Assessment of changes in synaptic density in the zQ175DN mouse model of Huntington's disease: a [18F]SynVesT-1 study

Abstract

Huntington's disease (HD) is a neurodegenerative disorder characterized by involuntary movements, cognitive decline and psychiatric problems. HD has been associated with synaptic dysfunction and loss of the synaptic vesicle protein 2A (SV2A). SV2A can readily be quantified via positron emission tomography (PET) using the selective and high affinity SV2A radiotracer [¹⁸F]SynVesT-1 that we previously characterized in C57BL/6J mice. Here, we performed dynamic [¹⁸F]SynVesT-1 PET to characterize SV2A levels at various disease stages in another HD mouse model, zQ175DN, at 3 and 6 months (M) (longitudinal) and 10 M and 16 M (cross-sectional). We also conducted ex vivo SV2A immunofluorescent staining and [³H]UCB-J and [³H]SynVesT-1 autoradiography at 16 M. Dynamic [¹⁸F]SynVesT-1 PET revealed comparable V_T(IDIF) values between male and female 3 M and 6 M old zQ175DN mice. A significant age effect was found in the motor cortex and hippocampus between 3 M and 6 M. From 3 M to 10 M, no significant difference was found between heterozygous and wild-type mice. At 16 M, however, significant V_T(IDIF) differences were observed between genotypes in the motor cortex (-9.1 ± 3.5 %, p = 0.038), hippocampus (-7.5 ± 3.3, p = 0.036) and thalamus (-8.9 ± 3.1 %, p = 0.016). Ex vivo analyses did not confirm the observed deficits at 16 M, likely due to the decreased sensitivity compared to PET. However, [³H]SynVesT-1 and [³H]UCB-J autoradiography displayed the same outcome, ruling out a radioligand-specific effect. [¹⁸F]SynVesT-1 PET identified mild SV2A deficits in the zQ175DN model of HD at 16 M, whereas no significant SV2A deficits were detected at younger ages.

Keywords: Huntington’s disease; Mouse model; Positron emission tomography; Synapse; Synaptic density; Synaptic vesicle protein 2A.

Graphical abstract

Fig. 1

Study design. All three cohorts included heterozygous (HET) and wild-type (WT) mice. Male (M) and female (F) zQ175DN were acquired for the longitudinal cohort (3 M, 6 M). Only males were acquired for the cross-sectional cohorts (10 M, 16 M). Abbreviations: ARG = Autoradiography with [³H]UCB-J and [³H]SynVesT-1. IF = Anti-SV2A immunofluorescent staining. PET = Positron emission tomography with [¹⁸F]SynVesT-1.

Fig. 2

Evaluation of V_T(IDIF) sex differences. Quantification of the V_T(IDIF) for wild-type (WT) mice at 3 M and 6 M of age (a and b, respectively) and heterozygous (HET) mice at 3 M and 6 M of age (c and d, respectively). n = 10–13 per group and age. Multiple unpaired t-tests. Abbreviations: striatum (STR), motor cortex (MC), hippocampus (HIP), thalamus (THAL), cerebellum (CB), Male (M), Female (F).

Fig. 3

Longitudinal SV2A quantification. (a) V_T(IDIF) parametric maps for wild-type (WT) and heterozygous (HET) mice aged 3 months (3 M) and 6 months (6 M). (b) V_T(IDIF) quantification and evaluation of WT/HET differences at 3 M and 6 M of age. Mixed effects model analysis. n = 22–24 per genotype and age. Abbreviations: striatum (STR), motor cortex (MC), hippocampus (HIP), thalamus (THAL), cerebellum (CB).

Fig. 4

Cross-sectional SV2A quantification. (a) V_T(IDIF) parametric maps for wild-type (WT) and heterozygous (HET) mice aged 10 months (10 M) and 16 months (16 M). (b, c) V_T(IDIF) quantification and evaluation of WT/HET differences at 10 M (b) and 16 M (c) of age. n = 18–22 per group. Multiple unpaired t-tests. *p < 0.05. Abbreviations: striatum (STR), motor cortex (MC), hippocampus (HIP), thalamus (THAL), cerebellum (CB).

Fig. 5

Ex vivo analyses. (a) [³H]SynVesT-1 exemplary image and SV2A quantification for wild-type (WT) and heterozygous (HET) zQ175DN mice (n = 15 WT, 14 HET). Standard series in nCi/mg reported on figure. (b) [³H]UCB-J exemplary image and SV2A quantification (n = 14 WT, 14 HET except THAL HET n = 13) for WT and HET zQ175DN mice. Standard series in nCi/mg reported on figure. Exemplary images from panel 5a and 5b were obtained from the same male WT mouse (adjacent brain slices). (c) Exemplary images of the striatum (STR) and cortex (CTX) obtained through immunofluorescent (IF) SV2A staining and quantification of SV2A as percentage (%) positive area through IF staining (n = 15 WT, 15 HET). CTX and STR WT n = 13 for SV2A IF. Both exemplary images in panel c originate from the same male WT mouse. Scale bar: 200 µm. Statistics: multiple unpaired t-tests for all graphs. Abbreviations: striatum (STR), cortex (CTX), hippocampus (HIP), thalamus (THAL).