Cell biologies
Abstract
Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is caused by mutations in SACS gene encoding sacsin, a huge protein highly expressed in cerebellar Purkinje cells (PCs). ARSACS patients, as well as mouse models, display early degeneration of PCs, but the underlying mechanisms remain unexplored, with no available treatments. In this work, we demonstrated aberrant calcium (Ca2+) homeostasis and its impact on PC degeneration in ARSACS. Mechanistically, we found pathological elevation in Ca2+-evoked responses in Sacs-/- PCs, as the result of defective mitochondria and ER trafficking to distal dendrites and strong downregulation of key Ca2+ buffer-proteins. Alteration of cytoskeletal linkers, that we identified as specific sacsin interactors, likely account for faulty organellar trafficking in Sacs-/- cerebellum. Based on this pathogenetic cascade, we treated Sacs-/- mice with Ceftriaxone, a repurposed drug which exerts neuroprotection by limiting neuronal glutamatergic stimulation, and thus Ca2+ fluxes into PCs. Ceftriaxone treatment significantly improved motor performances of Sacs-/- mice, at both pre- and post-symptomatic stages. We correlated this effect to restored Ca2+ homeostasis, which arrests PC degeneration and attenuates secondary neuroinflammation. These findings disclose new key steps in ARSACS pathogenesis and support further optimization of Ceftriaxone in pre-clinical and clinical settings for the treatment of ARSACS patients.
Authors
Andrea Del Bondio, Fabiana Longo, Daniele De Ritis, Erica Spirito, Paola Podini, Bernard Brais, Angela Bachi, Angelo Quattrini, Francesca Maltecca
Abstract
Leber congenital amaurosis (LCA) is a group of inherited retinal diseases (IRDs) characterized by the early onset and rapid loss of photoreceptor cells. Despite the discovery of a growing number of genes associated with this disease, the molecular mechanisms of photoreceptor cell degeneration of most LCA subtypes remain poorly understood. Here, using retina-specific affinity proteomics combined with ultrastructure expansion microscopy (U-ExM), we reveal the structural and molecular defects underlying LCA type 5 (LCA5) with nanoscale resolution. We show that LCA5-encoded lebercilin, together with retinitis pigmentosa 1 protein (RP1) and the intraflagellar transport (IFT) proteins IFT81 and IFT88, localize at the bulge region of the photoreceptor outer segment (OS), a region crucial for OS membrane disc formation. Next, we demonstrate that mutant mice deficient for lebercilin exhibit early axonemal defects at the bulge region and the distal OS, accompanied by reduced levels of RP1 and IFT proteins, affecting membrane disc formation and presumably leading to photoreceptor death. Finally, AAV-based LCA5 gene augmentation partially restores the bulge region, preserves OS axoneme structure and membrane disc formation, and results in photoreceptor cell survival. Our approach thus provides a next level of assessment of retinal (gene) therapy efficacy at the molecular level.
Authors
Siebren Faber, Olivier Mercey, Katrin Junger, Alejandro Garanto, Marius Ueffing, Rob W.J. Collin, Karsten Boldt, Paul Guichard, Virginie Hamel, Ronald Roepman
Abstract
Sorbitol dehydrogenase (SORD) deficiency has been identified as the most frequent autosomal recessive form of hereditary neuropathy. Loss of SORD causes high sorbitol levels in tissues due to the inability to convert sorbitol to fructose in the two-step polyol pathway, leading to degenerative neuropathy. The underlying mechanisms of sorbitol-induced degeneration have not been fully elucidated, and no current FDA-approved therapeutic options are available to reduce sorbitol levels in the nervous system. Here, in a Drosophila model of SORD deficiency, we showed synaptic degeneration in the brain, neurotransmission defect, locomotor impairment, and structural abnormalities in the neuromuscular junctions. In addition, we found reduced ATP production in the brain and reactive oxygen species accumulation in the central nervous system (CNS) and muscle, indicating mitochondrial dysfunction. Applied Therapeutics, Inc has developed a CNS-penetrant next-generation aldose reductase inhibitor (ARI), AT-007 (govorestat), which inhibits the conversion of glucose to sorbitol. AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, iPSC-derived motor neurons, and Drosophila brains. AT-007 feeding in Sord-deficient Drosophila mitigated synaptic degeneration and significantly improved synaptic transduction, locomotor activity, and mitochondrial function. Moreover, AT-007 treatment significantly reduced ROS accumulation in Drosophila CNS, muscle, and patient-derived fibroblasts. These findings uncover the molecular and cellular pathophysiology of SORD neuropathy and provide a potential treatment strategy for patients with SORD deficiency.
