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Erythropoietin on a tightrope: balancing neuronal and vascular protection between intrinsic and extrinsic pathways.

Enthusiasm for erythropoietin (EPO) as a broad cytoprotective agent continues to increase at an almost exponential rate. The premise that EPO was required only for erythropoiesis was eventually shed by recent work demonstrating the existence of EPO and its receptor in other organs and tissues outside of the liver and the kidney, such as the brain and heart. As a result, EPO has been identified as a possible candidate in the formulation of therapeutic strategies for both cardiac and nervous system diseases. EPO has been shown to mediate an array of vital cellular functions that involve progenitor stem cell development, cellular protection, angiogenesis, DNA repair, and cellular longevity. An important requirement to achieve the goal of preventing or even reducing cellular injury by any cytoprotective agent is the ability to uncover the cellular pathways that ultimately drive a cell to its demise. We present for consideration several critical cellular pathways modulated by EPO that involve Janus kinase 2 (Jak2), the serine-threonine kinase Akt, forkhead transcription factors, glycogen synthase kinase-3beta (GSK-3beta), cellular calcium, protein kinase C, caspases, as well as the control of inflammatory microglial activation. As we continue to gain new insight into these pathways, EPO should emerge as a critical agent for the development, maturation, and survival of cells throughout the body.

Animals↗

The science of weaning: when and how?

Weaning patients from long-term mechanical ventilation continues to be a goal of clinicians and scientists and the hospitals charged with their care. This article describes the science of the "wean" and the "how" of weaning. A goal of scientists has been to develop predictors that determine accurately the optimal time to initiate weaning. Unfortunately to date none has emerged as superior. Quite simply, predictors do not predict. In contrast, methods that decrease variation in care practices have demonstrated positive outcomes. The methods include protocols for weaning trials and sedation and other system initiatives inclusive of a multidisciplinary plan of care or clinical pathway.

Clinical Protocols↗

Serine utilization in mouse liver: influence of caloric restriction and aging.

The influence of caloric restriction (CR) on the activities of hepatic serine metabolizing enzymes in young (3 months) and old (30 months) mice was studied. Serine dehydratase (SDH) activity increased markedly with age in both diet groups and in old mice was higher in the CR group. No effects of CR were observed in the young. Serine:pyruvate transaminase (SPT) and glycerate kinase activities were unaffected by age and diet. However, glycerate dehydrogenase activity was decreased in old CR mice but not in young CR. The results of this study show that long-term CR influenced serine utilization only in the pathway catalyzed by SDH. This suggests that in mouse liver this pathway is critical for serine utilization in gluconeogenesis, while the SPT pathway plays a minor role. The increase in SDH activity with long-term CR is consistent with sustained increase in gluconeogenesis.

Aging↗

Collagen-homology domain 1 deletion mutant of Shc suppresses transformation mediated by neu through a MAPK-independent pathway.

Shc proteins are implicated in coupling receptor tyrosine kinase to the mitogen-activated protein kinase (MAPK) pathway by recruiting Grb2/SOS to the plasma membrane. To better understand the role of Shc in the oncogenesis by point-mutation activated neu (p185*), we transfected a Shc mutant (ShcdeltaCHI), which lacks the Grb2 binding site Y317 by deletion of collagen-homology domain 1, into p185*-transformed NIH3T3 cells. The cellular transformation phenotypes were found to be largely suppressed by expression of ShcdeltaCH1. Although ShcdeltaCH1 still retained another Grb2 binding site (Y239/240), we did not detect its physical association with Grb2. We also found that ShcdeltaCH1 could associate with p185*; however, this association did not interfere with the endogenous Shc-p185* interaction or the Shc-Grb2 interaction. In addition, p185*-mediated MAPK and Elk activation likewise were not inhibited by ShcdeltaCH1 expression. Taken together, these data demonstrate that ShcdeltaCH1 suppresses the transformation induced by activated neu through a MAPK-independent pathway, indicating that Shc may be involved in other signal pathway(s) critical for cellular transformation in addition to the MAPK pathway.

Adaptor Proteins, Signal Transducing↗

Low concentrations of immunoglobulin G antibodies to Salmonella serogroup C in C2 deficiency: suggestion of a mannan-binding lectin pathway-dependent mechanism.

The influence of complement on immune responses to polysaccharides is debatable. We examined the serum concentrations of IgM and IgG antibody against Salmonella O-antigen specific oligosaccharides representing the serogroups B, C and D, and against capsular polysaccharides of Streptococcus pneumoniae serotypes 6 and 23 in C2-deficient adults and in healthy controls. A sharp contrast of findings was found for antibodies against the CO antigen, an activator of the mannan-binding lectin (MBL) pathway of complement activation. The C2-deficient group showed normal IgM and markedly low IgG antibody levels. Similar findings were made in adults with low concentrations of MBL. This suggests that the recruitment of classical pathway C3 convertase through the MBL pathway is critically involved in isotype switching of antibodies against MBL pathway activating antigens during immune system maturation. The findings imply a new role of the MBL pathway, and an additional link between innate and acquired immunity. Specific IgM against BO was moderately low in C2 deficiency. Other differences for the Salmonella antigens were not found. Markedly raised IgM antibody levels against pneumococcal polysaccharides in C2 deficiency probably Salmonella reflected past infections. The absence of a concomitant increase of specific IgG might possibly be explained by impaired IgM to IgG switching.

Adult↗