The influence of storage temperature during machine perfusion on preservation quality of marginal donor livers

Background

Although non-heart-beating donors have the potential to increase the number of available organs, the livers are used very seldom because of the risk of primary non-function. There is evidence that machine perfusion is able to improve the preservation of marginal organs, and therefore we evaluated in our study the influence of the perfusate temperature during oxygenated machine perfusion on the graft quality.

Methods

Livers from male Wistar rats were harvested after 60-min warm ischemia induced by cardiac arrest. The portal vein was cannulated and the liver flushed with Lifor® (Lifeblood Medical, Inc.) organ preservation solution for oxygenated machine perfusion (MP) at 4, 12 or 21 °C. Other livers were flushed with HTK and stored at 4 °C by conventional cold storage (4 °C-CS). Furthermore two groups with either warm ischemic damage only or without any ischemic damage serve as control groups. After 6 h of either machine perfusion or cold storage all livers were normothermic reperfused with Krebs–Henseleit buffer, and functional as well as structural data were analyzed.

Results

Contrary to livers stored by static cold storage, machine perfused livers showed independently of the perfusate temperature a significantly decreased enzyme release of hepatic transaminases (ALT) during isolated reperfusion. Increasing the machine perfusion temperature to 21 °C resulted in a marked reduction of portal venous resistance and an increased bile production.

Conclusions

Oxygenated machine perfusion improves viability of livers after prolonged warm ischemic damage. Elevated perfusion temperature of 21 °C reconstitutes the hepatic functional capacity better than perfusion at 4 or 12 °C.     

Pacemaking by HCN channels requires interaction with phosphoinositides

Hyperpolarization-activated, cyclic-nucleotide-gated (HCN) channels mediate the depolarizing cation current (termed I(h) or I(f)) that initiates spontaneous rhythmic activity in heart and brain. This function critically depends on the reliable opening of HCN channels in the subthreshold voltage-range. Here we show that activation of HCN channels at physiologically relevant voltages requires interaction with phosphoinositides such as phosphatidylinositol-4,5-bisphosphate (PIP(2)). PIP(2) acts as a ligand that allosterically opens HCN channels by shifting voltage-dependent channel activation approximately 20 mV toward depolarized potentials. Allosteric gating by PIP(2) occurs in all HCN subtypes and is independent of the action of cyclic nucleotides. In CNS neurons and cardiomyocytes, enzymatic degradation of phospholipids results in reduced channel activation and slowing of the spontaneous firing rate. These results demonstrate that gating by phospholipids is essential for the pacemaking activity of HCN channels in cardiac and neuronal rhythmogenesis.     

An evolutionary strategy for all-atom folding of the 60-amino-acid bacterial ribosomal protein l20

We have investigated an evolutionary algorithm for de novo all-atom folding of the bacterial ribosomal protein L20. We report results of two simulations that converge to near-native conformations of this 60-amino-acid, four-helix protein. We observe a steady increase of "native content" in both simulated ensembles and a large number of near-native conformations in their final populations. We argue that these structures represent a significant fraction of the low-energy metastable conformations, which characterize the folding funnel of this protein. These data validate our all-atom free-energy force field PFF01 for tertiary structure prediction of a previously inaccessible structural family of proteins. We also compare folding simulations of the evolutionary algorithm with the basin-hopping technique for the Trp-cage protein. We find that the evolutionary algorithm generates a dynamic memory in the simulated population, which leads to faster overall convergence.     

ABC A-subfamily transporters: structure, function and disease

ABC transporters constitute a family of evolutionarily highly conserved multispan proteins that mediate the translocation of defined substrates across membrane barriers. Evidence has accumulated during the past years to suggest that a subgroup of 12 structurally related "full-size" transporters, referred to as ABC A-subfamily transporters, mediates the transport of a variety of physiologic lipid compounds. The emerging importance of ABC A-transporters in human disease is reflected by the fact that as yet four members of this protein family (ABCA1, ABCA3, ABCR/ABCA4, ABCA12) have been causatively linked to completely unrelated groups of monogenetic disorders including familial high-density lipoprotein (HDL) deficiency, neonatal surfactant deficiency, degenerative retinopathies and congenital keratinization disorders. Although the biological function of the remaining 8 ABC A-transporters currently awaits clarification, they represent promising candidate genes for a presumably equally heterogenous group of Mendelian diseases associated with perturbed cellular lipid transport. This review summarizes our current knowledge on the role of ABC A-subfamily transporters in physiology and disease and explores clinical entities which may be potentially associated with dysfunctional members of this gene subfamily.     

