Expression of mitogen-activated protein kinases in human renal dysplasia

Inhibition of the p38 MAPK pathway ameliorates renal fibrosis in an NPHP2 mouse model

BACKGROUND

Nephronophthisis (NPHP), the most frequent genetic cause of end-stage kidney disease in children and young adults, is characterized by a variable number of renal cysts associated with cortical tubular atrophy and interstitial fibrosis. The p38 mitogen-activated protein kinase (MAPK) pathway is an important intracellular signaling pathway involved in the production of profibrotic mediators. The relationship between p38 MAPK and renal fibrosis in NPHP2 is unknown.

METHODS

We administered a selective p38 MAPK inhibitor, FR167653, in a NPHP2 mouse model (inv/inv, invΔC mice) from 3 to 6 weeks old, and the kidneys were examined at 6 weeks of age. Phosphorylation of p38 MAPK (p-p38 MAPK) protein levels, the degree of renal fibrosis, messenger RNA (mRNA) levels for extracellular matrix genes and mRNA levels for transforming growth factor in the kidneys were studied. Effect of an extracellular signal-regulated protein kinase (ERK) kinase (MEK) inhibitor on renal fibrosis was also evaluated.

RESULTS

Expression of extracellular matrix genes and p-p38 MAPK were increased in the NPHP2 mouse model kidney. FR167653 successfully decreased p-p38 MAPK levels, the degree of fibrosis and extracellular matrix gene expressions. However, the FR167653 did not prevent cyst expansion, abnormal cell proliferation and acceleration of apoptosis and did not influence ERK activation. In contrast, MEK inhibition reduced both cyst expansion and fibrosis without affecting p38 MAPK activation.

CONCLUSIONS

These results suggest that inhibition of p38 MAPK reduced renal fibrosis but not cyst expansion, cell proliferation and apoptosis in NPHP2 model mice. Our results suggest that p38 MAPK and ERK signaling pathways independently affect renal fibrosis in inv mutant mice.

Cyclic stretch induces proliferation and TGF-β1-mediated apoptosis via p38 and ERK in ureteric bud cells

We previously reported that p38 mitogen-activated protein kinase (p38) and phosphorylated ERK are upregulated in cyst epithelium of human renal dysplasia and obstructive uropathy in fetal lambs (Omori S, Fukuzawa R, Hida M, Awazu M. Kidney Int 61: 899–906, 2002; Omori S, Kitagawa H, Koike J, Fujita H, Hida M, Pringle KC, Awazu M. Kidney Int 73: 1031–1037, 2008). Dysplastic epithelium is characterized by proliferation, apoptosis, and upregulation of Pax2 and transforming growth factor (TGF)-β1. In the present study, we investigated whether cyclic mechanical stretching of ureteric bud cells, a mimic of the hydrodynamic derangement after fetal urinary tract obstruction, reproduces events seen in vivo. Cyclic stretch activated p38 and ERK and upregulated Pax2 expression in a time-dependent manner in ureteric bud cells. Stretch-stimulated Pax2 expression was suppressed by a p38 inhibitor, SB203580, or a MEK inhibitor, PD98059. 5-Deoxyuridine incorporation was increased by stretch at 24 h, which was also abolished by SB203580 or PD98059. On the other hand, apoptosis was not induced at 24 h by stretch but was significantly increased at 48 h. TGF-β1 secretion was increased by stretch at 24 h, which was inhibited by SB203580 or PD98059. Inhibition of p38 or ERK as well as anti-TGF-β antibody abolished the stretch-induced apoptosis. Finally, exogenous TGF-β1 induced apoptosis of ureteric bud cells, which was inhibited by SB203580 and PD98059. In conclusion, cyclic stretch induces Pax2 upregulation, proliferation, and TGF-β1-mediated apoptosis, features characteristic of dysplastic epithelium, via p38 and ERK in ureteric bud cells.

