Activation of the D2 dopamine receptor hampers the protective effect of the A2A adenosine receptor on TDP‐43 mislocalization

Abstract

TAR DNA‐binding protein (TDP‐43) is an RNA‐binding protein that exists mostly in the nucleus and regulates transcription and RNA splicing. Mislocalization of TDP‐43 to the cytoplasm has been observed in several neurodegeneration diseases, such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), and is believed to initiate the pathogenesis of TDP‐43 proteinopathy. We have previously published that several adenosine analogues (T1‐11 and its analogues) prevented the reactive oxygen species (ROS)‐induced TDP‐43 mislocalization in a mouse motor neuron cell line (NSC34) via the A2A adenosine receptor (A2AR), and prevented the degenerated motor functions in a TDP‐43 transgenic ALS mouse model. In the striatum, previous studies suggest that A2AR and the D2 dopamine receptor (D2R) formed dimmer and negatively cross‐regulated each other's functions. In the present study, we first demonstrated that A2AR and D2R both exist in the motor neurons of the spinal cord of normal subjects and ALS patients by using immunofluorescence assay. Expression of both A2AR and D2R in NSC34 cells led to dimer formation as assessed using the proximity ligation assay (in situ PLA). No change in the binding affinity of T1‐11 was observed when A2AR formed dimmer with D2R. Nonetheless, activation of D2R reversed the A2AR‐mediated prevention of ROS‐induced AMPK activation and TDP‐43 mislocalization in NSC34 cells. Given that D2R agonists have been commonly used in clinical settings, the impact of D2R activation on the normalization of TDP‐43 mislocalization by A2AR in ALS warrants further investigation.