Post-translational modification of Sox11 regulates RGC survival and axon regeneration
The failure of adult CNS neurons to survive and regenerate their axons after injury or in neurodegenerative disease remains a major target for basic and clinical neuroscience. Recent data demonstrated in the adult mouse that exogenous expression of Sry-related high-mobility-box 11 (Sox11) promotes optic nerve regeneration after optic nerve injury, but exacerbates the death of a subset of retinal ganglion cells, alpha-RGCs. During development, Sox11 is required for RGC differentiation from retinal progenitor cells (RPCs), and we found that mutation of a single residue to prevent sumoylation at lysine 91 (K91) increased nuclear localization and RGC differentiation in vitro. Here we explored whether this Sox11 manipulation similarly has stronger effects on RGC survival and optic nerve regeneration. In vitro, we found that non-SUMOylatable Sox11K91A leads to RGC death and suppresses axon outgrowth in primary neurons. We furthermore found that Sox11K91A more strongly promotes axon regeneration but also increases RGC death after optic nerve injury in vivo in adult mouse. RNA sequence data showed that Sox11 and Sox11K91A increase the expression of key signaling pathway genes associated with axon growth and regeneration but downregulated Spp1 and Opn4 expression in RGC cultures, consistent with negatively regulating the survival of α-RGCs and ipRGCs. Thus Sox11 and its sumoylation site at K91 regulate gene expression, survival and axon growth in RGCs and may be explored further as potential regenerative therapies for optic neuropathy.
Significance Statement Sox11 expression promotes optic nerve regeneration but also increases RGC death after optic nerve injury. Here we demonstrate that mutation of a single SUMOylation site on Sox11 (Sox11K91A) leads to stronger effects in vivo. RNA sequencing analysis reveals that Sox11 and Sox11K91A differentially regulate downstream gene expression related to axon growth and guidance. Understanding these effects of post-translational modification of Sox11 in regulating regeneration in vivo suggests a potent therapeutic strategy for vision restoration in optic neuropathies.