The presence of exudative thickening of Bowman's capsule predict poor prognosis in diabetic kidney disease

Background: The relationship between Bowman's capsule thickening and progression of diabetic kidney disease (DKD) remains uncertain. Methods: Renal biopsy specimens from 145 DKD patients and 20 control subjects were evaluated for Bowman's capsule thickness. Immunohistochemical staining assessed col4 alpha 2, laminin fi1, and albumin expression. In a discovery cohort of 111 DKD patients with eGFR >= 30 ml/min/1.73 m2, thickening was classified as fibrotic or exudative. The composite endpoint included CKD stage 5, dialysis initiation, and renal disease-related death. Prognosis was analyzed using Kaplan -Meier and Cox regression analyses. Two validation cohorts were included. Results: Three types of thickening were observed: fibrotic, exudative, and periglomerular fibrosis. Parietal epithelial cell matrix protein accumulation contributed to fibrotic thickening, while albumin was present in exudative thickening. Bowman's capsule was significantly thicker in DKD patients (5.74 +/- 2.09 mu m) compared to controls (3.38 +/- 0.43 mu m, P < 0.01). In discovery cohort, the group of exudative thickning had a poorer prognosis(median time 20 months vs 57 months, P = 0.000). Cox multivariate analysis revealed that exudative thickening of Bowman's capsule were associated with a poor prognosis. The validation cohorts confirmed the result. Conclusions: Various mechanisms contribute to Bowman's capsule thickening in DKD. The proportion of exudative thickening may serve as a valuable prognostic indicator for DKD patients.