Soy isoflavones ameliorate experimental colitis by targeting ERα/NLRP3 inflammasome pathways

Abstract

Soy isoflavones (SIFs) are selective estrogen receptor modulators (SERMs) that have anti-inflammatory activities. Our previous study found that estrogen receptor α (ERα) directly regulates the NLRP3 transcription and NLRP3 inflammasome assembly. Therefore, we hypothesized that SIFs alleviate colitis via an ERα-dependent mechanism by targeting the NLRP3 inflammasome. The influence of SIFs on colitis and the potential mechanisms were thoroughly determined in this study. The results suggested that SIFs ameliorated dextran sodium sulfate (DSS)-induced body weight loss, reduced disease activity index and promoted the recovery of colon pathological damage in mice. Moreover, expression of the NLRP3 inflammasome was significantly inhibited, and the release of IL-1β and IL-18 was suppressed by SIFs. Furthermore, ERα blockade ameliorated DSS-induced inflammatory responses in the intestine, and SIFs markedly suppressed the expression of ERα in a dose-dependent manner. Our study demonstrated that the protective therapeutic action of SIFs on DSS-induced colitis depended on inhibition of ERα and subsequent NLRP3 inflammasome activation, and SIFs are promising therapeutic agents for the treatment of colitis.

Introduction

Inflammatory bowel disease (IBD) is chronic, relapsing inflammatory disorder of the gastrointestinal tract that is a global health problem with sustained increasing incidence [[1],2]. The precise pathogenesis of IBD has not yet been ascertained, but breakdown of the epithelial barrier followed by aberrant immune responses of the host immune system is widely considered to be the basis of IBD [3]. As an important part of the host immune system, inflammasomes are involved in inflammatory gut diseases [4]. To date, many inflammasomes have been identified; among them, the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is the most fully characterized inflammasome and can assemble into large cytosolic complexes and promote the maturation and secretion of the proinflammatory cytokines IL-1β and IL-18 upon cellular infection or stress [5]. A study demonstrated that NLRP3-deficient mice had attenuated colitis and reduced mortality [6]. Further, in our previous study, we also found that the NLRP3 inflammasome played an important role in IBD [7,8]. Thus, inhibition of NLRP3 inflammasome activation may be beneficial for the treatment of IBD.

In our previous studies, we proved that the nonsteroidal estrogenic mycotoxin zearalenone relieved the inflammatory reaction in colon tissue due to its estrogenic activity [7]. Furthermore, we confirmed that estrogen receptor α (ERα) and NLRP3 were differentially expressed in normal colon and cancer cells [9]. More importantly, we identified that ERα was the transcriptional regulator of NLRP3, and both regulated NLRP3 expression and promoted NLRP3 inflammasome colocalization [10]. Similar results were obtained in other studies. Armstrong et al. found that epithelial cells within tumors had dramatically increased ERα mRNA and protein expression compared with that of nondiseased mice [11]. ERα-deficient mice showed a significantly reduced incidence of severe disease in dextran sodium sulfate (DSS)-induced colitis [12]. Therefore, we hypothesized that ERα regulates inflammatory pathways, and inhibiting ERα might be a possible strategy for IBD treatment.

Soy foods have been consumed for centuries in Asian countries and are especially in demand in China [13]. Soybeans contain many natural active substances, and they are the richest sources of SIFs in the human diet. Recent studies revealed that SIFs has many benefits, such as effects against cancer, cardiovascular disease, hyperlipidemia and osteoporosis [14,15]. In particular, studies have proven that SIFs have positive effects in the prevention and treatment of inflammatory disorders and diarrheal diseases [[16], [17], [18]]. For example, dietary isoflavones are helpful for individuals with ulcerative colitis who are in remission [19] and alleviate DSS-induced inflammation in mice by inhibiting TLR4/MyD88 signaling [20]. SIFs are typical phytoestrogens that compete with endogenous estrogens to bind with estrogen receptors and exert their effects [21]. However, whether SIFs can alleviate colitis by regulating estrogen receptors and whether the NLRP3 inflammasome plays a key role in this process remain unknown. In this study, we investigated the influence of SIFs on experimental colitis, and the results showed that SIFs ameliorated DSS-induced experimental colitis by targeting ERα/NLRP3 inflammasome pathways. Our study provides new insights into the mechanisms underlying the pharmacological effects of SIFs on colitis, which contribute to novel strategies for the management of colitis.