bims-bicyki Biomed News
on Bicaudal-C1 and interactors in cystic kidney disease
Issue of 2020‒11‒22
fifteen papers selected by
Céline Gagnieux
École Polytechnique Fédérale de Lausanne (EPFL)

  1. J Cell Sci. 2020 Nov 16. pii: jcs.255562. [Epub ahead of print]
      Approximately 15% of autosomal dominant polycystic kidney disease (ADPKD) is caused by variants in PKD2 PKD2 encodes polycystin-2, which forms an ion channel in primary cilia and endoplasmic reticulum (ER) membranes of renal collecting duct cells. Elevated internal Ca2+ modulates polycystin-2 voltage dependent gating and subsequent desensitization- two biophysical regulatory mechanisms that control its function at physiological membrane potentials. Here, we refute the hypothesis that Ca2+ occupancy of the polycytsin-2 intracellular EF hand is responsible for these forms of channel regulation, and if disrupted, results in ADPKD. We identify and introduce mutations that attenuate Ca2+-EF hand affinity but find channel function is unaltered in the primary cilia and ER membranes. We generated two new mouse strains that harbor distinct mutations that abolish Ca2+-EF hand association but do not result in a PKD phenotype. Our findings suggest additional Ca2+ binding sites within polycystin-2 or Ca2+-dependent modifiers are responsible for regulating channel activity.
    Keywords:  ADPKD; Biophysics; Calcium regulation; Ion channels; Polycytsin; Primary cilia
  2. Am J Case Rep. 2020 Nov 18. 21 e927188
      BACKGROUND Autosomal dominant polycystic kidney disease (ADPKD) is frequently associated with liver cysts, but an association with giant cavernous liver hemangioma is not mentioned in the literature. CASE REPORT We report the case of a 41-year-old man with ADPKD, secondary arterial hypertension, and stage 4 chronic kidney disease who presented with a 2-week history of persistent pain at the base of the right hemithorax and in the right hypochondrium. An ultrasound examination and a contrast-enhanced computed tomography scan revealed a giant cavernous liver hemangioma. Surgery was intially taken into account (however, twice delayed because of the COVID-19 pandemic) but later refused because it would have left the patient with dangerously few liver parenchyma. CONCLUSIONS To our knowledge, this is the first reported case of ADPKD associated with cavernous liver hemangioma. Vascular endothelial growth factor could be the pathophysiological link between the 2 conditions. Further research may unravel the molecular biology that underlies this possible association, pointing to new therapeutic avenues for ADPKD.
  3. J Matern Fetal Neonatal Med. 2020 Nov 18. 1-6
      OBJECTIVE: This study aimed to evaluate liver malformations and intrahepatic bile ductal ectasia and dilatation (IBDED) in cases of prenatal diagnosis of autosomal recessive polycystic kidney disease (ARPKD) using magnetic resonance imaging (MRI).METHODS: This retrospective study involved 209 cases referred for fetal MRI studies (f-MRI) from March 2004 and December 2019, suspicious of congenital renal disease. Fetuses that met the criteria for ARPKD were selected.
    RESULTS: Six cases were diagnosed as ARPKD (2.8%). The median gestational age at MRI examination was 28 weeks (24-36 weeks). IBDED was observed in 84% of cases. Moreover, 66% presented multilobar liver lesions, and 33% exhibited monolobar lesions. The "central dot sign" (CDS) was found in half of the cases.
    CONCLUSION: In this case series of prenatal diagnosis of ARPKD using f-MRI, IBDED was present in the majority of the cases, and the CDS was noted in half of the cases.
