Agonist-dependent and -independent dopamine-1-like receptor signalling differentially regulates downstream effectors

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Dopaminergic system dysregulation is implicated in neurological disorders like schizophrenia and bipolar disorder.
• Constitutive receptor signaling's role in energy metabolism remains underexplored, despite potential therapeutic benefits of inverse agonists over neutral antagonists.

Purpose of the Study:

• To investigate the impact of constitutive dopamine-1 receptor (D1R) and dopamine-5 receptor (D5R) signaling on downstream cellular targets.
• To elucidate the mechanisms by which D5R constitutive activity influences energy metabolism and protein expression.

Main Methods:

• Utilized transiently and stably transfected HEK293T cells to study D1R and D5R signaling.
• Assessed Na+/H+ exchanger (NHE) activity and glucose degradation.
• Quantified mRNA levels of key metabolic proteins (e.g., Na, K-ATPase, NHE isoforms) following agonist treatment.
• Investigated the role of G protein-coupled receptor kinase 2 (GRK2) in D5R signaling.

Main Results:

• High constitutive activity of D5R correlated with increased NHE activity and accelerated glucose degradation.
• Increased transcription and translation of Na, K-ATPase-α3 and NHE-2 were observed due to constitutive D5R signaling.
• Chronic agonist treatment elevated mRNA levels of Na,K-ATPase-α2, NHE-2, and NHE-3.
• GRK2 regulated constitutive D5R activation of a cAMP response element-based reporter without altering cell-surface receptor levels.

Conclusions:

• Constitutive D5R activity significantly influences cellular energy metabolism, affecting ion transport and glucose processing.
• Agonist-induced D5R activity leads to distinct changes in gene expression compared to constitutive signaling.
• D5R exhibits differential regulation of protein activity and expression based on its signaling state (constitutive vs. agonist-induced).