Modulation of the FXR/TLR4 Pathway and Ferroptosis in NiONP-Induced Collagen Formation: Insights from hsa_circ_0001944

Study Background and Research Question

Nickel oxide nanoparticles (NiONPs) are increasingly prevalent in industrial applications, raising concerns about their potential to induce organ toxicity, particularly liver fibrosis. Hepatic stellate cells (HSCs), when activated in response to injury or toxicants, play a central role in fibrogenesis through excessive collagen deposition. While previous studies have implicated non-coding RNAs, nuclear receptor pathways, and ferroptosis—a form of iron-dependent cell death—in liver injury, the interplay among these mechanisms in the context of NiONP exposure remains poorly understood. The central research question addressed by Zhou et al. (2025) is: How does the circular RNA hsa_circ_0001944 regulate the FXR/TLR4 signaling axis and ferroptosis to influence NiONP-induced collagen formation in human HSCs?

Key Innovation from the Reference Study

The core innovation of this work lies in delineating a mechanistic link between the non-coding RNA hsa_circ_0001944, the farnesoid X receptor (FXR), toll-like receptor 4 (TLR4), and ferroptosis in the setting of NiONP-induced fibrogenesis. By integrating bioinformatics with cellular models, the authors demonstrate that hsa_circ_0001944 positively regulates FXR expression, which in turn suppresses TLR4 and facilitates ferroptotic cell death, collectively attenuating collagen deposition in LX-2 cells. This represents a significant advance in understanding the molecular underpinnings of environmentally induced liver fibrosis and positions the FXR/TLR4/ferroptosis axis as a promising target for antifibrotic research.

Methods and Experimental Design Insights

The study employed a multifaceted approach combining in vivo and in vitro models. Initially, rat models of liver fibrosis and the human LX-2 HSC line were used to characterize the effects of NiONP exposure on FXR, TLR4, and ferroptosis markers. Key experimental interventions included:

• Treatment of LX-2 cells with NiONPs to induce collagen deposition and simulate fibrotic activation.
• Pharmacological modulation using the non-steroidal FXR agonist GW4064, TLR4 inhibitor TAK-242, and ferroptosis inducer Erastin.
• Overexpression and knockdown of hsa_circ_0001944 to define its regulatory influence on FXR and downstream pathways.
• Assessment of ferroptosis via markers such as glutathione peroxidase 4 (GPX4), glutathione (GSH), and lipid peroxidation byproducts.
• Quantification of collagen I and III (COL1A1, COL3A1) as readouts of fibrogenesis.
• Bioinformatics prediction and experimental validation of the circRNA-FXR regulatory relationship.

This design allowed for both mechanistic dissection and functional validation of the implicated pathways.

Protocol Parameters

• NiONP challenge: LX-2 cells were exposed to nickel oxide nanoparticles at concentrations inducing fibrogenic activation, as modeled in vitro.
• FXR activation: GW4064 was applied to LX-2 cells at nanomolar concentrations consistent with its EC₅₀ for FXR activation (reported at 15–90 nM), to probe downstream effects on TLR4 and ferroptosis markers.
• TLR4 inhibition: TAK-242 was used alongside GW4064 to dissect the relationship between FXR activation and TLR4 signaling.
• Ferroptosis modulation: Erastin was employed to validate the role of ferroptosis in collagen deposition outcomes.
• CircRNA manipulation: Overexpression vectors for hsa_circ_0001944 were transfected into LX-2 cells to assess regulatory impacts on the FXR/TLR4/ferroptosis axis and collagen synthesis.

Core Findings and Why They Matter

The main findings of this study provide new mechanistic insight into how environmental nanoparticles can drive fibrogenesis via complex molecular crosstalk:

• NiONP exposure decreased FXR expression and increased TLR4 expression in both rat liver tissues and LX-2 cells, correlating with increased collagen deposition and alterations in ferroptosis-related markers (Zhou et al., 2025).
• Pharmacological FXR activation with GW4064 restored FXR levels, suppressed TLR4 expression, enhanced ferroptosis features (e.g., decreased GPX4 and GSH, increased lipid peroxidation), and significantly reduced collagen I/III deposition in LX-2 cells.
• TLR4 inhibition (TAK-242) and induction of ferroptosis (Erastin) independently alleviated collagen deposition, supporting the notion that both TLR4 suppression and ferroptosis activation are antifibrotic in this context.
• hsa_circ_0001944 was downregulated by NiONP exposure. Overexpression of this circRNA increased FXR, decreased TLR4, promoted ferroptosis, and reduced collagen accumulation, thus establishing a regulatory axis from circRNA to nuclear receptor to innate signaling and cell death.

Collectively, these results suggest that boosting FXR activity—either via endogenous regulation by circRNAs or with non-steroidal agonists—may offer a targeted strategy to limit fibrosis following nanoparticle exposure. The dual effects on both inflammatory and ferroptotic pathways point to a multi-modal mechanism of antifibrotic protection.

Comparison with Existing Internal Articles

Several internal resources have previously highlighted the utility of GW4064 as a selective farnesoid X receptor agonist in metabolic and fibrosis research. For example, a recent thought-leadership article (Strategic FXR Activation with GW4064) discusses how GW4064 enables precise dissection of the FXR/TLR4/ferroptosis axis, echoing the mechanistic insights from the current reference study. Another guide (GW4064: Non-Steroidal FXR Agonist for Advanced Metabolic Assays) provides detailed experimental workflows for FXR pathway interrogation in both metabolic and fibrosis models, reinforcing the protocol parameters validated by Zhou et al. Notably, these internal articles emphasize GW4064's low nanomolar potency and its benchmark status for FXR activation in cholesterol and triglyceride regulation—features directly leveraged in the present study to parse downstream signaling effects. However, the current reference paper takes an important step further by mapping the upstream regulation (via hsa_circ_0001944) and the downstream crosstalk with ferroptosis, providing a more comprehensive model for antifibrotic intervention.

Limitations and Transferability

While the study delivers a compelling mechanistic framework, some limitations should be noted:

• Model specificity: Most experiments were performed in the LX-2 cell line, a widely used but in vitro system. In vivo validation beyond initial rat studies will be necessary for translational relevance.
• Nanoparticle relevance: The findings are specific to NiONP-induced fibrogenesis; applicability to other fibrotic drivers or nanoparticle types remains to be established.
• CircRNA-FXR axis: While bioinformatics and overexpression studies suggest regulation, additional mechanistic work is needed to confirm direct molecular interactions and rule out parallel pathways.
• Therapeutic translation: GW4064, while effective as a research tool, has solubility and stability constraints (product information), limiting its suitability for in vivo or clinical application.

Despite these caveats, the study provides a valuable template for dissecting nuclear receptor signaling and ferroptosis in fibrogenic responses.

Research Support Resources

Researchers interested in modeling FXR activation in hepatic stellate cell or fibrosis assays may utilize GW4064 (SKU B1527), a potent non-steroidal FXR agonist supplied by APExBIO, to replicate or extend the workflows detailed in this study. Its high selectivity and nanomolar potency for FXR make it a standard reference compound in metabolic and fibrotic research. However, users should be aware of its limited solubility and stability, and consult recent methodological guides (scenario-driven best practices) for optimal experimental design. GW4064 is best suited for in vitro and mechanistic studies of FXR signaling pathways relevant to cholesterol, triglyceride, and bile acid metabolism.