In situ expression of the early growth response gene-1 during murine nephrogenesis

The role of chromatin-related epigenetic modulations in CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) represent a major health burden in humans. Phenotypes range from renal hypoplasia or renal agenesis, cystic renal dysplasia, duplicated or horseshoe kidneys to obstruction of the ureteropelvic junction, megaureters, duplicated ureters, urethral valves or bladder malformations. Over the past decade, next-generation sequencing has identified numerous causative genes; however, the genetic basis of most cases remains unexplained. It is assumed that environmental factors have a significant impact on the phenotype, but, overall, the pathogenesis has remained poorly understood. Interestingly however, CAKUT is a common phenotypic feature in two human syndromes, Kabuki and Koolen-de Vries syndrome, caused by dysfunction of genes encoding for KMT2D and KANSL1, both members of protein complexes playing an important role in histone modifications. In this chapter, we discuss current knowledge regarding epigenetic modulation in renal development and a putatively under-recognized role of epigenetics in CAKUT.

Non-myogenic Contribution to Muscle Development and Homeostasis: The Role of Connective Tissues

Skeletal muscles belong to the musculoskeletal system, which is composed of bone, tendon, ligament and irregular connective tissue, and closely associated with motor nerves and blood vessels. The intrinsic molecular signals regulating myogenesis have been extensively investigated. However, muscle development, homeostasis and regeneration require interactions with surrounding tissues and the cellular and molecular aspects of this dialogue have not been completely elucidated. During development and adult life, myogenic cells are closely associated with the different types of connective tissue. Connective tissues are defined as specialized (bone and cartilage), dense regular (tendon and ligament) and dense irregular connective tissue. The role of connective tissue in muscle morphogenesis has been investigated, thanks to the identification of transcription factors that characterize the different types of connective tissues. Here, we review the development of the various connective tissues in the context of the musculoskeletal system and highlight their important role in delivering information necessary for correct muscle morphogenesis, from the early step of myoblast differentiation to the late stage of muscle maturation. Interactions between muscle and connective tissue are also critical in the adult during muscle regeneration, as impairment of the regenerative potential after injury or in neuromuscular diseases results in the progressive replacement of the muscle mass by fibrotic tissue. We conclude that bi-directional communication between muscle and connective tissue is critical for a correct assembly of the musculoskeletal system during development as well as to maintain its homeostasis in the adult.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.

Dedifferentiation and proliferation of surviving epithelial cells in acute renal failure

In contrast to the heart or brain, the kidney can completely recover from an ischemic or toxic insult that results in cell death. During recovery from ischemia/reperfusion injury, surviving tubular epithelial cells dedifferentiate and proliferate, eventually replacing the irreversibly injured tubular epithelial cells and restoring tubular integrity. Repair of the kidney parallels kidney organogenesis in the high rate of DNA synthesis and apoptosis and in patterns of gene expression. As has been shown by proliferating cell nuclear antigen and 5-bromo 2'-deoxyuridine labeling studies and, in unpublished studies, by counting mitotic spindles identified by labeling with antitubulin antibody, the proliferative response is rapid and extensive, involving many of the remaining cells of the proximal tubule. This extensive proliferative capacity is interpreted to reflect the intrinsic ability of the surviving epithelial cell to adapt to the loss of adjacent cells by dedifferentiating and proliferating. Adhesion molecules likely play important roles in the regulation of renal epithelial cell migration, proliferation, and differentiation, as do cytokines and chemokines. Better understanding of all of the characteristics resulting in dedifferentiation and proliferation of the proximal tubule epithelial cell and cell-cell and cell-matrix interactions important for this repair function will lead to novel approaches to therapies designed to facilitate the processes of recovery in humans.

