Insulin-like growth factor (IGF) and IGF binding protein gene expression in multicystic renal dysplasia

Outcomes of solitary functioning kidneys-renal agenesis is different than multicystic dysplastic kidney disease

BACKGROUND

Multicystic dysplastic kidney (MCDK) disease and unilateral renal agenesis (URA) are well-known causes of a solitary functioning kidney (SFK) and are associated with long-term kidney injury. The aims of this study were to characterize the natural history of SFK at our center, define the risk factors associated with chronic kidney injury, and identify distinguishing features between URA and MCDK that predict outcome.

METHODS

This was a retrospective cohort study of 230 SFK patients. We compared MCDK (n=160) and URA (n=70) according to clinical features at diagnosis and kidney outcomes over follow-up. Univariate and multivariate binary regression analysis was used to determine independent risk factors for chronic kidney injury, defined as the composite outcome of hypertension, proteinuria, or chronic kidney disease (eGFR <60 mL/min/1.73m²).

RESULTS

URA had a higher prevalence of comorbid genetic syndromes (15 vs. 6%, p=0.04), non-renal anomalies (39 vs. 11%, p<0.001), and congenital anomalies of the kidney and urinary tract (CAKUT) (51 vs. 26%, p<0.001) than MCDK. Over follow-up, URA experienced more hypertension (19 vs. 3%, p=0.002), proteinuria (12 vs. 3%, p=0.03), and the composite outcome (19 vs. 6%, p=0.003) than MCDK. Independent risk factors for chronic kidney injury included CAKUT (OR 5.01, p=0.002) and URA (OR 2.71, p=0.04).

CONCLUSIONS

In our population, URA was more likely to have associated syndromes or anomalies, and to have worse outcomes over time than MCDK. URA diagnosis was an independent risk factor for chronic kidney injury. Our results will be used to develop a standardized clinical pathway for SFK management. A higher resolution version of the Graphical abstract is available as Supplementary information.

Congenital Anomalies of the Kidney and the Urinary Tract (CAKUT)

This article reviews the majority of Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) with emphasis in Pediatric Pathology describing and illustrating lesions as varied as ureteral duplications, ureteropelvic junction obstruction, horseshoe kidney, posterior urethral valve and prune belly syndrome, obstructive renal dysplasia, nonmotile ciliopathies and several syndromes associated with renal malformations (Meckel-Joubert, short rib, Bardet-Biedl, asplenia/polysplenia, hereditary renal adysplasia, Zellweger, trisomies, VACTER-L, Potter, caudal dysplasia, and sirenomelia), as well as ADPK, and ARPK. The purpose of this review is not only to describe the congenital renal anomalies, but also to analyze the more recent therapeutic interventions that may modify the natural history of some of these severe conditions.

Insulin-like growth factors and kidney disease

Insulin-like growth factors (IGF-1 and IGF-2) are necessary for normal growth and development. They are related structurally to proinsulin and promote cell proliferation, differentiation, and survival, as well as insulin-like metabolic effects, in most cell types and tissues. In particular, IGFs are important for normal pre- and postnatal kidney development. IGF-1 mediates many growth hormone actions, and both growth hormone excess and deficiency are associated with perturbed kidney function. IGFs affect renal hemodynamics both directly and indirectly by interacting with the renin-angiotensin system. In addition to the IGF ligands, the IGF system includes receptors for IGF-1, IGF-2/mannose-6-phosphate, and insulin, and a family of 6 high-affinity IGF-binding proteins that modulate IGF action. Disordered regulation of the IGF system has been implicated in a number of kidney diseases. IGF activity is enhanced in early diabetic nephropathy and polycystic kidneys, whereas IGF resistance is found in chronic kidney failure. IGFs have a potential role in enhancing stem cell repair of kidney injury. Most IGF actions are mediated by the tyrosine kinase IGF-1 receptor, and inhibitors recently have been developed. Further studies are needed to determine the optimal role of IGF-based therapies in kidney disease.

