Currently, the pathogenesis of nephrotic syndrome remains uncertain, but examination of affected kidney tissue reveals pronounced podocyte injury, characterized by extensive fusion, vacuolation, degeneration, and shedding. Podocyte damage, marked by the disappearance or apoptosis of foot processes, compromises the glomerular filtration barrier, allowing unfiltered macromolecules to enter the urine and exacerbating kidney damage (Teh et al., 2022). Podocytes, specialized epithelial cells in the glomerulus, form foot processes and slit diaphragms essential for glomerular filtration barrier integrity (Zhou et al., 2017). Their unique molecular and charge-barrier properties safeguard glomerular endothelial cells and the basement membrane from potential harm (Mallipattu and Kravets, 2020, Trimarchi, 2020).

Macrophages, essential innate immune cells, exert significant influence across all stages of kidney injury. Their activation status, often described as 'macrophage polarization', delineates their functional phenotype. Two primary phenotypes, M1 and M2, are recognized, with contrasting roles akin to accelerators and brakes in inflammation modulation. Notably, M1 macrophages predominate in pro-inflammatory activities during the acute phase of nephropathy, while M2 macrophages predominantly secrete anti-inflammatory cytokines, thereby mitigating inflammation(Müller et al., 2017; Liu et al., 2023)). The levels of podocin and nephrin in podocytes are altered by M1 macrophages, resulting in dysfunction of glomerular endothelial cells and podocytes, which impairs kidney filtration and leads to proteinuria(Li et al., 2020). Moreover, macrophages have been implicated in the repair of high-sugar-induced podocyte damage, potentially through M2 polarization pathways (Ji et al., 2019). Further investigations highlight the significant role of macrophage phenotypic balance in podocyte injury. Elevated M1 levels and decreased M2 levels on macrophage surfaces have been observed to contribute to podocyte injury in vivo. Notably, M2 macrophages have been shown to regulate the miR-93–5p/TLR4 pathway, thereby protecting podocytes from LPS-induced damage (Jiandong et al., 2019, Wang et al., 2022). Additionally, M2 macrophages can repair podocyte damage by correcting cytoskeletal defects and boosting podocyte mobility (Zhang et al., 2020).

Astragali Radix (AR), a medicine and food homologous plant, has been demonstrated to be effective in treating CKD. Astragaloside IV (ASIV), a key constituent of AR, has been found to exhibit advantageous properties in the treatment of nephropathy, including improving renal function, slowing disease progression, and safeguarding podocytes against injury. AR has been shown to prevent and treat nephritis and nephrotic syndrome in clinic (Wen et al., 2017). Previously, we demonstrated that AR could slow the progression of kidney disease by ameliorating podocyte injury (Li et al., 2020). Additionally, our previous studies showed that ASIV, a main effective ingredient extracted from AR, has the effect of improving adriamycin-induced nephropathy (Li et al., 2020). However, the majority of studies predominantly focus on the direct effects of drugs on podocytes, with limited attention to the macrophages' protective effects. Our previous study indicated that macrophages exhibit a more significant involvement in ASIV intervention in adriamycin-induced nephropathy in rats. Therefore, this study investigated the protective effects of podocyte by promoting macrophage M2 polarization with the intervention of ASIV.

Although many studies have shown that ASIV is a potential activator of PPARγ, most focus solely on its effects on podocytes (Xing et al., 2021). The involvement of macrophages in kidney diseases is of significant importance. ASIV can improve kidney injury and reduce early inflammation, which is associated with promoting the differentiation of macrophages from the M1 to the M2. This is likely due to the NF-κB (p65)/HIF-1α pathway being inhibited by ASIV (Tang et al., 2022). Additionally, Macrophage polarization is associated with cell metabolism, particularly lipid metabolism (Wang et al., 2019). Lipid metabolism is reprogrammed during macrophage polarization. Fatty acid intake is increased and enzymes related to lipid metabolism are altered (Zhu et al., 2014). Moreover, lipidomic profiling results indicate a correlation between macrophage polarization and lipid metabolism (Lee et al., 2017).

The nuclear receptor PPARgamma (PPARγ) is a lipid sensor and plays a crucial role in macrophage polarization, inhibiting M1 responses while promoting M2 responses (Yunna et al., 2020). There is research suggesting that ASIV promotes M2 macrophage polarization by increasing PPAR protein expression or regulating inflammatory cytokine secretion. However, there are few reports on the specific mechanism underlying M2 polarization of macrophage through lipid metabolism regulation, as well as the potential of M2 macrophages in repairing podocyte injury (Ying et al., 2021).

This study aims to investigate whether ASIV protects podocytes from injury by promoting M2 macrophage polarization and to elucidate its potential protective mechanisms through lipidomics analysis. Additionally, molecular docking will be employed to further validate the mechanism of ASIV, providing a theoretical foundation for its application in the treatment of kidney diseases and suggesting innovative strategies for the development of future drugs.