Cytoglobin: a novel globin type ubiquitously expressed in vertebrate tissues

Vertebrates possess multiple respiratory globins that differ in terms of structure, function, and tissue distribution. Three types of globins have been described so far: hemoglobin facilitates the transport of oxygen in the blood, myoglobin serves oxygen transport and storage in the muscle, and neuroglobin has a yet unidentified function in nerve cells. Here we report the identification of a fourth and novel type of globin in mouse, man, and zebrafish. It is expressed in apparently all types of human tissue and therefore has been called cytoglobin (CYGB). Mouse and human CYGBs comprise 190 amino acids; the zebrafish CYGB, 174 amino acids. The human CYGB gene is located on chromosome 17q25. The mammalian genes display a unique exon-intron pattern with an additional exon resulting in a C-terminal extension of the protein, which is absent in the fish CYGB. Phylogenetic analyses suggest that the CYGBs had a common ancestor with vertebrate myoglobins. This indicates that the vertebrate myoglobins are in fact a specialized intracellular globin that evolved in adaptation to the special needs of muscle cells.

Neuroglobin and cytoglobin in search of their role in the vertebrate globin family

Neuroglobin and cytoglobin are two recent additions to the family of heme-containing respiratory proteins of man and other vertebrates. Here, we review the present state of knowledge of the structures, ligand binding kinetics, evolution and expression patterns of these two proteins. These data provide a first glimpse into the possible physiological roles of these globins in the animal's metabolism. Both, neuroglobin and cytoglobin are structurally similar to myoglobin, although they contain distinct cavities that may be instrumental in ligand binding. Kinetic and structural studies show that neuroglobin and cytoglobin belong to the class of hexa-coordinated globins with a biphasic ligand-binding kinetics. Nevertheless, their oxygen affinities resemble that of myoglobin. While neuroglobin is evolutionarily related to the invertebrate nerve-globins, cytoglobin shares a more recent common ancestry with myoglobin. Neuroglobin expression is confined mainly to brain and a few other tissues, with the highest expression observed in the retina. Present evidence points to an important role of neuroglobin in neuronal oxygen homeostasis and hypoxia protection, though other functions are still conceivable. Cytoglobin is predominantly expressed in fibroblasts and related cell types, but also in distinct nerve cell populations. Much less is known about its function, although in fibroblasts it might be involved in collagen synthesis.

Androglobin: a chimeric globin in metazoans that is preferentially expressed in Mammalian testes

Comparative genomic studies have led to the recent identification of several novel globin types in the Metazoa. They have revealed a surprising evolutionary diversity of functions beyond the familiar O(2) supply roles of hemoglobin and myoglobin. Here we report the discovery of a hitherto unrecognized family of proteins with a unique modular architecture, possessing an N-terminal calpain-like domain, an internal, circular permuted globin domain, and an IQ calmodulin-binding motif. Putative orthologs are present in the genomes of many metazoan taxa, including vertebrates. The calpain-like region is homologous to the catalytic domain II of the large subunit of human calpain-7. The globin domain satisfies the criteria of a myoglobin-like fold but is rearranged and split into two parts. The recombinantly expressed human globin domain exhibits an absorption spectrum characteristic of hexacoordination of the heme iron atom. Molecular evolutionary analyses indicate that this chimeric globin family is phylogenetically ancient and originated in the common ancestor to animals and choanoflagellates. In humans and mice, the gene is predominantly expressed in testis tissue, and we propose the name "androglobin" (Adgb). Expression is associated with postmeiotic stages of spermatogenesis and is insensitive to experimental hypoxia. Evidence exists for increased gene expression in fertile compared with infertile males.

Neuroglobin and cytoglobin: genes, proteins and evolution

Hemoglobin and myoglobin are oxygen transport and storage proteins of most vertebrates. Neuroglobin (Ngb) and cytoglobin (Cygb)--two recent additions to the vertebrate globin superfamily--have still disputed functions. Combining the data from all available resources, we investigate the evolution of these novel globins. Both Ngb and Cygb show little sequence variation in vertebrate evolution, suggesting conserved structures and functions, and an important role in the animal's metabolism. Exon-intron patterns remained unchanged in Ngb and Cygb, with the exception of the addition of a 3' exon to Cygb early in mammalian evolution. In phylogenetic analyses, Ngb forms a common branch with globin X, another recently identified globin with undefined function in lower vertebrates, and with some invertebrate nerve globins. This shows an early divergence of this branch in animal evolution. Cygb is related to myoglobin, and associated with an eye-specific globin from birds. The pattern of globin evolution shows that proteins with clear respiratory roles evolved independently from intracellular globins with uncertain functions. This result suggests either multiple independent functional changes or a yet undefined respiratory role of tissue globins like Ngb and Cygb.

