Increased caspase activation and decreased TDP-43 solubility in progranulin knockout cortical cultures
Van Broeckhoven, Christine
Faculty of Medicine and Health Sciences
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Journal of neurochemistry. - Oxford
, p. 735-747
University of Antwerp
Null mutations in progranulin (GRN) are associated with frontotemporal lobar degeneration characterized by intraneuronal accumulation of TAR DNA-binding protein- 43 (TDP-43). However, the mechanism by which GRN-deficiency leads to neurodegeneration remains largely unknown. In primary cortical neurons derived from Grn knockout (Grn-/-) mice, we found that Grn-deficiency causes significantly reduced neuronal survival and increased caspase-mediated apoptosis, which was not observed in primary mouse embryonic fibroblasts (MEFs) derived from Grn-/- mice. Also, neurons derived from Grn-/- mice showed an increased amount of phosphorylated TDP-43 accumulations. Furthermore, proteasomal inhibition with MG132 caused increased caspase-mediated TDP-43 fragmentation and accumulation of detergent-insoluble 35-and 25-kDa C-terminal fragments (CTFs) in Grn-/- neurons and MEFs. Interestingly, fulllength TDP-43 also accumulated in the detergent-insoluble fraction, and caspaseinhibition prevented MG132-induced generation of TDP-43 CTFs but did not block the pathological conversion of full-length TDP-43 from soluble to insoluble species. These data suggest that GRN functions as a survival factor for cortical neurons and GRNdeficiency causes increased susceptibility to cellular stress. This leads to increased aggregation and accumulation of full-length TDP-43 along with its C-terminal derivatives by both caspase-dependent and independent mechanisms.