Selective inhibition of a regulatory subunit of protein phosphatase 1 restores proteostasis

Many biological processes are regulated through the selective dephosphorylation of proteins. Protein serine-threonine phosphatases are assembled from catalytic subunits bound to diverse regulatory subunits that provide substrate specificity and subcellular localization. We describe a small molecule, guanabenz, that bound to a regulatory subunit of protein phosphatase 1, PPP1R15A/GADD34, selectively disrupting the stress-induced dephosphorylation of the α subunit of translation initiation factor 2 (eIF2α). Without affecting the related PPP1R15B-phosphatase complex and constitutive protein synthesis, guanabenz prolonged eIF2α phosphorylation in human stressed cells, adjusting the protein production rates to levels manageable by available chaperones. This favored protein folding and thereby rescued cells from protein misfolding stress. Thus, regulatory subunits of phosphatases are drug targets, a property used here to restore proteostasis in stressed cells.

Radiation-induced perturbation of cell-to-cell signalling and communication

The investigation of the bystander phenomena (i.e. the induction of damage in cells not directly traversed by radiation) is strictly related to the study of the mechanisms of intercellular communication and of the perturbative effects of radiation. A new possible way to try to solve the bystander puzzle is through a 'systems radiation biology' approach with the total integration of experimental and theoretical activities. In particular, this contribution will focus on: (1) 'ad hoc' experiments designed to quantify key parameters involved in intercellular signalling (focusing, as a pilot study, on release, decay and internalization of interleukine-6 molecules, their modulation by radiation, and possible differences between in vivo/in vitro behaviour); (2) the implementation and the development of two different modelling approaches: a stochastic model (based on a Monte Carlo code) that takes account of the local mechanisms of release and internalization of signalling molecules (e.g. cytokines) and an analytical model where signal molecules are treated as a population and their temporal behaviour is described by differential equations. This approach provided instruments to investigate the complex phenomena of signal transmission and the role of cell communication to guarantee (maintain) the robustness of the in vitro experimental systems against the effects of perturbations.

Status and development of allied health personnel in cardiothoracic surgery in Latin America

INTRODUCTION

The role of allied health personnel (not physician) in cardiothoracic surgery has evolved substantially since the beginnings of this discipline in the 70´s, especially in developed countries.

METHODS

To explore the status of allied health personnel in cardiothoracic surgery in Latin America, a research was geared to know the general context of human resources in public health and specifically in cardiothoracic surgery. Official data from the World Health Organization and the Pan American Health Organization were acquired. An on-line survey was sent to Latin-American cardiothoracic surgeons through either scientific societies or personal e-mail, to get direct information on human resources management of the surgical services.

RESULTS

There is lack of information on the medical literature regarding the allied health personnel activities in the region. Sixty one Latin American cardiothoracic centers answered the survey. The survey revealed that the profile of the allied health personnel is outlined by nurses, perfusion and anesthesiology technicians; whose routine activities are restricted to minor controls.

CONCLUSIONS

At the moment, the lack of information and official data generates difficulties in analyzing the development status of allied health personnel in cardiothoracic surgery departments in the region of Latin America. In the light of the results and growing interest of developed countries in incorporating the allied health personnel to improve the work capacity and the quality of care in cardiothoracic surgery centers, it would be sensible to develop policies oriented to train and organize this activity in Latin America.

Exposure of hydrophobic surfaces initiates aggregation of diverse ALS-causing superoxide dismutase-1 mutants

The copper-zinc superoxide dismutase-1 (SOD1) is a highly structured protein and, a priori, one of the least likely proteins to be involved in a misfolding disease. However, more than 140, mostly missense, mutations in the SOD1 gene cause aggregation of the affected protein in familial forms of amyotrophic lateral sclerosis (ALS). The remarkable diversity of the effects of these mutations on SOD1 properties has suggested that they promote aggregation by a variety of mechanisms. Experimental assessment of surface hydrophobicity using a sensitive fluorescent-based assay, revealed that diverse ALS-causing mutations provoke SOD1 aggregation by increasing their propensity to expose hydrophobic surfaces. These findings could not be anticipated from analysis of the amino acid sequence. Our results uncover the biochemical nature of the misfolded aggregation-prone intermediate and reconcile the seemingly diverse effects of ALS-causing mutations into a unifying mechanism. Furthermore, the method we describe here will be useful for investigating and interfering with aggregation of various proteins and thereby provide insight into the molecular mechanisms underlying many neurodegenerative diseases.

