bims-bicyki Biomed News
on Bicaudal-C1 and interactors in cystic kidney disease
Issue of 2020‒12‒20
fourteen papers selected by
Céline Gagnieux
École Polytechnique Fédérale de Lausanne (EPFL)

  1. Diagnostics (Basel). 2020 Dec 16. pii: E1099. [Epub ahead of print]10(12):
      Ciliopathies are a group of multi-organ diseases caused by the disruption of the primary cilium. This event leads to a variety of kidney disorders, including nephronophthisis, renal cystic dysplasia, and renal cell carcinoma (RCC). Primary cilium contributes to the regulation of the cell cycle and protein homeostasis, that is, the balance between protein synthesis and degradation by acting on the ubiquitin-proteasome system, autophagy, and mTOR signaling. Many proteins are involved in renal ciliopathies. In particular, fibrocystin (PKHD1) is involved in autosomal recessive polycystic kidney disease (ARPKD), while polycystin-1 (PKD1) and polycystin-2 (PKD2) are implicated in autosomal dominant polycystic kidney disease (ADPKD). Moreover, primary cilia are associated with essential signaling pathways, such as Hedgehog, Wnt, and Platelet-Derived Growth Factor (PDGF). In this review, we focused on the ciliopathies associated with kidney diseases, exploring genes and signaling pathways associated with primary cilium and the potential role of cilia as therapeutic targets in renal disorders.
    Keywords:  ciliopathies; fibrocystin; kidney; polycystic kidney disease; polycystin-1; polycystin-2; renal cell carcinoma
  2. Turk J Med Sci. 2020 Dec 14.
      BACKGROUND: In children with autosomal dominant polycystic kidney disease (ADPKD), clinical manifestations range from severe neonatal presentation to renal cysts found by chance. We aimed to evaluate demographic, clinical, laboratory findings, and genetic analysis of children with ADPKD.METHODS: We evaluated children diagnosed with ADPKD between January 2006 and January 2019. The diagnosis was established by family history, ultrasound findings, and/or genetic analysis. The demographic, clinical, and laboratory findings were evaluated retrospectively. Patients <10 years and ?10 years at the time of diagnosis were divided into 2 groups and parameters were compared between the groups.
    RESULTS: There were 41 children (M/F:18/23) diagnosed with ADPKD. The mean age at diagnosis was 7.2±5.1 (0.6?16.9) years and the follow-up duration was 59.34±40.56(8-198) months. Five patients (12%) were diagnosed as very early onset ADPKD. All patients had a positive family history. Genetic analysis was performed in 29 patients (PKD1 mutations in 21, PKD2 mutations in 1, no mutation in 3). Cysts were bilateral in 35 (85%) of the patients. Only one patient had hepatic cysts. No valvular defect was defined in 12 patients detected. Only 1 patient had hypertension. None of them had chronic kidney disease. No difference could be demonstrated in gender, laterality of the cysts, maximum cyst diameter, cyst or kidney enlargement, follow-up duration, or GFR at last visit between Groups 1 and 2.
    CONCLUSIONS: The majority of children with ADPKD had preserved renal functions and slight cyst enlargement during their follow up. However, may have different renal problems deserving closed follow-up.
    Keywords:  Autosomal dominant polycystic kidney disease; children
  3. Mol Med. 2020 12 11. 26(1): 128
      Autosomal dominant polycystic kidney disease (ADPKD) is an inherited chronic kidney disorder (CKD) that is characterized by the development of numerous fluid-filled cysts in kidneys. It is caused either due to the mutations in the PKD1 or PKD2 gene that encodes polycystin-1 and polycystin-2, respectively. This condition progresses into end-stage renal disorder if the renal or extra-renal clinical manifestations remain untreated. Several clinical trials with a variety of drugs have failed, and the only Food and Drugs Administration (FDA) approved drug to treat ADPKD to date is tolvaptan that works by antagonizing the vasopressin-2 receptor (V2R). The pathology of ADPKD is complex and involves the malfunction of different signaling pathways like cAMP, Hedgehog, and MAPK/ERK pathway owing to the mutated product that is polycystin-1 or 2. A measured yet substantial number of preclinical studies have found pioglitazone to decrease the cystic burden and improve the renal function in ADPKD. The peroxisome proliferator-activated receptor-gamma is found on the epithelial cells of renal collecting tubule and when it gets agonized by pioglitazone, confers efficacy in ADPKD treatment through multiple mechanisms. There is only one clinical trial (ongoing) wherein it is being assessed for its benefits and risk in patients with ADPKD, and is expected to get approval from the regulatory body owing to its promising therapeutic effects. This article would encompass the updated information on the epidemiology, pathophysiology of ADPKD, different mechanisms of action of pioglitazone in the treatment of ADPKD with preclinical and clinical shreds of evidence, and related safety updates.
