Human papillomavirus (HPV) stands out as the most prevalent viral infection affecting reproductive tracts, with the vast majority of sexually active individuals acquiring the virus at some point in their lives [10]. Notably, HPV-associated oral diseases are on the rise, occurring in individuals with both intact and compromised immune systems [11]. HPVs employ diverse strategies to target immune signaling pathways [11]. In our study, we observed a potent induction of inflammation by HPV in oral epithelial cells. Importantly, IL37 demonstrated a significant ability to attenuate HPV-induced inflammation in oral epithelial cells. Mechanistically, our findings highlight the critical involvement of the PI3K/AKT/mTOR signaling pathway in mediating the effects of IL37 on HPV-induced inflammation in oral epithelial cells.

It has been documented that HPV 16 induces varying degrees of chronic inflammation, ranging from mild to severe inflammation in oropharyngeal squamous cell carcinoma (OPSCC) [11]. HPV E5, E6, and E7 have been implicated in the onset of HPV-induced inflammation by upregulating the expression of cyclooxygenase (COX)−2 and prostaglandin (PG) E2, subsequently activating the COX-PG pathway [12]. Studies have reported that HPVs can enhance inflammatory cell infiltration (macrophages and neutrophils), elevate cytokine levels (IL-6, TNF-α, and IL-1β), chemokine levels (MCP-1), and levels of cell adhesion molecules (ICAM-1 and VCAM-1) in the lung [13]. Additionally, HPV oncogenes E5, E6, and E7 have been associated with the development of chronic inflammation through various mechanisms [14]. Similarly, in our present study, we observed that HPV E6 significantly increased the expression of cytokines, including IL18, IL8, and TNFɑ, in two types of oral epithelial cells (Fig. 1). This suggests that HPV may contribute to cancer development by modulating inflammation.

Accumulating evidence indicates that IL-37 is a distinctive member of the IL-1 family of cytokines, acting as a natural suppressor of inflammatory and immune responses [15]. Notably, IL-37 has been reported to suppress pro-inflammatory cytokines (IL-1 and IL-6) and lung inflammation induced by COVID-19 [16]. Furthermore, IL-37 is recognized as a potent anti-inflammatory cytokine with anti-tumor activity against hepatocellular carcinoma (HCC) in patients infected with hepatitis B virus (HBV) [17]. In our present study, we observed that IL37 significantly mitigated HPV-induced inflammation in oral epithelial cells (Fig. 2). This aligns with findings from Wang et al., who reported that IL-37 inhibited STAT3 expression at both mRNA and protein levels [18]. Consequently, IL37 is likely to play a crucial role in the context of HPV-induced inflammation.

The phosphatidylinositol-3-kinase (PI3K)/Akt and mammalian target of rapamycin (mTOR) (PI3K/AKT/mTOR) signaling pathways play crucial roles in various cellular activities [19]. Additionally, this signaling pathway has been implicated in inflammation [20]. Li et al. reported that IL-37 induced autophagy in hepatocellular carcinoma cells by inhibiting the PI3K/AKT/mTOR pathway [9]. Consistent with this, our study also revealed that IL-37 could inhibit the PI3K/AKT/mTOR pathway (Fig. 3, 4, 5, and 6). Furthermore, the PI3K/AKT/mTOR signaling pathway has been closely associated with HPV-driven head and neck carcinogenesis [21]. It was also found to regulate the virus/host cell crosstalk in HPV-positive cervical cancer cells [22]. Enhancing our understanding of how the PI3K/Akt/mTOR signaling pathway contributes to the immortalization and carcinogenesis of HPV-transduced cells is crucial for developing novel strategies to prevent and treat HPV-induced cancers [23]. In our study, we demonstrated that KD of PI3K, AKT, or mTOR compromised the suppressive effect of IL37 on HPV-induced cytokine release (Fig. 3, 4, 5, and 6). Consistently, in our previous study, it was demonstrated that HPV significantly induced inflammation in both types of oral epithelial cells, and IL-37 attenuated HPV induced inflammation of oral epithelial cells via regulating autophagy [8]. Thus, our findings support the notion that IL37 suppresses HPV-induced inflammation by inhibiting the PI3K/Akt/mTOR signaling pathway.

Although the present study demonstrated that IL-37 attenuated HPV induced inflammation of oral epithelial cells via inhibiting PI3K/AKT/mTOR. Some limitations are wanted to be solved in the future studies. For example, two specific types of oral epithelial cells may not fully represent the heterogeneity of oral epithelial cells in vivo. Different subsets of oral epithelial cells, such as those from distinct anatomical locations within the oral cavity (e.g., buccal mucosa, gingiva, tongue epithelium), could potentially exhibit varying responses to HPV infection and IL-37 modulation. All investigations were conducted in vitro, which, despite allowing for precise control of variables and molecular manipulations, lacks the systemic and physiological context of the human body. Thus, in the future, exploration should aim to validate the in vitro findings in animal models. The development of small molecule agonists or enhancers of IL-37 function could be explored, along with the use of targeted inhibitors of the PI3K/AKT/mTOR pathway to optimize the cytokine's anti-inflammatory effects in the context of HPV infection.