Experimental upregulation of Lancl1 promotes axon regeneration after optic nerve injury in vivo.

Lanthionine synthetase C-like protein (Lancl) gene family members 1-3 play roles in responses to oxidative stress and cellular metabolic processes. Lancl1 in particular functions as a neuroprotective factor in the central nervous system (CNS), but it is unknown whether experimentally upregulating Lancl1 in neurons could also repair injured circuits by regenerating damaged axons. We recently identified Lancl1 as a gene upregulated in response to an axon-regenerating treatment, which prompted us to ask here if Lancl1 could directly repair injured axons. First, we characterized expression of Lancl1-3 family genes in single-cell RNA-seq (scRNA-seq)-profiled retinal ganglion cell (RGC) CNS projection neurons, then we investigated through gain-of-function experiments whether Lancl1 promotes axon regeneration after CNS injury in vivo, and finally we tested if Lancl1 transgene activates the mTOR pathway's pS6 marker, which is associated with Pten knockout-promoted axon regeneration. We show that within the retina, Lancl1 and Lancl2 are enriched in the RGCs, whereas Lancl3 is not considerably expressed in retinal cell types. Within the RGCs, there is moderate subtype-to-subtype variability in Lancl1 and Lancl2 expression, whereas Lancl3 is enriched in αRGCs but expressed at modest levels. We then found that after optic nerve injury, Lancl1 transgene targeted to RGCs through intravitreal AAV2 promotes neuroprotection and axon regeneration, with axons extending through the full-length of the optic nerve when co-treated with a fibronectin-based recombinant small protein. However, we did not find that Lancl1 transgene activates the mTOR pathway's pS6 marker in injured RGCs. Thus, Lancl1 is a novel axon regeneration-promoting factor with a therapeutic potential for treating CNS injury and disease, and future studies need to investigate downstream mechanisms of its neurotherapeutic efficacy.