Melatonin Enhances Autophagy to Reduce Hypertrophic Scar Formation

Study Background and Research Question

Hypertrophic scars (HS) are a prevalent form of pathological skin fibrosis following injury, burns, or surgery, characterized by abnormal proliferation of dermal fibroblasts and excessive extracellular matrix (ECM) deposition. Conventional therapeutic strategies, including corticosteroids, laser therapy, and silicon-based treatments, often provide incomplete relief and are associated with relapses or side effects. Recent research has suggested that dysregulated autophagy—the cellular process for degrading and recycling cytoplasmic content—may contribute to persistent fibrotic responses. Melatonin, a pineal hormone best known for its role in circadian regulation, also exhibits antioxidant, anti-inflammatory, and autophagy-modulating activities. However, the precise mechanisms by which melatonin may influence HS progression remained unclear. The present study (Dong et al., 2024) addressed whether melatonin can mitigate HS formation by regulating autophagy in human hypertrophic scar fibroblasts (HSFs) and in vivo models, and elucidated the underlying signaling pathways.

Key Innovation from the Reference Study

The central innovation of this research lies in demonstrating that melatonin inhibits fibroblast-driven scar formation by enhancing autophagy via MT2 receptor-mediated suppression of the PI3K/Akt/mTOR pathway. Notably, the study provides mechanistic evidence that melatonin disrupts the binding of the MT2 receptor with PI3K (p110β), thereby reducing Akt/mTOR signaling and promoting autophagic flux in HSFs. This mechanistic insight positions autophagy enhancement as a viable therapeutic target for fibrotic skin diseases, moving beyond symptomatic management to address underlying cellular dysfunction.

Methods and Experimental Design Insights

The authors used a robust combination of in vitro and in vivo models to interrogate melatonin’s anti-fibrotic effects. Primary HSFs derived from human HS tissue and normal skin fibroblasts (NFs) served as cellular models. Functional assays included measurements of cell migration, contraction, and production of collagen and α-smooth muscle actin (α-SMA)—hallmarks of fibrogenic activity. Autophagic activity was assessed by monitoring autophagosome formation and key protein markers. To determine the involved signaling pathways, the study combined RNA-sequencing, bioinformatics analyses, and immunoblotting for PI3K/Akt/mTOR components.

For in vivo validation, a rabbit ear hypertrophic scar model was employed, with direct melatonin administration. The study also used pharmacological modulators: autophagy inhibitor (3-methyladenine, 3-MA), Akt activator (SC79), and MT2 antagonist (4-phenyl-2-propionamidotetralin, 4-P-PDOT) to dissect causality in pathway modulation.

Protocol Parameters

• Melatonin treatment: Dose and timing optimized for both HSF cultures and rabbit ear models; details are given in the original article.
• Autophagy inhibition: 3-MA was applied to validate the necessity of autophagic processes in mediating anti-fibrotic effects.
• Signaling modulation: Use of SC79 (Akt activator) and 4-P-PDOT (MT2 antagonist) confirmed pathway specificity.
• Functional and molecular readouts: Fibroblast migration, contraction, collagen/α-SMA expression, and autophagic marker quantification were systematically assessed.

Core Findings and Why They Matter

Melatonin administration led to significant reduction in HSF migration, contractility, collagen synthesis, and α-SMA expression, both in vitro and in the rabbit ear HS model. Mechanistically, melatonin suppressed Akt/mTOR pathway activation by interfering with MT2-PI3K(p110β) interaction, as evidenced by protein-protein interaction analyses and pathway-specific immunoblots. Importantly, autophagic flux was markedly increased upon melatonin treatment, and reversal of these effects by autophagy inhibition, Akt activation, or MT2 antagonism confirmed the centrality of this axis.

The study’s findings have direct translational relevance: enhancing autophagy in dermal fibroblasts emerges as a promising strategy to attenuate pathological scarring. Moreover, targeting the MT2-PI3K/Akt/mTOR signaling interface could yield more selective and effective anti-fibrotic interventions with fewer side effects than broad immunosuppressive regimens.

Comparison with Existing Internal Articles

While the reference study primarily focuses on autophagy and signaling modulation in skin fibrosis, oxidative stress and redox imbalance are also implicated in fibrotic progression. Advanced ROS detection workflows, such as those described in "2,7-Dichlorodihydrofluorescein Diacetate for ROS Assays: Advanced Applications" and "2,7-Dichlorodihydrofluorescein diacetate: Redox Signaling Insights", provide methodological frameworks to monitor intracellular oxidative stress in models of inflammation and fibrosis. These studies highlight how probes like DCFH-DA are essential for quantifying the impact of interventions—such as melatonin—on ROS dynamics using fluorescence microscopy, flow cytometry, or plate-based assays. Thus, integrating ROS analysis with autophagy and signaling assessments can offer a multidimensional understanding of anti-fibrotic mechanisms.

Limitations and Transferability

Despite its strengths, several limitations warrant consideration. The use of animal models and primary human fibroblasts provides strong translational relevance, but interspecies and inter-individual variability may influence therapeutic outcomes. The study’s focus on the MT2-PI3K/Akt/mTOR axis, while mechanistically detailed, does not exclude contributions from other melatonin receptors or signaling pathways. In addition, while autophagy enhancement proved beneficial in this context, excessive or dysregulated autophagy may have adverse effects in other tissues or disease stages, underscoring the need for precise modulation. Finally, the broader applicability to other fibrotic diseases remains to be established in future research.

Research Support Resources

To facilitate similar research workflows, validated reagents for intracellular ROS detection and oxidative stress quantification are crucial. 2,7-Dichlorodihydrofluorescein diacetate (DCFH-DA, SKU C3890) from APExBIO is a widely adopted, cell-permeable fluorogenic probe for monitoring ROS in live-cell models, compatible with fluorescence microscopy, flow cytometry, and plate-based oxidative stress assays. When designing experiments on autophagy, fibrosis, or redox signaling, researchers should incorporate appropriate controls and consider probe-specific limitations to ensure reliable quantification. For further workflow optimization and advanced troubleshooting, see in-depth protocol recommendations in recent methodological reviews.