Advertisement

Podocytes

The Role of Lysosomes in the Development of Nephrotic Syndrome
  • Marica Giliberti
    Affiliations
    Nephrology Unit, Department of Emergency and Transplant Organs, University Aldo Moro of Bari, Bari, Italy
    Search for articles by this author
  • Adele Mitrotti
    Affiliations
    Nephrology Unit, Department of Emergency and Transplant Organs, University Aldo Moro of Bari, Bari, Italy
    Search for articles by this author
  • Loreto Gesualdo
    Correspondence
    Address correspondence to Loreto Gesualdo, M.D., F.E.R.A., Nephrology, Dialysis and Transplantation Unit, Aldo Moro University of Bari, Azienda Ospedaliero-Universitaria Consorziale Policlinico, Piazza Giulio Cesare, 11 - 70124 Bari, Italy.
    Affiliations
    Nephrology Unit, Department of Emergency and Transplant Organs, University Aldo Moro of Bari, Bari, Italy
    Search for articles by this author
Open ArchivePublished:April 16, 2020DOI:https://doi.org/10.1016/j.ajpath.2020.04.001
      Podocytes are terminal, visceral epithelial cells that lack proliferative properties, making intracellular homeostasis essential for their integrity. Podocytes are characterized by interdigitating foot processes. Secondary foot processes surround glomerular basement membrane and together with the glomerular basement membrane and endothelial cells generate the glomerular filtration barrier, regulating the protein traffic through our kidneys. Podocytes are critical for the maintenance of glomerular morphology and function. Furthermore, they represent a frequent target of injury, as it happens in case of genetic mutations, immune disorders, infections, hemodynamic defects, toxic exposure, or metabolic alteration.
      • Wiggins R.C.
      The spectrum of podocytopathies: a unifying view of glomerular diseases.
      Congenital or acquired alterations in podocytes are frequently involved in different kidney diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, Fabry disease, diabetic nephropathy, HIV-associated nephropathy, lupus nephritis, and preeclampsia.
      • Wiggins R.C.
      The spectrum of podocytopathies: a unifying view of glomerular diseases.
      • Watanabe A.
      • Feltran L.S.
      • Sampson M.G.
      Genetics of nephrotic syndrome presenting in childhood: core curriculum 2019.
      • Jefferson J.A.
      • Nelson P.J.
      • Najafian B.
      • Shankland S.J.
      Podocyte disorders: core curriculum 2011.
      These conditions are mostly characterized by proteinuria and eventually by a full nephrotic syndrome.
      Lysosomes represent an essential intracellular component with digestive and recycling properties.
      • Li G.
      • Kidd J.
      • Li P.L.
      Podocyte lysosome dysfunction in chronic glomerular diseases.
      Lysosomes are critical for cellular activity in podocytes,
      • Pavenstädt H.
      • Kriz W.
      • Kretzler M.
      Cell biology of the glomerular podocyte.
      due to their scavenging ability, as demonstrated by the emerging knowledge that lysosome dysfunction may relate with glomerular disease.
      Mutations in genes encoding for lysosomal proteins or proteins involved in lysosomal activity are known causes of genetically determined nephropathies, such as Fabry disease, Tay-Sachs disease, cystinosis, and Nieman-Pick disease. ASAH1 encodes for lysosomal acid ceramidase (AC) and ASAH1 mutations in humans cause autosomal recessive disorders, such as Farber lipogranulomatosis and spinal muscular atrophy with progressive myoclonic epilepsy.
      • Park J.H.
      • Schuchman E.H.
      Acid ceramidase and human disease.
      • Sugita M.
      • Dulaney J.T.
      • Moser H.W.
      Ceramidase deficiency in Farber's disease (lipogranulomatosis).
      • Zhou J.
      • Tawk M.
      • Tiziano F.D.
      • Veillet J.
      • Bayes M.
      • Nolet F.
      • Garcia V.
      • Servidei S.
      • Bertini E.
      • Castro-Ciner F.
      • Renda Y.
      • Carpentier S.
