Immunomodulatory Effects of Poly-D,L-Lactic Acid on LL-37-Driven Rosacea-like Inflammation via Suppression of mTORC1...

Rosacea is a chronic inflammatory skin disorder driven by dysregulated cathelicidin processing and excessive LL-37, which triggers a circuit involving Toll-like receptor 2 (TLR2)/kallikrein-5 (KLK5)-dependent amplification and downstream mechanistic target of rapamycin complex 1 (mTORC1), NF-κB, and NLR family pyrin domain containing 3 (NLRP3) inflammasome pathways. We hypothesized that poly-D,L-lactic acid (PDLLA) could attenuate this inflammatory cascade by inducing macrophage-derived interleukin (IL)-10. PDLLA increased IL-10 secretion from THP-1-derived macrophages in a dose-dependent manner. In LL-37-stimulated HaCaT keratinocytes, LL-37 decreased phosphorylated signal transducer and activator of transcription (pSTAT3)/STAT3, DNA damage-inducible transcript 4 (DDIT4), and phosphorylated AMP-activated protein kinase (pAMPK)/AMPK while increasing phosphorylated protein kinase B (pAKT)/AKT and mTORC1 activation; conditioned media from PDLLA-treated macrophages (CM_PDLLA) restored pSTAT3/STAT3, DDIT4, and pAMPK/AMPK, reduced pAKT/AKT, and suppressed pmTOR/mTOR. CM_PDLLA attenuated downstream inflammatory responses, including NF-κB nuclear translocation, VEGF production, and NLRP3-inflammasome-mediated IL-18 secretion. These findings were validated using an intradermal LL-37-injected mouse model. Compared with the normal control/saline group, LL-37/saline decreased IL-10, pSTAT3/STAT3, DDIT4, and pAMPK/AMPK while increasing pAKT/AKT, pmTOR/mTOR, pS6K/S6K, TLR2/KLK5/LL-37, NF-κB, VEGF, and NLRP3 inflammasome/IL-18 signaling; PDLLA partially restored the STAT3/DDIT4-AMPK regulatory pattern and suppressed these disease-associated signals. Consequently, PDLLA treatment led to a pronounced reduction in clinical lesion area. Overall, PDLLA may attenuate LL-37-driven cutaneous inflammation by promoting an IL-10-linked STAT3/DDIT4-AKT/AMPK program that suppresses mTORC1 and disrupts cathelicidin amplification, supporting its potential as an injectable immunomodulatory approach for rosacea-like skin inflammation.