Inhibition of IRF3 expression reduces TGF-β1-induced proliferation of hepatic stellate cells

STING inhibitors and degraders: Potential therapeutic agents in inflammatory diseases

The regulation of the STING (stimulator of interferon genes) pathway represents a promising target for a range of inflammatory diseases. This review provides an overview of the structure of STING and discusses the mechanisms by which the cyclic GMP-AMP synthase (cGAS)-STING pathway is associated with various autoinflammatory and autoimmune diseases. We explore how targeting STING inhibition or degradation can alleviate excessive inflammatory signaling and improve efficacy. Emerging strategies include inhibiting STING expression by covalently binding compounds or using ligands that target the binding pocket. In addition, selective degradation of STING via the ubiquitin-proteasome system or the lysosomal pathway shows promise. In addition, we explore the implications of modulating the cGAS-STING pathway in the context of various inflammatory diseases. Finally, we summarize the chemical properties of recently developed STING compounds and their potential clinical applications. By comprehensively reviewing the current understanding of the role of STING in inflammation and the therapeutic potential of targeting STING, we aim to identify new avenues of intervention that could improve outcomes for patients with inflammatory diseases. This review highlights the important role of STING in the regulation of inflammation and its potential as a target for innovative therapeutic strategies.

Stromal Interferon Regulatory Factor 3 Can Antagonize Human Papillomavirus Replication by Supporting Epithelial-to-Mesenchymal Transition

Epithelia contribute to the innate immune system through barrier formation and through signaling to immune cells. When the barrier is breached, epithelial cells undergo epithelial-to-mesenchymal transition (EMT) as part of the wound healing process. EMT is largely directed by signals from the stromal microenvironment, including transforming growth factor beta (TGFβ1), and antagonizes normal epithelial differentiation. How EMT and innate immunity may be connected molecularly has not been explored, although both processes are likely to occur simultaneously. Keratinocytes are the host cell type for human papillomaviruses (HPV), which can induce EMT in certain conditions but also depend on differentiation for their replication. We previously found that the innate immune factor interferon regulatory factor 3 (IRF3) inhibits epithelial differentiation and reduces the expression of HPV16 late genes. Here we report that IRF3 in the stroma compartment promotes an EMT-like pattern of gene expression in an HPV16-containing epithelium. The depletion of stromal IRF3 resulted in the downregulation of TGFβ1-related signaling in both the stroma and epithelium. IRF3 binds to the TGFB1 promoter in human foreskin fibroblasts and is necessary for TGFB1 mRNA production. Because an EMT-like state is unfavorable for differentiation-dependent HPV16, we observed that all EMT markers examined were reduced in the presence of episomal HPV16. Together, we show that stromal IRF3 can disrupt epithelial differentiation and act as an anti-HPV factor through the regulation of EMT, linking wound healing and immunity.

STING Activation in Various Cell Types in Metabolic Dysfunction-Associated Steatotic Liver Disease

BACKGROUND

During the hepatic histological progression in metabolic dysfunction-associated steatotic liver disease (MASLD), the immunological mechanisms play a the pivotal role, especially when progressing to metabolic dysfunction-associated steatohepatitis (MASH). The discovery of the stimulator of interferon genes (STING) marked a significant advancement in understanding the immune system.

METHODS

We searched literature on STING involved in MASLD in PubMed to summarise the role of intrahepatic or extrahepatic STING signal pathways and the potential agonists or inhibitors of STING in MASLD.

RESULTS

Besides inflammation and type I interferon response induced by STING activation in the intrahepatic or extrahepatic immune cells, STING activation in hepatocytes leads to protein aggregates and lipid deposition. STING activation in hepatic macrophages inhibits autophagy in hepatocytes and promotes hepatic stellate cells (HSCs) activation. STING activation in HSCs promotes HSC activation and exacerbates liver sinusoidal endothelial cells (LSECs) impairment. However, it was also reported that STING activation in hepatic macrophages promotes lipophagy in hepatocytes and STING activation in HSCs leads to HSC senescence. STING activation in LSEC, inhibits angiogenesis. For extrahepatic tissue, STING signalling participates in the regulation of the intestinal permeability, intestinal microecology and insulin action in adipocytes, which were all involved in the pathogenesis of MASLD.

CONCLUSION

There're plenty of STING ligands in MASLD. How STING activation affects the intercellular conversation in MASLD deserves thorough investigation.

