Impact of Cellular Senescence on LCN2 Expression in Salivary Gland Epithelial Cells and Oral Keratinocytes.

LCN2 protein levels in serous acinar cells of salivary glands, oral epithelial cells, and saliva were higher in aged mice than in young mice.

• LCN2 was detected in serous acinar cells of salivary glands and oral epithelial cells of aged mice at higher levels than in young mice.
• Salivary LCN2 protein concentrations were also elevated in aged compared to young mice.
• This in vivo finding established an age-associated increase in LCN2 in oral-related tissues and fluids.

Replicative senescence and DNA damage-induced senescence did not increase LCN2 expression in primary oral keratinocytes and salivary gland epithelial cells.

• Both replicative senescence and DNA damage-induced senescence models were tested in primary oral keratinocytes and salivary gland epithelial cells.
• LCN2 expression was not upregulated in senescent cells compared to non-senescent controls in either cell type.
• Similar results were obtained for the SASP factors tumor necrosis factor-alpha and interleukin-1β (IL-1β), which also did not increase with cellular senescence in these cell types.

Cyclic GMP-AMP synthase (cGAS)-mediated induction of LCN2 expression was not operative in oral-related epithelial cells, and cGAS expression decreased with cellular senescence in these cells.

• Although cGAS-mediated induction of LCN2 expression has been reported in astrocytes, this pathway did not induce LCN2 expression in oral keratinocytes or salivary gland epithelial cells.
• cGAS expression decreased with cellular senescence in these oral-related epithelial cells.
• The cGAS ligand did not induce LCN2 expression in these cell types.

IL-1β treatment significantly induced LCN2 expression and secretion in oral-related epithelial cells, even when those cells were senescent.

• Exogenous IL-1β treatment induced LCN2 expression and secretion in both primary oral keratinocytes and salivary gland epithelial cells.
• This induction of LCN2 by IL-1β occurred even in senescent epithelial cells, indicating preserved IL-1β responsiveness after senescence.
• LCN2 expression is mainly regulated by NF-κB, which is also the primary transcriptional regulator of IL-1β signaling responses.

The source of IL-1β driving LCN2 upregulation with aging was identified as M1 macrophages that accumulate with inflammaging, not senescent fibroblasts.

• Senescent fibroblasts were tested and found not to be the source of IL-1β relevant to LCN2 induction in oral-related epithelial cells.
• M1 macrophages, which accumulate with inflammaging, were identified as the relevant source of IL-1β.
• This finding distinguishes the mechanism of age-related LCN2 upregulation from classical SASP-driven processes.

LCN2 is present in saliva and gingival crevicular fluid and possesses antimicrobial and immunomodulatory properties, and its expression in oral-related cells is primarily regulated by NF-κB.

• LCN2 is a glycoprotein secreted by immune cells, astrocytes, and epithelial cells.
• LCN2 is found in both saliva and gingival crevicular fluid.
• NF-κB is the main transcription factor regulating LCN2 expression, and NF-κB is also the primary regulator of the SASP.