Interspecies comparison of neuroglobin, cytoglobin and myoglobin: Sequence evolution and candidate regulatory elements

Neuroglobin and cytoglobin are two novel members of the vertebrate globin family. Their physiological role is poorly understood, although both proteins bind oxygen reversibly and may be involved in cellular oxygen homeostasis. Here we investigate the selective constraints on coding and non-coding sequences of the neuroglobin and cytoglobin genes in human, mouse, rat and fish. Neuroglobin and cytoglobin are highly conserved, displaying very low levels of non-synonymous nucleotide substitutions. An oxygen supply function predicts distinct modes of gene regulation, involving hypoxia-responsive transcription factors. To detect conserved candidate regulatory elements, we compared the neuroglobin and cytoglobin genes in mammals and fish. The myoglobin gene was included to test if it also contains hypoxia-responsive regulatory elements. Long conserved non-coding sequences, indicative of gene-regulatory elements, were found in the cytoglobin and myoglobin, but not in the neuroglobin gene. Sequence comparison and experimental data allowed us to delimit upstream regions of the neuroglobin and cytoglobin genes that contain the putative promoters, defining candidate regulatory regions for functional tests. The neuroglobin and the myoglobin genes both lack conserved hypoxia-responsive elements (HREs) for transcriptional activation, but contain conserved hypoxia-inducible mRNA stabilization signals in their 3' untranslated regions. The cytoglobin gene, in contrast, harbors both conserved HREs and mRNA stabilization sites, strongly suggestive of an oxygen-dependent regulation.

Differential Evolution of the Epidermal Keratin Cytoskeleton in Terrestrial and Aquatic Mammals

Keratins are the main intermediate filament proteins of epithelial cells. In keratinocytes of the mammalian epidermis they form a cytoskeleton that resists mechanical stress and thereby are essential for the function of the skin as a barrier against the environment. Here, we performed a comparative genomics study of epidermal keratin genes in terrestrial and fully aquatic mammals to determine adaptations of the epidermal keratin cytoskeleton to different environments. We show that keratins K5 and K14 of the innermost (basal), proliferation-competent layer of the epidermis are conserved in all mammals investigated. In contrast, K1 and K10, which form the main part of the cytoskeleton in the outer (suprabasal) layers of the epidermis of terrestrial mammals, have been lost in whales and dolphins (cetaceans) and in the manatee. Whereas in terrestrial mammalian epidermis K6 and K17 are expressed only upon stress-induced epidermal thickening, high levels of K6 and K17 are consistently present in dolphin skin, indicating constitutive expression and substitution of K1 and K10. K2 and K9, which are expressed in a body site-restricted manner in human and mouse suprabasal epidermis, have been lost not only in cetaceans and manatee but also in some terrestrial mammals. The evolution of alternative splicing of K10 and differentiation-dependent upregulation of K23 have increased the complexity of keratin expression in the epidermis of terrestrial mammals. Taken together, these results reveal evolutionary diversification of the epidermal cytoskeleton in mammals and suggest a complete replacement of the quantitatively predominant epidermal proteins of terrestrial mammals by originally stress-inducible keratins in cetaceans.

