Perineuronal nets and the neuronal extracellular matrix can be imaged by genetically encoded labeling of HAPLN1in vitroandin vivo

Abstract

Neuronal extracellular matrix (ECM) and a specific form of ECM called the perineuronal net (PNN) are important structures for central nervous system (CNS) integrity and synaptic plasticity. PNNs are distinctive, dense extracellular structures that surround parvalbumin (PV)-positive inhibitory interneurons with openings at mature synapses. Enzyme-mediated PNN disruption can erase established memories and re-open critical periods in animals, suggesting that PNNs are important for memory stabilization and conservation. Here, we characterized the structure and distribution of several ECM/PNN molecules around neurons in culture, brain slice, and whole mouse brain. While specific lectins are well-established as PNN markers and label a distinct, fenestrated structure around PV neurons, we show that other CNS neurons possess similar extracellular structures assembled around hyaluronic acid, suggesting a PNN-like structure of different composition that is more widespread. We additionally report that genetically encoded labeling of hyaluronan and proteoglycan link protein 1 (HAPLN1) reveals a PNN-like structure around many neuronsin vitroandin vivo. Our findings add to our understanding of neuronal extracellular structures and describe a new mouse model for monitoring live ECM dynamics.

Perineuronal Net Microscopy: From Brain Pathology to Artificial Intelligence

“…A knock-in transgenic mouse expressing the link protein HAPL1 fused to Venus has been generated via Crispr/Cas9 genome editing [90]. The construct is expressed in the brain, exhibiting a PNN-like structure on the neuronal surface, as visualized by confocal microscopy.…”