Melatonin (MT) plays a critical role in regulating rice responses to heavy metal stress. However, the mechanism by which MT alleviates copper (Cu) toxicity in rice remains insufficiently understood. In this study, excessive Cu increased endogenous MT level in rice roots, accompanied by enhanced gene expression involved in MT biosynthesis, suggesting its role in Cu stress responses. Exogenous MT reduced Cu accumulation and restored root growth in rice under Cu stress, thereby mitigating Cu-induced phytotoxicity. Mechanistically, MT increased the root pectin content and its Cu retention, thereby reducing Cu influx into the cytoplasm. Additionally, exogenous MT upregulated the expression of Heavy Metal ATPase 4 (OsHMA4) involved in vacuolar sequestration, as well as Cu efflux transporter genes OsHMA6 and OsHMA9. Conversely, it downregulated the plasma membrane Cu uptake-associated genes Copper Transporter (OsCOPT1, OsCOPT2, and OsCOPT3), the vacuolar Cu exporter OsCOPT7, and the xylem loading transporter gene OsHMA5, thereby alleviating Cu toxicity in rice. Furthermore, MT elevated nitric oxide (NO) levels in root tips, and application of the exogenous NO scavenger, 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), attenuated the mitigative effect of MT on excess Cu-stressed rice. In summary, MT alleviates Cu toxicity by reducing Cu binding to root cell walls, thereby limiting Cu uptake and translocation from roots to shoots. This process may depend on NO accumulation and provides new insights into the molecular mechanisms underlying MT-induced Cu tolerance in rice.

The cAMP response element-binding protein (CREB) and Period1 (Per1) have been implicated in depression, but their interactive mechanisms remain unclear. This studyinvestigated the integrative role of CREB and Per1 in depression and explores a potential strategy for rapid antidepressant treatment. Using a chronic unpredictable stress (CUS) model, we conducted behavioral assessments including the sucrose preference test, forced swimming test, elevated plus maze, and open field test. Gene expression was manipulated via stereotaxic surgery and RNA interference (RNAi), while protein levels and viral injection sites were verified through Western blot analysis and immunofluorescence. Additionally, we generated Per1 CRE knockout rats using CRISPR/Cas9, with genotypes confirmed by Sanger sequencing. CUS significantly reduced phosphorylated CREB (pCREB) and PER1 levels in the CA1 region. Both Per1 knockdown in CA1 and CRE sequence knockout induced depression-like behaviors, whereas Per2 knockdown in CA1 produced mania-like behaviors. Notably, CRE knockout in the Per1 promoter increased pCREB binding to the Per2 promoter, upregulating PER2 expression in the CA1 and resulting in depression-like phenotypes that are partially lithium-responsive. Treatment with the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) elevated pCREB and PER1 levels in the CA1 and elicited rapid antidepressant effects. These effects were present in heterozygotes but absent in homozygotes with a mutated Per1 CRE sequence. These results revealed the pivotal role of the pCREB-CRE-Per1 pathway in CUS-induced depression and its mediation of rapid antidepressant-like effects via adenosine A1 receptor activation. Moreover, the CRE sequence in the Per1 promoter may be a critical molecular link to the pathophysiology of bipolar depression.

ABSTRACTMultidrug resistance (MDR) is a major challenge in cancer chemotherapy. A critical factor contributing to MDR is overexpression of ATP‐binding cassette (ABC) transporters, such as ABCB1. Novel alternative therapeutic strategies are needed to overcome resistance associated with ABC transporters. In the present study, we aimed to elucidate the mechanisms by which melatonin overcomes ABCB1‐mediated MDR in cancer cells, with a focus on mitochondrial function. We analyzed the effects of melatonin (1 mM) on head and neck squamous cell carcinoma cell lines (CAL 27 and SCC‐9) overexpressing ABCB1 and exhibiting increased resistance to cisplatin (CDDP) compared to their parental cells. To further validate the role of melatonin in reversing ABCB1‐mediated MDR, we also evaluated its effects on doxorubicin‐resistant MCF‐7 breast cancer cells. We further examined the potential of melatonin to overcome MDR in CAL 27 xenografted mice. Here, we report that melatonin treatment specifically triggered reactive oxygen species (ROS) production in mitochondria and weakened chemoresistance. ROS oxidized NADH into NAD+, and limiting the availability of ATP for efflux pump activity. Additionally, melatonin decreased the number of mitochondria localized near the nucleus instead of the cytoplasm and downregulated ABCB1 expression. Intratumoral administration of melatonin effectively overcame CDDP resistance in CAL 27/ABCB1 xenografts, significantly reducing tumor volume and promoting apoptosis. These findings demonstrate that melatonin enhances chemosensitivity in ABCB1‐overexpressing cells by modulating mitochondrial metabolism, redox balance, and ABCB1 expression, highlighting its potential as an adjuvant therapy to overcome MDR.

