The clinical relevance of plasma CD147/basigin in biopsy-proven kidney diseases

Basigin is released in extracellular vesicles derived from the renal tubular epithelium in response to albuminuria

AIM

Irrespective of the cause, albumin/proteinuria induces tubulointerstitial damage and accelerates the progression of kidney diseases. Our series of studies demonstrated that proteinuria, an independent prognostic factor for chronic kidney disease (CKD), is correlated with urinary basigin/CD147 (Bsg) levels. We examined the morphology and origin of Bsg in the tubular lumen through the effects of filtered glucose and protein solutes on the tubules.

METHODS

Diabetic kidney disease (DKD) patients (N = 50) were treated with spironolactone 25 mg for 4 weeks or by conservative treatment. The associations between urinary Bsg values and clinical indicators were examined. Primary-cultured proximal tubular epithelial cells (PTECs) from human adult kidneys were exposed to high glucose or bovine serum albumin (BSA).

RESULTS

In patients with early phase DKD, urinary Bsg levels were closely correlated with proteinuria but not HbA1c. Full-length Bsg on extracellular vesicles (EVs) was investigated primarily in urine collected from DKD patients. EVs obtained from the urine of DKD patients included Bsg and SGLT2 proteins. Notably, spironolactone treatment concomitantly suppressed the release of Bsg-bearing EVs in correlation with decreased albuminuria. Exposure of PTECs to BSA (but not high glucose) enhanced the storage of supernatant Bsg in EVs despite the absence of exposure-specific changes in Bsg transcription.

CONCLUSION

Proteinuria induces the release of Bsg-bearing EVs derived from PTECs into the tubular lumen.

Role of MMP-2 and CD147 in kidney fibrosis

Matrix metalloproteinase-2 (MMP-2) and cluster of differentiation 147 (CD147) both play important roles in the development of kidney fibrosis, and CD147 can induce the production and activation of MMP-2. In the early stage of kidney fibrosis, MMP-2 promotes extracellular matrix (ECM) production and accelerates the development of kidney fibrosis, while in the advanced stage, MMP-2 activity decreases, leading to reduced ECM degradation and making it difficult to alleviate kidney fibrosis. The reason for the decrease in MMP-2 activity in the advanced stage is still unclear. On the one hand, it may be related to hypoxia and endocytosis, which lead to changes in the expression of MMP-2-related active regulatory molecules; on the other hand, it may be related to insufficient CD147 function. At present, the specific process by which CD147 is involved in the regulation of MMP-2 activity is not completely clear, and further in-depth studies are needed to clarify the roles of both factors in the pathophysiology of kidney fibrosis.

The Effects of EMMPRIN/CD147 on Late Function and Histopathological Lesions of the Renal Graft

Simple Summary

This study provided innovatory data regarding the role of EMMPRIN in long-term renal graft function and renal biopsy specimens in the form of interstitial fibrosis/tubular atrophy. The main cause of renal fibrosis is identified to be the activation and accumulation of fibroblasts and myofibroblasts in the interstitium, surrounded by increased amounts of extracellular matrix, and EMMPRIN has been proposed as a contributor factor. The study has evidenced that EMMPRIN displays adverse effects on renal graft survival in terms of the frequent occurrence of DGF, poorer short-term and long-term renal graft function, more profound fibrotic lesions in biopsy specimens, and the degree of proteinuria. This represents an opportunity for more accurate prediction of the post-transplant period and early, non-invasive detection of kidney graft dysfunction. Future studies need to further investigate the clinical significance of the presented results.

Abstract

Chronic kidney disease (CKD) is associated with renal fibrosis, and develops with the participation of fibroblasts and myofibroblasts from epithelial-to-mesenchymal transition (EMT). In cancer research, the key role of the glycoprotein CD147/EMMPRIN (extracellular matrix metalloproteinase inducer) in EMT has been proven. In this study, we evaluate how serum CD147/EMMPRIN affects long-term renal graft function and renal biopsy specimen lesions. In total, 49 renal graft recipients who had a renal biopsy within the last 18 months were retrospectively reviewed. At their most recent appointments, their serum concentrations of CD147/EMMPRIN and renal function were assessed. The occurrence of delayed graft function (DGF), estimated glomerular filtration rate (eGFR) at 1-year post-kidney transplantation (Tx) and the subsequent years of the follow-up period, and renal biopsy specimen lesions, mainly those related to renal fibrosis and tubular atrophy, were also evaluated. Results: CD147/EMMPRIN serum concentration correlated negatively with eGFR at the most recent appointment (ME 69 months) and with eGFR at 1 and 2 years after Tx (p < 0.05, R = −0.69, R = −0.39, and R = −0.40, respectively). CD147/EMMPRIN serum levels correlated positively with urine protein concentrations (p < 0.05, R = 0.73). A positive correlation was further found with the severity of renal biopsy specimen lesions such as interstitial fibrosis (CI), tubular atrophy (CT), double contours of the GBM (CG), mesangial matrix expansion (MM), and arteriolar hyalinosis (AH) (p < 0.05, R = 0.39, R = 0.29, R = 0.41, R = 0.32 and R = 0.40, respectively). Patients with a history of DGF had higher CD147/EMMPRIN serum concentrations (<0.05). Conclusions: CD147/EMMPRIN is linked to poorer long-term renal graft function. Additionally, a high serum concentration of CD147/EMMPRIN affects interstitial fibrosis tubular atrophy (IF/TA) lesions and proteinuria.

