The review, led by Joonbeom Kim and corresponding authors Woongjae Yoo and Hakdong Shin, organizes the literature according to fatigue phenotype, microbiome function, microbial metabolites, gut barrier markers, inflammatory responses and food-based interventions. This phenotype-by-phenotype approach matters because fatigue is not a single entity. Clinicians distinguish pathological fatigue, such as the post-exertional malaise that defines ME/CFS, from the ordinary tiredness that follows intense exercise or a poor night’s sleep. By sorting the evidence in this way, the authors show that while the specific microbial signatures differ across conditions, the underlying mechanisms converge on a handful of recurring themes.

The first and most heavily supported theme involves short-chain fatty acids, particularly butyrate. These molecules are produced by gut bacteria as they ferment dietary fiber, and they do far more than nourish colon cells. Butyrate strengthens the intestinal barrier, promotes the differentiation of regulatory T cells that keep inflammation in check, and influences energy metabolism throughout the body. Multiple studies of ME/CFS patients have documented reduced microbial diversity and a deficient capacity to produce butyrate. One prominent study cited in the review found that this functional deficit was associated with disturbances in bacterial network structure and with the severity of fatigue symptoms, suggesting that the loss of butyrate-producing bacteria may be a driver rather than a bystander.

A second recurring mechanism is gut barrier dysfunction and the microbial translocation that follows it. When the single-cell lining of the intestine is compromised, bacterial products such as lipopolysaccharide can cross into the bloodstream. In ME/CFS patients, researchers have detected elevated serum antibodies against enterobacterial LPS, a finding consistent with increased intestinal permeability. Similar disruptions have been reported in post-COVID syndrome: a 2025 study found gastrointestinal barrier disruption in patients experiencing long COVID fatigue. The consequence is a state of low-grade, systemic inflammation—sustained immune activation that the brain interprets, in part, as fatigue. This framing aligns with the broader biology of sickness behavior, in which inflammatory cytokines act on the central nervous system to promote the desire to rest and withdraw.

The review also highlights altered tryptophan metabolism as a critical link between microbes and the brain. Tryptophan is the dietary precursor of serotonin and a substrate for the kynurenine pathway, and gut bacteria exert substantial control over how much tryptophan crosses the intestinal wall and which metabolic fate it follows. Microbial shifts that favor the kynurenine route over serotonin synthesis can influence mood, sleep and central fatigue signaling, providing a plausible biochemical route by which gut dysbiosis translates into the profound exhaustion reported by patients. Metabolomic studies of ME/CFS have repeatedly cataloged disturbances in these and related pathways, reinforcing the picture of a systemic metabolic imbalance rather than a purely psychological phenomenon.

The gut-muscle axis emerges as a third mechanistic pillar, particularly relevant to exercise-induced fatigue and athletic performance. Skeletal muscle and gut microbes communicate bidirectionally: microbial metabolites such as short-chain fatty acids influence muscle oxidative capacity and inflammation, while exercise reshapes the microbiome. One striking example cited in the review is the identification, through meta-omics analysis of elite athletes, of a bacterial strain associated with enhanced performance via lactate metabolism—the microbe appears to help clear lactate produced during intense exertion. Studies in athletes and physically active adults have also reported associations between specific gut bacterial profiles and perceived energy and fatigue, and probiotic supplementation trials in sports populations have explored whether modulating the microbiome can mitigate gastrointestinal inflammation and the perception of fatigue during training.

When it comes to interventions, the review evaluates a broad portfolio of food-based approaches. Dietary fiber and prebiotics supply the fermentable substrates that butyrate-producing bacteria need, and fiber intake is consistently associated with microbiome-mediated health benefits. Fermented foods deliver live microbes together with bioactive metabolites. Probiotics—live microorganisms administered in adequate amounts—have shown modest promise in pilot trials, including a double-blind, placebo-controlled study of a probiotic in the emotional symptoms of chronic fatigue syndrome, and a notable randomized trial in Hong Kong that tested a synbiotic preparation called SIM01 in patients with post-acute COVID-19 syndrome, reporting improvements relative to placebo. Postbiotics, defined by an international consensus as inanimate microorganisms or their components that confer health benefits, offer an alternative for people who cannot tolerate live microbes. Polyphenols and bioactive polysaccharides round out the list; the latter have been proposed to exert anti-fatigue effects specifically through the gut-muscle axis, and heat-killed strains of Lactiplantibacillus plantarum TWK10 have been examined for effects on exercise performance and body composition.

