Letter to the Editor: Epiregulin-EGFR-ERK1/2 signaling as a therapeutic axis for rescuing mesenchymal stem cell dysfunction in inflammatory periodontal niches

Abstract

Periodontitis is a highly prevalent chronic inflammatory disease characterized by progressive destruction of periodontal supporting tissues and remains difficult to treat due to inflammation-induced impairment of regenerative responses. Persistent inflammatory niches suppress mesenchymal stem cell function, limiting the effectiveness of current regenerative therapies. Therefore, identifying factors that restore stem cell activity under inflammatory conditions is of significant clinical importance. We read with interest the study by Zhao et al entitled “Epiregulin enhances periodontal tissue regeneration by promoting bone marrow mesenchymal stem cell functions under inflammatory niches”. This article highlights the regenerative potential of epiregulin, which enhances bone marrow mesenchymal stem cell proliferation, migration, and osteogenic differentiation under inflammatory stress by activating the epidermal growth factor receptor-extracellular signal-regulated kinase signaling pathway, thereby promoting periodontal bone regeneration.

Key Words: Epiregulin; Mesenchymal stem cells; Periodontitis; Inflammatory niche; Epidermal growth factor receptor-extracellular signal-regulated kinase signaling

Core Tip: Epiregulin restores inflammation-impaired bone marrow mesenchymal stem cell function via epidermal growth factor receptor-extracellular signal-regulated kinase signaling, highlighting its potential as a promising therapeutic target for periodontal regeneration under inflammatory conditions. By activating this pathway, epiregulin rescues key stem cell functions, including proliferation, migration, and osteogenic differentiation, that are suppressed by inflammatory stimuli such as tumor necrosis factor-alpha, offering a mechanistically driven and inflammation-resilient strategy for periodontal tissue regeneration and clinical translation.

TO THE EDITOR

Periodontitis is a highly prevalent chronic inflammatory disease affecting nearly 50% of adults worldwide and remains a leading cause of tooth loss due to the progressive destruction of periodontal supporting tissues, including alveolar bone, periodontal ligament, and cementum. The persistent inflammatory microenvironment not only drives tissue breakdown but also compromises endogenous repair mechanisms, limiting the effectiveness of current therapeutic strategies[1].

Despite advances in guided tissue regeneration, biomaterial-based therapies, and stem cell-based approaches, clinical outcomes remain unpredictable in patients with chronic periodontitis. A major limitation is the inflammation-driven dysfunction of mesenchymal stem cells (MSCs), including bone marrow MSCs (BMSCs), which exhibit impaired proliferation, migration, and osteogenic differentiation in cytokine-rich environments[2,3]. These limitations underscore the need for regenerative strategies that remain effective under inflammatory stress.

In this context, Zhao et al[4] recently investigated the role of epiregulin in restoring periodontal regeneration under inflammatory conditions. Epiregulin, a member of the epidermal growth factor family, exerts its biological effects primarily by activating epidermal growth factor receptor (EGFR)-related signaling pathways and modulating tissue repair and inflammation[5].

Unlike conventional regenerative factors, which often lose efficacy in hostile inflammatory niches, epiregulin appears to preserve growth factor signaling and maintain stem cell functionality under inflammatory stress. The study systematically demonstrated that epiregulin counteracted inflammation-induced impairment of BMSCs and promoted regenerative phenotypes relevant to periodontal tissue repair, thereby positioning it as a potential inflammation-resilient therapeutic candidate.

Context and significance of the published study

Periodontal regeneration in the presence of chronic inflammation remains a major unresolved challenge in regenerative dentistry and stem cell-based therapies. Although MSCs possess considerable regenerative potential, their functional impairment within inflammatory periodontal niches has limited their clinical applicability. In this context, the study by Zhao et al[4] is particularly significant, as it directly addresses the critical gap between stem cell regenerative capacity and inflammation-mediated dysfunction.

By demonstrating that epiregulin restores key BMSC functions under inflammatory conditions and enhances periodontal bone regeneration in vivo, the study advances current understanding of how bioactive factors can modulate stem cell behavior within hostile microenvironments. Importantly, the work provides experimental evidence that regenerative failure in periodontitis may be overcome by targeting both stem cells and their inflammatory niche. These findings position epiregulin as a promising adjunct in periodontal regenerative strategies and provide a conceptual framework for the development of inflammation-resilient stem cell-based therapies.

