Objective Collateral arteriogenesis, the growth of existing arterial vessels to a larger diameter, is a fundamental adaptive response that is often critical for the perfusion and survival of tissues downstream of chronic arterial occlusion(s). Shear stress regulates arteriogenesis; however, the arteriogenic significance of flow direction reversal, occurring in numerous collateral artery segments after femoral artery ligation (FAL), is unknown. Our objective was to determine if flow direction reversal in collateral artery segments differentially regulates endothelial cell signaling and arteriogenesis. Approach and Results Collateral segments experiencing flow reversal after FAL in C57BL/6 mice exhibit increased pericollateral macrophage recruitment, amplified arteriogenesis (30% diameter and 2.8-fold conductance increases), and remarkably permanent (12 weeks post-FAL) remodeling. Genome-wide transcriptional analyses on HUVECs exposed to flow reversal conditions mimicking those occurring in-vivo yielded 10-fold more significantly regulated transcripts, as well as enhanced activation of upstream regulators (NFκB, VEGF, FGF2, TGFβ) and arteriogenic canonical pathways (PKA, PDE, MAPK). Augmented expression of key pro-arteriogenic molecules (KLF2, ICAM-1, eNOS) was also verified by qRT-PCR, leading us to test whether ICAM-1 and/or eNOS regulate amplified arteriogenesis in flow-reversed collateral segments in-vivo. Interestingly, enhanced pericollateral macrophage recruitment and amplified arteriogenesis was attenuated in flow-reversed collateral segments after FAL in ICAM-1−/− mice; however, eNOS−/− mice showed no such differences. Conclusions Flow reversal leads to a broad amplification of pro-arteriogenic endothelial signaling and a sustained ICAM-1-dependent augmentation of arteriogenesis. Further investigation of the endothelial mechanotransduction pathways activated by flow reversal may lead to more effective and durable therapeutic options for arterial occlusive diseases.

Cardiac hypertrophy has been well-characterized at the level of transcription. During cardiac hypertrophy, genes normally expressed primarily during fetal heart development are reexpressed, and this fetal gene program is believed to be a critical component of the hypertrophic process. Recently, alternative splicing of mRNA transcripts has been shown to be temporally regulated during heart development, leading us to consider whether fetal patterns of splicing also reappear during hypertrophy. We hypothesized that patterns of alternative splicing occurring during heart development are recapitulated during cardiac hypertrophy. Here we present a study of isoform expression during pressure-overload cardiac hypertrophy induced by 10 days of transverse aortic constriction (TAC) in rats and in developing fetal rat hearts compared to sham-operated adult rat hearts, using high-throughput sequencing of poly(A) tail mRNA. We find a striking degree of overlap between the isoforms expressed differentially in fetal and pressure-overloaded hearts compared to control: forty-four percent of the isoforms with significantly altered expression in TAC hearts are also expressed at significantly different levels in fetal hearts compared to control (P < 0.001). The isoforms that are shared between hypertrophy and fetal heart development are significantly enriched for genes involved in cytoskeletal organization, RNA processing, developmental processes, and metabolic enzymes. Our data strongly support the concept that mRNA splicing patterns normally associated with heart development recur as part of the hypertrophic response to pressure overload. These findings suggest that cardiac hypertrophy shares post-transcriptional as well as transcriptional regulatory mechanisms with fetal heart development.

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The goal of this work was to create a finite element micromechanical model of the myotendinous junction (MTJ) to examine how the structure and mechanics of the MTJ affect the local micro-scale strains experienced by muscle fibers. We validated the model through comparisons with histological longitudinal sections of muscles fixed in slack and stretched positions. The model predicted deformations of the A-bands within the fiber near the MTJ that were similar to those measured from the histological sections. We then used the model to predict the dependence of local fiber strains on activation and the mechanical properties of the endomysium. The model predicted that peak micro-scale strains increase with activation and as the compliance of the endomysium decreases. Analysis of the models revealed that, in passive stretch, local fiber strains are governed by the difference of the mechanical properties between the fibers and the endomysium. In active stretch, strain distributions are governed by the difference in cross-sectional area along the length of the tapered region of the fiber near the MTJ. The endomysium provides passive resistance that balances the active forces and prevents the tapered region of the fiber from undergoing excessive strain. These model predictions lead to the following hypotheses: (i) the increased likelihood of injury during active lengthening of muscle fibers may be due to the increase in peak strain with activation and (ii) endomysium may play a role in protecting fibers from injury by reducing the strains within the fiber at the MTJ.

In the preceding paper (1), we reported on the relative ability of various nucleotides related to nicofinamide adenine dinucleotide (NAD) to serve as cofactors for inhibition by diphtheria toxin of protein synthesis in cell-free extracts. Those few analogues which could replace NAD as activators of diphtheria toxin all proved to be nucleotides of demonstrated coenzyme activity. The results suggested that NAD and certain related substances are capable of interaction with the toxin protein. That diphtheria toxin does, in fact, reversibly bind one mole of NAD per mole of toxin was demonstrated by equilibrium dialysis and by gel filtration.In the present paper, we are reporting studies on the quantitative relationships between NAD, diphtheria toxin, and inhibition of peptide bond formation in cell-free extracts from various species. The data have led us to the conclusion that inhibition of protein synthesis, in vitro, results from reversible interaction between three components: toxin, NAD, and transferase II (2, 3). Reduction of NAD is not involved since it has been found that the inactivation of transferase II by toxin in mammalian cell extracts can be prevented and even reversed by relatively low concentrations of nicotinamide. Materials and MethodsReagents and Radioisotopes.--Materials used to determine amino acid incorporation in the cell-free systems were the same as in the preceding papers (1, 3). Nicotinamide, nicotinic acid, and pyridine-3-sulfonic acid were obtained from Nutritional Biochemical Corp., Cleveland,

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Glycogen Branching Enzyme Deficiency (GBED), a fatal condition recently identified in fetuses and neonatal foals of the Quarter Horse and Paint Horse lineages, is caused by a nonsense mutation in codon 34 of the GBE1 gene, which prevents the synthesis of a functional GBE protein and severely disrupts glycogen metabolism. The aims of this project were to determine the mutant GBE1 allele frequency in random samples from the major relevant horse breeds, as well as the frequency with which GBED is associated with abortion and early neonatal death using the tissue archives from veterinary diagnostic laboratories. The mutant GBE1 allele frequency in registered Quarter Horse, Paint Horse, and Thoroughbred populations was 0.041, 0.036, and 0.000, respectively. Approximately 2.5% of fetal and early neonatal deaths in Quarter Horse-related breeds submitted to 2 different US diagnostic laboratories were homozygous for the mutant GBE1 allele, with the majority of these being abortions. Retrospective histopathology of the homozygotes detected periodic acid Schiff's (PAS)-positive inclusions in the cardiac or skeletal muscle, which is characteristic of GBED, in 8 out of the 9 cases. Pedigree and genotype analyses supported the hypothesis that GBED is inherited as a simple recessive trait from a single founder. The frequency with which GBED is associated with abortion and neonatal mortality in Quarter Horse-related breeds makes the DNA-based test valuable in determining specific diagnoses and designing matings that avoid conception of a GBED foal.

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