COPD is the third leading cause of death worldwide, a progressive disease in which chronic inflammation and tissue damage produce irreversible airflow limitation. Cigarette smoke, the dominant risk factor, contains more than 7,000 compounds, including reactive oxygen species such as superoxide and hydroxyl radicals. Although the gaseous phase of smoke cannot easily cross cell membranes, the lipophilic components captured in cigarette smoke extract, including aldehydes and polycyclic aromatic hydrocarbons, can penetrate cells and reduce mitochondrial membrane potential and ATP production. The resulting damage activates immune cells, amplifies lung tissue destruction, and promotes COPD in susceptible individuals. Yet not all smokers develop the disease, and mounting evidence points to epigenetic mechanisms, including DNA methylation, as key players in determining who succumbs.

Mitochondria carry their own small genome, separate from the DNA housed in the nucleus, and this circular genome lacks the protective histone proteins that organize nuclear DNA. That absence has led researchers to focus on methylation of the mitochondrial DNA itself as a potential regulatory layer. Mitochondrial gene expression changes have already been documented in smokers: a comparative analysis found that 32 of 37 mitochondrial genes were upregulated in smokers with normal lung function, and lung epithelial cells from smokers show increased mitochondrial DNA copy number correlated with nuclear DNA methylation. Mitochondrial DNA methylation differences have also been reported in aging, metabolic disorders, neurodegeneration, and cardiovascular disease, making the mitochondrial epigenome an attractive suspect in COPD pathogenesis.

To test that suspicion, the Groningen team, led by Lin Liang and Irene H. Heijink, exposed human bronchial epithelial BEAS-2B cells to gradually increasing concentrations of cigarette smoke extract over periods ranging from four weeks to 25 weeks. Using Seahorse extracellular flux analysis, they measured the oxygen consumption rate, the gold-standard readout of mitochondrial respiration. After ten weeks of exposure reaching 5% smoke extract, the cells displayed a striking loss of respiratory capacity: basal respiration, ATP-linked respiration, and maximal respiration all fell significantly compared with unexposed controls, confirming that prolonged smoke exposure genuinely cripples mitochondrial energy production.

The damaged mitochondria were accompanied by a transcriptional response. Expression of the protein-coding mitochondrial genes MT-CYB and MT-CO2, which encode components of respiratory chain complexes III and IV, rose significantly in cells exposed to 5% and 6% smoke extract, along with the rRNA gene MT-RNR1 at the 5% time point. Because mitochondrial DNA copy number remained stable throughout the 25-week exposure, the researchers interpret this upregulation as a compensatory boost in transcriptional activity as the cells struggle to maintain energy output. Intriguingly, the elevation vanished by the 25-week mark at 10% smoke extract, suggesting that once dysfunction becomes severe enough, the compensatory capacity of mitochondrial gene regulation is itself overwhelmed.

The critical question was whether these changes were written into the mitochondrial epigenome. Using pyrosequencing targeted to the D-loop, the non-coding region harboring the mitochondrial promoters, and to the MT-CYB and MT-CO2 genes, the team measured methylation at individual cytosines, including the non-CpG sites that can be methylated in mitochondria. They complemented this with liquid chromatography tandem mass spectrometry to quantify global mitochondrial DNA methylation. The result was resoundingly negative: despite dramatic functional impairment and gene expression shifts, methylation in the long-term exposed BEAS-2B cells showed no statistically significant changes at any assessed site or across the whole mitochondrial genome. Some cytosines shifted consistently, but by less than 1%, a magnitude the authors consider biologically negligible.

Short-term exposure told a similar story. A 24-hour bath in 10% smoke extract triggered a massive surge in the oxidative stress marker HMOX1, upregulated more than 200-fold, and significantly reduced mitochondrial DNA copy number in BEAS-2B cells, possibly reflecting smoke-damaged mitochondria being cleared by mitophagy. Yet mitochondrial gene expression and methylation held steady. In the 16HBE bronchial epithelial cell line, which more faithfully mirrors primary airway cells, neither copy number nor gene expression budged after 24-hour exposures, although mean methylation of MT-CYB and MT-CO2 rose modestly at the 15% dose, hinting at a dose-dependent and cell-type-specific response that disappeared at 20%, where cellular tolerance may be exceeded.

