Thesis Defense - Guanhan Yao

Targeting Kcnn4 for Treatment of Autosomal Dominant Polycystic Kidney Disease

Guanhan Yao

Director : Marie Trudel

In person: 
IRCM Auditorium
110, avenue des Pins O, H2W 1R7 Montreal

Online (Zoom):
ID: 996 0775 0717
Code: 744703

Summary

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent genetic kidney disorder caused mainly by mutations in the PKD1 gene. ADPKD is characterized by progressive bilateral renal cyst formation and enlargement, driven by dysregulated processes such as cAMP-mediated hyperproliferation and excessive fluid secretion, culminating in renal insufficiency by mid-life. The only approved drug treatment for ADPKD, Tolvaptan, is effective but only in a subset of patients. Therefore, additional therapeutic candidates remain to be explored. As cyst growth in ADPKD is largely driven by uncontrolled fluid secretion and proliferation, great effort has been put into identifying potential therapeutic targets within the fluid secretory pathway. The currently accepted model requires active chloride secretion through apical Cftr into cyst lumen. Replenishment of chloride occurs through sustained stimulation of basolateral Nkcc1 which cotransports sodium and potassium. Sodium is likely balanced by Na+-K+-ATPase. How potassium is recycled is not completely understood. We speculated that the calcium activated potassium ion channel Kcnn4, a known regulator of proliferation and fluid transport, could be a potential candidate to fulfill this role. We hypothesized that inhibition of Kcnn4 could block potassium recycling and consequently reduce cyst fluid secretion, delaying cyst growth. To evaluate Kcnn4's potential as a therapeutic target for treatment of ADPKD, we targeted Kcnn4 ex vivo and in vivo using genetic and pharmacologic approaches and assessed key indicators of disease progression such as cystic indices, renal cAMP level and proliferative status. We found that Kcnn4 expression is consistently upregulated by 2- to 6-fold in four Pkd1 orthologous mouse models and by ~20-fold in human ADPKD kidneys. Ex vivo analysis demonstrated that Pkd1-/- metanephroi treated with Kcnn4 activator not only exacerbated cyst growth but even induced cysts in the otherwise non-cystic Pkd1+/+ metanephroi. Pkd1-/-; Kcnn4-/- metanephroi showed marked reduction in cyst formation and growth in comparison to Pkd1-/-. Moreover, a nontoxic Kcnn4 inhibitor substantially suppressed cyst growth and even promoted regression of established Pkd1-/- cysts. In parallel to Kcnn4 upregulation, in vivo analysis also revealed 4- to 16-fold elevation in renal cAMP that hyperactivated MAPK/ERK/c-Myc pathway and ciliary elongation. Kcnn4 genetic inactivation markedly suppressed cyst growth as determined by pronounced reduction or normalization of kidney weight, cyst number and area, cAMP levels, renal epithelial cell proliferation, fibrosis, ciliary length, and MAPK/ERK/c-Myc signaling. Importantly, kidney function and survival were strikingly improved in an adult-onset Pkd1 model upon Kcnn4 inactivation. Our drug repurposing trial of a Kcnn4 inhibitor, Senicapoc, revealed significant suppression of global cystic indices consistent with the results of in vivo Kcnn4 genetic inactivation. Overall, our study uncovered a hyperactive, cAMP-dependent Cftr/Nkcc1/Na+-K+-ATPase/Kcnn4 pro-secretory network that, when disrupted by targeting Kcnn4, severely limits disease progression. Our data strongly support Kcnn4 as a major regulator of Pkd1-associated cystogenesis through modulation of cyst-driven processes such as fluid secretion, proliferation, and fibrosis. These preclinical findings are highly promising toward repurposing Senicapoc for ADPKD clinical trial.