Leptin Modulates the Differentiation of Keratinocytes via Autophagy in Psoriasis Patients With Metabolic Syndrome
Authors: Song Cui-Hao , Wang Rui , Zhao Zhen-Kai , Zhang Yuan , Sun Jie , Zhang Xu , Ding Xiang-Yu , Bai Jia , Liang Xiao-Qiang , Wei Xuan-Jin , Liu Xiao-Ling , Yang Tao , Liang Xin-Lin , Li Cheng-Xin , Lin Bi-Wen 
Published: October 2023

Objective:
Psoriasis is associated with a high prevalence of metabolic syndrome (MS), and patients with concomitant psoriasis and MS are more severely affected and less responsive to treatment. However, the molecular mechanisms behind these effects are unknown. Recent studies have shown that leptin may serve as a molecular link between psoriasis and MS, suggesting that high leptin concentrations may exacerbate psoriasis. However, the molecular mechanism of this effect is still unclear. We aimed to investigate the effect of leptin on autophagy in patients with psoriasis.

Methods:
From January 2021 to June 2022 in PLA General Hospital, we enrolled 51 patients with psoriasis, including 21 patients with MS and 30 without MS, and 30 healthy controls who had undergone nevus surgery. We measured the epidermal leptin, P62, and LC3B concentratins of patients by immunohistochemistry, and measured the serum leptin concentration by enzyme-linked immunosorbent assay. We then performed correlation analyses to compare these proteins’ concentrations between patients with concomitant psoriasis and MS, patients with psoriasis alone, and healthy control groups. Additionally, we performed western blotting after in vitro culture of HaCaT cells with different concentrations of leptin and measured the expression levels of the autophagy markers Beclin1, LC3B, and P62; the differentiation markers K10, K16, and K17; and PI3K/AKT/mTOR signaling pathway-related proteins of HaCat cells. Next, we transfected ATG5 into HaCaT cells to revert autophagy and used the specific PI3K inhibitor LY294002 to block PI3K/AKT/mTOR signaling. The expression levels of K10, K16, and K17 of HaCat cells were again measured. One-way analysis of variance was used for the comparison of means of multiple samples, and LSD-t post hoc test was used for comparison between the 2 groups. The counting data were analyzed by the chi-square test. Correlations were evaluated by Pearson correlation analysis.

Results:
The serum leptin concentration was significantly higher in patients with concomitant psoriasis and MS than in patients with psoriasis alone, and healthy controls (1,330.0 ± 244.2 pg/mL, 1,041.0 ± 282.7 pg/mL, and 760.4 ± 361.1 pg/mL, P < 0.001). Optical density of epidermal leptin concentration was significantly higher in patients with psoriasis and MS than in patients with psoriasis alone and healthy controls (0.59 ± 0.15, 0.39 ± 0.12, and 0.27 ± 0.19, P < 0.001). The level of the autophagy marker LC3B was strongly reduced and that of P62 was strongly increased in the epidermis of patients with concomitant psoriasis and MS compared with patients with psoriasis alone and healthy controls (optical density value: LC3B: 0.27 ± 0.11, 0.29 ± 0.13, and 0.46 ± 0.17, P < 0.001; P62: 0.18 ± 0.08, 0.13 ± 0.03, and 0.10 ± 0.03, P < 0.001). We also observed a positive correlation between leptin and P62 concentrations in the blood (r = 0.40, P < 0.001) and epidermis (r = 0.27, P = 0.017), and a negative correlation between serum leptin concentrations and epidermal LC3B concentrations (r = −0.39, P < 0.001). In vitro, leptin significantly decreased Beclin1 and LC3B and increased P62. Western blotting showed that leptin treatment resulted in decreased expression of K10, and increased expressions of K16 and K17; when the decrease in autophagy was restored by ATG5, this phenomenon was reversed. In addition, leptin treatment significantly upregulated the expressions of phosphorylated PI3K, AKT, and mTOR in HaCaT cells compared with the control treatment; when the expression of phosphorylated PI3K was significantly inhibited by LY294002, leptin did not reverse the decreased expression of these proteins.

Conclusion:
Leptin is negatively associated with autophagy in psoriasis, and leptin markedly decreased autophagy and affected keratinocyte differentiation by downregulating autophagy via the PI3K/AKT/mTOR pathway. Our study enhances the understanding of leptin as the link between MS and psoriasis and provides potential therapeutic targets for patients with concomitant psoriasis and MS.