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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Mol. Biosci.</journal-id>
<journal-title>Frontiers in Molecular Biosciences</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Mol. Biosci.</abbrev-journal-title>
<issn pub-type="epub">2296-889X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">643997</article-id>
<article-id pub-id-type="doi">10.3389/fmolb.2021.643997</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Molecular Biosciences</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>HOXC13-AS Induced Extracellular Matrix Loss <italic>via</italic> Targeting miR-497-5p/ADAMTS5 in Intervertebral Disc</article-title>
<alt-title alt-title-type="left-running-head">Jing and Liu</alt-title>
<alt-title alt-title-type="right-running-head">HOXC13-AS Induced Extracellular Matrix Loss</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Jing</surname>
<given-names>Wanli</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Liu</surname>
<given-names>Wei</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1177051/overview"/>
</contrib>
</contrib-group>
<aff id="aff1">
<label>
<sup>1</sup>
</label>Department of Orthopaedics, Tianjin First Central Hospital, <addr-line>Tianjin</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<label>
<sup>2</sup>
</label>Department of Orthopaedics, Baodi Peopele&#x2019;s Hospital, <addr-line>Tianjin</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/129147/overview">Yasuhito Ishigaki</ext-link>, Kanazawa Medical University, Japan</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1229120/overview">Kangcheng Zhao</ext-link>, Huazhong University of Science and Technology, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/963266/overview">Zheng Li</ext-link>, Peking Union Medical College Hospital (CAMS), China</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Wei Liu, <email>yugt12@163.com</email>
</corresp>
<fn fn-type="other">
<p>This article was submitted to Cellular Biochemistry, a section of the journal Frontiers in Molecular Biosciences</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>02</day>
<month>07</month>
<year>2021</year>
</pub-date>
<pub-date pub-type="collection">
<year>2021</year>
</pub-date>
<volume>8</volume>
<elocation-id>643997</elocation-id>
<history>
<date date-type="received">
<day>19</day>
<month>03</month>
<year>2021</year>
</date>
<date date-type="accepted">
<day>05</day>
<month>05</month>
<year>2021</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2021 Jing and Liu.</copyright-statement>
<copyright-year>2021</copyright-year>
<copyright-holder>Jing and Liu</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these&#x20;terms.</p>
</license>
</permissions>
<abstract>
<p>
<bold>Background/Aims:</bold> LncRNAs are a new modulator in the development of intervertebral disc degeneration. However, the functional role and mechanism of HOXC13-AS in intervertebral disc degeneration remain unclear.</p>
<p>
<bold>Methods:</bold> qRT-PCR analysis was performed to measure the relative expression levels of HOXC13-AS and miR-497-5p, and the levels of IL-1&#x3b2;, IL-6, and TNF-&#x3b1; in the medium supernatant were analyzed by ELISA. The related mechanism between HOXC13-AS and miR-497-5p was detected by luciferase assays.</p>
<p>
<bold>Results:</bold> The results revealed that TNF-&#x3b1; and IL-1&#x3b2; induced HOXC13-AS expression in NP cells. HOXC13-AS was overexpressed in IDD specimens compared to control specimens, and higher expression of HOXC13-AS was correlated with high Pfirrmann scores. Ectopic expression of HOXC13-AS promoted MMP-3 and ADAMTS4 and inhibited aggrecan and collagen II expression in NP cells. Furthermore, overexpression of HOXC13-AS increased the expression of inflammatory cytokines, including IL-1&#x3b2;, IL-6, and TNF-&#x3b1;. Our results demonstrated that TNF-&#x3b1; and IL-1&#x3b2; induced ADAMTS5 expression and suppressed miR-497-5p expression. miR-497-5p was downregulated in IDD specimens compared to control specimens, and the lower expression of miR-497-5p was correlated with high Pfirrmann scores. The miR-497-5p level was negatively proportional to HOXC13-AS expression in IDD specimens. Luciferase analysis data indicated that ADAMTS5 was a direct target gene of miR-497-5p. HOXC13-AS induced inflammatory cytokine expression and ECM degradation by modulating miR-497-5p/ADAMTS5.</p>
