Amyloid β peptide directly impairs pineal gland melatonin synthesis and melatonin receptor signaling through the ERK pathway

Melatonin is the hormone produced by the pineal gland known to regulate physiologic rhythms and to display immunomodulatory and neuroprotective properties. It has been reported that Alzheimer disease patients show impaired melatonin production and altered expression of the 2 G protein-coupled melatonin receptors (MTRs), MT1 and MT2, but the underlying mechanisms are not known. Here we evaluated whether this dysfunction of the melatonergic system is directly caused by amyloid beta peptides (A beta(1-40) and A beta(1-42)). A beta treatment of rat pineal glands elicited an inflammatory response within the gland, evidenced by the up-regulation of 52 inflammatory genes, and decreased the production of melatonin up to 75% compared to vehicle-treated glands. Blocking NF-kappa B activity prevented this effect. Exposure of HEK293 cells stably expressing recombinant MT1 or MT2 receptors to A beta lead to a 40% reduction in [I-125] iodomelatonin binding to MT1. ERK1/2 activation triggered by MTRs, but not by the beta(2)-adrenergic receptor, was markedly impaired by A beta in HEK293 transfected cells, as well as in primary rat endothelial cells expressing endogenous MTRs. Our data reveal the melatonergic system as a new target of A beta, opening new perspectives to Alzheimer disease diagnosis and therapeutic intervention.