Targeted Depletion of Primary Cilia in Dopaminoceptive Neurons in a Preclinical Mouse Model of Huntington's Disease.

Rasem Mustafa,Joachim Kirsch,Kerry L Tucker,Grzegorz Kreiner,Rosanna Parlato,Amelia-Elise J Wood,Katarzyna Kamińska

doi:10.3389/fncel.2019.00565

Abstract

Multiple pathomechanisms triggered by mutant Huntingtin (mHTT) underlie progressive degeneration of dopaminoceptive striatal neurons in Huntington’s disease (HD). The primary cilium is a membrane compartment that functions as a hub for various pathways that are dysregulated in HD, for example, dopamine (DA) receptor transmission and the mechanistic target of rapamycin (mTOR) pathway. The roles of primary cilia (PC) for the maintenance of striatal neurons and in HD progression remain unknown. Here, we investigated PC defects in vulnerable striatal neurons in a progressive model of HD, the mHTT-expressing knock-in zQ175 mice. We found that PC length is affected in striatal but not in cortical neurons, in association with the accumulation of mHTT. To explore the role of PC, we generated conditional mutant mice lacking IFT88, a component of the anterograde intraflagellar transport-B complex lacking PC in dopaminoceptive neurons. This mutation preserved the expression of the dopamine 1 receptor (D1R), and the survival of striatal neurons, but resulted in a mild increase of DA metabolites in the striatum, suggesting an imbalance of ciliary DA receptor transmission. Conditional loss of PC in zQ175 mice did not trigger astrogliosis, however, mTOR signaling was more active and resulted in a more pronounced accumulation of nuclear inclusions containing mHTT. Further studies will be required of aged mice to determine the role of aberrant ciliary function in more advanced stages of HD.

Highlights

MATERIALS AND METHODSHuntington’s disease (HD) is an autosomal dominant progressive neurodegenerative disorder caused by the toxic expansion of CAG trinucleotide repeats at the N-terminus of the Huntingtin gene
The variability of disease onset and progression depends on the CAG number, and on genetic modifiers interacting with the Huntingtin mutation [Genetic Modifiers of Huntington’s Disease (GeMHD) Consortium (2015)]
We addressed the following three questions: (1) whether Primary cilia (PC) is altered in different neuronal types and HD stages; (2) what are the consequences of PC disruption in striatal neurons for their survival; and (3) to what extent these contribute to HD neuropathology in a neuronal population vulnerable in HD such as the striatum

Summary

MATERIALS AND METHODS

Huntington’s disease (HD) is an autosomal dominant progressive neurodegenerative disorder caused by the toxic expansion of CAG trinucleotide repeats at the N-terminus of the Huntingtin gene. A deeper understanding of the role of PC in mHTT-dependent neurotoxicity might help to identify new determinants modifying HD progression To this end, we monitored neuron- and stage-specific changes of PC structure in a full-length progressive mouse model of HD, called zQ175 (Menalled et al, 2012; Carty et al, 2015). To determine the number of striatal NeuN positive neurons showing PC stained by ACIII antibody eight non-consecutive free-floating cryosections per mouse were analyzed (one every fourth section, each 30 μm thick) in control and mutant mice. The number of GFAP, pS6 and p62 and EM48 positive cells per microscopic field was counted in at least four independent paraffin sections per mouse in the dorsolateral striatal region. Multiple comparisons were performed either by one-way ANOVA or by two-way ANOVA with post hoc analyses as indicated in the figure legends (GraphPad Prism Software Inc.)

RESULTS

DISCUSSION

ETHICS STATEMENT