Predictors of belief that genetic test information about hemochromatosis should be shared with family members

We queried 101,951 white, Hispanic, black, Asian, American Indian (i.e., American Indian or Alaska Native in the United States and North American Indian, Metis, or Inuit in Canada) and Pacific Islander (including Native Hawaiian) adults who agreed to be genotypically and phenotypically screened for hemochromatosis as part of the Hemochromatosis and Iron Overload Screening (HEIRS) study about their views on sharing genetic test information with family members. Multiple logistic regression (adjusting for study site, age group, race/ethnicity, preferred language, gender, education group, income group, SF-36 General Health and Mental Health subscales, perceived benefits and limitations of genetic testing, and belief that genetic testing is a good idea) evaluated independent predictors of responding "Strongly Agree" or "Agree" versus "Disagree" or "Strongly Disagree" to the statement "Information about a person's genetic risk should be shared with family members". Agreement that genetic risk information should be shared with family members was high (93% in the overall sample of 78,952 who answered this question), but differed among racial/ethnic groups. Hispanics were significantly less likely to agree that genetic test information should be shared with family members (i.e., 88% versus 92% or more among all other ethnicities). The relationship of perceived limitations and benefits of testing, gender, and age group to the belief that information should be shared differed among racial/ethnic groups, with Spanish-preferring Hispanics being the most different from other subgroups.     

Novel IL10 gene family associations with systemic juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common cause of chronic childhood disability and encompasses a number of disease subgroups. In this study we have focused on systemic JIA (sJIA), which accounts for approximately 11% of UK JIA cases. This study reports the investigation of three members of the IL10 gene family as candidate susceptibility loci in children with sJIA. DNA from 473 unaffected controls and 172 patients with sJIA was genotyped for a single nucleotide polymorphism (SNP) in IL19 and IL20 and two SNPs in IL10. We examined evidence for association of the four SNPs by single marker and haplotype analysis. Significant differences in allele frequency were observed between cases and controls, for both IL10-1082 (p = 0.031) and IL20-468 (p = 0.028). Furthermore, examination of the haplotypes of IL10-1082 and IL20-468 revealed greater evidence for association (global p = 0.0006). This study demonstrates a significant increased prevalence of the low expressing IL10-1082 genotype in patients with sJIA. In addition, we show a separate association with an IL20 polymorphism, and the IL10-1082A/IL20-468T haplotype. The two marker 'A-T' haplotype confers an odds ratio of 2.24 for sJIA. This positive association suggests an important role for these cytokines in sJIA pathogenesis.     

Interactions of the Human LIP5 Regulatory Protein with Endosomal Sorting Complexes Required for Transport

The endosomal sorting complex required for transport (ESCRT) pathway remodels membranes during multivesicular body biogenesis, the abscission stage of cytokinesis, and enveloped virus budding. The ESCRT-III and VPS4 ATPase complexes catalyze the membrane fission events associated with these processes, and the LIP5 protein helps regulate their interactions by binding directly to a subset of ESCRT-III proteins and to VPS4. We have investigated the biochemical and structural basis for different LIP5-ligand interactions and show that the first microtubule-interacting and trafficking (MIT) module of the tandem LIP5 MIT domain binds CHMP1B (and other ESCRT-III proteins) through canonical type 1 MIT-interacting motif (MIM1) interactions. In contrast, the second LIP5 MIT module binds with unusually high affinity to a novel MIM element within the ESCRT-III protein CHMP5. A solution structure of the relevant LIP5-CHMP5 complex reveals that CHMP5 helices 5 and 6 and adjacent linkers form an amphipathic “leucine collar” that wraps almost completely around the second LIP5 MIT module but makes only limited contacts with the first MIT module. LIP5 binds MIM1-containing ESCRT-III proteins and CHMP5 and VPS4 ligands independently in vitro, but these interactions are coupled within cells because formation of stable VPS4 complexes with both LIP5 and CHMP5 requires LIP5 to bind both a MIM1-containing ESCRT-III protein and CHMP5. Our studies thus reveal how the tandem MIT domain of LIP5 binds different types of ESCRT-III proteins, promoting assembly of active VPS4 enzymes on the polymeric ESCRT-III substrate.     

The inner-mitochondrial distribution of Oxa1 depends on the growth conditions and on the availability of substrates

The Oxa1 protein is a well-conserved integral protein of the inner membrane of mitochondria. It mediates the insertion of both mitochondrial- and nuclear-encoded proteins from the matrix into the inner membrane. We investigated the distribution of budding yeast Oxa1 between the two subdomains of the contiguous inner membrane--the cristae membrane (CM) and the inner boundary membrane (IBM)--under different physiological conditions. We found that under fermentable growth conditions, Oxa1 is enriched in the IBM, whereas under nonfermentable (respiratory) growth conditions, it is predominantly localized in the CM. The enrichment of Oxa1 in the CM requires mitochondrial translation; similarly, deletion of the ribosome-binding domain of Oxa1 prevents an enrichment of Oxa1 in the CM. The predominant localization in the IBM under fermentable growth conditions is prevented by inhibiting mitochondrial protein import. Furthermore, overexpression of the nuclear-encoded Oxa1 substrate Mdl1 shifts the distribution of Oxa1 toward the IBM. Apparently, the availability of nuclear- and mitochondrial-encoded substrates influences the inner-membrane distribution of Oxa1. Our findings show that the distribution of Oxa1 within the inner membrane is dynamic and adapts to different physiological needs.