The team then extended the work to primary airway epithelial cells isolated from six COPD patients, all with severe GOLD stage IV disease, and six non-COPD donors. Here the findings were equally unambiguous: mitochondrial gene expression, copy number, and methylation were indistinguishable between COPD and control cells, and 24-hour smoke extract exposure failed to alter any of these measures in either group. The authors caution that the modest donor numbers and the lack of information on the control donors’ sex, age, and smoking status could obscure subtler differences, and that the submerged culture conditions used here cannot capture the effects of the gaseous phase of smoke, which air-liquid interface cultures would expose.

Taken together, the study delivers a sobering message for the mitochondrial epigenetics field: mitochondrial DNA methylation appears not to be a dominant driver of the pathological changes that cigarette smoke inflicts on airway epithelium. The smoke-induced mitochondrial dysfunction seen in COPD likely arises through other mechanisms, while mild shifts in mitochondrial gene expression may be consequences rather than causes. The authors point toward promising future directions, including the emerging role of N6-methyladenine, a different DNA modification shown to regulate mitochondrial transcription and replication and to accumulate in mitochondrial DNA during aging across species. As researchers refine methods for measuring mitochondrial methylation, accounting for artifacts such as incomplete bisulfite conversion, the Groningen results provide a rigorous negative control that will help steer COPD research toward the molecular mechanisms that truly matter.

Subject of Research: Effects of cigarette smoke extract on mitochondrial function, gene expression, and mitochondrial DNA methylation in airway epithelial cells in relation to COPD

Article Title: The effects of cigarette smoke extract on mitochondrial function, mitochondrial gene expression and mitochondrial DNA methylation in airway epithelial cells

Article References: Liang, L., Wang, L., Jonker, M. R., Kosse, W., Jellema, P. G., Rots, M. G., & Heijink, I. H. (2025). The effects of cigarette smoke extract on mitochondrial function, mitochondrial gene expression and mitochondrial DNA methylation in airway epithelial cells. Epigenetics Communications, 6(1), Article 1. https://doi.org/10.1186/s43682-025-00040-4

Image Credits: AI Generated

DOI: 10.1186/s43682-025-00040-4

Keywords: mitochondrial DNA methylation, mitochondrial dysfunction, COPD, cigarette smoke extract, airway epithelial cells, mitochondrial gene expression, epigenetics, D-loop, oxygen consumption rate, oxidative stress, MT-CYB, MT-CO2

Mitochondrial ribosomes, or mitoribosomes, are specialized ribosomal complexes responsible for translating mitochondrial mRNAs into proteins crucial for respiratory function and energy metabolism. While the bacterial and cytosolic ribosomal structures have been extensively studied, plant mitochondrial ribosomes have remained, until now, a largely uncharted territory given their unique RNA and protein composition distinct from their animal counterparts. Leveraging cryo-EM technology, Waltz, Soufari, Bochler, and colleagues have rendered the first high-resolution look at this essential nanomachine embedded within plant cells.

Cryo-EM, a method that flash-freezes biomolecules and images them at cryogenic temperatures, has revolutionized structural biology. This approach circumvents the need for crystallization—especially difficult for large, flexible complexes—and produces near-atomic resolution maps. Using this technique, the researchers captured the plant mitoribosome’s architecture with unprecedented clarity, revealing its RNA-rich cores and associated protein regions that assemble into a functional ribosome distinct from previously characterized mitochondrial ribosomes in animals and fungi.

