EXTRACELLULAR MATRIX IN FETAL KIDNEY AFTER EXPERIMENTAL OBSTRUCTION

Plumbing the depths of urinary tract obstruction by using murine models

Urinary tract obstruction leads to obstructive nephropathy, which in turn, frequently results in renal failure. Congenital urinary tract obstruction can be traced back to errors during the organogenesis of the urinary system. A fundamental understanding of the causes of urinary tract obstruction and the developmental processes involved are critical for improving the diagnostic and therapeutic strategies for this disease. A number of laboratories, including ours, have been using genetically engineered and spontaneously occurring mouse models to study the primary causes and the pathogenesis of urinary tract obstruction. These studies have shown that urinary tract obstruction is a very heterogeneous disease that can be caused by a diverse set of factors targeting multiple levels of the urinary system. Accumulating evidence also indicates that the development of the urinary tract requires the integration of progenitor cells of diverse embryonic origins, leading to the formation of multiple junctions prone to developmental errors. In addition, the high sensitivity of the pyeloureteral peristaltic machinery to disturbance affecting the structural or functional integrity of its components also contributes to the high incidence rate of urinary tract obstruction.

Matrilysin (MMP-7) inhibition of BMP-7 induced renal tubular branching morphogenesis suggests a role in the pathogenesis of human renal dysplasia

Congenital renal dysplasia (RD) is a severe form of congenital renal malformation characterized by disruption of normal renal development with cyst formation, reduced or absent nephrons, and impaired renal growth. The authors previously identified that matrilysin (matrix metalloproteinase-7) was overexpressed in a microarray gene expression analysis of human RD compared to normal control kidneys. They now find that active matrilysin gene transcription and protein synthesis occur within dysplastic tubules and epithelial cells lining cysts in human RD by RT-PCR and immunohistochemistry. Similar staining patterns were seen in obstructed kidneys of pouch opossums that show histological features similar to that of human RD. In vitro, matrilysin inhibits formation of branching structures in mIMCD-3 cells stimulated by bone morphogenetic protein-7 (BMP-7) but does not inhibit hepatocyte growth factor-stimulated branching. BMP-7 signaling is essential for normal kidney development, and overexpression of catalytically active matrilysin in human embryonic kidney 293 cells reduces endogenous BMP-7 protein levels and inhibits phosphorylation of BMP-7 SMAD signaling intermediates. These findings suggest that matrilysin expression in RD may be an injury response that disrupts normal nephrogenesis by impairing BMP-7 signaling.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

Inhibition of histone deacetylase activity attenuates renal fibroblast activation and interstitial fibrosis in obstructive nephropathy

Activation of renal interstitial fibroblasts is critically involved in the development of tubulointerstitial fibrosis in chronic kidney diseases. In this study, we investigated the effect of trichostatin A (TSA), a specific histone deacetylase (HDAC) inhibitor, on the activation of renal interstitial fibroblasts in a rat renal interstitial fibroblast line (NRK-49F) and the development of renal fibrosis in a murine model of unilateral ureteral obstruction (UUO). alpha-Smooth muscle actin (alpha-SMA) and fibronectin, two hallmarks of fibroblast activation, were highly expressed in cultured NRK-49F cells, and their expression was inhibited in the presence of TSA. Similarly, administration of TSA suppressed the expression of alpha-SMA and fibronectin and attenuated the accumulation of renal interstitial fibroblasts in the kidney after the obstructive injury. Activation of renal interstitial fibroblasts was accompanied by phosphorylation of signal transducer and activator of transcription 3 (STAT3), and TSA treatment also abolished these responses. Furthermore, inhibition of the STAT3 pathway with AG490 inhibited expression of alpha-SMA and fibronectin in NRK-49F cells. Finally, TSA treatment inhibited tubular cell apoptosis and caspase-3 activation in the obstructive kidney. Collectively, we suggest that pharmacological HDAC inhibition may induce antifibrotic activity by inactivation of renal interstitial fibroblasts and inhibition of renal tubular cell death. STAT3 may mediate those actions of HDACs.

Timing of morphologic and apoptotic changes in the sheep fetal kidney in response to bladder outflow obstruction

PURPOSE

Posterior urethral valves are the main cause of bladder outflow obstruction in human fetuses. Thirty per cent of boys with valves develop end-stage renal disease, despite intervention in the postnatal period. The timing and mechanisms of renal damage in bladder outflow obstruction are unknown. We investigated the timing of changes in morphology and apoptosis in the fetal sheep kidney in response to obstruction.

MATERIALS AND METHODS

Thirty-three fetal lambs at day 70 of gestation underwent surgical creation of bladder outflow obstruction. Twenty-nine fetal lambs had sham surgery. Fetal kidneys were collected 2, 5, 10, 20 and 30 days after surgery. Renal histology was examined. Real-time PCR was used to quantify the renal cortical expression of the pro-apoptotic gene Bax and anti-apoptotic gene Bcl-X. The TUNEL technique was used to assess regional renal apoptosis in response to obstruction.