Fetal genitourinary anomalies--a pictorial review with postnatal correlation

An accurate diagnosis of fetal genitourinary abnormality is essential because some genitourinary abnormalities are associated with pulmonary hypoplasia, which ultimately affects the neonatal outcome. Adrenal masses are rare; however, presence of any lesion located at the superior pole of the kidney should raise the possibility of an adrenal mass. Fetal genital anomalies are rare as well and some of the most difficult to diagnose. A combination and pattern of findings allows for specific diagnosis of renal tract abnormalities. This article reviews the imaging appearance of fetal genitourinary abnormalities with perinatal imaging correlation where available.

Comparative immunohistochemical study of multicystic dysplastic kidneys with and without obstruction

Etiology of multicystic dysplastic kidney (MCDK) remains unknown. Not all cases are associated with obstruction. We compared by immunohistochemistry 17 cases of MCDK (10 cases with and seven without obstruction) to 17 controls and 20 fetal kidneys. TGF-β was negative in obstructive MCDKs and positive in nonobstructive MCDK. IGF2 was overexpressed in obstructive and underexpressed in nonobstructive MCDKs. PAX2, BCL-2, and β-catenin were expressed equally in obstructive and nonobstructive dysplasia. TGF-β and IGF2 work by different mechanisms in obstructive and nonobstructive MCDKs, but there are no differences among PAX 2, BCL-2, and β-catenin in obstructive versus nonobstructive dysplasia.

Failure to ubiquitinate c-Met leads to hyperactivation of mTOR signaling in a mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder that is caused by mutations at two loci, polycystin 1 (PKD1) and polycystin 2 (PKD2). It is characterized by the formation of multiple cysts in the kidneys that can lead to chronic renal failure. Previous studies have suggested a role for hyperactivation of mammalian target of rapamycin (mTOR) in cystogenesis, but the etiology of mTOR hyperactivation has not been fully elucidated. In this report we have shown that mTOR is hyperactivated in Pkd1-null mouse cells due to failure of the HGF receptor c-Met to be properly ubiquitinated and subsequently degraded after stimulation by HGF. In Pkd1-null cells, Casitas B-lineage lymphoma (c-Cbl), an E3-ubiquitin ligase for c-Met, was sequestered in the Golgi apparatus with α₃β₁ integrin, resulting in the inability to ubiquitinate c-Met. Treatment of mouse Pkd1-null cystic kidneys in organ culture with a c-Met pharmacological inhibitor resulted in inhibition of mTOR activity and blocked cystogenesis in this mouse model of ADPKD. We therefore suggest that blockade of c-Met is a potential novel therapeutic approach to the treatment of ADPKD.

Mesenchymal transition in kidney collecting duct epithelial cells

Progressive organ damage due to tissue scarring and fibrosis is a paradigm shared by numerous human diseases including chronic kidney disease. The purpose of this study was to confirm the hypothesis that collecting duct (CD) epithelial cells can undergo mesenchymal transition (EMT) in vitro. The mechanism by which CDs undergo EMT is complex and involves both early and late cellular events. Early events include rapid insulin-like growth factor (IGF)-induced Akt and GSK-3beta phosphorylation, associated with early disruption of E-cadherin-beta-catenin membrane colocalization, with translocation of E-cadherin to endosomes, with translocation of beta-catenin to the nucleus, and with an increase in Snail expression. Transforming growth factor-beta1, on the other hand, induced early activation of Smad3 and its translocation to the nucleus, Erk1/2 phosphorylation, and early disruption of membrane E-cadherin localization. The late consequences of these events included a phenotypic transformation of the cells to a mesenchymal morphology with associated increase in vimentin and alpha-smooth muscle actin protein expression and a decrease in total cellular E-cadherin expression, detectable as early as 24 h after stimulation.

