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To investigate the roles of the pulmonary microbiota and metabolism in fibrosis, we established a bleomycin (BLM)-induced mouse model at 14- and 28-day timepoints and performed integrated 16S rRNA gene amplicon sequencing and untargeted metabolomic analyses. Histological and Western blot analyses confirmed significant fibrotic changes and the upregulation of fibrotic markers. Microbiome profiling revealed marked dysbiosis after BLM exposure, characterized by reduced microbial diversity and enrichment of Klebsiella. LC-MS\u2013based metabolomic analysis identified substantial perturbations in the lung tissue metabolome, particularly in lipid metabolism, amino acid metabolism, and energy pathways. Correlation analysis indicated a strong positive association between the abundance of Klebsiella and the levels of specific dipeptides, including Ala-Hyp-Gly, Asp-His, and Asp-Asn. The accumulation of these dipeptides may reflect increased collagen degradation and turnover in fibrotic lungs. Collectively, our findings demonstrate that BLM-induced pulmonary fibrosis is accompanied by coordinated alterations in the lung microbiome and metabolome. Notably, microbial dysbiosis, particularly the expansion of Klebsiella, may be associated with alterations in amino acid metabolism and fibrotic progression.<\/jats:p>","DOI":"10.3390\/ijms27135895","type":"journal-article","created":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T10:01:17Z","timestamp":1782813677000},"page":"5895","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Integrated Analysis of the Lung Microbiome and Metabolome Reveals Associations Between Amino Acid Metabolism and Pulmonary Fibrosis in a Bleomycin-Induced Mouse Model"],"prefix":"10.3390","volume":"27","author":[{"given":"Chunjie","family":"Xu","sequence":"first","affiliation":[{"name":"Beijing Key Laboratory of Technology and Application for Anti-Infective New Drugs Research and Development, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, 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