<p>
<bold>Conclusion:</bold> HOXC13-AS may be a treatment target for&#x20;IDD.</p>
</abstract>
<kwd-group>
<kwd>HOXC13-AS</kwd>
<kwd>intervertebral disc</kwd>
<kwd>miR-497-5p</kwd>
<kwd>ADAMTS5</kwd>
<kwd>lncRNA</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<sec id="s1">
<title>Introduction</title>
<p>Low back pain (LBP) is a common disorder that is experimentally and clinically concerning (<xref ref-type="bibr" rid="B24">Setton and Chen, 2004</xref>; <xref ref-type="bibr" rid="B22">Seguin et&#x20;al., 2008</xref>; <xref ref-type="bibr" rid="B7">Inoue and Espinoza Orias, 2011</xref>). The etiology of LBP is still unclear, and the major cause of LBP is IDD (intervertebral disc degeneration) (<xref ref-type="bibr" rid="B20">Roughley, 2004</xref>; <xref ref-type="bibr" rid="B19">Raj, 2008</xref>; <xref ref-type="bibr" rid="B16">Loreto et&#x20;al., 2011</xref>). IDD is usually considered a natural process in intervertebral disc aging, but several cases have indicated accelerated disc degeneration according to genetic and environmental factors (<xref ref-type="bibr" rid="B8">Johnson and Roberts, 2003</xref>; <xref ref-type="bibr" rid="B9">Le Maitre et&#x20;al., 2005</xref>; <xref ref-type="bibr" rid="B10">Li et&#x20;al., 2012</xref>). Disc cells secrete anomalous inflammatory cytokines due to smoking, excessive biomechanical loading, genetic predisposition, aging, and decreased nutrient transport, which can result in disc cell apoptosis, autophagy and senescence (<xref ref-type="bibr" rid="B5">Furukawa et&#x20;al., 2009</xref>; <xref ref-type="bibr" rid="B4">Clouet et&#x20;al., 2011</xref>; <xref ref-type="bibr" rid="B26">Wang et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B11">Li et&#x20;al., 2017</xref>). However, the detailed mechanisms of these processes remain unknown.</p>
<p>LncRNAs are thought to be more than 200&#xa0;nt long with limited or no protein-coding capacity and are essential modulators in aspects of cell biology through regulation at the posttranscriptional, transcriptional, and chromatin organization levels (<xref ref-type="bibr" rid="B35">Zhang et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B38">Zhao et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B39">Zou et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B34">Yu et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B3">Cao et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B13">Li et&#x20;al., 2019</xref>). References have noted that lncRNAs play roles in cell molecular functions such as cell differentiation, metastasis, apoptosis, and proliferation (<xref ref-type="bibr" rid="B18">Pan et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B31">Xiao et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B32">Xu et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B33">Yang et&#x20;al., 2018</xref>). The dysregulation of lncRNAs occurs in most types of diseases, including scoliosis, Parkinson&#x2019;s disease, osteosarcoma, and IDD (<xref ref-type="bibr" rid="B30">Xi et&#x20;al., 2017</xref>; <xref ref-type="bibr" rid="B32">Xu et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B2">Boros et&#x20;al., 2020</xref>; <xref ref-type="bibr" rid="B15">Li et&#x20;al., 2020</xref>). Recently, <xref ref-type="bibr" rid="B6">Gao et&#x20;al. (2019)</xref> noted that HOXC13-AS was upregulated in HNSC samples and that HOXC13-AS knockdown suppressed cell invasion, proliferation and invasion by modulating HMGA2/miR-383-3p. <xref ref-type="bibr" rid="B13">Li et&#x20;al. (2019)</xref> noted that HOXC13-AS was overexpressed in breast tumor samples and that HOXC13-AS overexpression induced cell growth by sponging PTEN/miR-497-5p. However, the functional role and mechanism of HOXC13-AS in IDD remain unclear.</p>
