Increased caspase activation and decreased TDP-43 solubility in progranulin knockout cortical cultures.
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 derived from Grn(-/-) mice. Also, neurons derived from Grn(-/-) mice showed an increased amount of pTDP-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 in Grn(-/-) neurons and mouse embryonic fibroblasts. Interestingly, full-length TDP-43 also accumulated in the detergent-insoluble fraction, and caspase-inhibition prevented MG132-induced generation of TDP-43 C-terminal fragments 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 GRN-deficiency 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.
Kleinberger
Gernot
G
Department of Molecular Genetics, VIB, Universiteitsplein 1, Antwerpen, Belgium.
Wils
Hans
H
Ponsaerts
Peter
P
Joris
Geert
G
Timmermans
Jean-Pierre
JP
Van Broeckhoven
Christine
C
Kumar-Singh
Samir
S
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism; D000077155:Granulins; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010766:Phosphorylation; D000077153:Progranulins; D046988:Proteasome Endopeptidase Complex; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004268:DNA-Binding Proteins; D000077155:Granulins; C120204:Grn protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D000077153:Progranulins; D011994:Recombinant Proteins; D051058:Oncogene Protein v-akt; D020169:Caspases; D046988:Proteasome Endopeptidase Complex