Intra-renal and urinary mRNA expression of podocyte-associated molecules for the estimation of glomerular podocyte loss

Abstract

Background: Podocyte loss plays an important role in the pathogenesis of diabetic nephropathy, but counting the number of glomerular podocyte in renal biopsy specimen is a labor-intensive task. We study whether intra-renal and urinary messenger RNA expression of podocyte-associated molecules could be used to estimate glomerular podocyte number in patients with diabetic nephropathy. Method: We studied 21 consecutive patients with biopsy-proven diabetic nephropathy. The intra-renal and urinary mRNA expression of nephrin, podocin, and synaptopodin were measured by real-time quantitative polymerase chain reaction. Podocyte number was determined in micro-dissected glomerulus. The degree of histological scarring was quantified by morphometric analysis. Results: Glomerular podocyte number correlated with intra-renal expression of nephrin (r = 0.510, p = 0.044), podocin (r = 0.605, p = 0.013), and synaptopodin (r = 0.480, p = 0.060). Glomerular podocyte number also significantly correlated with urinary expression of synaptopodin (r = 0.595, p = 0.019) but not other targets. Baseline renal function correlated with intra-renal expression of nephrin (r = 0.617, p = 0.005), synaptopodin (r = 0.474, p = 0.040), and podocin (r = 0.443, p = 0.057). The degree of tubulointerstitial scarring also inversely correlated with intra-renal expression of nephrin (r = −0.462, p = 0.047), podocin (r = −0.458, p = 0.049), and synaptopodin (r = −0.500, p = 0.029) but not with urinary gene expression. Conclusion: Intra-renal expression of podocyte-associated molecules correlated with glomerular podocyte number, renal function, and tubulointerstitial scarring. The results suggest that intra-renal, but not urinary expression of podocyte-associated molecules, might be used to assess the degree of podocyte loss in diabetic nephropathy.

Keywords:

• diabetes mellitus
• podocyte number
• gene expression

Acknowledgments

This study was supported by the Hong Kong Society of Nephrology research grant and CUHK research account 6901031. We thank Professor John M. Basgen for his useful advice on podocyte counting, and Professor Chan Ho-Yin and Dr Law Tik-wan from the Department of Biochemistry, Chinese University of Hong Kong, for the technical support.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.