T. HEIKKINEN, T. BRAGGE, S. KOPONEN, T. PARKKARI, G. TOMBAUGH, S. GELMAN, S. ZHONG, L. DEVI, A. GHAVAMI, K. CIRILLO, A. BARRE, F. GACKIERE, D. GUIMOND, S. ZAPETTINI, B. SAVA, P. CHAUSSON, E. STEIDL, B. BUISSON, K. KUHLBRODT, A. KAKOULIDOU, S. JOBUSCH, K. TILLACK, A. GAERTNER, E. VAN DER KAM, R. Z. CHEN, D. HOWLAND, I. MUNOZ-SANJUAN, R. CACHOPE, J. ROSINSKI, V. BEAUMONT
Using a ZFN-mediated gene editing approach, a knock-in Long-Evans rat model of Huntington’s disease (Htt-Q130-LEH) was developed. The model carries a pure ∼130 CAG repeat followed by CAACAGCAGCAGCAACAG in Exon 1 of the endogenous rat Htt gene. The mHTT protein is expressed at ∼65% of the WT HTT protein throughout the CNS.
Heterozygote (HET) and wild type (WT) littermates were subjected to a battery of motor tests every 3 months (m) starting at 3 m of age, including fine motor kinematic analysis, open field, tapered beam balance, grip strength, and weekly bodyweight monitoring. In addition, in vivo tetrode recordings of cortico-striatal and cortico-subthalamic nucleus (STN) transmission were assessed at 12 m for evidence of altered cortico-basal ganglia function. Ex vivo analysis included MesoScaleDiscovery (MSD) quantitation of mHTT, immunohistochemical (IHC) assessment of mHTT aggregation, RNA sequencing, and analysis of striatal medium spiny neuron (MSN) membrane properties and synaptic activity between 3 – 12 m of age.
Until 6 months of age, HET Htt-Q130-LEH rats appear to be largely equivalent to their WT counterparts on all investigated parameters. However, with advancing age, HET rats start to display motor deficits, most notably as altered gait, decreased rearing and velocity in the open field. Bodyweight in male HET and WT rats is similar, whereas female HET rats are slightly heavier from 50 weeks onwards. At 12 m, in vivo electrophysiology showed that both cortico-striatal and cortico-STN transmission are significantly impaired in HET rats and striatal and cortical aggregates are detectable by MW8/4C9 MSD and S830 IHC analysis. Moreover, RNA sequencing revealed alterations in genes predominantly involved in GPCR / cAMP-mediated and calcium signaling, as well as neuro-inflammation. In summary, the Htt-Q130-LEH rat exhibits a relatively delayed onset of phenotype that will continue to be monitored at more advanced ages. This model may prove useful for further investigation of mHTT-induced neuropathophysiology.