Aging Affects Lipid Homeostasis in Lacrimal Glands by Upregulating Lipogenesis and Changing Its Specificity

The lacrimal gland (LG) develops age-related alterations. This study investigated the lipid content of the accumulated secretions within the murine aged LG.

C57BL/6J animals of different ages (3 months, 12 months, and 20-26 months) were used. Published data of bulk RNA sequencing of aged LGs were used to investigate lipid pathways. Exorbital LGs were excised for histology or PCR. Histologic sections were stained with standard histochemical stains or immunostained using anti-adiponectin, anti-perilipin 2 antibodies, and BODIPY dye. LG lipidomes were investigated using unbiased, untargeted high-resolution liquid chromatography/mass spectrometry (LC/MS), and the data were processed using unbiased, untargeted principal component and orthogonal projections to latent structure discriminant analyses.

Analyses of aged LGs revealed distinct changes in their state: immune infiltration without and with large dilated epithelial ducts. Sudan black and Oil Red O staining of cystic LG sections demonstrated lipid accumulation within the dilated epithelial ducts, accompanied by lymphocytic infiltration around dilated ductal structures. Bulk RNA sequencing of glands indicated upregulated transcription of genes associated with lipid metabolism, fatty acid synthesis, and lipid droplet formation. Adiponectin protein expression was restricted to ducts. Immunoreactivity to perilipin 2 and BODIPY was only observed in aged epithelial ducts. Moreover, lipidomic LC/MS analysis revealed a significant increase in the total lipid content in aged LGs compared to young LGs, with a pronounced accumulation in the neutral lipid fraction, particularly triglycerides.

The changes in LG lipidomes of aging mice indicate a considerable age-related shift in the specificity and efficacy of lipogenesis in LG.