The telomere story or the triumph of an open-minded research

The Nobel Assembly at Karolinska Institute has decided to award The Nobel Prize in Physiology or Medicine 2009 jointly to Elizabeth H. Blackburn, Carol W. Greider and Jack W. Szostak for the discovery of "how chromosomes are protected by telomeres and the enzyme telomerase". This discovery had major impacts within the scientific community and led to intense research in this field. All the studies performed are now the bases for future investigations and stimulate the development of potential new therapies.     

Risk factors for total joint arthroplasty infection in patients receiving tumor necrosis factor α-blockers: a case-control study

Introduction

The objective of this study was to assess natural microbial agents, history and risk factors for total joint arthroplasty (TJA) infections in patients receiving tumor necrosis factor (TNF)α-blockers, through the French RATIO registry and a case-control study.

Methods

Cases were TJA infections during TNFα-blocker treatments. Each case was compared to two controls (with TJA and TNFα-blocker therapy, but without TJA infection) matched on age (±15 years), TJA localization, type of rheumatic disorder and disease duration (±15 years). Statistical analyses included univariate and multivariate analyses with conditional logistic regression.

Results

In the 20 cases (18 rheumatoid arthritis), TJA infection concerned principally the knee (n = 12, 60%) and the hip (n = 5, 25%). Staphylococcus was the more frequent microorganism involved (n = 15, 75%). Four patients (20%) were hospitalized in an intensive care unit and two died from infection. Eight cases (40%) versus 5 controls (13%) had undergone primary TJA or TJA revision for the joint subsequently infected during the last year (P = 0.03). Of these procedures, 5 cases versus 1 control were performed without withdrawing TNFα-blockers (P = 0.08). In multivariate analysis, predictors of infection were primary TJA or TJA revision for the joint subsequently infected within the last year (odds ratio, OR = 88.3; 95%CI 1.1-7,071.6; P = 0.04) and increased daily steroid intake (OR = 5.0 per 5 mg/d increase; 1.1-21.6; P = 0.03). Case-control comparisons showed similar distribution between TNFα-blockers (P = 0.70).

Conclusions

In patients receiving TNFα-blockers, TJA infection is rare but potentially severe. Important risk factors are primary TJA or TJA revision within the last year, particularly when TNFα-blockers are not interrupted before surgery, and the daily steroid intake.     

Blockade of immunosuppressive cytokines restores NK cell antiviral function in chronic hepatitis B virus infection

NK cells are enriched in the liver, constituting around a third of intrahepatic lymphocytes. We have previously demonstrated that they upregulate the death ligand TRAIL in patients with chronic hepatitis B virus infection (CHB), allowing them to kill hepatocytes bearing TRAIL receptors. In this study we investigated whether, in addition to their pathogenic role, NK cells have antiviral potential in CHB. We characterised NK cell subsets and effector function in 64 patients with CHB compared to 31 healthy controls. We found that, in contrast to their upregulated TRAIL expression and maintenance of cytolytic function, NK cells had a markedly impaired capacity to produce IFN-γ in CHB. This functional dichotomy of NK cells could be recapitulated in vitro by exposure to the immunosuppressive cytokine IL-10, which was induced in patients with active CHB. IL-10 selectively suppressed NK cell IFN-γ production without altering cytotoxicity or death ligand expression. Potent antiviral therapy reduced TRAIL-expressing CD56(bright) NK cells, consistent with the reduction in liver inflammation it induced; however, it was not able to normalise IL-10 levels or the capacity of NK cells to produce the antiviral cytokine IFN-γ. Blockade of IL-10 +/- TGF-β restored the capacity of NK cells from both the periphery and liver of patients with CHB to produce IFN-γ, thereby enhancing their non-cytolytic antiviral capacity. In conclusion, NK cells may be driven to a state of partial functional tolerance by the immunosuppressive cytokine environment in CHB. Their defective capacity to produce the antiviral cytokine IFN-γ persists in patients on antiviral therapy but can be corrected in vitro by IL-10+/- TGF-β blockade.     

Replication Timing of Human Telomeres Is Chromosome Arm–Specific,Influenced by Subtelomeric Structures and Connected to Nuclear Localization

The mechanisms governing telomere replication in humans are still poorly understood. To fill this gap, we investigated the timing of replication of single telomeres in human cells. Using in situ hybridization techniques, we have found that specific telomeres have preferential time windows for replication during the S-phase and that these intervals do not depend upon telomere length and are largely conserved between homologous chromosomes and between individuals, even in the presence of large subtelomeric segmental polymorphisms. Importantly, we show that one copy of the 3.3 kb macrosatellite repeat D4Z4, present in the subtelomeric region of the late replicating 4q35 telomere, is sufficient to confer both a more peripheral localization and a later-replicating property to a de novo formed telomere. Also, the presence of β-satellite repeats next to a newly created telomere is sufficient to delay its replication timing. Remarkably, several native, non-D4Z4–associated, late-replicating telomeres show a preferential localization toward the nuclear periphery, while several early-replicating telomeres are associated with the inner nuclear volume. We propose that, in humans, chromosome arm–specific subtelomeric sequences may influence both the spatial distribution of telomeres in the nucleus and their replication timing.     