The authors are careful, however, to emphasize how much uncertainty remains. Many of the human studies to date are small, cross-sectional, or limited to stool-based 16S rRNA sequencing, which catalogs microbial species but says little about function. Causality is difficult to establish: fatigue can alter diet, sleep and physical activity, all of which in turn reshape the microbiome, so the observed associations could run in either direction or reflect shared underlying causes. Heterogeneity in case definitions—particularly for ME/CFS, for which multiple diagnostic criteria coexist—complicates comparisons across studies. The review therefore calls for controlled, phenotype-specific intervention trials that deploy multi-omics approaches, integrating metagenomics, metabolomics, immune profiling and host physiology to establish which microbial functions actually drive fatigue and which merely accompany it.

The implications, if the mechanistic picture holds up, are considerable. Fatigue underpins an enormous burden of disease worldwide, appearing in chronic infections, cancer, autoimmune conditions, depression and everyday life, yet treatment options remain limited largely to graded activity and cognitive-behavioral strategies, neither of which works for everyone. A microbiome-targeted framework would open the door to nutritional interventions that are comparatively safe, accessible and scalable: engineered prebiotic regimens to restore butyrate production, rationally selected probiotic or postbiotic formulations to reinforce barrier integrity and dampen inflammation, and dietary patterns designed to sustain a resilient gut ecosystem. The review’s authors, supported by Korea’s National Research Foundation and National Institute of Health, position food science as a central player in this emerging therapeutic landscape.

What makes the work timely is the post-pandemic context. Post-acute COVID-19 syndrome brought fatigue into global focus, with millions of patients experiencing persistent exhaustion months after infection, and studies documenting gut microbiota disturbances in prospective cohorts of these patients have fueled interest in microbial mechanisms of post-infectious fatigue. By drawing lines of continuity between ME/CFS—long dismissed by skeptics as a psychological illness—and long COVID, the review adds weight to the argument that fatigue syndromes have tangible, measurable biological underpinnings. The convergence of microbiome science, immunology and metabolomics is gradually replacing that skepticism with testable hypotheses about barrier failure, microbial metabolite deficits and chronic immune activation.

The Korean team’s synthesis does not claim to have solved fatigue. Rather, it maps the terrain: reduced short-chain fatty acid production, impaired butyrate capacity, leaky gut, microbial translocation, low-grade inflammation, disordered tryptophan metabolism, energy imbalance and gut-brain and gut-muscle signaling together form a plausible, evidence-backed architecture of fatigue-related vulnerability. What comes next—rigorous interventional trials, standardized phenotyping, and mechanistic studies that can distinguish cause from consequence—will determine whether the trillions of microbes in our intestines can be harnessed to restore what fatigue takes away.

Bronchopulmonary dysplasia is a chronic lung disease primarily affecting premature infants who receive prolonged oxygen therapy or mechanical ventilation. Characterized by abnormal lung development, inflammation, and impaired alveolarization, BPD remains a significant cause of morbidity and mortality. Central to its pathogenesis is the dysregulated immune response, particularly involving macrophages, whose activation state dictates inflammatory outcomes. Understanding the molecular regulators governing macrophage responses has remained a critical yet challenging frontier in neonatal medicine.

Pyroptosis, a form of programmed cell death distinct from apoptosis, is characterized by inflammasome activation and the formation of pores in the cell membrane, predominantly executed by GSDMD. This process results in the release of pro-inflammatory cytokines, amplifying immune responses. The study in focus meticulously investigates the effects of GSDMD deficiency in experimental models of BPD, revealing that the absence of GSDMD significantly mitigates lung injury by suppressing macrophage pyroptosis. This suppression leads to a dampened inflammatory milieu, which in turn promotes tissue repair and regeneration.