Key mechanistic insights: Epiregulin-EGFR-extracellular signal-regulated kinase axis

A central mechanistic contribution of the study[4] is elucidating the role of the epiregulin-EGFR-extracellular signal-regulated kinase (ERK) signaling axis in mediating epiregulin’s regenerative effects on BMSCs under inflammatory conditions. EGFR signaling is a well-established regulator of cellular proliferation, migration, and survival, and has been closely linked to tissue repair processes across multiple organ systems[6].

The authors demonstrated that epiregulin stimulation led to robust activation of EGFR and subsequent ERK phosphorylation, even in the presence of pro-inflammatory stimuli. This observation is particularly noteworthy, as chronic inflammation is known to suppress growth factor-mediated signaling pathways and impair stem cell functionality. The ability of epiregulin to maintain EGFR-ERK signaling under inflammatory stress suggests a plausible mechanism by which stem cell regenerative capacity may be preserved within hostile periodontal microenvironments[5].

Importantly, pharmacological inhibition of EGFR or ERK signaling markedly attenuated epiregulin-induced enhancement of BMSC proliferation, migration, and osteogenic differentiation. These findings provide strong evidence that the observed regenerative effects are mechanistically dependent on EGFR-ERK pathway activation rather than being merely correlative. While ERK signaling has also been implicated in osteogenic commitment and extracellular matrix production, whether ERK activation alone is sufficient to sustain long-term osteogenic stability under chronic inflammatory conditions remains to be determined[7].

A deeper mechanistic consideration concerns why EGFR-ERK signaling appears particularly pivotal in this context compared with other inflammation-associated pathways such as phosphoinositide 3-kinases (PI3K)/protein kinase B (AKT), signal transducers and activators of transcription 3 (STAT3), or nuclear factor kappa B (NF-κB). While PI3K/AKT and STAT3 primarily regulate survival and anti-apoptotic responses, and NF-κB predominantly orchestrates pro-inflammatory transcriptional programs, the ERK cascade occupies a distinct regulatory position at the intersection of proliferation and lineage commitment[8]. ERK activation has been closely linked to osteogenic differentiation by modulating transcription factors such as runt-related transcription factor 2 and downstream mineralization-associated genes. In inflammatory microenvironments, sustained NF-κB activity frequently suppresses osteogenic programs by prioritizing cytokine-driven stress responses. Targeted EGFR-ERK activation may therefore restore proliferative competence while simultaneously re-engaging osteogenic transcriptional machinery, making this pathway uniquely suited to counteract inflammation-induced stem cell dysfunction[9].

Strengths of the experimental design

A key strength of the study by Zhao et al[4] lies in its carefully structured experimental design, which effectively models the inflammatory microenvironment characteristic of periodontitis. Mouse BMSCs were obtained from Cyagen Biosciences (Guangzhou, Guangdong Province, China) and used at passages 6-8. Mesenchymal identity was confirmed by flow cytometry, demonstrating positive expression of CD29 and CD44 and negative expression of hematopoietic markers CD45 and CD117. Functional multipotency was validated through adipogenic differentiation assessed by Oil Red O staining[4]. To simulate inflammatory stress, cells were pretreated with 10 ng/mL tumor necrosis factor (TNF)-α prior to functional analyses. Recombinant human epiregulin (rhEREG; 25 ng/mL; Abcam, Code No. 50126, United Kingdom) was then administered to evaluate its capacity to restore regenerative function under inflammatory conditions.

Comprehensive functional assays - including scratch wound migration, Transwell chemotaxis, alkaline phosphatase activity, and Alizarin Red staining - demonstrated that rhEREG effectively rescued BMSC proliferation, migration, and osteogenic differentiation suppressed by TNF-α. Mechanistic specificity was rigorously validated by lentiviral-mediated EGFR knockdown with shRNA, with knockdown efficiency confirmed by reverse transcriptase-polymerase chain reaction and western blotting. Downstream signaling analysis revealed selective restoration of ERK1/2 phosphorylation following rhEREG treatment, while p38 mitogen-activated protein kinase (MAPK) and Jun N-terminal kinas pathways remained unaffected. Furthermore, pharmacological inhibition of ERK1/2 using U0126 (20 μM) attenuated the regenerative effects of rhEREG, thereby confirming the specificity of the EGFR-ERK axis in mediating the observed responses[4].

