Autolytic degradation of ocriplasmin: a complex mechanism unraveled by mutational analysis

Ocriplasmin, a truncated form of plasmin, is commercialized in the USA and in Europe under the trade name Jetrea(®), and indicated for the treatment of symptomatic vitreomacular adhesion and vitreomacular traction including when associated with macular hole ≤400 µm, respectively. We have shown in a previous study that ocriplasmin undergoes autolytic degradation when injected in eye vitreous, which leads to its rapid inactivation. In order to investigate this process further, we have introduced in ocriplasmin a variety of amino acid substitutions within or in the immediate vicinity of the three major autolytic cleavage sites. We demonstrate here that autolytic inactivation of ocriplasmin is a sequential process where initial cleavage occurs primarily between residues 156 and 157. Reduction or even blocking of autolysis can be achieved by mutating a limited number of key residues. In this study, we also report the identification of a series of ocriplasmin variants with improved resistance to autolysis and unimpaired catalytic activity. Such variants represent useful tools for the exploration of therapeutic approaches aiming at non-surgical resolution of vitreomacular adhesion.

Fluctuations of haemoglobinaemia in chronic haemodialysis patients

In March 2008 and June 2009, an ad hoc working group of nephrologists discussed the status of anaemia therapy with erythropoiesis-stimulating agents [ESA] in patients on chronic haemodialysis, the phenomenon of fluctuations of haemoglobinaemia, and the need for individualisation of ESA treatment. The working group put together the following statements: (1) ESAs increase the haemoglobin concentration and adaptations of the ESA dose adjust the response according to a negative-feedback loop. The long lag time between an ESA dose change and its effect on erythropoiesis is cumbersome. The optimal haemoglobin target concentration is different for every haemodialysis patient; the lowest haemoglobin concentration upon which one could consistently demonstrate a positive subjective and objective clinical benefit in chronic dialysis is 11 g/dL, in contrast to the lowest haemoglobin concentration of 10 g/dL recommended in the current EMEA label for ESAs. (2) Intra-individual fluctuation of haemoglobinaemia over time is unavoidable, not only due to the ESA dose/haemoglobin response interaction, but also, and more importantly, due to the occurrence of acute illnesses and exacerbations of co-morbid conditions. Many different methodologies to characterise haemoglobin variability have been described but there is currently no universally applied definition of the phenomenon. (3) An impact of the haemoglobin level and the amplitude of the haemoglobin fluctuations on patient outcome has been observed. Without disclosing any causal relationship, worse outcomes were associated with haemoglobin fluctuations around the lower target level, but later on, more simply linked to the relative time spent below the haemoglobin concentration of 11 g/dL and to the administration of inappropriately high ESA doses in order to achieve the recommended haemoglobin target range. A plausible mechanism might be that acute illnesses blunt the patients' basal ESA sensitivity; this leads to subnormal and/or varying haemoglobin levels, currently initiating an ESA dose increase. The longer it takes the patient to recover from the acute illness, the more the prolongation of the clinically poor condition is to some extent maintained by the persistence of low haemoglobinaemia and/or by the administration of high ESA doses, and, as such, on their turn possibly contributing to an ultimate poor outcome. In the absence of clinical trials, recommendations should be offered how to proceed with the administration of ESAs as optimal as possible in periods of clinical instability.

The lectin-like domain of thrombomodulin interferes with complement activation and protects against arthritis

BACKGROUND

Thrombomodulin (TM) is predominantly a vascular endothelial cell plasma membrane glycoprotein that, via distinct structural domains, interacts with multiple ligands, thereby modulating coagulation, fibrinolysis, complement activation, inflammation and cell proliferation. We previously reported that by mediating signals that interfere with mitogen-activated protein kinase and nuclear factor kappaB pathways, the amino-terminal C-type lectin-like domain of TM has direct anti-inflammatory properties.

METHODS

In the current study, we use murine models of acute inflammatory arthritis and biochemical approaches to assess the mechanism by which the lectin-like domain of TM modifies disease progression.

RESULTS

Mice lacking the lectin-like domain of TM (TM(LeD/LeD)mice) develop inflammatory arthritis that is more rapid in onset and more severe than that developed in their wildtype counterparts. In two models of arthritis, treatment of mice with recombinant soluble lectin-like domain of TM significantly suppresses clinical evidence of disease and diminishes monocyte/macrophage infiltration into the synovium, with weaker expression of the pro-inflammatory high mobility group box chromosomal protein 1. While thrombin-TM mediated activation of thrombin activatable fibrinolysis inhibitor inactivates complement factors C3a and C5a, we show that TM has a second independent mechanism to regulate complement: the lectin-like domain of TM directly interferes with complement activation via the classical and lectin pathways.

CONCLUSIONS

These data extend previous insights into the mechanisms by which TM modulates innate immunity, and highlight its potential as a therapeutic target for inflammatory diseases.

