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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Immunol.</journal-id>
<journal-title-group>
<journal-title>Frontiers in Immunology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Immunol.</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">1664-3224</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fimmu.2026.1641755</article-id>
<article-version article-version-type="Version of Record" vocab="NISO-RP-8-2008"/>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Original Research</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>Gut microbial alterations associated with the exacerbation of experimental autoimmune uveitis in PGRN-deficient mice</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author" equal-contrib="yes">
<name><surname>Zhou</surname><given-names>Wenjun</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="author-notes" rid="fn003"><sup>&#x2020;</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/1612166/overview"/>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
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<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="investigation" vocab-term-identifier="https://credit.niso.org/contributor-roles/investigation/">Investigation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &amp; editing</role>
</contrib>
<contrib contrib-type="author" equal-contrib="yes">
<name><surname>Zhang</surname><given-names>Song</given-names></name>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<xref ref-type="author-notes" rid="fn003"><sup>&#x2020;</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Formal analysis" vocab-term-identifier="https://credit.niso.org/contributor-roles/formal-analysis/">Formal analysis</role>
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</contrib>
<contrib contrib-type="author" corresp="yes">
<name><surname>Wang</surname><given-names>Chaokui</given-names></name>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="corresp" rid="c001"><sup>*</sup></xref>
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<aff id="aff1"><label>1</label><institution>Department of Ophthalmology, The Affiliated Yongchuan Hospital of Chongqing Medical University</institution>, <city>Chongqing</city>,&#xa0;<country country="cn">China</country></aff>
<aff id="aff2"><label>2</label><institution>State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University</institution>, <city>Nanjing</city>,&#xa0;<country country="cn">China</country></aff>
<aff id="aff3"><label>3</label><institution>Ophthalmology Medical Center, The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory for the Prevention and Treatment of Major Blinding Eye Diseases, Chongqing Branch (Municipality Division) of National Clinical Research Centre for Ocular Diseases</institution>, <city>Chongqing</city>,&#xa0;<country country="cn">China</country></aff>
<author-notes>
<corresp id="c001"><label>*</label>Correspondence: Chaokui Wang, <email xlink:href="mailto:wangchaokui1983@163.com">wangchaokui1983@163.com</email></corresp>
<fn fn-type="equal" id="fn003">
<label>&#x2020;</label>
<p>These authors have contributed equally to this work and share first authorship</p></fn>
</author-notes>
<pub-date publication-format="electronic" date-type="pub" iso-8601-date="2026-01-23">
<day>23</day>
<month>01</month>
<year>2026</year>
</pub-date>
<pub-date publication-format="electronic" date-type="collection">
<year>2026</year>
</pub-date>
<volume>17</volume>
<elocation-id>1641755</elocation-id>
<history>
<date date-type="received">
<day>05</day>
<month>06</month>
<year>2025</year>
</date>
<date date-type="accepted">
<day>06</day>
<month>01</month>
<year>2026</year>
</date>
<date date-type="rev-recd">
<day>29</day>
<month>12</month>
<year>2025</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2026 Zhou, Zhang and Wang.</copyright-statement>
<copyright-year>2026</copyright-year>
<copyright-holder>Zhou, Zhang and Wang</copyright-holder>
<license>
<ali:license_ref start_date="2026-01-23">https://creativecommons.org/licenses/by/4.0/</ali:license_ref>
<license-p>This is an open-access article distributed under the terms of the <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution License (CC BY)</ext-link>. 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 terms.</license-p>
</license>