      • Andrieu-Abadie N.
      • Gut I.
      • Levade T.
      • Topaloglu H.
      • Melki J.
      Spinal muscular atrophy associated with progressive myoclonic epilepsy is caused by mutations in ASAH1.
      In this issue of The American Journal of Pathology, Li et al
      • Li G.
      • Kidd J.
      • Kaspar C.
      • Dempsey S.
      • Bhat O.M.
      • Camus S.
      • Ritter J.K.
      • Gehr T.W.B.
      • Gulbins E.
      • Li P.L.
      Podocytopathy and nephrotic syndrome in mice with podocyte-specific deletion of the Asah1 gene: role of ceramide accumulation in glomeruli.
      demonstrated that ceramide accumulation in podocytes may lead to cellular damage and nephrotic syndrome, in mice. A knockout mouse strain (Asah1fl/fl/PodoCre) with a podocyte-specific deletion of the α subunit (main catalytic subunit) of lysosomal acid ceramidase (AC) was used in this study. Ceramide accumulation, determined by liquid chromatography–tandem mass spectrometry, was demonstrated in isolated glomeruli of Asah1fl/fl/PodoCre mice compared with their littermates.
      • Li G.
      • Kidd J.
      • Kaspar C.
      • Dempsey S.
      • Bhat O.M.
      • Camus S.
      • Ritter J.K.
      • Gehr T.W.B.
      • Gulbins E.
      • Li P.L.
      Podocytopathy and nephrotic syndrome in mice with podocyte-specific deletion of the Asah1 gene: role of ceramide accumulation in glomeruli.
      Ceramides are lipids belonging to the family of sphingolipids. They are converted in sphingomyelin first and then sphingolipids, the main component of plasma membrane. Plasma membranes are usually catabolized into lysosomes, where ceramides are generated from degradation of sphingolipids and then regenerated. The interest in the molecular biology and ceramide metabolism is due to the recognized link between cellular clearance dysfunction and the pathogenesis of some lysosome-related disorders.
      • Bellomo G.
      • Paciotti S.
      • Gatticchi L.
      • Parnetti L.
      The vicious cycle between α-synuclein aggregation and autophagic-lysosomal dysfunction.
      AC is responsible for the hydrolysis of ceramide into sphingosine and free fatty acid,
      • Gatt S.
      Enzymic hydrolysis and synthesis of ceramides.
      and it may have a role in the lysosomal system. Ceramide plays a central role in metabolism of other cellular sphingolipids; therefore, alterations in ceramide metabolism may result in different pathologies.
      The synthesis and accumulation of ceramide in response to cellular stress is known to mediate cancer cell death through various mechanisms, including apoptosis and autophagy. Enzyme ceramidase may represent a therapeutic target of cancer.
      • Govindarajah N.
      • Clifford R.
      • Bowden D.
      • Sutton P.A.
      • Parsons J.L.
      • Vimalachandran D.
      Sphingolipids and acid ceramidase as therapeutic targets in cancer therapy.
      • Ponnusamy S.
      • Meyers-Needham S.
      • Senkal C.E.
      • Saddoughi S.A.
      • Sentelle D.
      • Selvam S.P.
      • Salas A.
      • Ogretmen B.
      Sphingolipids and cancer: ceramide and sphingosine-1-phosphate in the regulation of cell death and drug resistance.
      • Ogretmen B.
      Sphingolipid metabolism in cancer signalling and therapy.
      In fact, AC is overexpressed in a variety of cancer cell lines, and the enzymatic inhibition by novel specific inhibitors or other traditional cancer agents, alone or in combination, induces apoptosis in cancer cells.
      • Roh J.L.
      • Park J.Y.
      • Kim E.H.
      • Jang H.J.
      Targeting acid ceramidase sensitises head and neck cancer to cisplatin.
      • Lai M.
      • Realini N.
      • La Ferla M.
      • Passalacqua I.
      • Matteoli G.
      • Ganesan A.
      • Pistello M.
      • Mazzanti C.M.
      • Piomelli D.
