Diabetes nephropathy (DN) is one of the most serious complications of diabetes and the leading cause of chronic kidney disease. It can lead to end-stage kidney disease and increased patient mortality rates [1], [2]. Additionally, DN-related morbidity rates have been increasing in recent years [3], [4]. However, the exact pathogenesis underlying the development of DN is not fully clear. Renal tubular injury has been demonstrated to be a critical pathogenetic mechanism in DN [5] and is often associated with poor prognosis [6]. Thus, attenuating tubular renal injury is essential for DN prevention and treatment. Currently, no effective therapeutic target has been identified, and the pathogenesis of renal tubular injury associated with DN requires further study.

Ferroptosis of renal tubular epithelial cells is an important factor in renal tubular injury in DN [7], [8]. Ferroptosis is a form of cell death that is characterized by the accumulation of lipid peroxidation and reactive oxygen species (ROS) in an iron-dependent manner. It leads to cell oxidative damage, the majority of which is mitochondrial damage. The key morphological features of ferroptosis are reduced mitochondrial volume, increased membrane density, and reduced or fully disappeared mitochondrial cristae [9]. The glutathione/glutathione peroxidase 4 (GSH/GPX4) axis is one of the key regulatory pathways of ferroptosis. GSH depletion and inactivation of GPX4 shift the oxidative balance in the cell, leading to the activation of signaling pathways that can induce oxidative death. Studies have shown that certain Chinese medicine components can delay DN progression by inhibiting ferroptosis [10], [11], [12] and dapagliflozin can ameliorate tubular damage in DN by inhibiting ferroptosis independently of glycemic control [13]. These are all associated with the remission of GSH/GPX4 axis inhibition. This suggests that the GSH/GPX4 axis plays an important role in ferroptosis of DN, but its specific molecular regulatory mechanism still needs to be thoroughly studied.

Dipeptidase 1 (DPEP1) is a zinc-dependent glycosylated homodimer metalloproteinase that is highly expressed at the brush border of proximal tubular epithelial cells [14], [15], [16]. It is considered as a hydrolytic dipeptide and is involved in the metabolism of leukotrienes and β-lactamase [16], [17]. DPEP1 has also been shown to delay the growth and invasion of various tumors, including colon cancer and liver cancer [18], [19], adhere to neutrophils [20], promote inflammation, and participate in renal ischemia–reperfusion injury [21]. Our biogenic analysis showed that DPEP1 was associated with DN ferroptosis, but its role in DN pathogenesis has not been studied in depth.

In this study, we assessed DPEP1 expression levels in kidney biopsies from DN patients and a mouse model. We knocked down DPEP1 expression in HK-2 cells to investigate the effect on ferroptosis in DN renal tubular epithelial cells. Furthermore, we explored the therapeutic potential of cilastatin, a DPEP1 inhibitor, in an established DN mouse model with a high-fat diet with streptozotocin (STZ, a pancreatic beta-cytotoxin). Overall, the present study aimed to elucidate the role of DPEP1 in ferroptosis in DN renal tubular epithelial cells.