Abstract
Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) share overlapping genetic causes and disease symptoms, and are linked neuropathologically by the RNA binding protein TDP-43 (TAR DNA binding protein-43 kDa). TDP-43 regulates RNA metabolism, trafficking, and localization of thousands of target genes. However, the cellular and molecular mechanisms by which dysfunction of TDP-43 contributes to disease pathogenesis and progression remain unclear. Severe changes in the structure of neuronal dendritic arbors disrupt proper circuit connectivity, which in turn could contribute to neurodegenerative disease. Although aberrant dendritic morphology has been reported in non-TDP-43 mouse models of ALS and in human ALS patients, this phenotype is largely unexplored with regards to TDP-43. Here we have employed a primary rodent neuronal culture model to study the cellular effects of TDP-43 dysfunction in hippocampal and cortical neurons. We show that manipulation of TDP-43 expression levels causes significant defects in dendritic branching and outgrowth, without an immediate effect on cell viability. The effect on dendritic morphology is dependent on the RNA-binding ability of TDP-43. Thus, this model system will be useful in identifying pathways downstream of TDP-43 that mediate dendritic arborization, which may provide potential new avenues for therapeutic intervention in ALS/FTD.
Highlights
Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are clinically linked, rapidly progressing neurodegenerative diseases that affect both distinct and overlapping regions of the brain
43 overexpression on neuronal morphology in hippocampal and cortical neurons, both of which are susceptible to neurodegeneration in ALS and FTD58–62
Neurons were co-transfected at 2 days in vitro (DIV) with a plasmid expressing GFP to visualize neuronal morphology, and either a plasmid expressing the human TAR DNA-binding protein of 43 kDa (TDP-43) gene under the control of a strong promoter at a concentration of 200 ng/well or 500 ng/well in a 24-well plate, or an empty vector control at 500 ng/well (Fig. 1a)
Summary
Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are clinically linked, rapidly progressing neurodegenerative diseases that affect both distinct and overlapping regions of the brain. Given that TDP-43 is involved in the splicing, transport, and stability of several mRNAs which encode proteins that play important roles in neuronal arbor elaboration and synaptic function[13,41,56,57], we asked whether TDP-43 dysfunction altered neuronal morphology. To explore this question, we took the approach of overexpressing or knocking down TDP-43 in cultured mammalian neurons isolated from rat hippocampus or cortex and asked if manipulating TDP-43 protein levels interfered with dendritic complexity. Our findings demonstrate that aberrant levels of TDP-43 disrupt neuronal morphology, an observation that has important implications for understanding disease pathology
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