DNA content, chromatin supraorganization, nuclear glycoproteins and RNA amounts in hepatocytes of mice expressing insulin-dependent diabetes

Reduction in Histone H3 Acetylation and Chromatin Remodeling in Corneas of Alloxan-Induced Diabetic Rats

PURPOSE

To evaluate acetylation of histone H3, chromatin remodeling, nuclear size and shape, DNA ploidy, and distribution of nucleolus organizing regions (NORs) in corneal epithelial and stromal cells of diabetic and nondiabetic rats.

METHODS

Diabetes was induced by a single intraperitoneal injection of alloxan. All diabetic rats (n = 20) included in the study had 4 weeks of moderate-to-severe hyperglycemia (plasma glucose levels >400 mg/dL). Acetylated histone H3 levels were quantified in corneal tissue using a colorimetric assay. Chromatin remodeling, nuclear sizes (area/perimeter) and shapes (circularity), and DNA ploidies were evaluated from Feulgen-stained tissue sections using video image analysis. Distributions of NORs were studied in tissue sections impregnated with silver ions. Ophthalmic clinical parameters, including corneal sensitivity, were investigated. Twenty nondiabetic rats were used as controls.

RESULTS

Acetylation of histone H3 was reduced in the corneas of the diabetic rats. Nuclei in corneal epithelial cells of diabetic rats compacted chromatin, increased in size, modified their shapes, and elevated DNA ploidy. The only nuclear change observed in the corneal stromal cells of diabetic rats was chromatin decompaction. The size of the silver-stained NOR did not differ between the study samples. The corneal sensitivity in diabetic rats was 51.8% lower than that in nondiabetic rats.

CONCLUSIONS

The results of this study show that alloxan-induced diabetes altered the histone H3 acetylation pattern and compromised the chromatin supraorganization in corneal tissue/cells. Continued research is needed to understand the clinical and morphofunctional significance of changes in corneal cell nuclei of diabetic individuals.

Polyploidy and nuclear phenotype characteristics of cardiomyocytes from diabetic adult and normoglycemic aged mice

The frequency of polyploid nuclei in the aging human heart is in sharp contrast with that in the human liver. An inverse pattern exists between the mouse heart and liver cells. Ploidy degrees in mouse hepatocytes under hyperglycemic conditions are elevated to higher levels than those in aged hepatocytes. In this study, image analysis cytometry was used to investigate the effect of diabetes and aging on Feulgen-DNA quantities, ploidy degrees, nuclear shapes and chromatin texture in mouse cardiomyocytes compared to previously reported data for mouse hepatocytes. Adult, non-obese diabetic (NOD) hyperglycemic and normoglycemic females and 56-week-old normoglycemic BALB/c females were used. A small percentage (∼7%) of the cardiomyocyte nuclei in severely hyperglycemic NOD adult mice possessed higher ploidy values than those in the 8-week-old normoglycemic mice. Surprisingly, the Feulgen-DNA values and the frequency of nuclei belonging to the 4C and 8C ploidy classes were even higher (∼6%) in normoglycemic NOD specimens than in age-matched hyperglycemic NOD specimens. Additionally, a pronounced elongated nuclear shape was observed especially in adult normoglycemic NOD mice. In conclusion, NOD mice, irrespective of their glycemic level, exhibit a moderate increase in ploidy degrees within cardiomyocyte nuclei during the adult lifetime. As expected, aging did not affect the Feulgen-DNA values and the ploidy degrees of cardiomyocytes in BALB/c mice. The differences in ploidy degrees and chromatin textures such as absorbance variability and entropy, between adult NOD and aged BALB/c mice are consistent with other reports, indicating dissimilarities in chromatin functions between diabetes and aging.

Short-Term Effects of Y-27632, a Rho-Associated Protein Kinase Inhibitor, on Chromatin Supraorganization and DNA Amount in Epithelial Cells of the Rat Cornea and Limbus

PURPOSE

To assess the short-term effects of instilling Y-27632, an inhibitor of Rho/Rho-associated protein kinases, on the chromatin supraorganization and DNA amount of corneal and limbal epithelial cells of healthy rats.

