Objective: Recent studies show that mutations and overexpression of the TARDBP gene causes pathological aggregates and inclusion bodies in neurons. This is one of the underlying causes of the progressive neuronal degeneration and apoptosis seen in motor neuron diseases. In this study, we investigated the morphological changes in the rat motor cortex after transduction of neurons by viral vectors expressing either full-length hTDP-43 or nuclear localization sequence-deleted hTDP-43 (hTDP-43-ΔNLS).
Methods: Experimental (hTDP-43 and hTDP-43-ΔNLS) and control (SF injected) groups of 4 week-old Sprague-Dawley rats (n=6, for each group) received intravenous injection of viral vectors (AAV2-9 serotype, 1.77x1012 vg/kg) designed under the control of a specific promoter (ubiquitin carboxyl-terminal hydrolase-L1). After intracardiac perfusion at postnatal day 80, serial frozen sections from the motor cortex were selected by using systematic random sampling approach. Neuronal profiles were stained by NeuN immunohistochemistry; whereas corticospinal motor neurons (CSMN) and callosal projection neurons (CPN) were labeled by Ctip-2 and Satb2 antibodies, respectively. Mean number of neurons in different cortical layers were counted, compared by using statistical methods.
Results: ANOVA results showed that mean number of total and CSMN were significantly (p<0.05 and p<0.001) lower in animals transduced with full length hTDP-43, while no significant difference was observed in CPN. On the other hand, transduction with hTDP-43-ΔNLS caused no significant alteration in the number of CSMN or CPN in comparison to controls.
Conclusion: Our data revealed that overexpression of fulllength hTDP-43 induced more profound motor neuron degeneration than those of NLS-deleted hTDP-43. Designing of viral vectors with cell type specific promoters allowed us to transfer the genes into a specific region and specific subgroups of neurons in the motor cortex. This transduction method might be instrumental for targeting other cell types for generating animal models of neurodegenerative diseases in future. This study is supported by TÜB‹TAK-Grant #116S408.