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The antiviral protein viperin regulates chondrogenic differentiation via CXCL10 protein secretion.

ABSTRACT: Viperin (also known as radical SAM domain-containing 2 (RSAD2)) is an interferon-inducible and evolutionary conserved protein that participates in the cell's innate immune response against a number of viruses. Viperin mRNA is a substrate for endoribonucleolytic cleavage by RNase mitochondrial RNA processing (MRP) and mutations in the RNase MRP small nucleolar RNA (snoRNA) subunit of the RNase MRP complex cause cartilage-hair hypoplasia (CHH), a human developmental condition characterized by metaphyseal chondrodysplasia and severe dwarfism. It is unknown how CHH-pathogenic mutations in RNase MRP snoRNA interfere with skeletal development, and aberrant processing of RNase MRP substrate RNAs is thought to be involved. We hypothesized that viperin plays a role in chondrogenic differentiation. Using immunohistochemistry, real-time quantitative PCR, immunoblotting, ELISA, siRNA-mediated gene silencing, plasmid-mediated gene overexpression, label-free MS proteomics, and promoter reporter bioluminescence assays, we discovered here that viperin is expressed in differentiating chondrocytic cells and regulates their protein secretion and the outcome of chondrogenic differentiation by influencing transforming growth factor ? (TGF-?)/SMAD family 2/3 (SMAD2/3) activity via C-X-C motif chemokine ligand 10 (CXCL10). Of note, we observed disturbances in this viperin-CXCL10-TGF-?/SMAD2/3 axis in CHH chondrocytic cells. Our results indicate that the antiviral protein viperin controls chondrogenic differentiation by influencing secretion of soluble proteins and identify a molecular route that may explain impaired chondrogenic differentiation of cells from individuals with CHH.

SUBMITTER: Steinbusch MMF

PROVIDER: S-EPMC6442052 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Project description:Mutations in the RMRP gene are the origin of cartilage-hair hypoplasia. Cartilage-hair hypoplasia is associated with severe dwarfism caused by impaired skeletal development. However, it is not clear why mutations in the RMRP gene lead to skeletal dysplasia. Viperin is a known substrate of RMRP. Since chondrogenic differentiation of the growth plate is required for development of the long bones, we hypothesized that viperin functions as a chondrogenic regulator downstream of RMRP. Viperin protein is expressed throughout the stages of chondrogenic differentiation in vivo. Viperin gene expression is increased during knockdown of Rmrp RNA in the ATDC5 model for chondrogenic differentiation. Viperin is expressed during ATDC5 chondrogenic differentiation. Viperin knockdown reduces, while viperin overexpression increases overall protein secretion, with CXCL10 identified as a potential target via mass spectrometry-proteomics. CXCL10 protein expression is reduced during knockdown and increased during overexpression of viperin and CXCL10 protein expression coincides with viperin expression in ATDC5 chondrogenic differentiation. Viperin knockdown induces, while viperin overexpression reduces TGFβ activity. Furthermore, viperin knockdown conditioned media increases, while viperin overexpression conditioned media reduces chondrogenic differentiation of ATDC5 cells. TGFβ target genes Pai1 and Smad7 are increased during knockdown and reduced during overexpression of viperin. Moreover, TGFβ activity is reduced when differentiating ATDC5 cells are exposed to CXCL10 and, acting as a viperin overexpression mimic, CXCL10 similarly reduces chondrogenic differentiation of ATDC5. Lastly, we show that in CHH patient cells, RMRP expression is reduced and viperin expression is increased, coinciding with reduced chondrogenic differentiation and increased CXCL10 expression, possibly explaining the CHH phenotype. Together our data show that viperin may play a pivotal role in chondrogenic differentiation, with potential consequences for cartilage-hair hypoplasia pathobiology.

Project description:BackgroundGEM (GTP-binding protein overexpressed in skeletal muscle) is one of the atypical small GTPase subfamily members recently identified as a regulator of cell differentiation. Abnormal chondrogenesis coupled with an imbalance in the turnover of cartilaginous matrix formation is highly relevant to the onset and progression of osteoarthritis (OA). However, how GEM regulates chondrogenic differentiation remains unexplored.MethodsCartilage tissues were obtained from OA patients and graded according to the ORASI and ICRS grading systems. The expression alteration of GEM was detected in the Grade 4 cartilage compared to Grade 0 and verified in OA mimic culture systems. Next, to investigate the specific function of GEM during these processes, we generated a Gem knockdown (Gem-Kd) system by transfecting siRNA targeting Gem into ATDC5 cells. Acan, Col2a1, Sox9, and Wnt target genes of Gem-Kd ATDC5 cells were detected during induction. The transcriptomic sequencing analysis was performed to investigate the mechanism of GEM regulation. Wnt signaling pathways were verified by real-time PCR and immunoblot analysis. Finally, a rescue model generated by treating Gem-KD ATDC5 cells with a Wnt signaling agonist was established to validate the mechanism identified by RNA sequencing analysis.ResultsA decreased expression of GEM in OA patients' cartilage tissues and OA mimic chondrocytes was observed. While during chondrogenesis differentiation and cartilage matrix formation, the expression of GEM was increased. Gem silencing suppressed chondrogenic differentiation and the expressions of Acan, Col2a1, and Sox9. RNA sequencing analysis revealed that Wnt signaling was downregulated in Gem-Kd cells. Decreased expression of Wnt signaling associated genes and the total β-CATENIN in the nucleus and cytoplasm were observed. The exogenous Wnt activation exhibited reversed effect on Gem loss-of-function cells.ConclusionThese findings collectively validated that GEM functions as a novel regulator mediating chondrogenic differentiation and cartilage matrix formation through Wnt/β-catenin signaling.

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The antiviral protein viperin regulates chondrogenic differentiation via CXCL10 protein secretion.

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