## 1 Introduction  
Diabetic kidney disease (DKD) has emerged as one of the fastest-growing causes of chronic kidney disease [1]. The clinical diagnosis of DKD includes three possibilities: diabetic nephropathy (DN), non-diabetic kidney disease (NDKD), and a combination of DN and NDKD. The treatment and prognosis of DN and NDKD differ significantly [2]. DN diagnosis relies on renal biopsy, an invasive procedure with potential risks, such as bleeding and kidney damage, which is not widely practiced and is unsuitable for monitoring treatment responses. Consequently, most cases of DN are clinically diagnosed. The primary laboratory markers for the clinical diagnosis of DN include albuminuria and reduced glomerular filtration rate. However, not all diabetes patients with abnormal laboratory markers have DN, and DN progression has been observed in the absence of these markers [3]. Given the complexities of DKD and the pressing need for more accurate and non-invasive early diagnostic biomarkers of DN, this area has experienced a surge in active research efforts [4, 5]. The identification of biomarkers in extracellular vesicles (EVs) has sparked a rapidly growing scientific field and renewed interest in biomarker discovery. EVs contain proteins, miRNAs, and mRNAs that reflect the pathophysiological state of their originating cells and are a rich source of potential biomarkers [6]. Urinary extracellular vesicles (uEVs), which are actively secreted by nephron-lining epithelial cells, are considered more specific and potentially sensitive [7]. In particular, proteins provide more direct information about disease progression than RNA. Proteomics may serve as a valuable tool for identifying novel uEVs biomarkers. Large-scale proteomic assessments supported the reliability of monitoring uEVs protein changes as a proxy for kidney alterations [8]. Additionally, uEVs represent kidney protein modifications more accurately compared with the whole urine samples, which contain only a few kidney-derived proteins. Approximately 3% of the total urinary protein from healthy subjects originates from uEVs, yielding a more than 30-fold enrichment of proteins that are minor components of whole urine and are thus readily detectable by protein mass spectrometry [9]. In addition, uEVs substantially reduce sample complexity compared to whole urine, particularly in kidney disease, where a larger amount of protein may be present. Several studies have provided strong evidence that uEVs-derived disease markers can be identified well before symptom onset, making them promising candidates for early-stage disease detection [10]. Renal biopsy, the current diagnostic method for DN, is invasive, limited by the number of obtainable glomeruli and focal sites, and may be insufficient to evaluate the whole-kidney injury. In contrast, uEVs represent the collective response of different renal cells in all renal units to various pathological stimuli, offering the potential to obtain comprehensive kidney information noninvasively and facilitate follow-up. uEVs proteins are an ideal source of biomarkers for kidney diseases. Proteins such as podocalyxin, C-megalin, AQP2, and dipeptidyl peptidase-IV in uEVs have recently emerged as potential DN biomarker candidates in various studies [11; 12; 13]. Despite their high sensitivity, these proteins lack specificity for DN diagnosis, which is a major barrier to the development of new kidney disease biomarkers. Phosphorylation events are considered critical factors in the early onset and progression of kidney disease [14; 15], providing more direct insights into disease status than total protein levels. However, urine-derived phosphoproteins have been largely unexplored because of the presence of phosphatases in urine and the low abundance of phosphoproteins in highly complex urine samples. Intriguingly, uEVs are highly stable membrane-enclosed vesicles that protect their contents from external proteases and phosphatases [16], potentially enabling the development of uEVs phosphoproteins as diagnostic tools for kidney diseases.