Unique lipoproteins secreted by primary astrocytes from wild type, apoE (-/-), and human apoE transgenic mice

Composition of central nervous system lipoproteins affects the metabolism of lipoprotein constituents within the brain. The epsilon4 allele of apolipoprotein E (apoE) is a risk factor for Alzheimer's disease via an unknown mechanism(s). As glia are the primary central nervous system cell type that synthesize apoE, we characterized lipoproteins secreted by astrocytes from wild type (WT), apoE (-/-), and apoE transgenic mice expressing human apoE3 or apoE4 in a mouse apoE (-/-) background. Nondenaturing size exclusion chromatography demonstrates that WT, apoE3, and apoE4 astrocytes secrete particles the size of plasma high density lipoprotein (HDL) composed of phospholipid, free cholesterol, and protein, primarily apoE and apoJ. However, the lipid:apoE ratio of particles containing human apoE is significantly lower than WT. ApoE localizes across HDL-like particle sizes. ApoJ localizes to the smallest HDL-like particles. ApoE (-/-) astrocytes secrete little phospholipid or free cholesterol despite comparable apoJ expression, suggesting that apoE is required for normal secretion of astrocyte lipoproteins. Further, particles were not detected in apoE (-/-) samples by electron microscopy. Nondenaturing immunoprecipitation experiments indicate that apoE and apoJ reside predominantly on distinct particles. These studies suggest that apoE expression influences the unique structure of astrocyte lipoproteins, a process further modified by apoE species.

Potassium transport by amino acid permeases in Saccharomyces cerevisiae

Deletion of the potassium transporter genes TRK1 and TRK2 impairs potassium uptake in Saccharomyces cerevisiae, resulting in a greatly increased requirement for the ion and the inability to grow on low pH medium. Selection for mutations that restored growth of trk1Delta trk2Delta cells on low pH (3.0) medium led to the isolation of a dominant suppressor that also partially suppressed the increased K+ requirement of these cells. Molecular analysis revealed the suppressor to be an allele of BAP2 that encodes a permease for branched chain amino acids. The suppressor mutation (BAP2-1) converts a phenylalanine codon, highly conserved among the amino acid permease genes, to a serine codon in a region predicted to lie within the sixth membrane-spanning domain. Generation of the analogous mutation in the histidine permease produced an allele, HIP1-293, that similarly suppressed the low pH sensitivity of trk1Delta trk2Delta cells. Suppression of trk1Delta trk2Delta phenotypes by BAP2-1 or HIP1-293 was correlated with increased Rb+ uptake. The presence of the substrate amino acids enhanced but was not essential for suppression of trk1Delta trk2Delta phenotypes and increased Rb+ uptake. The conserved site altered by the suppressor mutations appears to be important; his4 HIP1-293 cells show an increased requirement for histidine compared with his4 HIP1 cells.

Stabilization of thoracic and thoracolumbar fracture-dislocations with Harrington rods and sublaminar wires

Seventeen unstable thoracic and thoracolumbar fracture-dislocations have been treated by Harrington double-distraction rod technique supplemented by doubled 18-gauge stainless-steel wires applied to two intact laminae above and below the injury. Fourteen of the 17 cases were grossly comminuted and translated beyond 50% of the width of the spinal column. No external bracing was used in the 13 patients with neurologic deficits. At the time of follow-up examinations (greater than 22 months in all patients) there was no loss of reduction or fixation in any patient. Solid fusion was achieved in all patients.

Experimental evaluation of Harrington rod fixation supplemented with sublaminar wires in stabilizing thoracolumbar fracture-dislocations

Segments of the spinal column of calves were instrumented with Harrington rods with and without sublaminar wires. Grossly unstable lesions were created by resecting a 2-cm segment from the central spinal segment. Testing on an Instron tester documented the improvement in stability provided by the sublaminar wires in this grossly unstable experimental fracture. Improved stability was seen in resisting axial loading, lateral bending, and forward flexion loading. Rotational stability was particularly improved.