</permissions>
<abstract>
<sec>
<title>Purpose</title>
<p>Progranulin (PGRN) has been shown to play a protective role in the development of a variety of immune-mediated diseases, and the gut microbiome has been implicated in the pathogenesis of autoimmune diseases. In this study, we investigate the changes in the gut microbiota and their association with the severity of experimental autoimmune uveitis (EAU) in PGRN-deficient mice.</p>
</sec>
<sec>
<title>Methods</title>
<p>WT and PGRN-deficient C57BL/6 mice were used to induce EAU using interphotoreceptor-binding protein peptide. Gastrointestinal (GI) contents collected from both groups of induced EAU were subjected to 16S rRNA gene sequencing analysis.</p>
</sec>
<sec>
<title>Results</title>
<p>PGRN-deficient mice developed exacerbated EAU compared to wild-type (WT) mice. The microbial richness of the GI contents in PGRN-deficient EAU&#xa0;mice was significantly lower than in WT mice. The PGRN-deficient EAU mice&#xa0;showed a significantly reduced microbial abundance in five phyla, namely, <italic>Cyanobacteria</italic>, <italic>Epsilonbacteraeota</italic>, <italic>Firmicutes</italic>, <italic>Nitrospirae</italic>, and <italic>Patescibacteria</italic>, and a significantly increased abundance in the other four phyla, namely, <italic>Deferribacteres</italic>, <italic>Proteobacteria</italic>, <italic>Spirochaetes</italic>, and <italic>Tenericutes</italic>. More importantly, a newly emerged phylum named <italic>Chlamydiae</italic> was detected in the gut microbial community of PGRN-deficient EAU mice. The histopathological scores were significantly negatively correlated with gut microbial abundance and significantly positively correlated with chlamydial abundance.</p>
</sec>
<sec>
<title>Conclusion</title>
<p>Our results showed that PGRN plays a protective role in EAU, and the significant changes in the gut microbiome may be associated with the exacerbation of inflammation in the PGRN-deficient EAU mice.</p>
</sec>
</abstract>
<kwd-group>
<kwd>16S rRNA gene sequencing</kwd>
<kwd>autoimmune</kwd>
<kwd>gut microbiome</kwd>
<kwd>progranulin</kwd>
<kwd>uveitis</kwd>
</kwd-group>
<funding-group>
<funding-statement>The author(s) declared that financial support was received for this work and/or its publication. This study is funded by National Natural Science Foundation Project (82371046) and Chongqing Natural Science Foundation Project (CSTB2023NSCQ-MSX0306 and CSTB2024NSCQ-KJFZMSX0048).</funding-statement>
</funding-group>
<counts>
<fig-count count="4"/>
<table-count count="0"/>
<equation-count count="0"/>
<ref-count count="38"/>
<page-count count="8"/>
<word-count count="3113"/>
</counts>
<custom-meta-group>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Autoimmune and Autoinflammatory Disorders : Autoimmune Disorders</meta-value>
</custom-meta>
</custom-meta-group>
</article-meta>
</front>
<body>
<sec id="s1" sec-type="intro">
<title>Introduction</title>
<p>PGRN binds competitively to tumor necrosis factor receptor (TNFR) and is therefore considered to be an endogenous antagonist of TNF-&#x3b1;, and it has been shown to play a protective role in a variety of autoimmune diseases, including inflammatory bowel disease (<xref ref-type="bibr" rid="B1">1</xref>), osteoarthritis (<xref ref-type="bibr" rid="B2">2</xref>), and rheumatoid arthritis (<xref ref-type="bibr" rid="B3">3</xref>). However, PGRN has also been shown to play a pathogenic role in some disease models, including diabetes mellitus and lupus nephritis (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B5">5</xref>). In our study, we investigated the role of PGRN in experimental autoimmune uveitis (EAU), which shares clinical and immunopathological features with human uveitis. EAU is a classical animal model for the study of human uveitis and systemic autoimmune diseases. It can be induced in susceptible mouse strains (e.g., C57BL/6) by immunizing these mice with specific retinal antigens and adjuvants. Th1 and Th17 cells are thought to be effector immune cells that can induce or exacerbate inflammation, whereas Treg cells are thought to be a regulatory immune cell subset that can suppress it in this model (<xref ref-type="bibr" rid="B6">6</xref>).</p>