Importantly, translational relevance was enhanced by using a rat model of ligature-induced periodontitis. Local administration of rhEREG significantly enhanced periodontal bone regeneration, as evidenced by micro-computed tomography and histological analyses[4]. The concordance between in vitro mechanistic findings and in vivo regenerative outcomes underscores the robustness of the experimental framework and reinforces the therapeutic rationale for targeting EGFR-ERK signaling in inflammation-associated periodontal bone loss.

Points for discussion and scientific considerations

Importantly, the original study demonstrated statistically significant improvements in BMSC proliferation, migration, and osteogenic differentiation under inflammatory conditions. These in vitro findings were further supported by in vivo validation in a ligature-induced rat periodontitis model, where local epiregulin administration significantly enhanced alveolar bone regeneration, as confirmed by micro-computed tomography and histological analyses. Representative imaging data provided in the original article substantiate these quantitative outcomes and reinforce the robustness of the regenerative effects observed.

The study discussed herein identifies the epiregulin-EGFR-ERK axis as a potentially central regulatory mechanism in inflammation-compromised periodontal regeneration. While multiple signaling pathways - including PI3K/AKT, STAT3, and NF-κB - are activated in inflammatory microenvironments, the ERK cascade is thought to play an important role at the interface of proliferative expansion and osteogenic lineage commitment. PI3K/AKT and STAT3 primarily regulate cellular survival and anti-apoptotic signaling, whereas NF-κB orchestrates pro-inflammatory transcriptional programs that frequently suppress differentiation under chronic inflammatory stress[8]. In contrast, ERK activation has been shown to regulate osteogenic transcription factors such as runt-related transcription factor 2 and downstream mineralization-associated genes[9]. Within inflammatory niches where sustained NF-κB activity prioritizes stress-response pathways over regenerative programs, targeted EGFR-ERK activation may help restore both proliferative competence and osteogenic differentiation capacity[4].

Importantly, therapeutic strategies that solely suppress inflammatory mediators such as NF-κB may alleviate tissue destruction but do not actively restore osteogenic capacity. Likewise, activation of survival pathways such as PI3K/AKT enhances cell viability without necessarily promoting lineage commitment[10]. In contrast, ERK signaling integrates proliferative expansion with osteogenic transcriptional activation, positioning it as a more functionally comprehensive regenerative target. Targeting the EGFR-ERK axis, therefore, offers the strategic advantage of simultaneously restoring cell number and differentiation potential, rather than merely preventing inflammatory damage. This distinction underscores why the epiregulin-EGFR-ERK pathway may be particularly pivotal in inflammation-associated periodontal regeneration.

Supporting evidence from other dental stem cell populations further refines and contextualizes this mechanistic perspective. Cao et al[6] demonstrated that epiregulin promotes proliferation of stem cells from the dental apical papilla via activation of MEK/ERK and Jun N-terminal kinas signaling pathways, indicating a conserved pro-proliferative function across dental MSC subsets. In contrast, Ran et al[7] reported that depletion of endogenous EREG enhanced osteo/dentinogenic differentiation of dental pulp stem cells under inflammatory conditions through modulation of p38 MAPK and ERK signaling, suggesting that epiregulin may exert bidirectional or stage-dependent effects on lineage commitment depending on cellular identity and inflammatory context. When considered alongside the periodontal BMSC findings by Zhao et al[4], these studies collectively point toward a context-dependent regulatory role for epiregulin, in which proliferative support and differentiation outcomes are shaped by MAPK pathway balance, temporal signaling dynamics, and inflammatory intensity. Reconciling these observations underscores the importance of defining cell-specific and stage-specific signaling thresholds in the design of future periodontal regenerative strategies and highlights the nuanced biological complexity underlying EGFR-ERK-mediated tissue repair[4].

