Unusual presentation of distal ICA aneurysm in relation to dental abscess

Mycotic extracranial carotid artery aneurysms are a rare vascular phenomenon with a number of implicated pathogens, most commonly Staphylococcus aureus and Salmonella. Presentation of a mycotic extracranial carotid artery aneurysm after dental abscess or procedure is similarly not frequently described in the literature. We present a unique case of a large, distal mycotic internal carotid artery aneurysm, which developed secondary to Haemophilus parainfluenzae infection and dental abscess.

Endoscopic and fluoroscopic-guided closure of the eustachian tube using a biliary cytology brush and liquid embolic agent for a persistent CSF leak after schwannoma resection

Vestibular schwannoma is a known cause of progressive sensorineural hearing loss. Treatment options include observation, radiation therapy and surgical resection. Cerebrospinal fluid (CSF) fistula is a known postsurgical complication that can lead to CSF otorrhoea, rhinorrhoea or CSF leakage from the surgical wound. We present a case report of a patient who underwent vestibular schwannoma resection and postoperatively developed CSF rhinorrhoea, which was refractory to multiple attempts at surgical repair. This was successfully treated under endoscopic and fluoroscopic guidance using a biliary cytology brush to disrupt the surface of the eustachian tube followed by injection of n-Butyl cyanoacrylate.

Hemodynamic regulation of perivalvular endothelial gene expression prevents deep venous thrombosis

Deep venous thrombosis (DVT) and secondary pulmonary embolism cause approximately 100,000 deaths per year in the United States. Physical immobility is the most significant risk factor for DVT, but a molecular and cellular basis for this link has not been defined. We found that the endothelial cells surrounding the venous valve, where DVTs originate, express high levels of FOXC2 and PROX1, transcription factors known to be activated by oscillatory shear stress. The perivalvular venous endothelial cells exhibited a powerful antithrombotic phenotype characterized by low levels of the prothrombotic proteins vWF, P-selectin, and ICAM1 and high levels of the antithrombotic proteins thrombomodulin (THBD), endothelial protein C receptor (EPCR), and tissue factor pathway inhibitor (TFPI). The perivalvular antithrombotic phenotype was lost following genetic deletion of FOXC2 or femoral artery ligation to reduce venous flow in mice, and at the site of origin of human DVT associated with fatal pulmonary embolism. Oscillatory blood flow was detected at perivalvular sites in human veins following muscular activity, but not in the immobile state or after activation of an intermittent compression device designed to prevent DVT. These findings support a mechanism of DVT pathogenesis in which loss of muscular activity results in loss of oscillatory shear-dependent transcriptional and antithrombotic phenotypes in perivalvular venous endothelial cells, and suggest that prevention of DVT and pulmonary embolism may be improved by mechanical devices specifically designed to restore perivalvular oscillatory flow.

Hemodynamic Forces Sculpt Developing Heart Valves through a KLF2-WNT9B Paracrine Signaling Axis

Hemodynamic forces play an essential epigenetic role in heart valve development, but how they do so is not known. Here, we show that the shear-responsive transcription factor KLF2 is required in endocardial cells to regulate the mesenchymal cell responses that remodel cardiac cushions to mature valves. Endocardial Klf2 deficiency results in defective valve formation associated with loss of Wnt9b expression and reduced canonical WNT signaling in neighboring mesenchymal cells, a phenotype reproduced by endocardial-specific loss of Wnt9b. Studies in zebrafish embryos reveal that wnt9b expression is similarly restricted to the endocardial cells overlying the developing heart valves and is dependent upon both hemodynamic shear forces and klf2a expression. These studies identify KLF2-WNT9B signaling as a conserved molecular mechanism by which fluid forces sensed by endothelial cells direct the complex cellular process of heart valve development and suggest that congenital valve defects may arise due to subtle defects in this mechanotransduction pathway.

Cerebral cavernous malformations arise from endothelial gain of MEKK3-KLF2/4 signalling

Cerebral cavernous malformations (CCMs) are common inherited and sporadic vascular malformations that cause stroke and seizures in younger individuals¹. CCMs arise from endothelial cell loss of KRIT1, CCM2, or PDCD10, non-homologous proteins that form an adaptor complex². How disruption of the CCM complex results in disease remains controversial, with numerous signaling pathways (including Rho^3,4, SMAD⁵ and Wnt/β-catenin⁶) and processes such as endothelial-mesenchymal transition (EndMT)⁵ proposed to play causal roles. CCM2 binds MEKK3^7–11, and we have recently demonstrated that CCM complex regulation of MEKK3 is essential during vertebrate heart development¹². Here, we investigate this mechanism in CCM disease pathogenesis. Using a neonatal mouse model of CCM disease, we find that expression of the MEKK3 target genes KLF2 and KLF4, as well as Rho and ADAMTS protease activity, are increased in the endothelial cells of early CCM lesions. In contrast, we find no evidence of EndMT or increased SMAD or Wnt signaling during early CCM formation. Endothelial-specific loss of Mekk3, Klf2, or Klf4 dramatically prevents lesion formation, reverses the increase in Rho activity, and rescues lethality. Consistent with these findings in mice, we demonstrate that endothelial expression of KLF2 and KLF4 is elevated in human familial and sporadic CCM lesions, and that a disease-causing human CCM2 mutation abrogates MEKK3 interaction without affecting CCM complex formation. These studies identify gain of MEKK3 signaling and KLF2/4 function as causal mechanisms for CCM pathogenesis that may be targeted to develop new CCM therapeutics.