      Complete acid ceramidase ablation prevents cancer-initiating cell formation in melanoma cells.
      • Hanker L.C.
      • Karn T.
      • Holtrich U.
      • Gätje R.
      • Rody A.
      • Heinrich T.
      • Ruckhäberle E.
      • Engels K.
      Acid ceramidase (AC)–a key enzyme of sphingolipid metabolism–correlates with better prognosis in epithelial ovarian cancer.
      Farber disease is a rare lysosomal storage disorder in which the genetic mutation leads to decreased AC activity with ceramide accumulation, resulting in pathologic manifestations. Farber disease is typically based on the cardinal triad symptoms: subcutaneous nodules, joint pain, and voice hoarseness. These patients present enlarged liver and spleen along with neurologic and respiratory complications.
      • Yu F.P.S.
      • Amintas S.
      • Levade T.
      • Medin J.A.
      Acid ceramidase deficiency: farber disease and SMA-PME.
      However, any activity of ceramidase has not been recognized in kidney.
      Although intracellular ceramide protects against neoplasm development through the induction of cell death, studies have shown that the accumulation of ceramide in cells can be involved in development of diabetic complications. Ceramide, in fact, inhibits several intracellular insulin pathways
      • Chavez J.A.
      • Summers S.A.A.
      Ceramide-centric view of insulin resistance.
      : it activates a mitochondrial factor, the protein phosphatase 2A, able to inactivate Bcl-2, which is fundamental to controlling survival and apoptosis.
      • Ruvolo P.P.
      • Deng X.
      • Ito T.
      • Carr B.K.
      • May W.S.
      Ceramide induces Bcl2 dephosphorylation via a mechanism involving mitochondrial PP2A.
      Moreover, emerging lines of evidence indicate that renal lipid dysregulation is one of the factors responsible for the development of chronic kidney disease secondary to diabetic nephropathy.
      • Weinberg J.M.
      Lipotoxicity.
      ,
      • Guebre-Egziabher F.
      • Alix P.M.
      • Koppe L.
      • Pelletier C.C.
      • Kalbacher E.
      • Fouque D.
      • Soulage C.O.
      Ectopic lipid accumulation: a potential cause for metabolic disturbances and a contributor to the alteration of kidney function.
      AdipoRon in vitro, an orally active synthetic adiponectin agonist, binds both adiponectin receptors 1/2 and ameliorates particularly kidney diabetic complications. AdipoRon lowered cellular ceramide levels by activation of AC, which normalized ceramide to sphingosine-1 phosphate; it may prevent lipotoxicity in the kidney, particularly in both glomerular endothelial cells and podocytes. This process is mediated through an improvement in lipid metabolism and further prevents deterioration of renal function.
      • Choi S.R.
      • Lim J.H.
      • Kim M.Y.
      • Kim E.N.
      • Kim Y.
      • Choi B.S.
      • Kim Y.S.
      • Kim H.W.
      • Lim K.M.
      • Kim M.J.
      • Park C.W.
      Adiponectin receptor agonist AdipoRon decreased ceramide, and lipotoxicity, and ameliorated diabetic nephropathy.
      The pathogenicity of ceramide in podocytes is the main topic investigated by Li et al.
      • Li G.
      • Kidd J.
      • Kaspar C.
      • Dempsey S.
      • Bhat O.M.
      • Camus S.
      • Ritter J.K.
      • Gehr T.W.B.
      • Gulbins E.
      • Li P.L.
      Podocytopathy and nephrotic syndrome in mice with podocyte-specific deletion of the Asah1 gene: role of ceramide accumulation in glomeruli.
      They suggest that the ceramide accumulation in podocytes can cause cellular damage and nephrotic syndrome. Their model showed high proteinuria and albuminuria, unresponsive to the administration of the steroids. Although no alterations were observed in the glomeruli analyzed by light microscopy classic foot process effacement and microvillus transformation was observed in podocytes of 8-week–old mice using electron microscopy. It is unclear why the podocyte morphology remains unchanged in the 4-week–old mice. It is possible that the amount of ceramide accumulation in 4-week–old podocytes, due to AC mutation, is not toxic enough to generate podocyte dysfunction at this stage. Another possibility is that, in the early stage of development, podocytes still hold modular ability, temporarily keeping structural adaptation capacity. Further studies are required to investigate these aspects.