<p>Gut microbiota alterations critically regulate the immune system and influence disease severity in autoimmune models (<xref ref-type="bibr" rid="B7">7</xref>)&#x2014;for example, patients with Behcet&#x2019;s disease (BD) have a distinct gut microbiome signature compared to healthy controls, and the fecal transplantation into mice using feces from BD patients could exacerbate the disease activity and lead to an excessive production of pro-inflammatory cytokines (<xref ref-type="bibr" rid="B8">8</xref>). The EAU mice showed an altered microbiome compared to the non-immunized mice, and the clustering of gut microbial diversity was associated with clinical severity (<xref ref-type="bibr" rid="B9">9</xref>). Depletion or reduction of gut microbiota, particularly before disease induction, protects mice from severe EAU. This protection correlates with diminished retinal immune cell infiltration, reduced inflammatory T cell responses, and enhanced regulatory T cell populations in draining lymph nodes, indicating that microbiota modulates autoimmunity by shaping adaptive immunity during autoantigen recognition. Furthermore, specific probiotics can control inflammation in EAU (<xref ref-type="bibr" rid="B10">10</xref>, <xref ref-type="bibr" rid="B11">11</xref>). Similar findings in experimental autoimmune encephalomyelitis (EAE) demonstrate that commensal microbiota are necessary for autoimmune demyelination (<xref ref-type="bibr" rid="B12">12</xref>), and multiple sclerosis patients have an altered intestinal microbiota compared to healthy controls (<xref ref-type="bibr" rid="B13">13</xref>). Collectively, these findings underscore the critical role of gut microbiota in autoimmune pathogenesis.</p>
<p>Preliminary work by our team has shown that PGRN could significantly reduce EAU severity and could inhibit IRBP161&#x2013;180-specific Th1 and Th17 cell response and promote Treg cell expansion <italic>in vivo</italic> and <italic>in vitro</italic> (<xref ref-type="bibr" rid="B14">14</xref>). However, the exact mechanisms by which PGRN exert its protective role remains unclear. The gut microbiome has been considered to be implicated in the pathogenesis of autoimmune diseases. Therefore, we investigated whether there was a significant change in the gut microbiome in PGRN-deficient EAU mice and the association of the changes of gut microbiome with the severity of EAU.</p>
</sec>
<sec id="s2">
<title>Methods</title>
<sec id="s2_1">
<title>EAU induction</title>
<p>PGRN-deficient mice of C57BL/6 background were purchased from Jackson Laboratory. All mice were maintained in a specific pathogen-free facility. Animal experimental protocols were approved and performed under the Animal Care and Use Committee of the Chongqing Medical University. EAU was induced as previously described. Briefly, WT and PGRN-deficient mice (<italic>n</italic>&#xa0;=&#xa0;5) were immunized subcutaneously with 200 &#x3bc;L emulsion of 400 &#x3bc;g human IRBP651-670 (LAQGAYRTAVDLESLASQLT) in an equal volume of CFA containing 5 mg/ml <italic>Mycobacterium tuberculosis</italic> strain. Additionally, these mice also received a 1-&#x3bc;g intraperitoneal injection of <italic>Bordetella pertussis</italic> toxin (PTX, Sigma-Aldrich, St. Louis, MO, USA) (<xref ref-type="bibr" rid="B15">15</xref>). The experiments were conducted using 6&#x2013;8-week-old female mice.</p>
<p>For clinical grading of EAU, the right eyes from both groups were examined by slit lamp microscopy on day 13 after immunization, and the clinical severity of inflammation was graded by two independent ophthalmologists in a masked fashion according to previously described criteria (<xref ref-type="bibr" rid="B16">16</xref>, <xref ref-type="bibr" rid="B17">17</xref>). For histologic grading of EAU, the right eyes from both groups were enucleated, fixed, embedded in paraffin, sectioned, and stained with hematoxylin&#x2013;eosin (H&amp;E) on day 13 after immunization. Histological changes were graded by two independent observers in a masked fashion according to Caspi&#x2019;s criteria (<xref ref-type="bibr" rid="B18">18</xref>).</p>
</sec>
<sec id="s2_2">
<title>NovaSeq sequencing and bioinformatic analysis</title>
