Autophagy-based unconventional secretion of alarmin HMGB1 by keratinocytes plays a pivotal role in psoriatic skin inflammation

Abstract

Abstract The precise mechanism by which autophagy affects psoriasis is poorly understood. Here we show that keratinocytes (KCs) autophagy was activated in psoriatic lesions of patients and mice model, positively correlating with psoriatic severity, and could be inhibited by MAPK family (ERK, p38, JNK) inactivation, implying autophagy was associated with psoriatic inflammation. Indeed, impaired autophagy flux, caused by autophagy inhibitors or KC-specific deletion of Atg5, alleviated psoriasisform inflammation, demonstrating autophagy positively regulated psoriatic inflammation. We then found an autophagy-based unconventional secretory pathway (autosecretion), depended on Atg5 and GRASP55, promoted the psoriasiform KCs inflammation. Moreover, alarmin HMGB1 was more effective than other autosecretory proteins, IL-1β and IL-18, to regulate the psoriasiform cutaneous inflammation. HMGB1 neutralization in autophagy-efficient KCs vanished the psoriasiform inflammation differences between autophagy-efficient KCs and autophagy-deficient KCs. Conversely, recombinant HMGB1 almost completely restored the psoriasiform inflammation in autophagy-deficient KCs in vivo. These results suggested that HMGB1-associated autosecretion, not other intracellular autophagy pathways, played a pivotal role in cutaneous inflammation. Finally, we demonstrated that KC-specific HMGB1 deficient mice, but not DC- or myeloid cell-specific HMGB1 deficient mice, displayed attenuated psoriatic inflammation, due to the essential crosstalk between KC-specific HMGB1-associated autosecretion and γδT cells. Thus, we uncover a novel autophagy mechanism in psoriasis pathogenesis, and imply its clinical significance in psoriasis treatment.