Authors
Yi Zhu, Amanda G. Lobato, Adriana P. Rebelo, Tijana Canic, Natalie Ortiz Vega, Xianzun Tao, Sheyum Syed, Christopher Yanick, Mario Saporta, Michael Shy, Riccardo Perfetti, Shoshana Shendelman, Stephan L. Zuchner, R. Grace Zhai
Abstract
Tuberous Sclerosis Complex (TSC) is characterized by multi-system low-grade neoplasia involving the lung, kidneys, brain, and heart. Lymphangioleiomyomatosis (LAM) is a progressive pulmonary disease affecting almost exclusively women. TSC and LAM are both caused by mutations in TSC1 and TSC2 that results in mTORC1 hyperactivation. Here, we report that single-cell RNA sequencing of LAM lungs identified activation of genes in the sphingolipid biosynthesis pathway. Accordingly, the expression of acid ceramidase (ASAH1) and dihydroceramide desaturase (DEGS1), key enzymes controlling sphingolipid and ceramide metabolism, was significantly increased in TSC2-null cells. TSC2 negatively regulated the biosynthesis of tumorigenic sphingolipids, and suppression of ASAH1 by shRNA or the inhibitor ARN14976 (17a) resulted in markedly decreased TSC2-null cell viability. In vivo, 17a significantly decreased the growth of TSC2-null cell derived mouse xenografts and short-term lung colonization by TSC2-null cells. Combined rapamycin and 17a treatment synergistically inhibited renal cystadenoma growth in Tsc2+/- mice, consistent with increased ASAH1 expression and activity being rapamycin insensitive. Collectively, the present study identifies rapamycin-insensitive ASAH1 upregulation in TSC2-null cells and tumors and provides evidence that targeting aberrant sphingolipid biosynthesis pathways has potential therapeutic value in mTORC1-hyperactive neoplasms including TSC and LAM.
Authors
Aristotelis Astrinidis, Chenggang Li, Erik Y. Zhang, Xueheng Zhao, Shuyang Zhao, Minzhe Guo, Tasnim Olatoke, Ushodaya Mattam, Rong Huang, Alan Zhang, Lori Pitstick, Elizabeth J. Kopras, Nishant Gupta, Roman A. Jandarov, Eric P. Smith, Elizabeth Fugate, Diana Lindquist, Maciej M. Markiewski, Magdalena Karbowniczek, Kathryn A. Wikenheiser-Brokamp, Kenneth D. Setchell, Francis X. McCormack, Yan Xu, Jane Yu
Abstract
The adult mammalian heart has limited regenerative capacity, while the neonatal heart fully regenerates during the first week of life. Postnatal regeneration is mainly driven by proliferation of preexisting cardiomyocytes and supported by proregenerative macrophages and angiogenesis. Although the process of regeneration has been well studied in the neonatal mouse, the molecular mechanisms that define the switch between regenerative and nonregenerative cardiomyocytes are not well understood. Here, using in vivo and in vitro approaches, we identified the lncRNA Malat1 as a key player in postnatal cardiac regeneration. Malat1 deletion prevented heart regeneration in mice after myocardial infarction on postnatal day 3 associated with a decline in cardiomyocyte proliferation and reparative angiogenesis. Interestingly, Malat1 deficiency increased cardiomyocyte binucleation even in the absence of cardiac injury. Cardiomyocyte-specific deletion of Malat1 was sufficient to block regeneration, supporting a critical role of Malat1 in regulating cardiomyocyte proliferation and binucleation, a landmark of mature nonregenerative cardiomyocytes. In vitro, Malat1 deficiency induced binucleation and the expression of a maturation gene program. Finally, the loss of hnRNP U, an interaction partner of Malat1, induced similar features in vitro, suggesting that Malat1 regulates cardiomyocyte proliferation and binucleation by hnRNP U to control the regenerative window in the heart.
