Local Angiotensin Converting Enzyme 2 (ACE2) Enzymatic Activity Modulates Cholinergic Interneuron Function in the Dorsolateral Striatum

The renin angiotensin system (RAS) is an ancestrally ancient peptidergic signaling pathway best known for its role regulating blood pressure in the periphery. However, its presence and importance in the central nervous system has more recently been identified and is less well understood. Previous work shows RAS is expressed in the nigrostriatal pathway of the basal ganglia and has been implicated in basal ganglia disorders including Parkinson’s disease (PD) and levodopa-induced dyskinesia (LID). Interestingly, the canonical and noncanonical arms of the RAS pathway produce opposite effects on PD disease vulnerability and progression. The shift from the neurodegenerative canonical RAS to the neuroprotective noncanonical RAS is regulated by the enzymatic activity of angiotensin converting enzyme 2 (ACE2). To explore how RAS modulates basal ganglia function under physiological conditions, we assessed the expression of both canonical and noncanonical RAS in the dorsolateral striatum (DLS), a key integration hub for the basal ganglia, and found that ACE2 is broadly expressed in the region. Interestingly, cholinergic interneurons (CINs), an interneuron population essential for striatal function, showed unique enrichment of angiotensin II type 1 receptor (AT1R) and mas receptor (MasR), the receptor counterparts to the substrate and product of ACE2 activity. Reducing ACE2 enzymatic activity in the DLS, either through conditional ablation or pharmacological inhibition, altered how CINs respond to DA input during burst events, including a significant reduction in the amplitude of CIN pausing following DA burst release events. This pause is known to be modulated in part by dopamine D2 receptor activity, and AT1R and D2R have been shown to form heteromers capable of bidirectional inhibition in the striatum. AT1R inhibition and D2R agonism through coinjection of MLN4760 and quinpirole, respectively, reduced CIN activity in an additive manner as compared to each treatment alone and a proximity ligation assay on DLS sections revealed that AT1R and D2R colocalize within 40nm of each other on CINs. Functionally, unilateral ACE2 ablation in the DLS produced an ipsilateral turn bias without altering overall locomotion, consistent with altered striatal asymmetry. Bilateral ablation impaired motor learning in a rotarod paradigm, linking RAS-dependent CIN modulation to adaptive motor control. Taken together, these findings suggest that ACE2 regulates CIN sensitivity to dopaminergic input by maintaining the balance between AT1R- and MasR-mediated signaling. AT1R inhibits D2R-dependent CIN pauses, while ACE2 activity promotes MasR activation, which relieves this inhibition. Disruption of this balance such as in PD or COVID may therefore contribute to basal ganglia dysfunction through impaired dopaminergic–cholinergic integration. This work identifies a novel mechanism by which the brain RAS modulates striatal microcircuit function, bridging molecular signaling and motor learning.