    Keywords:  Cystic fibrosis; Hedgehog pathway; JAK2 protein; MAP kinase signaling system; PPAR gamma; Platelet endothelial cell adhesion molecule-1; Polycystin-1
  4. Kidney Dis (Basel). 2020 Nov;6(6): 407-413
      Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary nephropathy with few treatments to slow renal progression. The evidence on the effect of lipid-lowering agents (statins) on ADPKD progression remains inconclusive.Methods: We performed a systematic review and meta-analysis by searching the PubMed, Embase, Web of Science, and Cochrane databases (up to November 2019). Changes in estimated glomerular filtration rate (eGFR) and total kidney volume (TKV) were the primary outcomes. Mean differences (MDs) for continuous outcomes and 95% confidence intervals (CIs) were calculated by a random-effects model.
    Results: Five clinical studies with 648 participants were included. Statins did not show significant benefits in the yearly change in eGFR (4 studies, MD = -0.13 mL/min/m2, 95% CI: -0.78 to 0.52, p = 0.70) and the yearly change in TKV (3 studies, MD = -1.17%, 95% CI: -3.40 to 1.05, p = 0.30) compared with the control group. However, statins significantly decreased urinary protein excretion (-0.10 g/day, 95% CI: -0.16 to -0.03, p = 0.004) and serum low-density lipoprotein level (-0.34 mmol/L, 95% CI: -0.58 to -0.10, p = 0.006).
    Conclusion: Despite these proteinuria and lipid-lowering benefits, the effect of statins on ADPKD progression was uncertain.
    Keywords:  Autosomal dominant; Glomerular filtration rate; Meta-analysis; Polycystic kidney disease; Proteinuria; Statins
  5. Rev Med Liege. 2020 Dec;75(12): 775-780
      Polycystic kidney disease (PKD) is the most prevalent inherited kidney disease. The disease is usually asymptomatic until adulthood. End-stage renal disease occurs generally after the age of 55 years, with a large inter-individual variability. Renal cyst formation begins early in life, and animal models have shown that treatments able to prevent the cyst growth slow down the renal function decline. A treatment by tolvaptan is currently used in adults to decelerate PKD progression. Until now there is no consensus about the appropriate time to screen for PKD in children. However, these scientific progresses raise the interest of determining early (i.e. pediatric) predictive markers of renal function decline.
    Keywords:   Childhood ; Progression marker ; Treatment; Autosomal dominant polycystic kidney disease
  6. Nat Struct Mol Biol. 2020 Dec 14.
      Motile cilia power cell locomotion and drive extracellular fluid flow by propagating bending waves from their base to tip. The coordinated bending of cilia requires mechanoregulation by the radial spoke (RS) protein complexes and the microtubule central pair (CP). Despite their importance for ciliary motility across eukaryotes, the molecular function of the RSs is unknown. Here, we reconstituted the Chlamydomonas reinhardtii RS head that abuts the CP and determined its structure using single-particle cryo-EM to 3.1-Å resolution, revealing a flat, negatively charged surface supported by a rigid core of tightly intertwined proteins. Mutations in this core, corresponding to those involved in human ciliopathies, compromised the stability of the recombinant complex, providing a molecular basis for disease. Partially reversing the negative charge on the RS surface impaired motility in C. reinhardtii. We propose that the RS-head architecture is well-suited for mechanoregulation of ciliary beating through physical collisions with the CP.
  7. Cell Tissue Res. 2020 Dec 16.
      Cilia are evolutionarily conserved organelles that extend from the surface of cells and are found in diverse organisms from protozoans to multicellular organisms. Motile cilia play various biological functions by their beating motion, including mixing fluids and transporting food particles. Non-motile cilia act as sensors that signal cells about their microenvironment. In corals, cilia have been described in some of the cell layers but never in the calcifying epithelium, which is responsible for skeleton formation. In the present study, we used scanning electron microscopy and immunolabelling to investigate the cellular ciliature of the different tissue layers of the coral Stylophora pistillata, with a focus on the calcifying calicoblastic ectoderm. We show that the cilium of the calcifying cells is different from the cilium of the other cell layers. It is much shorter, and more importantly, its base is structurally distinct from the base observed in cilia of the other tissue layers. Based on these structural observations, we conclude that the cilium of the calcifying cells is a primary cilium. From what is known in other organisms, primary cilia are sensors that signal cells about their microenvironment. We discuss the implications of the presence of a primary cilium in the calcifying epithelium for our understanding of the cellular physiology driving coral calcification and its environmental sensitivity.