Influence of imatinib mesylate on radiosensitivity of astrocytoma cells

Imatinib mesylate (STI571), an inhibitor of alpha- and beta-platelet-derived growth factor receptors (PDGFR) and other tyrosine kinases, is a well established treatment for chronic myeloid leukaemia and gastrointestinal stromal tumours. Moreover, it is under investigation for the therapy of several other malignant tumours since protein kinases are frequently mutated or otherwise deregulated in human malignancies and they serve as a target for differentiating between tumour cells and normal tissues. The objective of this study was to determine whether gamma radiation could sensitize astrocytoma cell lines to the effects of imatinib in vitro. For this purpose, T98G and MOG-G-UVW astrocytoma cells were treated with imatinib alone or in combination with gamma radiation. The clonogenic survival assays performed with the combination of imatinib with radiation demonstrated that the drug had an additive antiproliferative effect in both cell lines considered. Imatinib confered greater radiosensitivity on the T98G tumour cells effecting a significant decrease in colony formation compared with radiation alone. These data provide a rationale to further investigate the combination of imatinib with radiation, keeping in mind that this may result in unexpected toxicities that are not observed with either treatment alone.

Misfolding of proteins with a polyglutamine expansion is facilitated by proteasomal chaperones

Deposition of misfolded proteins with a polyglutamine expansion is a hallmark of Huntington disease and other neurodegenerative disorders. Impairment of the proteolytic function of the proteasome has been reported to be both a cause and a consequence of polyglutamine accumulation. Here we found that the proteasomal chaperones that unfold proteins to be degraded by the proteasome but also have non-proteolytic functions co-localized with huntingtin inclusions both in primary neurons and in Huntington disease patients and formed a complex independently of the proteolytic particle. Overexpression of Rpt4 or Rpt6 facilitated aggregation of mutant huntingtin and ataxin-3 without affecting proteasomal degradation. Conversely, reducing Rpt6 or Rpt4 levels decreased the number of inclusions in primary neurons, indicating that endogenous Rpt4 and Rpt6 facilitate inclusion formation. In vitro reconstitution experiments revealed that purified 19S particles promote mutant huntingtin aggregation. When fused to the ornithine decarboxylase destabilizing sequence, proteins with expanded polyglutamine were efficiently degraded and did not aggregate. We propose that aggregation of proteins with expanded polyglutamine is not a consequence of a proteolytic failure of the 20S proteasome. Rather, aggregation is elicited by chaperone subunits of the 19S particle independently of proteolysis.

Mapping of the epitope of monoclonal antibody 2B4 to the proline-rich region of human Huntingtin, a region critical for aggregation and toxicity

Huntington's disease is a neurodegenerative disease caused by a polyglutamine (polyQ) expansion in Huntingtin, which provokes aggregation of a proteolytic amino-terminal fragment of the affected protein encompassing the polyQ expansion. Accumulation of mutant Huntingtin somehow triggers cellular dysfunction and leads to a progressive degeneration of striatal neurons. Despite considerable efforts, the function of Huntingtin as well as the precise molecular mechanisms by which the expanded polyQ elicits cellular dysfunction remain unclear. In addition, no treatment is available to prevent, cure, or even slow down the progression of this devastating disorder. Antibodies are valuable tools to understand protein function and disease mechanisms. Here, we have identified the epitope recognized by the mAb 2B4, a broadly used antibody generated against the amino-terminal region of Huntingtin, which detects both aggregated and soluble Huntingtin. The 2B4 antibody specifically recognizes amino acids 50-64 of human Huntingtin but not the murine homologous region. Furthermore, the 2B4 epitope resides within the proline-rich region of Huntingtin, which is critical for polyQ aggregation and toxicity. These properties suggest that the 2B4 antibody might be useful in antibody-based therapeutic strategies.