    Keywords:  Autosomal recessive polycystic kidney disease; ; central dot sign; ; intrahepatic bile ductal ectasia and dilatation; ; magnetic resonance imaging; prenatal diagnosis;
  4. Bone. 2020 Nov 11. pii: S8756-3282(20)30526-3. [Epub ahead of print] 115738
      Bone is a dynamic organ that is continuously modified during development, load-induced adaptation, and fracture repair. Understanding the cellular and molecular mechanisms for natural fracture healing can lead to therapeutics that enhance the quality of newly formed tissue, advance the rate of healing, or replace the need for invasive surgical procedures. Prx1-expressing cells in the periosteum are thought to supply the majority of osteoblasts and chondrocytes in the fracture callus, but the exact mechanisms for this behavior are unknown. The primary cilium is a sensory organelle that is known to mediate several signaling pathways involved in fracture healing and required for Prx1-expressing cells to contribute to juvenile bone development and adult load-induced bone formation. We therefore investigated the role of Prx1-expressing cell primary cilia in fracture repair by developing a mouse model that enabled us to simultaneously track Prx1 lineage cell fate and disrupt Prx1-expressing cell primary cilia in vivo. The cilium KO mice exhibited abnormally large calluses with significantly decreased bone formation and persistent cartilage nodules. Analysis of mRNA expression in the early soft callus revealed downregulation of osteogenesis, Hh signaling, and Wnt signaling, and upregulation of chondrogenesis and angiogenesis. The mutant mice also exhibited decreased Osx and Periostin but increased αSMA protein expression in the hard callus. We further used a Gli1LacZ reporter and found that Hh signaling was significantly upregulated in the mutant callus at later stages of healing. Interestingly, altered protein expression and Hh signaling did not correlate with labeled Prx1-lineage cells, suggesting loss of cilia altered Hh signaling non-autonomously. Overall, cilium KO mice demonstrated severely delayed and incomplete fracture healing, and our findings suggest Prx1-expressing cell primary cilia are necessary to tune Hh signaling for proper fracture repair.
    Keywords:  Hh signaling; Prx1; fracture repair; osteogenesis; primary cilium
  5. Cardiorenal Med. 2020 Nov 17. 1-12
      BACKGROUND: The pathophysiology of renal disease progression in autosomal-dominant polycystic kidney disease (ADPKD) involves not only cystogenesis but also endothelial dysfunction, leading to the activation of inflammatory and fibrotic pathways. This study evaluated the levels of biomarkers related to osmoregulation, immune system activation, and tubular injury in ADPKD patients with impaired or preserved renal function.METHODS: This study included 26 ADPKD patients with modestly impaired renal function (estimated glomerular filtration rate [eGFR] 45-70 mL/min/1.73 m2; Group A), 26 age- and sex-matched ADPKD patients with relatively preserved renal function (eGFR >70 mL/min/1.73 m2; Group B), and 26 age- and sex-matched controls (Group C). Serum levels of copeptin, the inflammasome nucleotide-binding and oligomerization domain-like receptors pyrin domain-containing protein 3 (NLRP3), and soluble urokinase-type plasminogen activator receptor (suPAR) were measured with ELISA techniques.
    RESULTS: Patients in Group A had higher levels of copeptin (median [interquartile range]: 50.44 [334.85] pg/mL), NLRP3 (5.86 [3.89] ng/mL), and suPAR (390.05 [476.53] pg/mL) compared to patients in Group B (32.38 [58.33], p = 0.042; 2.42 [1.96], p < 0.001; and 313.78 [178.85], p = 0.035, respectively) and Group C (6.75 [6.43]; 1.09 [0.56]; and 198.30 [28.53], respectively; p < 0.001 for all comparisons). Levels of all studied markers were also significantly higher in Group B patients compared to controls (p < 0.001), despite having similar eGFR. In patients with ADPKD, all studied biomarkers were correlated positively with asymmetric-dimethylarginine (ADMA) and endocan levels, and negatively with eGFR. ADMA and endocan levels were the only parameters independently associated with increased copeptin levels.
    CONCLUSIONS: This study showed that ADPKD patients with impaired and preserved renal function had higher copeptin, NLRP3, and suPAR levels than controls. Such findings support that cystogenesis and inflammation are associated with endothelial dysfunction, even in the early stages of ADKPD.
    Keywords:  Autosomal-dominant polycystic kidney disease (ADPKD); Copeptin; Endothelial dysfunction; Inflammation; NLRP3; suPAR
  6. Nat Cell Biol. 2020 Nov 16.
      The Hippo pathway plays critical roles in cell growth, differentiation, organ development and tissue homeostasis, whereas its dysregulation can lead to tumorigenesis. YAP and TAZ are transcription co-activators and represent the main downstream effectors of the Hippo pathway. Here, we show that heat stress induces a strong and rapid YAP dephosphorylation and activation. The effect of heat shock on YAP is dominant to other signals known to modulate the Hippo pathway. Heat shock inhibits LATS kinase by promoting HSP90-dependent LATS interaction with and inactivation by protein phosphatase 5. Heat shock also induces LATS ubiquitination and degradation. YAP and TAZ are crucial for cellular heat shock responses, including the heat shock transcriptome and cell viability. This study uncovers previously unknown mechanisms of Hippo regulation by heat shock, as well as physiological functions of YAP, in the heat stress response. Our observations also reveal a potential combinational therapy involving hyperthermia and targeting of the Hippo pathway.
