Epigenetics and cell death: DNA hypermethylation in programmed retinal cell death.

BackgroundVertebrate genomes undergo epigenetic reprogramming during development and disease. Emerging evidence suggests that DNA methylation plays a key role in cell fate determination in the retina. Despite extensive studies of the programmed cell death that occurs during retinal development and degeneration, little is known about how DNA methylation might regulate neuronal cell death in the retina.MethodsThe developing chicken retina and the rd1 and rhodopsin-GFP mouse models of retinal degeneration were used to investigate programmed cell death during retinal development and degeneration. Changes in DNA methylation were determined by immunohistochemistry using antibodies against 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC).ResultsPunctate patterns of hypermethylation paralleled patterns of caspase3-dependent apoptotic cell death previously reported to occur during development in the chicken retina. Degenerating rd1 mouse retinas, at time points corresponding to the peak of rod cell death, showed elevated signals for 5mC and 5hmC in photoreceptors throughout the retina, with the most intense staining observed in the peripheral retina. Hypermethylation of photoreceptors in rd1 mice was associated with TUNEL and PAR staining and appeared to be cCaspase3-independent. After peak rod degeneration, during the period of cone death, occasional hypermethylation was observed in the outer nuclear layer.ConclusionThe finding that cell-specific increases of 5mC and 5hmC immunostaining are associated with the death of retinal neurons during both development and degeneration suggests that changes in DNA methylation may play a role in modulating gene expression during the process of retinal degeneration. During retinal development, hypermethylation of retinal neurons associates with classical caspase-dependent apoptosis as well as caspase-3 independent cell death, while hypermethylation in the rd1 mouse photoreceptors is primarily associated with caspase-3 independent programmed cell death. These findings suggest a previously unrecognized role for epigenetic mechanisms in the onset and/or progression of programed cell death in the retina

Membrane-associated heparan sulfate is not required for rAAV-2 infection of human respiratory epithelia

BACKGROUND: Adeno-associated virus type 2 (AAV-2) attachment and internalization is thought to be mediated by host cell membrane-associated heparan sulfate proteoglycans (HSPG). Lack of HSPG on the apical membrane of respiratory epithelial cells has been identified as a reason for inefficient rAAV-2 infection in pulmonary applications in-vivo. The aim of this investigation was to determine the necessity of cell membrane HSPG for efficient infection by rAAV-2. RESULTS: Rates of transduction with rAAV2-CMV-EGFP3 in several different immortalized airway epithelial cell lines were determined at different multiplicities of infection (MOI) before and after removal of membrane HSPG by heparinase III. Removal of HSPG decreased the efficacy of infection with rAAV2 by only 30–35% at MOI ≤ 100 for all of respiratory cell lines tested, and had even less effect at an MOI of 1000. Studies in mutant Chinese Hamster Ovary cell lines known to be completely deficient in surface HSPG also demonstrated only moderate effect of absence of HSPG on rAAV-2 infection efficacy. However, mutant CHO cells lacking all membrane proteoglycans demonstrated dramatic reduction in susceptibility to rAAV-2 infection, suggesting a role of membrane glycosaminoglycans other than HSPG in mediating rAAV-2 infection. CONCLUSION: Lack of cell membrane HSPG in pulmonary epithelia and other cell lines results in only moderate decrease in susceptibility to rAAV-2 infection, and this decrease may be less important at high MOIs. Other cell membrane glycosaminoglycans can play a role in permitting attachment and subsequent rAAV-2 internalization. Targeting alternative membrane glycosaminoglycans may aid in improving the efficacy of rAAV-2 for pulmonary applications

Functional genomic screening identifies dual leucine zipper kinase as a key mediator of retinal ganglion cell death

Glaucoma, a major cause of blindness worldwide, is a neurodegenerative optic neuropathy in which vision loss is caused by loss of retinal ganglion cells (RGCs). To better define the pathways mediating RGC death and identify targets for the development of neuroprotective drugs, we developed a high-throughput RNA interference screen with primary RGCs and used it to screen the full mouse kinome. The screen identified dual leucine zipper kinase (DLK) as a key neuroprotective target in RGCs. In cultured RGCs, DLK signaling is both necessary and sufficient for cell death. DLK undergoes robust posttranscriptional up-regulation in response to axonal injury in vitro and in vivo. Using a conditional knockout approach, we confirmed that DLK is required for RGC JNK activation and cell death in a rodent model of optic neuropathy. In addition, tozasertib, a small molecule protein kinase inhibitor with activity against DLK, protects RGCs from cell death in rodent glaucoma and traumatic optic neuropathy models. Together, our results establish a previously undescribed drug/drug target combination in glaucoma, identify an early marker of RGC injury, and provide a starting point for the development of more specific neuroprotective DLK inhibitors for the treatment of glaucoma, nonglaucomatous forms of optic neuropathy, and perhaps other CNS neurodegenerations

