IL-17A, the effector cytokine of T helper (Th) 17 cells, plays a crucial role in the pathogenesis of psoriasis. The Notch1 and PI3K/AKT signaling pathways are implicated in Th17 cell differentiation and IL-17A production. The present study aimed to evaluate the regulatory effect of the Notch1/hairy and enhancer of split 1 (Hes1)-PTEN/AKT/IL-17A feedback loop on Th17 cell differentiation via the PI3K/AKT inhibitor LY294002 in a mouse model of psoriasis. Mice were randomly divided into 3 groups: a control group, a model group [5% imiquimod (IMQ)-induced group] and an intervention group (5% IMQ-induced plus LY294002-treated group). Skin structural characteristics were recorded and evaluated by hematoxylin and eosin staining. The weights of the spleens and inguinal lymph nodes were measured. Th17 cell percentage, as well as the mRNA and protein expression levels of Notch1, Notch1 intracellular domain (NICD1), Hes1, PTEN, AKT, phosphorylated (p)-AKT, mTOR complex 1 (mTORC1), p-mTORC1, S6 kinase (S6K)1, S6K2 and IL-17A were detected in skin samples of the three experimental groups. Additionally, splenic mononuclear cells from model mice were treated by 10 and 50 µM LY294002 to further evaluate its regulatory effect on Notch1/Hes1-PTEN/AKT/IL-17A feedback loop. Increased Th17 cell percentage, increased expression of Notch1, NICD1, Hes1, AKT, p-AKT, mTORC1, p-mTORC1, S6K1, S6K2 and IL-17A, and decreased PTEN levels were observed in model mice alongside marked psoriasis-like skin inflammation, splenomegaly and lymphadenopathy. LY294002 treatment significantly alleviated the severity of psoriasis-like skin inflammation in the intervention mice, attenuated the degree of epidermal hyperplasia and dermal inflammatory cell infiltration, and mitigated splenomegaly and lymphadenopathy. In addition, LY294002 treatment reversed the increased Th17 cell percentage, as well as the increased expression of Notch1, NICD1, Hes1, AKT, p-AKT, mTORC1, p-mTORC1, S6K1, S6K2 and IL-17A, and the decreased expression of PTEN. In vitro study from 5% IMQ-induced mouse splenic mononuclear cells presented that high dose of LY294002 exerted more obviously regulatory effect on Notch1/Hes1-PTEN/AKT/IL-17A feedback loop. The current findings suggested that the Notch1/Hes1-PTEN/AKT/IL-17A feedback loop regulates Th17 cell differentiation within the disease environment of psoriasis. Blocking the Notch1/Hes1-PTEN/AKT/IL-17A feedback loop may thus be a potential therapeutic method for management of psoriatic inflammation.

(IL)-17A, the effective factor of Th17 cells acts on important pathological role in the pathogenesis of psoriasis. Notch1/hairy and split 1 (Hes1) and PI3K/AKT signaling pathways are interpenetrated and involved in Th17 cell differentiation and IL-17A production. In this present study, we used imiquimod (IMQ)-induced mouse psoriatic skin inflammation to explore the possible mechanism of Notch1/Hes1-PTEN/AKT/IL-17A feedback loop in psoriasis by employing AKT inhibitor LY294002 as an intervention with the methods of flow cytometry analysis, reverse transcription-quantitative polymerase chain reaction, western blot, co-immunoprecipitation and immunofluorescence. Firstly, LY294002 inhibition can obviously alleviate the mouse psoriatic skin inflammation both in skin structural and histopathological characteristics, which is similar to the changes found in IL-17A antibody-treated mice. Additionally, the interaction between Notch1 intracellular domain (NICD1) and nuclear factor kappa B (NF-κB) activator 1 (Act1) was demonstrated. LY294002 interruption resulted in consistent changes in expression levels of key signaling molecules both in Notch1/Hes1 and PI3K/AKT signaling pathways in a time-dependent manner. Moreover, chloroquine (CQ) can partly reverse the inhibitory effects of LY294002 on the Notch1/Hes1-PTEN/AKT/IL-17A feedback loop by affecting Notch1 ubiquitination and lysosomal degradation. The present study showed that LY294002 can exert the inhibitory effect on Notch1/Hes1-PTEN/AKT/IL-17A feedback loop to regulate Th17 cell differentiation and IL-17A function in the process of psoriasis, which provides a new possible therapeutic strategy for psoriasis.

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