<p>16S rRNA gene sequencing analysis was conducted on fecal samples from four mice per group, which were randomly selected from the same cohort. The V3&#x2013;V4 region of the 16S rRNA gene was amplified using PCR with universal primer sets 338F-806R. The PCR products were purified using the Axyprep DNA Gel extraction kit (Axygen, USA). Finally, Illumina NovaSeq high-throughput sequencing was performed. The raw pair-end sequences were spliced, and then the low-quality sequences with quality scores &lt;20 and primers were removed using USEARCH (v11) (<xref ref-type="bibr" rid="B19">19</xref>). Operational taxonomic unit (OTU) representative sequences were generated using UNOISE3 with non-clustering denoise algorithm, and the OTU with a sequence number that represented less than 9 was removed (<xref ref-type="bibr" rid="B19">19</xref>). The OTU table was generated by the &#x201c;otutab&#x201d; command in USEARCH (v11). The taxonomic identities of representative OTU sequences were determined based on the SINTAX algorithm according to the Silva (v 138) database (<xref ref-type="bibr" rid="B20">20</xref>). The rooted phylogenetic trees were constructed by using the &#x201c;phylogeny&#x201d; command in QIIME2 (<xref ref-type="bibr" rid="B21">21</xref>). Finally, a total of 321 OTUs for prokaryotes was obtained. After being rarefied to the minimum sequence number in the samples, 49,995 sequences for bacteria were obtained in each sample. Microbial richness and Shannon index were estimated in R with the vegan package.</p>
</sec>
<sec id="s2_3">
<title>Statistical analysis</title>
<p>All data were expressed as means &#xb1; SEM. Differences in the clinical and histological score were determined using Wilcoxon rank-sum test. Differences in microbial diversity between different groups were determined using Wilcoxon rank-sum test. The normality and homogeneity of variance of all the data were tested using Shapiro and Levene&#x2019;s test, respectively. For the <italic>&#x3b2;</italic> taxonomic diversity, a Jaccard distance matrix at the OTU level among the samples was first created and analyzed by principal coordinates analysis (PCoA). The community composition dissimilarity matrix was calculated based on Bray&#x2013;Curtis distance. Generalized linear model (GLM) was used to analyze the relationship between microbial richness and the severity of EAU. All of the statistical analyses were performed based on the ggpur, vegan, psych, reshape2, and packages in R.</p>
</sec>
</sec>
<sec id="s3" sec-type="results">
<title>Results</title>
<sec id="s3_1">
<title>An exacerbation of EAU in PGRN-deficient mice</title>
<p>To investigate the role of PGRN in EAU, we induced uveitis in WT and PGRN-deficient mice on a C57BL/6 background. Clinical observations revealed that PGRN-deficient mice exhibited significantly higher scores compared to WT controls (<xref ref-type="fig" rid="f1"><bold>Figures&#xa0;1a, b</bold></xref>). Histologically, WT mice showed moderate chorioretinal lesions and cellular infiltration within the eyes. However, PGRN-deficient mice displayed more severe chorioretinal lesions, pronounced inflammatory cellular infiltration, and extensive retinal folding. The pathologic scores were significantly higher in the PGRN-deficient mice than those in WT controls (<xref ref-type="fig" rid="f1"><bold>Figures&#xa0;1c, d</bold></xref>).</p>
<fig id="f1" position="float">
<label>Figure&#xa0;1</label>
<caption>
<p>PGRN-deficient mice exhibit exacerbated EAU. WT and PGRN-deficient mice of C57BL/6 background (<italic>n</italic>&#xa0;=&#xa0;5) were induced for EAU. The right eye of each mouse was used for analysis. <bold>(a, b)</bold> PGRN-deficient mice had significantly higher clinical scores than WT controls. <bold>(a)</bold> Representative slit-lamp section images of the two groups on day 13 after immunization. <bold>(b)</bold> The clinical scores of the two groups were measured on day 13. Wilcoxon rank-sum test was used for the statistical analysis (<italic>P</italic>&#xa0;&lt;&#xa0;0.05, error bars, SD). <bold>(c, d)</bold> The pathologic scores were significantly higher in the PGRN-deficient mice than those in WT controls. <bold>(c)</bold> The pathologic scores of the two EAU groups were measured on day 13. Wilcoxon rank-sum test was used for the statistical analysis (<italic>P</italic>&#xa0;&lt;&#xa0;0.05, error bars, SD). <bold>(d)</bold> Representative H&amp;E-stained sections of EAU eyes on day 13 after immunization. Scale bar, 30 &#xb5;m. EAU, experimental autoimmune uveitis; PGRN-/-, PGRN-deficient; wild, wild type.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-17-1641755-g001.tif">