Building upon these mechanistic insights, we propose a dual-action conceptual framework in which epiregulin may not only restore stem cell function but also potentially modulate the inflammatory microenvironment. However, this hypothesis requires further experimental validation. Through EGFR-ERK activation in BMSCs, epiregulin restores intrinsic regenerative capacity under cytokine-induced suppression. Concurrently, EGFR signaling in resident immune or stromal cells may influence cytokine production and inflammatory resolution pathways, potentially attenuating excessive NF-κB-driven responses. Within this integrated model, epiregulin may coordinate intrinsic stem cell activation with partial recalibration of the microenvironment, thereby contributing to a more permissive regenerative milieu. A testable hypothesis emerging from this framework is that epiregulin treatment may simultaneously suppress TNF-α-mediated NF-κB activation while enhancing ERK-dependent osteogenic transcription within the same inflammatory context. Experimental validation using immune-stem cell co-culture systems, pathway-specific inhibition assays, and cytokine profiling would help clarify this proposed bidirectional regulatory mechanism.

Despite the compelling findings, several limitations warrant consideration. The in vitro inflammatory conditions represent simplified models that do not fully capture the complexity of chronic periodontal lesions, which involve dynamic interactions among immune cells, stromal components, and the extracellular matrix. In addition, signaling pathway crosstalk remains incompletely defined, particularly involving PI3K/AKT, NF-κB, and p38 MAPK pathways. While the EGFR-ERK axis appears central, interactions with pathways such as PI3K/AKT, NF-κB, and p38 MAPK may influence overall cellular responses. Furthermore, although short-term osteogenic outcomes are encouraging, the long-term stability and functional integration of regenerated tissue remain to be established. Importantly, sustained activation of EGFR signaling has been associated with proliferative effects in other contexts, raising potential safety considerations that warrant careful evaluation. Addressing these limitations will be critical for translating epiregulin-based strategies into clinical applications.

Translational considerations and clinical perspective

Translating these findings into clinical application will require careful optimization of delivery strategies, dosing parameters, and safety profiles. Localized and temporally controlled approaches will be particularly important to maximize therapeutic efficacy while minimizing potential adverse effects associated with sustained EGFR activation[11].

From a clinical perspective, these findings are particularly relevant within the evolving framework of personalized regenerative medicine. Periodontitis exhibits substantial heterogeneity in inflammatory burden and tissue destruction among patients. Therapeutic strategies capable of restoring stem cell function within inflammation-compromised niches may therefore enable stratified or inflammation-adapted regenerative interventions. By integrating pathway-specific activation with potential microenvironmental modulation, epiregulin-based approaches may represent a next-generation strategy that extends beyond conventional osteoinductive paradigms and addresses a critical barrier in periodontal regeneration - namely, inflammation-induced stem cell dysfunction.

Future directions

Future investigations should extend beyond simplified inflammatory models to incorporate more physiologically relevant systems. For instance, co-culture models integrating BMSCs with macrophages or T lymphocytes under inflammatory stimulation would help delineate how epiregulin modulates immune-stem cell crosstalk within periodontal niches. Temporal signaling analyses examining early vs sustained EGFR-ERK activation could clarify whether transient or prolonged pathway engagement optimally supports osteogenesis without inducing adverse effects[12]. Additionally, three-dimensional inflammatory organoid models or microfluidic “periodontitis-on-a-chip” platforms may better recapitulate cytokine gradients and extracellular matrix interactions observed in vivo[13].

Biomaterial-assisted delivery systems such as injectable hydrogels, collagen-based scaffolds, or nanoparticle-mediated controlled-release platforms could be explored to localize epiregulin activity and minimize systemic exposure. Dose-response and long-term safety studies in large-animal models will be critical for evaluating regenerative durability and potential off-target effects of sustained EGFR activation[14]. These technically defined strategies may provide a rational framework for advancing epiregulin-based periodontal regeneration toward clinical implementation.

CONCLUSION

In conclusion, the study by Zhao et al[4] demonstrates that epiregulin restores BMSC proliferation, migration, and osteogenic differentiation under inflammatory conditions by activating the EGFR-ERK signaling pathway, thereby enhancing periodontal bone regeneration. Beyond these findings, this article proposes that epiregulin may also influence the inflammatory microenvironment; however, this remains to be experimentally validated. These observations highlight inflammation-adapted regenerative targeting as a promising therapeutic strategy.