  7. Invest Ophthalmol Vis Sci. 2020 Nov 02. 61(13): 29
      Purpose: Lysophosphatidic acid (LPA) and soluble interleukin-6 receptor (sIL6R) are elevated in primary open angle glaucoma (POAG). LPA and IL6 modulate in response to biomechanical stimuli and converge on similar fibrotic phenotypes. Thus, we determined whether LPA and IL6 trans-signaling (IL6/sIL6R) interact via Yes-associated protein (YAP)/Transcriptional coactivator with a PDZ-binding motif (TAZ) or Signal transducer and activator of transcription 3 (STAT3) pathways in human trabecular meshwork (hTM) cells.Methods: Confluent primary hTM cells were serum starved for 24 hours, and treated with vehicle, LPA (20 µM), IL6 (100 ng/mL)/sIL6R (200 ng/mL), or both (LPA + IL6/sIL6R) for 24 hours, with or without a YAP inhibitor (verteporfin; 2 µM) or STAT3 inhibitor (2 µM). Expression of key receptors and ligands, signaling mediators, actomyosin machinery, cell contractility, and extracellular matrix (ECM) targets of both signaling pathways was determined by immunocytochemistry, RT-qPCR, and Western blotting.
    Results: LPA and IL6 trans-signaling coupling overexpressed/activated receptors and ligands, glycoprotein-130, IL6, and autotaxin; signaling mediators, YAP, TAZ, Pan-TEAD, and phosphorylated STAT3 (pSTAT3); actomyosin and contractile machinery components, myosin light chain 2 (MLC2), phosphorylated MLC2, rho-associated protein kinase 1, filamentous actin, and α-smooth muscle actin; and fibrotic ECM proteins, collagen I and IV, fibronectin, laminin, cysteine-rich angiogenic inducer 61, and connective tissue growth factor in hTM cells; mostly beyond LPA or IL6 trans-signaling alone. Verteporfin inhibited YAP, TAZ, and pSTAT3, with concomitant abrogation of aforementioned fibrotic targets; the STAT3 inhibitor was only partially effective.
    Conclusions: These data suggest synergistic crosstalk between LPA and IL6 trans-signaling, mediated by YAP, TAZ, and pSTAT3. By completely inhibiting these mediators, verteporfin may be more efficacious in ameliorating LPA and/or IL6 trans-signaling-induced ocular hypertensive phenotypes in hTM cells.
  8. Curr Opin Cell Biol. 2020 Nov 12. pii: S0955-0674(20)30145-9. [Epub ahead of print]67 141-146
      Organism development requires fine-tuning of the cell number by apoptosis and cell division, as well as proper cell fate specification. These processes are achieved through the integration of intracellular signals and intercellular interactions with neighboring cells as well as the extracellular environment. Apoptosis, a form of cell death typically associated with development and homeostasis, is mainly regulated by the caspase family of proteases. Although caspases are known to initiate and execute apoptosis, it is also known that low caspase levels have a broad spectrum of nonapoptotic functions, including differentiation and organ growth. These different roles of caspases raise intriguing questions: how are caspase levels regulated and what defines the balance between life and death? In this review, we focus on some recent findings that highlight how nonlethal levels of caspase activity, transcriptional coregulator Yes-associated protein (YAP), and mechanical factors influence each other in determining cell fate. We further discuss a possibility that the mechanical signals encountered by cells could regulate the level of caspase activity by mechanics through YAP and, in turn, how this determines whether a cell is susceptible or resistant to undergoing apoptosis in response to cell death stimuli.
    Keywords:  Apoptosis; Caspase; Differentiation; Mechanics; Mechanobiology; YAP
  9. FASEB J. 2020 Nov 17.
      During the last decades intermediate filaments (IFs) have emerged as important regulators of cellular signaling events, ascribing IFs with functions beyond the structural support they provide. The organ and developmental stage-specific expression of IFs regulate cell differentiation within developing or remodeling tissues. Lack of IFs causes perturbed stem cell differentiation in vasculature, intestine, nervous system, and mammary gland, in transgenic mouse models. The aberrant cell fate decisions are caused by deregulation of different stem cell signaling pathways, such as Notch, Wnt, YAP/TAZ, and TGFβ. Mutations in genes coding for IFs cause an array of different diseases, many related to stem cell dysfunction, but the molecular mechanisms remain unresolved. Here, we provide a comprehensive overview of how IFs interact with and regulate the activity, localization and function of different signaling proteins in stem cells, and how the assembly state and PTM profile of IFs may affect these processes. Identifying when, where and how IFs and cell signaling congregate, will expand our understanding of IF-linked stem cell dysfunction during development and disease.