METHODS

Longitudinal sections (7 μm) of enucleated eyes of healthy rats that received, by instillation, balanced salt solution with or without 10 mM of Y-27632 daily for 7 or 15 days, were subjected to the Feulgen reaction. Feulgen-stained nuclei of corneal and limbal epithelial cells were studied by microscopy and video image analysis to establish the nuclear size (area and perimeter), supraorganization of chromatin (texture and degrees of condensation), and the Feulgen-DNA amount.

RESULTS

Instillation of Y-27632 for up to 15 days did not change the size of the nucleus or the chromatin texture of corneal and limbal epithelial cells. Samples treated with Y-27632 for 7 days showed condensed chromatin and a high Feulgen-DNA amount. Both corneal and limbal epithelium showed the presence of near-tetraploid nuclei corresponding to cells in the S and G2 phases of the cell cycle. The degrees of condensation and Feulgen-DNA amount of the nuclei of epithelial cells of the cornea and limbus of eyes from rats receiving Y-27632 for 15 days did not differ from control (no drug).

CONCLUSIONS

Changes in chromatin supraorganization and DNA amount, such as seen in this study, are indicative of cell proliferation and do not seem to be associated with disturbances in gene activity and transcription of DNA.

Polarization microscopy of extended chromatin fibers

Analysis of the formation of extended chromatin fibers (ECFs) in response to the action of gravity following lysis by hypertonic and detergent solutions is a useful technical procedure relevant for studies of the positioning of particular DNA signals on chromatin filaments. Additionally, if toluidine blue molecules are allowed to bind electrostatically to available DNA phosphates on ECFs, the birefringence brightness generated in these filaments, as observed by polarization microscopy, facilitates the description of the frequency of ECF formation and extension of the chromatin filaments generated. Thus, different patterns of DNA-nuclear matrix protein associations related to varying transcriptional activities and chromatin organization in isolated cells can be assessed. A technique for producing ECFs in different isolated cell types under variable physiological and/or pathological conditions is detailed in this chapter.

Effects of hyperglycemia and aging on nuclear sirtuins and DNA damage of mouse hepatocytes

In normal aging, nuclear sirtuin levels decline and specific histone acetylation increases. In diabetic mice, Sirt1 and Sirt6 levels increase, which may induce gluconeogenesis through the PGC-1α pathway and DNA repair of the oxidative damage caused by hyperglycemia.

Hyperglycemia, like aging, induces chromatin remodeling in mouse hepatocytes in comparison to normoglycemia and younger age, respectively. Changes in glucose metabolism also affect the action and expression of sirtuins, promoting changes in chromatin conformation and dynamics. Here we investigate the abundance and activity of the nuclear sirtuins Sirt1, Sirt6, and Sirt7 in mouse hepatocytes in association with specific histone acetylation, DNA damage, and the activation of nucleolar organizing regions (NORs) in hyperglycemic nonobese diabetic (NOD) and old normoglycemic BALB/c mouse strains. Higher levels of Sirt1 and PGC-1α and increased expression of gluconeogenesis pathway genes are found in the hyperglycemic NOD mice. Increased Sirt6 abundance is found in the hyperglycemic NOD mice, which might increase DNA damage repair. With aging, lower Sirt1 abundance and activity, increased acetylated histone modifications and Sirt7 levels, and NOR methylation are found. Thus, whereas in normal aging cell metabolism is reduced, in the diabetic mice a compensatory mechanism may elevate Sirt1 and Sirt6 levels, increasing gluconeogenesis and DNA repair from the oxidative damage caused by hyperglycemia. Therefore understanding the regulation of epigenetic factors in diabetes and aging is crucial for the development of new therapeutic approaches that could prevent diseases and improve quality of life.

Polyploidy and chromatin remodeling in hepatocytes from insulin-dependent diabetic and normoglycemic aged mice

