rasa1-related arteriovenous malformation is driven by aberrant venous signalling.

Arteriovenous malformations (AVMs) develop where abnormal endothelial signalling allows direct connections between arteries and veins. Mutations in RASA1, a Ras GTPase activating protein, lead to AVMs in humans and, as we show, in zebrafish rasa1 mutants. rasa1 mutants develop cavernous AVMs that subsume part of the dorsal aorta and multiple veins in the caudal venous plexus (CVP) - a venous vascular bed. The AVMs progressively enlarge and fill with slow-flowing blood. We show that the AVM results in both higher minimum and maximum flow velocities, resulting in increased pulsatility in the aorta and decreased pulsatility in the vein. These hemodynamic changes correlate with reduced expression of the flow-responsive transcription factor klf2a. Remodelling of the CVP is impaired with an excess of intraluminal pillars, which is a sign of incomplete intussusceptive angiogenesis. Mechanistically, we show that the AVM arises from ectopic activation of MEK/ERK in the vein of rasa1 mutants, and that cell size is also increased in the vein. Blocking MEK/ERK signalling prevents AVM initiation in mutants. Alterations in venous MEK/ERK therefore drive the initiation of rasa1 AVMs.

Vessel Metrics: A software tool for automated analysis of vascular structure in confocal imaging.

Images contain a wealth of information that is often under analyzed in biological studies. Developmental models of vascular disease are a powerful way to quantify developmentally regulated vessel phenotypes to identify the roots of the disease process. We present vessel Metrics, a software tool specifically designed to analyze developmental vascular microscopy images that will expedite the analysis of vascular images and provide consistency between research groups. We developed a segmentation algorithm that robustly quantifies different image types, developmental stages, organisms, and disease models at a similar accuracy level to a human observer. We validate the algorithm on confocal, lightsheet, and two photon microscopy data in a zebrafish model expressing fluorescent protein in the endothelial nuclei. The tool accurately segments data taken by multiple scientists on varying microscopes. We validate vascular parameters such as vessel density, network length, and diameter, across developmental stages, genetic mutations, and drug treatments, and show a favorable comparison to other freely available software tools. Additionally, we validate the tool in a mouse model. Vessel Metrics reduces the time to analyze experimental results, improves repeatability within and between institutions, and expands the percentage of a given vascular network analyzable in experiments.

Epidemiology of E. coli in Cystic Fibrosis Airways Demonstrates the Capacity for Persistent Infection but Not Patient-Patient Transmission.

Escherichia coli is frequently isolated from the respiratory secretions of cystic fibrosis (CF) patients yet is not considered a classical CF pathogen. Accordingly, little is known about the natural history of this organism in the CF airways, as well as the potential for patient-to-patient transmission. Patients attending the Calgary Adult CF Clinic (CACFC) between January 1983 and December 2016 with at least one E. coli-positive sputum culture were identified by retrospective review. Annual E. coli isolates from the CACFC biobank from each patient were typed by pulsed-field gel electrophoresis (PFGE) and isolates belonging to shared pulsotypes were sequenced. Single nucleotide polymorphism (SNP) and phylogenetic analysis were used to investigate the natural history of E. coli infection and identify potential transmission events. Forty-five patients with E. coli-positive sputum cultures were identified. Most patients had a single infection episode with a single pulsotype, while replacement of an initial pulsotype with a second was observed in three patients. Twenty-four had E. coli recovered from their sputum more than once and 18 patients had persistent infections (E. coli carriage >6 months with ≥3 positive cultures). Shared pulsotypes corresponded to known extraintestinal pathogenic E. coli strains: ST-131, ST-73, and ST-1193. Phylogenetic relationships and SNP distances among isolates within shared pulsotypes were consistent with independent acquisition of E. coli by individual patients. Most recent common ancestor date estimates of isolates between patients were inconsistent with patient-to-patient transmission. E. coli infection in CF is a dynamic process that appears to be characterized by independent acquisition within our patient population and carriage of unique sets of strains over time by individual patients.