    Keywords:  Acetylated tubulin; Biomineralization; Calicoblastic ectoderm; Cilium; Scanning electron microscopy
  8. J Mol Biol. 2020 Dec 15. pii: S0022-2836(20)30684-7. [Epub ahead of print] 166759
      Anti-CRISPRs are protein inhibitors of CRISPR-Cas systems. They are produced by phages and other mobile genetic elements to evade CRISPR-Cas-mediated destruction. Anti-CRISPRs are remarkably diverse in sequence, structure, and functional mechanism; thus, structural and mechanistic investigations of anti-CRISPRs continue to yield exciting new insights. In this study, we used nuclear magnetic resonance (NMR) spectroscopy to determine the solution structure of AcrIE2, an anti-CRISPR that inhibits the type I-E CRISPR-Cas system of Pseudomonas aeruginosa. Guided by the structure, we used site-directed mutagenesis to identify key residues that are required for AcrIE2 function. Using affinity purification experiments, we found that AcrIE2 binds the type I-E CRISPR-Cas complex (Cascade). In vivo transcriptional assays, in which Cascade was targeted to promoter regions, demonstrated that Cascade still binds to DNA in the presence of AcrIE2. This is the first instance of a type I anti-CRISPR that binds to a CRISPR-Cas complex but does not prevent DNA-binding. Another unusual property of AcrIE2 is that the effect of Cascade:AcrIE2 complex binding to promoter regions varied depending on the position of the binding site. Most surprisingly, Cascade:AcrIE2 binding led to transcriptional activation in some cases rather than repression, which did not occur when Cascade alone bound to the same sites. We conclude that AcrIE2 operates through a distinct mechanism compared to other type I anti-CRISPRs. While AcrIE2 does not prevent Cascade from binding DNA, it likely blocks subsequent recruitment of the Cas3 nuclease to Cascade thereby preventing DNA cleavage.
    Keywords:  CRISPR; NMR structure; anti-CRISPR; mechanism; mutagenesis
  9. Kidney Med. 2020 Nov-Dec;2(6):2(6): 762-770
      Important advances have been made regarding the diagnosis and management of polycystic kidney diseases. Care of patients with polycystic kidney diseases has moved beyond supportive care for complications and chronic kidney disease to new potentially disease-modifying therapies. Recently, the role of noncoding RNAs, in particular microRNAs, has been described in polycystic kidney diseases. microRNAs are involved in the regulation of gene expression, in which PKD1, PKD2, and other genes that contribute to the pathogenesis of polycystic kidney diseases are considerable participants. Seminal studies have highlighted the potential importance of microRNAs as new therapeutic targets and innovative diagnostic and/or prognostic biomarkers. Furthermore, an anti-miR-17 drug has advanced through preclinical autosomal dominant polycystic disease studies, and an anti-miR-21 drug has already cleared a phase 1 clinical trial. Most probably, new drugs in the microRNA research field will be yielded as a result of ongoing and planned therapeutic trials. To provide a foundation for understanding microRNA functions as a disease-modifying therapeutic drug in novel targeted therapies, in this narrative review we present an overview of the current knowledge of microRNAs in the pathogenesis of polycystic kidney diseases.
    Keywords:  miR-21; miR17∼92; microRNA; polycystic kidney disease; signaling pathway
  10. Nat Struct Mol Biol. 2020 Dec 14.
      In motile cilia, a mechanoregulatory network is responsible for converting the action of thousands of dynein motors bound to doublet microtubules into a single propulsive waveform. Here, we use two complementary cryo-EM strategies to determine structures of the major mechanoregulators that bind ciliary doublet microtubules in Chlamydomonas reinhardtii. We determine structures of isolated radial spoke RS1 and the microtubule-bound RS1, RS2 and the nexin-dynein regulatory complex (N-DRC). From these structures, we identify and build atomic models for 30 proteins, including 23 radial-spoke subunits. We reveal how mechanoregulatory complexes dock to doublet microtubules with regular 96-nm periodicity and communicate with one another. Additionally, we observe a direct and dynamically coupled association between RS2 and the dynein motor inner dynein arm subform c (IDAc), providing a molecular basis for the control of motor activity by mechanical signals. These structures advance our understanding of the role of mechanoregulation in defining the ciliary waveform.
  11. Mol Cells. 2020 12 15.
      Cilia are important eukaryotic cellular compartments required for diverse biological functions. Recent studies have revealed that protein targeting into the proper ciliary subcompartments is essential for ciliary function. In Drosophila chordotonal cilium, where mechano-electric transduction occurs, two transient receptor potential (TRP) superfamily ion channels, TRPV and TRPN, are restricted to the proximal and distal subcompartments, respectively. To understand the mechanisms underlying the sub-ciliary segregation of the two TRPs, we analyzed their localization under various conditions. In developing chordotonal cilia, TRPN was directly targeted to the ciliary tip from the beginning of its appearance and was retained in the distal subcompartment throughout development, whereas the ciliary localization of TRPV was considerably delayed. Lack of intraflagella transport-related proteins affected TRPV from the initial stage of its pre-ciliary trafficking, whereas it affected TRPN from the ciliary entry stage. The ectopic expression of the two TRP channels in both ciliated and nonciliated cells revealed their intrinsic properties related to their localization. Taken together, our results suggest that subciliary segregation of the two TRP channels relies on their distinct intrinsic properties, and begins at the initial stage of their pre-ciliary trafficking.
