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 col4α2, laminin β1, 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 μm) compared to controls (3.38 ± 0.43 μm, 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.