Relationship between proinflammatory cytokines (Il-1beta, Il-18) and leukocyte telomere length in mild cognitive impairment and Alzheimer's disease.

Inflammation plays a crucial role in Alzheimer's disease (AD). AD neurodegeneration and concurrent involvement of the peripheral immune system may promote leukocyte division and telomere shortening. We examined genotypes and plasma levels of two proinflammatory cytokines, IL-1beta and IL-18, and leukocyte telomere length (LTL) in patients with mild cognitive impairment (MCI) and AD. We wanted to determine whether changes in plasma IL-1beta and IL-18 levels, together with LTL shortening, could be diagnostic for disease progression from MCI to AD. Median plasma IL-1beta levels were in the order MCI patients (2.2 pg/ml) < AD patients (4.0 pg/ml), both of which differed significantly from the controls (0.0 pg/ml). In the AD patients, the lowest IL-1beta levels were associated with the presence of the C allele of IL-1beta rs16944 SNP. Median plasma IL-18 levels were in the order MCI patients (116.3 pg/ml) > AD patients (85.8 pg/ml), both of which were significantly higher than in the controls (17.6 pg/ml). Analysis of LTL showed a progressive reduction in the order controls > MCI > AD patients (p < 0.0001). Overall LTL reduction was correlated with increased plasma IL-1beta levels, substantiating the hypothesis that inflammatory processes secondary to neuroinflammation may trigger telomere attrition. Changes in plasma IL-1beta and Il-18 levels, and LTL seem to reflect shifts in AD stage; they may have potential use as blood biomarkers to monitor disease onset and progression from MCI to AD.

Common variants of human TERT and TERC genes and susceptibility to sporadic Alzheimers disease.

Studies investigating telomere length in association with cognitive decline, dementia, and sporadic Alzheimer's disease (AD) have frequently found shorter telomeres to be associated with the development of AD and telomerase expression with pathological processes in AD. Human telomerase is constituted by two components: the telomerase reverse transcriptase (TERT) and the telomerase RNA component (TERC). Genetic variation at the two loci has been investigated in relation to telomere length, longevity, and common diseases of advanced age, but not in relation to AD. We examined three polymorphisms of the TERT gene (VNTR MNS16A, rs2853691, rs33954691) and three polymorphisms of the TERC gene (rs12696304, rs3772190, rs16847897) in a sample of 220 AD patients and 146 controls. MNS16A LL genotype was found to be associated with an increased risk of AD only in males [interaction term adjusted OR=3.55 (95% CI 1.2-10.2)]. The three TERC single nucleotide polymorphisms are in strict linkage disequilibrium and their genotype combinations influenced the age at AD onset (AAO). The combined genotype GG-TT-CC was associated with a mean AAO six years lower (70.5±6.7) than that associated with the other genotype combinations (76.04±6.7, p=0.01). The fact that the MNS16 L allele has been reported to lower TERT expression, and that the TERC alleles G, T, C (rs12696304, rs3772190, rs16847897 in this order have been repeatedly found associated with shorter LTL, seems to corroborate the hypothesis of a role of telomere length and telomerase in AD susceptibility.

tRNA prefers to kiss.

Six RNA aptamers that bind to yeast phenylalanine tRNA were identified by in vitro selection from a random-sequence pool. The two most abundantly represented aptamers interact with the tRNA anticodon loop, each through a sequence block with perfect Watson-Crick complementarity to the loop. It was possible to truncate one of these aptamers to a simple hairpin loop that forms a classical 'kissing complex' with the anticodon loop. Three other aptamers have nearly complete complementarity to the anticodon loop. The sixth aptamer has two sequence blocks, one complementary to the tRNA T loop and the other to the D loop; this aptamer binds better to a mutant tRNA that disrupts the normal D-loop/T-loop tertiary interaction than to the wild-type tRNA. Selection of complements to tRNA loops occurred despite an attempt to direct binding to tertiary structural features of tRNA. This serves as a reminder of how special the RNA-RNA interactions are that are not based on complementarity. Nonetheless, these aptamers must present the tRNA complement in some special structural context; the simple single-strand complement of the anticodon loop did not bind tRNA effectively.

Influence of substrate structure on cleavage by hammerhead ribozyme.

We compared the cleavage by a hammerhead ribozyme of a wild-type precursor tRNA (pre-tRNA leu(3)) and a structurally altered mutant form. We also analyzed the cleavage reactions of these tRNAs catalyzed by a ribozyme variant that was designed to complement the mutant precursor tRNA. Kinetic analyses reveal that the kcat values are nearly the same for the wild-type and the mutant substrate RNAs. However, the Km values differ considerably, being higher for the wild-type substrate. Thus, the formation of the ribozyme-substrate complex, but not the chemical cleavage step, is affected by these changes. Time course studies were performed, at different temperatures, to estimate the efficiency of the cleavage reactions and the effect of temperature. The cleavage of mutant precursor tRNA is generally faster than the wild-type at all temperatures analyzed. These results suggest that substrate structures can limit ribozyme efficiency, presumably by hindering the hybridization step.

A newt ribozyme: a catalytic activity in search of a function.

We analyzed the cleavage properties and the transcription regulation of the newt (Triturus vulgaris meridionalis) self-cleaving RNA. In vitro self-cleavage of model oligoribonucleotides occurs within a double hammerhead structure. In addition, an entire ribozyme molecule, as well as its catalytic domain, "trans-cleaves" in vitro appropriate oligoribonucleotide substrates. Signals encoded within the ribozyme DNA sequences regulate the ribozyme transcription, which is RNA polymerase II dependent. Finally, the deduced secondary structure of the self-cleaving RNA appears to be conserved in evolutionarily distant newt species. These features suggest that the newt ribozyme could play some role in the cell, possibly related to its cleavage properties.