Mairin from Huangqi Decoction Mitigates Liver Cirrhosis through Suppression of Pro-inflammatory Signaling Pathways: A Network Pharmacology and Experimental Study

Background::

Liver cirrhosis is a consequence of various chronic liver conditions and may lead to liver failure and cancer. Huangqi Decoction (HQD) is a Traditional Chinese Medicine (TCM) effective for treating liver conditions, including cirrhosis. Therefore, both the active ingredients and the pharmacological actions of HQD deserve further exploration. The active components and pharmacological actions of HQD in preventing and treating liver cirrhosis were investigated using network pharmacology. The actions of the principal active ingredient, Mairin, were investigated empirically.

Methods::

Using network pharmacology, the critical components of HQD were identified from multiple databases, and UPLC screening and targets were investigated using Swiss Target Prediction. Targets associated with liver cirrhosis were identified using the GeneCards database. GO and KEGG enrichment analysis of targets that overlapped between HQD and cirrhosis were analyzed in DAVID, and a “component-target-pathway” network for HQD was created in Cytoscape 3.7.2. The biological functions of the key active component, Mairin, were investigated using in silico docking, cell experiments, and evaluation in a carbon-tetrachloride (CCl4)-induced mouse model of liver cirrhosis. CCK-8 and F-actin assays were used to measure cell viability and hepatic stellate cell (HSC) activation, respectively; fibrosis was measured by histological and immunohistochemical evaluations, and the levels of the cirrhosis-related protein α-SMA and predicted essential target proteins in the PI3KAKT, NFκB-IκBα, and NLRP3-IL18 pathways were determined by western blotting.

Results::

Fourteen active HQD components, 72 targets, and 10 pathways common to HQD and cirrhosis were identified. Network analysis indicated the association of Mairin with most targets and with inflammation through the PI3K/Akt, NF-κB, and NLRP3 pathways. Dose-dependent reductions in the activation and proliferation of LX-2 cells after Mairin treatment were observed. Mairin reversed the histopathological changes in the livers of cirrhosis model mice. Mairin also significantly reduced the α-SMA, NF-κB, IκBα, NLRP3, and IL-18 protein levels while increasing those of p- PI3K and p-Akt, suggesting that Mairin mitigates liver cirrhosis through modulation of the PI3KAKT, NFκB-IκBα, and NLRP3-IL18 pathways.

Conclusions::

Using a comprehensive investigative process involving network pharmacology, bioinformatics, and experimental verification, it was found that Mairin, an active component of HQD, may be useful for developing specific treatments for preventing and treating liver cirrhosis.

Hepatocyte GPCR signaling regulates IRF3 to control hepatic stellate cell transdifferentiation

BACKGROUND

Interferon Regulatory Factor 3 (IRF3) is a transcription factor that plays a crucial role in the innate immune response by recognizing and responding to foreign antigens. Recently, its roles in sterile conditions are being studied, as in metabolic and fibrotic diseases. However, the search on the upstream regulator for efficient pharmacological targeting is yet to be fully explored. Here, we show that G protein-coupled receptors (GPCRs) can regulate IRF3 phosphorylation through of GPCR-Gα protein interaction.

RESULTS

IRF3 and target genes were strongly associated with fibrosis markers in liver fibrosis patients and models. Conditioned media from MIHA hepatocytes overexpressing IRF3 induced fibrogenic activation of LX-2 hepatic stellate cells (HSCs). In an overexpression library screening using active mutant Gα subunits and Phos-tag immunoblotting, Gαs was found out to strongly phosphorylate IRF3. Stimulation of Gαs by glucagon or epinephrine or by Gαs-specific designed GPCR phosphorylated IRF3. Protein kinase A (PKA) signaling was primarily responsible for IRF3 phosphorylation and Interleukin 33 (IL-33) expression downstream of Gαs. PKA phosphorylated IRF3 on a previously unrecognized residue and did not require reported upstream kinases such as TANK-binding kinase 1 (TBK1). Activation of Gαs signaling by glucagon induced IL-33 production in hepatocytes. Conditioned media from the hepatocytes activated HSCs, as indicated by α-SMA and COL1A1 expression, and this was reversed by pre-treatment of the media with IL-33 neutralizing antibody.

