and protect neurons from oxidative stress and neurotoxins. In various neurological and psychiatric conditions, such as schizophrenia and Alzheimer's disease, the integrity or density of PNNs is often altered, contributing to cognitive deficits or impaired recovery. Consequently, PNNs have emerged as a significant therapeutic target for neuroregeneration and the treatment of neuropsychiatric disorders. Experimental strategies include using the enzyme Chondroitinase ABC to degrade PNN components or small molecules like 4-methylumbelliferone to inhibit their synthesis, thereby reactivating neuroplasticity to promote functional recovery after injury or to enhance cognitive flexibility. However, therapeutic modulation must be carefully balanced to avoid maladaptive plasticity or increased neuronal vulnerability.

Other names

Perineuronal netsNeural extracellular matrixBrain extracellular matrix complexChondroitin sulfate proteoglycan matrix

Enzymatic degradation of chondroitin sulfate proteoglycans (CSPGs) and hyaluronan to reopen critical periods of plasticity; inhibition of hyaluronan synthase to prevent matrix assembly; modulation of matrix metalloproteinases (MMPs) to alter matrix integrity.