Delving deeper into the mechanistic pathways, the researchers demonstrate that GSDMD deficiency skews macrophage polarization from the pro-inflammatory M1 phenotype towards the anti-inflammatory and reparative M2 phenotype. This polarization shift is crucial because M2 macrophages facilitate the resolution of inflammation and contribute to tissue remodeling, both of which are vital in the context of lung injury and recovery. The study employs state-of-the-art techniques, including flow cytometry, immunohistochemistry, and gene expression profiling, to validate these findings across in vitro and in vivo models.

Importantly, the authors highlight how their findings challenge previous paradigms that primarily targeted inflammation globally without considering the intricacies of macrophage subtypes and their cell death modalities. By pinpointing GSDMD-driven pyroptosis as a modifiable pathway, this research opens new avenues for targeted therapeutics that could enhance clinical outcomes in BPD without compromising necessary immune defenses.

The pathological role of pyroptosis in BPD is particularly compelling because it lies at the intersection of immune defense and deleterious inflammation. While pyroptosis aids in fighting pathogens, its excessive activation exacerbates tissue damage. The study’s revelation that GSDMD deficiency strikes a balance by curtailing excessive pyroptosis, yet preserving beneficial immune responses, adds nuance to our understanding of neonatal lung inflammation.

Another compelling aspect of this research is its potential translational impact. Therapeutic strategies designed to inhibit GSDMD or its downstream effectors could be envisioned as adjunct treatments in neonatal intensive care units. For premature infants vulnerable to BPD, such interventions might reduce the incidence or severity of lung injury, diminish the need for invasive ventilation, and improve long-term respiratory outcomes.

The research team also emphasizes the broader implications of their work for other inflammatory diseases involving macrophage pyroptosis. Given that GSDMD-mediated pyroptosis plays a role in autoimmune diseases, sepsis, and cancer, the insights gained from this study could inspire cross-disciplinary therapeutic innovations. Understanding how GSDMD modulates immune homeostasis could thus have ripple effects across multiple fields of medicine.

While the study focuses on experimental models, including genetically modified mice deficient in GSDMD, the authors advocate for future clinical investigations to validate these mechanisms in human subjects. They propose exploring biomarkers reflective of pyroptosis and macrophage polarization in neonatal patients as potential tools for early diagnosis or therapeutic monitoring.

The intricate interplay between cell death modalities and immune cell polarization exemplified in this study underscores the complexity of immune regulation in tissue injury. By maneuvering the balance between destructive pyroptosis and reparative macrophage activity, GSDMD emerges as a master regulator in BPD pathology. This insight not only enriches our understanding but also exemplifies how molecular research can pave the way for precision medicine.

Moreover, the research raises intriguing questions about the potential side effects of modulating pyroptosis. Since this cell death pathway is integral to host defense, therapeutic strategies must finely tune rather than completely inhibit pyroptosis to preserve immune competence. Carefully designed drug delivery systems and dosing regimens could address these challenges, ensuring maximal benefit with minimal risk.

In summary, this seminal work by Yang and colleagues represents a significant leap forward in neonatal lung disease research. By uncovering the dual role of GSDMD in driving macrophage pyroptosis and influencing polarization, their study offers a promising target to attenuate bronchopulmonary dysplasia. This breakthrough not only advances scientific knowledge but also holds the promise of improving the lives of countless premature infants worldwide.

As this research garners attention, the scientific community awaits further studies to explore the clinical applicability of these findings. The potential to modulate immune responses through targeting GSDMD and macrophage phenotypes could herald a new era in neonatal care, where inflammation-induced lung injuries are not an inevitable consequence of prematurity but a manageable condition.

Future research directions might include the development of specific GSDMD inhibitors, the exploration of combination therapies with existing anti-inflammatory agents, and investigations into other cell types affected by pyroptosis in BPD. Such comprehensive approaches could refine strategies to improve neonatal outcomes and reduce the burden of chronic lung disease.

The integration of advanced molecular techniques and animal models in this study exemplifies the power of translational research. By bridging laboratory discoveries with clinical challenges, this work embodies the progress toward personalized medicine, where genetic and molecular profiles guide individualized treatment plans.

In conclusion, the attenuation of bronchopulmonary dysplasia through GSDMD deficiency underscores a vital nexus between programmed cell death, immune regulation, and tissue repair. This discovery not only enriches our comprehension of BPD pathophysiology but also charts a promising course for innovative therapies that could transform neonatal healthcare.