The role of the type I insulin-like growth factor receptor (IGF-IR) in glomerular integrity

Insulin-like growth factors (IGFs) have been implicated in normal mammalian kidney development. To confirm a role for the IGF system in podocyte and glomerular integrity, we generated a transgenic mouse that expresses a dominant-negative type 1 IGF receptor (IGF-IR) and determined the structural and functional consequences. Using a 4.25kb fragment of the murine nephrin promoter, the dominant-negative construct was expressed exclusively in the kidney, confirmed by Southern blot and RT-PCR analysis. IGF-Ir486(FLAGstop) protein localized specifically to the glomerular podocyte based on FLAG immunohistochemistry and on co-localization with nephrin and podocin. Wild type and transgenic glomeruli expressed both the alpha- and beta-subunits of the endogenous IGF-IR, with normal expression of both nephrin and podocin. Although the animals were viable and phenotypically normal, histological analysis of the kidneys revealed abnormal and small glomeruli with dilated glomerular capillaries and condensed podocyte nuclei, while ultra-structural examination revealed diffuse but segmental podocyte foot process broadening, fusion, and effacement. Explanted glomeruli from transgenic animals demonstrated a significant inhibition of podocyte cell outgrowth when compared to controls. These studies suggest that IGF signaling is essential for maintaining the integrity of the podocyte and that alterations of IGF signaling may play a role in progressive glomerular disease.

A familial case of multicystic dysplastic kidney

A familial case of multicystic dysplastic kidney (MCDK) is described. The proband is a one-year-old boy with left MCDK, and his father was also revealed to have unilateral MCDK. The mother had two abortions; the second pregnancy was terminated because of bilateral MCDK of the fetus (Potter anomaly). The two patients and the aborted male fetus did not have any malformations except for MCDK. Thus in this family MCDK occurs as an isolated phenomenon in three individuals within two generations, presumably as a result of autosomal dominant inheritance.

Increased expression of insulin-like growth factors in progressive glomerulonephritis of the MRL/lpr mouse

Glomerulonephritis is an important complication of systemic lupus erythematosus (SLE). The tissue distribution and exact role of the insulin-like growth factors (IGFs) in the development of lupus nephritis in the MRL/lpr mouse model have not been established. The present study was undertaken to evaluate the changes over time in mRNA and peptide expression of IGF-I and IGFBP-2 in the MRL/lpr mouse. Using in situ hybridization and immunocytochemistry techniques, the expression of IGF-I and IGFBP-2 in MRL/lpr mouse was examined and compared to their congenic normal MRL-++ mouse counterparts from nine to 24 weeks of age. In the MRL-++ and MRL/lpr mouse kidneys, IGF-I and IGFBP-2 mRNA expression was limited to the cortical and medullary collecting ducts, while their immunoreactivity (IR) was localized to the cortical and medullary collecting ducts, loop of Henle, glomeruli and proximal tubules. Over time, and with progression of disease, the MRL/lpr mice displayed a significant increase in IGF-I IR and a modest increase in IGFBP-2 IR within the outer cortical glomeruli, which was associated with a significant increase in glomerulosclerosis and glomerular cell proliferation and with a significant decrease in renal function. In conclusion, this overexpression of IGF-I and IGFBP-2 within the glomeruli of the MRL/lpr mouse kidney supports their potential role in the alterations in renal function and morphology that accompany lupus nephritis.

Altered primate glomerular development due to in utero urinary tract obstruction

BACKGROUND

In utero urinary tract obstruction is an important cause of newborn and childhood renal failure. Ureteric obstruction during active nephrogenesis results in cystic renal dysplasia; the earlier and longer the obstruction the more severe the histopathological changes of dysplasia. We have reported on a non-human primate model of non-surgical in utero fetal ureteric obstruction that accurately reflects the human equivalent of obstructive renal dysplasia. A striking feature of this model is the effect of obstruction on normal glomerular development and podocyte survival.

METHODS

To study the effect of urinary obstruction on glomerular development, kidneys were studied from fetuses undergoing unilateral ureteric obstruction by ultrasound guided injection of alginate beads as early as 75 days gestation (term gestation = 165 +/- 10 days). These kidneys displayed all the features of human obstructive cystic dysplasia, had reduced weights, and significant deficiencies in terminal ureteric duct branching.

RESULTS

A combination of histochemistry, histomorphometry, and immunocytochemistry was used to demonstrate deficient cortical ureteric duct development and branching, reduced glomerular number, and altered glomerular basement membrane formation with in utero urinary tract obstruction.

