Aging hematopoietic stem cells decline in function and exhibit epigenetic dysregulation.

Age-related defects in stem cells can limit proper tissue maintenance and hence contribute to a shortened lifespan. Using highly purified hematopoietic stem cells from mice aged 2 to 21 mo, we demonstrate a deficit in function yet an increase in stem cell number with advancing age. Expression analysis of more than 14,000 genes identified 1,500 that were age-induced and 1,600 that were age-repressed. Genes associated with the stress response, inflammation, and protein aggregation dominated the up-regulated expression profile, while the down-regulated profile was marked by genes involved in the preservation of genomic integrity and chromatin remodeling. Many chromosomal regions showed coordinate loss of transcriptional regulation; an overall increase in transcriptional activity with age and inappropriate expression of genes normally regulated by epigenetic mechanisms was also observed. Hematopoietic stem cells from early-aging mice expressing a mutant p53 allele reveal that aging of stem cells can be uncoupled from aging at an organismal level. These studies show that hematopoietic stem cells are not protected from aging. Instead, loss of epigenetic regulation at the chromatin level may drive both functional attenuation of cells, as well as other manifestations of aging, including the increased propensity for neoplastic transformation.

Hematopoietic fingerprints: an expression database of stem cells and their progeny.

Hematopoietic stem cells (HSCs) continuously regenerate the hematologic system, yet few genes regulating this process have been defined. To identify candidate factors involved in differentiation and self-renewal, we have generated an expression database of hematopoietic stem cells and their differentiated progeny, including erythrocytes, granulocytes, monocytes, NK cells, activated and naive T cells, and B cells. Bioinformatic analysis revealed HSCs were more transcriptionally active than their progeny and shared a common activation mechanism with T cells. Each cell type also displayed unique biases in the regulation of particular genetic pathways, with Wnt signaling particularly enhanced in HSCs. We identified approximately 100-400 genes uniquely expressed in each cell type, termed lineage "fingerprints." In overexpression studies, two of these genes, Zfp 105 from the NK cell lineage, and Ets2 from the monocyte lineage, were able to significantly influence differentiation toward their respective lineages, demonstrating the utility of the fingerprints for identifying genes that regulate differentiation.

A protein-protein interaction network for human inherited ataxias and disorders of Purkinje cell degeneration.

Many human inherited neurodegenerative disorders are characterized by loss of balance due to cerebellar Purkinje cell (PC) degeneration. Although the disease-causing mutations have been identified for a number of these disorders, the normal functions of the proteins involved remain, in many cases, unknown. To gain insight into the function of proteins involved in PC degeneration, we developed an interaction network for 54 proteins involved in 23 inherited ataxias and expanded the network by incorporating literature-curated and evolutionarily conserved interactions. We identified 770 mostly novel protein-protein interactions using a stringent yeast two-hybrid screen; of 75 pairs tested, 83% of the interactions were verified in mammalian cells. Many ataxia-causing proteins share interacting partners, a subset of which have been found to modify neurodegeneration in animal models. This interactome thus provides a tool for understanding pathogenic mechanisms common for this class of neurodegenerative disorders and for identifying candidate genes for inherited ataxias.

Environmental uses of the NIH-EPA chemical information system.

A publicly accessible computer system for chemical information has been developed jointly by a number of agencies of the U.S. government. The system contains spectroscopic, crystallographic, toxicological, and regulatory data for more than 200,000 chemicals. The entire data base may be searched for a particular chemical structure or substructure, whose properties may then be retrieved. Alternatively, searching with numeric properties data is possible, permitting the identification of chemicals. Access is by local telephone call, and the system is used on a fee-for-service basis by organizations in over 20 countries. An important application of the system is to problems of chemical pollution.

Production of a dimer of 2-acetylaminofluorene during the sulfation of N-hydroxy-2-acetylaminofluorene in vitro.

During the sulfation of N-hydroxy-2-acetylaminofluorene (NOH-2AAF) by rat liver 100,000 g supernatant fraction in vitro, an unidentified metabolite is produced which accounts for 22% of the N-OH-2AAF metabolized. This product has been characterized as the 2AAF dimer, 1-(N-2'-fluorenylacetamido-2-acetylaminofluorene) by comparing its TLC, HPLC, UV, and mass spectral properties with a synthetic standard which was prepared from the reaction of N-acetoxy-2-acetylaminofluorene (N-AcO-2AAF) with 2AAF. Increasing amounts of 2AAF added to the incubation mixture of N-OH-[acetyl-14C]2AAF and rat liver 100,000 g supernatant fraction decreased the irreversible binding of 14C to protein, and increased the formation of 2AAF dimer proportionately. This suggests that the 2AAF dimer is formed from the reaction of 2AAF and the electrophilic species produced from the sulfated N-OH-2AAF. In the presence of the 9,000 g fraction of rat liver, the dimer of 2AAF was aroximately 1/25 as active as 2AAF in producing mutations in the Salmonella mutagenesis test system.

Haemodynamic effects of atenolol in patients with coronary artery disease.

The haemodynamic effects of atenolol, a new cardioselective beta-blocking agent, have been studied at rest in 8 patients with coronary artery disease. The drug was administered intravenously in cumulative doses of 0.03, 0.06, and 0.12 mg/kg body weight. A significant decrease in heart rate was associated with a fall in cardiac output. However, this cardiac output fall was not entiely rate dependent, since stroke volume fell significantly both during spontaneous sinus rhythm and when heart rate was maintained constant by atrial pacing. A dose related and significant reduction occurred in left ventricular dP/dt max without significant change in left ventricular filling pressure or mean aortic pressure. Total peripheral resistance at rest rose after atenolol. The haemodynamic findings more closely resemble those which follow intravenous propranolol than those after intravenous practolol in a similar group of patients. These actions of atenolol suggest that it may be a useful agent in the treatment of patients with angina pectoris.

Structure of poly 8-bromoadenylic acid; conformational studies by CPF energy calculations.

Poly 8-bromoadenylic acid [poly(BBrA)] is the only known all-syn polynucleotide. It shows a helix-coil transition with a melting curve centred around 55 degrees C. Energy calculations based on classical potential functions have been used to explore the three-dimensional structure of this polymer in helix and random coil. It is concluded that the ordered state is a helix of two parallel strands with a two-fold rotation axis, and the duplex is stabilised by hydrogen bonds involving N1 and H6. Each strand has a conformation with C3' endo geometry, phi' = 216 degrees, omega' = 280 degrees, omega = 294 degrees, phi = 179 degrees, chi = 243 degrees and psi = 57 degrees. Such a conformation leads to approximately 8 nucleotide units per turn of the helix and an axial rise of 3.9A degrees. The structure of poly(8BrA) has been compared with that of the related polymer poly(A) which forms a double helical structure in acidic conditions with bases in the anti conformation and with interstrand hydrogen-bonds between N7 and H6. This is the first time that a specific geometrical model of a novel polynucleotide structure has been produced initially by potential energy calculations, though such calculations on a number of known structures have been reported previously.