Subject of Research: The role of Gasdermin D (GSDMD) deficiency in attenuating bronchopulmonary dysplasia (BPD) by suppressing macrophage pyroptosis and promoting M2 macrophage polarization.

Article Title: GSDMD deficiency attenuates BPD by suppressing macrophage pyroptosis and promoting M2 polarization.

Article References:
Yang, X., Wang, X., Yang, Y. et al. GSDMD deficiency attenuates BPD by suppressing macrophage pyroptosis and promoting M2 polarization. Cell Death Discov. (2025). https://doi.org/10.1038/s41420-025-02872-4

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41420-025-02872-4

The Notch signaling pathway, a highly conserved cell communication system, is well-known for its pivotal role in determining cell differentiation and fate across various tissues. Its involvement in hematopoiesis, particularly in the regulation of progenitor cells that give rise to diverse myeloid lineages, has garnered increasing interest. However, a detailed exploration of its influence on monocyte progenitors, especially under inflammatory stimuli, had remained elusive until now.

Researchers focused on trilineage progenitors derived from human peripheral blood monocytes, which possess the remarkable capacity to differentiate into three distinct effector cell types: macrophages, dendritic cells, and osteoclasts. These cell types are integral players in immune defense, antigen presentation, and bone remodeling, respectively. Understanding the cues that drive progenitors toward one lineage or another under inflammatory conditions is critical for manipulating immune responses and attenuating pathological processes.

Employing a suite of sophisticated molecular and cellular techniques, the study meticulously dissected the role Notch signaling exerts when progenitors encounter inflammatory cytokines and environmental stressors. The researchers activated and inhibited components of the Notch pathway, observing consequent changes in gene expression, surface marker profiles, and functional capacities of differentiating cells. This comprehensive approach shed light on the dynamic interplay between external inflammatory cues and intrinsic Notch-mediated regulatory mechanisms.

A salient discovery of this investigation was the identification of distinct Notch-dependent transcriptional signatures that bias progenitor commitment towards macrophage or dendritic cell lineages. Under inflammatory conditions, heightened Notch activity preferentially steered progenitors to adopt macrophage phenotypes characterized by enhanced phagocytic and pro-inflammatory functions. Conversely, attenuation of Notch signaling skewed differentiation in favor of dendritic cells, which are vital for antigen presentation and activation of adaptive immunity.

Intriguingly, the study revealed that Notch signaling also inhibits osteoclastogenesis from monocyte progenitors in inflamed environments, suggesting a protective mechanism against pathological bone resorption commonly observed in chronic inflammatory diseases such as rheumatoid arthritis. This nuanced regulation underscores Notch’s role as a multifunctional gatekeeper balancing immune defense and tissue homeostasis.

Delving deeper into molecular pathways, the team elucidated that Notch signaling modulates key transcription factors including NF-κB, IRF8, and PU.1, which are instrumental in lineage specification. These factors orchestrate gene networks that define terminal differentiation programs and functional phenotypes. The crosstalk between Notch and these transcriptional regulators represents a sophisticated regulatory nexus modulating progenitor plasticity.

Another pivotal facet of the study involved the temporal dynamics of Notch activation. Researchers demonstrated that early versus late activation of Notch signals yields divergent differentiation outcomes, emphasizing the importance of signal timing in hematopoietic programming. Such temporal control mechanisms could be exploited to fine-tune immune responses for therapeutic benefit.

Furthermore, the findings implicate inflammatory cytokines such as TNF-α and IL-6 as modulators of Notch receptor and ligand expression on progenitor cells, thereby integrating extrinsic inflammatory signals with intrinsic differentiation programs. This interface constitutes an adaptive regulatory loop whereby systemic inflammation directly influences progenitor cell fate via Notch pathways.

Implications of these insights are profound, especially for designing targeted immunotherapies. By manipulating Notch signaling components within monocyte progenitors, it may be possible to recalibrate immune responses in diseases characterized by dysregulated inflammation and aberrant myeloid cell function, including autoimmune disorders, chronic infections, and cancer.

