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Phosphatidylserine inhibits and calcium promotes model membrane fusion.

ABSTRACT: PEG-mediated fusion of SUVs composed of dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine, sphingomyelin, cholesterol, and dioleoylphosphatidylserine was examined to investigate the effects of PS on the fusion mechanism. Lipid mixing, content mixing, and content leakage measurements were carried out with vesicles containing from 0 to 8 mol % PS and similar amounts of phosphatidylglycerol. Fitting these time courses globally to a 3-state (aggregate, intermediate, pore) sequential model established rate constants for each step and probabilities of lipid mixing, content mixing, and leakage in each state. Charged lipids inhibited both the rates of intermediate and pore formation as well as the extents of lipid and contents mixing, although electrostatics were not solely responsible for inhibition. Ca(2+) counteracted this inhibition and increased the extent of fusion in the presence of PS to well beyond that seen in the absence of charged lipids. The effects of both PS and Ca(2+) could be interpreted in terms of a previous proposal for the nature of lipid fluctuations that account for transition states for the two steps of the fusion process examined. The results suggest a more significant role for Ca(2+)-lipid interactions than is acknowledged in current thinking about cell membrane fusion.

SUBMITTER: Tarafdar PK

PROVIDER: S-EPMC3491704 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Phosphatidylserine inhibits and calcium promotes model membrane fusion.

Tarafdar Pradip K PK Chakraborty Hirak H Dennison S Moses SM Lentz Barry R BR

Biophysical journal 20121101 9

PEG-mediated fusion of SUVs composed of dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine, sphingomyelin, cholesterol, and dioleoylphosphatidylserine was examined to investigate the effects of PS on the fusion mechanism. Lipid mixing, content mixing, and content leakage measurements were carried out with vesicles containing from 0 to 8 mol % PS and similar amounts of phosphatidylglycerol. Fitting these time courses globally to a 3-state (aggregate, intermediate, pore) sequential mode ...[more]

PMID: 23199916

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Project description:Study designExperimental porcine anterior cervical discectomy and fusion (ACDF) model: a proof-of-concept study.ObjectiveThe effect of monetite synthetic bone graft (SBG) containing calcium pyrophosphate and β-tricalcium phosphate on cervical spinal fusion in a noninstrumented two-level large animal model.Summary of background dataACDF is the gold standard surgical technique for the treatment of degenerative cervical spinal diseases. However, pseudarthrosis associated with increased patient morbidity occurs in ∼2.6% of the surgeries. SBG may enhance bony fusion and subsequently decrease the risk of pseudarthrosis. Recent studies on monetite-based SBGs for use in large cranial defects in humans have shown promising bone healing results, necessitating further investigation of their use in cervical spinal fusion.Materials and methodsFour adult female Danish Göttingen minipigs received partial cervical anterior discectomy and intervertebral defects at an upper and lower level. One defect was filled with SBG, and the other was left empty. Bony fusion was evaluated using computed tomography (CT) at three-month intervals for 12 months. Fifteen months postsurgery, the animals were euthanized for further ex vivo qualitative histopathologic and micro-CT evaluations. Fusion rates were compared using the Fisher exact test at each time point.ResultsIncreased interbody bony fusion rates were observed at SBG levels (4/4) compared with control levels (0/4) evaluated by CT at 6 and 9 months postsurgery ( P =0.029). Fusion was observed at all SBG levels 12 months postsurgery and at only one control level. Histopathologic evaluation confirmed high-quality interbody bony fusion at all SBG levels and fusion by spondylosis at one control level.ConclusionThis proof-of-concept study provides preliminary evidence of a novel, calcium pyrophosphate-containing, and β-tricalcium phosphate-containing monetite SBG that promotes bony fusion compared with a negative control in a clinically relevant porcine model of ACDF.

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Phosphatidylserine inhibits and calcium promotes model membrane fusion.

Publications

Phosphatidylserine inhibits and calcium promotes model membrane fusion.

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