Evolution of the globin gene family in deuterostomes: lineage-specific patterns of diversification and attrition

In the Metazoa, globin proteins display an underlying unity in tertiary structure that belies an extraordinary diversity in primary structures, biochemical properties, and physiological functions. Phylogenetic reconstructions can reveal which of these functions represent novel, lineage-specific innovations, and which represent ancestral functions that are shared with homologous globin proteins in other eukaryotes and even prokaryotes. To date, our understanding of globin diversity in deuterostomes has been hindered by a dearth of genomic sequence data from the Ambulacraria (echinoderms + hemichordates), the sister group of chordates, and the phylum Xenacoelomorpha, which includes xenoturbellids, acoelomorphs, and nemertodermatids. Here, we report the results of a phylogenetic and comparative genomic analysis of the globin gene repertoire of deuterostomes. We first characterized the globin genes of the acorn worm, Saccoglossus kowalevskii, a representative of the phylum Hemichordata. We then integrated genomic sequence data from the acorn worm into a comprehensive analysis of conserved synteny and phylogenetic relationships among globin genes from representatives of the eight lineages that comprise the superphylum Deuterostomia. The primary aims were 1) to unravel the evolutionary history of the globin gene superfamily in deuterostomes and 2) to use the estimated phylogeny to gain insights into the functional evolution of deuterostome globins. Results of our analyses indicate that the deuterostome common ancestor possessed a repertoire of at least four distinct globin paralogs and that different subsets of these ancestral genes have been retained in each of the descendant organismal lineages. In each major deuterostome group, a different subset of ancestral precursor genes underwent lineage-specific expansions of functional diversity through repeated rounds of gene duplication and divergence. By integrating results of the phylogenetic analysis with available functional data, we discovered that circulating oxygen-transport hemoglobins evolved independently in several deuterostome lineages and that intracellular nerve globins evolved independently in chordates and acoelomorph worms.

Globin genes are present in Ciona intestinalis

The key position of the Ciona intestinalis basal to the vertebrate phylogenetic tree brings up the question of which respiratory proteins are used by the tunicate to facilitate oxygen transport and storage. The publication of the Ciona draft genome sequence suggests that globin genes are completely missing and that-like some molluscs and arthropods-the sea squirt uses hemocyanin instead of hemoglobin for respiration. However, we report here the presence and expression of at least four distinct globin gene/protein sequences in Ciona. This finding is in agreement with the ancestral phylogeny of the vertebrate globins. Moreover, it seems likely that the Ciona hemocyanin-like sequences have enzymatic instead of respiratory functions.

Maturation of fastest afferent and efferent central and peripheral pathways: no evidence for a constancy of central conduction delays

The maturation of the fastest afferent and efferent central and peripheral pathways was analysed using the recording of somatosensory evoked potentials of the median nerve stimulation for afferent conduction and magnetoelectrical stimulation of motor cortex to the thenar muscles for efferent conduction. Both afferent and efferent central pathways showed a prolonged maturational pattern with adult values being reached by the age of 5 to 7 years for the afferent and by the age of around 10 years for the efferent pathway. In contrast, the maturation for peripheral afferent and efferent pathways showed a similar trend with a fairly constant conduction velocity reached around the age of 3 years. There was no evidence for a constancy of central conduction delays in both afferent and efferent pathway which has been supposed as a possible mechanism for a temporal stability in feedback loops involved in motor learning processes during development. It is concluded that the prolonged maturational central conduction time precludes the usage of a fixed temporal timing pattern during development in the human sensory motor system.

The globin gene family of the cephalochordate amphioxus: implications for chordate globin evolution

BACKGROUND

The lancelet amphioxus (Cephalochordata) is a close relative of vertebrates and thus may enhance our understanding of vertebrate gene and genome evolution. In this context, the globins are one of the best studied models for gene family evolution. Previous biochemical studies have demonstrated the presence of an intracellular globin in notochord tissue and myotome of amphioxus, but the corresponding gene has not yet been identified. Genomic resources of Branchiostoma floridae now facilitate the identification, experimental confirmation and molecular evolutionary analysis of its globin gene repertoire.

RESULTS

We show that B. floridae harbors at least fifteen paralogous globin genes, all of which reveal evidence of gene expression. The protein sequences of twelve globins display the conserved characteristics of a functional globin fold. In phylogenetic analyses, the amphioxus globin BflGb4 forms a common clade with vertebrate neuroglobins, indicating the presence of this nerve globin in cephalochordates. Orthology is corroborated by conserved syntenic linkage of BflGb4 and flanking genes. The kinetics of ligand binding of recombinantly expressed BflGb4 reveals that this globin is hexacoordinated with a high oxygen association rate, thus strongly resembling vertebrate neuroglobin. In addition, possible amphioxus orthologs of the vertebrate globin X lineage and of the myoglobin/cytoglobin/hemoglobin lineage can be identified, including one gene as a candidate for being expressed in notochord tissue. Genomic analyses identify conserved synteny between amphioxus globin-containing regions and the vertebrate β-globin locus, possibly arguing against a late transpositional origin of the β-globin cluster in vertebrates. Some amphioxus globin gene structures exhibit minisatellite-like tandem duplications of intron-exon boundaries ("mirages"), which may serve to explain the creation of novel intron positions within the globin genes.

