The protective effect of Lcn2 activation on salivary gland injury in sialadenitis

Sialadenitis represents an intricate inflammatory condition affecting the salivary glands, marked by tissue damage, inflammation, and compromised secretory function, though targeted therapeutic approaches with proven efficacy continue to be scarce. Lipocalin-2 (Lcn2), a versatile protein that participates in inflammation and apoptosis regulation, has been associated with numerous inflammatory conditions. The present research examined the protective function of Lcn2 in sialadenitis, with particular focus on its anti-inflammatory and anti-apoptotic mechanisms as well as its latent capacity as a therapeutic target. Lcn2-associated alterations in salivary gland tissues and cells were evaluated through assessments of inflammatory injury, apoptotic markers (caspase-3, Bax, Bcl2), and functional molecules critical for glandular secretion (AQP5, MUC1, α-amylase) using human samples, LPS-induced murine models, RNA sequencing, immunohistochemistry, Western blotting, and siRNA-mediated Lcn2 knockdown. To further assess the functional role of Lcn2, mice were administered adeno-associated virus 2 (AAV2) to suppress Lcn2 expression during LPS-induced sialadenitis. LPS treatment markedly induced glandular damage, inflammation, and apoptosis, accompanied by robust upregulation of Lcn2. Lcn2 co-localized with caspase-3 in epithelial cells, and its suppression aggravated apoptosis and inflammation, whereas AAV2-mediated Lcn2 knockdown exacerbated tissue injury and disrupted secretion-related protein expression. Mechanistically, Lcn2 knockdown further enhanced LPS-induced phosphorylation of NF-κB p65, JNK, and p38. Inhibition of NF-κB with BAY11-7082 abolished the excessive inflammatory response, while inhibition of JNK with SP600125 attenuated the pro-apoptotic effect of Lcn2 silencing. Moreover, molecular docking and co-immunoprecipitation confirmed a direct physical interaction between Lcn2 and Bcl2. Conversely, Lcn2 overexpression alleviated these deleterious effects by modulating apoptotic and inflammatory mediators. Collectively, these findings demonstrate that Lcn2 confers protection against salivary gland injury in sialadenitis by regulating apoptosis and inflammation, at least partially via directly binding to Bcl2 and suppressing NF-κB and JNK/p38 MAPK signaling pathways, highlighting Lcn2 as one prospective therapeutic target for alleviating salivary gland dysfunction and inflammation.