Abstract Background Psoriasis is a refractory immune-related disease. In recent years, it has been discovered that mesenchymal stem cells (MSCs) can be used as a new therapeutic approach for psoriasis, but their potential therapeutic mechanism remains unclear. This study aims to explore the role of MSCs in the treatment of psoriasis. Methods We employed a mouse psoriasis model induced by imiquimod (IMQ) in vivo and a co-culture system of MSCs and HaCaT keratinocytes (KCs) cell line in vitro. These approaches allowed us to investigate the effect of MSCs on the levels of inflammatory factors and the activation of inflammasomes in both contexts. Mouse-targeted amino acid sequencing, transmission electron microscopy for in vitro observation, immunofluorescence for both in vivo and in vitro analyses, and siRNA transfection in vitro were employed in this study. Results Our results showed that MSCs significantly improved the skin lesion of mice with psoriasis, and reduced the levels of inflammatory factors and chemokines including IL-1β, IL-6, IL-8, TNF-α, MCP-1, CCL7, CCL20 and CCL27 in the mouse skin lesion areas and M5- induced psoriatic KCs models in vitro. Likewise, MSCs repaired the skin barrier by enhancing claudin-1 expression in vivo. In addition, MSCs increased KRT1 and decreased KRT6 levels in vivo and in vitro. Amino acid metabolism analysis showed that MSCs could improve the serine metabolism level in the mouse skins and upregulated the key enzyme phosphoserine phosphatase (PSPH) in serine metabolism. In vitro experiments demonstrated that knockdown of PSPH could reverse the therapeutic effects of MSCs on psoriasis. Furthermore, studies in vitro and in vivo revealed that MSCs can activate the PINK1-Parkin pathway. It was specifically manifested by elevated levels of PINK1, Parkin, p-Parkin, Beclin-1, and LC3B-II/I, coupled with a reduction in P62 protein. Subsequently, the activation of PINK1-Parkin led to decreased expressions of IL-1β, IL-6, IL-8, TNF-α, CCL7, CCL20, CCL27, and MCP-1. In vitro and in vivo experiments indicated that MSCs can reduce the levels of IL-1β, IL-6, IL-8, TNF-α, CCL7, CCL20, CCL27, and MCP-1 by inhibiting the activation of NLRP3 inflammasomes. Meanwhile, PSPH knockdown in vitro can reverse the activating effects of MSCs on the PINK1-Parkin, as shown by decreased levels of PINK, Parkin, p-Parkin, Beclin-1, and LC3B-II/I, concurrently with an elevation in P62.. Conclusions The results of this study indicated that MSCs can alleviate IMQ-induced psoriasiform dermatitis in mice by upregulating serine metabolism. The key serine metabolism enzyme PSPH may enhance PINK1/Parkin-mediated mitochondrial autophagy in psoriatic HaCaT and inhibit NLRP3 inflammasome activation in HaCaT cells, thereby alleviating skin inflammatory responses and suppressing skin p roliferation in psoriatic mice. Graphical Abstract
Lin et al. (Sat,) studied this question.