Mitochondrial Dysfunction and Decrease in Body Weight of a Transgenic Knock-in Mouse Model for TDP-43

Carola Stribl,Jan Rozman,Wolfgang Hans,Aladin Samara,Lisa Glasl,Marion Horsch,Martin Klingenspor,Birgit Rathkolb,Thomas Klopstock,Sabine M Hölter,Eckhard Wolf,Manuela Neumann,Lore Becker,Axel Walch ,Valérie Gailus‐Durner ,Martin Hrabě De Angelis ,Wolfgang Wurst,Regina Peis,Andreas S Reichert,Michaela Aichler,Helmut Fuchs,Frauke Neff,Sebastian Koob,Thomas Floss,Dietrich Trümbach,Elisabeth Kremmer,Johannes Beckers

doi:10.1074/jbc.m113.515940

Abstract

The majority of amyotrophic lateral sclerosis (ALS) cases as well as many patients suffering from frontotemporal lobar dementia (FTLD) with ubiquitinated inclusion bodies show TDP-43 pathology, the protein encoded by the TAR DNA-binding protein (Tardbp) gene. We used recombinase-mediated cassette exchange to introduce an ALS patient cDNA into the mouse Tdp-43 locus. Expression levels of human A315T TDP-43 protein were 300% elevated in heterozygotes, whereas the endogenous mouse Tdp-43 was decreased to 20% of wild type levels as a result of disturbed feedback regulation. Heterozygous TDP-43(A315TKi) mutants lost 10% of their body weight and developed insoluble TDP-43 protein starting as early as 3 months after birth, a pathology that was exacerbated with age. We analyzed the splicing patterns of known Tdp-43 target genes as well as genome-wide gene expression levels in different tissues that indicated mitochondrial dysfunction. In heterozygous mutant animals, we observed a relative decrease in expression of Parkin (Park2) and the fatty acid transporter CD36 along with an increase in fatty acids, HDL cholesterol, and glucose in the blood. As seen in transmission electron microscopy, neuronal cells in motor cortices of TDP-43(A315TKi) animals had abnormal neuronal mitochondrial cristae formation. Motor neurons were reduced to 90%, but only slight motoric impairment was detected. The observed phenotype was interpreted as a predisease model, which might be valuable for the identification of further environmental or genetic triggers of neurodegeneration.

Highlights

Mutations in TDP-43 are frequently found in ALS patients
We propose a model in which the negative feedback loop of TDP-43 is critical for development of TDP-43 pathology; once the TDP-43 protein is located in the cytoplasm, as a result of either TDP-43 protein modification, modified interaction partners, or yet unidentified cellular stressors, the feedback loop in the nucleus
As we show, elevated levels of TDP-43 (A315T) do not necessarily lead to the formation of insoluble protein

Summary

Conclusion

Elevation of A315T TDP-43 was insufficient to cause ALS in this mutant. Significance: This TDP-43 allele could be valuable in determining genetic or environmental factors that cause full-blown FTLD or ALS. Expression levels of human A315T TDP-43 protein were 300% elevated in heterozygotes, whereas the endogenous mouse Tdp-43 was decreased to 20% of wild type levels as a result of disturbed feedback regulation. Transgenic overexpressors down-regulated endogenous TDP-43 levels, whereas heterozygous TDP-43 knock-out mice showed an increased expression of the wild type allele. A number of transgenic mice expressing wild type or mutant human TDP-43 have been established, showing either early lethality or severe motor dysfunction shortly after birth [35,36,37]. No mouse model so far has shown all of the features of ALS It is not yet clear under which conditions TDP-43 pathology develops in vivo and what the role of the mutations for the progression of the disease is. In order to investigate the role of a TDP-43 mutation under physiological conditions, we generated a mouse line expressing a human TDP-43 cDNA, carrying an A315T mutation under the control of the endogenous Tardbp promoter

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION