| The concept that the podocyte is the major culprit in the progression of renal diseases has been well established in the past 5 years. Considerable progress in the identification of podocyte specific proteins and their role in disease have been made. However, significant gaps concerning the role of growth factors in podocyte biology exist, in part due to a lack of appropriate models to study the podocyte. The hypothesis of this study is Insulin-like growth factor signaling inhibits podocyte apoptosis. The goals of this thesis are two fold; (1) develop models to study the podocyte and (2) determine role of the IGF system in these models.; To provide evidence for our hypothesis I utilized the podocyte marker complement receptor c3b (CR1) described in Chapter 2 to identify human fetal podocytes in a cell culture system. I cultured and characterized podocytes using specific morphological characteristics and positive immuno-reactivity with podocyte specific markers WT-1, synaptopodin and CR1. After the establishment of this cell culture system, I determined the role of IGF-II in podocyte mitogenesis and demonstrated IGF-II was mildly mitogenic.; The second objective explored the possibility that IGFs may have additional biological actions on the podocyte. I demonstrated a marked increase in podocyte apoptosis in response to etoposide which was abrogated by co-incubating with IGF-I. The IGF-I protective effect was elicited through activation of the IGF-IR, the PI3K pathway and anti-apoptosic protein bad. Therefore, these data strongly support IGF-IR induced signaling in protecting human fetal podocyte survival in vitro.; My final objective highlighted the importance of IGF signaling in podocyte survival by generating a transgenic mouse expressing a dominant negative IGF-IR exclusively in the podocyte. Histological analysis revealed abnormal glomeruli consistent with damage or loss of the podocyte. These abnormalities were confirmed by ultra-structural examination of the podocyte which demonstrated alterations in the podocyte, consistent with apoptosis.; I have demonstrated IGF is an important regulator of kidney homeostasis by maintaining podocyte survival in both human and mouse podocytes. Furthermore, IGF signaling may be a potential target pathway for limiting the progression of renal disease. |