<p>We found that HOXC13-AS was overexpressed in IDD specimens compared to control specimens and that HOXC13-AS induced inflammatory cytokine expression and ECM degradation.</p>
</sec>
<sec sec-type="materials|methods" id="s2">
<title>Materials and Methods</title>
<sec id="s2-1">
<title>Sample Selection and Cell Transfection</title>
<p>Human IVD specimens from IDD patients and vertebral fracture cases were collected from our hospital. All patients underwent lumbar MRI, and the degree of disc degeneration was analyzed using modified Pfirrmann scoring. The NP cell line was obtained from ScienCell (San Diego, California, United&#x20;States, No. Catalog &#x23;4800) and was cultured in F12/DMEM supplemented with streptomycin, penicillin, and serum. siRNA-NC and ADAMTS5 siRNA, pcDNA-HOXC13-AS and pcDNA-control, miR-497-5p scramble, and the mimics were synthetized by GenePharma. These vectors were transfected into NP cells using Lipofectamine 2000. The study was approved by the ethics committee of Tianjin First Central Hospital and followed the Declaration of Helsinki. Written consents were obtained from all&#x20;cases.</p>
</sec>
<sec id="s2-2">
<title>Luciferase Assays</title>
<p>miR-497-5p was predicted to link with the ADAMTS5&#x20;3&#x2032;-UTR using TargetScan software. Wild-type (WT) and mutant (Mut)-type 3&#x2032; UTR fragments of ADAMTS5 were cloned by PCR. NP cells were cultured in 96-well dishes and cotransfected with Mut ADAMTS5 3&#x2032; UTR and WT ADAMTS5 3&#x2032; UTR and miR-497-5p scramble and mimic. After 48&#xa0;h, the luciferase value was analyzed using a luciferase analysis kit (Promega).</p>
</sec>
<sec id="s2-3">
<title>ELISA</title>
<p>The levels of IL-1&#x3b2;, IL-6, and TNF-&#x3b1; in the medium supernatant were analyzed by ELISA (IL-1&#x3b2;, IL-6, and TNF-&#x3b1;, R&#x26;D Systems) following the manufacturer&#x2019;s instructions.</p>
</sec>
<sec id="s2-4">
<title>qRT-PCR</title>
<p>A TRIzol kit (Invitrogen) was used to extract RNA from NP cells and specimens. RT-qPCR analysis was applied to study HOXC13-AS, mRNA, and miR-497-5p expression levels using SYBR Reagent (TaKaRa, Beijing) on an ABI 7300 PCR system (Applied Biosystems, MA). The PCR primers were as follows: HOXC13-AS qF: TCC&#x200b;CAC&#x200b;GGC&#x200b;TTT&#x200b;CTT&#x200b;AGG&#x200b;TCA, HOXC13-AS qR: GAC&#x200b;TCA&#x200b;ATT&#x200b;CCA&#x200b;CGG&#x200b;AGA&#x200b;TGC; ADAMTS5 qF: GAG&#x200b;GAT&#x200b;TTA&#x200b;TGT&#x200b;GGG&#x200b;CAT&#x200b;CAT&#x200b;TCA&#x200b;TGT&#x200b;G, ADAMTS5 qR: CAT&#x200b;ATG&#x200b;GTC&#x200b;CCA&#x200b;ACG&#x200b;TCT&#x200b;GC; miR-497-5p qF: CAG&#x200b;CAG&#x200b;CAC&#x200b;ACT&#x200b;GTG&#x200b;GTT&#x200b;TGT; U6 qF: CTCGCTTCGGCAGCACA, qR: AAC&#x200b;GCT&#x200b;TCA&#x200b;CGA&#x200b;ATT&#x200b;TGC&#x200b;GT; GAPDH qF: GCT&#x200b;CTC&#x200b;TGC&#x200b;TCC&#x200b;TCC&#x200b;TGT&#x200b;TC, qR: ACG&#x200b;ACC&#x200b;AAA&#x200b;TCC&#x200b;GTT&#x200b;GAC&#x200b;TC. U6 was used as a control for miR-497-5p, and GAPDH was applied for other genes.</p>
</sec>
<sec id="s2-5">
<title>Statistical Assay</title>
<p>The results are expressed as the means&#x20;&#xb1; SD. Statistical assays were carried out using SPSS, and significant differences were determined with Student&#x2019;s <italic>t</italic>&#x20;test. Spearman&#x2019;s two-tailed correlation analysis was used for HOXC13-AS and miR-497-5p expression. <italic>p</italic>&#x20;&#x3c; 0.05 was set to be statistically significant.</p>
</sec>
</sec>
<sec sec-type="results" id="s3">
<title>Results</title>
<sec id="s3-1">