CONCLUSIONS

These data suggest that urinary tract obstruction during active nephrogenesis results in a defect in ureteric duct branching morphogenesis, and altered vascularization of the glomerulus with consequent podocyte dropout and decreased glomerular number. These abnormalities reflect human renal dysplasia, which is associated with compromised postnatal renal function and, thus, should be predictive of postnatal outcome.

Expression of mitogen-activated protein kinases in human renal dysplasia

BACKGROUND

We previously reported that the expression of mitogen-activated protein kinases (MAPKs) is developmentally regulated. Dysregulation of MAPKs may lead to kidney malformation. Thus, we investigated the expression of MAPKs in human renal dysplasia, one of the most common kidney malformations.

METHODS

Prenatal (gestational ages 20 to 36 weeks, N = 6) and postnatal (2 years old, N = 1) dysplastic kidneys, and normal kidneys (gestational ages 19 to 34 weeks, N = 4) were examined. Immunohistochemical studies were performed using antibodies against extracellular signal-regulated kinase (ERK), p38 MAPK (p38), c-Jun N-terminal kinase (JNK), phospho-MAPKs (P-MAPKs), and proliferating cell nuclear antigen (PCNA). Apoptosis was detected by the TUNEL method.

RESULTS

In dysplastic kidneys, proliferation was prominent in dysplastic tubules and also found in cyst epithelia. TUNEL staining was detected in dysplastic tubules and cysts, and occasionally in undifferentiated cells. p38 and anti-phospho-p38 (P-p38) were strongly expressed in dysplastic epithelia, but not detected in normal kidneys at any stage examined. On the other hand, JNK and P-JNK were positive in tubular epithelia of normal kidneys, whereas their expression was barely detectable in dysplastic tubules and cysts. ERK was expressed in all tubular segments, and P-ERK was detected in distal tubules and collecting ducts of normal kidneys. Dysplastic kidney epithelia stained exclusively positive for ERK and P-ERK.

CONCLUSIONS

p38 is ectopically expressed, and JNK is down-regulated in dysplastic kidney epithelia. Furthermore, dysplastic epithelia are exclusively positive for ERK and P-ERK. Activated p38 and ERK may mediate hyperproliferation of dysplastic tubules resulting in cyst formation, whereas down-regulated JNK expression may be the cause or the result of an undifferentiated state of dysplastic epithelia.

Congenital obstructive uropathy: its origin and contribution to end-stage renal disease in children

Most children with end-stage renal failure are born with abnormal kidneys, with fetal obstructive uropathy accounting for about half these cases. Posterior urethral valves (PUV) is overwhelmingly the most common, specific diagnosis, and is confined to boys. In general, the condition is sporadic, although familial cases have been reported, perhaps suggesting that genetic factors play a role in pathogenesis. PUV can present antenatally, detected on routine fetal ultrasonography, or postnatally, when it is associated with renal failure and bladder dysfunction. Advances in postnatal surgery and medical management have reduced the mortality in PUV, but it is uncertain whether antenatal diagnosis or treatment (eg, with vesicoamniotic shunts) improves long-term renal outcome. Other disorders associated with human fetal obstructive uropathy are urethral atresia, the prune belly syndrome, and multicystic dysplastic kidney. The nephropathy associated with fetal obstructive uropathy is renal dysplasia and comprises undifferentiated and metaplastic tissues. Several studies in animals and in humans suggest that fetal urine flow impairment causes deregulation of renal precursor cell turnover and expression of growth factor/survival and transcription factor genes. Furthermore, some of these morphologic and molecular changes can be ameliorated experimentally by fetal surgical decompression or administration of specific growth factors.

