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Increased epithelial cell proliferation and abnormal extracellular matrix in rat polycystic kidney disease
K Ramasubbu1, N Gretz, S Bachmann
1Department of Anatomy, Klinikum Mannheim, University of Heidelberg, Germany.
Insights
Cell proliferation in kidney tubules precedes cyst formation in polycystic kidney disease (PKD). This study in the Han:SPRD rat model reveals increased cell division in normal-appearing tubules, indicating early disease changes.
Area of Science:
- Nephrology
- Cell Biology
- Genetics
Background:
- Polycystic kidney disease (PKD) is characterized by renal cyst formation, driven by tubular epithelial cell proliferation.
- The Han:SPRD rat serves as a valuable model for studying inherited PKD, particularly autosomal dominant PKD (ADPKD), due to its similarities to human disease.
- Understanding early cellular events is crucial for developing effective therapeutic strategies for PKD.
Purpose of the Study:
- To quantify in vivo cell proliferation rates in the Han:SPRD rat model of PKD in a cell type-specific manner.
- To investigate the relationship between cell proliferation and extracellular matrix expression during cystogenesis.
- To elucidate the temporal sequence of cell proliferation and cyst formation in early-stage PKD.
Main Methods:
- Immunohistochemistry using an antibody against proliferating cell nuclear antigen (PCNA) to determine the proliferation index (PI).
- In situ hybridization to detect messenger RNA (mRNA) for collagen I and IV, key extracellular matrix components.
- Analysis of both heterozygously (cy/+) and homozygously (cy/cy) affected Han:SPRD rats at different ages.
Main Results:
- Significantly increased PI values were observed in normal-appearing tubules of PKD kidneys even in early disease stages, preceding overt cyst formation.
- Epithelial cell proliferation was most pronounced in proximal tubule-derived cysts, with less significant changes in distal cysts.
- Increased epithelial and interstitial cell proliferation correlated with the overexpression of collagen I and IV mRNA, suggesting altered cell-matrix interactions.
Conclusions:
- Enhanced epithelial and interstitial cell proliferation are key events that precede and coincide with cystic malformation in the Han:SPRD rat model of ADPKD.
- Altered cell-matrix interactions appear to play a direct role in disrupting epithelial differentiation during PKD progression.
- These findings highlight the importance of targeting cell proliferation and cell-matrix dynamics in the development of PKD therapies.
Abstract:
Proliferation of renal tubular epithelial cells is considered a major factor leading to cyst formation in human polycystic kidney disease (PKD). The Han:SPRD rat model for inherited PKD permits a close scrutiny, especially for early stages of the disease, and shows numerous similarities to human autosomal dominant PKD (ADPKD). In this study, the exact in vivo proliferation rate in Han:SPRD rat kidneys was evaluated in a cell type-specific manner, using immunohistochemistry with antibody to proliferating cell nuclear antigen (PCNA). The proliferation index (PI; percentage of PCNA-positive cell nuclei) was determined in normal and cystically altered tissue, and a relationship between proliferative activity and alterations in extracellular matrix expression was established using in situ hybridization for collagen I and IV mRNA. Heterozygously affected rats (cy/+) showed strong increases of PI values in cystically altered nephron portions that were mostly derived from proximal tubule. Cell proliferation obviously preceded cyst formation, because early in the progression of the disease, the normal-appearing tubules from PKD kidneys had markedly increased PI values compared with healthy controls (14.1-fold in 3-mo-old rats and 11.9-fold in 12-mo-old rats; P < 0.05), whereas later stages revealed a more generalized cystic degeneration of the nephron, with increases in PI between 14- and 82-fold, depending on the respective category of cystic epithelia. In cysts with a distal phenotype, changes were less pronounced. No significant differences were encountered between the two age groups. Proliferation was also present in interstitial cells, whereas glomeruli were unchanged. Increases in epithelial and interstitial proliferation coincided with an overexpression of matrix compounds. For comparison, changes in homozygously affected rats (cy/cy) showed up to several hundred-fold elevated PI values. These results indicate that in the Han:SPRD model for ADPKD, cystic malformation of the nephron is preceded by and coincides with enhanced epithelial and interstitial cell proliferation. Altered cell-matrix interactions seem to be directly involved in the disruption of epithelial differentiation.