calpain and Frontotemporal-Lobar-Degeneration

TAR DNA-binding protein-43 (TDP-43) pathology, which includes the presence of abnormal TDP-43-containing inclusions with a loss of nuclear TDP-43 in affected neurons, is a pathological hallmark of amyotrophic lateral sclerosis (ALS) and/or frontotemporal lobar degeneration (FTLD). TDP-43 in the pathological brains and spinal cords of ALS/FTLD patients is abnormally fragmented and phosphorylated. It is believed that the generation of aggregation-prone TDP-43 fragments initiates TDP-43 pathology, and we previously reported that calpain has an important role in the generation of such aggregation-prone TDP-43 fragments. However, the role of phosphorylation in TDP-43 pathology has not been largely elucidated, despite previous observations that several kinases and their kinases are involved in TDP-43 phosphorylation. Here, we investigated the role of TDP-43 phosphorylation in the calpain-dependent cleavage of TDP-43 and found that phosphorylated, full-length TDP-43 and calpain-dependent TDP-43 fragments were more resistant to cleavage by calpain than endogenous full-length TDP-43 was. These results suggest that both phosphorylated and calpain-cleaved TDP-43 fragments persist intracellularly for a length of time that is sufficient for self-aggregation, thereby serving as seeds for inclusions.

Topics: Amyotrophic Lateral Sclerosis; Calpain; DNA-Binding Proteins; Frontotemporal Lobar Degeneration; HeLa Cells; Humans; Phosphorylation; Protein Aggregates

Protein aggregates are a common feature of neurodegenerative syndromes. Specific protein fragments were found to be aggregated in disorders including Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease. Here, we show that the natural C-terminal fragments of Tau, TDP43, and α-synuclein are short-lived substrates of the Arg/N-end rule pathway, a processive proteolytic system that targets proteins bearing "destabilizing" N-terminal residues. Furthermore, a natural TDP43 fragment is shown to be metabolically stabilized in Ate1(-/-) fibroblasts that lack the arginylation branch of the Arg/N-end rule pathway, leading to accumulation and aggregation of this fragment. We also found that a fraction of Aβ42, the Alzheimer's disease-associated fragment of APP, is N-terminally arginylated in the brains of 5xFAD mice and is degraded by the Arg/N-end rule pathway. The discovery that neurodegeneration-associated natural fragments of TDP43, Tau, α-synuclein, and APP can be selectively destroyed by the Arg/N-end rule pathway suggests that this pathway counteracts neurodegeneration.

Topics: alpha-Synuclein; Amino Acid Sequence; Amyloid beta-Protein Precursor; Animals; Arginine; Brain; Calpain; Cell Extracts; DNA-Binding Proteins; Frontotemporal Lobar Degeneration; Half-Life; HEK293 Cells; Humans; Matrix Metalloproteinase 3; Mice; Mice, Transgenic; Molecular Sequence Data; Neurodegenerative Diseases; NIH 3T3 Cells; Peptide Fragments; Protein Stability; Proteolysis; Reticulocytes; Saccharomyces cerevisiae; tau Proteins