CONCLUSIONS

Gαs-coupled GPCR signaling increases IRF3 phosphorylation through cAMP-mediated activation of PKA. This leads to an increase of IL-33 expression, which further contributes to HSC activation. Our findings that hepatocyte GPCR signaling regulates IRF3 to control hepatic stellate cell transdifferentiation provides an insight for understanding the complex intercellular communication during liver fibrosis progression and suggests therapeutic opportunities for the disease. Video Abstract.

Oroxylin A activates ferritinophagy to induce hepatic stellate cell senescence against hepatic fibrosis by regulating cGAS-STING pathway

In recent study, the pathological mechanism of liver fibrosis has been associated with hepatic stellate cell (HSC) senescence. Targeted induction of HSC senescence is considered as a new strategy to remove activated HSC. Nevertheless, little is known about the role of ferritinophagy in cell senescence. In this study, we reported that Oroxylin A from Scutellaria baicalensis Georgi can regulate HSC senescence induced by ferritinophagy through the cGAS-STING pathway to reduce liver fibrosis. We first found that Oroxylin A treatment alleviated the pathological changes of liver fibrosis, reduced collagen deposition, and significantly inhibited liver fibrosis. Interestingly, Oroxylin A treatment can activate HSC ferritinophagy and further induce HSC senescence. It is noteworthy that ferritinophagy is mediated by nuclear receptor coactivator 4 (NCOA4), an important selective mediator for ferritin degradation. NCOA4 siRNA causes Oroxylin A to reduce the degree of telomerase activity in HSCs and induce the expression of senescence markers, such as SA-β-Gal and related marker proteins. Importantly, the cGAS-STING pathway is crucial to the activation of HSC ferritinophagy by Oroxylin A. Specifically, Oroxylin A can promote the secretion of cytokines like IFN-β by the cGAS-STING pathway to regulate ferritinophagy. cGAS siRNA resulted in a dose-dependent decrease in the expression of NCOA4, a significant reduction in the expression level of autophagy-related phenotype, and a decrease in the content of ROS and iron ions in HSCs. In conclusion, we identified the new role of ferritinophagy and the GAS-STING pathway in Oroxylin A -mediated anti-hepatic fibrosis.

Metabonomic analysis of the anti-hepatic fibrosis effect of Ganlong capsules

Context: Hepatic fibrosis is a progressive condition, often attributed to metabolic disorders, which may promote cirrhosis and liver cancer. Ganlong capsules derived from Periplaneta Americana have been shown to have a therapeutic effect on liver fibrosis but little is known about the molecular mechanisms involved. Objective: To investigate the metabolic modulations produced by Ganlong capsules in liver fibrosis. Methods: A carbon tetrachloride- (CCl₄) treated rat model of liver fibrosis was constructed and Ganlong capsules administered. Levels of serum liver enzymes and pathological changes to the liver were evaluated. Non-targeted metabolomics of liver, serum and urine were used to investigate metabolic regulatory mechanisms. Results: Ganlong capsules reduced serum levels of liver enzymes and improved pathological changes in the rat model of fibrosis. Non-targeted metabolomics showed that Ganlong capsules ameliorated pathways of glycerophospholipid, linoleic acid, pyrimidine, glycine, butyric acid, valine, serine, threonine and arachidonic acid metabolism and biosynthesis of leucine and isoleucine. Such pathways influence the development of CCl₄-induced liver fibrosis. Conclusion: Ganlong capsules had an anti-fibrotic hepatoprotective effect and regulated lipid, butyric acid, amino acid and arachidonic acid metabolism.

Anthocyanin-Rich Extract of Red Cabbage Attenuates Advanced Alcohol Hepatotoxicity in Rats in Association with Mitochondrial Activity Modulation

Aim

The liver is the main target for alcohol-induced injury. The aims of this work were to carry out further research into the mechanisms of liver damage induced by long-term administration of high-dose ethanol to rats and to evaluate the hepatoprotective potential of red cabbage (Brassica oleracea var. capitata f. rubra) anthocyanins (RCE).

Material/Methods

Male albino Wistar rats were divided into four groups. Group 1 was the control. Groups 2 through 4 received ethanol (4 g/kg body weight, 8 weeks). Group 3 received 11 mg RCE/kg and Group 4 received 22 mg RCE/kg. Dry lyophilised RCE was prepared from fresh red cabbage and analysed. We then evaluated the liver histology, mitochondrial respiration, and biochemical and immunological parameters in these groups of rats.

