Abstract

A comparative study on the alcohol dehydrogenase (ADH) Class I gene cluster in primates:
duplicated genes "escaped" from homogenization via gene conversion (?)

Hiroki Oota, Casey Dunn, William C. Speed, Andrew J. Pakstis, Judith. R. Kidd and Kenneth. K. Kidd

Gene duplication and conversion are key mechanisms for genome evolution. Recent studies show that gene conversion is a very common phenomenon in various genomes, and there are various lines of evidence that duplicated genes have been homogenized by gene conversion(s). To diverge, the new gene(s) generated by duplication(s) should have a strong selective advantage, "escaping" from the homogenization. The ADH gene family exists widely in the genomes of many organisms, and provides a fine evolutionary model. Humans have seven ADH genes classified into five classes; the Class I ADH genes (ADH1A, ADH1B, ADH1C) expressed primarily in liver are the main enzymes catalyzing ethanol oxidization. These Class I genes show very high nucleotide similarity both in exons (>90%) and introns (>70%), suggesting duplication events occurred probably within the primate lineage because it is known that mice and rats have only one Class I gene. We analyze nucleotide sequences of introns from all three Class I genes for five primates species, and compare the sequences with those of human. Here we discuss about (1) why such similar genes are present in humans, and (2) whether the similarity is generated by gene conversion(s).

Photodiagnostic test procedures: an algorithm to diagnose patients with photosensitivity

Percy Lehmann

Diagnosis of photodermatoses is based on the patient's history, morphology of the lesions, histopathology and the results of phototesting. However, generally accepted guidelines for phototesting are lacking. Laboratory data may help to exclude differential diagnoses, e.g., porphyrias. In most photodermatoses, however, they are of no help. Since skin lesions often subside rapidly after sun exposure, it is desirable to induce the dermatosis in a given test area with appropriate testprotocols. This is most important in case a patient presents with a vague medical history of sun sensitivity without permanent skin lesions. Progress has been made to induce in loco a variety of photodermatoses or photoaggravated dermatoses, e.g., polymorphous light eruption, hydroa vacciniformia, chronic actinic dermatitis (including persistent light eruption), solar urticaria and lupus erythematosus. At our Department of Dermatology all patients with a history of photosensitivity undergo an multistep phototest work-up including the following procedures:

a) Determination of threshold doses for erythema [minimal erythema dose (MED)－UVB] and pigmentation [(immediate pigment darkening, (IPD), minimal tanning dose, (MTD)];
b) Reproduction of specific skin lesions by provocative phototesting with standardized irradiation protocols;
and
c) Identification of photosensitizers by photopatch test and systemic photochallenge.

Reversing EMT

Jun-ichi Hanai

Epithelial-mesenchymal transition (EMT) is a process whereby epithelial cell layers lose polarity and cell-cell contacts and undergo a massive cytoskeleton reorganization involving the remodeling of the actin microfilament mesh. Concurrent with a loss of epithelial cell adhesion components, cells undergoing EMT acquire expression of mesenchymal components and manifest a migratory phenotype, that is a fundamental process govering morphogenesis in multicellular organisms during embryonic development. This EMT process, first appreciated by developmental biologists in the early 1980s, is now attracting increasing attention from oncologists and nephrologists, because the process is also reactivated in a variety of diseases including fibrosis and in the progression of carcinoma. EMT is always associated with acquisition of cell motility. In some cases, cells undergoing EMT start synthesizing extracellular matrix molecules such as fibronectin and certain types of collagen. They may also synthesize proteolytic enzymes involved in matrix degradation that contribute to cell motility and invasiveness. However, not all EMTs exhibit the whole range of changes listed here. The transformation of mesenchyme to epithelium (MET), the reverse of EMT, also occurs during embryonic development. The differentiation of the metanephric blastema provides a striking example of MET, which is controlled by factors secreted from the ureteric bud, and these epithelial inducers have been purified from ureteric bud cell lines. These molecules are endogeneous MET inducers. We have tested some of these (BMP7 and lipocalin 2) for their epithelial inducing activities in the context of tumor biology and fibrosis and these results with potential therapeutic applications have been discussed.

