Molecular Identity and Location Influence Purkinje Cell Vulnerability in Autosomal-Recessive Spastic Ataxia of Charlevoix-Saguenay Mice

Abstract

Patterned cell death is a common feature of many neurodegenerative diseases. In patients with autosomal-recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) and mouse models of ARSACS, it has been observed that Purkinje cells in anterior cerebellar vermis are vulnerable to degeneration while those in posterior vermis are resilient. Purkinje cells are known to express certain molecules in a highly stereotyped, patterned manner across the cerebellum. One patterned molecule is zebrin, which is expressed in distinctive stripes across the cerebellar cortex. The different zones delineated by the expression pattern of zebrin and other patterned molecules have been implicated in the patterning of Purkinje cell death, raising the question of whether they contribute to cell death in ARSACS. We found that zebrin patterning appears normal prior to disease onset in Sacs–/– mice, suggesting that zebrin-positive and -negative Purkinje cell zones develop normally. We next observed that zebrin-negative Purkinje cells in anterior lobule III were preferentially susceptible to cell death, while anterior zebrin-positive cells and posterior zebrin-negative and -positive cells remained resilient even at late disease stages. The patterning of Purkinje cell innervation to the target neurons in the cerebellar nuclei (CN) showed a similar pattern of loss: neurons in the anterior CN, where inputs are predominantly zebrin-negative, displayed a loss of Purkinje cell innervation. In contrast, neurons in the posterior CN, which is innervated by both zebrin-negative and -positive puncta, had normal innervation. These results suggest that the location and the molecular identity of Purkinje cells determine their susceptibility to cell death in ARSACS.

Loss of Flocculus Purkinje Cell Firing Precision Leads to Impaired Gaze Stabilization in a Mouse Model of Spinocerebellar Ataxia Type 6 (SCA6)

“…Molecular layer height is altered in other mouse models of ataxia, and in some cases is restricted to specific regions of the cerebellum (SCA1: [ 27 ]; SCA2: [ 28 ]; SCA17: [ 29 ]). Similarly, Purkinje cell loss is seen in multiple mouse models of ataxia, particularly at advanced disease stages, and can also be region specific [ 27 , 30 , 31 , 32 , 33 ]. We performed immunohistochemistry with anti-calbindin antibody to label Purkinje cells in the flocculus of litter-matched wild-type and SCA6 84Q mice at 7.5–8 months.…”

“…It is generally believed that cerebellar cell loss follows a trend; the zebrin-positive flocculonodular lobules of cerebellum are considered to be more resistant to neurodegeneration as compared to anterior cerebellum [ 50 ]. (Additionally, in a mouse model of ARSACS, both the zebrin identity and anterior-posterior location of Purkinje cells determined their susceptibility to disease insult, both at the level of Purkinje cell loss and loss of innervation to the cerebellar nuclei [ 33 ]. Moreover, higher levels of sphingosine kinases, which are also thought to be protective against neurodegeneration, have been reported in the flocculonodular lobules compared to the anterior vermis [ 30 ].…”

“…Fixed tissue slices were prepared as described previously [ 33 ]. Mice were deeply anesthetized with intraperitoneal injection of 2,2,2-tribromoethanol (Avertin) prior to intracardiac perfusion with an initial flush of ice-cold phosphate-buffered saline (PBS, 0.1M, pH 7.4) with 5.6 µg/mL heparin salt.…”

“…We used anti-calbindin antibody to label Purkinje cells for morphological analysis. We have previously shown that this approach is a robust method for quantifying Purkinje cell degeneration and loss in another ataxia model, proving more effective than a fluorescent Nissl-like marker for carrying out Purkinje cell counts [ 33 ]. Immunohistochemistry was performed on free floating slices.…”

Cerebellar neuronal dysfunction accompanies early motor symptoms in spinocerebellar ataxia type 3

“…Lobules I-V have Purkinje cells that are predominantly zebrin II negative, whereas lobules VI-X have more zebrin II positive Purkinje cells ( Arancillo et al, 2015 ; Cerminara et al, 2015 ). Several different patterns of Purkinje cell degeneration have been noted in many models of cerebellar ataxia ( Cerminara et al, 2015 ; Toscano Márquez et al, 2021 ). However, it is unclear how Purkinje cells are differentially affected by the different mutations leading to cerebellar ataxia.…”