Intercellular junctions of hyperplastic retinal pigment epithelium

In rats with retinopathies induced by excess fluorescent light or injections of urethane, the retinal pigment epithelium (RPE) undergoes focal hyperplasia. Neither intravascularly injected horseradish peroxidase or lanthanum nitrate penetrated the sensory retina at these hyperplastic sites. Electron microscopy revealed that this was due to the persistence of intact tight junctions among a single layer of hyperplastic cells facing the sensory retina. These junctions prevented intraocularly injected microperoxidase from passing as well. Cells within the hyperplastic foci were connected only by adherent junctions that presented no permeability barrier.     

Apoptosis initiated by Bcl-2-regulated caspase activation independently of the cytochrome c/Apaf-1/caspase-9 apoptosome

Apoptosis is an evolutionarily conserved cell suicide process executed by cysteine proteases (caspases) and regulated by the opposing factions of the Bcl-2 protein family. Mammalian caspase-9 and its activator Apaf-1 were thought to be essential, because mice lacking either of them display neuronal hyperplasia and their lymphocytes and fibroblasts seem resistant to certain apoptotic stimuli. Because Apaf-1 requires cytochrome c to activate caspase-9, and Bcl-2 prevents mitochondrial cytochrome c release, Bcl-2 is widely believed to inhibit apoptosis by safeguarding mitochondrial membrane integrity. Our results suggest a different, broader role, because Bcl-2 overexpression increased lymphocyte numbers in mice and inhibited many apoptotic stimuli, but the absence of Apaf-1 or caspase-9 did not. Caspase activity was still discernible in cells lacking Apaf-1 or caspase-9, and a potent caspase antagonist both inhibited apoptosis and retarded cytochrome c release. We conclude that Bcl-2 regulates a caspase activation programme independently of the cytochrome c/Apaf-1/caspase-9 'apoptosome', which seems to amplify rather than initiate the caspase cascade.     

Das Strukturbild der Arterienwand unter lebensnahen Präparationsbedingungen und seine physiologische und pathologische Bedeutung

Summary At first sight it seems impossible to obtain a picture of arterial structure fixed in the true conditions of life. The arterial wall particularly is exposed to severe forces of alteration at the moment of death. Even before autolysis and rigor mortis, it is submitted to a triple trauma: the sudden cessation of rhythmical pulsation, the emptying of the lumina and the blood coagulation. Nevertheless precisely, these factors give us a simple and relatively safetest for deciding whether a histological preparation corresponds to the true life conditions; we may assume this to be so when the lumen of small blood vessels is full ofuncoagulated blood. Studies on such preparations show that during life there are no particular annular and longitudinal muscle fibres in the arterial wall, it is rather theplasticity and activity of a unitary musculature which determines the appearance of variously oriented fibers in histological preparations. As for the elastic tissue, it appears as a continuous line, when in activity; curvatures or ruptures mean a limitation or suppression of the elastic function. Observations on the so-called regulating apparatus in arteries of man, completed by others on dogs under influence of adrenalin, lead one to consider the particular relationship of clear muscle cells and elastic elements as themorphological equivalent of vasoconstrictive action. These results call for a revision of some histological, histopathological and even physiological concepts, such as the accepted histological views on the existence of arterial closure apparatus. The aspects described as sphincters, Polster, bourrelets, valves are not permanent structures butsnapshots of moving parts of the arterial wall. The clear muscular cells named epitheloid cells, Quellzellen, Leiomyoblasts are muscle fibers quasi surprised by the fixation in theactive state.     

Linear ubiquitination prevents inflammation and regulates immune signalling

Members of the tumour necrosis factor (TNF) receptor superfamily have important functions in immunity and inflammation. Recently linear ubiquitin chains assembled by a complex containing HOIL-1 and HOIP (also known as RBCK1 and RNF31, respectively) were implicated in TNF signalling, yet their relevance in vivo remained uncertain. Here we identify SHARPIN as a third component of the linear ubiquitin chain assembly complex, recruited to the CD40 and TNF receptor signalling complexes together with its other constituents, HOIL-1 and HOIP. Mass spectrometry of TNF signalling complexes revealed RIP1 (also known as RIPK1) and NEMO (also known as IKKγ or IKBKG) to be linearly ubiquitinated. Mutation of the Sharpin gene (Sharpin(cpdm/cpdm)) causes chronic proliferative dermatitis (cpdm) characterized by inflammatory skin lesions and defective lymphoid organogenesis. Gene induction by TNF, CD40 ligand and interleukin-1β was attenuated in cpdm-derived cells which were rendered sensitive to TNF-induced death. Importantly, Tnf gene deficiency prevented skin lesions in cpdm mice. We conclude that by enabling linear ubiquitination in the TNF receptor signalling complex, SHARPIN interferes with TNF-induced cell death and, thereby, prevents inflammation. Our results provide evidence for the relevance of linear ubiquitination in vivo in preventing inflammation and regulating immune signalling.