Systems analysis of plasma IgG intact N-glycopeptides from patients with chronic kidney diseases via EThcD-sceHCD-MS/MS

Immunoglobulin G (IgG) molecules modulate an immune response. However, site-specific N-glycosylation signatures of plasma IgG in patients with chronic kidney disease (CKD) remain unclear. This study aimed to propose a novel method to explore the N-glycosylation pattern of IgG and to compare it with reported methods. We separated human plasma IgG from 58 healthy controls (HC) and 111 patients with CKD. Purified IgG molecules were digested by trypsin. Tryptic peptides without enrichment of intact N-glycopeptides were analyzed using a combination of electron-transfer/higher-energy collisional dissociation (EThcD) and stepped collision energy/higher-energy collisional dissociation (sceHCD) mass spectrometry (EThcD-sceHCD-MS/MS). This resulted in higher spectral quality, more informative fragment ions, higher Byonic score, and nearly twice the depth of intact N-glycopeptide identification than sceHCD or EThcD alone. Site-specific N-glycosylation mapping revealed that intact N-glycopeptides were differentially expressed in HC and CKD patients; thus, it can be a diagnostic tool. This study provides a method for the determination of glycosylation patterns in CKD and a framework for understanding the role of IgG in the pathophysiology of CKD. Data are available via ProteomeXchange with identifier PXD027174.

Bone Morphogenetic Proteins (BMPs), Extracellular Matrix Metalloproteinases Inducer (EMMPRIN), and Macrophage Migration Inhibitory Factor (MIF): Usefulness in the Assessment of Tubular Dysfunction Related to Chronic Kidney Disease (CKD)

Bone morphogenetic proteins (BMP), extracellular matrix metalloproteinases inducer (EMMPRIN), and macrophage migration inhibitory factor (MIF) are known to be closely connected to renal tubule damage by experimental data; however, this has not been analyzed in children with chronic kidney disease (CKD). The aim of this study was to determine their usefulness in the assessment of CKD-related tubular dysfunction. The study group consisted of 61 children with CKD stages 1–5 and 23 controls. The serum and urine concentrations of BMP-2, BMP-6, EMMPRIN, and MIF were assessed by ELISA and their fractional excretion (FE) was calculated. The serum and urine concentrations of BMP-2, BMP-6, EMMPRIN, and MIF were significantly elevated in children with CKD vs. controls. The FE of BMP-2, FE BMP-6, and EMMPRIN increased significantly in CKD stages 1–2, but exceeded 1% in CKD stages 3–5. FE MIF became higher than in controls no sooner than in CKD 3–5, but remained below 1%. The FE values for BMP-2, BMP-6, and EMMPRIN of <1% may result from the tubular adaptive mechanisms, whereas those surpassing 1% suggest irreversible tubular damage. The analysis of serum/urinary concentrations and fractional excretion of examined parameters may allow the assessment of CKD-related tubular dysfunction.

Characterization of CD147, CA9, and CD70 as Tumor-Specific Markers on Extracellular Vesicles in Clear Cell Renal Cell Carcinoma

Extracellular vesicles (EVs) are secreted by healthy and tumor cells and are involved in cell–cell communication. Tumor-released EVs could represent a new class of biomarkers from liquid biopsies. The aim of this study was to identify tumor-specific EV markers in clear cell renal carcinoma (ccRCC) using cell lines and patient-derived tissue samples. EVs from ccRCC cell lines (786-O, RCC53, Caki1, and Caki2) and patient tissues were isolated via ultracentrifugation. EVs were characterized using transmission electron microscopy, nanoparticle tracking analysis, and Western blotting using exosome and putative tumor markers (epithelial cell adhesion molecule (EpCAM), carbonic anhydrase 9 (CA9), CD70, CD147). The tumor markers were verified using immunohistochemistry. CA9 was expressed in Caki2 cells and EVs, and CD147 was found in the cells and EVs of all tested ccRCC cell lines. In tumor tissues, we found an increased expression of CA9, CD70, and CD147 were increased in cell lysates and EV fractions compared to normal tissues. In contrast, EpCAM was heterogeneously expressed in tumor samples and positive in normal tissue. To conclude, we developed an effective technique to isolate EVs directly from human tissue samples with high purity and high concentration. In contrast to EpCAM, CA9, CD70, and CD147 could represent promising markers to identify tumor-specific EVs in ccRCC.

CD147/Basigin Deficiency Prevents the Development of Podocyte Injury through FAK Signaling

Podocytes, which are susceptible to injury by various stimuli and stress, are critical regulators of proteinuric kidney diseases, regardless of the primary disease and pathogenesis. We further confirmed a significant correlation between urinary CD147/basigin (Bsg) levels and proteinuria in patients with focal segmental glomerulosclerosis. However, the molecular mechanism of podocyte injury involving Bsg is not fully understood. Here, the involvement of Bsg in the pathogenesis of podocyte injury was elucidated. Healthy podocytes rarely express Bsg protein. In two independent mouse models, including adriamycin-induced nephropathy and N^ω-nitro-l-arginine methyl ester (l-name)-induced endothelial dysfunction, Bsg induction in injured podocytes caused podocyte effacement, which led to development of proteinuria. Bsg silencing in cultured podocytes exposed to transforming growth factor-β suppressed focal adhesion rearrangement and cellular motility via the activation of β₁ integrin-focal adhesion kinase-matrix metallopeptidase signaling. In addition, induction of vascular endothelial growth factor and endothelin-1, which are implicated in podocyte-to-endothelial cross-communication, was lower in the supernatants of cultured Bsg-silenced podocytes stimulated with transforming growth factor-β. In this setting, Bsg may be involved in a physiological positive feedback loop that accelerates podocyte cell motility and depolarization. The current study thus suggests that Bsg silencing via suppression of β₁ integrin-focal adhesion kinase-matrix metallopeptidase signaling may be an attractive therapeutic strategy for the maintenance of podocytes in patients with proteinuric kidney diseases.