Through a unique collaborative effort with the Division of Pediatric Nephrology, there is a specific focus on the normal and abnormal development of the kidney and urinary tract (including kidney, renal pelvis, ureter, bladder, trigone, and urethra). With the development of a strain of mice that exhibit birth defects of the urogenital system similar to those seen in humans, there is now an animal model with which to study the things that go wrong during development. The researchers work closely with other world class developmental scientists from the departments of Cell Biology, Pathology, Anatomy, and Biochemistry. The common goal is to develop new treatment and/or diagnostic modalities that translate directly to patient care.
It is known that 0.2-0.9% of human fetuses have congenital anomalies (birth defects) of the kidney and urinary tract (CAKUT). In recent years, thanks to advancements in diagnostic technology, the ability to prenatally detect many CAKUT has improved greatly. Nevertheless, CAKUT remain a primary cause of kidney failure in infants and children yet the causes remain unclear. This is further complicated by the fact that there have been no animal models that have abnormalities of the kidney and urinary tract that mimic those found in humans. New technology, however, now allows us to use experimental animals to investigate the possible causes of these anomalies.
Preliminary results have shown that angiotensin II promotes mesenchymal cell apoptosis only in the presence of intact AT2 (angiotensin type 2) receptors, and thus inactivation of these receptors in null mutant animals have lead to functional and structural abnormalities of the urinary tract. Researchers here are now investigating whether abnormal apoptosis of these mesenchymal cells results in abnormal differentiation of the developing kidney, renal pelvis and ureter.
Current research within our department involves the intricate study of the developing of the mouse urinary tract in both normal animals as well as abnormal ones who have a deletion in the angiotensin type 2 (AT2) receptor gene and have been found to have CAKUT. Embryonic as well as postnatal tissues from the animals are being studied. Specifically, immunologic staining will permit assessment of mesenchymal differentiation, which regulates the developing kidney and urinary tract. Researchers are also examining the difference between the AT2 null mutant and wild type urinary tract development and to evaluate the specific pathway by which angiotensin II, through AT2 the receptor, directs normal ureteral development.
CAKUT is a leading cause of surgery and kidney failure in infants and children. By learning how the abnormalities occur, and by increasing our understanding of the disease processes, we hope to find new and improved ways to diagnose, treat, and possibly prevent birth defects of the urinary tract.
Also, genetic studies of inherited polycystic kidney disease (PKD) in man and animal models have clearly shown that numerous genetic mutations result in various forms of PKD. In addition, other genes appear to significantly alter the clinical manifestations and progression of PKD. The disease is characterized by massive renal enlargement associated with the growth of fluid filled intrarenal cysts. The factors that convert the normal kidney cells into abnormal ones responsible for fluid accumulation in the cyst have yet to be elucidated. Identification and characterization of the disease genes and their modifiers will provide a better understanding of the pathways and the cellular processes important in stabilizing this critical organ. We have identified a gene (Nek1) altered by the murine recessive kat, kat2J, kat3J mutations that leads to a latent onset slowly progressing form of PKD with renal pathology similar to the human autosomal dominant PKD. Further, we have mapped modifier genes that alter the severity of the kidney disease caused by the loss of Nek1 function. Based on the clinical manifestation seen in the mutants due to the loss of Nek1 function, we think that in the kidney, the NEK1 protein belongs to a developmentally regulated signaling pathway that either directly or indirectly affects transport functions and thus cyst formation. We are currently analyzing the expression pattern, tissue distribution and renal subcellular localization of Nek1 gene products in control and mutant animals during development, isolating protein factors that interact with NEK1 using biochemical and genetic approach, and assessing the effect of different domains of NEK1 on certain key kinase-signaling pathway. Thus, our findings have opened new avenues for studying renal cyst formation and identifying possible modes of therapy for this serious human disease.
Dr. Bhowmick has multiple federally funded projects primarily focusing on the role of the cytokine transforming growth factor-beta (TGFß) in the prostate and the bladder. These studies employ a number of mouse, xenograft, and cell culture models. The project that addresses bladder outlet/urethral obstruction disease that commonly develop bladder fibrosis affect pediatric community. It is the leading cause of renal failure and renal transplantation in the pediatric population. Adult patients also develop bladder obstruction associated fibrosis. Interestingly, following corrective surgery to relieve the obstruction, males consistently display a continued bladder fibrosis and poor outcome. Despite our knowledge of the expression of estrogen receptor isoforms in the bladder, little is known in regards to bladder estrogen responsiveness. A similar gender disparity is observed in the incidences of other hyperplastic pathologies (e.g. liver, kidney, heart). Rapid bladder growth associated partial obstruction of the urethra and embryonic bladder development involves stromal-epithelial interactions. The removal of obstruction induces apoptosis of the urothelial and connective tissue components in the bladder associated with increased TGFß. However, chronic obstruction leads to fibrosis, characterized by recruitment of inflammatory cells, increased extracellular matrix production, and elevated expression of members of the TGFß family and its receptors in both stroma and epithelium. Thus TGFß exhibits a paradoxical role on the bladder stroma that is difficult to identify in the in vivo complexities of epithelial and stromal interactions.
To identify the role of TGFß signaling in the bladder stroma, fibroblast-specific conditional knockout mouse of the type II TGFß receptor gene (Tgfbr2) was generated. The bladders of homozygous Tgfbr2 stromal knockout male mice displayed a marked hypertrophy in the lamina propria and smooth muscle layers, in the absence of visible urethral obstruction by 8 weeks of age. However age matched female mice of the same genotype maintained bladder architecture similar to wild type littermate controls. The goal of this project is to specifically identify the TGFß-mediated signals in the stroma that mediate bladder estrogen responsiveness. The disparity among fibroblast-Tgfbr2 knockout male and female mice suggests the interaction of TGFß signaling with estrogen signaling pathways in the bladder stroma.