      Normally, acid sphingomyelinase catalyzes the hydrolysis of the sphingomyelin, producing ceramide. Li et al
      • Park J.H.
      • Schuchman E.H.
      Acid ceramidase and human disease.
      also found a protective role of acid sphingomyelinase deletion in a knockout mouse cell line with a podocyte-specific deletion of the α subunit of acid ceramidase.
      The use of AdipoRon in diabetic nephropathy reduces the levels of ceramide in podocytes.
      • Choi S.R.
      • Lim J.H.
      • Kim M.Y.
      • Kim E.N.
      • Kim Y.
      • Choi B.S.
      • Kim Y.S.
      • Kim H.W.
      • Lim K.M.
      • Kim M.J.
      • Park C.W.
      Adiponectin receptor agonist AdipoRon decreased ceramide, and lipotoxicity, and ameliorated diabetic nephropathy.
      The pathogenetic hypothesis of nephrotic syndrome onset secondary to accumulation of ceramide in podocytes is convincing, although it needs further examination.
      If the relationship between ceramide accumulation and the development of some forms of nephrotic syndrome is confirmed, it would be useful to investigate Asah1 variants, together with the other known genes responsible for nephrotic syndrome, through next-generation sequencing or whole generation sequencing techniques.
      Should the hypothesis of Li et al
      • Li G.
      • Kidd J.
      • Kaspar C.
      • Dempsey S.
      • Bhat O.M.
      • Camus S.
      • Ritter J.K.
      • Gehr T.W.B.
      • Gulbins E.
      • Li P.L.
      Podocytopathy and nephrotic syndrome in mice with podocyte-specific deletion of the Asah1 gene: role of ceramide accumulation in glomeruli.
      be true, it will open new diagnostic and pathogenetic definitions for the so-called idiopathic steroid-resistant nephrotic syndromes, in the era of precision medicine, and will offer new powerful therapeutic possibilities.
      Furthermore, linking nephrotic syndrome to lysosomal storage disorder represents a new paradigm of research in which new insights may be born. However, future treatment strategies, such as the use of enzyme replacement therapies, would need to be investigated.
      Enzyme replacement therapy is currently the standard of care for several lysosomal storage disorders: Gaucher disease, Pompe disease, Fabry disease, mucopolysaccharidosis (MPS) I, II, and VI, neuronal ceroid lipofuscinosis type 2, and Niemann-Pick B.
      In Fabry disease, podocytes have been implicated because of the accumulation of globotriaosylceramide. Proteinuria is also present in Fabry disease, and it is not responsive to steroid therapy; it is usually subnephrotic.
      • Najafian B.
      • Tøndel C.
      • Svarstad E.
      • Gubler M.C.
      • Oliveira J.P.
      • Mauer M.
      Accumulation of globotriaosylceramide in podocytes in fabry nephropathy is associated with progressive podocyte loss.
      This highlights the important role of lysosomes in the development of kidney podocyte damage.
      The role of lysosomes in maintaining the integrity of podocytes is evidenced by recent studies on rituximab, a chimeric human IgG1 anti-CD20 monoclonal antibody with significant activity against CD20+ B cells. This monoclonal medication has been adopted from the treatment of hematological diseases, and it has been successfully used in the treatment of some glomerulonephritides and nephrotic syndrome conditions, with a probably immunologic pathogenesis. The first aim of rituximab is to recognize CD20 on B lymphocytes, but it might also bind sphingomyelin–phosphodiesterase acid–like 3b and regulate acid-sphyngomyelinase activity.
      • Fornoni A.
      • Sageshima J.
      • Wei C.
      • Merscher-Gomez S.
      • Robier A.P.
      • Jauregui A.N.
      • Li J.
      • Mattiazzi A.
