Mitochondrial reverse electron transport (RET) represents a fundamental but potentially hazardous metabolic process in eukaryotic cells. This review systematically examines current understanding of RET mechanisms and their pathophysiological consequences. RET occurs when electrons flow inversely from reduced coenzyme Q (CoQH₂) to complex I, driven by excessive reduction of the CoQ pool and elevated mitochondrial membrane potential, resulting in substantial superoxide production. While moderate RET contributes to physiological redox signaling, sustained RET activation leads to oxidative damage and activates regulated cell death pathways. Notably, RET demonstrates metabolic duality: it facilitates ATP generation through NAD⁺ reduction while simultaneously inducing mitochondrial dysfunction via reactive oxygen species overproduction. Pathologically, RET has been implicated in myocardial ischemia–reperfusion injury, neurodegenerative disorders including Alzheimer’s diseases, and exhibits context-dependent roles in tumor progression. Emerging evidence also suggests RET involvement in microbial pathogenesis through modulation of host immune responses. These findings position RET as a critical regulatory node in cellular metabolism with broad implications for human diseases. Future investigations should focus on developing tissue-specific RET modulators and elucidating the molecular switches governing its activation threshold, which may yield novel therapeutic strategies for diverse pathological conditions.

Mitochondrial dysfunction is a key early pathological process in neurodegenerative diseases (NDs), leading to oxidative stress, impaired energy metabolism, and neuronal apoptosis prior to the onset of clinical symptoms. Although mitochondria represent important therapeutic targets, effective interventions targeting mitochondrial function remain limited. This review summarizes current evidence regarding the mechanisms by which melatonin protects mitochondria and evaluates its therapeutic relevance, with a primary focus on Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease—the major protagonists of NDs—while briefly covering other NDs such as amyotrophic lateral sclerosis, multiple sclerosis, and prion diseases. Melatonin selectively accumulates in neuronal mitochondria and exerts neuroprotection through multiple pathways: (1) direct scavenging of reactive oxygen species (ROS); (2) transcriptional activation of antioxidant defenses via the SIRT3 and Nrf2 pathways; (3) regulation of mitochondrial dynamics through DRP1 and OPA1; and (4) promotion of PINK1- and Parkin-mediated mitophagy. Additionally, melatonin exhibits context-dependent pleiotropy: under conditions of mild mitochondrial stress, it restores mitochondrial homeostasis; under conditions of severe mitochondrial damage, it promotes pro-survival autophagy by inhibiting the PI3K/AKT/mTOR pathway, thereby conferring stage-specific therapeutic advantages. Overall, melatonin offers a sophisticated mitochondria-targeting strategy for the treatment of NDs. However, successful clinical translation requires clarification of receptor-dependent signaling pathways, development of standardized dosing strategies, and validation in large-scale randomized controlled trials.

Cancer-associated fibroblasts (CAFs), as the “architect” of the immune microenvironment in lung cancer, play a multidimensional role in tumor progression and immune regulation. In this review, we summarize the heterogeneity of the origin and the molecular phenotype of CAFs in lung cancer, and explore the complex interactions between CAFs and multiple components of the tumor microenvironment, including the regulatory relationships with innate immune cells (e.g., tumor-associated macrophages, tumor-associated neutrophils), adaptive immune cells (e.g., T cells), and extracellular matrix (ECM). CAFs significantly influence tumor progression and immunomodulation through the secretion of cytokines, remodeling of the ECM, and the regulation of immune cell function significantly affects the immune escape and treatment resistance of tumors. In addition, this review also deeply explored the synergistic regulatory relationship between CAF and radiotherapy, revealing the key role of CAF in radiotherapy-induced remodeling of the immune microenvironment, which provides a new perspective for optimizing the comprehensive treatment strategy of lung cancer. By comprehensively analyzing the multidimensional roles of CAF and its interaction with radiotherapy, this review aims to provide a theoretical basis for the precise regulation of the immune microenvironment and clinical treatment of lung cancer.

Increased stemness of cancer cells exacerbates radioresistance, thereby greatly limiting the efficacy of radiotherapy. In order to study the changes in cancer cell stemness during radiotherapy, we established a radioresistance model of human non-small cell lung cancer A549 cells and obtained A549 radioresistant cells (A549-RR). We sampled the cells at different time points during the modeling process and investigated the heterogeneity of each group of cells using single-cell sequencing. Cells in the early stages of fractionated irradiation were found to be significantly up-regulated in stemness, and a subpopulation of cells producing this response was screened and referred to as “radiation-induced stemness-responsive cancer cells”. They were undergoing stemness response, energy metabolism reprogramming, and progressively differentiating into cells with more diverse and malignant phenotypes in order to attenuate the killing effect of radiation. Furthermore, we demonstrated that such responses might be driven by the activation of the EGFR-Hippo signaling pathway axis, which also plays a crucial role in the development of radioresistance. Our study reveals the dynamic evolution of cell subpopulation in cancer cells during fractionated radiotherapy; the early stage of irradiation can determine the destiny of the radiation-induced stemness-responsive cancer cells. The activation of stemness-like phenotypes during the development of radioresistance is not the result of dose accumulation but occurs during the early stage of radiotherapy with relatively low-dose irradiation. The degree of the radiation-induced stemness response of cancer cells mediated by the EGFR-Hippo signaling pathway might be a potential predictor of the efficacy of radiotherapy and the development of radioresistance.

Hypoxia-induced radioresistance remains a major obstacle in non-small cell lung cancer (NSCLC) radiotherapy. This study investigates whether artificially activating mitochondrial reverse electron transfer (RET) can enhance radiosensitivity in NSCLC by triggering oxidative stress. An in vitro hypoxia/reoxygenation (H/R) model was established in A549 cells to assess reactive oxygen species (ROS) levels, mitochondrial function, and metabolic alterations using fluorescence probes, flow cytometry, confocal microscopy, and targeted metabolomics. Mitochondrial complex inhibitors and dimethyl succinate (DM-S) were employed to validate the RET mechanism, and radiosensitivity was evaluated through clonogenic survival, apoptosis assays, and γ-H2AX staining. In vivo, A549 tumor-bearing mice received high oxygen (95% O₂) combined with DM-S and localized irradiation (4 Gy); tumor growth, histopathology, and immunohistochemistry were examined. H/R triggered substantial mitochondrial ROS production via complex I-mediated RET, dependent on a high mitochondrial membrane potential and electron transport chain imbalance, with succinate accumulation serving as a key metabolic switch. Exogenous DM-S exacerbated H/R-induced oxidative damage, DNA fragmentation (8-OHdG elevation, mtDNA integrity loss), and mitochondrial network disruption. H/R combined with DM-S significantly enhanced in vitro radiosensitivity, reducing clonogenic survival and increasing apoptosis to 53.4% ± 1.9% versus 10.3% ± 1.2% with irradiation alone. In vivo, the combination therapy markedly suppressed tumor growth, induced apoptosis and oxidative lipid damage (4-HNE), alleviated hypoxia (reduced HIF-1α), and showed no overt toxicity. These findings demonstrate that activating mitochondrial RET effectively enhances radiosensitivity in NSCLC. Succinate metabolism is a critical therapeutic target, and combining high oxygen with a succinate analog represents a promising radiosensitization strategy for hypoxic tumors.