High dopamine impairs early neuronal identity and morphology in human hippocampal progenitor cells

Adult hippocampal neurogenesis (AHN) supports learning, memory, and emotional regulation, and is regulated by intrinsic and extrinsic factors. Dopamine influences neurogenesis in animal models, but its direct effects on human hippocampal progenitors and receptor-specific mechanisms remain unclear. This study examined the dose-dependent effects of dopamine on proliferation, differentiation, and survival of human hippocampal progenitor cells (HPC0A07/03) in vitro, and assessed dopamine D4 receptor (DRD4) involvement. Cells were treated with dopamine (1-150 µM) under proliferation and differentiation conditions, with DRD4 modulated via selective agonist, antagonist, or combined treatment. Proliferation (Ki67), stemness (SOX2, Nestin), neuronal differentiation (DCX, MAP2), apoptosis (CC3), total cell counts, and morphology (cytoplasmic area) were assessed using immunocytochemistry, alongside targeted gene expression analysis of cellular stress- and neurogenesis-related pathways. Treatment with supraphysiological dopamine concentration (150 µM) significantly reduced cell counts during differentiation and decreased SOX2 expression during proliferation, suggesting impaired survival and reduced stemness. Complementary transcriptional changes supported a stress-associated cellular response at high dopamine concentrations. Elevated dopamine (150 µM) also increased cytoplasmic area in immature DCX+ neurons during the differentiation phase, suggesting altered morphological maturation. Moderate dopamine concentration (30 µM) showed a trend toward increased proliferation and higher cell counts. No significant changes occurred for other markers or following DRD4 modulation. These findings indicate that dopamine's effects on human hippocampal progenitors are dose-dependent: supraphysiological levels may compromise survival and progenitor identity, potentially via stress-related mechanisms, whereas moderate levels may support neurogenic processes. Understanding this dose-dependent balance has implications for neurological and psychiatric disorders involving dopaminergic dysregulation.