TERF Wars: Introduction

No abstract available

Small RNAs Prevent Transcription-Coupled Loss of Histone H3 Lysine 9 Methylation in Arabidopsis thaliana

In eukaryotes, histone H3 lysine 9 methylation (H3K9me) mediates silencing of invasive sequences to prevent deleterious consequences including the expression of aberrant gene products and mobilization of transposons. In Arabidopsis thaliana, H3K9me maintained by SUVH histone methyltransferases (MTases) is associated with cytosine methylation (5meC) maintained by the CMT3 cytosine MTase. The SUVHs contain a 5meC binding domain and CMT3 contains an H3K9me binding domain, suggesting that the SUVH/CMT3 pathway involves an amplification loop between H3K9me and 5meC. However, at loci subject to read-through transcription, the stability of the H3K9me/5meC loop requires a mechanism to counteract transcription-coupled loss of H3K9me. Here we use the duplicated PAI genes, which stably maintain SUVH-dependent H3K9me and CMT3-dependent 5meC despite read-through transcription, to show that when PAI sRNAs are depleted by dicer ribonuclease mutations, PAI H3K9me and 5meC levels are reduced and remaining PAI 5meC is destabilized upon inbreeding. The dicer mutations confer weaker reductions in PAI 5meC levels but similar or stronger reductions in PAI H3K9me levels compared to a cmt3 mutation. This comparison indicates a connection between sRNAs and maintenance of H3K9me independent of CMT3 function. The dicer mutations reduce PAI H3K9me and 5meC levels through a distinct mechanism from the known role of dicer-dependent sRNAs in guiding the DRM2 cytosine MTase because the PAI genes maintain H3K9me and 5meC at levels similar to wild type in a drm2 mutant. Our results support a new role for sRNAs in plants to prevent transcription-coupled loss of H3K9me

Other retinal degeneration models with elevated 5mC levels.

<p>(A) P24 rhoGFP homozygous mice with sporadic PR loss with 5mC staining (magenta) in the ONL (green = GFP in rods). (B–C) Subcellular localization of 5mC (magenta; B) enveloped within a photoreceptor cell body expressing GFP (green; C). (D–F) 5mC staining of a wild type one month-old mouse retina explant undergoing progressive photoreceptor degeneration after 4, 7 and 9 days in vitro (DIV), respectively. ONL = outer nuclear layer; INL = inner nuclear layer; GCL = ganglion cell layer. Scale bars = 20 µM (A) and 100 µM (F).</p

Comparison of cCaspase3 and TUNEL co-labeling with 5mC in the developing chicken retina.

<p>(A) Low magnification of 5mC and cCaspase3 staining at E11. (B) Nuclear counterstaining of a low magnification section. (C) 5mC and (D) cCaspase3 staining. Colocalization of 5mC (+) and cCaspase3 (+) cells indicated by white arrows overlaid in (E). Dark arrows indicate 5mC (+) cells that are cCaspase3 (−). (F) 5mC and (G) TUNEL staining at E11. (H) Co-localization indicated by white arrows. TUNEL (+) but 5mC (−) indicated by a dark arrow. ONL = outer nuclear layer; INL = inner nuclear layer; IPL = inner plexiform layer; GCL = ganglion cell layer. Scale bars = 100 µM in A–B; 75 µM in C–H.</p

Cell death markers double labeled with 5mC (+) or 5hmC (+) photoreceptors in <i>rd1</i> mouse retinas.

<p>Retinas from P14 <i>rd1</i> mice were double-labeled with TUNEL stain (A, D and G) and 5mC (B and E) or 5hmC (H) with central (A–C, G–I) and peripheral retina (D–F) shown accordingly. Discrete signals for cCaspase3 (J) and 5mC (K) labeling show virtually no overlap in signals (L). Overlap in signals are indicated by white arrows as shown in panels C, F and I. Cells labeled with one marker but not the other are indicated with dark vertical arrows. ONL = outer nuclear layer; INL = inner nuclear layer; GCL = ganglion cell layer. Scale bars = 50 µM.</p

5mC accumulation in the early developing chicken embryo.

<p>(A1) A diagram indicating the relative cross sectioned region of tissues studied (lowercase letters correspond to the respective panels below). (A2) A representative embryo at E3.5. (B) 5mC deposits in neurons lining the midbrain optic tectum and (C) a region corresponding to the developing heart. (D) The region adjacent to the neural tube (nt), notochord (nc) and aorta (a). (E1 & F1) Hoechst nuclear counterstained retinal sections correspond to sections in E2 and F2, respectively. (E2) 5mC in the developing retina, lens and surrounding mesenchyme. (F2) 5hmC in the developing retina. Arrows indicate 5mC (+) and 5hmC (+) cells. Scale bars = 100 µM in D, 75 µM in E2 and 50 µM in F2.</p