Possible role of WT1 in a human fetus with evolving bronchial atresia, pulmonary malformation and renal agenesis

Every Beat You Take-The Wilms' Tumor Suppressor WT1 and the Heart

Nearly three decades ago, the Wilms’ tumor suppressor Wt1 was identified as a crucial regulator of heart development. Wt1 is a zinc finger transcription factor with multiple biological functions, implicated in the development of several organ systems, among them cardiovascular structures. This review summarizes the results from many research groups which allowed to establish a relevant function for Wt1 in cardiac development and disease. During development, Wt1 is involved in fundamental processes as the formation of the epicardium, epicardial epithelial-mesenchymal transition, coronary vessel development, valve formation, organization of the cardiac autonomous nervous system, and formation of the cardiac ventricles. Wt1 is further implicated in cardiac disease and repair in adult life. We summarize here the current knowledge about expression and function of Wt1 in heart development and disease and point out controversies to further stimulate additional research in the areas of cardiac development and pathophysiology. As re-activation of developmental programs is considered as paradigm for regeneration in response to injury, understanding of these processes and the molecules involved therein is essential for the development of therapeutic strategies, which we discuss on the example of WT1.

Mesothelium and Malignant Mesothelioma

The mesothelium is an epithelial structure derived from the embryonic mesoderm. It plays an important role in the development of a number of different organs, including the heart, lungs, and intestines. In this publication, we discuss aspects of the development of the mesothelium, where mesothelial structures can be found, and review molecular and cellular characteristics associated with the mesothelium. Furthermore, we discuss the involvement of the mesothelium in a number of disease conditions, in particular in the pathogenesis of mesotheliomas with an emphasis on malignant pleural mesothelioma (MPM)—a primary cancer developing in the pleural cavity.

The development of hepatic stellate cells in normal and abnormal human fetuses - an immunohistochemical study

The precise embryological origin and development of hepatic stellate cells is not established. Animal studies and observations on human fetuses suggest that they derive from posterior mesodermal cells that migrate via the septum transversum and developing diaphragm to form submesothelial cells beneath the liver capsule, which give rise to mesenchymal cells including hepatic stellate cells. However, it is unclear if these are similar to hepatic stellate cells in adults or if this is the only source of stellate cells. We have studied hepatic stellate cells by immunohistochemistry, in developing human liver from autopsies of fetuses with and without malformations and growth restriction, using cellular Retinol Binding Protein-1 (cRBP-1), Glial Fibrillary Acidic Protein (GFAP), and α-Smooth Muscle Actin (αSMA) antibodies, to identify factors that influence their development. We found that hepatic stellate cells expressing cRBP-1 are present from the end of the first trimester of gestation and reduce in density throughout gestation. They appear abnormally formed and variably reduced in number in fetuses with abnormal mesothelial Wilms Tumor 1 (WT1) function, diaphragmatic hernia and in ectopic liver nodules without mesothelium. Stellate cells showed similarities to intravascular cells and their presence in a fetus with diaphragm agenesis suggests they may be derived from circulating stem cells. Our observations suggest circulating stem cells as well as mesothelium can give rise to hepatic stellate cells, and that they require normal mesothelial function for their development.

Abnormal WT1 expression in human fetuses with bilateral renal agenesis and cardiac malformations

BACKGROUND

Bilateral renal agenesis has multiple etiologies. Animal models have provided useful information on possible causes of this condition, but its etiology in humans is less clear. We recently described autopsy findings of two human fetuses with bilateral renal agenesis and abnormal expression of WT1 (Wilms tumor 1) in liver mesothelium.

METHODS

We have identified 14 additional fetuses with bilateral renal agenesis from autopsies performed in our institution over the past 10 years and subjected archival liver biopsy specimens from these cases to immunohistochemistry for WT1, as well as α-smooth muscle actin (α-SMA) and desmin to assess liver mesenchymal abnormalities.

RESULTS

Six of seven fetuses with combined bilateral renal agenesis and cardiac anomalies showed abnormalities of WT1 expression in liver mesothelial cells, which was not seen in other fetuses with bilateral renal agenesis. Except in one case, the fetuses with renal agenesis and cardiac defects also showed liver mesenchymal anomalies (assessed by increased α-SMA expression), which was not present in other renal agenesis fetuses.

CONCLUSIONS

WT1 is widely expressed in mesothelial cells during development, and we hypothesized that some of the defects are caused by abnormal function of mesenchyme derived from mesothelial cells, similar to the mesothelium-derived defects proposed in animal models. The methods we used are available to many laboratories and can be applied to archival paraffin tissue blocks. We suggest that future similar studies could help to expand the understanding of renal agenesis in humans and could help to subclassify this condition. This would be useful in patient management and counseling.