<title>TNF-&#x3b1; and IL-1&#x3b2; Induced HOXC13-AS and ADAMTS5 Expression and Suppressed miR-497-5p Expression</title>
<p>First, we noted that treatments with TNF-&#x3b1; and IL-1&#x3b2; induced HOXC13-AS expression in a dose-dependent manner in NP cells (<xref ref-type="fig" rid="F1">Figures 1A,B</xref>). The miR-497-5p expression levels were decreased in NP cells treated with TNF-&#x3b1; and IL-1&#x3b2; (<xref ref-type="fig" rid="F1">Figures 1C,D</xref>). Moreover, treatments with TNF-&#x3b1; and IL-1&#x3b2; increased ADAMTS5 expression in a dose-dependent manner in NP cells (<xref ref-type="fig" rid="F1">Figures&#x20;1E,F</xref>).</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>TNF-&#x3b1; and IL-1&#x3b2; induced HOXC13-AS and ADAMTS5 expression and suppressed miR-497-5p expression. <bold>(A)</bold> TNF-&#x3b1; induced HOXC13-AS expression in a dose-dependent manner in NP cells. <bold>(B)</bold> HOXC13-AS expression was measured by qRT-PCR. <bold>(C)</bold> miR-497-5p expression was decreased in NP cells treated with TNF-&#x3b1;. <bold>(D)</bold> miR-497-5p expression was detected by qRT-PCR. <bold>(E)</bold> TNF-&#x3b1; treatment increased ADAMTS5 expression in a dose-dependent manner in NP cells. <bold>(F)</bold> ADAMTS5 expression was determined by qRT-PCR. &#x2a;<italic>p</italic>&#x20;&#x3c; 0.05, &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01, and &#x2a;&#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.001.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g001.tif"/>
</fig>
</sec>
<sec id="s3-2">
<title>HOXC13-AS was Upregulated in IDD Specimens</title>
<p>We then determined that HOXC13-AS was overexpressed in IDD specimens compared to control specimens by RT-qPCR (<xref ref-type="fig" rid="F2">Figure&#x20;2A</xref>). Moreover, the higher expression of HOXC13-AS was correlated with high Pfirrmann scores (<xref ref-type="fig" rid="F2">Figure&#x20;2B</xref>).</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>HOXC13-AS was upregulated in IDD specimens. <bold>(A)</bold> HOXC13-AS was overexpressed in IDD specimens compared to control specimens by RT-qPCR. <bold>(B)</bold> Higher expression of HOXC13-AS was correlated with high Pfirrmann scores. &#x2a;<italic>p</italic>&#x20;&#x3c; 0.05, &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01, and &#x2a;&#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c;&#x20;0.001.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g002.tif"/>
</fig>
</sec>
<sec id="s3-3">
<title>miR-497-5p was Downregulated in IDD Specimens</title>
<p>Then, we found that miR-497-5p was downregulated in IDD specimens compared to control specimens by RT-qPCR (<xref ref-type="fig" rid="F3">Figure&#x20;3A</xref>). Moreover, the lower expression of miR-497-5p was correlated with high Pfirrmann scores (<xref ref-type="fig" rid="F3">Figure&#x20;3B</xref>). The miR-497-5p level was negatively proportional to HOXC13-AS expression in IDD specimens (<xref ref-type="fig" rid="F3">Figure&#x20;3C</xref>).</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>miR-497-5p was downregulated in IDD specimens. <bold>(A)</bold> miR-497-5p was downregulated in IDD specimens compared to control specimens by RT-qPCR. <bold>(B)</bold> Lower expression of miR-497-5p was correlated with high Pfirrmann scores. <bold>(C)</bold> miR-497-5p expression was negatively proportional to HOXC13-AS expression in IDD specimens. &#x2a;<italic>p</italic>&#x20;&#x3c; 0.05, &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01, and &#x2a;&#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.001.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g003.tif"/>
</fig>
</sec>
<sec id="s3-4">
<title>miR-497-5p Targets ADAMTS5 Expression in NP Cells</title>