Surface properties and implantation site affect the capsular fibrotic overgrowth

Transplantation of encapsulated pancreatic islets is a promising approach for the treatment of type 1 diabetes. Large-scale application of this technique, however, is hampered by insufficient biocompatibility of the capsules. In this study, we have evaluated the biocompatibility of a new synthetic material with six different chemical groups on their surface (amino, carboxy-sulfate, carboxylate, hydroxylate, sulfate, and PMMA) used for the fabrication of the microcapsules. Eight Lewis rats were inoculated with a suspension of empty capsules made for each candidate material in the retroperitoneal ileopsoas muscle and renal subcapsular space. Four weeks later kidney and muscle containing the capsules were explanted, paraffin embedded, sectioned and stained with Sirius Red and Masson's Trichrome for histological analysis. The amount of fibrosis was also ultrastructurally evaluated with scanning electron microscopy. The samples were then subjected to digitalized quantitative analysis using specific software to determine the degree of fibrotic overgrowth. The quantification of collagen deposition, calculated in proximity of the microcapsules, was expressed as a percentage of the total area and can be considered a good index for the biocompatibility, an essential prerequisite for functional pancreatic islet transplantation. The results show that subcapsular renal space is the best implantation site and the positive surface charge induces a more intense collagen synthesis.

Usefulness of PCR strategies for early diagnosis of Chagas' disease reactivation and treatment follow-up in heart transplantation

Heart transplantation (HTx) is a useful therapy for end-stage Chagaś cardiomyopathy; however, Chagas reactivation remains a mayor complication. Parasitological methods offer poor diagnostic sensitivity, and use of more sensitive tools such as the Polymerase chain reaction (PCR) is usually necessary. In the present study, reactivation incidence and PCR usefulness for early reactivation diagnosis, as well as for treatment response evaluation during follow-up, were analyzed using Strout parasite detection test, in 10 of 222 consecutive HTx patients suffering Chagas cardiomyopathy. PCR strategies targeted to minicircle sequences (kDNA, detection limit 1 parasite/ 10 mL blood) and miniexon genes (SL-DNA, 200 parasite/10 mL) were performed to compare parasite burdens between samples. No patients received prophylactic antiprotozoal therapy (benznidazole). Five patients (50%) exhibited clinical reactivation within a mean period of 71.6 days; positive Strout results were observed in most cases presenting clinical manifestations. kDNA-PCR was positive 38-85 days before reactivation, whereas SLDNA-PCR became positive only 7-21 days later, revealing post-HTx parasitic load enhancement present prior to clinical reactivation development. Reactivations were successfully treated with benznidazole and generated negative PCR results. Results observed in this study indicate the value of PCR testing for an early diagnosis of Chagas reactivation as well as for monitoring treatment efficacy.

Effect of Preservation Solution on Graft Viability in Single-Lung Transplantation From Heart-Beating Donors in Pigs

BACKGROUND

Low-potassium-dextran preservation solution Perfadex (PER) may provide better outcome of transplanted lungs than high-potassium Euro-Collins (EC) solution. However, there are no comparative studies of the recipient inflammatory response to the graft.

PURPOSE

The purpose of this study was to compare EC versus PER as preservation solutions with respect to the functional performance and inflammatory response in single-lung transplantation from heart-beating donors in pigs.

