Liguo Yin,1,2 Hanbo Yang,3 Min Fu,1,2 Yanyan Bai,1,2 Naiwen Hu,1,2 Hongsheng Sun1,2 

1Department of Rheumatology and Immunology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, People’s Republic of China; 2Department of Rheumatology and Immunology, Shandong Provincial Hospital, Cheeloo College of Medicine, Shandong University, Jinan, People’s Republic of China; 3Department of Rheumatology, China-Japan Friendship Hospital, Beijing, People’s Republic of China

Correspondence: Hongsheng Sun, Email 13869192509@126.com

Purpose: Dermatomyositis (DM) is an inflammatory myopathy characterized by chronic muscle inflammation and damage. Although the pathogenesis of DM has been widely reported to be related to chronic inflammation, the role of ubiquitin E3 ligases in DM remains unclear. In the current study, we aimed to investigate the biological roles of ubiquitin E3 ligase in DM.
Methods: Deseq2 was used to screen the differential express genes in DM public datasets. Quantitative real time PCR and Western blot were used to examine the mRNA and protein levels. Co-immunoprecipitation assays were used to investigate the protein interactions between proteins. Dual-luciferase reporter assays were applied to investigate the regulation between transcription factors and targets.
Results: In the current study, we screened public DM-related datasets and focused on ubiquitin-proteasome-related enzymes. Ultimately, we identified the ubiquitin E3 ligase FBXO4. FBXO4 was significantly upregulated in DM muscle tissues compared to normal controls. In human muscle cells (LHCN-M2), FBXO4 knockout led to significant upregulation of genes related to muscle cell differentiation and significant downregulation of genes enriched in cell cycle pathways, as revealed by RNA-seq. These results suggest that FBXO4 knockout promotes muscle cell differentiation. Mechanistic studies showed that FBXO4 ubiquitinates and degrades β-catenin, thereby inhibiting the Wnt/β-catenin signaling pathway and suppressing muscle cell differentiation. On the other hand, FBXO4 may promote muscle cell apoptosis in DM by degrading MCL1. Additionally, we found that FBXO4 is regulated by the IFNα/JAK/STAT1 signaling pathway in DM and identified FBXO4 as a direct target of STAT1.
Conclusion: In conclusion, our findings suggest that IFNα/JAK/STAT1 signaling pathway elevates the expression of FBXO4 in DM and then it contributes to muscle atrophy by inhibiting differentiation and promoting apoptosis. Targeting FBXO4 may offer a novel therapeutic approach for DM.

Keywords: dermatomyositis, IFNα/JAK/STAT1 axis, FBXO4, Wnt/β-catenin signaling, muscle cell differentiation