Results

The rat intoxication caused steatohepatitis characterised by macro- and microvesicular steatosis, ballooning and fatty liver dystrophies, lymphocytic infiltration, neutral lipid accumulation, and elevations of the serum activities of the liver injury marker enzymes. The treatment of alcohol-administered rats with RCE (mainly, cyanidin-3-diglucoside-5-glucoside, cyanidin-3-coumaroylrutinoside-5-hexoside, cyanidin-3-feruloylrutinoside-5-hexoside, delphinidin-3-feruloylrutinoside-hexoside) dose-dependently alleviated these pathological changes: The sizes of hepatocyte lipid vacuoles and the inflammatory signs were decreased, and the levels of the rat serum biochemical markers of liver injury, proinflammatory cytokines TNFα and IL-6, and the adipokine leptin (and not TGFβ) were significantly reversed. The RCE administration during intoxication completely recovered the changed liver mitochondria respiration rates and the ADP/O coefficient, as well as the phagocytic index and neutrophil metabolic activity in the blood. In experiments in vitro, RCE (13.6 μg/ml) modulated the respiratory parameters of isolated rat liver mitochondria, dissipated mitochondrial membrane potential, and inhibited the Ca2+-induced mitochondrial permeability transition.

Conclusion

The red cabbage anthocyanins could be useful for treatment of alcoholic liver injury due to their Ca2+-ionophoric/protonophoric activity, influence on Ca2+ homeostasis, and improving mitochondrial functions and inflammatory status.

The Cytosolic DNA-Sensing cGAS-STING Pathway in Liver Diseases

Inflammation is regulated by the host and is a protective response activated by the evolutionarily conserved immune system in response to harmful stimuli, such as dead cells or pathogens. cGAS-STING pathway is a vital natural sensor of host immunity that can defend various tissues and organs against pathogenic infection, metabolic syndrome, cellular stress and cancer metastasis. The potential impact of cGAS-STING pathway in hepatic ischemia reperfusion (I/R) injury, alcoholic/non-alcoholic steatohepatitis (ASH), hepatic B virus infection, and other liver diseases has recently attracted widespread attention. In this review, the relationship between cGAS-STING pathway and the pathophysiological mechanisms and progression of liver diseases is summarized. Additionally, we discuss various pharmacological agonists and antagonists of cGAS-STING signaling as novel therapeutics for the treatment of liver diseases. A detailed understanding of mechanisms and biology of this pathway will lay a foundation for the development and clinical application of therapies for related liver diseases.

Multiple Roles of Black Raspberry Anthocyanins Protecting against Alcoholic Liver Disease

This study aimed to investigate the protective effect of black raspberry anthocyanins (BRAs) against acute and subacute alcoholic liver disease (ALD). Network analysis and docking study were carried out to understand the potential mechanism. Thereafter, the serum biochemical parameters and liver indexes were measured, the histopathological changes of the liver were analyzed in vivo. The results showed that all tested parameters were ameliorated after the administration of BRAs with alcohol. Meanwhile, there was increased protein expression of NF-κB and TGF-β in extracted livers, which was associated with hepatitis and hepatic fibrosis. Furthermore, BRAs and cyanidin-3-O-rutinoside exhibited cytotoxic effects on t-HSC/Cl-6, HepG2, and Hep3B and induced the apoptosis of HepG2 cells; downregulated the protein expression level of Bcl-2; upregulated the level of Bax; and promoted the release of cytochrome C, cleaved caspase-9, cleaved caspase-3, and cleaved PARP in HepG2 cells. In addition, the antioxidant activity of BRAs was tested, and the chemical components were analyzed by FT-ICR MS. The results proved that BRAs exert preventive effect on ALD through the antioxidant and apoptosis pathways.

(2-Carboxyethyl) dimethylsulfonium bromide supplementation in non-fish meal diets for on-growing grass carp (Ctenopharyngodon idella): Beneficial effects on immune function of the immune organs via modulation of NF-κB and TOR signalling pathway

