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Altering a histone H3K4 methylation pathway in glomerular podocytes promotes a chronic disease phenotype.

Lefevre GM, Patel SR, Kim D, Tessarollo L, Dressler GR - PLoS Genet. (2010)

Bottom Line: Loss of PTIP resulted in subtle changes in gene expression patterns prior to the onset of a renal disease phenotype.Chromatin immunoprecipitation showed a loss of PTIP binding and lower H3K4 methylation at the Ntrk3 (neurotrophic tyrosine kinase receptor, type 3) locus, whose expression was significantly reduced and whose function may be essential for podocyte foot process patterning.These data demonstrate that alterations or mutations in an epigenetic regulatory pathway can alter the phenotypes of differentiated cells and lead to a chronic disease state.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Methylation of specific lysine residues in core histone proteins is essential for embryonic development and can impart active and inactive epigenetic marks on chromatin domains. The ubiquitous nuclear protein PTIP is encoded by the Paxip1 gene and is an essential component of a histone H3 lysine 4 (H3K4) methyltransferase complex conserved in metazoans. In order to determine if PTIP and its associated complexes are necessary for maintaining stable gene expression patterns in a terminally differentiated, non-dividing cell, we conditionally deleted PTIP in glomerular podocytes in mice. Renal development and function were not impaired in young mice. However, older animals progressively exhibited proteinuria and podocyte ultra structural defects similar to chronic glomerular disease. Loss of PTIP resulted in subtle changes in gene expression patterns prior to the onset of a renal disease phenotype. Chromatin immunoprecipitation showed a loss of PTIP binding and lower H3K4 methylation at the Ntrk3 (neurotrophic tyrosine kinase receptor, type 3) locus, whose expression was significantly reduced and whose function may be essential for podocyte foot process patterning. These data demonstrate that alterations or mutations in an epigenetic regulatory pathway can alter the phenotypes of differentiated cells and lead to a chronic disease state.

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Ultrastructural Analysis of PTIP− Kidneys.Podocytes of PTIP− mice showed progressive foot process disorganization and effacement, as observed by scanning (A–C, G, H) and transmission (D–F, I, J) electron microscopy. Podocyte foot processes of 3-month-old PTIP+ mice were regularly interdigitated (A, D, G), whereas those of age-matched PTIP− podocytes (B, C, E, F, H) displayed varying degrees of disorganization (B, E) and effacement (C, F). Note that slit diaphragms could still be observed between foot processes during the early stages of disorganization (E, arrows). G–J) In addition to the foot process alterations, capillary loop deformation/enlargement (H, J) and mesangium expansion (J, asterisks) were observed in glomeruli of 12-month-old (G, H) and 3-month-old (I, J) mice analyzed by EM. Scale bars: (A–C) 1 µm; (D–F) 100 nm; (G–J) 2 µm.
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pgen-1001142-g004: Ultrastructural Analysis of PTIP− Kidneys.Podocytes of PTIP− mice showed progressive foot process disorganization and effacement, as observed by scanning (A–C, G, H) and transmission (D–F, I, J) electron microscopy. Podocyte foot processes of 3-month-old PTIP+ mice were regularly interdigitated (A, D, G), whereas those of age-matched PTIP− podocytes (B, C, E, F, H) displayed varying degrees of disorganization (B, E) and effacement (C, F). Note that slit diaphragms could still be observed between foot processes during the early stages of disorganization (E, arrows). G–J) In addition to the foot process alterations, capillary loop deformation/enlargement (H, J) and mesangium expansion (J, asterisks) were observed in glomeruli of 12-month-old (G, H) and 3-month-old (I, J) mice analyzed by EM. Scale bars: (A–C) 1 µm; (D–F) 100 nm; (G–J) 2 µm.

Mentions: At the light microscopy level, the effects of PTIP loss on glomerular architecture seemed minimal at 3 months of age, yet the levels of albumin in the urine suggested significant functional defects. Thus, we utilized scanning and transmission electron microscopy to characterize the podocytes at the ultra structural level (Figure 4). Scanning electron micrographs revealed disorganized foot processes at 3 months. While PTIP+ podocytes had regularly arrayed tertiary foot-processes that were almost parallel (Figure 4A), the PTIP− podocyte foot processes were much more irregular and flattened. The parallel pattern of interdigitation was clearly different and resembled a jigsaw puzzle with random patterning (Figure 4B, 4C). Transmission electron micrographs at 3 months also revealed that the slit-diaphragms were not evenly spaced and fusion of foot processes was frequent (Figure 4D–4F). By 12 months, the remaining podocytes in the PTIP− kidneys were broader, flatter and displayed significant fusion or effacement (Figure 4G, 4H), consistent with the high levels of albumin detected in the urine. These data demonstrate that the initial glomerular phenotype in PTIP− kidneys is due primarily to differences in podocyte foot process morphology, which occurs prior to the loss of cell bodies.


