Abstract The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes. Our study was designed to determine the concentration-dependent permeability characteristics for immature (GV) and mature (MII) bovine oocytes in the presence of ethylene glycol (EG) and dimethyl sulphoxide (Me 2 SO), and to compare two different modeling approaches: the two parameter (2P) model and a nondilute transport model. Membrane permeability parameters were determined by consecutively exposing oocytes to increasing concentrations of Me 2 SO or EG. Higher water permeability was observed for MII oocytes than GV oocytes in the presence of both Me 2 SO and EG, and in all cases the water permeability was observed to decrease as CPA concentration increased. At high CPA concentrations, the CPA permeability was similar for Me 2 SO and EG, for both MII and GV oocytes, but at low concentrations the EG permeability of GV oocytes was substantially higher. Predictions of cell volume changes during CPA addition and removal indicate that accounting for the concentration dependence of permeability only has a modest effect, but there were substantial differences between the 2P model and the nondilute model during CPA removal, which may have implications for design of improved methods for bovine oocyte vitrification.
Progression of cystic kidney disease has been linked to activation of the mTORC1 signaling pathway. Yet the utility of mTORC1 inhibitors to treat patients with polycystic kidney disease remains controversial despite promising preclinical data. To define the cell intrinsic role of mTORC1 for cyst development, the mTORC1 subunit gene Raptor was selectively inactivated in kidney tubular cells lacking cilia due to simultaneous deletion of the kinesin family member gene Kif3A. In contrast to a rapid onset of cyst formation and kidney failure in mice with defective ciliogenesis, both kidney function, cyst formation discerned by magnetic resonance imaging and overall survival were strikingly improved in mice additionally lacking Raptor. However, these mice eventually succumbed to cystic kidney disease despite mTORC1 inactivation. In-depth transcriptome analysis revealed the rapid activation of other growth-promoting signaling pathways, overriding the effects of mTORC1 deletion and identified cyclin-dependent kinase (CDK) 4 as an alternate driver of cyst growth. Additional inhibition of CDK4-dependent signaling by the CDK4/6 inhibitor Palbociclib markedly slowed disease progression in mice and human organoid models of polycystic kidney disease and potentiated the effects of mTORC1 deletion/inhibition. Our findings indicate that cystic kidneys rapidly adopt bypass mechanisms typically observed in drug resistant cancers. Thus, future clinical trials need to consider combinatorial or sequential therapies to improve therapeutic efficacy in patients with cystic kidney disease.Graphical abstract
In polycystic kidney disease (PKD), fluid-filled cysts arise from tubules in kidneys and other organs. Human kidney organoids can reconstitute PKD cystogenesis in a genetically specific way, but the mechanisms underlying cystogenesis remain elusive. Here we show that subjecting organoids to fluid shear stress in a PKD-on-a-chip microphysiological system promotes cyst expansion via an absorptive rather than a secretory pathway. A diffusive static condition partially substitutes for fluid flow, implicating volume and solute concentration as key mediators of this effect. Surprisingly, cyst-lining epithelia in organoids polarize outwards towards the media, arguing against a secretory mechanism. Rather, cyst formation is driven by glucose transport into lumens of outwards-facing epithelia, which can be blocked pharmacologically. In PKD mice, glucose is imported through cysts into the renal interstitium, which detaches from tubules to license expansion. Thus, absorption can mediate PKD cyst growth in human organoids, with implications for disease mechanism and potential for therapy development.
The mammalian target of rapamycin (mTOR) pathway is a therapeutic target in polycystic kidney disease (PKD), but mTOR inhibitors such as everolimus have failed to show efficacy at tolerated doses in clinical trials. Here, we introduce AV457, a novel rapalog developed to reduce side effects, and assess its dose-dependent safety and efficacy versus everolimus in PKD1-/- and PKD2-/- human kidney organoids, which form cysts in a PKD-specific way. Both AV457 and everolimus reduce cyst growth over time. At intermediate doses, AV457 exhibits an improved safety profile relative to everolimus, with comparable efficacy. Target engagement assays confirm mTOR pathway inhibition and greater selectivity of AV457 for mTOR complex 1 versus complex 2, compared to everolimus. AV457 thus provides a more favorable balance of safety and efficacy for PKD compared to everolimus and merits further consideration as an investigational therapeutic.
