Ramelteon suppresses astrocytic senescence via MT1-cAMP axis to protect dopaminergic neurons

Introduction Astrocytic senescence is increasingly recognized as a critical contributor to the pathogenesis of Parkinson’s disease (PD). Ramelteon, a clinically approved MT1/MT2 melatonin receptor agonist, has demonstrated neuroprotective effects in various neurological disorders. However, whether Ramelteon can inhibit astrocytic senescence and the underlying mechanisms remain unknown. Methods An in vivo MPTP-induced mouse model of PD was used to evaluate the therapeutic potential of Ramelteon. An in vitro long-term culture-induced replicative senescence model (40 days in vitro , DIV) and MPP + -induced premature senescence model in primary astrocytes were employed. Immunoblotting, real-time quantitative PCR, immunofluorescence, SA-β-gal staining, and immunohistochemistry were performed to assess astrocytic senescence, dopaminergic neuronal survival, and motor function. Results Ramelteon treatment significantly attenuated MPTP-induced dopaminergic neuronal loss in the substantia nigra compacta (SNc) and improved motor deficits in mice. In vitro , Ramelteon markedly suppressed both replicative and MPP + -induced astrocytic senescence, as evidenced by decreased p16 Ink4a and SA-β-gal activity, restored LaminB1 expression, and reduced senescence-associated secretory phenotype (SASP) factors ( IL-6 , IL-1β , CXCL10 , and MMP9 ). Mechanistically, knockdown of Mtnr1a (encoding MT1), but not Mtnr1b (encoding MT2), largely abolished the anti-senescence effects of Ramelteon. MT1 activation inhibited adenylate cyclase (AC) activity and reduced intracellular cyclic adenosine monophosphate (cAMP) levels. Notably, senescent astrocytes exhibited elevated cAMP levels, and the cAMP inhibitor SQ22536 mimicked while the cAMP analog dbcAMP reversed the anti-senescence effects of Ramelteon. Furthermore, Ramelteon reduced mitochondrial ROS (mitoROS) production in senescent astrocytes through MT1-cAMP signaling. Discussion Our findings demonstrate that Ramelteon inhibits astrocytic senescence through MT1 receptor-mediated cAMP suppression and mitochondrial ROS reduction, thereby protecting DA neurons in a PD mouse model. This study identifies Ramelteon as a potential therapeutic agent for PD by suppressing astrocytic senescence through MT1 activation.