Tofacitinib counteracts IL-6 overexpression induced by deficient autophagy: Implications in Sjögren's syndrome

Objective: Altered homeostasis of salivary gland (SG) epithelial cells in Sjögren's syndrome (SS) could be the initiating factor that leads to inflammation, secretory dysfunction and autoimmunity. Autophagy is an important homeostatic mechanism, whose deficiency is associated with inflammation and accumulation of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) components. We aimed to evaluate whether autophagy is altered in labial SG (LSG) epithelial cells from primary SS (pSS) patients and whether this contributes to inflammation through the JAK-STAT pathway. Furthermore, we investigated the anti-inflammatory effect of the JAK inhibitor tofacitinib in autophagy-deficient (ATG5 knockdown) three-dimensional (3D)-acini. Methods: We analysed LSG biopsies from 12 pSS patients with low focus score and 10 controls. ATG5-deficient 3D-acini were generated and incubated with IL-6 in the presence or absence of tofacitinib. Autophagy markers, pro-inflammatory cytokine expression, and JAK-STAT pathway activation were evaluated by PCR or western blot, along with correlation analyses between the evaluated markers and clinical parameters. Results: LSG from pSS patients showed increased p62 and decreased ATG5 expression, correlating negatively with increased activation of JAK-STAT pathway components (pSTAT1 and pSTAT3). Increased expression of STAT1 and IL-6 correlated with EULAR Sjögren's syndrome disease activity index and the presence of anti-Ro antibodies. ATG5-deficient 3D-acini reproduced the findings observed in LSG from pSS patients, showing increased expression of pro-inflammatory markers such as IL-6, which was reversed by tofacitinib. Conclusion: Decreased expression of ATG5 in LSG epithelial cells from pSS patients possibly contributes to increased inflammation associated with JAK-STAT pathway activation, as evidenced in ATG5-deficient 3D-acini. Interestingly, these results suggest that tofacitinib could be used as an anti-inflammatory agent in pSS patients.