Irritable bowel syndrome (IBS), a chronic functional gastrointestinal disease characterized by abdominal pain accompanying defecation or change in bowel patterns, affects approximately 20 % of the global population [1]. Diarrhea predominant-irritable bowel syndrome (IBS-D), the main subtype of IBS, accounts for 46 % of all IBS patients [2]. IBS-D not only deteriorates patients' quality of life, but also imposes considerable burdens on their families and society [3]. Current studies indicates that IBS-D may involve various pathophysiological mechanisms, such as gut-brain axis dysregulation, gut microecological imbalance, visceral hypersensitivity, gut barrier dysfunction and gut immune activation [3]. Despite these insights, the precise pathophysiological mechanisms underlying IBS-D is still incompletely understood. Moreover, the diagnosis of IBS-D remains challenging due to the lack of specific clinical manifestations and biomarkers. Current treatment strategies for IBS-D include lifestyle and dietary intervention, laxatives or gastrointestinal motility agents, probiotics, spasmolytic drugs, and anti-depressant drugs, yet many patients continue to experience uncontrolled symptoms, highlighting the limitations of existing therapies [4]. All of these challenges highlight an incomplete understanding of IBS-D, underscoring the necessity for more in-depth exploration [5].

In recent years, numerous studies have highlighted the role of mast cells (MCs) in the pathogenesis of IBS-D. This finding is supported by increased MCs counts and enhanced MCs activation in IBS-D patients, which are strongly associated with abdominal pain [6,7]. Risk factors for IBS-D, encompassing dietary habits, psychological stress, infections, and gut microbiota imbalances, are potentially related to MCs activation [4]. Once activated, MCs promote visceral hypersensitivity and impair gut barrier function, thereby causing the occurrence of IBS-D- related symptoms [8]. However, the precise mechanisms underlying MCs activation in IBS-D remain incompletely understood. Elucidating the mechanism of MCs activation is essential for the management of IBS-D.

Cold-inducible RNA-binding protein (CIRP) was initially identified and extensively studied as a stress-response protein [9]. Numerous stress conditions, such as hypoxia, ultraviolet exposure, glucose deprivation, and heat stress, have been shown to robustly induce the expression of CIRP [10]. More recently, CIRP has emerged as an important immunomodulatory molecule, exerting regulatory effects on various immune cells, including macrophages [11], neutrophils [12], lymphocytes [13], and dendritic cells [14]. Additionally, CIRP was implicated in sodium dextran sulfate-induced gut inflammation and associated colon cancer, which was fulfilled via its regulation of immune response and cell apoptosis [15]. However, the regulatory role of CIRP in MCs and its involvement in IBS-D remain obscure.

Therefore, we hypothesized that CIRP exerts activating effects on MCs, which subsequently perform a pivotal role in IBS-D. This study aimed to: 1) to evaluate the expression of CIRP in IBS-D; 2) to clarify the function and mechanism of CIRP in gut barrier function and visceral sensitivity in IBS-D; 3) to verify the activating mechanism of CIRP on MCs by binding to TLR4 and upregulating TRPV1 expression.