Altered protein acetylation in polyglutamine diseases.

Polyglutamine diseases are hereditary neurodegenerative disorders caused by the expansion of a CAG repeat in the disease gene. A dominant gain of function is associated with these expanded alleles. The resulting elongated polyglutamine repeats are thought to cause structural changes in the affected proteins, leading to aberrant interactions such as those that allow formation of extra- and intranuclear aggregates. However, self-association is not the only interaction the polyglutamine domain is capable of mediating. Many cellular proteins can be sequestered into inclusions or bound by more soluble forms of the mutant proteins. One group of proteins that binds to and whose activity may be altered by polyglutamines is Histone Acetyltransferases (HATs). HATs are responsible for the acetylation of histones and several other important proteins and this modification results in altered function of the target protein. HATs regulate cellular processes at levels as different as modifying transcriptional competence of chromosomes, temporal regulation of promoter activity and protein activation / inactivation. Recent studies show that the altered balance between protein acetylation and deacetylation may be a key process contributing to expanded polyglutamine-induced pathogenesis. The restoration of this balance is possible by the genetic or pharmacological reduction of the opposing enzyme group, i.e. the Histone Deacetylases (HDACs). Recent progress in HDAC research has made the development of inhibitors of specific HDAC family proteins possible and these compounds could be effective candidates for treatment of these devastating diseases.

Histone deacetylase inhibitors arrest polyglutamine-dependent neurodegeneration in Drosophila.

Proteins with expanded polyglutamine repeats cause Huntington's disease and other neurodegenerative diseases. Transcriptional dysregulation and loss of function of transcriptional co-activator proteins have been implicated in the pathogenesis of these diseases. Huntington's disease is caused by expansion of a repeated sequence of the amino acid glutamine in the abnormal protein huntingtin (Htt). Here we show that the polyglutamine-containing domain of Htt, Htt exon 1 protein (Httex1p), directly binds the acetyltransferase domains of two distinct proteins: CREB-binding protein (CBP) and p300/CBP-associated factor (P/CAF). In cell-free assays, Httex1p also inhibits the acetyltransferase activity of at least three enzymes: p300, P/CAF and CBP. Expression of Httex1p in cultured cells reduces the level of the acetylated histones H3 and H4, and this reduction can be reversed by administering inhibitors of histone deacetylase (HDAC). In vivo, HDAC inhibitors arrest ongoing progressive neuronal degeneration induced by polyglutamine repeat expansion, and they reduce lethality in two Drosophila models of polyglutamine disease. These findings raise the possibility that therapy with HDAC inhibitors may slow or prevent the progressive neurodegeneration seen in Huntington's disease and other polyglutamine-repeat diseases, even after the onset of symptoms.

Production and properties of antiserum for radioimmunoassay of serum conjugated chenodeoxycholic acid and its preliminary application.

Sensitive tritiated radioimmunoassay was developed for conjugated chenodeoxycholic acid, using immunogen prepared by the mixed anhydride method. The obtained molar bile salt-BSA ratio in the immunogen was 19:1. The distinguishing features of the immunization procedure were a preliminary vaccination of the animal with antitubercular vaccine (VDS), and the administration of very small doses of immunogen (50 micrograms). Assay sensitivity for this bile salt fell in the picomole range with the standard curve extending from 1.5 to 150 pmol. Specificity of the antiserum was compared with that of the commercially available "Glycochenodeoxycholic acid RIA kit" (Nordiclab Oy, Oulu, Finland), and proved to be satisfactory. Fasting serum conjugated chenodeoxycholic acid concentration in 25 healthy subjects and 15 patients with cirrhosis was 0.63 mumol/l and 43.05 mumol/l, respectively. The assay was performed on unextracted sera.

Study of nucleic acid metabolism in two astronauts.

During the last years data have evidenced that alteration in nucleic acid metabolism, expecially increased urinary excretion of modified nucleosides reflects physiological changes in living organism. In relation with the Soyuz-36-Salyut-6-Soyuz-35 mission in 1980 urinary nucleoside excretion of two astronauts /B.F., V.K./ were traced. Individual daily urine samples were collected for 4 days before starting and 6 days after landing and were analysed with improved analytical procedures /affinity chromatography, high Performance liquid chromatography/. Levels of 1-methylinosine, 1-methylguanosine and N,2,2-dimethylguanosine in urine were determined. Thus recorded changes differ considerably at two astronauts. One of the /V.K./ excreted nucleosides normally, another /B.F./ showed increase to 200-400 % levels excretion of above nucleosides on the second day after landing. The peak values disappeared on the 3-6 days after. To interpret this phenomenon extreme factors of space-flight /weightlessness, stress, radiations, etc./ have to be taken into consideration. However, we attach importance to training of astronauts. During the last decade data have evidenced that alterations in the metabolism of nucleic acids especial increased urinary excretion of modified nucleosides reflects physiological and in some cases pathological changes in living organism. In relation with the Soyuz-36-Salyut-6-Soyuz 35 mission urinary excretion of certain modified nucleosides of two astronauts /B.F. and V.K./ were measured. The aim of the measurements was: how the metabolism of transfer ribonucleic acids /tRNAs/ referring to cosmic flight, how it is reflected in urinary excretions of modified nucleosides. For these purposes we studied the excretion of methylguanosine, dimethylguanosine and methylinosine. These nucleosides are the normal minor components of tRNA.