Alterations in coagulation and fibrinolysis in ARDS

Lorraine B. Ware

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are common causes of acute respiratory failure. Mortality from ALI/ARDS is unacceptably high (30－50%) and no specific therapy is beneficial other than a protective mechanical ventilation strategy. Evidence from our laboratory and other investigators suggests that both systemic and intraalveolar coagulation and fibrinolysis are abnormal in patients with ALI/ARDS with a shift towards a procoagulant, antifibrinolytic state. The upregulation of coagulation and downregulation of fibrinolysis in the injured alveolus may be an important factor in the pathogenesis of ALI/ARDS, modulating the formation and resolution of lung injury. Initiation of coagulation also has potent proinflammatory effects that may contribute to the intra-alveolar and systemic inflammatory cascade that characterizes acute lung injury. However, the factors that govern the intra-alveolar coagulation environment are not known. Our lab has been investigating the hypothesis that the alveolar epithelium actively modulates intra-alveolar coagulation and fibrinolysis. Exposure of the alveolar epithelium to a proinflammatory stimulus leads to altered expression and activity of key proteins in the coagulation and fibrinolysis cascades including tissue factor, thrombomodulin, endothelial protein C receptor and plasminogen activator inhibitor-1. Modulation of both the systemic and the intra-alveolar coagulation and fibrinolytic cascades may be a novel therapeutic target in ALI/ARDS.

Role of IGF-I as a neuroprotective factor

Ignacio Torres Aleman

IGF-I belongs to the insulin family of peptide hormones displaying an ample spectrum of actions throughout the body. In the brain, IGF-I participates in a network of protective signaling between different cell types, including neurons, glia, vessel endothelia and choroid plexus epithelium, and the periphery. Neuroprotective activities of IGF-I range from those addressing basic cell needs such as energy balance or oxygen supply to brain-specific requirements such as modulation of neuronal plasticity underlying cognitive performance. Recent developments in animal models of human disease emphasize the potential therapeutic utility of IGF-I and its downstream targets in brain illnesses such as Alzheimer’s dementia or cerebellar ataxia, and underscore the important role played by non-neuronal cells in IGF-I neuroprotection. While novel findings indicate that blood-borne IGF-I is an important, and somewhat unexpected trophic source for brain cells, the precise role played by brain IGF-I is still not clear. Similarly, molecular pathways of IGF-I neuroprotection remain largely uncharted. Work in progress indicates new molecular targets of IGF-I neuroprotection including the phosphatases calcineurin and PTEN in the astrocytic reaction to inflammatory challenge and oxidative stress respectively, or the endocytic epithelial receptor LRP2/megalin in brain clearance of amyloid. Understanding the role played by IGF-I in the adult brain will surely illuminate essential aspects of neuroprotective mechanisms and help us develop new therapeutic avenues.

Mechanisms of UV-induced immunosuppression

Thomas Schwarz

Ultraviolet radiation (UV), in particular the UVB range, suppresses the immune system in several ways. UVB inhibits antigen presentation, induces the release of immunosuppressive cytokines and causes apoptosis of leukocytes. UVB, however, does not cause general immunosuppression but rather inhibits immune reactions in an antigen-specific fashion. Epicutaneous application of contact allergens onto UV-exposed skin does not cause sensitization but induces antigen-specific tolerance since such an individual cannot be sensitized against the very same allergen at a later time point, although the sensitization against other allergens is not impaired. This specific immunosuppression is due to the development of antigen-specific suppressor/regulatory T cells. UVB-induced DNA damage is a major molecular trigger of UV-mediated immunosuppression. Reduction of DNA damage via exogenous DNA repair enzymes mitigates UV-induced immunosuppression. Likewise IL-12 which exhibits the capacity to reduce DNA damage is able to prevent UV-induced immunosuppression and even to break established tolerance. Presentation of the antigen by UV-damaged but still living Langerhans cells containing UV-induced DNA damage in the lymph nodes appears to be an essential requirement for the development of regulatory T cells. Recent experimental data indicate that photopheresis which is highly beneficial in the treatment of autoimmune diseases, transplant rejection and graft-versushost- disease, might also work via the induction of regulatory T cells. While in this case the development of regulatory T cells may be regarded as beneficial they can also be harmful since they play an important role in photocarcinogenesis. Studies addressing the molecular mechanisms underlying UV-induced immunosuppression will contribute to a better understanding how UV acts as a pathogen but on the other hand can be also used as a therapeutic tool.