Systemic lupus erythematosus (SLE) is an autoimmune disorder featuring abnormal B cell differentiation and excessive autoantibody production, leading to multiorgan damage. Despite advances in understanding SLE pathogenesis, the molecular mechanisms driving aberrant B cell differentiation remain elusive. Melatonin, a neuroendocrine hormone with immunomodulatory properties, has been shown to regulate immune responses, but its role in B cell differentiation and SLE is poorly understood. This study investigates the role of melatonin and its receptors in B cell differentiation and SLE pathogenesis. We observed reduced serum melatonin levels and decreased expression of melatonin receptors in B cells from SLE patients and MRL/Lpr mice. Activation of melatonin receptors inhibited the protein kinase A (PKA) signaling pathway and reduced phosphorylation of cyclic-AMP response binding protein (CREB), leading to epigenetic downregulation of PRDM1 and IRF4, key transcription factors for plasmablast and plasma cell differentiation. Consequently, melatonin receptor activation suppressed abnormal B cell differentiation into antibody-secreting cells. Our findings highlight melatonin and its receptor signaling as potential therapeutic targets for SLE and other autoimmune diseases mediated by aberrant antibody-secreting cell activity. This study provides novel insights into the protective role of melatonin in SLE and offers a promising avenue for developing targeted therapies.

Melatonin (MEL) is a hormone whose secretion is regulated by daily and seasonal environmental light cycles. MEL production is strictly limited to the night and is inhibited by light. Besides exhibiting chronobiotic properties, MEL possesses vasoactive properties mediated by the plasma membrane melatonin receptors (MT1/MT2) and ion channels expressed in the vascular system. Therefore, it is important to understand the distribution and functions of these receptors in the vascular system. In this review, we analyzed 50 studies to map the expression of MT1/MT2 receptors in the vascular system and elucidate their mechanisms of action, modulation factors, and implications for vascular reactivity. The findings of this review indicate that MT1 and/or MT2 receptors are expressed heterogeneously across different vascular layers, including the cerebral vascular bed, caudal arteries of rats, mesenteric vascular bed, coronary arteries, aorta, and other vessels. In the cerebral vascular bed, the receptor expression is reduced during pathological conditions, advanced age, and the estrous cycle. Furthermore, MEL directly induces vasoconstriction by inhibiting cAMP and BKca channels via MEL membrane receptors. In rat caudal arteries, the receptor expression is regulated by conditions similar to those in the cerebral vascular bed. However, MEL demonstrated potentiating effects on pre-contracted vessels and vasorelaxant effects, probably via MT1 and MT2 receptors, respectively. The data obtained from the mesenteric vascular bed demonstrate that hypertension negatively modulates receptor expression and the vasorelaxant effect of MEL is mediated by the activation of both BKca channels and MEL receptors. In coronary arteries, MEL inhibits vasorelaxation. This effect is mediated by MT2 through the activation of BKca channels and stimulation of phosphodiesterase 5, which differs from the vasorelaxant effects observed in caudal arteries. The aorta is the only vessel in which the expression of these receptors has been investigated in humans, and is restricted to MT2. Furthermore, this is the only vessel in which the circadian profile of MT1 receptor expression has been analyzed in rats; however, no differences were observed between the evaluated phases. The expression of functionally active receptors was also detected in other vessels, such as the pulmonary, umbilical, and placental arteries. In general, we observed that MEL membrane receptors are widely expressed in the vascular system. The evidence obtained through this review suggests that the responses triggered by MEL in the vascular system vary depending on the vascular bed analyzed and hormone concentration. Furthermore, MT1 receptors likely mediate vasoconstrictor effects, whereas MT2 receptors mediate vasorelaxant effects. Additionally, there is a gap in the literature as very few studies have addressed the effects of circadian variations on the expression of these receptors, highlighting an important area for further research.

Soil contamination by microplastics (MPs) and heavy metals has become a global ecological and environmental issue and poses considerable threats to crop production and human health. In plants, melatonin (MT) functions as a powerful biostimulant, orchestrating vital physiological processes and enhancing stress tolerance. In this study, through controlled pot experiments, how exogenous MT (0.1 mmol L⁻¹) modulates maize responses to low-density polyethylene (LDPE) MPs, cadmium (Cd), and their combination was investigated. Simultaneous exposure to LDPE MPs and Cd exacerbated oxidative damage, inhibited chlorophyll biosynthesis, suppressed photosynthetic capacity, and reduced biomass in maize plants, alongside increasing shoot and root Cd²⁺ levels. Conversely, exogenous MT application reduced the malondialdehyde content by 12.5% under combined stress conditions, indicating a substantial reduction in oxidative damage. Additionally, MT inhibited the absorption and accumulation of Cd²⁺, increased the chlorophyll content, enhanced the photosynthetic efficiency, improved the plant height and stem diameter, thereby increasing maize plant biomass by 5.6%. MT also increased the activity of reactive oxygen species scavenging antioxidant enzymes and promoted the biosynthesis of non-enzymatic antioxidants such as proline and soluble sugars. Metabolomic analysis revealed that exogenous MT treatment significantly affected the levels of 210 metabolites. Notably, key metabolic pathways, including purine metabolism, phenylpropanoid biosynthesis, and tryptophan metabolism, were upregulated, indicating their pivotal role in the stress response mechanism of plants. These results reveal that exogenous MT effectively alleviates the synergistic phytotoxicity of PE MPs and Cd in maize plants, underscoring its promise as a practical strategy for enhancing crop resilience in contaminated environments.