<p>We utilized TargetScan software to predict that miR-497-5p was linked to the ADAMTS5&#x20;3&#x2032;-UTR (<xref ref-type="fig" rid="F4">Figure&#x20;4A</xref>). miR-497-5p was obviously upregulated in NP cells after treatment with the miR-497-5p mimic (<xref ref-type="fig" rid="F4">Figure&#x20;4B</xref>). Luciferase analysis data suggested that miR-497-5p overexpression inhibited the luciferase value of the wild-type reporter gene but not the mutated 3&#x2032;UTR vector (<xref ref-type="fig" rid="F4">Figure&#x20;4C</xref>). Ectopic miR-497-5p expression decreased ADAMTS5 levels in NP cells (<xref ref-type="fig" rid="F4">Figure&#x20;4D</xref>). HOXC13-AS was obviously upregulated in NP cells after treatment with the pcDNA-HOXC13-AS vector (<xref ref-type="fig" rid="F4">Figure&#x20;4E</xref>). Upregulation of HOXC13-AS expression inhibited miR-497-5p expression in NP cells (<xref ref-type="fig" rid="F4">Figure&#x20;4F</xref>). Overexpression of HOXC13-AS suppressed ADAMTS5 expression in NP cells (<xref ref-type="fig" rid="F4">Figure&#x20;4G</xref>).</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>miR-497-5p targets ADAMTS5 expression in NP cells. <bold>(A)</bold> miR-497-5p was predicted to link with the ADAMTS5&#x20;3&#x2032;-UTR using TargetScan software. <bold>(B)</bold> miR-497-5p was obviously upregulated in NP cells after treatment with the miR-497-5p mimic. <bold>(C)</bold> Luciferase analysis data showed that miR-497-5p overexpression inhibited the luciferase expression of the wild-type reporter gene but not the mutated 3&#x2032;UTR vector. <bold>(D)</bold> Ectopic miR-497-5p expression decreased ADAMTS5 levels in NP cells. <bold>(E)</bold> HOXC13-AS expression was measured by qRT-PCR. <bold>(F)</bold> Upregulation of HOXC13-AS expression inhibited miR-497-5p expression in NP cells. <bold>(G)</bold> ADAMTS5 expression was measured by qRT-PCR. &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g004.tif"/>
</fig>
</sec>
<sec id="s3-5">
<title>HOXC13-AS Induced Inflammatory Cytokine Expression and ECM Degeneration</title>
<p>Ectopic expression of HOXC13-AS enhanced MMP-3 (<xref ref-type="fig" rid="F5">Figure&#x20;5A</xref>) and ADAMTS4 (<xref ref-type="fig" rid="F5">Figure&#x20;5B</xref>) expression in NP cells. Overexpression of HOXC13-AS decreased aggrecan (<xref ref-type="fig" rid="F5">Figure&#x20;5C</xref>) and collagen II (<xref ref-type="fig" rid="F5">Figure&#x20;5D</xref>) expression in NP cells. By ELISA, we determined that elevated expression of HOXC13-AS increased the expression levels of three inflammatory cytokines, IL-1&#x3b2; (<xref ref-type="fig" rid="F5">Figure&#x20;5E</xref>), IL-6 (<xref ref-type="fig" rid="F5">Figure&#x20;5F</xref>), and TNF-&#x3b1; (<xref ref-type="fig" rid="F5">Figure&#x20;5G</xref>).</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>HOXC13-AS induced inflammatory cytokine expression and ECM degeneration. <bold>(A)</bold> MMP-3 expression was measured by qRT-PCR. <bold>(B)</bold> Ectopic expression of HOXC13-AS promoted ADAMTS4 expression in NP cells. <bold>(C)</bold> Aggrecan expression was determined by qRT-PCR. <bold>(D)</bold> Collagen II expression was measured by qRT-PCR. <bold>(E)</bold> IL-1&#x3b2; expression was determined by ELISA. <bold>(F)</bold> IL-6 expression was determined by ELISA. <bold>(G)</bold> TNF-&#x3b1; expression was determined by ELISA. &#x2a;&#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.001.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g005.tif"/>
</fig>
</sec>
<sec id="s3-6">
<title>miR-497-5p Suppressed Inflammatory Cytokine Expression and ECM Degeneration</title>
<p>Overexpression of miR-497-5p inhibited MMP-3 (<xref ref-type="fig" rid="F6">Figure&#x20;6A</xref>) and ADAMTS4 (<xref ref-type="fig" rid="F6">Figure&#x20;6B</xref>) expression in NP cells. Ectopic expression of miR-497-5p enhanced aggrecan (<xref ref-type="fig" rid="F6">Figure&#x20;6C</xref>) and collagen II (<xref ref-type="fig" rid="F6">Figure&#x20;6D</xref>) expression in NP cells. By ELISA, we showed that elevated expression of miR-497-5p increased the expression levels of three inflammatory cytokines, IL-1&#x3b2; (<xref ref-type="fig" rid="F6">Figure&#x20;6E</xref>), IL-6 (<xref ref-type="fig" rid="F6">Figure&#x20;6F</xref>), and TNF-&#x3b1; (<xref ref-type="fig" rid="F6">Figure&#x20;6G</xref>).</p>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption>