CONCLUSIONS

The identification of putative orthologs of vertebrate globin variants in the B. floridae genome underlines the importance of cephalochordates for elucidating vertebrate genome evolution. The present study facilitates detailed functional studies of the amphioxus globins in order to trace conserved properties and specific adaptations of respiratory proteins at the base of chordate evolution.

The nerve hemoglobin of the bivalve mollusc Spisula solidissima: molecular cloning, ligand binding studies, and phylogenetic analysis

Members of the hemoglobin (Hb) superfamily are present in nerve tissue of several vertebrate and invertebrate species. In vertebrates they display hexacoordinate heme iron atoms and are typically expressed at low levels (microM). Their function is still a matter of debate. In invertebrates they have a hexa- or pentacoordinate heme iron, are mostly expressed at high levels (mM), and have been suggested to have a myoglobin-like function. The native Hb of the surf clam, Spisula solidissima, composed of 162 amino acids, does not show specific deviations from the globin templates. UV-visible and resonance Raman spectroscopy demonstrate a hexacoordinate heme iron. Based on the sequence analogy, the histidine E7 is proposed as a sixth ligand. Kinetic and equilibrium measurements show a moderate oxygen affinity (P(50) approximately 0.6 torr) and no cooperativity. The histidine binding affinity is 100-fold lower than in neuroglobin. Phylogenetic analysis demonstrates a clustering of the S. solidissima nerve Hb with mollusc Hbs and myoglobins, but not with the vertebrate neuroglobins. We conclude that invertebrate nerve Hbs expressed at high levels are, despite the hexacoordinate nature of their heme iron, not essentially different from other intracellular Hbs. They most likely fulfill a myoglobin-like function and enhance oxygen supply to the neurons.

FOXF1 Mediates Endothelial Progenitor Functions and Regulates Vascular Sprouting

Endothelial colony forming cells (ECFC) or late blood outgrowth endothelial cells (BOEC) have been proposed to contribute to neovascularization in humans. Exploring genes characteristic for the progenitor status of ECFC we have identified the forkhead box transcription factor FOXF1 to be selectively expressed in ECFC compared to mature endothelial cells isolated from the vessel wall. Analyzing the role of FOXF1 by gain- and loss-of-function studies we detected a strong impact of FOXF1 expression on the particularly high sprouting capabilities of endothelial progenitors. This apparently relates to the regulation of expression of several surface receptors. First, FOXF1 overexpression specifically induces the expression of Notch2 receptors and induces sprouting. Vice versa, knock-down of FOXF1 and Notch2 reduces sprouting. In addition, FOXF1 augments the expression of VEGF receptor-2 and of the arterial marker ephrin B2, whereas it downmodulates the venous marker EphB4. In line with these findings on human endothelial progenitors, we further show that knockdown of FOXF1 in the zebrafish model alters, during embryonic development, the regular formation of vasculature by sprouting. Hence, these findings support a crucial role of FOXF1 for endothelial progenitors and connected vascular sprouting as it may be relevant for tissue neovascularization. It further implicates Notch2, VEGF receptor-2, and ephrin B2 as downstream mediators of FOXF1 functions.

