Chronic kidney disease (CKD) represents a significant global public health crisis, characterized by the progressive and irreversible decline in kidney function that culminates in end-stage renal disease (ESRD) [1]. Globally, CKD affects over 10% of the population and acts as a leading cause of mortality. It is strongly associated with increased cardiovascular risk and profoundly reduced health-related quality of life [1]. The pathological hallmark and ultimate determinant of CKD progression is tubulointerstitial fibrosis, the severity of which correlates directly with functional loss [2,3]. Mechanistically, the transforming growth factor-β (TGF-β)/SMAD family member 3 (Smad3) signaling pathway stands out as the principal, non-redundant driver of fibrotic remodeling [4]. Specifically, activation of Smad3 is central to this process; compelling evidence shows that its genetic ablation provides robust protection against fibrosis, while its sustained activation dramatically accelerates disease progression across diverse models [5,6]. Therefore, the TGF-β/Smad3 axis is universally recognized as a compelling therapeutic target for halting CKD. Despite this strong validation, clinically effective anti-fibrotic agents capable of safely and specifically interfering with this pivotal pathway remain urgently needed.

Recent studies have increasingly demonstrated that natural compounds can protect against CKD through coordinated modulation of key signaling pathways involved in inflammation, oxidative stress, and fibrosis. For instance, acteoside-containing caffeic acid was shown to ameliorate CKD in adenine-induced rats by inhibiting aryl hydrocarbon receptor (AHR) nuclear translocation and regulating downstream Nuclear Factor-κB (NF-κB)/Nuclear factor erythroid 2-related factor 2 (Nrf2) signaling, thereby suppressing renal inflammation and fibrosis [7]. Along similar lines, geniposidic acid attenuated chronic tubulointerstitial nephropathy by modulating the AHR-mediated NF-κB/Nrf2 axis, leading to reduced oxidative stress and improved renal function [8]. Complementing these findings, barleriside A, an AHR antagonist, protected podocytes from injury by concurrently mitigating oxidative stress and inflammation, further highlighting the therapeutic value of targeting AHR signaling in CKD [9]. Beyond AHR-related mechanisms, the flavonoid fisetin exerted anti-fibrotic effects by specifically inhibiting Acyl-CoA Synthetase Long-Chain Family Member 4 (ACSL4)-mediated tubular ferroptosis, thereby reducing tubular injury, inflammatory responses, and extracellular matrix deposition in fibrotic kidneys [10]. Collectively, these studies illustrate that natural compounds can intervene in multiple, complementary molecular pathways to attenuate CKD progression, providing a compelling rationale for exploring similar bioactive agents in renal fibrosis.

Given the limited success of conventional drug development, natural products offer a rich and structurally diverse reservoir for novel therapeutic discovery. Notably, multiple studies have demonstrated that these natural compounds can attenuate CKD progression by inhibiting the TGF-β1/Smad signaling pathway, a key driver of renal fibrosis [11]. Curdione, a major sesquiterpenoid derived from Curcumae Rhizoma [12], has previously demonstrated promising activities against various pathologies, including protection against focal cerebral ischemia-reperfusion injury [13] and robust effects on anti-oxidative stress [14], apoptosis [15], and ferroptosis [16] in models like myocardial infarction or cardiotoxicity. Crucially, curdione has also been reported to possess anti-fibrotic activity in both pulmonary [17] and hepatic (liver) [18] fibrosis models. These findings strongly suggest that its therapeutic potential extends to pathological tissue remodeling. However, despite this accumulating evidence of its anti-fibrotic capacity in other organs, the specific role of curdione in renal fibrosis-including its precise molecular targets and downstream mechanisms has yet to be systematically elucidated. Addressing this gap is critical to validating curdione as a viable anti-fibrotic candidate for CKD.

Recent advancements have highlighted filamin binding LIM protein 1 (Fblim1) as an underappreciated yet potentially critical regulator of both extracellular matrix dynamics and TGF-β signaling [19,20]. Supporting this link, a recent study reported that a Fblim1-positive subset of CAF (Cancer-Associated Fibroblast) was highly correlated with increased TGF-β expression, elevated mesenchymal marker levels, and an immunosuppressive tumor microenvironment, suggesting a strong association between Fblim1 and the TGF-β/Smad pathway. Furthermore, a recent investigation into hepatic fibrosis demonstrated that the knockdown of Fblim1 significantly suppressed TGF-β/Smad-regulated liver fibrosis.

Given that curdione has been previously implicated in regulating the TGF-β/Smad pathway [17], and Fblim1 has also been validated as a regulator of this same axis [20], we hypothesized that curdione might exert its anti-fibrotic effect by modulating Fblim1 expression and subsequent TGF-β/Smad signaling. To test this, we first confirmed the protective effect of Curdione against renal fibrosis in both the Unilateral Ureteral Obstruction (UUO) mouse model and in vitro models. Building on this confirmation, we then found that curdione significantly altered Fblim1 expression, and we subsequently confirmed the direct binding between curdione and Fblim1 using cellular thermal shift assay (CETSA) and drug affinity responsive target stability (DARTS) assays. Furthermore, to definitively establish the functional relationship between Curdione and Fblim1, we performed rescue experiments by overexpressing Fblim1 both in vivo and in vitro to assess the mechanism underlying Curdione’s anti-fibrotic activity.