Yukinari Yamaguchi

Epithelial-Mesenchymal Transition as a Potential Explanation for Podocyte Depletion in Diabetic Nephropathy

BACKGROUND Depletion of glomerular podocytes is an important feature of progressive diabetic nephropathy. Although the most plausible explanation for this podocyte depletion is detachment from the glomerular basement membrane after cellular apoptosis, the mechanism is unclear. Fibroblast-specific protein 1 (FSP1; encoded by the S100A4 gene) is a member of the S100 family of calcium-binding proteins and is constitutively expressed in the cytoplasm of tissue fibroblasts or epithelial cells converted into fibroblasts by means of epithelial-mesenchymal transition. STUDY DESIGN Retrospective cross-sectional analysis. SETTINGS & PARTICIPANTS 109 patients with type 2 diabetes mellitus, of whom 43 (39%) underwent kidney biopsy. PREDICTOR Clinical stage (4 categories) and histological grade (5 categories) of diabetic nephropathy. OUTCOME FSP1 expression in podocytes in urine and glomeruli in kidney biopsy specimens. MEASUREMENTS Immunohistochemistry, real-time polymerase chain reaction, and in situ hybridization. RESULTS 38 of 109 patients (35%) were normoalbuminuric, 16 (15%) had microalbuminuria, 8 (7%) had macroalbuminuria, and 47 (43%) had decreased kidney function. Approximately 95% of podocytes in urine sediment were not apoptotic, and 86% expressed FSP1. The number of FSP1-positive podocytes in urine sediment was significantly larger in patients with macroalbuminuria than in those with normoalbuminuria (P = 0.03). Intraglomerular expression of FSP1 occurred almost exclusively in podocytes from patients with diabetes, and the number of FSP1-positive podocytes was larger in glomeruli showing diffuse mesangiopathy than in those showing focal mesangiopathy (P = 0.01). The number also was larger in glomeruli with nodular lesions than in those without nodular lesions (P < 0.001). FSP1-positive podocytes selectively expressed Snail1 and integrin-linked kinase, a known trigger for epithelial-mesenchymal transition. LIMITATIONS Nonrepresentative study population. CONCLUSIONS These results suggest that the appearance of FSP1 in podocytes of patients with diabetes is associated with more severe clinical and pathological findings of diabetic nephropathy, perhaps because of induction of podocyte detachment through epithelial-mesenchymal transition-like phenomena.

Decreased renal α-Klotho expression in early diabetic nephropathy in humans and mice and its possible role in urinary calcium excretion

Hypercalciuria is one of the early manifestations of diabetic nephropathy. We explored here the role of α-Klotho, a protein expressed predominantly in distal convoluted tubules that has a role in calcium reabsorption. We studied 31 patients with early diabetic nephropathy and compared them with 31 patients with IgA nephropathy and 7 with minimal change disease. Renal α-Klotho expression was significantly lower and urinary calcium excretion (UCa/UCr) significantly higher in diabetic nephropathy than in IgA nephropathy or minimal change disease. Multiple regression analyses indicated that α-Klotho mRNA was inversely correlated with calcium excretion. We next measured these parameters in a mouse model of streptozotocin (STZ)-induced diabetic nephropathy, characterized by glomerular hyperfiltration, as seen in early diabetic nephropathy. We also confirmed a reduction of renal α-Klotho mRNA down to almost 50% and enhanced calcium excretion in mice with STZ-induced diabetic nephropathy in comparison with nondiabetic mice. Hypercalciuria was exacerbated in heterozygous α-Klotho knockout mice in comparison with wild-type mice, each with STZ-induced diabetic nephropathy. Thus, α-Klotho expression was decreased in distal convoluted tubules in diabetic nephropathy in humans and mice. Renal loss of α-Klotho may affect urinary calcium excretion in early diabetic nephropathy.

Prediction of corticosteroid responsiveness based on fibroblast-specific protein 1 (FSP1) in patients with IgA nephropathy

BACKGROUND Corticosteroids are frequently used to treat patients with active IgA nephropathy (IgAN); however, there have been few reports describing factors that are predictive of the response to corticosteroid treatment. The purpose of this study is to determine the extent to which fibroblast-specific protein 1-positive (FSP1(+)) cells are predictive of corticosteroid responsiveness in patients with IgAN. METHODS Fifty biopsy-proven IgAN patients who received corticosteroid therapy were enrolled and followed for 7.1 +/- 3.0 years. FSP1(+) cells were identified using an anti-FSP1 antibody. RESULTS Twelve patients showed progression of renal impairment or no reduction of urinary protein (non-responders) after steroid therapy. In the remaining 38 patients, renal function was stable during follow-up, and their urinary protein declined to <1.0 g/day (responders). Serum creatinine, estimated GFR, severity of mesangial proliferation, percent glomerulosclerosis/total glomeruli, extent of interstitial damage and FSP1(+) cell number were all significantly higher in non-responders than in responders. Cox regression analysis using two covariates with every possible combination of factors indicated that FSP1(+) cell number was the strongest and most significant predictor of corticosteroid responsiveness. When IgAN patients had >32.6 FSP1(+) cells/HPF at diagnosis, they were the more likely to show steroid resistance. CONCLUSION FSP1(+) cell number can serve as an excellent predictor of corticosteroid responsiveness in patients with IgAN.