Authors
Galip S. Aslan, Nicolas Jaé, Yosif Manavski, Youssef Fouani, Mariana Shumliakivska, Lisa Kettenhausen, Luisa Kirchhof, Stefan Günther, Ariane Fischer, Guillermo Luxán, Stefanie Dimmeler
Abstract
WHIM syndrome is an inherited immune disorder caused by an autosomal dominant heterozygous mutation in CXCR4. The disease is characterized by neutropenia/leukopenia (secondary to retention of mature neutrophils in bone marrow), recurrent bacterial infections, treatment-refractory warts, and hypogammaglobulinemia. All mutations reported in WHIM patients lead to the truncations in the C-terminal domain of CXCR4, R334X being the most frequent. This defect prevents receptor internalization and enhances both calcium mobilization and ERK phosphorylation, resulting in increased chemotaxis in response to the unique ligand CXCL12. Here, we describe 3 patients presenting neutropenia and myelokathexis, but normal lymphocyte count and immunoglobulin levels, carrying what we believe to be a novel Leu317fsX3 mutation in CXCR4, leading to a complete truncation of its intracellular tail. The analysis of the L317fsX3 mutation in cells derived from patients and in vitro cellular models reveals unique signaling features in comparison with R334X mutation. The L317fsX3 mutation impairs CXCR4 downregulation and β-arrestin recruitment in response to CXCL12 and reduces other signaling events — including ERK1/2 phosphorylation, calcium mobilization, and chemotaxis — all processes that are typically enhanced in cells carrying the R334X mutation. Our findings suggest that, overall, the L317fsX3 mutation may be causative of a form of WHIM syndrome not associated with an augmented CXCR4 response to CXCL12.
Authors
Rajesh Kumar, Samantha Milanesi, Martyna Szpakowska, Laura Dotta, Dario Di Silvestre, Anna Maria Trotta, Anna Maria Bello, Mauro Giacomelli, Manuela Benedito, Joana Azevedo, Alexandra Pereira, Emilia Cortesao, Alessandro Vacchini, Alessandra Castagna, Marinella Pinelli, Daniele Moratto, Raffaella Bonecchi, Massimo Locati, Stefania Scala, Andy Chevigné, Elena M. Borroni, Raffaele Badolato
Abstract
Necrotizing enterocolitis (NEC) is a deadly gastrointestinal disease of premature infants that is associated with an exaggerated inflammatory response, dysbiosis of the gut microbiome, decreased epithelial cell proliferation, and gut barrier disruption. We describe an in vitro model of human neonatal small intestinal epithelium (Neonatal-Intestine-on-a-Chip) that mimics key features of intestinal physiology. This model utilizes premature infant intestinal enteroids grown from surgically harvested intestinal tissue and co-cultured with human intestinal microvascular endothelial cells within a microfluidic device. We used our Neonatal-Intestine-on-a-Chip to recapitulate NEC pathophysiology by adding infant-derived microbiota. This model, named NEC-on-a-Chip, recapitulates the predominant features of NEC including significant upregulation of pro-inflammatory cytokines, decreased intestinal epithelial cell markers, reduced epithelial proliferation, and disrupted epithelial barrier integrity. NEC-on-a-Chip provides an improved preclinical model of NEC that facilitates comprehensive analysis of the pathophysiology of NEC using precious clinical samples. This model is an advance towards a personalized medicine approach to test new therapeutics for this devastating disease.
Authors
Wyatt E. Lanik, Cliff J. Luke, Lila S. Nolan, Qingqing Gong, Lauren C. Frazer, Jamie M. Rimer, Sarah E. Gale, Raymond Luc, Shay S. Bidani, Carrie A. Sibbald, Angela N. Lewis, Belgacem Mihi, Pranjal Agrawal, Martin Goree, Marlie M. Maestas, Elise Hu, David G. Peters, Misty Good
Abstract
Despite recent progress in the identification of mediators of podocyte injury, mechanisms underlying podocyte loss remain poorly understood, and cell-specific therapy is lacking. We previously reported that KIBRA, KIdney and BRAin expressed protein, encoded by WWC1, promotes podocyte injury in vitro through activation of the Hippo signaling pathway. KIBRA expression is increased in the glomeruli of patients with focal segmental glomerulosclerosis (FSGS), and KIBRA depletion in vivo is protective against acute podocyte injury. Here, we tested the consequences of transgenic podocyte-specific WWC1 expression in immortalized human podocytes and in mice, and we explored the association between glomerular WWC1 expression and glomerular disease progression. We found that KIBRA overexpression in immortalized human podocytes promoted cytoplasmic localization of YAP (Yes-associated protein), induced actin cytoskeletal reorganization, and altered focal adhesion expression and morphology. Transgenic WWC1 (KIBRA OE) mice were more susceptible to acute and chronic glomerular injury, with evidence of YAP inhibition in vivo. Of clinical relevance, glomerular WWC1 expression negatively correlated with renal survival among patients with primary glomerular diseases. These findings highlight the importance of KIBRA-YAP signaling to the regulation of podocyte structural integrity and identify KIBRA-mediated injury as a potential target for podocyte-specific therapy in glomerular disease.
