12/15-lipoxygenase orchestrates murine wound healing via PPARγ-activating oxylipins acting holistically to dampen inflammation.

Abstract

12/15-lipoxygenase (12/15-LOX, <i>Alox15</i>) generates bioactive oxygenated lipids during inflammation, however its homeostatic role(s) in normal healing are unclear. Here, the role of 12/15-LOX in resolving skin wounds was elucidated, focusing on how its lipids act together in physiologically relevant amounts. In mice, wounding caused acute appearance of 12/15-LOX-expressing macrophages and stem cells, coupled to early generation of ~12 monohydroxy-oxylipins and enzymatically oxidized phospholipids (eoxPL). <i>Alox15</i> deletion increased collagen deposition, stem cell/fibroblast proliferation, IL6/pSTAT3, pSMAD3, and interferon (IFN)-γ levels. Conversely, CD206 expression, F480+ cells, and MMP9 and MMP2 activities were reduced. <i>Alox15^-/-</i> skin was deficient in PPARγ/adiponectin activity. Furthermore, while pro-inflammatory genes were upregulated as normal during wounding, many including <i>Il6, Il1b, ccl4, Cd14, Cd274, Clec4d, Clec4e, Csf3, Cxcl2, and miR-21</i> failed to revert to baseline during healing, indicating disruption of PPARγ's anti-inflammatory brake on NLRP3/inflammasome and TGF-β signaling. Reconstituting <i>Alox15^-/-</i> wounds with a physiological mixture of <i>Alox15</i>-derived primary oxylipins generated by healing wounds restored MMP and dampened collagen deposition. The oxylipin mixture activated the PPARγ response element in vitro, while in vivo, its coactivator, <i>Helz2</i>, was significantly upregulated as well as several fatty acid and prostaglandin PPARγ ligands. Additional inflammatory and proliferative gene networks impacted by <i>Alox15^-/-</i> included <i>Elf4, Cebpb</i>, and Tcf3. In summary, 12/15-LOX generates abundant monohydroxy oxylipins that act together via PPARγ. The identification of multiple gene alterations reveals several targets for treating nonhealing wounds. Our studies demonstrate that 12/15-LOX oxylipins act in concert, dampening inflammation in vivo, revealing the need to consider lipid signaling holistically.