Diabetes mellitus (DM) and chronic kidney disease (CKD) are highly prevalent in world populations, and recent reports reveal a consistent rise in the globe (Deng et al., 2021; Navaneethan et al., 2023). Both disease entities are associated with high disease-related morbidity and mortality, positioning them as significant global public health concerns. DM induces pathological alterations encompassing abnormalities in the glomerular, tubulointerstitial, and vascular compartments. These changes manifest as diabetic nephropathy (DN), a hallmark complication of DM characterized by reduced renal function and proteinuria. (Qi et al., 2017; Wang et al., 2023; Zimmet et al., 2016). DN develops in approximately 40% of individuals with DM and has now been established as the predominant cause of end-stage renal disease worldwide, representing a major public health challenge in nephrology and endocrinology (Ayinde et al., 2020; Burrows et al., 2022). Acute kidney injury (AKI) is a frequently encountered critical illness in clinical practice, with the rapid loss of renal function being its cardinal feature. Individuals with DN are highly susceptible to a variety of risk factors for AKI(Advani, 2020). Consequently, DN patients constitute a high-risk population for AKI, with an incidence rate five times higher than that of non-DN patients. (Vijayan, 2021). AKI superimposed on DN (AKI-on-DN) significantly aggravates the process of renal fibrosis in DN and prompts a rapid deterioration of renal function. This situation greatly accelerates the progression of DN to end-stage renal disease, seriously endangering the lives of patients and imposing a burden on medical resources (He et al., 2017; Kelly et al., 2009; Thakar et al., 2011). Notwithstanding that AKI emerging within the context of DN represents a frequently witnessed clinical phenomenon, the intricate and specific mechanisms underpinning the pathological alterations by which it drives the progression of CKD remain incompletely elucidated.

The human gut harbors a complex ecosystem of approximately 1013 to 1014 microorganisms that play crucial roles in host metabolism and disease pathogenesis. Emerging evidence highlights the significant involvement of gut microbiota and their metabolites in the progression of DN and subsequent renal fibrosis, critically influences the pathogenesis and progression of diabetic kidney disease (Chen et al., 2023; Linh et al., 2022; Zeng et al., 2024). Dysbiosis-driven disruption of these processes promotes systemic inflammation, oxidative stress, and renal fibrosis, thereby accelerating diabetic kidney disease deterioration. (Mao et al., 2023; Zaky et al., 2021). Patients with diabetic kidney disease exhibit distinct gut dysbiosis characterized by reduced populations of beneficial short chain fatty acid producing bacteria and increased abundance of pathogenic species that generate uremic toxins (Huo et al., 2023; Liu et al., 2024). These microbial alterations contribute to kidney injury through diverse mechanisms, including the production of profibrotic metabolites such as trimethylamine N-oxide and indoxyl sulfate, which activate renal fibroblasts; the disruption of intestinal barrier function, resulting in systemic inflammation; and the modulation of immune responses that facilitate extracellular matrix deposition (Hobby et al., 2019). Following episodes of AKI, these gut-derived factors may exacerbate the progression of chronic fibrosis by persistently activating profibrotic signaling pathways. Recent studies demonstrate that interventions targeting the gut-kidney axis, such as probiotic supplementation or dietary modulation of microbiota, can attenuate renal fibrosis in animal models (Tian et al., 2023; Zhao et al., 2022; Zhou et al., 2022). However, the precise molecular mechanisms by which specific bacterial metabolites influence the AKI-accelerated progression of DN toward end-stage renal disease remain incompletely understood, particularly regarding their effects on tubular cell senescence, macrophage polarization, and myofibroblast activation. Elucidating these pathways may reveal novel therapeutic strategies to interrupt the progression of diabetic kidney disease.

In this study, we investigated the role of gut microbiota and their metabolites in AKI-on-DN using db/db mice treated with folic acid (FA) to establish the disease model. Through 16S rRNA gene sequencing and metabolomic profiling, we identified significant alterations in gut microbial composition and specific metabolite changes in AKI-on-DN mice. Notably, our findings revealed that eicosapentaenoic acid (EPA), a metabolite derived from the microbiota, exhibits protective effects against renal fibrosis. Through mechanistic studies utilizing macrophage depletion techniques, we demonstrated that EPA primarily mediates its nephroprotective effects by inhibiting macrophage to myofibroblast transition (MMT), a critical pathogenic mechanism underlying renal fibrogenesis. These findings elucidate a previously unidentified gut-kidney axis pathway, in which EPA mitigates renal fibrosis progression by modulating MMT. The study provides mechanistic evidence underscoring EPA-mediated immunometabolic modulation as a promising therapeutic target for AKI-on-DN.