One of the most striking features of the plant mitochondrial ribosome revealed by this structure is the unusually high RNA content. Unlike animal mitoribosomes that have comparatively diminished rRNA content, plant mitoribosomes retain extensive RNA expansion segments. These RNA elements are hypothesized to influence ribosomal stability, fidelity, and interaction with mitochondrial mRNAs, positing a divergent evolutionary path shaped by the unique bioenergetic and genetic demands of plant mitochondria.

Moreover, the study delineates the numerous ribosomal proteins that coexist with the RNA core, many of which are plant-specific or bear remarkable modifications indicative of adaptation to the plant mitochondrial environment. The interplay between RNA expansion segments and these protein components likely underpins specialized functions such as selective translation initiation and complex assembly/disassembly dynamics essential for mitochondrial regulation under varied metabolic states.

Understanding this ribosomal machinery is crucial, considering mitochondria’s role beyond ATP production. They participate in signaling pathways regulating growth, programmed cell death, and responses to biotic and abiotic stresses. As the plant mitochondrial ribosome orchestrates mitochondrial gene expression, insights into its structure illuminate the mechanisms dictating mitochondrial biogenesis and function, contributing to broader comprehension of plant resilience and productivity.

The study also sets a new benchmark for exploring ribosome heterogeneity within the plant kingdom. Given that ribosomes adapt to fulfill specialized roles—sometimes called “specialized ribosomes”—the detailed plant mitoribosome structure invites further research into how structural variations confer selective translational control. Such investigations could lead to manipulations of mitochondrial translation to enhance crop yield or tolerance to environmental challenges.

Importantly, the research provides a framework for understanding mitochondrial diseases and defects arising from impaired ribosomal function. Although most mitochondrial dysfunction research has focused on animals, plant mitochondrial pathologies, such as cytoplasmic male sterility influencing hybrid seed production, could now be dissected at the molecular level. The new structural insights pave the way for engineering ribosome-targeted interventions that modulate mitochondrial activity in plants to improve agricultural traits.

Technologically, the study exemplifies the power of cutting-edge cryo-EM combined with advanced computational methods to unravel complex macromolecular assemblies. Detailed models created from the data will serve as templates for comparative analyses and molecular docking studies, facilitating drug design and synthetic biology applications aiming to reprogram mitochondrial translation.

The authors emphasize the potential for the observed RNA structures to serve as novel interfaces for protein synthesis regulators, including translational activators and mitochondrial RNA-binding proteins. These findings underscore a sophisticated coordination network between the ribosome and mitochondrial gene expression machinery, possibly tailored by plants for rapid adaptation to fluctuating energy demands.

Beyond the mechanistic details, this high-resolution plant mitoribosome structure provides a valuable resource for evolutionary studies, illuminating how ribosomes have diversified and specialized across the tree of life. Such evolutionary insights deepen our grasp of fundamental biological processes and may inspire biomimetic designs in nanotechnology and synthetic biology.

While the current structure represents a major leap forward, researchers anticipate that studying the ribosome in various functional states—such as during translation initiation, elongation, and termination—will yield further mechanistic insights, revealing dynamic conformational changes and regulatory checkpoints unique to plant mitochondria.

This discovery offers an exciting vista onto the delicate balance life maintains between its nuclear and organellar genomes, with the mitoribosome at the heart of this relationship. As plants face mounting environmental changes, understanding this nexus will be crucial to unlocking strategies for sustainable agriculture and ecology in the future.

In sum, the elucidation of the RNA-rich plant mitochondrial ribosome structure by Waltz et al. stands as a paradigm-shifting achievement, answering longstanding questions about mitochondrial gene expression in plants and opening fertile ground for diverse scientific explorations. The implications resonate not only within fundamental biology but also in biotechnology, agriculture, and medicine.

As these molecular portraits continue to sharpen, the scientific community eagerly awaits the next chapters in mitoribosome research, fueled by this first detailed glimpse of the plant’s mitochondrial protein factory—an intricate molecular masterpiece fundamental to life’s endurance and flourishing.

