Cortico-striatal synaptic dysfunction is an early hallmark of Huntington's disease (HD), yet the mechanisms underlying synapse loss and its reversibility remain poorly understood. Brain cholesterol is essential for neuronal and synaptic function, and dysregulated cholesterol metabolism has emerged as a key feature of HD, with reduced cholesterol biosynthesis reported in rodent models and cholesterol replenishment shown to be beneficial. Consistent with these findings, GWAS identified HD modifier loci outside canonical DNA repair pathways, including MED15, which among its functions supports SREBF2-mediated transcription of cholesterol biosynthesis genes, and a chr22 locus encompassing SREBF2, the master regulator of cholesterol biosynthesis. These findings suggest that pathways regulating cholesterol homeostasis may contribute to modifying the course of HD. Here, we show that increasing cholesterol availability prevents synapse loss and restores cortico-striatal connectivity in HD models. Cholesterol supplementation restores excitatory synapse density in vivo and in vitro. In primary HD neurons, cholesterol stabilizes dendritic spines and promotes the enrichment of GluA1-containing AMPA receptors in mature mushroom spines during chemically induced long-term potentiation, consistent with improved synaptic plasticity. Using microfluidic devices to spatially resolve the cortico-striatal circuit, we identified a compartment-specific mechanism whereby cholesterol delivery to cortical neurons is necessary and sufficient to restore cortico-striatal connectivity, whereas cholesterol administration to the striatal compartment selectively restores intra-striatal inhibitory synapses. Mechanistically, NMDA receptor and BDNF/TrkB signalling mediate the cholesterol-dependent restoration of synaptic connectivity, establishing cholesterol as a critical regulator of cortico-striatal synaptic integrity in HD and supporting targeting cholesterol homeostasis as a therapeutic strategy to restore synaptic function.
Allegra Lenci, Michela Villa, Andrea Scolz et al.· Pharmacological Research· 0 citations
Expansion of CAG repeats in HTT exon 1 is the acknowledged driver of Huntington’s disease. Alternative processing of HTT pre-mRNA generates the truncated HTT1a transcript, translated into a toxic peptide. While its dependence on CAG length is well documented, the role of adjacent sequences - particularly the Proline-Rich Domain (PRD) - remains unexplored. Using our HuntEx1-engineered mouse embryonic stem cell platform, we show that human PRD promotes HTT1a production, whereas its replacement with mouse PRD in an otherwise human exon 1 markedly reduces HTT1a levels. Mechanistically, we find that the PRD shapes mRNA structure, and motif analysis identifies Serine-Arginine Splicing Factor 7 (SRSF7) binding sites in mouse but not in human PRD. Their targeted mutation confirms SRSF7’s regulatory role in suppressing HTT1a production. Our findings establish the PRD as a key cis-regulator of HTT1a biogenesis, demonstrating that HTT toxicity also depends on sequence context, and highlighting splicing-based, PRD-focused therapeutic avenues. CAG repeat expansion drives Huntington’s disease, but additional sequence features influencing HTT toxicity are less defined. Here, the authors show that the proline‑rich domain regulates HTT1a transcript production via mRNA structure and SRSF7 binding, revealing sequence context-dependent control of toxic HTT generation.
Camilla Maffezzini, R. Iennaco, Andrea Scolz et al.· Nature Communications· 0 citations
The Huntingtin gene (HTT) contains a conserved, yet expandable CAG repeat within exon 1. While the pathogenic expansion in Huntington’s Disease (HD) is well studied, the role of surrounding domains remains unclear. Using genome-edited mini-organoids and neurons, we dissected HTT exon 1 and found species-specific toxicity: the human variant caused more severe deficits than the mouse. Swapping the proline-rich domain (PRD) - the most divergent region - revealed its key role: the mouse PRD mitigated, while the human PRD worsened neuronal phenotypes. Omics profiling showed that pathogenic human exon 1 induced broad protein dysregulation, largely reversed by mouse PRD replacement. Bioinformatics implicated the actin cytoskeleton and transcriptional coactivator MKL2/MRTFB. We validated MKL2/MRTFB dysregulation in HD models and showed that restoring its expression rescued neuronal abnormalities. These findings highlight the PRD’s contribution to HD toxicity and point to MKL2/MRTFB and the cytoskeleton as candidate mediators.
R. Iennaco, Camilla Maffezzini, Simone Maestri et al.· bioRxiv· 1 citation
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