The treatment of prostate cancer (PCa) remains challenging, and while melatonin (MEL) has demonstrated therapeutic potential, its precise mechanisms require further elucidation. Through integrated in vitro, in vivo, and bioinformatics analyses, this study demonstrated that MEL functioned as a novel ferroptosis inducer in PCa by disrupting androgen receptor (AR) liquid-liquid phase separation (LLPS). We found that MEL effectively inhibited PCa proliferation, migration, and invasion in vitro while suppressing tumor growth safely in mice models. Mechanistically, MEL impaired AR LLPS dynamics, reducing AR-driven transcription of minichromosome maintenance protein 5 (MCM5). MCM5 was a clinically relevant biomarker associated with aggressive PCa and poor survival. Crucially, downregulated MCM5 attenuated its physical interaction with NRF2, leading to uncontrolled activation of the NRF2/HMOX1 pathway, GPX4 suppression, and accumulation of ferroptosis hallmarks. These findings defined an AR/MCM5/NRF2 axis regulating ferroptosis susceptibility, establishing MEL as the first-reported ferroptosis inducer that expands the mechanistic foundation and therapeutic potential of MEL-based PCa treatment strategies.

Aging is associated with increased susceptibility to bacterial infections, particularly multidrug-resistant (MDR) strains, which often result in antibiotic treatment failure and high mortality rates in the elderly. However, effective preventive and therapeutic strategies remain limited. Herein, we showed that aged mice exhibited higher susceptibility to colistin-resistant Salmonella enterica serotype Typhimurium and methicillin-resistant Staphylococcus aureus compared to young mice. Notably, pre-supplementation with melatonin, a hormone markedly reduced in the aging gut, effectively restricted MDR bacterial infections in aged mice by enhancing microbial colonization resistance. Mechanistically, melatonin-induced alterations in the gut microbiota, particularly the enrichment of butyrate-producing bacteria including Faecalibaculum, Muribaculaceae, and Ruminococcus, played a pivotal role in enhancing resistance to pathogenic bacteria. Elevated gut butyrate levels following melatonin pre-supplementation not only preserved intestinal barrier integrity and mitigated inflammaging, but also directly inhibited pathogenic bacterial growth by disrupting intracellular pH homeostasis, leading to proton motive force dissipation and metabolic disturbances. These findings underscore melatonin and its metabolite, butyrate, as promising candidates for the prevention of MDR bacterial infections in the aging population.

The purpose of this 1-year study was to assess the effect of osteogenic loading combined with melatonin on musculoskeletal health and well-being in a population with osteopenia. Participants were randomized into one of four groups and received mock loading plus plant fiber as placebo (ML/Placebo), mock loading plus 5 mg melatonin (ML/Melatonin), osteogenic loading plus placebo (OL/Placebo), and osteogenic loading plus 5 mg melatonin (OL/Melatonin). The loading protocol was designed to deliver multiples of body weight (MOB; 1-2 MOB for mock loading and 1.5-4.2 MOB for osteogenic loading) to the upper body (targeting the arm, chest, and shoulders), core (targeting the spine and core stability), lower body (targeting the legs and hip) and postural (targeting the spine and posture). Following these interventions, musculoskeletal health was measured by DXA and functional testing using timed-up-and-go (TUG) and sit-to-stand (STS) assessments. Markers of bone health (e.g., P1NP, CTX, CRP, cortisol, and melatonin) were assessed in urine collected during the night (10 pm-6 am). Mental health assessments were conducted using PSS, CES-D, STAI and QualiOst. Time-dependent increases in the amount of force exerted (in lbs) were observed in the OL groups for all musculoskeletal systems targeted, compared to those participants receiving ML. Over 12mos, compared to baseline, participants in the OL/Melatonin group had statistically significant increases in lumbar spine T-scores (mean difference [MD] = 0.13, standard deviation [SD] = 0.05, p = 0.015) and BMD (MD = 0.013, SD = 0.006, p = 0.021). No other statistically significant effects were noted for T-scores, BMD, or FRAX scores. Additionally, no significant differences were observed when T-scores were compared between groups. Functional assessments at 12mos revealed increases in TUG times (MD = -1.7, SD = 0.3, p = 0.002) from baseline and deterioration for STS (MD = 2.8, SD = 0.59, p = 0.004) from month 03 for ML/placebo group, which did not occur for the other interventions. Correlation analysis revealed negative associations between TUG performance and CTX levels starting at 3mos in the OL/Melatonin group (r = -0.960, p = 0.04). The change in STS repetitions over a 12-month period (12mo-0mo) was negatively associated with the P1NP:CTX ratio (r = -0.978, p = 0.02) and positively associated with melatonin levels in the OL/Melatonin group (r = 0.958, p = 0.04). No changes in nocturnal output of CRP or cortisol and subject-reported outcomes were observed for any of the interventions within and between groups. The results from this study reveal that osteogenic loading combined with melatonin may be an alternative therapeutic intervention for those with osteopenia.