A glial perspective on the extracellular matrix and perineuronal net remodeling in the central nervous system

Abstract

A structural scaffold embedding brain cells and vasculature is known as extracellular matrix (ECM). The physical appearance of ECM in the central nervous system (CNS) ranges from a diffused, homogeneous, amorphous, and nearly omnipresent matrix to highly organized distinct morphologies such as basement membranes and perineuronal nets (PNNs). ECM changes its composition and organization during development, adulthood, aging, and in several CNS pathologies. This spatiotemporal dynamic nature of the ECM and PNNs brings a unique versatility to their functions spanning from neurogenesis, cell migration and differentiation, axonal growth, and pathfinding cues, etc., in the developing brain, to stabilizing synapses, neuromodulation, and being an active partner of tetrapartite synapses in the adult brain. The malleability of ECM and PNNs is governed by both intrinsic and extrinsic factors. Glial cells are among the major extrinsic factors that facilitate the remodeling of ECM and PNN, thereby acting as key regulators of diverse functions of ECM and PNN in health and diseases. In this review, we discuss recent advances in our understanding of PNNs and how glial cells are central to ECM and PNN remodeling in normal and pathological states of the CNS.

Perineuronal nets support astrocytic ion and glutamate homeostasis at tripartite synapses

“…Not so when the PNNs are disrupted and Glu spills out of the synapses as evident from increased [Glu] in the perisynaptic space. As PNNs are known to be degraded by proteolytic enzymes including MMPs and ADAMTSs [6,36,37], it is easy to envision how brain inflammation in the context of injury or disease will break down PNNs and hence allow spillage of K + and Glu into the perisynaptic space. Increases in K + and Glu are known contributors to epilepsy, and at least in glioma-associated epilepsy, it has been demonstrated that inhibition of PNN proteolysis suppresses seizures [22].…”

“…4) is defined. AldheGFP signal (5), is binarized using automated OTSU function (6), and pericellular AldheGFP area (7), is extracted by intersecting ( 4) and (6) binary images. Synaptic marker vGlut1 (8), image is processed with an automated peak detection function to detect vGlut1 puncta (8).…”

“…Neurons and astrocytes are also embedded in an extracellular matrix (ECM) made up of proteoglycans, glycoproteins, and polysaccharides. Neurons and astrocytes each synthesize defined ECM constituents including hyaluronan (HA), chondroitin sulfate proteoglycans (CSPGs) such as aggrecan, brevican, versican and neurocan, Tenascin R (Tn-R), and link proteins such as Crtl1 and Bral2 [5,6]. Specific ECM constituents have been shown to directly interact with synaptic receptors and ion channels [7][8][9] thereby affecting synaptic vesicle release [10], dendritic spine morphology [11][12][13][14], and the structural integrity of synapses [13,15].…”

Regulation of Expression of Extracellular Matrix Proteins by Differential Target Multiplexed Spinal Cord Stimulation (SCS) and Traditional Low-Rate SCS in a Rat Nerve Injury Model

“…Changes in neural plasticity are part of the central sensitization process which derives from neuroimmune and neuroinflammatory processes resulting from peripheral nerve injury. The involvement of microglial and astrocyte activation as a result of these is clearly linked to the reshaping of the ECM and concomitant changes in the intercellular interactions at the synapse, which ultimately affect cell signaling and neurotransmission [ 56 ]. The effects of astrocyte activation on expression levels of proteins in the ECM that are associated with this process is also confirmed by our analyses.…”

Single-nucleus profiling identifies accelerated oligodendrocyte precursor cell senescence in a mouse model of Down Syndrome

“…Further, we observed increased accessibility at several CSPG loci, including Tnr, Bcan, Vcan, Acan, and Ncan 107 (Figure 5C). CSPGs have been found to negatively regulate OPC proliferation, differentiation and remyelination, as well as induce production of pro-inflammatory cytokines 108,109 . Similar to our findings in snRNAseq data, we found that Ts65Dn OPCs exhibited an increase in accessibility at several endoprotease loci, including Mmp15/19, Adam12, and Adamts5/17 loci (Figure 5C), all of which play a role in modulating neuroimmune activity through the regulation of pro-inflammatory cytokine availability and signaling 73,74 .…”