Brucella spp noncanonical LPS: structure, biosynthesis, and interaction with host immune system

Brucella spp. are facultative intracellular pathogens that have the ability to survive and multiply in professional and non-professional phagocytes, and cause abortion in domestic animals and undulant fever in humans. Several species are recognized within the genus Brucella and this classification is mainly based on the difference in pathogenicity and in host preference. Brucella strains may occur as either smooth or rough, expressing smooth LPS (S-LPS) or rough LPS (R-LPS) as major surface antigen. This bacterium possesses an unconventional non-endotoxic lipopolysaccharide that confers resistance to anti-microbial attacks and modulates the host immune response. The strains that are pathogenic for humans (B. abortus, B. suis, B. melitensis) carry a smooth LPS involved in the virulence of these bacteria. The LPS O-chain protects the bacteria from cellular cationic peptides, oxygen metabolites and complement-mediated lysis and it is a key molecule for Brucella survival and replication in the host. Here, we review i) Brucella LPS structure; ii) Brucella genome, iii) genes involved in LPS biosynthesis; iv) the interaction between LPS and innate immunity.     

On the theory of noncovalent binding

It is widely accepted that the binding constant of a receptor and ligand can be written as a two-body integral involving the interaction energy of the receptor and the ligand. Interestingly, however, three different theories of binding in the literature dictate three distinct integrals. The present study uses theory, as well as simulations of binding experiments, to test the validity of the three integrals. When binding is measured by a signal that detects the ligand in the binding site, the most accurate results are obtained by an integral of the Boltzmann factor, where the bound complex is defined in terms of an exclusive binding region. A novel prediction of this approach, that expanding a ligand can increase its binding constant, is borne out by the simulations. The simulations also show that abnormal binding isotherms can be obtained when the region over which the signal is detected deviates markedly from the exclusion zone. Interestingly, the binding constant measured by equilibrium dialysis, rather than by monitoring a localized signal, can yield a binding constant that differs from that obtained from a signal measurement, and that is matched best by the integral of the Mayer factor.     

Calculation of cyclodextrin binding affinities: energy, entropy, and implications for drug design

The second generation Mining Minima method yields binding affinities accurate to within 0.8 kcal/mol for the associations of alpha-, beta-, and gamma-cyclodextrin with benzene, resorcinol, flurbiprofen, naproxen, and nabumetone. These calculations require hours to a day on a commodity computer. The calculations also indicate that the changes in configurational entropy upon binding oppose association by as much as 24 kcal/mol and result primarily from a narrowing of energy wells in the bound versus the free state, rather than from a drop in the number of distinct low-energy conformations on binding. Also, the configurational entropy is found to vary substantially among the bound conformations of a given cyclodextrin-guest complex. This result suggests that the configurational entropy must be accounted for to reliably rank docked conformations in both host-guest and ligand-protein complexes. In close analogy with the common experimental observation of entropy-enthalpy compensation, the computed entropy changes show a near-linear relationship with the changes in mean potential plus solvation energy.     

Characterization of the Arabidopsis lysine-rich arabinogalactan-protein AtAGP17 mutant (rat1) that results in a decreased efficiency of agrobacterium transformation

Arabinogalactan-proteins (AGPs) are a family of complex proteoglycans widely distributed in plants. The Arabidopsis rat1 mutant, previously characterized as resistant to Agrobacterium tumefaciens root transformation, is due to a mutation in the gene for the Lys-rich AGP, AtAGP17. We show that the phenotype of rat1 correlates with down-regulation of AGP17 in the root as a result of a T-DNA insertion into the promoter of AGP17. Complementation of rat1 plants by a floral dip method with either the wild-type AGP17 gene or cDNA can restore the plant to a wild-type phenotype in several independent transformants. Based on changes in PR1 gene expression and a decrease in free salicylic acid levels upon Agrobacterium infection, we suggest mechanisms by which AGP17 allows Agrobacterium rapidly to reduce the systemic acquired resistance response during the infection process.     

Paracoccidioides brasiliensis exoantigens: recognition by IgG from patients with different clinical forms of paracoccidioidomycosis

Serum antibodies against antigens of Paracoccidioides brasiliensis have been one of the major diagnostic indicators of paracoccidioidomycosis (PCM). In the present study, released antigen preparations (exoAg) obtained from P. brasiliensis isolates were characterized in terms of their protein components electrophoretically detectable and recognizable by sera (IgG) of patients. Among five different isolates (DGO, C-9, BAT, Pb-18 and B-339) the electrophoretic profiles of exoAg varied greatly. A total of 28 different components were detected, 11 of them shared by all isolates. The most representative preparation was BAT-exoAg, which presented the largest number of protein bands (23) and the highest frequency of reacting bands (19) with sera from patients with active PCM (n = 40). Six bands reacted with more than 20% of sera. Independently of clinical forms, the sera recognized the 43-kDa (97% of tested sera), 160-kDa (78% of tested sera) and 70-kDa (60% of tested sera) antigens more frequently. Sera from patients with severe forms of acute (n = 14) or chronic (n = 10) PCM recognized a greater number of antigens, with a higher frequency, than those from moderate forms. The most pronounced reduction in reactivity was provided by sera of patients that became asymptomatic at the beginning of treatment. Remnant reactivity with BAT-exoAg was detected after clinical recovery, especially with those of 43, 70 and 160 kDa. The latter presented a stable recognition frequency (60%) during the entire follow-up, allowing us to suppose that the IgG reactivity against the 160-kDa antigen constitutes a possible persistent marker of P. brasiliensis infection.