Keloid is a representative chronic fibroproliferative condition that occurs after tissue injury. Emerging evidence showed that activation of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is involved in the pro-inflammatory response in injured tissues. However, the role of NLRP3 inflammasome in keloid progression remains unclear. Notch signaling, which activates NLRP3 inflammasome, is known to contribute to scar formation in keloid, but the cause of enhanced Notch signaling in keloid is not clear. We sought to investigate whether autophagy regulates Notch1 signaling in keloid fibroblasts and determine whether Notch1 signaling might regulate NLRP3 inflammasomes and myofibroblast differentiation. An in vitro model of keloid was established by culturing primary keloid fibroblasts from patients. Expression levels of Notch1, NLRP3 inflammasome proteins, pro-inflammatory cytokines, and myofibroblast markers in keloid fibroblasts were examined and compared with those in normal fibroblasts. Autophagy known to mediate Notch1 degradation was also monitored in fibroblasts. Small interfering RNA (siRNA) targeting Notch1 was used to transfect keloid fibroblasts to further examine the role of Notch signaling in NLRP3 inflammasome activation. Expression levels of Notch1 and NLRP3 inflammasome in keloid fibroblasts increased compared to those in normal fibroblasts. Such increases were accompanied by increased LC3 levels and reduced autophagic flux. Notch1 silencing in keloid fibroblasts by siRNA transfection significantly suppressed increased levels of overall NLRP3 inflammasome complex proteins, NF-kB, and α-smooth muscle actin. Autophagy induction by rapamycin treatment in keloid fibroblasts effectively suppressed expression levels of Notch1 and NLRP3 inflammasome proteins. Decreased autophagy activity in keloid can result in Notch1-mediated myofibroblast activation and NLRP3 inflammasome signaling activation which is critical for chronic inflammation. Collectively, these results identify Notch1 as a novel activator of NLRP3 inflammasome signaling leading to chronic tissue damage and myofibroblast differentiation in keloid progression.

Autophagy is a major degradation pathway that removes harmful intracellular substances to maintain homeostasis. Various stressors, such as starvation and oxidative stress, upregulate autophagy, and the dysregulation of autophagy is associated with various human diseases, including cancer and skin diseases. The skin is the first defense barrier against external environmental hazards such as invading pathogens, ultraviolet rays, chemical toxins, and heat. Although the skin is exposed to various stressors that can activate autophagy, the roles of autophagy in the skin have not yet been fully elucidated. Accumulating evidence suggests that autophagy is closely associated with pathogenesis and the treatment of immune-related skin diseases. In this study, we review how autophagy interacts with skin cells, including keratinocytes and immune cells, enabling them to successfully perform their protective functions by eliminating pathogens and maintaining skin homeostasis. Furthermore, we discuss the implications of autophagy in immune-related skin diseases, such as alopecia areata, psoriasis, and atopic dermatitis, and suggest that a combination of autophagy modulators with conventional therapies may be a better strategy for the treatment of these diseases.