Subject of Research: Structural characterization of the RNA-rich mitochondrial ribosome in plants using cryo-electron microscopy.

Article Title: Addendum: Cryo-EM structure of the RNA-rich plant mitochondrial ribosome.

Article References:
Waltz, F., Soufari, H., Bochler, A. et al. Addendum: Cryo-EM structure of the RNA-rich plant mitochondrial ribosome. Nat. Plants (2026). https://doi.org/10.1038/s41477-025-02209-0

Image Credits: AI Generated

Leiomyosarcoma, a subtype of soft tissue sarcoma notorious for its aggressive phenotype and resistance to conventional therapies, has long presented a formidable challenge to clinicians. Researchers have struggled to develop effective treatments for these tumors because of their complex molecular landscape and adaptive resistance mechanisms. The identification of a novel compound that can directly bind to mitochondrial DNA and disrupt its expression heralds a paradigm shift in how this intractable disease might be combated at the cellular level.

The team, led by Malavasi, Picco, and Mallavarapu, embarked on this study with the goal of developing a compound capable of selectively targeting the mitochondrial minor groove DNA — a niche often overlooked by traditional DNA-binding drugs. Minor-groove binders typically interact with the DNA helix in a sequence-specific manner, influencing gene expression. However, as the mitochondrial genome is distinct and encased within the organelle, targeting it requires molecules with unique physicochemical properties to permeate mitochondrial membranes and exert localized action without compromising nuclear DNA integrity.

This newly identified minor-groove DNA binder exhibits a high affinity for mitochondrial DNA sequences crucial to the expression of genes involved in oxidative phosphorylation. By binding to these sites, it effectively suppresses mitochondrial transcription, leading to a profound disruption in mitochondrial bioenergetics. The inhibition of mitochondrial gene expression culminates in the collapse of mitochondrial membrane potential, a critical event that precipitates cellular apoptosis specifically in tumor cells reliant on mitochondrial function for survival.

Traditional chemotherapeutics often induce apoptosis through nuclear DNA damage, which can provoke deleterious side effects due to lack of specificity. In contrast, this novel agent’s ability to induce apoptosis via mitochondrial gene repression offers a level of precision hitherto unseen. This specificity not only minimizes collateral damage to healthy cells but also targets a vital vulnerability of cancer cells that exploit mitochondrial metabolism to fuel their rapid proliferation and resistance.

Enabling this breakthrough was the discovery that leiomyosarcoma cells are particularly dependent on mitochondrial gene expression for their survival and proliferation. Unlike many other tumor types, these cells exhibit heightened mitochondrial bioenergetic activity, making them uniquely susceptible to disruptions in mitochondrial DNA transcription. This vulnerability was exploited by the minor-groove binder, whose selective targeting induced apoptosis exclusively in cancer cells, sparing normal tissues.

Beyond the biochemical interactions, the research team employed cutting-edge imaging and molecular biology techniques to confirm the intracellular localization of the compound within mitochondria. Fluorescent tagging and advanced microscopy allowed for the visualization of drug accumulation within the organelle, solidifying the mechanistic understanding of its mode of action. Concurrently, gene expression profiling revealed a significant downregulation of mitochondrial genes post-treatment without affecting nuclear-encoded genes, underscoring the compound’s selectivity.

Moreover, the study reports that the novel binder achieves its therapeutic effect by disrupting the mitochondrial transcription machinery’s access to DNA, thereby causing a marked reduction in essential mitochondrial RNAs. This repression cascades into a breakdown of the electron transport chain components’ expression, drastically impairing ATP production. The energy crisis induced in the tumor cells triggers intrinsic apoptotic pathways, a process elegantly validated through caspase activation assays.

Importantly, the therapeutic window of this DNA binder has been characterized through extensive in vitro and in vivo studies. Normal cells exhibit robust resistance to this compound, highlighting a differential vulnerability that could minimize off-target effects. Animal models bearing leiomyosarcoma xenografts demonstrated significant tumor regression without observable systemic toxicity, a promising indication for translational potential.