<p>miR-497-5p suppressed inflammatory cytokine expression and ECM degeneration. <bold>(A)</bold> MMP-3 expression was detected by qRT-PCR. <bold>(B)</bold> Overexpression of miR-497-5p suppressed ADAMTS4 expression in NP cells. <bold>(C)</bold> Aggrecan expression was measured by qRT-PCR. <bold>(D)</bold> Collagen II expression was detected by qRT-PCR. <bold>(E)</bold> IL-1&#x3b2; expression was determined by ELISA. <bold>(F)</bold> IL-6 expression was determined by ELISA. <bold>(G)</bold> TNF-&#x3b1; expression was determined by ELISA. &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g006.tif"/>
</fig>
</sec>
<sec id="s3-7">
<title>HOXC13-AS Induced Inflammatory Cytokine Expression and ECM Degradation by Modulating miR-497-5p/ADAMTS5</title>
<p>We then explored the effects of three different treatment conditions on inflammatory cytokine expression and ECM degradation in NP cells. ADAMTS5 was obviously downregulated in NP cells after treatment with ADAMTS5 siRNA (<xref ref-type="fig" rid="F7">Figure&#x20;7A</xref>). HOXC13-AS promoted ADAMTS4 and MMP-3 expression, while ADAMTS5 siRNA inhibited this function (<xref ref-type="fig" rid="F7">Figures 7B,C</xref>). HOXC13-AS overexpression inhibited aggrecan and collagen II expression, while downregulation of ADAMTS5 expression enhanced this effect (<xref ref-type="fig" rid="F7">Figures 7D,E</xref>). Elevated expression of HOXC13-AS promoted the expression of three inflammatory cytokines, IL-1&#x3b2;, IL-6, and TNF-&#x3b1;, while inhibition of ADAMTS5 expression decreased this effect (<xref ref-type="fig" rid="F7">Figures 7F&#x2013;H</xref>).</p>
<fig id="F7" position="float">
<label>FIGURE 7</label>
<caption>
<p>HOXC13-AS induced inflammatory cytokine expression and ECM degradation by modulating miR-497-5p/ADAMTS5. <bold>(A)</bold> ADAMTS5 was obviously downregulated in NP cells after treatment with ADAMTS5 siRNA. <bold>(B)</bold> ADAMTS4 expression was measured by qRT-PCR. <bold>(C)</bold> MMP-3 expression was measured by qRT-PCR. <bold>(D)</bold> Aggrecan expression was measured by qRT-PCR. <bold>(E)</bold> OXC13-AS overexpression inhibited collagen II expression, while downregulation of ADAMTS5 expression enhanced this effect. <bold>(F)</bold> IL-1&#x3b2; expression was determined by ELISA. <bold>(G)</bold> IL-6 expression was determined by ELISA. <bold>(H)</bold> TNF-&#x3b1; expression was determined by ELISA. &#x2a;<italic>p</italic>&#x20;&#x3c; 0.05, &#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.01, and &#x2a;&#x2a;&#x2a;<italic>p</italic>&#x20;&#x3c; 0.001.</p>
</caption>
<graphic xlink:href="fmolb-08-643997-g007.tif"/>
</fig>
</sec>
</sec>
<sec sec-type="discussion" id="s4">
<title>Discussion</title>
<p>Recently, abundant references have illustrated that lncRNA dysregulation is involved in the development of several diseases, including IDD (<xref ref-type="bibr" rid="B12">Li et&#x20;al., 2018</xref>). In Ruan&#x2019;s study, p53, p21, and NEAT1 were overexpressed in IDD samples, and ectopic expression of NEAT1 promoted ECM degradation by regulating MAPK/ERK1/2 pathway signaling expression (<xref ref-type="bibr" rid="B21">Ruan et&#x20;al., 2018</xref>). Wang showed that linc-ADAMTS5 was negatively correlated with RREB1 to suppress ADAMTS5 and ECM degeneration in IDD (<xref ref-type="bibr" rid="B27">Wang K. et&#x20;al., 2017</xref>). Moreover, <xref ref-type="bibr" rid="B28">Wang X. B. et&#x20;al. (2017)</xref> found that RP11-296A18.3 was overexpressed in IDD samples and that RP11-296A18.3 knockdown decreased NP cell growth and ECM synthesis by modulating miR-138/HIF1A expression. <xref