Inhibition of Jumonji demethylases reprograms severe dilated cardiomyopathy and prolongs survival

Hypertrophic/dilated cardiomyopathy, often a prequel to heart failure, is accompanied by maladaptive transcriptional changes that contribute to arrythmias and contractile misfunction. Transgenic mice constitutively expressing high levels of calcineurin are known to develop extreme heart hypertrophy, which progresses to dilated cardiomyopathy, and to die several weeks after birth. Here, we characterized aberrant transcriptional and epigenetic pathways in this mouse model and established a pharmacological approach to treat established cardiomyopathy. We found that H3K4me3 (trimethyl histone 3 lysine 4) and H3K9me3 (trimethyl histone 3 lysine 9) Jumonji histone demethylases are markedly increased at the protein level and show enhanced enzymatic activity in diseased hearts. These epigenetic regulators continued to increase with time, further affecting cardiac gene expression. Our findings parallel the lower H3K4me3 and H3K9me3 levels seen in human patients. Inhibition of Jumonji demethylase activities in vivo results in lower histone demethylase enzymatic function in the heart and higher histone methylation levels and leads to partial reduction of heart size, reversal of maladaptive transcriptional programs, improved heart function, and prolonged survival. At the molecular level, target genes of transcription factor myocyte enhancer factor 2 are specifically regulated in response to pharmacological or genetic inhibition of Jumonji demethylases. Similar transcriptional reversal of disease-associated genes is seen in a second disease model based on cardiac mechanical overload. Our findings validate pharmacological inhibitors of Jumonji demethylases as potential therapeutics for the treatment of cardiomyopathies across disease models and provide evidence of the reversal of maladaptive transcriptional reprogramming leading to partial restoration of cardiac function. In addition, this study defines pathways of therapeutic resistance upregulated with disease progression.

Abstract 261: Robust Cardioprotection Afforded by a Previously Unrecognized Link between the Unfolded Protein Response and the Hexosamine Biosynthetic Pathway

Background: The hexosamine biosynthetic pathway (HBP) generates UDP-GlcNAc (uridine diphosphate N-acetylglucosamine) for glycan synthesis and O-linked GlcNAc (O-GlcNAc) protein modifications. Despite the established role of the HBP in glucose metabolism and multiple diseases, regulation of the HBP remains largely undefined.

Methods & Results: Here, we show that spliced Xbp1 (Xbp1s), the most conserved signal transducer of the unfolded protein response (UPR), is a direct transcriptional activator of the HBP. We demonstrate that the UPR triggers activation of the HBP by means of Xbp1s-dependent transcription of genes coding for key, rate-limiting enzymes. We establish that this previously unrecognized UPR-HBP axis is triggered in a variety of stress conditions known to promote O-GlcNAc modification. We go on to demonstrate that Xbp1s, acutely stimulated by ischemia/reperfusion (I/R) in heart, confers robust cardioprotection against I/R injury. We also show that HBP induction is required for this cardioprotective response. Mechanistically, HBP may mediate the adaptive branch of the UPR by activating autophagy and ER-associated degradation.

Conclusion: These studies reveal that Xbp1s couples the UPR to the HBP, promoting robust cardioprotection during I/R.

Misdiagnosis of Hydrophilic Acrylic Intraocular Lens Optic Opacification

PURPOSE

To report 8 patients with misdiagnosis of MemoryLens intraocular lens (IOL) late postoperative calcification and the resulting potentially avoidable procedures leading to secondary complications.

DESIGN

Retrospective interventional case series.

PARTICIPANTS

Eight patients with an opacified hydrophilic acrylic MemoryLens.

METHODS

Eight cases of MemoryLens IOL opacification that were originally misdiagnosed were reviewed. The following parameters were noted: baseline patient characteristics, time frame of IOL opacification, original misdiagnosis, subsequent surgical procedures, and postexplantation outcomes and complications. Two explanted lenses from this series were available for laboratory analyses. They underwent gross and light microscopic evaluation and scanning electron microscopy with energy-dispersive x-ray spectroscopy (EDS).

MAIN OUTCOME MEASURES

Patient parameters noted above. The IOLs were examined for distribution, structure, and composition of the deposits causing opacification of their optic components.

RESULTS

All 8 patients' IOLs were implanted between August 1999 and March 2000. Complaints of decreased visual function occurred 13 to 58 months after implantation. Half of the patients were initially diagnosed as having posterior capsular opacification and underwent neodymium:yttrium-aluminum-garnet laser capsulotomy. The other half were initially diagnosed with some form of vitreous involvement and underwent vitrectomies. Six of the 8 patients underwent subsequent lens exchanges, with 3 of them having postexchange complications including endophthalmitis, cystoid macular edema, and retinal detachment. Scanning electron microscopy with EDS confirmed the presence of calcified deposits on the surface of the 2 explants available for analysis. The deposits also stained positive for calcium.

CONCLUSIONS

Despite previous reports, misdiagnosis of MemoryLens IOL calcification leading to optic opacification still occurs. Not recognizing this process can lead to potentially avoidable surgical procedures and increased risk of complications after repeated interventions.

The role of the proteasomal ATPases and activator monoubiquitylation in regulating Gal4 binding to promoters

Recent studies have shown that the intersection between transcription and proteins involved in the ubiquitin-proteasome pathway encompasses both proteolytic and nonproteolytic functions. Examples of the latter type include evidence that monoubiquitylation of some transcriptional activators stimulates their activity. In addition, the proteasomal ATPases are recruited to many active promoters through binding to activators and play an important, nonproteolytic role in promoter escape and elongation. In this study, we report the discovery of a new nonproteolytic activity of the proteasome (specifically the proteasomal ATPases): the active destabilization of activator-promoter complexes. This reaction depends on the presence of an activation domain and ATP. Destabilization is inhibited in vitro and in vivo if the protein is monoubiquitylated or if ubiquitin is genetically fused to the activator. The fact that monoubiquitylated activator is resistant to the "stripping" activity of the proteasomal ATPases may explain, in part, why some activators require this modification in order to function efficiently.

Correlates of high-density lipoprotein cholesterol in black and white women

The relationships of high-density lipoprotein (HDL) cholesterol with body composition, leisure-time physical activity, cigarette smoking, and education were examined in a community-based sample of 480 Black and 1337 White women. Univariate and multivariate analyses indicated inverse associations of HDL with body mass index and waist-to-hip ratio in both groups, and with cigarette smoking and low educational attainment among White women only. Since correlates of HDL cholesterol differ for Black and White women, further investigation of the differences in these correlates is warranted.

Recognition of model DNA replication forks by the SV40 large tumor antigen

The ability of the SV40 large tumor antigen (T antigen), a DNA helicase, to bind to model DNA replication forks was tested. DNA fork molecules were constructed either from two partially complementary oligonucleotides or from a single oligonucleotide able to form a 'panhandle' structure. T antigen specifically recognized the two-strand fork in a reaction dependent on the presence of ATP, dATP, or non-hydrolyzable analogs of ATP. T antigen asymmetrically bound the two-strand fork, protecting from nuclease cleavage a fork-proximal region on only one of the two strands. The asymmetric binding is consistent with the 3'-->5' directionality of the DNA helicase activity of T antigen. An analogous region on the one-strand fork was also bound by T antigen, suggesting that T antigen does not require a free single-stranded end to load onto the fork. Use of chemically modified DNA substrates indicated that T antigen binding to the fork utilized important contacts with the DNA sugar-phosphate backbone.