The immune function of immune organs is extremely crucial for maintaining organism health status, which ultimately affects fish growth. Our previous study has found that dietary supplementation of (2-carboxyethyl)dimethylsulfonium Bromide (Br-DMPT) in non-fish meal (NFM) diet could promote the growth of grass carp (Ctenopharyngodon idella), whereas the underlying reason or mechanism for this results is largely unclear. Herein, we further explored whether dietary supplementation of Br-DMPT promoted fish growth is connected with the enhanced immune function in the immune organs (the head kidney, spleen and skin). In this study, 540 fish (216.49 ± 0.29 g) were irregularly distributed to six groups with three replicates (30 fish replicate^-1) and fed corresponding diets group containing a fish meal (FM) diet group and five different NFM diets supplemented with gradational Br-DMPT (0-520.0 mg/kg level) group for 60 days. After the 60-days feeding trial, 8 fish from each replicate were selected and then conducted a challenge test with A. hydrophila for 14 days. Our results indicated that in the NFM diets, appropriate Br-DMPT: (1) significantly decreased the morbidity of skin haemorrhage and lesion after A. hydrophila infection (P < 0.05). (2) significantly improved the innate and adaptive immune components (lysozyme, complement 3, immunoglobulin M and antibacterial peptides et al.) (P < 0.05). (3) increased the gene expressions of main anti-inflammatory cytokines partially by referring to TOR signalling pathway, and decreased the gene expressions of main pro-inflammatory cytokines partially by referring to NF-kB signalling pathway (P < 0.05). Strikingly, no statistical difference could be found in the most of above immune parameters between 260.0 mg/kg Br-DMPT diet group and FM diet group (P > 0.05). Taken together, in non-fish meal diet, appropriate supplementation of Br-DMPT could improve the disease resistance capacity, non-specific immunity and ameliorate inflammation, and simultaneously could mitigate these adverse effects induced by the non-fish meal diet in fish immune organs. Moreover, this study may be helpful to decipher the underlying mechanisms of how Br-DMPT promote fish growth by immune organs and also provide scientific theoretical evidence for the future application of Br-DMPT as a new immunopotentiator in aquaculture industry.

Platyconic Acid A, Platycodi Radix-Derived Saponin, Suppresses TGF-1-induced Activation of Hepatic Stellate Cells via Blocking SMAD and Activating the PPAR Signaling Pathway

Platycodi radix is a widely sold health food worldwide, which contains numerous phytochemicals that are beneficial to health. Previously, we reported that saponin from the roots of Platycodi radix-derived saponin inhibited toxicant-induced liver diseases. Nevertheless, the inhibitory effect of platyconic acid A (PA), the active component of Platycodi radix-derived saponin, on the anti-fibrotic activity involving the SMAD pathway remains unclear. We investigated the inhibitory effects of PA on TGF-β1-induced activation of hepatic stellate cells (HSCs). PA inhibited TGF-β1-enhanced cell proliferation, as well as expression of α-SMA and collagen Iα1 in HSC-T6 cells. PA suppressed TGF-β1-induced smad2/3 phosphorylation and smad binding elements 4 (SBE4) luciferase activity. Reversely, PA restored TGF-β1-reduced expression of smad7 and peroxisome proliferator-activated receptor (PPAR)γ. PA also repressed TGF-β1-induced phosphorylation of Akt and MAPKs. In summary, the results suggest that the inhibitory effect of PA on HSCs occurs through the blocking of SMAD-dependent and SMAD-independent pathways, leading to the suppression of α-SMA and collagen Iα1 expression.

Research progress on the anti-hepatic fibrosis action and mechanism of natural products

Hepatic fibrosis is the most common pathological feature of most chronic liver diseases, and its continuous deterioration gradually develops into liver cirrhosis and eventually leads to liver cancer. At present, there are many kinds of drugs used to treat liver fibrosis. However, Western drugs tend to only target single genes/proteins and induce many adverse reactions. Most of the mechanisms and active ingredients of traditional Chinese medicine (TCM) are not clear, and there is a lack of unified diagnosis and treatment standards. Natural products, which are characterized by structural diversity, low toxicity, and origination from a wide range of sources, have unique advantages and great potential in anti-liver fibrosis. This article summarizes the work done over the previous decade, on the active ingredients in natural products that are reported to have anti-hepatic fibrosis effects. The effective anti-hepatic fibrosis ingredients identified can be generally divided into flavonoids, saponins, polysaccharides and alkaloids. Mechanisms of anti-liver fibrosis include inhibition of liver inflammation, anti-lipid peroxidation injury, inhibition of the activation and proliferation of hepatic stellate cells (HSCs), modulation of the synthesis and secretion of pro-fibrosis factors, and regulation of the synthesis and degradation of the extracellular matrix (ECM). This review provides suggestions for the development of anti-hepatic fibrosis drugs.

