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BackgroundThere is currently no effective treatment for promoting regeneration of injured nerves in patients who have sustained injury to the central nervous system such as spinal cord injury. Chondroitinase ABC is an enzyme, which promotes neurite outgrowth and regeneration. It has shown considerable promise as a therapy for these conditions. The aim of the study is to determine if targeting chondroitinase ABC expression to the neuronal axon can further enhance its ability to promote axon outgrowth. Long-distance axon regeneration has not yet been achieved, and would be a significant step in attaining functional recovery following spinal cord injury.Methodology/principal findingsTo investigate this, neuronal cultures were transfected with constructs encoding axon-targeted chondroitinase, non-targeted chondroitinase or GFP, and the effects on neuron outgrowth and sprouting determined on substrates either permissive or inhibitory to neuron regeneration. The mechanisms underlying the observed effects were also explored. Targeting chondroitinase to the neuronal axon markedly enhances its ability to promote neurite outgrowth. The increase in neurite length is associated with an upregulation of β-integrin staining at the axonal cell surface. Staining for phosphofocal adhesion kinase, is also increased, indicating that the β-integrins are in an activated state. Expression of chondroitinase within the neurons also resulted in a decrease in expression of PTEN and RhoA, molecules which present a block to neurite outgrowth, thus identifying two of the pathways by which ChABC promotes neurite outgrowth.Conclusions / significanceThe novel finding that targeting ChABC to the axon significantly enhances its ability to promote neurite extension, suggests that this may be an effective way of promoting long-distance axon regeneration following spinal cord injury. It could also potentially improve its efficacy in the treatment of other pathologies, where it has been shown to promote recovery, such as myocardial infarction, stroke and Parkinson's disease.

BACKGROUND: There is very little reported in the literature about the relationship between modifications of bacterial proteins and their secretion by mammalian cells that synthesize them. We previously reported that the secretion of the bacterial enzyme Chondroitinase ABC by mammalian cells requires the strategic removal of at least three N-glycosylation sites. The aim of this study was to determine if it is possible to enhance the efficacy of the enzyme as a treatment for spinal cord injury by increasing the quantity of enzyme secreted or by altering its cellular location. METHODOLOGY/PRINCIPAL FINDINGS: To determine if the efficiency of enzyme secretion could be further increased, cells were transfected with constructs encoding the gene for chondroitinase ABC modified for expression by mammalian cells; these contained additional modifications of strategic N-glycosylation sites or alternative signal sequences to direct secretion of the enzyme from the cells. We show that while removal of certain specific N-glycosylation sites enhances enzyme secretion, N-glycosylation of at least two other sites, N-856 and N-773, is essential for both production and secretion of active enzyme. Furthermore, we find that the signal sequence directing secretion also influences the quantity of enzyme secreted, and that this varies widely amongst the cell types tested. Last, we find that replacing the 3'UTR on the cDNA encoding Chondroitinase ABC with that of β-actin is sufficient to target the enzyme to the neuronal growth cone when transfected into neurons. This also enhances neurite outgrowth on an inhibitory substrate. CONCLUSION/SIGNIFICANCE: Some intracellular trafficking pathways are adversely affected by cryptic signals present in the bacterial gene sequence, whilst unexpectedly others are required for efficient secretion of the enzyme. Furthermore, targeting chondroitinase to the neuronal growth cone promotes its ability to increase neurite outgrowth on an inhibitory substrate. These findings are timely in view of the renewed prospects for gene therapy, and of direct relevance to strategies aimed at expressing foreign proteins in mammalian cells, in particular bacterial proteins.