Relationship between the accuracy of glycemic markers and the chronic kidney disease stage in patients with type 2 diabetes mellitus.

BACKGROUND It is important to establish glycemic markers which reflect accurate glycemic status in advanced chronic kidney disease (CKD) patients; however, adequate glycemic markers have not been established. We evaluated the accuracy of glycemic markers in non-dialysis CKD patients. PATIENTS AND METHODS 139 non-dialysis CKD patients with diabetes were enrolled. The patients were divided into three groups as follows: group 1 (G1), patients with an estimated glomerular filtration rate (eGFR) >= 60 mL/min/1.73 m2; group 2 (G2), 30 ≤ eGFR < 60; and group 3 (G3), eGFR < 30. The patients were also classified by serum albumin: patients with serum albumin >= 3.5 g/dL as group S1 (S1) and serum albumin < 3.5 as group S2 (S2). RESULTS Glycated hemoglobin (A1C) was positively correlated with random PG in G1 and G2; however, no significant correlation was observed in G3. Whereas glycated albumin (GA) was correlated with random PG in S1, there was no significant correlation in S2. To clarify the significance of A1C and GA, the relationships among A1C, GA, and various clinical parameters were examined. GA was correlated with serum albumin and the urinary albumin-creatinine ratio, whereas A1C was significantly correlated with hemoglobin, the dose of recombinant human erythropoietin, and eGFR. CONCLUSION A1C was affected by eGFR, and GA was influenced by hypoalbuminemia; therefore, it is necessary to choose adequate glycemic markers according to the CKD stage and serum albumin level. GA is a superior glycemic marker in patients with eGFR < 30 mL/min/1.73 m2 and serum albumin >= 3.5 g/dL.

Clinical Significance of Fibroblast-Specific Protein-1 Expression on Podocytes in Patients with Focal Segmental Glomerulosclerosis

Backgrounds/Aims: We previously reported that fibroblast-specific protein 1 (FSP1) is a marker of epithelial-mesenchymal transition (EMT) in tubulointerstitial fibrosis. The EMT-like changes observed in podocytes are reportedly associated with podocyte detachment which may cause focal glomerulosclerosis. Methods: In cross-sectional studies, we analyzed podocyte expression of FSP1 immunohistochemically using renal biopsy specimens from 31 patients with focal segmental glomerulosclerosis (FSGS) and 39 patients with minimal change disease (MCD). We also semiquantitatively analyzed glomerular expression of FSP1 mRNA using laser capture microdissection and real-time PCR. Results: We found that FSP1 was localized to podocytes in both FSGS and MCD patients; however, the number of FSP1+ podocytes per glomerular profile was significantly higher in patients with FSGS than in those with MCD, and there was a corresponding difference in the levels of FSP1 mRNA. FSP1+ podocyte counts per glomerular profile in FSGS patients correlated significantly with the prevalence of glomerulosclerosis and the extent of interstitial type-I collagen-positive areas. Conclusion: Taken together, these data suggest that podocyte expression of FSP1 could shed light on the potential linkage between EMT-like changes, detachment of podocytes from the glomerular basal membrane and the pathophysiology underlying FSGS.

Urinary FSP1 Is a Biomarker of Crescentic GN

Fibroblast-specific protein 1 (FSP1)-expressing cells accumulate in damaged kidneys, but whether urinary FSP1 could serve as a biomarker of active renal injury is unknown. We measured urinary FSP1 in 147 patients with various types of glomerular disease using ELISA. Patients with crescentic GN, with or without antinuclear cytoplasmic antibody-associated GN, exhibited elevated levels of urinary FSP1. This assay had a sensitivity of 91.7% and a specificity of 90.2% for crescentic GN in this sample of patients. Moreover, we found that urinary FSP1 became undetectable after successful treatment, suggesting the possible use of FSP1 levels to monitor disease activity over time. Urinary FSP1 levels correlated positively with the number of FSP1-positive glomerular cells, predominantly podocytes and cellular crescents, the likely source of urinary FSP1. Even in patients without crescent formation, patients with high levels of urinary FSP1 had large numbers of FSP1-positive podocytes. Taken together, these data suggest the potential use of urinary FSP1 to screen for active and ongoing glomerular damage, such as the formation of cellular crescents.