Moreover, the selective inhibition of Notch pathways to prevent excess osteoclast formation could herald new treatments for inflammatory bone loss, offering a dual benefit of immune modulation and preservation of skeletal integrity. The translational potential of these findings positions Notch signaling as a promising target in the development of next-generation immunomodulators.

This study also underscores the critical importance of studying human cells within physiologically relevant inflammatory milieus, moving beyond animal models to capture the complexity and heterogeneity of human immune regulation. Such approaches are essential for bridging the gap between bench research and clinical application.

While the results provide compelling evidence for Notch’s multifaceted roles, the authors acknowledge limitations, including the need for in vivo validation and exploration of Notch interactions with other signaling pathways such as Wnt and Hedgehog. Future research is poised to untangle these complex networks, offering richer insights into immune progenitor biology.

In conclusion, this groundbreaking investigation delineates how Notch signaling dynamically governs the fate of human peripheral blood monocyte trilineage progenitors under inflammatory conditions, finely tuning the balance between macrophage, dendritic cell, and osteoclast lineages. These findings invigorate the field with fresh mechanistic understanding and lay a robust foundation for harnessing Notch pathways in therapeutic innovation.

As chronic inflammatory conditions continue to impose significant health burdens worldwide, the modulation of progenitor cell fate through Notch offers a beacon of hope. The ability to direct immune cell differentiation with precision could revolutionize treatment paradigms, enabling tailored interventions that restore immune equilibrium without broad immunosuppression.

The research community and clinical practitioners alike will keenly watch forthcoming studies that build upon these seminal discoveries. By integrating molecular insights with clinical needs, the path toward transformative immune therapies may be rapidly accelerated, fulfilling the promise of precision medicine.

Continued investment in decoding cell signaling mechanisms and their contextual dependencies remains paramount. The elucidation of Notch’s role herein exemplifies the power of fundamental research to illuminate complex biological systems and inspire novel therapeutic strategies.

This study handles complexities of immune differentiation with elegant experimental strategies, offering clarity into a previously obscure regulatory axis. Its publication marks a significant milestone in both immunology and cell biology, likely to galvanize further inquiries and technological advancements.

The intersection of Notch signaling and inflammatory microenvironments unveiled by this research reflects the evolving landscape of hematopoietic science, one where signaling pathways are viewed not in isolation but as integrated systems influencing disease outcomes and clinical opportunities alike.

Subject of Research: The influence of Notch signaling on the lineage commitment of human peripheral blood monocyte trilineage progenitors under inflammatory conditions.

Article Title: Effects of Notch signaling on the lineage commitment of human peripheral blood monocyte trilineage progenitor under inflammatory conditions.

Article References:
Aničić, S., Filipović, M., Krešić, I. et al. Effects of Notch signaling on the lineage commitment of human peripheral blood monocyte trilineage progenitor under inflammatory conditions. Cell Death Discov. 11, 519 (2025). https://doi.org/10.1038/s41420-025-02807-z

Image Credits: AI Generated

DOI: 10 November 2025

A groundbreaking study, published in April 2025 in Genes & Immunity, sheds new light on this domain by unveiling the dynamic role of a specific long noncoding RNA, designated PARAL1, in modulating myeloid dendritic cell differentiation and Toll-like receptor (TLR) signaling pathways. This work broadens our molecular comprehension of how lncRNAs contribute not only to inflammation and immunity but also to the pivotal processes that enable dendritic cells to effectively sense, respond to, and communicate pathogenic insults.

Dendritic cells emerge from monocytes through a complex differentiation process driven by a tightly regulated gene expression program. This transformation equips DCs with the ability to capture antigens, process them, and present these peptides on their surface, thereby activating naive T cells and shaping the adaptive immune response. The researchers embarked on an ambitious project to profile the landscape of lncRNA expression during the monocyte-to-DC (moDC) transition, employing next-generation RNA sequencing technologies to map changes over time with remarkable precision.

Their RNA-seq data revealed a distinct repertoire of differentially expressed lncRNAs that track the trajectory of moDC differentiation. Intriguingly, many of these identified lncRNAs exhibited expression patterns uniquely tailored to dendritic cells rather than being shared with related myeloid lineages such as classically activated M1 or alternatively activated M2 macrophages. This finding underscores the specificity of lncRNA-mediated regulatory networks pertinent to the dendritic cell lineage and suggests specialized molecular circuits that confer unique functional identities.