Management of therapy-resistant systemic lupus erythematosus with rituximab: report of a case and review of the literature

Therapy of systemic lupus erythematosus (SLE) with major organ involvement consists of aggressive immunosuppression with glucocorticoids and cytotoxic agents. When remission is achieved, maintenance therapy is begun to reduce the risk of relapse while minimizing toxicity. Remission with standard therapy is, however, not always achieved. We discribe a women with SLE and microangiopathic haemolytic anaemia and thrombocytopenia, pneumonitis and nephritis refractory to high-dose steroids, pulse cyclophosphamide, plasmapheresis and intravenous immunoglobulins. The anti-CD20 monoclonal antibody rituximab was administered, resulting in major clinical and biochemical improvement. Therapy-resistant SLE generally has an ominous prognosis. A few anecdotal reports and small open studies describe beneficial effects of rituximab in these cases. Rituximab may be a promising new approach to improve the dismal outcome of therapy-resistant SLE.

Active genes in junk DNA? Characterization of DUX genes embedded within 3.3 kb repeated elements

The human genome contains hundreds of repeats of the 3.3 kb family in regions associated with heterochromatin. We have previously isolated a 3.3 kb-like cDNA encoding a double homeodomain protein (DUX1). Demonstration that the protein was expressed in human rhabdomyosarcoma TE671 cells, and characterization of a homologous promoter suggested that functional DUX genes might be present in 3.3 kb elements. In the present study, we describe two nearly identical 3.3 kb/DUX genes derived from PAC 137F16 (DUX3), and TE671 genomic DNA (DUX5), both mapping to all the acrocentric chromosomes. Their promoters harbor a GC and a TATAA box, and the open reading frame of the intronless structural part encodes two DUX proteins differing by alternative translation initiation. The shorter protein of the DUX5 gene is identical to DUX1. Using a protein truncation test, we could show that these two proteins are encoded by total RNA, but not by poly (A)(+) RNA, from different human tissues and cell lines. Our results indicate that active genes of unusual structure are present in chromosome regions characterized by large amounts of heterochromatic repetitive DNA.

1,25-Dihydroxyvitamin D(3) induction of the tissue-type plasminogen activator gene is mediated through its multihormone-responsive enhancer

Tissue-type plasminogen activator (t-PA) is a positive modulator of the plasminogen-plasmin system, which is involved in bone remodeling. In the present study, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] was found to stimulate t-PA gene expression in ROS17/2.8 osteosarcoma cells. Transient transfection analysis and in vitro DNA binding studies identified two vitamin D-responsive elements (VDRE) in the human t-PA enhancer. The first VDRE (bp -7175 to -7146) comprised an inverted palindrome separated by 9 bp (IP9) overlapping a palindrome separated by 3 bp. The second VDRE (bp -7315 to -7302) is an IP2 element overlapping the previously identified retinoic acid-responsive element. 1,25(OH)(2)D(3) treatment of primary osteoblasts derived from t-PAlacZ transgenic mice containing 9 kb of 5' sequence of the human t-PA gene increased the number of lacZ-positive cells, fitting with the probability model of enhancer function.

Nucleotide sequence of the partially deleted D4Z4 locus in a patient with FSHD identifies a putative gene within each 3.3 kb element

Facioscapulohumeral muscular dystrophy (FSHD) is linked to the polymorphic D4Z4 locus on chromosome 4q35. In non-affected individuals, this locus comprises 10-100 tandem copies of members of the 3.3kb dispersed repeat family. Deletions leaving 1-8 such repeats have been associated with FSHD, for which no candidate gene has been identified. We have determined the complete nucleotide sequence of a 13.5kb EcoRI genomic fragment comprising the only two 3.3kb elements left in the affected D4Z4 locus of a patient with FSHD. Sequence analyses demonstrated that the two 3.3kb repeats were identical. They contain a putative promoter that was not previously detected, with a TACAA instead of a TATAA box, and a GC box. Transient expression of a luciferase reporter gene fused to 191bp of this promoter, demonstrated strong activity in transfected human rhabdomyosarcoma TE671 cells that was affected by mutations in the TACAA or GC box. In addition, these 3.3kb repeats include an open reading frame (ORF) starting 149bp downstream from the TACAA box and encoding a 391 residue protein with two homeodomains (DUX4). In-vitro transcription/translation of the ORF in a rabbit reticulocyte lysate yielded two (35)S Cys/ (35)S Met labeled products with apparent molecular weights of 38 and 75kDa on SDS-PAGE, corresponding to the DUX4 monomer and dimer, respectively. In conclusion, we propose that each of the 3.3kb elements in the partially deleted D4Z4 locus could include a DUX4 gene encoding a double homeodomain protein.

