Melatonin Modulates Astrocyte Inflammatory Response and Nrf2/SIRT1 Signaling Pathways in Adult Rat Cortical Cultures

<b>Background/Objectives:</b> The cerebral cortex is critical for neurological functions that are strongly affected by the aging process. Astrocytes play a central role in maintaining neurotransmitter balance and regulating antioxidant and anti-inflammatory responses, but these physiological functions may also decline with age. This study aimed to investigate the effects of melatonin, a molecule with known antioxidant, anti-inflammatory and neuroprotective properties, on astrocytes of mature cortical tissue obtained from adult Wistar rats. <b>Methods:</b> Primary cortical astrocyte cultures were obtained from neonatal and 90-day-old Wistar rats and treated with melatonin (300 µM for 24 h). We assessed cell viability and metabolism (MTT and extracellular lactate levels), glutamine synthetase (GS) activity, glutathione (GSH) content, release of cytokines, and the expression of genes and proteins associated with oxidative stress and inflammation by RT-qPCR and Western blotting. <b>Results:</b> Melatonin did not affect cell viability or lactate production. Moreover, there were no changes in GS activity, a key enzyme in glutamate metabolism, or in GSH levels, an antioxidant defense molecule synthesized by astrocytes. However, melatonin significantly reduced the expression of the nuclear factor <i>NFκB</i>, cyclooxygenase 2 (<i>COX-2</i>), and inducible nitric oxide synthase (<i>iNOS</i>), while increasing interleukin 6 and 10 levels. Melatonin also upregulated the gene expression of the transcriptional factors <i>Nrf2</i> and sirtuin 1 (<i>SIRT1</i>) and downregulated AMP-activated protein kinase (<i>AMPK</i>) and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (<i>PGC-1α</i>), while PGC-1α protein levels remained unchanged. A complementary analysis of astrocytes obtained from neonatal rats showed that melatonin did not change metabolic or redox parameters under basal conditions. <b>Conclusions:</b> Melatonin exerted anti-inflammatory effects on adult astrocyte cultures, likely through modulation of protective signaling pathways, such as Nrf2/SIRT1. These findings highlight the potential role of melatonin in preserving astrocytic function and mitigating age-related neuroinflammatory processes.