IGF-II and IGF binding protein (IGFBP-1, IGFBP-3) gene expression in fetal rhesus monkey tissues during the second and third trimesters

The IGF system is a key modulator of somatic fetal growth. Studies with human fetal tissues have shown a specific spatial and temporal pattern of expression of IGF and IGF binding protein (IGFBP) mRNAs, but have been limited to defined periods during gestation (i.e. 8-20 wk gestation) because of tissue availability. To fully assess the role of these peptides in the primate growth process, a longitudinal study was conducted that focused on the expression of IGF-II and IGFBP-1 and IGFBP-3 genes in the rhesus monkey (Macaca mulatta). Liver, kidney, brain, and lung were collected from rhesus monkey fetuses approximately every 2 wk from 65 (early second trimester) through 150 d gestation (term 165 +/- 10 d) (n = 50), then processed for in situ hybridization using radiolabeled human cDNAs. IGF-II mRNA was abundantly expressed in fetal kidney (maturing glomerulus, supporting mesenchyme, cells of the developing nephrons), liver (hepatocytes), cerebral cortex (choroid plexus, capillaries), and lung (blood vessels, connective tissues, lamina propria, cartilage framework). IGFBP-1 was expressed only in the hepatocytes and IGFBP-3 mRNA was modestly expressed within the kidney (developing nephrons, collecting system mesenchyme), and liver (hepatocytes). These studies have shown that (1) IGF-II, IGFBP-1, and IGFBP-3 are expressed in specific cell types of the fetal monkey indicating a paracrine/autocrine role during development; (2) changes in IGF-II and IGFBP mRNA expression occur with advancing gestation; and (3) fetal monkey tissues express IGF-II and IGFBPs in a similar manner when compared with the human fetus.

Fetal rhesus monkey model of obstructive renal dysplasia

BACKGROUND

Disorders of kidney development represent a major cause of renal failure and end-stage renal disease in the pediatric population. To understand further the prenatal pathogenesis of obstructive renal dysplasia, a fetal monkey model was developed using ultrasound-guided techniques.

METHODS

Ureteropelvic obstruction (N = 13) was induced during the early or late second trimester by the injection of purified guluronic alginate spheres. All fetuses were monitored sonographically, and then fetal tissues were removed at varying time points during the second and third trimesters.

RESULTS

There was no evidence of oligohydramnios during the course of gestation, and the obstructed kidneys were typically progressively smaller than the contralateral (nonobstructed) kidneys when monitored sonographically over time. Obstructed kidneys displayed most features of renal dysplasia, including numerous cortical cysts of various sizes derived predominantly from collecting ducts and glomeruli. Mesenchymal changes included expansion of both the cortical and medullary interstitium, as well as mesenchymal-myocyte transformation, expressed as pericystic and peritubular fibromuscular collar formation. An important feature of this model was the disruption of normal glomerular development and architecture, associated with significant podocyte apoptosis, evident as early as the prevascularized S-shaped nephron. As in other models, collecting duct cell apoptosis was apparent, particularly in areas of cyst formation and cellular atrophy.

CONCLUSIONS

These results demonstrate the importance of this nonhuman primate model for exploring the pathophysiology of congenital obstructive uropathy and highlight the potential role of podocyte injury in determining long-term renal function associated with this condition.

Potential biological role of transforming growth factor-beta1 in human congenital kidney malformations

Transformations between epithelial and mesenchymal cells are widespread during normal development and adult disease, and transforming growth factor-beta1 (TGF-beta1) has been implicated in some of these phenotypic switches. Dysplastic kidneys are a common cause of chronic kidney failure in young children and result from perturbed epithelial-mesenchymal interactions. In this study, we found that components of the TGF-beta1 axis were expressed in these malformations: TGF-beta1 mRNA and protein were up-regulated in dysplastic epithelia and surrounding mesenchymal cells, whereas TGF-beta receptors I and II were expressed in aberrant epithelia. We generated a dysplastic kidney epithelial-like cell line that expressed cytokeratin, ZO1, and MET, and found that exogenous TGF-beta1 inhibited proliferation and decreased expression of PAX2 and BCL2, molecules characterizing dysplastic tubules in vivo. Furthermore, addition of TGF-beta1 specifically induced morphological changes compatible with a shift to a mesenchymal phenotype, accompanied by loss of ZO1 at cell borders and up-regulation of the mesenchymal markers alpha-smooth muscle actin and fibronectin. The descriptive and functional data presented in this report potentially implicate TGF-beta1 in the pathobiology of dysplastic kidneys and our results provide preliminary evidence that an epithelial-to-mesenchymal phenotypic switch may be implicated in a clinically important developmental aberration.