MATERIALS AND METHODS

The donor left lung flushed with the corresponding cold preservation solution was stored at 3 degrees C for 3 hours. We assessed hemodynamic values and pulmonary function in the recipient over a 2-hour reperfusion period calculated as percent of basal values, and expressed as mean of the reperfusion period. Interleukin-8 (IL-8) concentration in the donor was estimated in bronchoalveolar lavage fluid 2 hours after recipient reperfusion. Biopsies of the donor right lung and the transplanted lung were obtained to measure myeloperoxidase (MPO) activity. IL-8 and MPO values were expressed as percent of the donor value. We evaluated the wet/dry pulmonary weight ratio (W/D), polymorphonuclear neutrophil count (PMN), and a score of histological damage in the transplanted graft.

RESULTS

Pulmonary function evaluated by % static: 66.6 +/- 6.8 (EC), 82.3 +/- 10.2 (PER), and dynamic: 74.0 +/- 7.3 (EC), 89.3 +/- 7.7 (PER) compliances, as well as % IL-8: 562.5 +/- 168.6 (EC), 232.3 +/- 148.7 (PER), % MPO: 485.9 +/- 194.9 (EC), 140.8 +/- 21.1 (PER), W/D: 9.9 +/- 3.1 (EC), 6.8 +/- 1.4 (PER), PMN 13.5 +/- 6.8 (EC), 5.5 +/- 3.3 (PER) and the histological damage score: 3.0 +/- 1.5 (EC), 0.7 +/- 0.4 (PER) showed significant differences between the EC and the PER (P < .01).

CONCLUSIONS

PER affords good lung preservation with early graft function and modest evidences of inflammation, lung injury, and edema compared with the EC perfused lung.

Critical Role of the Proline-rich Region in Huntingtin for Aggregation and Cytotoxicity in Yeast

Nine neurodegenerative diseases, such as Huntington, are caused by a polyglutamine (poly(Q)) expansion in otherwise unrelated proteins. Although poly(Q) expansion causes aggregation of the affected proteins, the protein context might determine the selective neuronal vulnerability found in each disease. Here we have report that, although expression of Huntingtin derivatives with a pathological poly(Q) expansion are innocuous in yeast, deletion of the flanking proline-rich region alters the shape and number of poly(Q) inclusions and unmasks toxic properties. Strikingly, deletion of Hsp104 increases the size of inclusions formed by expanded poly(Q) lacking the proline-rich region and abolishes toxicity. Overexpression of the chaperones Hsp104 or Hsp70 rescues growth defects in affected cells without resolving inclusions. However, aggregates formed by nontoxic Huntingtin derivatives or by toxic derivatives cured by chaperones are physically distinct from aggregates formed by toxic proteins. This study identifies the proline-rich region in Huntingtin as a profound cis-acting modulator of expanded poly(Q) toxicity and distinguishes between aggregates of toxic or non-toxic proteins.

Histochemical study of cardiac mast cells degranulation and collagen deposition: interaction with the cathecolaminergic system in the rat

Although their role in the cardiovascular system is still largely unknown, mast cells are present in the myocardium of both experimental animals and humans. Interestingly, cathecolaminergic nerve fibres and mast cells are often described in close morphological and functional interactions in various organs. In the present study we investigated the effects of chronic interference with beta-adrenergic receptors (via either sympathectomy or beta-blockade) on cardiac mast cell morphology/activation and on interstitial collagen deposition. In rats subjected to chemical sympathectomizy with the neurotoxin 6-hydroxydopamine (6-OHDA) we observed a significant increase of mast cell density, and in particular of degranulating mast cells, suggesting a close relationship between the cardiac catecholaminergic system and mast cell activation. In parallel, chronic 6-OHDA treatment was associated with increased collagen deposition. The influence of the beta-adrenergic receptor component was investigated in rats subjected to chronic propranolol administration, that caused a further significant increase in mast cell activation associated with a lower extent of collagen deposition when compared to chemical sympathectomy. These data are the first demonstration of a close relationship between rat cardiac mast cell activation and the catecholaminergic system, with a complex interplay with cardiac collagen deposition. Specifically, abrogation of the cardiac sympathetic efferent drive by chemical sympathectomy causes mast cell activation and interstitial fibrosis, possibly due to the local effects of the neurotoxin 6-hydroxydopamine. In contrast, beta-adrenergic blockade is associated with enhanced mast cell degranulation and a lower extent of collagen deposition in the normal myocardium. In conclusion, cardiac mast cell activation is influenced by beta-adrenergic influences.