RESULTS

Changes in renal morphology were evident as early as 2 days after surgery in fetuses with bladder outflow obstruction, and progressed over 20-30 days to cystic renal dysplasia. Bladder outflow obstruction increased the renal cortical expression of Bax relative to Bcl-X. Tubular apoptosis peaked after 2 days of obstruction. Blastemal apoptosis peaked after 5 days of obstruction.

CONCLUSIONS

Changes in pro- and anti-apoptotic gene expression in the fetal renal cortex, and alterations in the number of apoptotic cells and renal morphology are evident soon after the onset of bladder outflow obstruction. These findings suggest that damage to the developing fetal kidney begins to occur at the onset of obstruction. Attempts to preserve renal function by antenatal interventions may best be achieved by early treatment.

Complete Unilateral Ureteral Obstruction in the Fetal Lamb. Part II: Long-Term Outcomes of Renal Tissue Development

PURPOSE

We analyzed the dynamics of the renal tissue response to experimental fetal urinary flow impairment concerning renal morphology, extracellular matrix composition, regulators of connective tissue degradation and PAX2 protein expression.

MATERIALS AND METHODS

A total of 26 fetal lambs underwent surgical unilateral ureteral obstruction at 90 days of gestation and 14 twin matched animals served as controls. Kidneys were harvested 10, 20 and 40 days after the prior procedure in groups 1 to 3, respectively and in 1-month-old lambs (group 4). Morphological analysis was done using light microscopy. Picrosirius red staining was used to evaluate the area occupied by extracellular matrix components. Collagen I, III and IV, alpha-smooth muscle actin, MMP-1, 2 and 9, TIMP-1 and 2 and PAX2 protein were assessed using immunochemistry.

RESULTS

All obstructed kidneys were hydronephrotic without dysplasia. Hypoplasia resulting from a decreased NGG was observed. The inflammatory response to obstruction was poor in fetal obstructed kidneys. From 10 days after obstruction interstitial fibrosis was noted and confirmed by an increase in picrosirius red staining. In obstructed kidneys immunochemistry showed an increase in collagen deposition beginning from the papillae and extending through the whole parenchyma. Aberrant interstitial collagen IV deposition was observed. The increase in alpha-smooth muscle actin staining was mainly localized in the blastema and interstitial cells in obstructed kidneys. MMP and TIMP immunostaining was mainly present in tubules throughout the whole nephrogenic period and persisted in mature kidneys. Beginning from 20 days after obstruction a progressive increase in MMP and TIMP expression was noted. This was associated with ectopic expression in the medullary tubules. PAX2 protein was highly expressed in the nephrogenic zone, decreasing progressively to being markedly decreased in control lamb kidneys. No difference was found in PAX2 expression during the fetal period when comparing unobstructed and obstructed kidneys, it but remained strongly expressed in the dilated collecting ducts of obstructed lambs.

CONCLUSIONS

Complete unilateral ureteral obstruction performed in fetal lambs at 90 days of gestation led to pure hydronephrotic transformation, hypoplasia and a marked increase in connective tissue deposition. Inflammatory infiltrates and PAX2 dysregulation were not seen as having a decisive role in these modifications.

Altered expression of immune modulator and structural genes in neonatal unilateral ureteral obstruction

BACKGROUND

Congenital obstructive nephropathy is a condition characterized by hydronephrosis, tubular dilatation, apoptosis, and atrophy, as well as interstitial cellular infiltration and progressive interstitial fibrosis. The renal consequences of chronic unilateral ureteral obstruction (UUO) in the neonatal rat are similar to those of clinical congenital obstructive nephropathy.

METHODS

To define alterations in renal gene expression induced by chronic neonatal UUO, Sprague-Dawley rats were subjected to UUO or sham operation within the first 2 days of life, and kidneys were harvested after 12 days.

RESULTS

Microarray analysis revealed that the mRNA expression of multiple immune modulators, including krox24, interferon-gamma regulating factor-1 (IRF-1), monocyte chemoattractant protein-1 (MCP-1), interleukin-1beta (IL-1beta), CCAAT/enhancer binding protein (C/EBP), p21, c-fos, c-jun, and pJunB, was significantly increased in obstructed compared to sham-operated kidneys (all P < 0.05). Western blot analysis revealed significant changes in immune modulator protein abundance in the obstructed versus sham-operated kidney for krox24 (P = 0.0004), IRF-1 (P = 0.005), MCP-1 (P = 0.01), and JunD (P = 0.0008). Alternatively, the abundance of all of the immune modulator proteins was similar in sham-operated and obstructed kidneys in rats subjected to acute (4 days) neonatal UUO. Microarray analysis studies also reveal that structural genes that comprise the cytoskeleton and cell matrix are significantly up-regulated by chronic neonatal UUO, including calponin, desmin, dynamin, and lumican (all P < 0.05).

CONCLUSION

Multiple genes are aberrantly expressed in the kidney of rats subjected to chronic neonatal UUO. Elucidation of these genes involved in neonatal UUO may lead to new insight about congenital obstructive nephropathy.