Heteroreceptor Complexes Formed by Dopamine D1, Histamine H3, and N-Methyl-D-Aspartate Glutamate Receptors as Targets to Prevent Neuronal Death in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder causing progressive memory loss and cognitive dysfunction. Anti-AD strategies targeting cell receptors consider them as isolated units. However, many cell surface receptors cooperate and physically contact each other forming complexes having different biochemical properties than individual receptors. We here report the discovery of dopamine D-1, histamine H-3, and N-methyl-D-aspartate (NMDA) glutamate receptor heteromers in heterologous systems and in rodent brain cortex. Heteromers were detected by co-immunoprecipitation and in situ proximity ligation assays (PLA) in the rat cortex where H-3 receptor agonists, via negative cross-talk, and H-3 receptor antagonists, via cross-antagonism, decreased D-1 receptor agonist signaling determined by ERK1/2 or Akt phosphorylation, and counteracted D-1 receptor-mediated excitotoxic cell death. Both D-1 and H-3 receptor antagonists also counteracted NMDA toxicity suggesting a complex interaction between NMDA receptors and D-1-H-3 receptor heteromer function. Likely due to heteromerization, H-3 receptors act as allosteric regulator for D-1 and NMDA receptors. By bioluminescence resonance energy transfer (BRET), we demonstrated that D-1 or H-3 receptors form heteromers with NR1A/NR2B NMDA receptor subunits. D-1-H-3-NMDA receptor complexes were confirmed by BRET combined with fluorescence complementation. The endogenous expression of complexes in mouse cortex was determined by PLA and similar expression was observed in wild-type and APP/PS1 mice. Consistent with allosteric receptor-receptor interactions within the complex, H-3 receptor antagonists reduced NMDA or D-1 receptor-mediated excitotoxic cell death in cortical organotypic cultures. Moreover, H-3 receptor antagonists reverted the toxicity induced by (1-42)-amyloid peptide. Thus, histamine H-3 receptors in D-1-H-3-NMDA heteroreceptor complexes arise as promising targets to prevent neurodegeneration.