Altering a histone H3K4 methylation pathway in glomerular podocytes promotes a chronic disease phenotype.

Lefevre GM, Patel SR, Kim D, Tessarollo L, Dressler GR - PLoS Genet. (2010)

Ultrastructural Analysis of PTIP− Kidneys.Podocytes of PTIP− mice showed progressive foot process disorganization and effacement, as observed by scanning (A–C, G, H) and transmission (D–F, I, J) electron microscopy. Podocyte foot processes of 3-month-old PTIP+ mice were regularly interdigitated (A, D, G), whereas those of age-matched PTIP− podocytes (B, C, E, F, H) displayed varying degrees of disorganization (B, E) and effacement (C, F). Note that slit diaphragms could still be observed between foot processes during the early stages of disorganization (E, arrows). G–J) In addition to the foot process alterations, capillary loop deformation/enlargement (H, J) and mesangium expansion (J, asterisks) were observed in glomeruli of 12-month-old (G, H) and 3-month-old (I, J) mice analyzed by EM. Scale bars: (A–C) 1 µm; (D–F) 100 nm; (G–J) 2 µm.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2965754&req=5

pgen-1001142-g004: Ultrastructural Analysis of PTIP− Kidneys.Podocytes of PTIP− mice showed progressive foot process disorganization and effacement, as observed by scanning (A–C, G, H) and transmission (D–F, I, J) electron microscopy. Podocyte foot processes of 3-month-old PTIP+ mice were regularly interdigitated (A, D, G), whereas those of age-matched PTIP− podocytes (B, C, E, F, H) displayed varying degrees of disorganization (B, E) and effacement (C, F). Note that slit diaphragms could still be observed between foot processes during the early stages of disorganization (E, arrows). G–J) In addition to the foot process alterations, capillary loop deformation/enlargement (H, J) and mesangium expansion (J, asterisks) were observed in glomeruli of 12-month-old (G, H) and 3-month-old (I, J) mice analyzed by EM. Scale bars: (A–C) 1 µm; (D–F) 100 nm; (G–J) 2 µm.
Mentions: At the light microscopy level, the effects of PTIP loss on glomerular architecture seemed minimal at 3 months of age, yet the levels of albumin in the urine suggested significant functional defects. Thus, we utilized scanning and transmission electron microscopy to characterize the podocytes at the ultra structural level (Figure 4). Scanning electron micrographs revealed disorganized foot processes at 3 months. While PTIP+ podocytes had regularly arrayed tertiary foot-processes that were almost parallel (Figure 4A), the PTIP− podocyte foot processes were much more irregular and flattened. The parallel pattern of interdigitation was clearly different and resembled a jigsaw puzzle with random patterning (Figure 4B, 4C). Transmission electron micrographs at 3 months also revealed that the slit-diaphragms were not evenly spaced and fusion of foot processes was frequent (Figure 4D–4F). By 12 months, the remaining podocytes in the PTIP− kidneys were broader, flatter and displayed significant fusion or effacement (Figure 4G, 4H), consistent with the high levels of albumin detected in the urine. These data demonstrate that the initial glomerular phenotype in PTIP− kidneys is due primarily to differences in podocyte foot process morphology, which occurs prior to the loss of cell bodies.

Bottom Line: Loss of PTIP resulted in subtle changes in gene expression patterns prior to the onset of a renal disease phenotype.Chromatin immunoprecipitation showed a loss of PTIP binding and lower H3K4 methylation at the Ntrk3 (neurotrophic tyrosine kinase receptor, type 3) locus, whose expression was significantly reduced and whose function may be essential for podocyte foot process patterning.These data demonstrate that alterations or mutations in an epigenetic regulatory pathway can alter the phenotypes of differentiated cells and lead to a chronic disease state.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Methylation of specific lysine residues in core histone proteins is essential for embryonic development and can impart active and inactive epigenetic marks on chromatin domains. The ubiquitous nuclear protein PTIP is encoded by the Paxip1 gene and is an essential component of a histone H3 lysine 4 (H3K4) methyltransferase complex conserved in metazoans. In order to determine if PTIP and its associated complexes are necessary for maintaining stable gene expression patterns in a terminally differentiated, non-dividing cell, we conditionally deleted PTIP in glomerular podocytes in mice. Renal development and function were not impaired in young mice. However, older animals progressively exhibited proteinuria and podocyte ultra structural defects similar to chronic glomerular disease. Loss of PTIP resulted in subtle changes in gene expression patterns prior to the onset of a renal disease phenotype. Chromatin immunoprecipitation showed a loss of PTIP binding and lower H3K4 methylation at the Ntrk3 (neurotrophic tyrosine kinase receptor, type 3) locus, whose expression was significantly reduced and whose function may be essential for podocyte foot process patterning. These data demonstrate that alterations or mutations in an epigenetic regulatory pathway can alter the phenotypes of differentiated cells and lead to a chronic disease state.

Show MeSH
Related in: MedlinePlus