Novel Insights on Notch signaling pathways in liver fibrosis

Liver fibrosis is characterized by an increased and altered deposition of extracellular matrix (ECM) proteins that make up excessive tissue scarring and promote chronic liver injury. Activation of hepatic stellate cells (HSCs) is a pivotal cellular event in the progression of liver fibrosis. However, the mechanisms involved in the development of liver fibrosis are only now beginning to be unveiled. The Notch pathway is a fundamental and highly conserved pathway able to control cell-fate, including cell proliferation, differentiation, apoptosis, regeneration and other cellular activities. Recently, the deregulation of Notch cascade has been found involved in many pathological processes, including liver fibrosis. These data give evidence for a role for Notch signaling in liver fibrosis. In addition，more and more date are available on the role of Notch pathways in the process. Therefore, this review focuses on the current knowledge about the Notch signaling pathway, which dramatically takes part in HSC activation and liver fibrosis, and look ahead on new perspectives of Notch signaling pathway research. Furthermore, we will summarize this new evidence on the different interactions in Notch signaling pathway-regulated liver fibrosis, and support the potentiality of putative biomarkers and unique therapeutic targets.

Editor's Highlight: Candidate Risk Factors and Mechanisms for Tolvaptan-Induced Liver Injury Are Identified Using a Collaborative Cross Approach

Clinical trials of tolvaptan showed it to be a promising candidate for the treatment of Autosomal Dominant Polycystic Kidney Disease (ADPKD) but also revealed potential for idiosyncratic drug-induced liver injury (DILI) in this patient population. To identify risk factors and mechanisms underlying tolvaptan DILI, 8 mice in each of 45 strains of the genetically diverse Collaborative Cross (CC) mouse population were treated with a single oral dose of either tolvaptan or vehicle. Significant elevations in plasma alanine aminotransferase (ALT) were observed in tolvaptan-treated animals in 3 of the 45 strains. Genetic mapping coupled with transcriptomic analysis in the liver was used to identify several candidate susceptibility genes including epoxide hydrolase 2, interferon regulatory factor 3, and mitochondrial fission factor. Gene pathway analysis revealed that oxidative stress and immune response pathways were activated in response to tolvaptan treatment across all strains, but genes involved in regulation of bile acid homeostasis were most associated with tolvaptan-induced elevations in ALT. Secretory leukocyte peptidase inhibitor (Slpi) mRNA was also induced in the susceptible strains and was associated with increased plasma levels of Slpi protein, suggesting a potential serum marker for DILI susceptibility. In summary, tolvaptan induced signs of oxidative stress, mitochondrial dysfunction, and innate immune response in all strains, but variation in bile acid homeostasis was most associated with susceptibility to the liver response. This CC study has indicated potential mechanisms underlying tolvaptan DILI and biomarkers of susceptibility that may be useful in managing the risk of DILI in ADPKD patients.

IRF3 signaling pathway serves an important role in poly(I:C)-induced procollagen reduction in human skin fibroblasts

Pattern recognition receptors (PRRs) are part of the immune system. They can recognize pathogen‑associated molecular patterns (PAMPs). Toll‑like receptors (TLRs) and retinoic acid‑inducible gene 1 (RIG‑1)‑like receptors (RLRs) are 2 types of PRR in the innate immune system. Double‑stranded RNA (dsRNA) can exist as a PAMP, including dsRNA viruses. dsRNA is known as a ligand not only for TLR3 but also for RLRs, including melanoma differentiation‑associated gene 5 and RIG‑1. Collagen is the main structural protein in the extracellular space in the skin. Recently, it was reported that treatment of a synthetic dsRNA, poly(I:C), decreases procollagen expression in skin fibroblasts. However, signaling pathways involved in this process have not yet been fully elucidated. The present study further explored the underlying signaling pathways involved in the processes. It was demonstrated by western blotting that treatment of poly(I:C), but not another PAMP, Pam3CSK4, inhibited procollagen expression in cultured human skin fibroblasts. Treatment of poly(I:C)and Pam3CSK4 induced activation of the mitogen‑activated protein kinases and the nuclear factor‑κB pathways. However, only poly(I:C), but not Pam3CSK4, induced the activation of the interferon regulatory factor 3 (IRF3) pathway. By using specific inhibitors, it was demonstrated that inhibition of IRF3 pathway relieved poly(I:C)‑induced procollagen reduction. In conclusion, IRF3 signaling pathway serves an important role in poly(I:C)‑induced procollagen reduction in skin fibroblasts. This suggests that the IRF3 signaling pathway may be a key target for collagen regulation in the skin.