From this pool of DC-enriched lncRNAs, the team singled out PARAL1 for comprehensive functional analysis. Using targeted RNA interference (RNAi) and overexpression methodologies, they demonstrated that modulating PARAL1 levels had profound effects on the phenotypic markers characteristic of mature dendritic cells. Specifically, PARAL1 silencing diminished the expression of key DC surface markers, while its overexpression enhanced them, signifying a direct role in sculpting the mature dendritic cell state.

Crucially, the impact of PARAL1 extended beyond surface phenotype into the realm of innate immune sensing. Toll-like receptors (TLRs) serve as crucial sentinels detecting conserved pathogen-associated molecular patterns (PAMPs), triggering downstream signaling cascades that orchestrate inflammatory responses. The study revealed that PARAL1 positively regulates the expression of multiple TLRs, thereby amplifying the sensitivity and responsiveness of DCs to microbial challenges.

Upon stimulation with TLR agonists, PARAL1-depleted dendritic cells exhibited markedly reduced phosphorylation levels of central transcription factors including NF-κB, IRF3, and IRF7. These factors are essential mediators of gene expression programs that drive inflammation, antiviral responses, and cytokine production. This observation substantially corroborates the hypothesis that PARAL1 potentiates TLR signaling pathways, acting as a molecular amplifier within the innate immune response circuitry.

The mechanistic dissection went further; silencing PARAL1 precipitated a significant downregulation of a suite of NF-κB-induced genes. Given that NF-κB signaling is a cornerstone of inflammatory gene expression, this downregulation translated into functional consequences: DCs deficient in PARAL1 displayed a time-dependent inhibition of proinflammatory cytokine secretion following TLR stimulus. This reveals that PARAL1 not only influences receptor expression levels but also profoundly affects downstream inflammatory effector functions.

Beyond innate immunity, the ability of dendritic cells to process and present antigenic peptides to T lymphocytes is indispensable for mobilizing adaptive immunity. The study utilized antigen processing assays and T cell co-culture experiments to establish that PARAL1 knockdown significantly impaired these key DC functions. The diminished antigen presentation capacity indicates a critical role of this lncRNA in linking innate sensing to adaptive immune activation, thereby ensuring a coordinated immune defense.

The implications of these findings are far-reaching. By characterizing PARAL1 as a novel regulatory node integrating DC differentiation, TLR-dependent signal transduction, and antigen presentation, the study paves the way for new therapeutic strategies aimed at modulating immune responses. Enhancing PARAL1 function could potentiate vaccine efficacy or boost immunity against infections, whereas inhibiting its activity might ameliorate pathological inflammation seen in autoimmune diseases.

Additionally, the study advances our fundamental understanding of lncRNAs, highlighting their sophistication as more than mere transcriptional noise. Rather, they are dynamic regulators capable of exerting precise control over immune cell identity and function. The specificity of PARAL1’s expression in dendritic cells further exemplifies how lncRNAs can confer lineage- and context-dependent regulatory specificity.

Future investigations are poised to explore the molecular interactome of PARAL1—identifying the RNA-binding proteins, chromatin modifiers, or microRNAs it may engage with to execute its functions. Moreover, determining whether PARAL1 homologs exist in murine models or other species will aid in developing preclinical models to test the translational potential of targeting this lncRNA.

This study is a testament to the power of integrating transcriptomic analyses with functional immunology, revealing previously uncharted layers of immune regulation. As we continue to unravel the complexities of noncoding RNA biology, discoveries such as PARAL1 invigorate the prospect of harnessing the noncoding genome to refine immune therapies, opening new frontiers in precision medicine.

In summary, the characterization of PARAL1 reveals a sophisticated lncRNA that orchestrates multiple facets of dendritic cell biology—driving differentiation, amplifying innate immune receptor pathways, and enabling effective antigen presentation. This multifaceted regulatory module enhances the immune system’s capacity to detect and respond to pathogens, underscoring the intricate molecular choreography underpinning immune defense.