WT1 proteins: functions in growth and differentiation

The Wilms' tumor 1 gene (WT1) has been identified as a tumor suppressor gene involved in the etiology of Wilms' tumor. Approximately 10% of all Wilms' tumors carry mutations in the WT1 gene. Alterations in the WT1 gene have also been observed in other tumor types, such as leukemia, mesothelioma and desmoplastic small round cell tumor. Dependent on the tumor type, WT1 proteins might either function as tumor suppressor proteins or as survival factors. Mutations in the WT1 gene can also result in congenital abnormalities as observed in Denys-Drash and Frasier syndrome patients. Mouse models have proven the critical importance of WT1 expression for the development of several organs, including the kidneys, the gonads and the spleen. The WT1 proteins seem to perform two main functions. They regulate the transcription of a variety of target genes and may be involved in post-transcriptional processing of RNA. The WT1 gene encodes at least 24 protein forms. These isoforms have partially distinct biological functions and effects, which in many cases are also specific for the model system in which WT1 is studied. This review discusses the molecular mechanisms by which the various WT1 isoforms exert their functions in normal development and how alterations in WT1 may lead to developmental abnormalities and tumor growth.

EGR-1 enhances tumor growth and modulates the effect of the Wilms' tumor 1 gene products on tumorigenicity

The Wilms' tumor 1 gene (WT1) encodes a transcription factor of the zinc-finger family and is homozygously mutated or deleted in a subset of Wilms' tumors. Through alternative mRNA splicing, the gene is expressed as four main polypeptides that differ by a stretch of 17 amino acids just N-terminal of the four zinc-fingers and three amino acids between zinc fingers 3 and 4. We have previously shown that expression of the WT1(-/-) isoform, lacking both inserts, increases the tumor growth rate of the adenovirus-transformed baby rat kidney (AdBRK) cell line 7C3H2, whereas expression of the WT1(-/+) isoform, lacking the 17aa insert, strongly suppresses the tumorigenic phenotype. In the present study we show that expression of these splice variants does not affect the tumorigenic potential of the similar AdBRK cell line, 7C1T1. In contrast to the 7C3H2 cell line, this AdBRK cell line expresses high endogenous levels of EGR-1 (early growth response-1) protein, a transcription factor structurally related to WT1. Ectopic expression of EGR-1 in the 7C3H2 AdBRK cells significantly increases their in vivo growth rate and nullifies the tumor suppressor activity of the WT1(-/+) protein. Furthermore, we find that EGR-1 levels are elevated in some Wilms' tumors. These data are the first to show that EGR-1 overexpression causes enhanced tumor growth and that WT1 and EGR-1 exert antagonizing effects on growth regulation in baby rat kidney cells, which might reflect the situation in some Wilms' tumors.

Wilms tumor and multicystic dysplastic kidney disease

PURPOSE

There is ongoing controversy concerning the management of multicystic dysplastic kidney disease, particularly with regard to the potential for malignant transformation. Our report fuels the debate by adding the 2 youngest patients in whom malignancy was present from birth or developed subsequently.

MATERIALS AND METHODS

Two well documented cases of malignancy associated with multicystic dysplastic kidney disease are presented in 2 female infants (5 and 3 months old). The 5-month-old female infant was followed for multicystic dysplastic kidney disease and had no evidence of tumor either antenatally or at birth. The 3-month-old presented with hypertension and interventricular septal defect. A renal tumor was present on initial ultrasound.

RESULTS

Even though malignant degeneration is rare in multicystic dysplastic kidney disease, 9 cases have been reported in the literature so far. Of these cases 3 were Wilms tumor, 5 were renal cell carcinomas and 1 mesothelioma.

CONCLUSIONS

Our 2 cases lend support to the surgical management of multicystic dysplastic kidney disease, particularly as nephrectomy can now be performed in a day surgery setting with minimal morbidity. Only the risks of coexisting malignancy and possible malignant degeneration transformation are specifically addressed in this article. Other complications of multicystic dysplastic kidney disease such as hypertension, infection, abdominal pain, hematuria and persistent dysplastic renal tissue despite ultrasonographic resolution of multicystic dysplastic kidney disease are additional risk factors to be considered. A recommendation for nephrectomy in all cases of multicystic dysplastic kidney disease cannot be based only on these 2 cases. Several other factors must be weighed before making that decision.