<alt-text content-type="machine-generated">Close-up images and graphs comparing eyes of wild-type and PGRN knockout mice. Panel (a) shows eye photographs. Panel (b) is a clinical score graph, with the PGRN knockout group scoring higher (P=0.041). Panel (c) depicts a pathological score graph, also showing higher scores for the knockout group (P=0.013). Panel (d) features histological sections of eyes, with noticeable differences between the wild-type and knockout mice.</alt-text>
</graphic></fig>
</sec>
<sec id="s3_2">
<title>Changes in microbial diversity and community composition in PGRN-deficient EAU mice</title>
<p>To explore the gut microbiota changes associated with the exacerbation of EAU in PGRN-deficient mice, we employed 16S rRNA gene sequencing analysis. Our results indicated a significant reduction in intestinal microbial diversity in PGRN-deficient EAU mice compared to their WT counterparts (Wilcoxon rank-sum test, <italic>P</italic>&#xa0;&lt;&#xa0;0.05; <xref ref-type="fig" rid="f2"><bold>Figure&#xa0;2a</bold></xref>). Furthermore, the PCoA diagram revealed a pronounced difference in microbial community composition between WT and PGRN-deficient EAU mice (PERMANOVA, <italic>P</italic>&#xa0;=&#xa0;0.001; <xref ref-type="fig" rid="f2"><bold>Figure&#xa0;2b</bold></xref>). At the phylum level, the intestinal microbial community of WT EAU mice was predominantly composed of three phyla&#x2014;<italic>Firmicutes</italic>, <italic>Bacteroidetes</italic>, and <italic>Epsilonbacteraeota</italic>&#x2014;which collectively accounted for 91.96% of the community (<xref ref-type="fig" rid="f2"><bold>Figure&#xa0;2c</bold></xref>). In contrast, in PGRN-deficient EAU mice, the combined percentage of <italic>Bacteroidetes</italic>, <italic>Firmicutes</italic>, and <italic>Epsilonbacteraeota</italic> dropped to 58.49%, with <italic>Spirochaetes</italic> and <italic>Tenericutes</italic> emerging as the next most prevalent phyla in the gut microbial community (<xref ref-type="fig" rid="f2"><bold>Figure&#xa0;2c</bold></xref>).</p>
<fig id="f2" position="float">
<label>Figure&#xa0;2</label>
<caption>
<p>Significant differences in the microbial diversity and community composition between WT and PGRN-deficient EAU mice. <bold>(a)</bold> The microbial diversity, as indicated by alpha diversity measured with the Shannon index, was significantly reduced in PGRN-deficient EAU mice compared to WT controls. Wilcoxon rank-sum test was used for the statistical analysis (<italic>P</italic>&#xa0;&lt;&#xa0;0.05). <bold>(b)</bold> PCoA ordinations of prokaryotic community profiles revealed a significant difference between the two groups (<italic>P</italic>&#xa0;=&#xa0;0.001). <bold>(c)</bold> The overall community composition of prokaryotes differed between WT and PGRN-deficient EAU mice. The percentage of the three dominant phyla, including Firmicutes, Bacteroidetes, and Epsilonbacteraeota, was reduced in PGRN-deficient mice. EAU, experimental autoimmune uveitis; PGRN-/-, PGRN-deficient; wild, wild type.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-17-1641755-g002.tif">
<alt-text content-type="machine-generated">Chart (a) shows a box plot of prokaryotic richness, indicating higher values in the Wild group compared to PGRN−/−, with a significant difference (T-test, P &lt; 0.05). Chart (b) is a PCoA plot with PGRN−/− and Wild groups displayed distinctly. Chart (c) depicts the relative abundance of different bacterial phyla between the two groups, showing variations in composition percentages.</alt-text>
</graphic></fig>
</sec>
<sec id="s3_3">
<title>Changes in microbial phylum level in PGRN-deficient EAU mice</title>
<p>We analyzed the differences in microbial phylum levels between PGRN-deficient EAU and WT EAU mice using Wilcoxon rank-sum test. Our analysis identified a total of 10 significantly different phyla, with five upregulated and five downregulated, in PGRN-deficient EAU mice compared to WT EAU mice (<xref ref-type="fig" rid="f3"><bold>Figure&#xa0;3</bold></xref>). Specifically, the abundance of <italic>Cyanobacteria</italic>, <italic>Epsilonbacteraeota</italic>, <italic>Firmicutes</italic>, <italic>Nitrospirae</italic>, and <italic>Patescibacteria</italic> was significantly lower in PGRN-deficient EAU mice (<xref ref-type="fig" rid="f3"><bold>Figures&#xa0;3a&#x2013;e</bold></xref>, <italic>P</italic>&#xa0;&lt;&#xa0;0.05). Conversely, the abundance of <italic>Deferribacteres</italic>, <italic>Proteobacteria</italic>, <italic>Spirochaetes</italic>, and <italic>Tenericutes</italic> was significantly higher in PGRN-deficient EAU mice. Interestingly, a newly detected phylum, identified as <italic>Chlamydiae</italic>, was present in the intestinal microbial community of PGRN-deficient EAU (which comprised approximately 1% of the total microbiome), but it was absent in WT EAU mice (<xref ref-type="fig" rid="f3"><bold>Figures&#xa0;3f&#x2013;j</bold></xref>, P &lt;&#xa0;0.05).</p>
