One hundred fifty years ago glial cells were discovered as a second, non-neuronal, cell type in the central nervous system. To ascribe a function to these new, enigmatic cells, it was suggested that they either glue the neurons together (the Greek word “γλια” means “glue”) or provide a robust scaffold for them (“support cells”). Although both speculations are still widely accepted, they would actually require quite different mechanical cell properties, and neither one has ever been confirmed experimentally. We investigated the biomechanics of CNS tissue and acutely isolated individual neurons and glial cells from mammalian brain (hippocampus) and retina. Scanning force microscopy, bulk rheology, and optically induced deformation were used to determine their viscoelastic characteristics. We found that ( i ) in all CNS cells the elastic behavior dominates over the viscous behavior, ( ii ) in distinct cell compartments, such as soma and cell processes, the mechanical properties differ, most likely because of the unequal local distribution of cell organelles, ( iii ) in comparison to most other eukaryotic cells, both neurons and glial cells are very soft (“rubber elastic”), and ( iv ) intriguingly, glial cells are even softer than their neighboring neurons. Our results indicate that glial cells can neither serve as structural support cells (as they are too soft) nor as glue (because restoring forces are dominant) for neurons. Nevertheless, from a structural perspective they might act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as a soft substrate required for neurite growth and facilitating neuronal plasticity.

Increased stiffness of reactive glial cells may impede neurite growth and contribute to the poor regenerative capabilities of the mammalian central nervous system. We induced reactive gliosis in rodent retina by ischemia‐reperfusion and assessed intermediate filament (IF) expression and the viscoelastic properties of dissociated single glial cells in wild‐type mice, mice lacking glial fibrillary acidic protein and vimentin ( GFAP ^−/− Vim ^−/− ) in which glial cells are consequently devoid of IFs, and normal Long‐Evans rats. In response to ischemia‐reperfusion, glial cells stiffened significantly in wild‐type mice and rats but were unchanged in GFAP ^−/− Vim ^−/− mice. Cell stiffness (elastic modulus) correlated with the density of IFs. These results support the hypothesis that rigid glial scars impair nerve regeneration and that IFs are important determinants of cellular viscoelasticity in reactive glia. Thus, therapeutic suppression of IF up‐regulation in reactive glial cells may facilitate neuroregeneration.—Lu, Y.‐B., Iandiev, I., Hollborn, M., Korber, N., Ulbricht, E., Hirrlinger, P. G., Pannicke, T., Wei, E.‐Q., Bringmann, A., Wol‐burg, H., Wilhelmsson, U., Pekny, M., Wiedemann, P., Reichenbach, A., Kas, J. A. Reactive glial cells: increased stiffness correlates with increased intermediate filament expression. FASEB J. 25, 624–631 (2011). www.fasebj.org

Rationale: Idiopathic pulmonary fibrosis (IPF) is an irreversible, fatal interstitial lung disease lacking specific therapeutics. Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the nicotinamide adenine dinucleotide (NAD) salvage biosynthesis pathway and a cytokine, has been previously reported as a biomarker for lung diseases; however, the role of NAMPT in pulmonary fibrosis has not been elucidated.

Ubiquitin (Ub) is an important signaling protein. Recent studies have shown that Ub can be enzymatically phosphorylated at S65, and that the resulting pUb exhibits two conformational states—a relaxed state and a retracted state. However, crystallization efforts have yielded only the structure for the relaxed state, which was found similar to that of unmodified Ub. Here we present the solution structures of pUb in both states obtained through refinement against state-specific NMR restraints. We show that the retracted state differs from the relaxed state by the retraction of the last β-strand and by the extension of the second α-helix. Further, we show that at 7.2, the pK_a value for the phosphoryl group in the relaxed state is higher by 1.4 units than that in the retracted state. Consequently, pUb exists in equilibrium between protonated and deprotonated forms and between retracted and relaxed states, with protonated/relaxed species enriched at slightly acidic pH and deprotonated/retracted species enriched at slightly basic pH. The heterogeneity of pUb explains the inability of phosphomimetic mutants to fully mimic pUb. The pH-sensitive conformational switch is likely preserved for polyubiquitin, as single-molecule FRET data indicate that pH change leads to quaternary rearrangement of a phosphorylated K63-linked diubiquitin. Because cellular pH varies among compartments and changes upon pathophysiological insults, our finding suggests that pH and Ub phosphorylation confer additional target specificities and enable an additional layer of modulation for Ub signals.

Lung ischemia-reperfusion injury (LIRI) is associated with many diseases, including primary graft dysfunction after lung transplantation, and has no specific and effective therapies. Necroptosis contributes to the pathogenesis of ischemia-reperfusion injury. Necrostatin-1 (Nec-1), the necroptosis inhibitor targeting RIPK1, has been reported to alleviate ischemia-reperfusion injury in various organs. However, the underlying mechanism of Nec-1 in LIRI remains unclear. In this paper, an in vivo LIRI model was built up by left lung hilar clamping in mice, and an in vitro cold ischemia-reperfusion (CI/R) model using BEAS-2B cells was applied to mimic the lung transplantation setting. We found Nec-1 significantly alleviated ischemia-reperfusion-induced lung injury, cytokine releasing, and necroptosis of epithelial cells in mouse lungs. In vitro, Nec-1 also mitigated CI/R-induced cell death and inflammatory responses in BEAS-2B cells, and these protective effects were achieved by simultaneously inhibiting the formation of necrosome and RIPK1-dependent apoptosis. However, Nec-1 decreased the necrosome number but increased the apoptosis level in lung tissues after ischemia reperfusion. We further clarified that Nec-1 could also attenuate lung injury by promoting neutrophil apoptosis from flow cytometry. In conclusion, Nec-1 alleviated lung ischemia-reperfusion injury by inhibiting necroptosis and apoptosis of epithelial cells and promoting the apoptosis of neutrophils. Thus, Nec-1 could be a promising medication against primary graft dysfunction after lung transplantation.