ref-type="bibr" rid="B6">Gao et&#x20;al. (2019)</xref> noted that HOXC13-AS was upregulated in HNSC samples and that HOXC13-AS knockdown suppressed cell invasion, proliferation, and invasion by modulating HMGA2/miR-383-3p. <xref ref-type="bibr" rid="B14">Li X. W. et&#x20;al. (2019)</xref> noted that HOXC13-AS was overexpressed in breast tumor samples and that HOXC13-AS overexpression induced cell growth by sponging PTEN/miR-497-5p. Our research revealed that TNF-&#x3b1; and IL-1&#x3b2; induced HOXC13-AS expression in NP cells. HOXC13-AS was overexpressed in IDD specimens compared to control specimens, and higher expression of HOXC13-AS was correlated with high Pfirrmann scores. Ectopic expression of HOXC13-AS promoted MMP-3 and ADAMTS4 and inhibited aggrecan and collagen II expression in NP cells. Overexpression of miR-497-5p suppressed inflammatory cytokine expression and ECM degeneration in NP cells. Furthermore, overexpression of HOXC13-AS increased the expression levels of three inflammatory cytokines, IL-1&#x3b2;, IL-6, and TNF-&#x3b1;.</p>
<p>LncRNAs act as posttranscriptional modulators of miRNA expression by functioning as &#x201c;sponges&#x201d; (<xref ref-type="bibr" rid="B1">Bian et&#x20;al., 2017</xref>; <xref ref-type="bibr" rid="B25">Tian et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B36">Zhang et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B3">Cao et&#x20;al., 2019</xref>). In line with previous data, we noted that upregulation of HOXC13-AS expression inhibited miR-497-5p expression in NP cells (<xref ref-type="bibr" rid="B14">Li et&#x20;al., 2019</xref>). Furthermore, we utilized TargetScan software to predict that miR-497-5p was linked to the ADAMTS5&#x20;3&#x2032;-UTR. Luciferase analysis data suggested that ADAMTS5 was a direct gene of miR-497-5p. Previous studies have suggested that ADAMTS5 plays critical roles in the progression of IDD (<xref ref-type="bibr" rid="B17">Ngo et&#x20;al., 2017</xref>; <xref ref-type="bibr" rid="B29">Wang et&#x20;al., 2018</xref>). In Seki&#x2019;s study, they showed that ADAMTS5 siRNA injection inhibited NP sample degradation and ameliorated histologic and MRI grades (<xref ref-type="bibr" rid="B23">Seki et&#x20;al., 2009</xref>). <xref ref-type="bibr" rid="B37">Zhao et&#x20;al. (2011)</xref> indicated that IL-1&#x3b2; promoted ADAMTS-5 expression in NP cells. Our results illustrated that TNF-&#x3b1; and IL-1&#x3b2; induced ADAMTS5 expression and suppressed miR-497-5p expression. miR-497-5p was downregulated in IDD specimens compared to control specimens, and the lower expression of miR-497-5p was correlated with high Pfirrmann scores. The miR-497-5p expression level was negatively proportional to HOXC13-AS expression in IDD specimens. HOXC13-AS induced inflammatory cytokine expression and ECM degradation by modulating miR-497-5p/ADAMTS5.</p>
<p>To conclude, we found that HOXC13-AS was overexpressed in IDD specimens compared to control specimens and that HOXC13-AS induced inflammatory cytokine expression and ECM degradation by modulating miR-497-5p/ADAMTS5. These results suggest that HOXC13-AS may be a treatment target for&#x20;IDD.</p>
</sec>
</body>
<back>
<sec id="s5">
<title>Data Availability Statement</title>
<p>The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.</p>
</sec>
<sec id="s6">
<title>Ethics Statement</title>
<p>The studies involving human participants were reviewed and approved by the ethics committee of Tianjin First Central Hospital. The patients/participants provided their written informed consent to participate in this&#x20;study.</p>
</sec>
<sec id="s7">
<title>Author Contributions</title>
<p>WL and WJ have all contributed to the design and writing of the manuscript.</p>
</sec>
<sec sec-type="COI-statement" id="s8">
<title>Conflict of Interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
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