<fig id="f3" position="float">
<label>Figure&#xa0;3</label>
<caption>
<p>Microbial phylum-level differences between PGRN-deficient EAU and WT EAU mice. A total of 10 phyla (five upregulated and five downregulated) were identified as significantly different between PGRN-deficient EAU and WT EAU mice. <bold>(a&#x2013;e)</bold> The abundance of Cyanobacteria, Epsilonbacteraeota, Firmicutes, Nitrospirae, and Patescibacteria was decreased in PGRN-deficient EAU mice. <bold>(f&#x2013;j)</bold> The abundance of Deferribacteres, Proteobacteria, Spirochaetes, and Tenericutes was significantly increased. Additionally, the Chlamydiae phylum was newly detected in the intestinal microbial community of PGRN-deficient EAU mice. Wilcoxon rank-sum test was used for the statistical analysis. EAU, experimental autoimmune uveitis; PGRN-/-, PGRN-deficient; WT, wild type. *, P&lt;0.05; **, P&lt;0.01; ***, P&lt;0.001.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-17-1641755-g003.tif">
<alt-text content-type="machine-generated">Bar charts compare bacterial phyla abundance between PGRN-/- and wild-type groups. Significant differences are highlighted for Cyanobacteria, Epsilonbacteraeota, Firmicutes, Nitrospirae, Patescibacteria, Deferribacteres, Chlamydiae, Proteobacteria, Spirochaetes, and Tenericutes, using P-values and asterisks to denote significance levels.</alt-text>
</graphic></fig>
</sec>
<sec id="s3_4">
<title>Association of microbial richness and <italic>Chlamydiae</italic> abundance with EAU severity</title>
<p>We examined the correlation between changes in microbial richness and <italic>Chlamydiae</italic> abundance with the histopathological score using GLM analysis. Our analysis revealed a significant negative correlation between gut microbial richness and the histopathological score (<xref ref-type="fig" rid="f4"><bold>Figure&#xa0;4a</bold></xref>; <italic>r</italic>&#xa0;=&#xa0;-0.74, <italic>P</italic>&#xa0;&lt;&#xa0;0.05). Additionally, we identified a significant positive correlation between the abundance of the newly detected <italic>Chlamydiae</italic> phylum in PGRN-deficient EAU mice and the pathological score (<xref ref-type="fig" rid="f4"><bold>Figure&#xa0;4b</bold></xref>; <italic>r</italic>&#xa0;=&#xa0;0.57, <italic>P</italic>&#xa0;&lt;&#xa0;0.05).</p>
<fig id="f4" position="float">
<label>Figure&#xa0;4</label>
<caption>
<p>Association of microbial changes with the severity of EAU. <bold>(a)</bold> Negative association between the microbial richness and the histopathological score of EAU (<italic>r</italic>&#xa0;=&#xa0;-0.74, <italic>P</italic>&#xa0;=&#xa0;0.035). <bold>(b)</bold> Positive association between the Chlamydiae abundance and EAU histopathological score (<italic>r</italic>&#xa0;=&#xa0;0.57, <italic>P</italic>&#xa0;=&#xa0;0.014). Each point (including circles and triangles) represents an individual mouse. Generative language model (GLM) was used for the statistical analysis.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-17-1641755-g004.tif">
<alt-text content-type="machine-generated">Two scatter plots show relationships between pathological scores and microbial data. Plot (a) depicts a negative correlation between microbial richness and pathological score (r = -0.74, p = 0.035). Plot (b) shows a positive correlation between Chlamydiae abundance and pathological score (r = 0.57, p = 0.014). Data points represent PGRN-/- and Wild groups.</alt-text>
</graphic></fig>
</sec>
</sec>
<sec id="s4" sec-type="discussion">
<title>Discussion</title>
<p>In the present study, we evaluated the impact of PGRN deficiency on experimental autoimmune uveitis (EAU) and investigated the gut microbiota changes in the induced uveitis in PGRN-deficient mice. Our data showed that PGRN deficiency could lead to an exacerbated EAU and distinct alterations to the gut microbiota. These changes to the gut microbiota may be associated with the exacerbation of inflammation in PGRN-deficient mice.</p>
