Chondroitin Sulfate Expression in Perineuronal Nets After Goldfish Spinal Cord Lesion

Abstract

Perineuronal nets (PNNs) surrounding neuronal cell bodies regulate neuronal plasticity during development, but their roles in regeneration are unclear. In the PNNs, chondroitin sulfate (CS) is assumed to be involved in inhibiting contact formation. Here, we examined CS expression in PNNs in the ventral horn of a goldfish hemisected spinal cord in which descending axons regenerate beyond the lesion to connect with distal spinal neurons. In intact fish, chondroitin sulfate A (CS-A)–positive PNNs accounted for 5.0% of HuC/D-immunoreactive neurons, and 48% of choline acetyltransferase (ChAT)-immunoreactive neurons. At 2, 4 and 8 weeks after spinal hemisection, CS-A–positive PNNs accounted for 8.4%–9.9% of HuC/D-immunoreactive neurons, and 50%–60% of ChAT-immunoreactive neurons, which was not significantly different from intact fish. Chondroitin sulfate C (CS-C)–positive PNNs accounted for 6.4% of HuC/D-immunoreactive neuron, and 67% of ChAT-immunoreactive neurons in intact fish. At 2, 4 and 8 weeks after spinal hemisection, CS-C–positive PNNs accounted for 7.9%, 5.5% and 4.3%, respectively, of HuC/D-immunoreactive neurons, and 65%, 52% and 42%, respectively, of ChAT-immunoreactive neurons, demonstrating a significant decrease at 4 and 8 weeks after spinal hemisection. Among ventral horn neurons that received descending axons labeled with tetramethylrhodamine dextran amine (RDA) applied at the level of the first spinal nerve, CS-A–positive PNNs accounted for 53% of HuC/D-immunoreactive neurons. At 2 and 4 weeks after spinal hemisection, CS-A–positive PNNs accounted for 57% and 56% of HuC/D-immunoreactive neurons, which was not significantly different from intact fish. CS-C–positive PNNs, accounted for 48% of HuC/D-immunoreactive neurons that received RDA-labeled axons. At 2 and 4 weeks after spinal hemisection, CS-C–positive PNNs significantly decreased to 22% of the HuC/D-immunoreactive neurons, and by 4 weeks after spinal hemisection they had returned to 47%. These findings suggest that CS expression is maintained in the PNNs after spinal cord lesion, and that the descending axons regenerate to preferentially terminate on neurons not covered with CS-C–positive PNNs. Therefore, CS-C in the PNNs possibly inhibits new contact with descending axons, and plasticity in the spinal neurons might be endowed by downregulation of CS-C in the PNNs in the regeneration process after spinal hemisection in goldfish.

Link Protein 1 Is Involved in the Activity-Dependent Modulation of Perineuronal Nets in the Spinal Cord

“…Prior studies have already described changes in PNN remodeling following SCI in WT mice [11,25,26]. In agreement with our previous results analyzing the changes in PNN structure after a thoracic cord contusion [11], we observed reduced PNN thickness around disconnected lumbar motoneurons.…”

The Role and Modulation of Spinal Perineuronal Nets in the Healthy and Injured Spinal Cord

“…Reduced staining of aggrecan around lumbar MN was reported 35 days after a thoracic SCI, recovering normal levels at later stages (Sánchez-Ventura et al, 2020 ). Similar findings were described after hemisection in goldfish (Takeda et al, 2018 ). A study evaluating aggrecan synthesis and degradation found a significant decline in aggrecan levels after SCI too (Lemons et al, 2001 ).…”

“…Perineuronal nets are specialized ECM that encapsulate the soma and the proximal dendrites of some neurons in the CNS. This mesh-like structure has been described in various mammals [e.g., rodents (Kalb and Hockfield, 1988 ; Galtrey et al, 2008 ), cats (Hockfield, 1983 ), dogs (Atoji et al, 1997 ), sheep (Härtig et al, 2017 ), primates (Mueller et al, 2016 ), and humans (Jäger et al, 2013 )] and non-mammal species [e.g., fish (Takeda et al, 2018 ), birds (Balmer et al, 2009 ), frogs (Gaál et al, 2014 ), and chickens (Morawski et al, 2009 )]. Among all of them, spinal PNNs have been characterized in fish, rodents, cats, primates, and humans.…”

Perineuronal Nets in the CNS: Architects of Memory and Potential Therapeutic Target in Neuropsychiatric Disorders

“…Previous studies revealed that the administration of ChABC after spinal cord injury removed CS-GAGs from PNNs at the lesion site, thus promoting plasticity and nerve regeneration in long tracts entering the lesion site. In goldfish with a spinal hemisection, plasticity in the spinal neurons might be restored by downregulation of CS in the PNNs in the regeneration process [ 93 ]. Moreover, the administration of ChABC degrades CSPGs in the PNNs and appears to boost the plasticity of spinal neurons and to promote the sprouting of spared long tract axons [ 94 ].…”