Involvement of Sp1 in basal and retinoic acid induced transcription of the human tissue-type plasminogen activator gene

Transcription of the human tissue-type plasminogen activator (t-PA) gene is regulated by a multi-hormonal responsive enhancer at -7 kb. Transient co-transfections of Drosophila SL2 and human HT1080 fibrosarcoma cells with t-PA reporter constructs showed that Sp1 and Sp3 activate the t-PA promoter. Moreover Sp1 (but not Sp3) binding to the promoter is involved in induction by retinoic acid (RA), a response mediated through the enhancer. The role of Sp1 is specific, since mutation of the CRE element in the promoter did not affect response to RA. In contrast, the glucocorticoid induction mediated by the enhancer is independent of these Sp1 and CRE elements.

Identification of a multihormone responsive enhancer far upstream from the human tissue-type plasminogen activator gene

A 2.4-kilobase (kb) DNA fragment, located 7.1 kb upstream from the human tissue-type plasminogen activator (t-PA) gene (t-PA2.4), acts as an enhancer which is activated by glucocorticoids, progesterone, androgens, and mineralocorticoids. Transient expression of t-PA-chloramphenicol acetyltransferase reporter constructs in HT1080 human fibrosarcoma cells identified a glucocorticoid responsive unit with four functional binding sites for the glucocorticoid receptor, located between bp -7,501 and -7,974. The region from bp -7,145 to -9,578 (t-PA2.4) was found to confer a cooperative induction by dexamethasone and all-trans-retinoic acid (RA) to its homologous and a heterologous promoter, irrespective of its orientation. The minimal enhancer, defined by progressive deletion analysis, comprised the region from -7.1 to -8.0 kb (t-PA0.9) and encompassed the glucocorticoid responsive unit and the previously identified RA-responsive element located at -7.3 kb (Bulens, F., Ibañez-Tallon, I., Van Acker, P., De Vriese, A., Nelles, L., Belayew, A., and Collen, D. (1995) J. Biol. Chem. 270, 7167-7175). The amplitude of the synergistic response to dexamethasone and RA increased by reducing the distance between the enhancer and the proximal t-PA promoter. The synergistic interaction was also observed between the aldosterone and the RA receptors. It is postulated that the t-PA0.9 enhancer might play a role in the hormonal regulation of the expression of human t-PA in vivo.

Retinoic acid induction of human tissue-type plasminogen activator gene expression via a direct repeat element (DR5) located at -7 kilobases

All-trans-retinoic acid (RA) and retinoids induce synthesis of tissue-type plasminogen activator (t-PA) in endothelial and neuroblastoma cells in vitro and in rats in vivo. In HT1080 fibrosarcoma cells, induction of t-PA-related antigen secretion and t-PA mRNA steady state levels by RA were found to depend on de novo protein and mRNA synthesis. Fragments derived from the 5'-flanking region of the t-PA gene (+197 to -9578 base pairs (bp)) were linked to the chloramphenicol acetyltransferase gene. Transfection studies demonstrated that the region spanning bp -7145 to -9578 mediated induction by RA. A functional retinoic acid response element (RARE), consisting of a direct repeat of the GGGTCA motif spaced by 5 nucleotides (t-PA/DR5), was localized at -7.3 kilobases. The t-PA/DR5 element interacted with the heterodimer composed of retinoic acid receptor alpha and retinoid X receptor alpha in vitro, whereas its mutation abolished induction by RA in transient expression. In human EA.hy926 hybrid endothelial and in SK-N-SH neuroblastoma cells, the activity of t-PA/DR5 was found to be independent of the intervening sequence (-632 to -7144 bp) and of its distance from the transcription initiation site. Staurosporine, an inhibitor of protein kinase activity, inhibited induction by RA, suggesting that it required protein phosphorylation.

Influence of vasoactive intestinal polypeptide and NG-nitro-L-arginine methyl ester on cholinergic neurotransmission in the rat gastric fundus

The possible modulating effect of vasoactive intestinal polypeptide (VIP) and nitric oxide (NO), on cholinergic neurotransmission was assessed in longitudinal muscle strips of rat gastric fundus. VIP and NO are the putative co-transmitters of the inhibitory non-adrenergic non-cholinergic (NANC) neurones in this tissue. VIP concentration dependently inhibited cholinergic contractions induced by 2-min transmural stimulation, relaxed tissues, the tone of which was continuously raised by transmural stimulation, and shifted to the right the frequency-response curves for contraction induced by transmural stimulation with a cumulative increase of frequency. The same effect was found when contractions were induced with methacholine, suggesting that only functional antagonism at the postsynaptic smooth muscle cell level is involved. On 30-min incubations, 3 x 10(-4) M NG-nitro-L-arginine methyl ester (L-NAME) potentiated cholinergic responses to 20-s transmural stimulation, while not influencing contractions of similar amplitude evoked by methacholine; the cholinergic responses to 2-min transmural stimulation were also not influenced. The potentiating effect of L-NAME was prevented by L-arginine but not D-arginine. These results suggest that endogenous NO released from the inhibitory NANC neurones during short trains of transmural stimulation interferes with cholinergic neurotransmission either by functional antagonism of acetylcholine at the postsynaptic level or by presynaptic inhibition of acetylcholine release.