Demonstration of a factor in fraction I of reticulocyte lysates necessary for the steady state accumulation of ubiquitin conjugates of des-75-76-ubiquitin

Addition of des-75-76-ubiquitin (ubiquitin lacking its two C-terminal glycine residues) to reticulocyte lysates leads to the inhibition of proteolysis and the formation of conjugates between it and native ubiquitin, as demonstrated by the incorporation of both 125I-labeled des-75-76-ubiquitin and 125I-labeled ubiquitin into these conjugates. Conjugate formation is blocked by methylation of the amino groups of des-75-76-ubiquitin, consistent with the concept that the conjugates represent attachment of the ubiquitin alpha-carboxyl group to amino groups of des-75-76-ubiquitin. The lack of significant direct competition for conjugate formation by typical ubiquitinatable proteolysis substrates or by des-73-76-ubiquitin, together with differences in conjugate formation between des-73-76-ubiquitin and des-75-76-ubiquitin demonstrated earlier, indicates that the enzyme involved recognizes the ubiquitin sequence as a substrate for ubiquitination. Increasing concentrations of native ubiquitin first increase and then reduce the steady state level of conjugates of the des-75-76-protein, the inhibitory effects of high concentrations consistent with competition by native ubiquitin for conjugate formation. Upon fractionation of reticulocyte lysates, a factor essential to the net synthesis of conjugates of des-75-76-ubiquitin was demonstrated to be present in Fraction I and to behave as a protein of molecular weight 38,000. The role in this system of a factor from Fraction I other than ubiquitin indicates that a novel pathway is involved.

Binding and fluorescence studies of the relationship between neurophysin-peptide interaction and neurophysin self-association: an allosteric system exhibiting minimal cooperativity

The mechanism of peptide-enhanced neurophysin self-association was investigated to address questions raised by the crystal structure of a neurophysin-dipeptide complex. The dependence on protein concentration of the binding of a broad range of peptides to the principal hormone-binding site confirmed that occupancy of this site alone, and not a site that bridges the monomer-monomer interface, is the trigger for enhanced dimerization. For the binding of most peptides to the principal hormone-binding site on bovine neurophysin I, the affinity of each dimer site was at least 10 times that of monomer under the conditions used. No interactions between the two sites of the dimer were evident. Fluorescence polarization studies of pressure-induced dimer dissociation indicated that the volume change for this reaction was almost 4 times greater in the liganded than in the unliganded state, pointing to a significant alteration of the monomer-monomer interface upon peptide binding. Novel conformational changes in the vicinity of the single neurophysin tyrosine, Tyr-49, induced by pressures lower than required for subunit dissociation, were also observed. The bovine neurophysin I dimer therefore appears to represent an allosteric system in which there is thermodynamic and functional communication between each binding site and the monomer-monomer interface, but no communication across the interface to the binding site of the other subunit. A model for the peptide-enhanced dimerization is proposed in which intersubunit contacts between monomers reduce the large unfavorable free energy associated with binding-induced intrasubunit conformational change. Structural origins of the lack of communication across the interface are suggested on the basis of the low volume change associated with dimerization in the unliganded state and monomer-monomer contacts in the crystal structure. Potential roles for the peptide alpha-amino group and position 2 phenyl ring in triggering conformational change are discussed.

Structural and functional changes associated with modification of the ubiquitin methionine

The effects of oxidation and cleavage of Met-1 of ubiquitin on conformation and biological activity were individually investigated. Proton NMR studies demonstrated that oxidation to the sulfone led to restricted structural perturbations at neutral pH, particularly in the vicinity of Ile-61. Below pH 3, in the presence of acetic acid, oxidation to the sulfone facilitated a conformational expansion demonstrable by retardation on gel electrophoresis and CD changes below 210 nm. The predominant phase of the low-pH transition did not involve significant changes in alpha-helix content, indicating the capacity of ubiquitin for limited structural transitions. Cleavage of Met-1 by CNBr, on the other hand, was associated with a global unfolding transition below pH 4 that involved a major loss of alpha-helix. Differences in the behavior of the native and des-Met proteins at low pH indicate that Met-1 contributes a minimum of 3.4 kcal/mol to the stability of the native conformation. Two Met-1 sulfoxide isomers, of markedly different conformational stability, were formed by treatment of ubiquitin with H2O2. One isomer was similar in stability to the sulfone, while the other was intermediate in stability between the sulfone and des-Met proteins, the differences potentially interpretable in terms of the geometry of the Met-1-Lys-63 hydrogen bond. The overall activities of the oxidized and des-Met derivatives in ATP-dependent proteolysis differed subtly from that of native ubiquitin. The unresolved sulfoxides exhibited an approximately 50% increase in activity, while the sulfone and des-Met proteins exhibited a 50% decrease in activity at low concentrations and normal activity at higher concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of ubiquitin-dependent proteolysis by des-Gly-Gly-ubiquitin: implications for the mechanism of polyubiquitin synthesis

Cleavage of the two carboxyl-terminal glycine residues from native ubiquitin yields the proteolysis-incompetent derivative des-Gly-Gly-ubiquitin. We report here that this derivative inhibits the ATP-dependent degradation of casein and is multi-ubiquitinated but not degraded by reticulocyte lysates. Inhibition of proteolysis diminished with increasing concentration of native ubiquitin, but was not reduced by increased casein concentration. Cleavage of the last four residues from ubiquitin yielded a derivative that was a weaker inhibitor of proteolysis and a poorer substrate for ubiquitination. These results suggest that the conjugation of ubiquitin to ubiquitin during polyubiquitin synthesis involves a specific conjugation system that recognizes ubiquitin and some of its derivatives, but not general proteolysis substrates, as ubiquitin acceptors.