Improved lentiviral transduction of ALS motoneurons in vivo via dual targeting

Treatment of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease, is hampered by its complex etiology and lack of efficient means for targeted transfer of therapeutics into motoneurons. The objective of this research was engineering of a versatile motoneuron targeting adapter - a full-length atoxic tetanus toxin fused to core-streptavidin (CS-TeTIM) - for retro-axonal transduction of viral vectors; validation of the targeting efficiency of CS-TeTIM in vivo, by expression of green fluorescence protein (GFP) reporter in motoneurons of presymptomatic and symptomatic ALS-like SOD1^G93A mice, and comparison with age-matched controls; and appraisal of lentiviral transduction with CS-TeTIM relative to (1) a H _C binding fragment of tetanus toxin CS-TeTx(H_C), (2) rabies glycoprotein (RG), and (3) a CS-TeTIM-RG dual targeting approach. CS-TeTIM and CS-TeTx(H_C) were engineered using recombinant technology and site-directed mutagenesis. Biotinylated vectors, pseudotyped with vesicular stomatitis virus glycoprotein (VSV-G) or RG, were linked to these adaptors and injected intraperitoneally (ip) into presymptomatic (12 weeks old), symptomatic SOD1^G93A (22 weeks old) or wild type control mice, followed by monitoring of GFP expression in the spinal cord and supraspinal motor structures with quantitative PCR and immuno-histochemistry. Transcripts were detected in the spinal cord and supraspinal motor structures of all mice 2 weeks after receiving a single ip injection, although in symptomatic SOD1^G93A animals reporter RNA levels were lower compared to presymptomatic and wild-type controls irrespective of the targeting approach. GFP transduction with CS-TeTIM proved more efficient than CS-TeTx(H_C) across all groups while CS-TeTIM-RG dual-targeted vectors yielded the highest transcript numbers. Importantly, in both wild-type and presymptomatic SOD1^G93A mice strong colabeling of choline-acetyltransferase (ChAT) and GFP was visualized in neurons of the brain stem and spinal cord. CS-TeTIM, a versatile adaptor protein for targeted lentiviral transduction of motoneurons, has been engineered and its competence assessed relative to CS-TeTx(H_C) and RG. Evidence has been provided that highlights the potential usefulness of this novel recombinant tool for basic research with implications for improved transfer of therapeutic candidates into motoneurons for the amelioration of ALS and related diseases.