Activated extracellular signal-regulated kinase correlates with cyst formation and transforming growth factor-beta expression in fetal obstructive uropathy

Human renal dysplasia is frequently associated with urinary tract obstruction and the abnormal expression of mitogen-activated protein kinase (MAPK). Here, we determined the renal responses and MAPK expression in developing kidneys that were obstructed in fetal lambs. Kidneys were harvested at various times after obstruction (gestation day 60) through normal term (day 145). Dilation of Bowman's capsule and proximal tubules was seen 2 days after obstruction and involved the whole cortex 18 days later, with numerous cysts present throughout the kidney at term. The proliferation marker Ki-67 and transforming growth factor-beta (TGF-beta) were detected 2 days after obstruction and progressively increased in tubules, cysts, and the interstitium. In control kidneys, p38 was expressed in tubules only during the fetal stage, whereas phosphorylated extracellular signal-regulated kinase (P-ERK) was limited to ureteric buds and collecting ducts at all stages examined. However, Jun-N-terminal kinase (JNK) was absent in the fetal kidney but present in tubules at term. In obstructed kidneys, cyst epithelia were positive for p38 and P-ERK but negative for JNK throughout all stages. These studies show that P-ERK correlated spatially and temporally with Ki-67 and TGF-beta expression, which suggests that ERK may contribute to cyst formation and fibrosis in the obstructed fetal kidney.

Branching morphogenesis of the ureteric epithelium during kidney development is coordinated by the opposing functions of GDNF and Sprouty1

Branching of ureteric bud-derived epithelial tubes is a key morphogenetic process that shapes development of the kidney. Glial cell line-derived neurotrophic factor (GDNF) initiates ureteric bud formation and promotes subsequent branching morphogenesis. Exactly how GDNF coordinates branching morphogenesis is unclear. Here we show that the absence of the receptor tyrosine kinase antagonist Sprouty1 (Spry1) results in irregular branching morphogenesis characterized by both increased number and size of ureteric bud tips. Deletion of Spry1 specifically in the epithelium is associated with increased epithelial Wnt11 expression as well as increased mesenchymal Gdnf expression. We propose that Spry1 regulates a Gdnf/Ret/Wnt11-positive feedback loop that coordinates mesenchymal-epithelial dialogue during branching morphogenesis. Genetic experiments indicate that the positive (GDNF) and inhibitory (Sprouty1) signals have to be finely balanced throughout renal development to prevent hypoplasia or cystic hyperplasia. Epithelial cysts develop in Spry1-deficient kidneys that share several molecular characteristics with those observed in human disease, suggesting that Spry1 null mice may be useful animal models for cystic hyperplasia.

Extracellular signal-regulated kinase inhibition slows disease progression in mice with polycystic kidney disease

The expression of mitogen-activated protein kinases (MAPK) in DBA/2-pcy/pcy (pcy) mice, a murine model of polycystic kidney disease was investigated. Proliferating cell nuclear antigen-positive cells were recognized in cyst epithelium from embryonic day 14.5 to 25 wk of age. Extracellular signal-regulated kinase (ERK) was expressed in the renal tubules of control and pcy mice, but stronger immunostaining was observed in cyst epithelium. Phosphorylated ERK was detected only in pcy mice and was localized predominantly in the cysts. p38 MAPK (p38) was no longer expressed after birth in controls but was detected in the cyst epithelium and in occasional tubular cells of pcy mice at all stages examined. c-Jun N-terminal kinase (JNK) was expressed in all tubular segments of controls after neonatal day 7, whereas in pcy kidneys, tubules became positive for JNK after 8 wk, and the cysts expressed little JNK. Administration of an oral MAP/ERK kinase inhibitor, PD184352, 400 mg/kg per d, to 10-wk-old pcy mice daily for the first week and then every third day for 6 additional weeks significantly decreased BP, kidney weight, serum creatinine level, and water intake and significantly increased urine osmolality. The cystic index and expression of phosphorylated ERK and ERK were significantly lower in PD184352-treated pcy mice. These results demonstrate that the expression of MAPK is dysregulated in cyst epithelium and that inhibition of ERK slowed the progression of renal disease in pcy mice.

Signals which build a tubule

The phenomenon of branching morphogenesis is a fundamental process critical for development of several tubular organs including lung, mammary gland, and kidney. In the case of kidney, the ureteric bud (UB) that extends out from a pre-existing epithelial tube, the Wolffian duct, gives rise to the branched collecting duct system while the surrounding metanephric mesenchyme undergoes mesenchymal-epithelial transition to form the proximal parts of the nephron. These events are mediated by several soluble factors that act in a cooperative fashion either as pro or anti tubulogenic factors. Among the growing list of such molecules are the members of the FGF, TGF-beta, and Wnt families as well as GDNF, HGF, and EGF. Cells respond to these soluble factors by initiating signaling pathways that regulate cell proliferation, cell migration and cell morphogenesis. These signaling pathways are also regulated in parallel by cell-cell and cell-matrix interactions, leading to the complex events necessary for tubule formation. Recent in-vitro and in-vivo studies have begun to shed light on the overall regulation of this phenomenon while the specific subcellular mechanisms are only beginning to be understood. This review focuses on our understanding of the morphogenic responses that regulate in-vitro tubulogenesis and how they may help us to ultimately understand this process in vivo in the kidney.

