Aberrant MUC1 accumulation in salivary glands of Sjögren’s syndrome patients is reversed by TUDCA in vitro

Abstract

Objectives Xerostomia in SS patients has been associated with low quality and quantity of salivary mucins, which are fundamental for the hydration and protection of the oral mucosa. The aim of this study was to evaluate if cytokines induce aberrant mucin expression and whether tauroursodeoxycholic acid (TUDCA) is able to counteract such an anomaly. Methods Labial salivary glands from 16 SS patients and 15 control subjects, as well as 3D acini or human submandibular gland cells stimulated with TNF-α or IFN-γ and co-incubated with TUDCA, were analysed. mRNA and protein levels of Mucin 1 (MUC1) and MUC7 were determined by RT-qPCR and western blot, respectively. Co-immunoprecipitation and immunofluorescence assays for mucins and GRP78 [an endoplasmic reticulum (ER)-resident protein] were also performed. mRNA levels of RelA/p65 (nuclear factor-κB subunit), TNF-α, IL-1β, IL-6, SEL1L and EDEM1 were determined by RT-qPCR, and RelA/p65 localization was evaluated by immunofluorescence. Results MUC1 is overexpressed and accumulated in the ER of labial salivary gland from SS patients, while MUC7 accumulates throughout the cytoplasm of acinar cells; however, MUC1, but not MUC7, co-precipitated with GRP78. TUDCA diminished the overexpression and aberrant accumulation of MUC1 induced by TNF-α and IFN-γ, as well as the nuclear translocation of RelA/p65, together with the expression of inflammatory and ER stress markers in 3D acini. Conclusion Chronic inflammation alters the secretory process of MUC1, inducing ER stress and affecting the quality of saliva in SS patients. TUDCA showed anti-inflammatory properties decreasing aberrant MUC1 accumulation. Further studies are necessary to evaluate the potential therapeutic effect of TUDCA in restoring glandular homeostasis in SS patients.

Tauroursodeoxycholate—Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives

“…It is already well established that inflammatory responses are activated in many types of diseases including hepatic ischemia reperfusion (HIR) [160], asthma [161], neurological disorders [162,163], or Sjögren's syndrome (SS) [164]. Moreover, a crosstalk between inflammation and ER stress exists, in a way that UPR pathways intersect with a multitude of stress and inflammatory signaling networks including the JNK-AP-1-, NFκB-, and IκB kinase (IKK)-dependent pathways [12].…”

“…Modulation of ER stress has also been considered to be engaged in anti-inflammatory properties of TUDCA in allergic airway disease [161,169] and Sjögren's syndrome [164]. TUDCA decreased ER stress and attenuated pulmonary levels of the pro-inflammatory cytokines IL-6 and IL-33 and chemokines CCL20/macrophage inflammatory protein 3 α (MIP3α), C-C motif chemokine ligand 11 (CCL11/eotaxin-1), and CXCL1/keratinocyte-derived chemokine (KC) in mice [161].…”

“…TUDCA decreased ER stress and attenuated pulmonary levels of the pro-inflammatory cytokines IL-6 and IL-33 and chemokines CCL20/macrophage inflammatory protein 3 α (MIP3α), C-C motif chemokine ligand 11 (CCL11/eotaxin-1), and CXCL1/keratinocyte-derived chemokine (KC) in mice [161]. Also, treatment with TUDCA exerted a beneficial outcome in reversing aberrant mucin 1 (MUC1) accumulation in salivary glands of SS-suffering individuals [164]. In experimental conditions, TUDCA reduced TNF-α and IFN-γ-induced up-regulation of pro-inflammatory markers such as TNF-α, IL-1β, and IL-6, and alleviated NF-κB activation [164].…”

“…Also, treatment with TUDCA exerted a beneficial outcome in reversing aberrant mucin 1 (MUC1) accumulation in salivary glands of SS-suffering individuals [164]. In experimental conditions, TUDCA reduced TNF-α and IFN-γ-induced up-regulation of pro-inflammatory markers such as TNF-α, IL-1β, and IL-6, and alleviated NF-κB activation [164]. Interestingly, contradictory modes of action of TUDCA have been further suggested.…”

“…Preferential direct binding to ATF6α receptor and alleviation of ER stress have been proposed as primary effects of TUDCA in a murine model of allergic airway disease [161]. In contrast, ER stress-relieving activity of TUDCA has been suggested to be a secondary effect of reduced expression of pro-inflammatory mediators, rather than its primary mode of action in Sjögren's syndrome [164]. This suggests that TUDCA-mediated interplay between ER stress and inflammatory responses might be more complex and further analyses are still necessary to comprehensively solve this issue.…”