    Keywords:  Drosophila; cilia; ciliary sub-compartment; intraflagella transport; transient receptor potential channel
  12. Front Cell Neurosci. 2020 ;14 572434
      In the past, most inner ear diseases were thought to start with the impairment of the sensory epithelium of the cochlea before subsequently progressing to secondary neural degeneration. However, recent studies show that loss of primary synapses accompanied by excitotoxic degeneration of peripheral axons is likely to be the underlying pathology in sensorineural hearing loss. Rho-associated coiled-coil containing protein kinase (ROCK) inhibition has been reported to have neuroprotective and regenerative effects on synaptic pathways. Therefore, we analyzed the effect of ROCK inhibition using Y-27632 in a model of peripheral axonal damage in the spiral ganglion neurons created using the glutamate agonists, N-methyl-D-aspartate (NMDA) and kainic acid, to induce excitotoxic trauma in the explanted cochlea. The number of axons projecting to hair cells in the cochlea treated with Y-27632 was significantly greater than those in the cochlea treated only with NMDA + kainic acid. Furthermore, there was a significant increase in synapses between the spiral ganglion and the inner hair cells in the cochlea treated with Y-27632. The findings of this study suggest that ROCK inhibition could be a potential strategy for the regeneration of peripheral axons in the spiral ganglion and synapse formation in the inner hair cells of a cochlea that has sustained excitotoxic injury, which is one of the primary etiologies of inner ear disease.
    Keywords:  Rho-associated coiled-coil containing protein kinase; Y-27632; cochlea; hearing loss; inner ear; regeneration; spiral ganglion; synapse
  13. J Cell Sci. 2020 Dec 11. pii: jcs.249078. [Epub ahead of print]
      Cell-cell junction formation requires actin cytoskeletal remodeling. Here we show that PLEKHG4B, a Rho-guanine nucleotide exchange factor (Rho-GEF), plays a crucial role in epithelial cell-cell junction formation. Knockdown of PLEKHG4B decreased Cdc42 activity and tended to increase RhoA activity in A549 cells. A549 monolayer cells showed 'closed junctions' with closely packed actin bundles along the cell-cell contacts, but PLEKHG4B knockdown suppressed closed junction formation and exhibited 'open junctions' with split actin bundles located away from the cell-cell boundary. In calcium-switch assays, PLEKHG4B knockdown delayed the conversion of open junctions to closed junctions and β-catenin accumulation at cell-cell junctions. Further, PLEKHG4B knockdown abrogated the reduction in myosin activity normally seen in the later stage of junction formation. The aberrant myosin activation and impairments in closed junction formation in PLEKHG4B-knockdown cells were reverted by ROCK inhibition or LARG/PDZ-RhoGEF knockdown. These results suggest that PLEKHG4B enables actin remodeling during epithelial cell-cell junction maturation, probably by reducing myosin activity in the later stage of junction formation, through suppressing LARG/PDZ-RhoGEF and RhoA-ROCK activities. We also showed that annexin-A2 participates in PLEKHG4B localization to cell-cell junctions.
    Keywords:  Actin organization; Annexin-A2; Cell adhesion; Myosin; PLEKHG4B; Rho-GEF
  14. Mol Biol Cell. 2020 Dec 16. mbcE20070480
      Although the actomyosin cytoskeleton has been implicated in clathrin-mediated endocytosis, a clear requirement for actomyosin in clathrin-independent endocytosis (CIE) has not been demonstrated. We discovered that the Rho-associated kinase ROCK2 is required for CIE of MHCI and CD59 through promotion of myosin II activity. Myosin IIA promoted internalization of MHCI and myosin IIB drove CD59 uptake in both HeLa and polarized Caco2 intestinal epithelial cells. In Caco2 cells, myosin IIA localized to the basal cortex and apical brush border and mediated MHCI internalization from the basolateral domain, while myosin IIB localized at the basal cortex and apical cell-cell junctions and promoted CD59 uptake from the apical membrane. Atomic force microscopy demonstrated that myosin IIB mediated apical epithelial tension in Caco2 cells. Thus, specific cargoes are internalized by ROCK2-mediated activation of myosin II isoforms to mediate spatial regulation of CIE, possibly by modulation of local cortical tension.