Renal dysplasia and urinary tract infection in a Bull Mastiff puppy

Renal dysplasia and concurrent pyelonephritis were diagnosed in a 15-week-old female Bull Mastiff which presented with clinical signs compatible with chronic renal failure. Ultrasound examination was consistent with renal dysplasia and clinical pathology supported a diagnosis of chronic renal failure and urinary tract infection. Renal histological examination demonstrated inflammation and scarring with concurrent tubular dysplasia and persisting primitive glomeruli, although the presence of chronic inflammation complicated interpretation. It is uncertain whether renal dysplasia was inherited or due to a urinary tract infection acquired in the neonatal period. Renal dysplasia has not previously been reported in the Bull Mastiff breed.

Effects of PD98059 on proliferation of rat cultured hepatic stellate cells stimulated by acetaldehyde

AIM

To study the effects of PD98059, the specific blocking agent of MEK1, on the proliferation of hepatic stellate cells and expression of Proliferating Cell Nuclear Antigen in rat hepatic stellate cells (HSC).

METHODS

HSC stimulated by acetaldehyde were cultured. The cell growth was evaluated by MTT colorimetric assay. Proliferating cell nuclear antigen (PCNA) was examined by immunocytochemical staining.

RESULTS

PD98059 of 20 μmol/L had an inhibitory effect on proliferation of HSC (P<0.05, 0.109±0.020 vs 0.146±0.030), which was more obvious when cells exposed to PD98059 at 50 and 100 μmol /L (P<0.05, 0.081±0.010, 0.056±0.020 vs 0.146±0.030), and the expression of PCNA also showed a descending tendency with the increase of PD98059 concentration (P<0.05, 0.62±0.09, 0.47±0.04, 0.34±0.04 vs 0.740.05)

CONCLUSION

PD98059 inhibits proliferation of HSC and expression of PCNA, which is correlated with the decreased activity of PCNA.

Activation of the ERK pathway precedes tubular proliferation in the obstructed rat kidney

BACKGROUND

In vitro studies suggest that activation of the extracellular signal-regulated kinase (ERK) pathway plays a critical role in the proliferation of tubular epithelial and myofibroblast-like cells. However, little is known of ERK activation in individual cell types in normal or diseased kidney. The aims of this study were to (1) localize ERK activation within the kidney, and (2) examine the relationship between ERK activation and cell proliferation in the injured kidney.

METHODS

Unilateral ureteric obstruction (UUO) was induced in groups of six Wistar rats, which were killed at 30 minutes, 6 hours, and 1, 4, or 7 days after obstruction. Activation of ERK was identified using antibodies specific for the phosphorylated form of ERK (pERK) in Western blots and immunostaining. Proliferating cells were detected using bromodeoxyuridine (BrdU).

RESULTS

Western blotting showed abundant expression of the two ERK isoforms, ERK-1 and ERK-2, in normal rat kidney. Low levels of activated ERK (pERK-2> pERK-1) were detected in normal rat kidney by Western blotting. Immunostaining showed that ERK activation in normal kidney was largely restricted to collecting ducts in the outer medulla. Within 30 minutes of ureter obstruction, Western blotting showed a sixfold increase in ERK activation followed by a second peak (14-fold increase) on days 4 and 7. The initial peak of ERK activation was localized to medullary collecting ducts and the thick ascending limb of Henle (TALH), whereas the second peak corresponded to a progressive increase in ERK activation in dilated collecting ducts and in interstitial cells in the cortex. Proliferation of tubular epithelial cells closely followed the pattern of ERK activation, being evident first in medullary collecting ducts and TALH on day 1, and then in cortical collecting ducts from day 4.

CONCLUSION

This study has identified a discrete pattern of ERK activation in normal rat kidney and an increase in ERK activation following obstruction. The temporal and spatial relationship in which ERK activation preceded tubular cell proliferation suggest that ERK signaling plays a key role in tubular epithelial cell proliferation in the injured kidney.