Lung transplant at the Favaloro Foundation: A 13-year experience

BACKGROUND

The outcomes of lung transplantation (LT) are well known in developed countries, but not in Latin America. Our objective was to report the LT experience at a single center in Argentina.

METHODS

From June 1994 to February 2003, the 54 LT that were performed included 36 single-lung transplants SLT (45.5%) and 18 double-lung transplants (DSLT) (22.7%). Indications for SLT (n = 36) were emphysema (n = 23) and pulmonary fibrosis (n = 13); for DSLT (n = 18), bronchiectasis (n = 8), cystic fibrosis (n = 8), pulmonary emphysema (n = 1), and bronchiolitis obliterans syndrome caused by graft-versus-host disease after bone-marrow transplantation (n = 1). A univariate analysis, chi-square test with Yates' correction was used for qualitative variables; Wilcoxon-Mann-Whitney test, for quantitative and ordinal variables. Survivals were estimated by the Kaplan-Meier method.

RESULTS

In-hospital mortality (HM) was 21.1%. Among SLT, early death was due to sepsis in six patients and by ischemia-reperfusion injury (IRI) and acute rejection in other two. In DSLT, two patients died due to IRI and one, sepsis. The overall estimated survival rates at 1, 2, and 4 years were 70.1% +/- 6.5%, 54.3% +/- 7.2%, and 44.3% +/- 7.9%, respectively. The median overall survival was 26.5 (10 to 34) months. When HM was excluded, survival at 4 years was 51.3% +/- 8.7%. The estimated survival at 3 years was 43.3% +/- 9.3% for SLT and 58.7% +/- 13% for DSLT (P = 6). Survival differences according to the baseline diagnosis were not significant (P =.6). Median follow-up time (percentiles 25 to 75) was 16 (2 to 27) months.

CONCLUSIONS

Our LT program shows similar results to those reported by the International Society for Heart and Lung Transplantation for developed countries.

Orthotopic heart transplantation in elderly patients: A 10-year experience at a single center

INTRODUCTION

A consensus has not yet been reached regarding the indications for orthotopic heart transplantation (OHT) in elderly patients or the age limit contraindicating the procedure. The objective of this study was to assess OHT outcomes to determine whether elderly patients benefit from the procedure.

METHODS

From February 1993 to February 2003, 178 OHTs were performed on recipients of mean age 47.4 +/- 15 years (range, 4 to 74) including 80.3% men. The population was divided into two groups: group A included patients >/= 60 years, and group B those younger than that age. Survival was analyzed for the overall population and for both age groups during a 10-year follow-up period.

RESULTS

Group A included 36 patients (20.8%) and group B 142 patients (79.2%). Mean age was 63.7 +/- 2.9 years (60 to 74) in A, and 43 +/- 13.9 years (4 to 59) in B. In-hospital mortality was significantly higher among group A (n = 11, 31.4%) compared to B (n = 17, 12.1%, P =.008). Survival at 1, 5, and 10 years was 61.5% +/- 8%, 58.1% +/- 8.3%, and 49.8% +/- 10.5% group A; and 84.2% +/- 3%, 73.7% +/- 4.1%, and 69.9% +/- 4.7 for group B. Elderly patients showed a lower survival rate (49.8%) compared with the younger group (69.9%) at 10-year follow-up (P =.007). Conditional survival at 9 years failed to show significant differences (A 72.2% vs B 79.6%, P =.4).

CONCLUSION

In our population, elderly recipients showed a higher in-hospital mortality. However, when the first post-OHT year was excluded, we found similar survival rates for both age groups.