Authors
Kristin Meliambro, Yanfeng Yang, Marina de Cos, Estefania Rodriguez-Ballestas, Caroline Malkin, Jonathan C. Haydak, John R. Lee, Fadi Salem, Laura H. Mariani, Ronald E. Gordon, John M. Basgen, Huei Hsun Wen, Jia Fu, Evren U. Azeloglu, John Cijiang He, Jenny S. Wong, Kirk N. Campbell
Abstract
Pulmonary fibrosis is potentiated by a positive feedback loop involving the extracellular sialidase enzyme NEU3 causing release of active TGF-β1, and TGF-β1 upregulating NEU3 by increasing translation without affecting mRNA levels. In this report, we elucidate the TGF-β1 upregulation of translation mechanism. In human lung fibroblasts, TGF-β1 increased levels of proteins, including NEU3, by increasing translation of the encoding mRNAs without significantly affecting levels of these mRNAs. 180 of these mRNAs share a common 20 nucleotide motif. Deletion of this motif from NEU3 mRNA eliminated the TGF-β1 upregulation of NEU3 translation, while insertion of this motif in two mRNAs insensitive to TGF-β1 caused TGF-β1 to upregulate their translation. RNA-binding proteins including DDX3 bind the RNA motif, and TGF-β1 regulates their protein levels and/or binding to the motif. We found that DDX3 is upregulated in the fibrotic lesions in pulmonary fibrosis patients, and inhibiting DDX3 in fibroblasts reduced TGF-β1 upregulation of NEU3 levels. In the mouse bleomycin model of pulmonary fibrosis, injections of the DDX3 inhibitor RK-33 potentiated survival and reduced lung inflammation, fibrosis, and lung tissue levels of DDX3, TGF-β1, and NEU3. These results suggest that inhibiting a mRNA-binding protein that mediates TGF-β1 upregulation of translation can reduce pulmonary fibrosis.
Authors
Wensheng Chen, Darrell Pilling, Richard H. Gomer
Abstract
We examine whether calcineurin or protein-phosphatase-2B (PP2B) regulates the basolateral Kir4.1/Kir5.1 in distal-convoluted-tubule (DCT). Application of tacrolimus (FK506) or cyclosporine-A (CsA) increased whole-cell-Kir4.1/Kir5.1-mediated-K+-currents and hyperpolarized DCT-membrane. Moreover, FK506-induced-stimulation of Kir4.1/Kir5.1 was absent in kidney-tubule-specific 12-kDa-FK506-binding-protein knockout-mice (Ks-FKBP-12-KO). In contrast, CsA still stimulated Kir4.1/Kir5.1 of the DCT in Ks-FKBP-12-KO mice, suggesting that FK506-induced stimulation of Kir4.1/Kir5.1 was due to inhibiting PP2B. Single-channel-patch-clamp experiments demonstrated that FK506 or CsA stimulated the basolateral Kir4.1/Kir5.1-activity of DCT, defined by NPo (a product of channel-Number- and- Open-Probability). However, this effect was absent in the DCT treated with Src-family-protein-tyrosine-kinase (SFK) inhibitor or hydroxyl-peroxide which stimulates SFK. Fluorescence-image demonstrated that CsA-treatment increased membrane-staining-intensity of Kir4.1 in the DCT of Kcnj10flox/flox mice. Moreover, CsA-treatment has no obvious effect on pNCC expression in Ks-Kir4.1-KO mice. Immunoblotting showed that acute FK506 treatment increased pNCC-expression in Kcnj10flox/flox mice, but this effect was attenuated in Ks-Kir4.1-KO mice. In vivo measurement of thiazide-induced-renal-Na+ excretion demonstrated that FK506 enhanced thiazide-induced natriuresis. This effect was absent in Ks-FKBP-12-KO mice and blunted in Ks-Kir4.1-KO mice. We conclude that inhibition of PP2B stimulates Kir4.1/Kir5.1 of DCT and NCC, and that PP2B-inhibition-induced stimulation of NCC is partially achieved by stimulation of the basolateral Kir4.1/Kir5.1.
Authors
Dan-Dan Zhang, Xin-Peng Duan, Kerim Mutig, Franziska Rausch, Yu Xiao, Jun-Ya Zheng, Dao-Hong Lin, Wen-Hui Wang
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