With an ever-expanding appreciation for the regulatory roles of noncoding RNAs, this pioneering work galvanizes efforts to decipher the vast functional repertoire encoded within our genomes. PARAL1 stands out as a paradigm of lncRNA function in immunity, heralding a new era where the noncoding transcriptome becomes a central focus of immunological research and therapeutic innovation.

Subject of Research: Long noncoding RNA regulation of myeloid dendritic cell differentiation and Toll-like receptor signaling

Article Title: Long noncoding RNA PARAL1 regulates myeloid dendritic cell differentiation and TLR signaling

Article References:
Naqvi, R.A., Valverde, A., Shukla, D. et al. Long noncoding RNA PARAL1 regulates myeloid dendritic cell differentiation and TLR signaling. Genes Immun 26, 151–165 (2025). https://doi.org/10.1038/s41435-025-00323-9

Image Credits: AI Generated

DOI: 10.1038/s41435-025-00323-9 (April 2025)

The study, led by Kinsella et al. and published in Nature Microbiology, delves into the role of the autophagy-related protein ATG5 in modulating neutrophil responses during Mtb infection in mice. While ATG5 is traditionally recognized for its key role in autophagy — the cellular recycling pathway crucial for clearing damaged organelles and intracellular bacteria — this research uncovers an autophagy-independent function of ATG5 in neutrophils. Specifically, the researchers demonstrated that ATG5 acts as a critical suppressor of type I interferon (IFN)-mediated neutrophil effector functions, which if unchecked, potentiate inflammation and tissue damage during TB.

Neutrophils are renowned for their rapid recruitment to sites of infection, where they unleash a barrage of antimicrobial weapons. One pivotal effector mechanism is the release of neutrophil extracellular traps (NETs) — web-like chromatin structures laden with antimicrobial proteins that can ensnare and kill pathogens. However, excessive NETosis, the process of NET release, has been implicated in tissue injury and exacerbation of disease in various inflammatory disorders. A central discovery from Kinsella and colleagues’ work is that ATG5 deficiency in neutrophils leads to hyperactivation of a type I IFN-driven pathway that triggers overproduction of NETs during Mtb infection.

By employing sophisticated genetic mouse models — notably Atg5^fl/fl-LysM-Cre mice in which ATG5 is specifically deleted in myeloid cells including neutrophils — the researchers demonstrated a marked increase in early susceptibility to Mtb infection compared to control animals. This susceptibility was closely tied to dysregulated neutrophil responses, characterized by heightened release of NETs mediated through increased activity of peptidylarginine deiminase 4 (PAD4). PAD4 is an enzyme responsible for histone citrullination, a critical step in chromatin decondensation essential for NET formation. Their data revealed that in the absence of ATG5, type I IFN signaling upregulated PAD4-mediated histone citrullination, fueling excessive NET release.

The consequences of this dysregulation extend beyond NETosis. The study also elucidated that ATG5 mitigates neutrophil chemotaxis and swarming — collective migration of neutrophils to infection foci — by suppressing excessive secretion of the chemokine CXCL2, which is inducible by type I IFNs. This dual control by ATG5 serves to temper the amplitude of neutrophil infiltration and activation during the early phase of Mtb infection, thus protecting host tissues from collateral damage. The investigators used a combination of in vivo infection models and in vitro systems to validate these findings, confirming the autophagy-independent role of ATG5 in calibrating the type I IFN neutrophil axis.

Type I interferons, including IFN-α and IFN-β, are central antiviral cytokines that orchestrate complex immune responses. However, their role in bacterial diseases such as TB has been controversial and context-dependent. Elevated type I IFN signatures have been correlated with poor disease prognosis in TB patients, often linked to increased inflammation and immune evasion by the pathogen. The current study provides mechanistic insights into how type I IFNs can drive pathological neutrophil activation via PAD4 and NETosis, a process normally restrained by ATG5. This knowledge enhances our understanding of the dual-edged nature of type I IFN signaling during bacterial infections.

Furthermore, the findings have pragmatic implications for host-directed therapy—a therapeutic approach that aims to modulate the host immune response instead of directly targeting the pathogen. Since excessive neutrophil-mediated inflammation contributes to TB pathology, selectively augmenting the function of ATG5 or mimicking its regulatory effects could offer new avenues to limit immunopathology while preserving antimicrobial defense. Targeting the PAD4-NET pathway or CXCL2-mediated neutrophil recruitment also emerges as a viable strategy to quell damaging inflammation in TB.