Gene duplications and gene loss in the epidermal differentiation complex during the evolutionary land-to-water transition of cetaceans

Major protein components of the mammalian skin barrier are encoded by genes clustered in the Epidermal Differentiation Complex (EDC). The skin of cetaceans, i.e. whales, porpoises and dolphins, differs histologically from that of terrestrial mammals. However, the genetic regulation of their epidermal barrier is only incompletely known. Here, we investigated the EDC of cetaceans by comparative genomics. We found that important epidermal cornification proteins, such as loricrin and involucrin are conserved and subtypes of small proline-rich proteins (SPRRs) are even expanded in numbers in cetaceans. By contrast, keratinocyte proline rich protein (KPRP), skin-specific protein 32 (XP32) and late-cornified envelope (LCE) genes with the notable exception of LCE7A have been lost in cetaceans. Genes encoding proline rich 9 (PRR9) and late cornified envelope like proline rich 1 (LELP1) have degenerated in subgroups of cetaceans. These data suggest that the evolution of an aquatic lifestyle was accompanied by amplification of SPRR genes and loss of specific other epidermal differentiation genes in the phylogenetic lineage leading to cetaceans.

Characterisation of microsatellite and SNP markers from Miseq and genotyping-by-sequencing data among parapatric Urophora cardui (Tephritidae) populations

Phylogeographic analyses of the gall fly Urophora cardui have in earlier studies based on allozymes and mtDNA identified small-scale, parapatrically diverged populations within an expanding Western Palearctic population. However, the low polymorphism of these markers prohibited an accurate delimitation of the evolutionary origin of the parapatric divergence. Urophora cardui from the Western Palearctic have been introduced into Canada as biological control agents of the host plant Cirsium arvense. Here, we characterise 12 microsatellite loci with hexa-, penta- and tetra-nucleotide repeat motifs and report a genotyping-by-sequencing SNP protocol. We test the markers for genetic variation among three parapatric U. cardui populations. Microsatellite variability (N = 59 individuals) was high: expected heterozygosity/locus/population (0.60–0.90), allele number/locus/population (5–21). One locus was alternatively sex-linked in males or females. Cross-species amplification in the sister species U. stylata was successful or partially successful for seven loci. For genotyping-by-sequencing (N = 18 individuals), different DNA extraction methods did not affect data quality. Depending on sequence sorting criteria, 1,177–2,347 unlinked SNPs and 1,750–4,469 parsimony informative sites were found in 3,514–5,767 loci recovered after paralog filtering. Both marker systems quantified the same population partitions with high probabilities. Many and highly differentiated loci in both marker systems indicate genome-wide diversification and genetically distinct populations.

Atrioventricular nodal ablation with pacemaker implant is associated with improved safety outcomes compared to pulmonary vein isolation of atrial fibrillation with heart failure

Background

Pulmonary vein isolation (PVI) and atrioventricular nodal ablation (AVNA) with pacemaker implant have both been advocated for patients with atrial fibrillation (AF) and heart failure with reduced ejection fraction (HFrEF). Direct comparisons between the two are limited.

Purpose

We sought to compare outcomes and complications following PVI versus AVNA with implant of a cardiac implantable electronic device (CIED) among patients with AF and HFrEF.

Methods

We queried the National Inpatient Sample from 2011 to 2019, using relevant ICD-9 and -10 diagnostic and procedural codes for AF, HFrEF, ablation, and CIED implant to identify our study cohort. Exclusion criteria included presence of a pre-existing CIED, ventricular arrhythmias, non-AF supraventricular arrhythmias, and surgical AF ablation. Baseline characteristics included age, sex, race, and comorbidities related to AF and cardiovascular disease. Severity of comorbidities was assessed via Deyo-Charlson Comorbidity Index (Deyo-CCI). Outcomes investigated include all-cause mortality, major adverse cardiovascular events (MACE), extra-cardiac procedural complications, length of stay, and total hospital charges. Outcomes associations were analyzed using multivariate logistic regression adjusted for baseline characteristics that were significantly different (P<0.05) between cohorts expressed as adjusted odds ratios (aOR) and 95% confidence intervals (CI). SPSS v28.0 (IBM, Armonk, NY) was used to carry out all calculations.

Results

We identified 3,565 encounters for PVI and 1,355 for AVNA with CIED implant among hospitalized patients with AF and HFrEF. Patients who underwent AVNA were more often older (73.8 vs 66.2 years), with more severe comorbidities (mean Deyo-CCI score 2.9 vs 2.6) and were more likely to have an emergent procedure performed (81.3% vs 69.7%; p<0.001 for all). However, the AVNA cohort had less mortality (0.5% vs 1.2%, p=0.03), MACE (6.1% vs 7.8%, p=0.04), and total complications (12.7% vs 16.3%, p=0.002), but longer hospital stay (8.0 vs 6.5 days) and higher total charges ($201,100 vs $159,382; p<0.001 for both). After adjusting for confounders, AVNA remained independently associated with decreased odds of mortality (aOR: 0.370; 95% CI [0.159–0.862], p=0.02), MACE (aOR: 0.552; 95% CI [0.420–0.726], p<0.001), and total complications (aOR: 0.708; 95% CI [0.589–0.852], p<0.001).