      • Ciancio G.
      • Chen L.
      • Zilleruelo G.
      • Abitbol C.
      • Chandar J.
      • Seeherunvong W.
      • Ricordi C.
      • Ikehata M.
      • Rastaldi M.P.
      • Reiser J.
      • Burke G.W.
      Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis.
      In conclusion, podocytes are complex cells whose alterations may result in the pathologic loss of protein in the urine. Mutations implicated in nephrotic syndrome in children and adults largely include genes encoding the structural proteins of podocytes. Lysosomal disorders, characterized by the accumulation of metabolites like ceramide, may be part of podocyte-related diseases. Investigation of the glomerular genomic background in the patients affected by lysosome disorder may provide new interesting insights in kidney diseases. This opens the door not only to new pathogenic scenarios of nephrotic syndromes but above all therapeutic outlines, in terms of both enzyme replacement therapy and targeted gene therapy.

      References

        • Wiggins R.C.
        The spectrum of podocytopathies: a unifying view of glomerular diseases.
        Kidney Int. 2007; 71: 1205-1214
        • Watanabe A.
        • Feltran L.S.
        • Sampson M.G.
        Genetics of nephrotic syndrome presenting in childhood: core curriculum 2019.
        Am J Kidney Dis. 2019; 74: 549-557
        • Jefferson J.A.
        • Nelson P.J.
        • Najafian B.
        • Shankland S.J.
        Podocyte disorders: core curriculum 2011.
        Am J Kidney Dis. 2011; 58: 666-677
        • Li G.
        • Kidd J.
        • Li P.L.
        Podocyte lysosome dysfunction in chronic glomerular diseases.
        Int J Mol Sci. 2020; 21: 1559
        • Pavenstädt H.
        • Kriz W.
        • Kretzler M.
        Cell biology of the glomerular podocyte.
        Physiol Rev. 2003; 83: 253-307
        • Park J.H.
        • Schuchman E.H.
        Acid ceramidase and human disease.
        Biochim Biophys Acta. 2006; 1758: 2133-2138
        • Sugita M.
        • Dulaney J.T.
        • Moser H.W.
        Ceramidase deficiency in Farber's disease (lipogranulomatosis).
        Science. 1972; 178: 1100-1102
        • Zhou J.
        • Tawk M.
        • Tiziano F.D.
        • Veillet J.
        • Bayes M.
        • Nolet F.
        • Garcia V.
        • Servidei S.
        • Bertini E.
        • Castro-Ciner F.
        • Renda Y.
        • Carpentier S.
        • Andrieu-Abadie N.
        • Gut I.
        • Levade T.
        • Topaloglu H.
        • Melki J.
        Spinal muscular atrophy associated with progressive myoclonic epilepsy is caused by mutations in ASAH1.
        Am J Hum Genet. 2012; 91: 5-14
        • Li G.
        • Kidd J.
        • Kaspar C.
        • Dempsey S.
        • Bhat O.M.
        • Camus S.
        • Ritter J.K.
        • Gehr T.W.B.
        • Gulbins E.
        • Li P.L.
        Podocytopathy and nephrotic syndrome in mice with podocyte-specific deletion of the Asah1 gene: role of ceramide accumulation in glomeruli.
        Am J Pathol. 2020; 190: 1211-1223
        • Bellomo G.
        • Paciotti S.
        • Gatticchi L.
        • Parnetti L.
        The vicious cycle between α-synuclein aggregation and autophagic-lysosomal dysfunction.
        Mov Disord. 2020; 35: 34-44
        • Gatt S.
        Enzymic hydrolysis and synthesis of ceramides.
        J Biol Chem. 1963; 238: 3131-3133
        • Govindarajah N.
        • Clifford R.
        • Bowden D.
        • Sutton P.A.
        • Parsons J.L.
        • Vimalachandran D.
        Sphingolipids and acid ceramidase as therapeutic targets in cancer therapy.
        Crit Rev Oncol Hematol. 2019; 138: 104-111
        • Ponnusamy S.