Notably, this research underscores the importance of cell-type specific functions of autophagy proteins beyond classical autophagy. ATG5 exemplifies a multifunctional regulator that integrates signals from innate immune pathways to fine-tune neutrophil effector responses. This highlights the complexity of immune regulation at the molecular level and invites further investigation into ATG5’s role in other infectious and inflammatory diseases driven by neutrophils.

In the experimental design, the use of LysM-Cre recombinase allowed for precise deletion of ATG5 in myeloid lineage cells, ensuring that observed phenotypes were attributable to neutrophil dysfunction. The researchers complemented genetic models with functional assays for NET formation, histone citrullination, chemokine secretion, and neutrophil swarming behavior. The robust connection between increased PAD4 activity and NET release in ATG5-deficient neutrophils was corroborated with molecular markers, solidifying the link between ATG5 and suppression of pathological neutrophil activation.

These findings also bring to light the multifaceted consequences of type I IFN signaling during TB. While type I IFNs play protective antiviral roles, their aberrant activation during Mtb infection skews neutrophil function toward damaging hyperinflammation. ATG5 acts as an essential brake, preventing this immune circuit from tipping toward disease exacerbation. This nuanced regulation may explain some of the contradictory clinical observations regarding type I IFN’s impact on TB progression.

Moreover, the study raises intriguing questions about how ATG5 intersects with other signaling pathways in neutrophils and whether its modulation could influence chronic inflammation and fibrosis seen in TB and other lung diseases. Delineating the crosstalk between autophagy-related proteins and immune signaling networks presents fertile ground for future research that may extend beyond infectious disease paradigms.

Given the global burden of tuberculosis, which remains a leading cause of morbidity and mortality worldwide, advancing our understanding of immune regulation at the cellular and molecular level is paramount. Studies like this shed light on fundamental processes governing neutrophil behavior and provide a foundation for the rational design of therapies aimed at enhancing host resilience without exacerbating tissue injury. Such host-directed strategies are particularly appealing in the era of rising antibiotic resistance, where augmenting the body’s intrinsic defenses could complement or circumvent traditional antimicrobial treatments.

In summary, the work by Kinsella et al. identifies ATG5 as a master regulator of neutrophil effector functions modulated by type I interferons during Mtb infection. By restraining PAD4-driven histone citrullination and NET release, and by dampening CXCL2-mediated neutrophil swarming, ATG5 ensures balanced neutrophil activity that limits immunopathology and controls infection. This autophagy-independent function of ATG5 expands the paradigm of immune regulation and opens new avenues for targeted interventions to improve outcomes in tuberculosis and potentially other neutrophil-associated inflammatory diseases.

As tuberculosis remains a global health threat, the implications of this research are profound. Potential therapies derived from this mechanistic insight could transform how clinicians approach the delicate management of inflammation in infectious diseases. Modulating ATG5 pathways or their downstream effectors may enable the development of novel treatments that prevent the damaging hyperinflammatory responses characteristic of severe TB, ultimately reducing morbidity and mortality.

The unveiling of ATG5’s dual role exemplifies how advances in molecular immunology continue to unravel the intricate choreography of host-pathogen interactions and inflammatory regulation. With further validation and translation into human studies, targeting the ATG5-neutrophil axis might soon become a cornerstone of host-directed immunotherapies designed to tame inflammation without compromising microbial control.

Subject of Research: Regulation of neutrophil effector functions by ATG5 during Mycobacterium tuberculosis infection mediated via type I interferon signaling pathways.

Article Title: ATG5 suppresses type I IFN-dependent neutrophil effector functions during Mycobacterium tuberculosis infection in mice.

Article References:
Kinsella, R.L., Sur Chowdhury, C., Smirnov, A. et al. ATG5 suppresses type I IFN-dependent neutrophil effector functions during Mycobacterium tuberculosis infection in mice. Nat Microbiol (2025). https://doi.org/10.1038/s41564-025-01988-8

Image Credits: AI Generated