mCherry Lentivirus

Selective neuronal vulnerability in neurodegenerative diseases remains poorly defined. Using the ATXN1[82Q] model of spinocerebellar ataxia type 1 (SCA1), researchers explored the hypothesis that regional differences in Purkinje neuron degeneration might provide new insights into selective vulnerability. Researchers found that ATXN1[82Q] Purkinje neurons in the anterior cerebellum degenerated earlier than neurons in the tubercular region, and this early degeneration was associated with selective dysregulation of ion channel transcripts and altered Purkinje neuron firing. To understand the basis for the selective dysregulation of channel transcripts, researchers identified a modest increase in expression of the ATXN1 corepressor Capicua (Cic) in Purkinje neurons in the anterior cerebellum. Importantly, disruption of the association between ATXN1 and Cic rescued levels of these ion channel transcripts, whereas lentiviral overexpression of Cic in the nodular zone accelerated aberrant Purkinje neuron firing and neurodegeneration. These findings reinforce the central role of Cic in the cerebellar pathophysiology of SCA1 and suggest that only modest reductions in Cic could have profound therapeutic impacts in SCA1.

To investigate the causal relationship between regional differences in Cic expression and ion channel dysregulation, researchers used lentiviral vectors to increase Cic expression in the nodular zone. When Cic lentivirus was co-injected with mCherry lentivirus, mCherry expression was reliably overexpressed in the posterior half of lobule IX within the tubercle region (Figure 1A), so patch clamp recordings were performed on Purkinje neurons in this region. At 10 days post-injection, a significant fraction of Purkinje neurons from lobule IX were found to display irregular spikes or depolarization blocks in ATXN1[82Q] mice injected with Cic lentivirus (Figure 1B and C). Cic-dependent disruption of Purkinje neuron pacemaking was associated with a decrease in AHP (Figure 1D). These findings suggest that increased Cic levels render ATXN1[82Q] Purkinje neurons hyperexcitable. Furthermore, ATXN1[82Q] mice injected with Cic lentivirus showed accelerated Purkinje neuron degeneration in the tubercle region 70 days after injection (Figure 1E and F). These data demonstrate that only modestly greater expression of Cic and Cic-dependent hyperexcitability are likely to be responsible for accelerated degeneration of anterior cerebellar Purkinje neurons in ATXN1[82Q] mice.

Figure 1. Increased Cic expression results in Purkinje neuron hyperexcitability and accelerates Purkinje neuron degeneration. (Chopra R, et al., 2020)