Regulation of perineuronal net components in the synaptic bouton vicinity on lumbar α-motoneurons in the rat after spinalization and locomotor training: New insights from spatio-temporal changes in gene, protein expression and WFA labeling.

Chondroitin sulfate proteoglycans (CSPGs) consist of core proteins and glycosaminoglycan side chains. Tenascins, and hyaluronan and proteoglycan link protein 1 (HAPLN), link CSPGs with a hyaluronan backbone to constitute perineuronal nets (PNNs), which ensheath preferentially highly active neurons to maintain architecture and stabilize synapses, but restrict repair plasticity. Spinal cord injury increases CSPG core protein levels in the lesion proximity, limiting permissiveness of the extracellular milieu for fiber regrowth, however regulation of PNNs structure in the vicinity of distant α-motoneurons (MNs) in the course of degeneration and reorganization of their inputs requires research. Here, we examined early and late changes in CSPGs, HAPLN1, tenascin-R, and glial activation along the spinal cord in male rats with complete spinal cord transection (Th10), and their impact on PNNs ensheathing lumbar MNs innervating ankle extensor and flexor muscles, which are in different loading states in paraplegic rats. We show that (1) distance from the lesion site and time after injury (2-5 weeks) differentiate degree of changes in transcription rates (measured with RT-qPCR) of PNNs proteins with increased CSPGs and decreased HAPLN1 transcripts, suggesting long-term PNN destabilization in majority of spinal segments, (2) in lumbar segments PNN composition is not MN-class (extensor vs flexor) specific, both showing early decrease and late upregulation of Wisteria floribunda agglutinin (WFA) labeling in vicinity of synaptic boutons on MNs, (3) long-term locomotor training tends to reduce WFA(+) PNNs, but not their protein components (immunofluorescence measurements) around MNs. Our results suggest that training-induced regulation may target glycan structures of CSPGs.