Evaluation of renal clinicopathological changes in IgA nephropathy by urinary podocytes excretion and podocalyxin expression.

Objective: To explore the association of urinary podocyte excretion and renal expression of podocyte-specific marker podocalyxin (PCX) with clinicopathological changes in immunoglobulin A nephropathy (IgAN).

Methods: Morning urine samples from IgAN patients and healthy controls were collected. The expression of glomerular PCX was quantified in 50 IgAN patients diagnosed by renal biopsy. IgAN was classified based on the Lee's Grading system and scored according to the Katafuchi semiquantitative criteria. Morphological evaluation of podocyte was determined by electron microscopy.

Results: The amount of urinary podocytes in the IgAN patients was significantly higher than that in the healthy controls (p < 0.01). Pairwise comparison among Lee's grades of IgAN showed that the median of urinary podocytes in Lee's I-II group was lower than that in Lee's III, IV, and V groups (p < 0.05); group III lower than group V (p < 0.05). The positive rate of urinary podocytes was the highest in Lee's IV and V groups (100%), and lowest in Lee's I-II group (55%). Multiple comparison among groups of Lee's grades of IgAN showed that the glomerular PCX expression in Lee's I-II group was higher than that in Lee's III, IV, and V groups (p < 0.05); groups III and IV higher than group V (p < 0.05). The amount of urinary podocytes in IgAN patients was negatively correlated with PCX expression (r = -0.702, p < 0.01), but positively correlated with 24-h urinary protein (r = 0.465, p < 0.01) and glomerular (r = 0.233, p < 0.01) and renal tubular pathological scores (r = 0.307, p < 0.05). The glomerular PCX expression was negatively correlated with 24-h urinary protein (r = -0.367, p < 0.05) and glomerular (r = -0.560, p < 0.05) and tubular pathological scores (r = -0.377, p < 0.05). Electron microscopy showed significant changes in podocytes of IgAN, especially in the foot process.

Conclusion: The amount of urinary podocyte can reflect the loss of podocytes in renal tissue, which may be a marker of IgAN progression.