Distinct pathways leading to TDP-43-induced cellular dysfunctions

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• TAR DNA-binding protein of 43 kDa (TDP-43) is a key protein in inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP).
• The precise mechanisms of TDP-43-induced neuronal dysfunction and death are not fully understood.

Purpose of the Study:

• To investigate the distinct cytotoxic effects of full-length TDP-43 (FL-TDP) and its C-terminal fragment (CTF) in neuronal cells.
• To elucidate the molecular mechanisms underlying TDP-43-mediated neurodegeneration in ALS and FTLD-TDP.

Main Methods:

• Overexpression of FL-TDP and TDP-43 CTF in SH-SY5Y cells using a lentiviral system.
• Confocal microscopy to analyze protein localization and aggregate formation.
• Assessment of cell death, caspase activation, and cell cycle progression.
• Analysis of RNA polymerase II and transcription factor co-localization with TDP-43 aggregates.
• Examination of TDP-43 pathology in human FTLD-TDP brain samples.

Main Results:

• FL-TDP overexpression in SH-SY5Y cells led to significant cell death, caspase activation, and G2/M phase growth arrest, indicating apoptosis induction.
• TDP-43 CTF expression resulted in cytoplasmic aggregates but without significant cell death compared to FL-TDP.
• RNA polymerase II and transcription factors (Sp1, CREB) were found co-localized with TDP-43 CTF aggregates, suggesting transcriptional dysregulation.
• Accumulation of RNA polymerase II in TDP-43 inclusions was observed in FTLD-TDP patient brains.
• Apoptosis was not detected in neurons with phosphorylated and aggregated TDP-43 pathology in FTLD-TDP brains.

Conclusions:

• Different TDP-43 species (FL-TDP vs. CTF) exert distinct cytotoxic effects through separate pathways.
• FL-TDP overexpression can directly induce neuronal apoptosis.
• TDP-43 CTF aggregation may lead to neurodegeneration via transcriptional dysregulation through sequestration of essential factors.
• These distinct mechanisms likely contribute to the diverse pathological cascades in ALS and FTLD-TDP.