    Keywords:  cell signaling; cytoskeleton; differentiation; regeneration; stem cells
  10. PLoS One. 2020 ;15(11): e0242626
      PURPOSE: This study aimed to investigate the effects of substratum stiffness on the sensitivity of human conjunctival fibroblasts to transforming growth factor (TGF)-β, and to explore the molecular mechanism of action.METHODS: Human conjunctival fibroblasts were cultured on collagen-coated plastic or silicone plates. The stiffness of the silicone plates was 0.2 or 64 kPa. Cells were treated by 2.5 ng/mL TGF-β2 with or without fibroblast growth factor (FGF)-2 (0-100 ng/mL) for 24 h or 48 h. The protein expression levels were determined by Western blot analysis. Cell proliferation was assessed using the WST-8 assay.
    RESULTS: FGF-2 suppressed the TGF-β-induced expression of α-smooth muscle actin (SMA) and collagen type I (Col I), but not fibronectin (FN). Both FGF-2 and TGF-β2 increased cell proliferation without an additive effect. The induction of α-SMA by TGF-β2 was decreased on the soft substratum, without any change in the expression level or subcellular location of Yes-associated protein/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). FGF-2 suppressed TGF-β-induced α-SMA expression even on the soft substratum.
    CONCLUSIONS: FGF-2 treatment and a soft substratum suppressed TGF-β-induced transdifferentiation of conjunctival fibroblasts into myofibroblasts. FGF-2 attenuated the TGF-β-induced expression of α-SMA, even on a soft substratum.
  11. Adv Mater. 2020 Nov 18. e2006986
      The extracellular matrix (ECM) undergoes dynamic remodeling and progressive stiffening during tissue regeneration and disease progression. However, most of the artificial ECMs and in vitro disease models are mechanically static. Here, a self-strengthening polymer coating mimicking the dynamic nature of native ECM is designed to study the cellular response to dynamic biophysical cues and promote cell mechanical sensitive response. Spiropyran (SP) is utilized as dynamic anchor group to regulate the strength of cell adhesive peptide ligands. Benefiting from spontaneous thermal merocyanine-to-spiropyran (MC-SP) isomerization, the resulting self-responsive coating displays dynamic self-strengthening of interfacial interactions. Comparing with the static and all of the previous dynamic artificial ECMs, cells on this self-responsive surface remodel the weakly bonded MC-based coatings to activate α5β1 integrin and Rac signaling in the early adhesion stage. The subsequent MC-to-SP conversion strengthens the ligand-integrin interaction to further activate αvβ3 integrin and RhoA/ROCK signaling in the latter stage. This sequential process enhances cellular mechanotransduction as well as the osteogenic differentiation of mesenchymal stem cells (MSCs). It is worth emphasizing that the self-strengthening occurs spontaneously in the absence of any stimulus, making it especially useful for implanted scaffolds in regenerative medicine.
