Dnajc3 (HSP40) Modulates Axon Regeneration in the Mouse Optic Nerve

Background The present study is designed to identify the genes modulating optic nerve regeneration in the mouse. Using the BXD mouse strains as a genetic mapping panel, we examined differential responses to axon regeneration in order to map genomic loci modulating axonal regeneration.

Methods To study regeneration in the optic nerve, Pten was knocked down in the retinal ganglion cells using adeno-associated virus (AAV) delivery of an shRNA, followed by the induction of a mild inflammatory response by an intravitreal injection of Zymosan with CPT-cAMP. The axons of the retinal ganglion cells were damaged by optic nerve crush (ONC). Following a 12-day survival period, regenerating axons were labeled by Cholera Toxin B. Two days later, the regenerating axons within the optic nerve were examined to determine the number of regenerating axons and the distance traveled down the optic nerve. An integral genomic map was made using the regenerative response. Candidate genes were tested by knocking down expression using shRNA or by overexpressing the gene in AAV vectors.

Results The analysis revealed a considerable amount of differential axonal regeneration across all 33 BXD strains, demonstrated by the number of axons regenerating and the length of the regenerating axons. Some strains (BXD99, BXD90, and BXD29) demonstrated significant axonal regeneration; while other strains (BXD13, BXD18, and BXD34) had very little axon regrowth. Within the regenerative data, there was a 4-fold increase in distance regenerated and a 7.5-fold difference in the number of regenerating axons. These data were used to map a quantitative trait locus modulating axonal regeneration to Chromosome 14 (115 to 119 Mb). Within this locus were 16 annotated genes. Subsequent testing revealed that one candidate gene, Dnajc3, modulates axonal regeneration. Knocking down of Dnajc3 led to a decreased regeneration response in the high regenerative strains (BXD90), while overexpression of Dnajc3 resulted in an increased regeneration response in C57BL/6J and a low regenerative strain (BXD34).

Conclusion In this study, Dnajc3 (encodes Heat Shock Protein 40, HSP40, a molecular chaperone) was identified as a modulator of axon regeneration in mice. This is the first report defining the role of Dnajc3 (HSP40) in axon regeneration.