Intervening upregulated SLC7A5 could mitigate inflammatory mediator by mTOR-P70S6K signal in rheumatoid arthritis synoviocytes

Jing Xu,Jiaxiang Zhang,Shemin Lu,Liesu Meng,Wenhua Zhu,Si Wang,Jiawen Xu,Congshan Jiang,Yongsong Cai,Xipeng Wang,Fujun Zhang,Ke Xu,Yan Han,Yuanxu Guo,Peng Xu,Manman Geng,Qilan Ning

doi:10.1186/s13075-020-02296-8

Jing Xu, Jiaxiang Zhang + Show 15 more

Open Access

https://doi.org/10.1186/s13075-020-02296-8

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Abstract

ObjectiveThe disruption of metabolic events and changes to nutrient and oxygen availability due to sustained inflammation in RA increases the demand of bioenergetic and biosynthetic processes within the damaged tissue. The current study aimed to understand the molecular mechanisms of SLC7A5 (amino acid transporter) in synoviocytes of RA patients.MethodsSynovial tissues were obtained from OA and RA patients. Fibroblast-like synoviocytes (FLS) were isolated, and SLC7A5 expression was examined by using RT-qPCR, immunofluorescence, and Western blotting. RNAi and antibody blocking treatments were used to knockdown SLC7A5 expression or to block its transporter activities. mTOR activity assay and MMP expression levels were monitored in RA FLS under amino acid deprivation or nutrient-rich conditions.ResultsRA FLS displayed significantly upregulated expression of SLC7A5 compared to OA FLS. Cytokine IL-1β was found to play a crucial role in upregulating SLC7A5 expression via the NF-κB pathway. Intervening SLC7A5 expression with RNAi or blocking its function by monoclonal antibody ameliorated MMP3 and MMP13 protein expression. Conversely, upregulation of SLC7A5 or tryptophan supplementation enhanced mTOR-P70S6K signals which promoted the protein translation of MMP3 and MMP13 in RA FLS.ConclusionActivated NF-κB pathway upregulates SLC7A5, which enhances the mTOR-P70S6K activity and MMP3 and MMP13 expression in RA FLS.

Highlights

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a global prevalence of 0.24% [1], characterized by synovial hyperplasia and progressive destruction of mainly the small joints
Solute carrier family 7 member 5 (SLC7A5) expression is upregulated in fibroblast-like synoviocytes from RA patients To investigate the involvement of SLC7A5 in RA pathogenesis, synovial tissues were collected from RA and OA patients
Immunofluorescence staining of the synovial tissues from RA patients revealed that SLC7A5 was overexpressed and co-localized in vimentin-positive cells (FLS) (Fig. 1f, g)

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a global prevalence of 0.24% [1], characterized by synovial hyperplasia and progressive destruction of mainly the small joints. RA FLSs are described to present a tumor-like phenotype [3], with increased invasiveness into the extracellular matrix (ECM), which further exacerbates synovial hyperplasia and joint damage [4, 5]. These quickly proliferated FLS demand high energy, which is well associated with highlevel transportation and consumption of glucose and amino acids. The conditional knockout of Slc7a5 showed that Slc7a5 worked as a checkpoint in T cell activation via the mTORC1 complex [11]. An mRNA expression profiling study has documented the elevated levels of SLC7A5 in RA synovial tissue [14]

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