Changes in polyploidization, chromatin supraorganization, and chromatin accessibility were investigated in hepatocytes collected from adult, nonobese diabetic (NOD) mice with increasing hyperglycemia and compared with adult normoglycemic controls and 56-week-old normoglycemic BALB/c mice. Our goal was to determine the changes in ploidy degrees and chromatin characteristics in mouse hepatocytes that are associated with insulin-dependent diabetes and to detect similarities in these aspects with those verified with aging, with greater accuracy than previous studies. Image analysis of Feulgen-stained nuclei revealed changes in ploidy degrees and chromatin supraorganization. Chromatin accessibility was assessed with micrococcal nuclease (MNase) digestion. Increased polyploidy was associated with increasing levels of glycemia, and this trend toward polyploidy was found even under normoglycemic conditions in NOD mice. Although high degrees of ploidy were also detected in aged BALB/c mice, the magnitude of polyploidy was not the same magnitude as that in the diabetic mice. While there was increased homogeneity of chromatin packaging with increasing polyploidy under conditions of severe hyperglycemia (and even under conditions of normoglycemia) in NOD mice, an inverse relationship was observed in aged BALB/c mice. Chromatin accessibility to MNase increased under severe hyperglycemia and advanced age, but it was much higher in the diabetic mice. In conclusion, although similarities in polyploidy were observed between the hepatocytes from increasingly hyperglycemic adult mice and those from normoglycemic aged mice, the relationship between chromatin remodeling and increases in ploidy degrees was not the same between the hepatocytes of these two groups. These findings demonstrate that strict similarities between diabetes and aging are not always true at the cellular level. This discordance is likely due to differences in the metabolic state of mouse hepatocytes during aging and diabetic conditions consequent to specificities in their gene regulatory programs.

Chromatin remodeling, cell proliferation and cell death in valproic acid-treated HeLa cells

Background

Valproic acid (VPA) is a potent anticonvulsant that inhibits histone deacetylases. Because of this inhibitory action, we investigated whether VPA would affect chromatin supraorganization, mitotic indices and the frequency of chromosome abnormalities and cell death in HeLa cells.

Methodology/Principal Findings

Image analysis was performed by scanning microspectrophotometry for cells cultivated for 24 h, treated with 0.05, 0.5 or 1.0 mM VPA for 1–24 h, and subjected to the Feulgen reaction. TSA-treated cells were used as a predictable positive control. DNA fragmentation was investigated with the TUNEL assay. Chromatin decondensation was demonstrated under TSA and all VPA treatments, but no changes in chromosome abnormalities, mitotic indices or morphologically identified cell death were found with the VPA treatment conditions mentioned above, although decreased mitotic indices were detected under higher VPA concentration and longer exposure time. The frequency of DNA fragmentation identified with the TUNEL assay in HeLa cells increased after a 24-h VPA treatment, although this fragmentation occurred much earlier after treatment with TSA.

Conclusions/Significance

The inhibition of histone deacetylases by VPA induces chromatin remodeling in HeLa cells, which suggests an association to altered gene expression. Under VPA doses close to the therapeutic antiepileptic plasma range no changes in cell proliferation or chromosome abnormalities are elicited. The DNA fragmentation results indicate that a longer exposure to VPA or a higher VPA concentration is required for the induction of cell death.

Somatic polyploidy promotes cell function under stress and energy depletion: evidence from tissue-specific mammal transcriptome

Polyploid cells show great among-species and among-tissues diversity and relation to developmental mode, suggesting their importance in adaptive evolution and developmental programming. At the same time, excessive polyploidization is a hallmark of functional impairment, aging, growth disorders, and numerous pathologies including cancer and cardiac diseases. To shed light on this paradox and to find out how polyploidy contributes to organ functions, we review here the ploidy-associated shifts in activity of narrowly expressed (tissue specific) genes in human and mouse heart and liver, which have the reciprocal pattern of polyploidization. For this purpose, we use the modular biology approach and genome-scale cross-species comparison. It is evident from this review that heart and liver show similar traits in response to polyploidization. In both organs, polyploidy protects vitality (mainly due to the activation of sirtuin-mediated pathways), triggers the reserve adenosine-5'-triphosphate (ATP) production, and sustains tissue-specific functions by switching them to energy saving mode. In heart, the strongest effects consisted in the concerted up-regulation of contractile proteins and substitution of energy intensive proteins with energy economic ones. As a striking example, the energy intensive alpha myosin heavy chain (providing fast contraction) decreased its expression by a factor of 10, allowing a 270-fold increase of expression of beta myosin heavy chain (providing slow contraction), which has approximately threefold lower ATP-hydrolyzing activity. The liver showed the enhancement of immunity, reactive oxygen species and xenobiotic detoxication, and numerous metabolic adaptations to long-term energy depletion. Thus, somatic polyploidy may be an ingenious evolutionary instrument for fast adaptation to stress and new environments allowing trade-offs between high functional demand, stress, and energy depletion.