    Keywords:  adhesive force; biointerfaces; cells; mechanotransduction; self-strengthening
  12. Int J Mol Sci. 2020 Nov 18. pii: E8711. [Epub ahead of print]21(22):
      Liver fibrosis represents the wound healing response to sustained hepatic injury with activation of hepatic stellate cells (HSCs). The I148M variant of the PNPLA3 gene represents a risk factor for development of severe liver fibrosis. Activated HSCs carrying the I148M variant display exacerbated pro-inflammatory and pro-fibrogenic features. We aimed to examine whether the I148M variant may impair Hedgehog and Yap signaling, as key pathways implicated in the control of energy expenditure and maintenance of myofibroblastic traits. First, we show that TGF-β rapidly up-regulated the PNPLA3 transcript and protein and Yap/Hedgehog target gene expression. In addition, HSCs overexpressing PNPLA3 I148M boosted anaerobic glycolysis, as supported by higher lactate release and decreased phosphorylation of the energy sensor AMPK. These cells displayed higher Yap and Hedgehog signaling, due to accumulation of total Yap protein, Yap promoter activity and increased downstream targets expression, compared to WT cells. HSCs exposed to TGF-β and leptin rapidly increased total Yap, together with a reduction in its inhibited form, phosphorylated Yap. In line, Yap-specific inhibitor Verteporfin strongly abolished Yap-mediated genes expression, at baseline as well as after TGF-β and leptin treatments in HSCs with I148M PNPLA3. Finally, Yap transcriptional activity was strongly reduced by a combination of Verteporfin and Rosiglitazone, a PPARγ synthetic agonist. In conclusion, HSCs carrying the PNPLA3 variant show activated Yap/Hedgehog pathways, resulting in altered anaerobic glycolysis and enhanced synthesis of Hedgehog markers and sustained Yap signaling. TGF-β and leptin exacerbate Yap/Hedgehog-related fibrogenic genes expression, while Yap inhibitors and PPARγ agonists abrogate these effects in PNPLA3 I148M carrying HSCs.
    Keywords:  cell metabolism; genetic polymorphism; intracellular signaling; non-alcoholic fatty liver disease
  13. Lab Invest. 2020 Nov 17.
      Focal segmental glomerulosclerosis (FSGS) is a chronic glomerular disease with poor clinical outcomes. Podocyte loss via apoptosis is one important mechanism underlying the pathogenesis of FSGS. Recently, Yes-associated-protein (YAP), a key downstream protein in the Hippo pathway, was identified as an activator for multiple gene transcriptional factors in the nucleus to control cell proliferation and apoptosis. To investigate the potential role of YAP in the progression of FSGS, we examined kidney samples from patients with minimal change disease or FSGS and found that increases in podocyte apoptosis is positively correlated with the cytoplasmic distribution of YAP in human FSGS. Utilizing an established mT/mG transgenic mouse model and primary cultured podocytes, we found that YAP was distributed uniformly in nucleus and cytoplasm in the podocytes of control animals. Adriamycin treatment induced gradual nuclear exclusion of YAP with enhanced phospho-YAP/YAP ratio, accompanied by the induction of podocyte apoptosis both in vivo and in vitro. Moreover, we used verteporfin to treat an Adriamycin-induced FSGS mouse model, and found YAP inhibition by verteporfin induced nuclear exclusion of YAP, thus increasing podocyte apoptosis and accelerating disease progression. Therefore, our findings suggest that YAP nuclear distribution and activation in podocytes is an important endogenous anti-apoptotic mechanism during the progression of FSGS.
  14. Cell Death Differ. 2020 Nov 18.
      The intestinal epithelium harbors a remarkable adaptability to undergo injury-induced repair. A key part of the regenerative response is the transient reprogramming of epithelial cells into a fetal-like state, which drives uniform proliferation, tissue remodeling, and subsequent restoration of the homeostatic state. In this review, we discuss how Wnt and YAP signaling pathways control the intestinal repair response and the transitioning of cell states, in comparison with the process of intestinal development. Furthermore, we highlight how organoid-based applications have contributed to the characterization of the mechanistic principles and key players that guide these developmental and regenerative events.
  15. Cell Rep. 2020 Nov 17. pii: S2211-1247(20)31394-2. [Epub ahead of print]33(7): 108405
      The NLRP3 inflammasome, a critical component of the innate immune system, induces caspase-1 activation and interleukin (IL)-1β maturation in response to microbial infection and cellular damage. However, aberrant activation of the NLRP3 inflammasome contributes to the pathogenesis of several inflammatory disorders, including cryopyrin-associated periodic syndromes, Alzheimer's disease, type 2 diabetes, and atherosclerosis. Here, we identify the receptor for activated protein C kinase 1 (RACK1) as a component of the NLRP3 complexes in macrophages. RACK1 interacts with NLRP3 and NEK7 but not ASC. Suppression of RACK1 expression abrogates caspase-1 activation and IL-1β release in response to NLRP3- but not NLRC4- or AIM2-activating stimuli. This RACK1 function is independent of its ribosomal binding activity. Mechanistically, RACK1 promotes the active conformation of NLRP3 induced by activating stimuli and subsequent inflammasome assembly. These results demonstrate that RACK1 is a critical mediator for NLRP3 inflammasome activation.
    Keywords:  Caspase-1; IL-1β; NEK7; NLRP3 inflammasome; RACK1