Arginase 1 is involved in lacrimal hyposecretion in male NOD mice, a model of Sjögren's syndrome, regardless of dacryoadenitis status

Key points: Few reports have explored the possibility of involvement of non-inflammatory factors in lacrimal hyposecretion in Sjögren's syndrome (SS). RNA-sequencing analysis revealed that only four genes, including Arginase 1, were downregulated in the lacrimal gland of SS model male mice (NOD mice) after onset of lacrimal hyposecretion and dacryoadenitis. Even in non-dacryoadenitis-type NOD mice, tear secretion and Arginase 1 expression remained low. An Arginase 1 inhibitor reduced tear secretion and partially reduced saliva secretion in BALB/c mice. The results indicate that a non-inflammatory factor, Arginase 1, is involved in lacrimal hyposecretion in male NOD mice, regardless of dacryoadenitis status.

Abstract: Lacrimal fluid (tears) is important for preservation of the ocular surface, and thus lacrimal hyposecretion in Sjögren's syndrome (SS) leads to reduced quality of life. However, the cause(s) of lacrimal hyposecretion remains unknown, even though many studies have been conducted from the perspective of inflammation. Here, we hypothesized that a non-inflammatory factor induces lacrimal hyposecretion in SS pathology, and to elucidate such a factor, we conducted transcriptome analysis of the lacrimal glands in male non-obese diabetic (NOD) mice as an SS model. The NOD mice showed inflammatory cell infiltration and decreased pilocarpine-induced tear secretion at and after 6 weeks of age compared to age-matched BALB/c mice. RNA-sequencing analysis revealed that only four genes, including Arginase 1, were downregulated, whereas many genes relating to inflammation were upregulated, in the lacrimal glands of male NOD mice after onset of lacrimal hyposecretion and dacryoadenitis (lacrimal gland inflammation). Changes in the level of Arginase 1 expression were confirmed by real-time RT-PCR and western blot analysis. Furthermore, non-dacryoadenitis-type NOD mice were used to investigate the relationships among Arginase 1 expression, lacrimal hyposecretion and dacryoadenitis. Interestingly, these NOD mice retained the phenotype of dacryoadenitis with regard to tear secretion and Arginase 1 expression level. An Arginase 1 inhibitor reduced tear secretion and partially reduced saliva secretion in BALB/c mice. In conclusion, a non-inflammatory factor, Arginase 1, is involved in lacrimal hyposecretion in male NOD mice, regardless of dacryoadenitis status. These results shed light on the pathophysiological role of Arginase 1 in SS (dry eye).