<p>In our study, we found that PGRN deficiency could exacerbate the severity of EAU by comparing the severity of inflammation in WT and PGRN-deficient EAU mice. Previous studies have shown that it plays a protective role in some autoimmune mouse models, such as collagen-induced arthritis, colitis, and osteoarthritis (<xref ref-type="bibr" rid="B3">3</xref>, <xref ref-type="bibr" rid="B22">22</xref>, <xref ref-type="bibr" rid="B23">23</xref>). However, PGRN mediates pro-inflammatory immune responses in systemic lupus erythematosus and in some inflammatory diseases, such as the pulmonary immunopathology during influenza virus infection and the lethal <italic>Candida albicans</italic> (<xref ref-type="bibr" rid="B24">24</xref>&#x2013;<xref ref-type="bibr" rid="B26">26</xref>). Collectively, these results suggest that PGRN exerts different roles in different immune or inflammatory conditions and that it exerts an important protective benefit in EAU.</p>
<p>In this study, we found that PGRN-deficient EAU mice exhibited significantly reduced gut microbial species richness and an altered community composition compared to wild-type (WT) EAU controls. In contrast, Gu et&#xa0;al. reported that PD-L1 deficiency increased microbial richness and modulated key bacterial families (<italic>Bacteroidaceae</italic>, <italic>Lachnospiraceae</italic>, and <italic>Ruminococcaceae</italic>) (<xref ref-type="bibr" rid="B27">27</xref>). These results suggest that PGRN may play a role in maintaining microbiota diversity, and that the decrease in microbial diversity observed in PGRN-deficient EAU mice may be associated with exacerbated uveitis. Our findings are in line with previous reports showing a decreased microbial diversity in the rheumatoid arthritis patients compared to healthy controls and the decreased species richness was associated with the rheumatoid factor levels and disease duration (<xref ref-type="bibr" rid="B28">28</xref>, <xref ref-type="bibr" rid="B29">29</xref>). However, our previous reports did not find a statistically significant difference in the &#x3b1;- diversity or &#x3b2;-diversity of species abundance between the uveitis patients with Vogt-Koyanagi-Harada (VKH) disease and normal controls (<xref ref-type="bibr" rid="B30">30</xref>). This difference may be due to the significant individual differences or to the small number of individuals in each category. In summary, these findings indicate an association between microbial diversity and the severity of autoimmune disease, studies are needed to establish the causality in further. We next analyzed the specific phylum-level alterations in the microbial composition involved in the exacerbation of EAU in PGRN-deficient mice. At the phylum level, the PGRN-deficient EAU mice showed a significant decrease in the proportion of <italic>Cyanobacteria</italic>, <italic>Epsilonbacteraeota</italic>, <italic>Firmicutes</italic>, <italic>Nitrospirae</italic>, and <italic>Patescibacteria</italic>. Our results are consistent with previous reports showing that <italic>Firmicutes</italic>, <italic>Nitrospirae</italic>, and <italic>Cyanobacteria</italic> were negatively associated with disease development. <italic>Firmicutes</italic> and <italic>Cyanobacteria</italic> are known to be the predominant bacteria in normal human gut (<xref ref-type="bibr" rid="B31">31</xref>). The instability or decrease in the number of <italic>Firmicutes</italic> and <italic>Cyanobacteria</italic> is referred to as &#x201c;microbial dysbiosis&#x201d; (<xref ref-type="bibr" rid="B32">32</xref>). Patients with rheumatoid arthritis had a reduced proportion of the <italic>Firmicutes</italic> phylum compared to normal controls (<xref ref-type="bibr" rid="B29">29</xref>). Patients with systemic lupus erythematosus had reduced levels of the <italic>Nitrospirae</italic> phylum (<xref ref-type="bibr" rid="B33">33</xref>). Regarding cyanobacteria, Zhu et&#xa0;al. reported that cyanobacterial abundance was significantly lower in patients with allergic rhinitis compared to&#xa0;the controls (<xref ref-type="bibr" rid="B34">34</xref>). These results suggest that <italic>Firmicutes</italic>, <italic>Nitrospirae</italic>, and <italic>Cyanobacteria</italic> are responsible for maintaining the micro-ecological balance, and the decrease in these microbial&#xa0;compositions was associated with the exacerbation of EAU. However, increased levels of <italic>Epsilonbacteraeota</italic> and <italic>Patescibacteria</italic> were observed in patients with osteoarthritis and ulcerative colitis, respectively (<xref ref-type="bibr" rid="B35">35</xref>, <xref ref-type="bibr" rid="B36">36</xref>). These discrepancies suggest that each disease has a unique microbiome composition.</p>