The implications of this research extend to the broader field of mitochondrial biology in cancer. The mitochondria’s role as a key regulator of cellular fate decisions — through bioenergetic and apoptotic pathways — underscores the value of targeting mitochondrial DNA as a therapeutic strategy. This study elegantly bridges the gap between basic mitochondrial genetics and clinical oncology, proposing a targeted modality that bypasses traditional nuclear DNA damage mechanisms.

Furthermore, this novel approach challenges the prevailing dogma that mitochondrial genomes are less druggable due to their compact size and unique histone-free structure. By designing a compound capable of engaging mitochondrial minor grooves, the researchers offer a blueprint for future development of mitochondrial gene expression modulators. The findings provoke reconsideration of mitochondrial DNA as a ‘therapeutic genome’ that may harbor untapped molecular targets for oncologic intervention.

The technology utilized to identify and validate the minor-groove DNA binder involved sophisticated high-throughput screening and structure-guided drug design methodologies. Computational modeling allowed the team to predict binding affinities and tailor molecular configurations enhancing mitochondrial entry and DNA interaction specificity. Such an integrative approach underscores how interdisciplinary strategies are essential to tackle complex biological challenges in cancer research today.

Looking ahead, the researchers envision expanding their molecular library to discover additional minor groove binders that modulate mitochondrial functions differently, potentially overcoming resistance mechanisms. Moreover, combining this agent with established chemotherapeutics or mitochondrial metabolism inhibitors could synergistically amplify anti-tumor efficacy, offering hope for patients grappling with refractory sarcomas.

In the sphere of therapeutic development, a critical next step is the initiation of early-phase clinical trials. These will ascertain the safety, dosing parameters, and pharmacodynamics of the compound in human subjects, focusing initially on patients with metastatic or unresectable leiomyosarcoma. The precision and specificity demonstrated in preclinical work augur well for clinical translational success, highlighting a promising new weapon in the oncologist’s arsenal.

This discovery also spotlights mitochondria’s emerging role as a key regulator not only of apoptosis but of tumor metabolism and microenvironmental interactions. The prospect of manipulating mitochondrial gene expression to activate apoptotic cascades represents a formidable strategy capable of circumventing common modes of cancer cell survival adaptation.

In conclusion, the identification of this novel minor-groove DNA binder marks a seminal advancement in targeted cancer therapeutics. By repressing mitochondrial gene expression and inducing mitochondrial-dependent apoptosis specifically in leiomyosarcoma cells, the compound offers a refined therapeutic approach that harnesses mitochondrial vulnerabilities intrinsic to aggressive tumors. This pioneering research paves the way for innovative treatments that could extend survival and improve quality of life for patients challenged by currently incurable soft tissue sarcomas.

As this research progresses toward clinical application, the oncology community eagerly anticipates confirmation of these findings in patient populations, potentially transforming therapeutic strategies against mitochondrial-dependent cancers. The convergence of mitochondrial biology and drug design exemplified in this study may well herald a new epoch in precision medicine, redefining how we confront the molecular intricacies of cancer.

Subject of Research: Identification and characterization of a novel minor-groove DNA binder that represses mitochondrial gene expression and induces apoptosis in highly aggressive leiomyosarcoma cells.

Article Title: Identification of a novel minor-groove DNA binder that represses mitochondrial gene expression and induces apoptosis in highly aggressive leiomyosarcoma cells.

Article References:
Malavasi, E., Picco, R., Mallavarapu, S. et al. Identification of a novel minor-groove DNA binder that represses mitochondrial gene expression and induces apoptosis in highly aggressive leiomyosarcoma cells. Cell Death Discov. 11, 524 (2025). https://doi.org/10.1038/s41420-025-02803-3

Image Credits: AI Generated

DOI: 10 November 2025