Conclusion

Despite older age with more severe comorbidities and less elective procedures, hospitalized patients with AF and HFrEF who underwent AVNA with CIED implant had improved safety outcomes compared to PVI. Further studies comparing the intermediate and long-term outcomes and efficacy between therapies are needed to better delineate which would best serve this population.

Funding Acknowledgement

Type of funding sources: None.

[Late results of implantation of dual head prostheses in hip para-articular fractures]

In the hospital of Aalen through the years 1985 to 1993 a total of 545 patients have been treated by using a "Duokopf"-prosthesis. The average age was 82.6 years. In a retrospective study the mobility and survival rate after surgery of 109 patients, who had undergone such treatment because of a hip fracture, were found out. The survival rate one year after surgery was within the range of the survival rate of the normal population at that age: The evaluation of the mobility one year after implantation with 57% surviving patients, who are able to walk without aid is a good result. None of the patients showed a protrusio acetabuli. Although the evaluation of the presented results is limited, since, due to the high average age, the mortality rate after surgery was extreme, the Duokopf prosthesis has proved to bring up good long term results.

Assessing outcomes following catheter ablation of ventricular tachycardia in patients with durable left ventricular assist devices

Background

Management of ventricular tachycardia (VT) after implant of a durable left ventricular assist device (LVAD) is challenging, without consensus on optimal therapy. Multiple small studies have examined catheter ablation of VT in these patients with low reported incidence of complications.

Purpose

We sought to evaluate periprocedural outcomes following VT ablation among LVAD recipients.

Methods

We queried the National Inpatient Sample from 2011 to 2019 to conduct our study. Baseline characteristics include age, sex, race, and comorbidities related to cardiovascular disease. Comorbidity severity was assessed using the Deyo-Charlson Comorbidity Index (Deyo-CCI). Patients with any supraventricular arrhythmias were excluded. Outcomes investigated include heart transplant procedure, all-cause mortality, major adverse cardiovascular events (MACE), and periprocedural complications. Multivariate regression was used to analyze outcomes associations adjusted for baseline characteristics that were significantly different (P<0.05) between cohorts expressed as adjusted odds ratios (aOR) and 95% confidence intervals (CI). SPSS v28.0 (IBM, Armonk, NY) was used to carry out all calculations.

Results

We identified 56 patients who underwent ablation among 2,202 LVAD recipients hospitalized for VT. Patients who underwent ablation were more likely to have ischemic cardiomyopathy (33.9% vs. 22.2%, p=0.03) or an automated implantable cardioverter-defibrillator (55.4% vs 34.3%, p=0.001). There were otherwise no significant differences between cohorts (mean Deyo-CCI score of 2.3 for both, p=0.48). Between those who did and did not undergo ablation, there were no significant differences in heart transplant (5.4 vs 5.0%, p=0.9), mortality (7.1% vs 7.0%, p=0.96), total strokes (3.6% vs 5.0%, p=0.48), myocardial infarction (3.6% vs 4.6%, p=0.71), overall MACE (8.9% vs 10.2%, p=0.26) or total complications (35.7% vs 41.9%, p=0.35). There were no incidents of pump thrombosis in the ablation group, but 92 events (4.3%) were found in the medical therapy group. Multivariate analysis affirmed no significant association between ablation and mortality (aOR 1.277, CI [0.450–3.629]), MACE (aOR 1.125, CI [0.436–2.902]), or total complications (aOR 0.932, CI [0.528–1.645]).

Conclusion

Overall complications following VT ablation among LVAD patients were higher than previously reported but no statistically significant differences were found compared to conservative management. While ablation appears safe to perform, particularly among those with structural heart disease and ischemic cardiomyopathy, longer duration studies are needed to determine the efficacy of this procedure.

Funding Acknowledgement

Type of funding sources: None.