Loss of epigenetic information as a cause of mammalian aging

All living things experience an increase in entropy, manifested as a loss of genetic and epigenetic information. In yeast, epigenetic information is lost over time due to the relocalization of chromatin-modifying proteins to DNA breaks, causing cells to lose their identity, a hallmark of yeast aging. Using a system called "ICE" (inducible changes to the epigenome), we find that the act of faithful DNA repair advances aging at physiological, cognitive, and molecular levels, including erosion of the epigenetic landscape, cellular exdifferentiation, senescence, and advancement of the DNA methylation clock, which can be reversed by OSK-mediated rejuvenation. These data are consistent with the information theory of aging, which states that a loss of epigenetic information is a reversible cause of aging.

DNA-Mediated Gene Therapy in a Mouse Model of Limb Girdle Muscular Dystrophy 2B

Mutations in the gene for dysferlin cause a degenerative disorder of skeletal muscle known as limb girdle muscular dystrophy 2B. To achieve gene delivery of plasmids encoding dysferlin to hind limb muscles of dysferlin knockout mice, we used a vascular injection method that perfused naked plasmid DNA into all major muscle groups of the hind limb. We monitored delivery by luciferase live imaging and western blot, confirming strong dysferlin expression that persisted over the 3-month time course of the experiment. Co-delivery of the follistatin gene, which may promote muscle growth, was monitored by ELISA. Immunohistochemistry documented the presence of dysferlin in muscle fibers in treated limbs, and PCR confirmed the presence of plasmid DNA. Because dysferlin is involved in repair of the sarcolemmal membrane, dysferlin loss leads to fragile sarcolemmal membranes that can be detected by permeability to Evan’s blue dye. We showed that after gene therapy with a plasmid encoding both dysferlin and follistatin, statistically significant reduction in Evan’s blue dye permeability was present in hamstring muscles. These results suggest that vascular delivery of plasmids carrying these therapeutic genes may lead to simple and effective approaches for improving the clinical condition of limb girdle muscular dystrophy 2B.

Testis and somatic Xrcc-1 DNA repair gene expression

The human XRCC1 gene has been shown to be involved in DNA strand-break repair using the Chinese hamster ovary cell mutant EM9. The purpose of this study was to characterize the expression of Xrcc-1 to determine if there is tissue-specific expression and to provide a baseline of information for future studies that may involve altering Xrcc-1 expression in mice. Normal young adult male testis and enriched populations of pachytene spermatocytes and round spermatids displayed significantly higher levels of Xrcc-1 expression than other mouse tissues, although Xrcc-1 transcripts were found in low abundance in all tested tissues. Cultured mouse cell lines displayed levels of expression similar to male germ cells, which is a striking contrast to the levels of expression obtained in somatic tissues from the mouse. The relatively high levels of expression identified in male germ cells indicate Xrcc-1 may have an important role in male germ cell physiology.

Brain and liver targeted overexpression of O6-methylguanine DNA methyltransferase in transgenic mice

O6-Methylguanine DNA methyltransferase (MGMT; EC 2.1.1.63) is an unusual DNA repair protein in that it directly and specifically repairs a premutagenic DNA lesion without involving other proteins. MGMT removes the alkyl group from O6-alkylguanine in DNA in a unique stoichiometric reaction by accepting the alkyl group on a cysteine residue. The intracellular level of MGMT varies among tissues and appears to be inversely correlated to tissue-specific tumorigenesis induced by monofunctional alkylating agents. Because MGMT acts in solo, genetic manipulation of its expression may provide valuable insight into its contribution to cellular resistance to alkylation toxicity and to tumor induction. The human MGMT full length cDNA has been fused with a portion of the human transferrin (TF) 5'-flanking region (TF/MGMT). Transgenic founder mice were produced carrying the TF/MGMT transgene and then bred to establish stable transgenic lines. Human MGMT transcripts were specifically expressed in abundance in transgenic brain and liver tissues. In vitro MGMT assays revealed approximately 150-fold and approximately 25-fold increases in MGMT activity in transgenic brain and liver extracts respectively. Western blot analysis confirmed that human MGMT protein is specifically synthesized in transgenic brain and liver tissues.

Demonstration of two forms of vitellogenin in serum of estradiol-17 beta-treated Indian major carp, Labeo rohita

Vitellogenin (Vg) synthesis was induced in the male and non-vitellogenic female Rohu, the Indian major carp, by estradiol-17 beta(E2) where effect was more in female. A crude preparation of Vg was isolated in the second peak after gel filtration on Ultrogel AcA 34 from the sera of vitellogenic female Rohu and E2-treated male and female Rohu. Estimation of alkali-labile phosphorus was shown to be used as an index of Vg. Native-PAGE analysis has revealed the presence of two forms of Vg (Vg1: 430,000 dalton and Vg2:240,000 dalton) in Vg fraction obtained after gel filtration as well as in the sera of E2-treated male and female Rohu. Immunological cross-reaction studies between antiserum to yolk protein and Vg fractions as well as the sera from E2-treated male and female Rohu further indicates the presence of two precipitin lines (not clearly visible as the two lines fused to form a thick line) suggesting the occurrence of two forms of Vg in the Rohu.

Clonogenic assay for Wilms' tumor: improved technique for obtaining single-cell suspensions and evidence for tumor cell specificity

Wilms' tumors from seven patients were dissociated by mechanical and enzymatic means; this technique resulted in single-cell suspensions for five specimens and a few aggregates for two. By dye exclusion, cell viability ranged from 56 to 100% (median, 92%). All seven preparations produced more than five colonies/2 x 10(5) cells plated. Forty-three colonies grown from cells of a glucose-6-phosphate dehydrogenase heterozygote were of the same glucose-6-phosphate dehydrogenase isoenzyme type as the original tumor, indicating that the assay is specific for tumor cells. We attribute the high rate of colony formation to an improved method of cell preparation (combined mechanical and enzymatic dissociation of tumors) which may be applicable to other primary human tumors assayed in the soft agar system.