Prone Positioning for ARDS. still misunderstood and misused

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by a non-cardiogenic pulmonary edema with bilateral chest X-ray opacities and hypoxemia refractory to oxygen therapy and low level of positive end-expiratory pressure (1). Recently, a large observational study reported an ARDS prevalence of 10.4% of all ICU admissions and of 23.4% of all subjects receiving mechanical ventilation (2). Despite these alarming numbers, according to the most recent literature, ARDS is still under-recognized, undertreated, and associated with a mortality rate that in the most severe forms is close to 50% (2)

Adaptation to G93A superoxide dismutase 1 in a motor neuron cell line model of amyotrophic lateral sclerosis. The role of glutathione

Motor neuron degeneration in amyotrophic lateral sclerosis involves oxidative damage. Glutathione (GSH) is critical as an antioxidant and a redox modulator. We used a motor neuronal cell line (NSC-34) to investigate whether wild-type and familial amyotrophic lateral sclerosis-linked G93A mutant Cu,Zn superoxide dismutase (wt ⁄G93ASOD1) modified the GSH pool and glutamate cysteine ligase (GCL), the rate-limiting enzyme for GSH synthesis. We studied the effect of various G93ASOD1 levels and exposure times. Mutant Cu,Zn superoxide dismutase induced an adaptive process involving the upregulation of GSH synthesis, even at very low expression levels. However, cells with a high level of G93ASOD1 cultured for 10 weeks showed GSH depletion and a decrease in expression of the modulatory subunit of GCL. These cells also had lower levels of GSH and GCL activity was not induced after treatment with the pro-oxidant tertbutylhydroquinone. Cells with a low level of G93ASOD1 maintained higher GSH levels and GCL activity, showing that the exposure time and the level of the mutant protein modulate GSH synthesis. We conclude that failure of the regulation of the GSH pathway caused by G93ASOD1 may contribute to motor neuron vulnerability and we identify this pathway as a target for therapeutic intervention

MAPK signaling promotes axonal degeneration by speeding the turnover of the axonal maintenance factor NMNAT2

Injury-induced (Wallerian) axonal degeneration is regulated via the opposing actions of pro-degenerative factors such as SARM1 and a MAPK signal and pro-survival factors, the most important of which is the NA

NMNAT1 inhibits axon degeneration via blockade of SARM1-mediated NAD+ depletion

Overexpression of the NAD(+) biosynthetic enzyme NMNAT1 leads to preservation of injured axons. While increased NAD(+) or decreased NMN levels are thought to be critical to this process, the mechanism(s) of this axon protection remain obscure. Using steady-state and flux analysis of NAD(+) metabolites in healthy and injured mouse dorsal root ganglion axons, we find that rather than altering NAD(+) synthesis, NMNAT1 instead blocks the injury-induced, SARM1-dependent NAD(+) consumption that is central to axon degeneration. DOI: http://dx.doi.org/10.7554/eLife.19749.00

WldS protein requires Nmnat activity and a short N-terminal sequence to protect axons in mice

The slow Wallerian degeneration (WldS) protein protects injured axons from degeneration. This unusual chimeric protein fuses a 70–amino acid N-terminal sequence from the Ube4b multiubiquitination factor with the nicotinamide adenine dinucleotide–synthesizing enzyme nicotinamide mononucleotide adenylyl transferase 1. The requirement for these components and the mechanism of WldS-mediated neuroprotection remain highly controversial. The Ube4b domain is necessary for the protective phenotype in mice, but precisely which sequence is essential and why are unclear. Binding to the AAA adenosine triphosphatase valosin-containing protein (VCP)/p97 is the only known biochemical property of the Ube4b domain. Using an in vivo approach, we show that removing the VCP-binding sequence abolishes axon protection. Replacing the WldS VCP-binding domain with an alternative ataxin-3–derived VCP-binding sequence restores its protective function. Enzyme-dead WldS is unable to delay Wallerian degeneration in mice. Thus, neither domain is effective without the function of the other. WldS requires both of its components to protect axons from degeneration

Activity-based E3 ligase profiling uncovers an E3 ligase with esterification activity

Ubiquitination is initiated by transfer of ubiquitin (Ub) from a ubiquitin-activating enzyme (E1) to a ubiquitin-conjugating enzyme (E2), producing a covalently linked intermediate (E2-Ub)(1). Ubiquitin ligases (E3s) of the 'really interesting new gene' (RING) class recruit E2-Ub via their RING domain and then mediate direct transfer of ubiquitin to substrates(2). By contrast, 'homologous to E6-AP carboxy terminus' (HECT) E3 ligases undergo a catalytic cysteine-dependent transthiolation reaction with E2-Ub, forming a covalent E3-Ub intermediate(3,4). Additionally, RING-between-RING (RBR) E3 ligases have a canonical RING domain that is linked to an ancillary domain. This ancillary domain contains a catalytic cysteine that enables a hybrid RING-HECT mechanism(5). Ubiquitination is typically considered a post-translational modification of lysine residues, as there are no known human E3 ligases with non-lysine activity. Here we perform activity-based protein profiling of HECT or RBR-like E3 ligases and identify the neuron-associated E3 ligase MYCBP2 (also known as PHR1) as the apparent single member of a class of RING-linked E3 ligase with esterification activity and intrinsic selectivity for threonine over serine. MYCBP2 contains two essential catalytic cysteine residues that relay ubiquitin to its substrate via thioester intermediates. Crystallographic characterization of this class of E3 ligase, which we designate RING-Cys-relay (RCR), provides insights into its mechanism and threonine selectivity. These findings implicate non-lysine ubiquitination in cellular regulation of higher eukaryotes and suggest that E3 enzymes have an unappreciated mechanistic diversity