Molecular Imbalances Between Striosome and Matrix Compartments Characterize the Pathogenesis and Pathophysiology of Huntington’s Disease Model Mouse

The pathogenesis and pathophysiology of Huntington's disease (HD) are still incompletely understood, despite the remarkable advances in identifying the molecular effects of the <i>Htt</i> mutation in this disease. Clinical positron emission tomography studies suggest that phosphodiesterase 10A (PDE10A) declines earlier than dopamine D1 and D2 receptors in HD, indicating that it might serve as a key molecular marker in understanding disease mechanisms. In movement disorders, mutations in the genes encoding PDE10A and G-protein α subunit (Gα_olf), both critical cAMP regulators in striatal spiny projection neurons, have been linked to chorea and dystonia. These observations highlight the potential importance of striatal cyclic AMP (cAMP) signaling in these disorders, but how such dysfunction could come is unknown. Here, we suggest that a key to understanding signaling dysfunction might be to evaluate these messenger systems in light of the circuit-level compartmental organization of the caudoputamen, in which there is particular vulnerability of the striosome compartment in HD. We developed machine learning algorithms to define with high precision and reproducibility the borders of striosomes in the brains of Q175 knock-in (Q175KI) HD mice from 3-12 months of age. We demonstrate that the expression of multiple molecules, including Gα_olf, PDE10A, dopamine D1 and D2 receptors, and adenosine A2A receptors, is significantly reduced in the striosomes of Q175KI mice as compared to wildtype controls, across 3, 6, and 12 months of age. By contrast, mu-opioid receptor (MOR1) expression is uniquely upregulated, suggesting a compartment-specific and age-dependent shift in molecular profiles in the Q175KI HD mouse model caudoputamen. These differential changes may serve as a useful platform to determine factors underlying the greater vulnerability of striatal projection neurons in the striosomes than in the matrix in HD.