Dysregulated Ca signaling, fluid secretion, and mitochondrial function in a mouse model of early Sjögren's disease.

The molecular mechanisms leading to saliva secretion are largely established, but factors that underlie secretory hypofunction, specifically related to the autoimmune disease Sjögren's syndrome (SS) are not fully understood. A major conundrum is the lack of association between the severity of salivary gland immune cell infiltration and glandular hypofunction. SS-like disease was induced by treatment with DMXAA, a small molecule agonist of murine STING. We have previously shown that the extent of salivary secretion is correlated with the magnitude of intracellular Ca signals (Takano et al., 2021). Contrary to our expectations, despite a significant reduction in fluid secretion, neural stimulation resulted in enhanced Ca signals with altered spatiotemporal characteristics in vivo. Muscarinic stimulation resulted in reduced activation of the Ca-activated Cl channel, TMEM16a, although there were no changes in channel abundance or absolute sensitivity to Ca. Super-resolution microscopy revealed a disruption in the colocalization of Inositol 1,4,5-trisphosphate receptor Ca release channels with TMEM16a, and channel activation was reduced when intracellular Ca buffering was increased. These data indicate altered local peripheral coupling between the channels. Appropriate Ca signaling is also pivotal for mitochondrial morphology and bioenergetics. Disrupted mitochondrial morphology and reduced oxygen consumption rate were observed in DMXAA-treated animals. In summary, early in SS disease, dysregulated Ca signals lead to decreased fluid secretion and disrupted mitochondrial function contributing to salivary gland hypofunction.