        • Meyers-Needham S.
        • Senkal C.E.
        • Saddoughi S.A.
        • Sentelle D.
        • Selvam S.P.
        • Salas A.
        • Ogretmen B.
        Sphingolipids and cancer: ceramide and sphingosine-1-phosphate in the regulation of cell death and drug resistance.
        Future Oncol. 2010; 6: 1603-1624
        • Ogretmen B.
        Sphingolipid metabolism in cancer signalling and therapy.
        Nat Rev Cancer. 2018; 18: 33-50
        • Roh J.L.
        • Park J.Y.
        • Kim E.H.
        • Jang H.J.
        Targeting acid ceramidase sensitises head and neck cancer to cisplatin.
        Eur J Cancer. 2016; 52: 163-172
        • Lai M.
        • Realini N.
        • La Ferla M.
        • Passalacqua I.
        • Matteoli G.
        • Ganesan A.
        • Pistello M.
        • Mazzanti C.M.
        • Piomelli D.
        Complete acid ceramidase ablation prevents cancer-initiating cell formation in melanoma cells.
        Sci Rep. 2017; 7: 7411
        • Hanker L.C.
        • Karn T.
        • Holtrich U.
        • Gätje R.
        • Rody A.
        • Heinrich T.
        • Ruckhäberle E.
        • Engels K.
        Acid ceramidase (AC)–a key enzyme of sphingolipid metabolism–correlates with better prognosis in epithelial ovarian cancer.
        Int J Gynecol Pathol. 2013; 32: 249-257
        • Yu F.P.S.
        • Amintas S.
        • Levade T.
        • Medin J.A.
        Acid ceramidase deficiency: farber disease and SMA-PME.
        Orphanet J Rare Dis. 2018; 13: 121
        • Chavez J.A.
        • Summers S.A.A.
        Ceramide-centric view of insulin resistance.
        Cell Metab. 2012; 15: 585-594
        • Ruvolo P.P.
        • Deng X.
        • Ito T.
        • Carr B.K.
        • May W.S.
        Ceramide induces Bcl2 dephosphorylation via a mechanism involving mitochondrial PP2A.
        J Biol Chem. 1999; 274: 20296-20300
        • Weinberg J.M.
        Lipotoxicity.
        Kidney Int. 2006; 70: 1560-1566
        • Guebre-Egziabher F.
        • Alix P.M.
        • Koppe L.
        • Pelletier C.C.
        • Kalbacher E.
        • Fouque D.
        • Soulage C.O.
        Ectopic lipid accumulation: a potential cause for metabolic disturbances and a contributor to the alteration of kidney function.
        Biochimie. 2013; 95: 1971-1979
        • Choi S.R.
        • Lim J.H.
        • Kim M.Y.
        • Kim E.N.
        • Kim Y.
        • Choi B.S.
        • Kim Y.S.
        • Kim H.W.
        • Lim K.M.
        • Kim M.J.
        • Park C.W.
        Adiponectin receptor agonist AdipoRon decreased ceramide, and lipotoxicity, and ameliorated diabetic nephropathy.
        Metabolism. 2018; 85: 348-360
        • Najafian B.
        • Tøndel C.
        • Svarstad E.
        • Gubler M.C.
        • Oliveira J.P.
        • Mauer M.
        Accumulation of globotriaosylceramide in podocytes in fabry nephropathy is associated with progressive podocyte loss.
        J Am Soc Nephrol. 2020; 31: 865-875
        • Fornoni A.
        • Sageshima J.
        • Wei C.
        • Merscher-Gomez S.
        • Robier A.P.
        • Jauregui A.N.
        • Li J.
        • Mattiazzi A.
        • Ciancio G.
        • Chen L.
        • Zilleruelo G.
        • Abitbol C.
        • Chandar J.
        • Seeherunvong W.
        • Ricordi C.
        • Ikehata M.
        • Rastaldi M.P.
        • Reiser J.
        • Burke G.W.
        Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis.
        Sci Transl Med. 2011; 3: 85ra46

      Linked Article