Targeting alarmin release reverses Sjogren's syndrome phenotype by revitalizing Ca²⁺ signalling

Primary Sjogren's syndrome (pSS) is a systemic autoimmune disease that is embodied by the loss of salivary gland function and immune cell infiltration, but the mechanism(s) are still unknown. The aim of this study was to understand the mechanisms and identify key factors that leads to the development and progression of pSS.

Immunohistochemistry staining, FACS analysis and cytokine levels were used to detect immune cells infiltration and activation in salivary glands. RNA sequencing was performed to identify the molecular mechanisms involved in the development of pSS. The function assays include in vivo saliva collection along with calcium imaging and electrophysiology on isolated salivary gland cells in mice models of pSS. Western blotting, real-time PCR, alarmin release, and immunohistochemistry was performed to identify the channels involved in salivary function in pSS.

We provide evidence that loss of Ca²⁺ signaling precedes a decrease in saliva secretion and/or immune cell infiltration in IL14α, a mouse model for pSS. We also showed that Ca²⁺ homeostasis was mediated by transient receptor potential canonical-1 (TRPC1) channels and inhibition of TRPC1, resulting in the loss of salivary acinar cells, which promoted alarmin release essential for immune cell infiltration/release of pro-inflammatory cytokines. In addition, both IL14α and samples from human pSS patients showed a decrease in TRPC1 expression and increased acinar cell death. Finally, paquinimod treatment in IL14α restored Ca²⁺ homeostasis that inhibited alarmin release thereby reverting the pSS phenotype.

These results indicate that loss of Ca²⁺ signaling is one of the initial factors, which induces loss of salivary gland function along with immune infiltration that exaggerates pSS. Importantly, restoration of Ca²⁺ signaling upon paquinimod treatment reversed the pSS phenotype thereby inhibiting the progressive development of pSS.