Targeting expression of expanded polyglutamine proteins to the endoplasmic reticulum or mitochondria prevents their aggregation

Aggregation of misfolded proteins is a characteristic of several neurodegenerative diseases. The huntingtin amino-terminal fragment with extended polyglutamine repeat forms aggregates closely associated with chaperones both in the cytoplasm and the nucleus. Because each cellular compartment contains distinct chaperones and because the molecular mechanisms controlling polyglutamine aggregation are largely unknown, we decided to investigate the influence of different cellular environments on the aggregation of this pathological protein. Here, we show that aggregation of a protein containing a polyglutamine stretch of pathological length is abolished when its expression is targeted to the endoplasmic reticulum. Once retrogradely transported outside the endoplasmic reticulum, the aggregation-prone polyglutamine-containing protein recovers its ability to aggregate. When expressed in the mitochondria, a protein containing 73 glutamines is entirely soluble, whereas the nucleocytosolic equivalent has an extremely high tendency to aggregate. Our data imply that polyglutamine aggregation is a property restricted to the nucleocytosolic compartment and suggest the existence of compartment-specific cofactors promoting or preventing aggregation of pathological proteins.

[Primary colonic lymphoma: report of two cases]

Primary colonic lymphoma is a rare condition. It may be associated with immunosuppressed states and inflammatory bowel disease. The pattern of presentation is not specific, this leads to lengthy in diagnosis. Authors report two personal cases and discuss the problem of diagnosis. Surgery followed by adjuvant chemotherapy is the standard treatment. Using this approach 5-years survival ranges from 27-55%.

Heat shock protein 90 modulates the unfolded protein response by stabilizing IRE1alpha

The molecular chaperone HSP90 regulates stability and function of multiple protein kinases. The HSP90-binding drug geldanamycin interferes with this activity and promotes proteasome-dependent degradation of most HSP90 client proteins. Geldanamycin also binds to GRP94, the HSP90 paralog located in the endoplasmic reticulum (ER). Because two of three ER stress sensors are transmembrane kinases, namely IRE1alpha and PERK, we investigated whether HSP90 is necessary for the stability and function of these proteins. We found that HSP90 associates with the cytoplasmic domains of both kinases. Both geldanamycin and the HSP90-specific inhibitor, 514, led to the dissociation of HSP90 from the kinases and a concomitant turnover of newly synthesized and existing pools of these proteins, demonstrating that the continued association of HSP90 with the kinases was required to maintain their stability. Further, the previously reported ability of geldanamycin to stimulate ER stress-dependent transcription apparently depends on its interaction with GRP94, not HSP90, since geldanamycin but not 514 led to up-regulation of BiP. However, this effect is eventually superseded by HSP90-dependent destabilization of unfolded protein response signaling. These data establish a role for HSP90 in the cellular transcriptional response to ER stress and demonstrate that chaperone systems on both sides of the ER membrane serve to integrate this signal transduction cascade.

Alterations in an IRE1-RNA complex in the mammalian unfolded protein response

IRE1 proteins mediate cellular responses to accumulation of malfolded proteins in the endoplasmic reticulum in the yeast and mammalian unfolded protein responses. A sensitive in vivo u.v. crosslinking assay showed that IRE1 proteins are intimately associated with RNA in mammalian cells. The IRE1-associated RNA fragments recovered by this assay were different in stressed and unstressed cells. The amount of RNA associated with IRE1 that could be revealed by end-labeling with T4 kinase was greater in IRE1-containing complexes isolated from stressed cells. Furthermore, the RNA fragments recovered from complexes found in stressed cells were shorter than those from unstressed cells, revealing a dynamic change in the IRE1-RNA complex during the UPR. Formation of the complex between IRE1 and RNA was dependent on both the kinase and endonuclease domains of IRE1, and involved pre-existing RNA species. When viewed in the context of the known importance of Ire1p-HAC1 mRNA interactions to the yeast unfolded protein response, these findings suggest that full-length mammalian IRE1s also engage RNA molecules as downstream effectors.