LAMP3 induces ectopic TLR7 expression in salivary gland epithelial cells and amplifies type I IFN production in Sjögren's disease.

OBJECTIVE: Lysosome-associated membrane protein 3 (LAMP3) misexpression in salivary gland epithelial cells plays a causal role in the development of salivary gland dysfunction and autoimmunity associated with Sjögren's disease (SjD). This study aimed to clarify how epithelial LAMP3 misexpression is induced in SjD.

METHODS: To explore upstream signaling pathways associated with LAMP3 expression, we conducted multiple RNA sequencing analyses of minor salivary glands from patients with SjD, submandibular glands from a mouse model of SjD, and salivary gland epithelial cell lines. A hypothesis generated by the RNA sequencing analyses was further tested by in vitro and in vivo assays with gene manipulation.

RESULTS: Transcriptome analysis suggested LAMP3 expression was associated with enhanced type I interferon (IFN) and IFNγ signaling pathways in patients with SjD. In vitro studies showed that type I IFN but not IFNγ stimulation could induce LAMP3 expression in salivary gland epithelial cells. Moreover, we discovered that LAMP3 overexpression could induce ectopic toll-like receptor 7 (TLR7) expression and type I IFN production in salivary gland epithelial cells both in vitro and in vivo. TLR7 knock-out mice did not develop any SjD-related symptoms following LAMP3 induction.

CONCLUSION: Epithelial LAMP3 misexpression can be induced through enhanced type I IFN response in salivary glands. In addition, LAMP3 can promote type I IFN production via ectopic TLR7 expression in salivary gland epithelial cells. This positive feed-back loop can contribute to maintaining LAMP3 misexpression and amplifying type I IFN production in salivary glands, which plays an essential role in the pathophysiology of SjD.