Molecular unbalances between striosome and matrix compartments characterize the pathogenesis of Huntington’s disease model mouse

The pathogenesis of Huntington’s disease is still incompletely understood, despite the remarkable advances in identifying the molecular effects of the Htt mutation in this disease. When we focus on movement disorders, clinical studies offer us some hints about this issue. Human studies employing positron emission tomography have identified a reduction in phosphodiesterase 10A (PDE10A) as the earliest event in the brain of patients with Huntington’s disease, which occurs about 25 years before symptom onset. A PDE10A mutation is also known to cause childhood-onset chorea. GNAL encodes the olfactory type G-protein α subunit (Gα _olf ), strongly expressed in the striatum, and its mutation causes familial dystonia. PDE10A and Gα _olf are both critical regulators of cyclic AMP and are abundant in striatal spiny projection neurons. These findings suggest that maintaining cyclic AMP levels in the striatum might be an essential target for the pathogenesis of movement disorders such as chorea and dystonia. Why and how these changes in the striatum cause movement disorder are still a mystery. Here we suggest that a key might be evaluating these messenger systems in light of the circuit-level compartmental organization of the striatum, in which there is particular vulnerability of the striosome compartment. We developed machine learning algorithms to define with high precision and reproducibility the borders of striosomes in the brains of q175 Huntington’s disease model mice from 3-12 months of age. We demonstrate that multiple molecules including Gα _olf , PDE10A, dopamine D1 and D2 receptors, adenosine 2A receptors, and mu-opioid receptors differentially change their expression patterns in striosomes across ages by comparison with their expression patterns in the matrix compartment. An early and pronounced differential vulnerability of striosomes has been demonstrated in studies of post-mortem Huntington’s brains. Our findings here, mapping the molecular distributions across age in a widely studied mouse model of Huntington’s disease, may help to pinpoint the pathogenic mechanisms of Huntington’s disease by demonstrating the differential molecular changes in the striosome compartment.