Multicystic renal dysplasia in a Japanese black bull

Multicystic renal dysplasia was found in a 6-day-old Japanese black bull. Grossly, both kidneys were markedly small (2.0 x 3.5 cm) with numerous cysts ranging from 1 to 8 mm in diameter. Histopathologically, both kidneys consisted of many irregularly enlarged cysts, immature glomeruli, small ducts and anomalous stromal connective tissues containing focal persistent mesenchyme characterized by a proliferation of stellate cells with myxomatous area. These features are compatible with those of multicystic renal dysplasia in humans and other mammals.

Diagnosis of fetal renal anomalies

Urinary tract abnormalities are fairly common in the perinatal period. Ultrasonography is an effective diagnostic tool for identifying fetal urinary tract anomalies and can be helpful in establishing prognosis and guiding treatment decisions. The sonographer is encouraged to characterize and localize the fetal urinary tract abnormality when identified. In doing so, the correct diagnosis can be selected from the differential possibilities, providing vital clinical information needed to develop a care plan for both the pregnant woman and her fetus.

Evaluation of metanephric maturation in a human fetal kidney explant model

We have developed a unique human fetal kidney explant model to study the role of the insulin-like growth factor (IGF) system in metanephric development. Kidneys from 10-18 wk gestation human abortuses were maintained in serum-free conditions and defined medium, which was shown to support the induction and differentiation of the viable metanephric blastema. Histologically the tissue remained viable to 192 h of serum-free culture, while metanephric differentiation, reflected by a shrinking nephrogenic zone and the formation of maturing S-shape and glomerular forms, was accelerated and occurred between 48 and 96 h. In the nephrogenic zone, a significant decrease in IGF-II gene expression occurred, which reflected the differentiation of the metanephric blastema cell mass, IGF-II expression persisted, however, in the expanded interstitial mesenchyme. With differentiation over 48 h an increase in IGFBP-2 and WT1 gene expression by Northern blot analysis occurred, and was localized by in situ hybridization to the differentiating glomerular epithelial cell mass. Analysis of the explant-conditioned media by Western ligand blot demonstrated an increase in the rate of IGF binding protein (IGFBP)-2 peptide production by the differentiating explant, consistent with an increase in IGFBP-2 gene expression and with metanephric differentiation. This pattern of temporal and spatial gene expression closely approximates that of normal in vivo fetal renal development and of glomerular epithelial cell differentiation.

Effects of PAX2 expression in a human fetal kidney (HEK293) cell line

PAX2, a member of the "paired-box" family of homeotic genes, is a nuclear transcription factor expressed in the early stages of nephrogenesis by induced blastemal cells as they progress from mesenchymal condensates to the "S-shaped" stage and also by the ureteric bud. Spontaneous mutations in one copy of PAX2 in humans causes a syndrome of proteinuric renal failure and coloboma of the eye (P. Sanyanusin et al., Nat. Genet. 9 (1995) 358-363); transgenic mice with disruption of the PAX2 gene are anephric (M. Torres et al., Development 121 (1995) 4057-4067. Although PAX2 is clearly critical for normal kidney development, its direct effects on kidney cell phenotype are unknown. To address this issue, we developed stable transfectants of the HEK293 human fetal kidney epithelial cell line expressing human PAX2 protein under tetracycline-regulatable promoter. In these cells, PAX2 had no effect on the proliferative rate, but increased the expression of the Wilms' tumor gene (2-fold) and E-cadherin (7-fold). PAX2 had a strong inhibitory effect on vimentin; vimentin/GAPDH mRNA ratio was suppressed to 8% of control whereas cytokeratin-18/GAPDH mRNA ratio was unchanged. During nephrogenesis, loss of vimentin and onset of low-level WT1 and E-cadherin expression occur in mesenchymal condensates. Our observations suggest that these events may be, in part, regulated by PAX2.