Doublecortin-like kinase 3 (DCLK3), a novel striatum-enriched species, is a modulator of mutant huntingtin in vivo
Résumé
Huntington's disease (HD) is a neurodegenerative disorder caused by an abnormal
CAG repeat expansion coding for an expanded polyglutamine tract in the protein
"huntingtin" (Htt). Although this mutant Htt (mHtt) is expressed ubiquitously
throughout the brain, the striatum is found preferentially affected. One hypothesis
to explain this particular vulnerability is that striatal neurons express a particular
set of proteins that make them highly vulnerable to mHtt. In order to further
examine this hypothesis, we carried out a transcriptome analysis of different brain
territories and identified more than 100 molecular markers i.e. transcripts that are
highly enriched in the mouse striatum. We recently focused our interest on a
subset of striatal-enriched transcripts of poorly characterized transcripts.
We here report the study of one of these markers, the CAMKII family-related
kinase DCLK3. We found that DCLK3 is mainly expressed in the adult striatum in
rodent with low level of expression in the newborn and striatal primary cultures.
Reduced mRNA levels of DCLK3 were found in the striatum of transgenic mouse
models of HD. We thus studied the effect of DCLK3 overexpression and knockdown
in a mouse model of HD using lentiviral vectors coding for a N-terminal
fragment of mHtt. DCLK3 and its related siRNA were delivered using lentiviral
vectors. Striatal degeneration produced by mHtt was characterized using
immunohistochemistry of DARPP32, Cytochrome oxidase and ubiquitin followed
by quantitative histological evaluation. Results showed that lenti-siRNA targeting
DCLK3 increased mHtt toxicity when compared to the control. On the contrary,
overexpression of DCLK3 reduced the striatal lesions produced by mHtt in vivo.
DCLK3 also decreased the number and size of ubiquitin-containing nuclear
inclusions. Current experiments are examining the mechanisms that could underlie
the neuroprotective effect of DCLK3 in striatal neurons. The present study suggests that DCLK3 is a potential modifier of the disease and might be
considered in HD therapy to slow disease progression.