Inflammation represents a multifaceted physiological response to detrimental stimuli, where controlled inflammation serves as a pivotal defense mechanism, whereas excessive inflammation can precipitate tissue damage[27]. Acting as the body's primary defense line against external pathogens, the skin functions to thwart harm from pathogens and environmental aggressors, thus upholding equilibrium in substance exchange between the internal and external milieus[28]. Within the skin microenvironment, a diverse array of immune cells orchestrates the maintenance of immunological balance[29], while non-immune cellular constituents, notably keratinocytes, modulate immune cell behavior through cytokine secretion[30]. These cytokines exert profound effects on immune cell function and play pivotal roles in the initiation, propagation, and perpetuation of cutaneous inflammation[31]. Given inflammation's dual nature, keratinocytes often act as initiators of the inflammatory cascade in numerous inflammatory skin disorders[32]. For instance, in acne pathogenesis, Propionibacterium acnes stimulates keratinocytes to release pro-inflammatory cytokines such as Interferon-gamma(IFN-γ), IL-1β, and TNF-α, thereby fostering acne inflammation[33]. Similarly, in conditions like atopic dermatitis and allergic dermatitis, epithelial-derived inflammatory mediators triggered by allergens play crucial roles in inducing type 2 immune responses, culminating in localized allergic skin manifestations[34]. Moreover, in afflictions like UV-induced photodamage, psoriasis, and lupus erythematosus, keratinocytes, due to extrinsic pressures or pathological insults, sustain injury, prompting the secretion of damage-associated molecular patterns, thereby exacerbating the underlying pathology [35–37]. Hence, in managing and ameliorating inflammatory skin disorders and cutaneous injuries, downregulating inflammatory cytokine expression in keratinocytes emerges as a pivotal therapeutic strategy[38].
The regulation of skin inflammation occurs across various biological communication levels, with Toll-Like Receptors (TLRs) playing a pivotal role in the immune and inflammatory responses of the skin[39]. Dysregulation of TLR-related pathways also significantly contributes to the pathogenesis of inflammatory skin diseases[40]. TLR-related pathways in skin tissue regulate essential biological processes, including inflammation, responses to environmental stress, maintenance of antimicrobial barrier function, and tissue repair[41]. Among these processes, TLR4 assumes a central role in triggering inflammatory signal transduction[42]. During this process, TLR4 binds to the adapter protein MYD88[43], initiating the activation of Interleukin-1 receptor-associated kinase (IRAKs) and Tumor Necrosis Factor Receptor-Associated Factor 6 (TRAF6) [44]. Subsequently, with the assistance of TAK1-Binding Proteins (TABs) and (Evolutionarily Conserved Signaling Intermediate in TOLL Pathways)ECSIT, TRAF6 activates (Transforming Growth Factor Beta-Activated Kinase 1)TAK1[43, 45]. The TAK1 complex then activates MAPK pathways such as Extracellular Signal-Regulated Kinase 1/2 (ERK1/2) or p38, and potentially leading to the activation of the NF-κΒ transcription factor. This activation results in the rapid transcriptional expression of cytokines such as IL-1β, IL-6, IL-8, and TNF-α[43, 46, 47], ultimately culminating in skin stress responses and inflammation. This biological process contributes to the development of various diseases, including impaired wound healing in diabetes, psoriasis, atopic dermatitis, UV-induced photodamage, and associated skin tumors [48]. Therefore, the co-regulation of TLR4 and its downstream pathways to mitigate the oscillation of inflammatory factors is considered a promising therapeutic strategy for addressing inflammatory skin diseases [49–51].
While traditional corticosteroids and immunosuppressive drugs have been used to alleviate skin inflammation, they come with potential risks of adverse reactions [52]. Natural extracts from traditional medicine offer higher safety profiles, opening up new possibilities for alternative therapies[53]. Paris polyphylla, a traditional medicinal herb, is primarily used in traditional Chinese medicine for its anti-inflammatory, anti-swelling, and pain-relieving properties, commonly employed in treating inflammatory and swelling-related diseases, with its primary indications being skin infections and tissue damage[16]. Modern pharmacological studies have found that the active ingredients in Paris polyphylla are mostly steroidal saponins[54], with research reporting that Polyphyllin I exhibits anti-inflammatory effects in joint and lung tissues[55, 56], while Polyphyllin H demonstrates steroid-like anti-inflammatory effects in skin tissues [57]. In this study, Paris polyphylla was chosen as the research subject to explore its inflammatory targets. Through protein-protein interaction (PPI) analysis, the most significantly affected targets were found to be IL6, IL-1B, TNF, and CXCL8. In cell experiments on inflammation, Paris polyphylla was found to alleviate the expression of IL-1β, IL-6, IL-8, and TNF-α in HaCat cells, whether in UVA-damaged models or LPS-induced bacterial stimulation, consistent with the results of PPI analysis. In terms of its mechanism of action, enrichment analysis revealed high enrichment not only in iinflammatory factor processes but also in toll-like receptor signaling pathways, MAPK pathways, and NFκB pathways. Among them, TLR4, MAPK3, and MYD88 were important nodes in the PPI network. Molecular docking revealed that Polyphyllin H, which significantly affects skin inflammation, has good binding activity with MAPK3 and MYD88. As previously mentioned, MYD88 is involved in TLR4-dependent activation of the inflammatory pathway, with MAPK3 (ERK1) closely involved. This pathway is triggered by external stimuli on the skin, ultimately resulting in the upregulation of various inflammatory mediators, including IL-1β, IL-6, IL-8, and TNF-α. The anti-inflammatory effects targeting this pathway were confirmed through network pharmacology and cell experiments involving Paris polyphylla.