Conditional Sox9 ablation reduces chondroitin sulfate proteoglycan levels and improves motor function following spinal cord injury

Abstract

Chondroitin sulfate proteoglycans (CSPGs) found in perineuronal nets and in the glial scar after spinal cord injury have been shown to inhibit axonal growth and plasticity. Since we have previously identified SOX9 as a transcription factor that upregulates the expression of a battery of genes associated with glial scar formation in primary astrocyte cultures, we predicted that conditional Sox9 ablation would result in reduced CSPG expression after spinal cord injury and that this would lead to increased neuroplasticity and improved locomotor recovery. Control and Sox9 conditional knock-out mice were subject to a 70 kdyne contusion spinal cord injury at thoracic level 9. One week after injury, Sox9 conditional knock-out mice expressed reduced levels of CSPG biosynthetic enzymes (Xt-1 and C4st), CSPG core proteins (brevican, neurocan, and aggrecan), collagens 2a1 and 4a1, and Gfap, a marker of astrocyte activation, in the injured spinal cord compared with controls. These changes in gene expression were accompanied by improved hind limb function and locomotor recovery as evaluated by the Basso Mouse Scale (BMS) and rodent activity boxes. Histological assessments confirmed reduced CSPG deposition and collagenous scarring at the lesion of Sox9 conditional knock-out mice, and demonstrated increased neurofilament-positive fibers in the lesion penumbra and increased serotonin immunoreactivity caudal to the site of injury. These results suggest that SOX9 inhibition is a potential strategy for the treatment of SCI.

The glial scar in spinal cord injury and repair

“…Moreover, using knock-out mice, S100A [79] and SoX9 [80] are also reported to be directly involved in glial scar formation by promoting reactive astrocytic migration and targeting CSPG deposition, respectively. in addition, a study of PKC disruption by the inhibitor Gö6976 has linked an increase in the regeneration of dorsal column axons with the inactivation of CSPGs after dorsal spinal cord hemisection [81] .…”

“…In the case of the interleukin-6 (IL-6) family, cytokines such as IL-6, leukemia inhibitory factor and ciliary neurotrophic factor, which undergo dimerization of the gp130 signal transduction subunit with other specific receptors, direct the activation of STAT3 and elicits changes in reactive astroglia and astrocytic scar formation [75][76][77] . .Moreover, using knock-out mice, S100A [79] and SoX9 [80] are also reported to be directly involved in glial scar formation by promoting reactive astrocytic migration and targeting CSPG deposition, respectively. in addition, a study of PKC disruption by the inhibitor Gö6976 has linked an increase in the regeneration of dorsal column axons with the inactivation of CSPGs after dorsal spinal cord hemisection [81] .…”

Scar-modulating treatments for central nervous system injury

“…CSPG deposition and collagenous scarring are reduced in the SCI lesion of SOX9 conditional knockout mice, suggesting that inhibition of SOX9 activity may become a novel therapeutic strategy for SCI [87] . phosphorylation, glial cell activation, and neurocan deposition after cortical injury in mice.…”

Central Nervous System Regenerative Failure: Role of Oligodendrocytes, Astrocytes, and Microglia

“…The early migratory response of astrocytes appears to be, at least in part, under the control of glycogen synthase kinase-3 (GSK-3) activity because acute treatment with a potent GSK-3 inhibitor accelerates migration, resulting in better sequestration of inflammatory cells and significantly enhanced functional improvement (Renault-Mihara et al 2011). Also, the transcription factor SOX9 appears to be a critical component of the pathway that leads to inhibitory matrix deposition in the lesion because its conditional KO leads to reduced expression of various CSPGs and improved locomotor function (Mckillop et al 2013). The architectural glial changes are under the control of STAT3.…”

“…Interestingly, denervated target regions, which are distant from the lesion, also undergo reactive glial changes, again associated with the production of sulfated proteo-glycans that are largely contained within the PNN (Massey et al 2006;Alilain et al 2011;Andrews et al 2012;Hansen et al 2013). The molecular triggers, which instigate up-regulation of these net-associated proteoglycans far from lesions, are largely unknown, but also appear to be regulated, in part, by the SOX9 transcription factor pathway (Mckillop et al 2013) as well as neuronal activity (Wang and Fawcett 2012). CSPG up-regulation within the PNN is extremely important because it serves to limit potential functional plasticity, which could occur via compensatory sprouting from surviving inputs (Hockfield et al 1990;Yamada et al 1997;Berardi et al 2004;Massey et al 2006;Pizzorusso et al 2006;Gogolla et al 2009;García-Alías et al 2011;Kwok et al 2011;Wang and Fawcett 2012;de Vivo et al 2013;Xue et al 2014).…”