We use multidisciplinary approaches ranging from human molecular genetics, molecular and cellular biology, biochemistry to developmental biology and mouse genetics to understand the physiology and pathophysiology of polycystins and polycystic kidney disease (PKD). Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic disorder in humans with an estimated prevalence of 1:1000 accounting for ±10% of patients undergoing dialysis, thus making it the third most common cause of ESRD in adults worldwide. The main characteristic of ADPKD is the progressive development of epithelial lined cysts in both kidney and liver, which results mainly in the manifestation of decreased renal function at early to mid-adult age. The rate of progression can vary significantly even in patients with the same inherited mutation and although a lot of research is being conducted on disease progression many questions remain about the mechanisms of cyst development. ADPKD is caused by mutations in two genes (PKD1 and PKD2) that encode polycystin-1 and polycystin-2, respectively. We have shown, by gene targeting experiments, a critical role of polycystin-1 in kidney and pancreas development. We demonstrated that polycystin-L and -2 are calcium-permeable cation channels, and that polycystin-1 acts as an atypical G-protein coupled receptor whose functionality is coupled with polycystin-2.

During development, tubules can arise from cells in many different starting conditions and configurations, and their lumen size is strictly controlled. Our premise is that these diverse pathways converge on a smaller number of common downstream mechanisms that directly control the organization of epithelial cells into tubules. These mechanisms are poorly understood and sit at the crossroads of developmental and cell biology. Cyst formation in PKD, by definition, is characterized by the dilation of tubules -the loss of normal size control of tubular lumen. Cell biological studies of polycystic kidney have shown that the loss of tube lumen size control is accompanies by increased cell proliferation, decreased cell differentiation and cell survival. Using cells cultured from mouse models defective in polycystin-1, we have recently demonstrated, for the first time, that polycystin-1 and -2 mediate mechanosensation in the primary cilium of kidney epithelium. Primary cilium of kidney epithelium has been previously proposed to be a mechanosensor with unknown molecular composition. Our data suggest polycystin-1 and -2 functions as a mechanosensitve receptor-channel complex that controls normal tubular morphogenesis.

Our current focus is to understand the downstream signaling events of the two ADPKD proteins. We are also studying the genetic modifiers that modulate disease severity. Polycystins are an expanding family with diverse functions in multiple tissues. Polycystin-2 has recently shown to control the determination of left-right body axis and fertility. We are also using multidisciplinary approaches to identify the functions of four new polycystins recently identified in our lab.

Techniques used include in vitro 3D tubulogenesis assays, live cell imaging, and in vivo tissue- and time- specific gene targeting, molecular cloning, yeast-two-hybrid assay, Western analysis, co-immunoprecipitation, Ca2+ imaging.

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