<p>In our study, we observed that PGRN-deficient EAU mice exhibited a significantly higher proportion of <italic>Deferribacteres</italic>, <italic>Proteobacteria</italic>, <italic>Spirochaetes</italic>, and <italic>Tenericutes</italic>. Notably, our findings relating to <italic>Proteobacteria</italic> are consistent with those of a previous study on ulcerative colitis, which showed the increased relative abundance of <italic>Proteobacteria</italic> at the phylum level in patients with active ulcerative colitis compared to healthy controls. Therefore, these two studies therefore suggest that <italic>Proteobacteria</italic>, which are normally minor phylum, increase in prevalence in these diseases (<xref ref-type="bibr" rid="B36">36</xref>). Besides these increased microbial compositions, we identified a new <italic>Chlamydiae</italic> phylum in PGRN-deficient EAU mice and found that <italic>Chlamydiae</italic> abundance was positively associated with EAU severity. <italic>Chlamydiae</italic> are Gram-negative bacteria with pathogenic potential for a wide variety of diseases. <italic>Chlamydia trachomatis</italic>, which represents the main human <italic>Chlamydia</italic> pathogenic species, is responsible for ocular infection (<xref ref-type="bibr" rid="B37">37</xref>). It has been reported that three types of antibodies to <italic>Chlamydiae</italic> are significantly more prevalent in patients with ocular inflammation than in healthy controls (<xref ref-type="bibr" rid="B38">38</xref>). Our sequencing data reflects gastrointestinal colonization. We therefore hypothesize that PGRN deficiency increases susceptibility to intestinal chlamydial colonization, which could indirectly exacerbate autoimmunity through molecular mimicry or generalized immune activation. These findings demonstrate an association between chlamydial abundance and EAU severity in PGRN-deficient mice. However, further studies are needed to clarify the causal relationship.</p>
<p>Our study is limited by the evaluation of only one time point and&#xa0;the small sample size, which make it challenging to draw definitive conclusions. However, we believe that our findings contribute to the growing body of literature on the gut microbiome and its potential role in autoimmune diseases. Further studies are needed to explore the relationship between PGRN, gut microbiota, and EAU.</p>
<p>In conclusion, our results demonstrate that PGRN exerts a protective role in EAU, and there was a significant alteration in the gut microbiota which may be associated with the severity of inflammation in PGRN-deficient EAU mice.</p>
</sec>
</body>
<back>
<sec id="s5" sec-type="data-availability">
<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" sec-type="ethics-statement">
<title>Ethics statement</title>
<p>The animal study was approved by Animal Care and Use Committee of the Chongqing Medical University. The study was conducted in accordance with the local legislation and institutional requirements.</p></sec>
<sec id="s7" sec-type="author-contributions">
<title>Author contributions</title>
<p>WZ: Data curation, Formal analysis, Investigation, Writing &#x2013; review &amp; editing. SZ: Formal analysis, Visualization, Writing &#x2013; review &amp; editing. CW: Conceptualization, Writing &#x2013; original draft, Writing &#x2013; review &amp; editing.</p></sec>
<sec id="s9" sec-type="COI-statement">
<title>Conflict of interest</title>
<p>The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p></sec>
<sec id="s10" sec-type="ai-statement">
<title>Generative AI statement</title>
<p>The author(s) declared that generative AI was not used in the creation of this manuscript.</p>
<p>Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If&#xa0;you identify any issues, please contact us.</p></sec>
<sec id="s11" sec-type="disclaimer">
<title>Publisher&#x2019;s note</title>
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