Initial gene vector dosing for studying symptomatology of amyotrophic lateral sclerosis in non-human primates.

BACKGROUND: Most amyotrophic lateral sclerosis (ALS) research has focused on mice, but there are distinct differences in the functional neuroanatomy of the corticospinal pathway in primates vs. rodents. A non-human primate model may be more sensitive and more predictive for therapeutic efficacy. METHODS: Rhesus macaques received recombinant adeno-associated virus (AAV9) encoding either the ALS-related pathological protein TDP-43 or a green fluorescent protein (GFP) control by intravenous administration. Motor function and electromyography were assessed over a nine-month expression interval followed by post-mortem analyses. RESULTS: Recombinant TDP-43 or GFP was stably expressed long term. Although the TDP-43 subjects did not manifest severe paralysis and atrophy, there were trends of a partial disease state in the TDP-43 subjects relative to the control. CONCLUSIONS: These data indicate that a higher gene vector dose will likely be necessary for more robust effects, yet augur that a relevant primate model is feasible.

Selective forelimb impairment in rats expressing a pathological TDP-43 25 kDa C-terminal fragment to mimic amyotrophic lateral sclerosis.

Pathological inclusions containing transactive response DNA-binding protein 43 kDa (TDP-43) are common in several neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). TDP-43 normally localizes predominantly to the nucleus, but during disease progression, it mislocalizes to the cytoplasm. We expressed TDP-43 in rats by an adeno-associated virus (AAV9) gene transfer method that transduces neurons throughout the central nervous system (CNS). To mimic the aberrant cytoplasmic TDP-43 found in disease, we expressed a form of TDP-43 with mutations in the nuclear localization signal sequence (TDP-NLS). The TDP-NLS was detected in both the cytoplasm and the nucleus of transduced neurons. Unlike wild-type TDP-43, expression of TDP-NLS did not induce mortality. However, the TDP-NLS induced disease-relevant motor impairments over 24 weeks. We compared the TDP-NLS to a 25 kDa C-terminal proaggregatory fragment of TDP-43 (TDP-25). The clinical phenotype of forelimb impairment was pronounced with the TDP-25 form, supporting a role of this C-terminal fragment in pathogenesis. The results advance previous rodent models by inducing cytoplasmic expression of TDP-43 in the spinal cord, and the non-lethal phenotype enabled long-term study. Approaching a more relevant disease state in an animal model that more closely mimics underlying mechanisms in human disease could unlock our ability to develop therapeutics.

Expansive gene transfer in the rat CNS rapidly produces amyotrophic lateral sclerosis relevant sequelae when TDP-43 is overexpressed.

Improved spread of transduction in the central nervous system (CNS) was achieved from intravenous administration of adeno-associated virus serotype-9 (AAV9) to neonatal rats. Spinal lower motor neuron transduction efficiency was estimated to be 78% using the highest vector dose tested at a 12-week interval. The widespread expression could aid studying diseases that affect both the spinal cord and brain, such as amyotrophic lateral sclerosis (ALS). The protein most relevant to neuropathology in ALS is transactive response DNA-binding protein 43 (TDP-43). When expressed in rats, human wild-type TDP-43 rapidly produced symptoms germane to ALS including paralysis of the hindlimbs and muscle wasting, and mortality over 4 weeks that did not occur in controls. The hindlimb atrophy and weakness was evidenced by assessments of rotarod, rearing, overall locomotion, muscle mass, and histology. The muscle wasting suggested denervation, but there was only 14% loss of motor neurons in the TDP-43 rats. Tissues were negative for ubiquitinated, cytoplasmic TDP-43 pathology, suggesting that altering TDP-43's nuclear function was sufficient to cause the disease state. Other relevant pathology in the rats included microgliosis and degenerating neuronal perikarya positive for phospho-neurofilament. The expression pattern encompassed the distribution of neuropathology of ALS, and could provide a rapid, relevant screening assay for TDP-43 variants and other disease-related proteins.

Frontotemporal lobar degeneration-related proteins induce only subtle memory-related deficits when bilaterally overexpressed in the dorsal hippocampus.

Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disease that involves cognitive decline and dementia. To model the hippocampal neurodegeneration and memory-related behavioral impairment that occurs in FTLD and other tau and TDP-43 proteinopathy diseases, we used an adeno-associated virus serotype 9 (AAV9) vector to induce bilateral expression of either microtubule-associated protein tau or transactive response DNA binding protein 43 kDa (TDP-43) in adult rat dorsal hippocampus. Human wild-type forms of tau or TDP-43 were expressed. The vectors/doses were designed for moderate expression levels within neurons. Rats were evaluated for acquisition and retention in the Morris water task over 12 weeks after gene transfer. Neither vector altered acquisition performance compared to controls. In measurements of retention, there was impairment in the TDP-43 group. Histological examination revealed specific loss of dentate gyrus granule cells and concomitant gliosis proximal to the injection site in the TDP-43 group, with shrinkage of the dorsal hippocampus. Despite specific tau pathology, the tau gene transfer surprisingly did not cause obvious neuronal loss or behavioral impairment. The data demonstrate that TDP-43 produced mild behavioral impairment and hippocampal neurodegeneration in rats, whereas tau did not. The models could be of value for studying mechanisms of FTLD and other diseases with tau and TDP-43 pathology in the hippocampus including Alzheimer's disease, with relevance to early stage mild impairment.