MTSviewer: a database to visualize mitochondrial targeting sequences, cleavage sites, and mutations on protein structures

Mitochondrial dysfunction is implicated in a wide array of human diseases ranging from neurodegenerative disorders to cardiovascular defects. The coordinated localization and import of proteins into mitochondria is an essential process that ensures mitochondrial homeostasis and consequently cell survival. The localization and import of most mitochondrial proteins are driven by N-terminal mitochondrial targeting sequences (MTS), which interact with import machinery and are removed by the mitochondrial processing peptidase (MPP). The recent discovery of internal MTS's - those which are distributed throughout a protein and act as import regulators or secondary MPP cleavage sites - has expanded the role of both MTS's and MPP beyond conventional N-terminal regulatory pathways. Still, the global mutational landscape of MTS's remains poorly characterized, both from genetic and structural perspectives. To this end, we have integrated a variety of prediction tools into one harmonized R/Shiny database called MTSviewer, which combines MTS predictions, MPP cleavage sites, genetic variants, pathogenicity predictions, and N-terminomics data with structural visualization using AlphaFold models. Using this platform, we have generated a list of disease-linked variants in protein MTS's and their predicted consequences as a resource for their functional characterization. Overall, MTSviewer is a platform that can be used to interrogate MTS mutations and their potential effects on import and proteolysis across the mitochondrial proteome.

DYNAMICS OF FREQUENCY AND PECULIARITIES OF THE STRUCTURE OF CONGENITAL MALFORMATIONS IN SOUTH UKRAINE (MONITORING STUDY)

Background. In Ukraine, the unfavorable demographic situation makes monitoring of the birth rate of children with congenital malformations urgent issue to identify regional features of epidemiology and develop methods for prenatal diagnosis and prognosis. Objective. Objective of this study is to characterize the frequency dynamics, to identify structural features of congenital malformations of newborns in Kherson region over a 20-year period (2000-2019) and to compare the prevalence of various nosological forms of malformations in the region, in Ukraine and in European countries. Methods. Research methods: epidemiological, medical-statistical. Results. In Kherson region, the average frequency of congenital malformations over the past 20 years is: for newborns – 31.57±1.25‰; for live births – 31.38±1.11‰; for stillborns – 197.7±0.65 per 10,000. In the structure of defects, cardiovascular malformations are leading (31.77%), musculoskeletal malformations (25.14%), genital malformations (17.5%). Increased prevalence of developmental anomalies in the region is mainly associated with an increase in the frequency of model malformations recorded by EUROCAT (r=0.69, p<0.05). The increase in the total frequency of congenital malformations is caused by increased number of births of children with cardiovascular defects (by 4.67‰), genital defects (by 1.21‰), other congenital malformations (by 1.55‰), multiple malformations (by 0.37‰). Conclusion. Monitoring results showed an increase in congenital malformations incidence in Kherson region over a 20-year period by 7.94‰ possibly caused by population decline due to negative natural and mechanical growth. The prevalence of hereditary defects is at the same level. The frequency of some nosological forms significantly exceeds in the region compare to that in Ukraine and Europe: cardiovascular defects – in 1.5 times, genital malformations – in nearly 3 times, musculoskeletal defects – almost twice.

Msx1 haploinsufficiency modifies the Pax9-deficient cardiovascular phenotype

Background Successful embryogenesis relies on the coordinated interaction between genes and tissues. The transcription factors Pax9 and Msx1 genetically interact during mouse craniofacial morphogenesis, and mice deficient for either gene display abnormal tooth and palate development. Pax9 is expressed specifically in the pharyngeal endoderm at mid-embryogenesis, and mice deficient for Pax9 on a C57Bl/6 genetic background also have cardiovascular defects affecting the outflow tract and aortic arch arteries giving double-outlet right ventricle, absent common carotid arteries and interruption of the aortic arch. Results In this study we have investigated both the effect of a different genetic background and Msx1 haploinsufficiency on the presentation of the Pax9-deficient cardiovascular phenotype. Compared to mice on a C57Bl/6 background, congenic CD1-Pax9–/– mice displayed a significantly reduced incidence of outflow tract defects but aortic arch defects were unchanged. Pax9–/– mice with Msx1 haploinsufficiency, however, have a reduced incidence of interrupted aortic arch, but more cases with cervical origins of the right subclavian artery and aortic arch, than seen in Pax9–/– mice. This alteration in arch artery defects was accompanied by a rescue in third pharyngeal arch neural crest cell migration and smooth muscle cell coverage of the third pharyngeal arch arteries. Although this change in phenotype could theoretically be compatible with post-natal survival, using tissue-specific inactivation of Pax9 to maintain correct palate development whilst inducing the cardiovascular defects was unable to prevent postnatal death in the mutant mice. Hyoid bone and thyroid cartilage formation were abnormal in Pax9–/– mice. Conclusions Msx1 haploinsufficiency mitigates the arch artery defects in Pax9–/– mice, potentially by maintaining the survival of the 3rd arch artery through unimpaired migration of neural crest cells to the third pharyngeal arches. With the neural crest cell derived hyoid bone and thyroid cartilage also being defective in Pax9–/– mice, we speculate that the pharyngeal endoderm is a key signalling centre that impacts on neural crest cell behaviour highlighting the ability of cells in different tissues to act synergistically or antagonistically during embryo development.

Zebrafish Models in Therapeutic Research of Cardiac Conduction Disease

Malfunction in the cardiac conduction system (CCS) due to congenital anomalies or diseases can cause cardiac conduction disease (CCD), which results in disturbances in cardiac rhythm, leading to syncope and even sudden cardiac death. Insights into development of the CCS components, including pacemaker cardiomyocytes (CMs), atrioventricular node (AVN) and the ventricular conduction system (VCS), can shed light on the pathological and molecular mechanisms underlying CCD, provide approaches for generating human pluripotent stem cell (hPSC)-derived CCS cells, and thus improve therapeutic treatment for such a potentially life-threatening disorder of the heart. However, the cellular and molecular mechanisms controlling CCS development remain elusive. The zebrafish has become a valuable vertebrate model to investigate early development of CCS components because of its unique features such as external fertilization, embryonic optical transparency and the ability to survive even with severe cardiovascular defects during development. In this review, we highlight how the zebrafish has been utilized to dissect the cellular and molecular mechanisms of CCS development, and how the evolutionarily conserved developmental mechanisms discovered in zebrafish could be applied to directing the creation of hPSC-derived CCS cells, therefore providing potential therapeutic strategies that may contribute to better treatment for CCD patients.

A Novel Art of Electrocardiogram Assessment in Zebrafish for Cardiovascular Disease Studies and Drug Screening

The zebrafish (Dario rerio) has proven to be an excellent animal model for biological research owing to its small size, low cost for maintenance, short generation time, amenable genetics, and optical transparency. Zebrafish have been extensively used in cardiovascular studies in which mutant lines with cardiovascular defects were introduced and analyzed. Despite the small size, technological advances have paved the way to effectively assess cardiac functions of zebrafish. Here, we present a novel art for long-term simultaneous monitoring and analysis of electrocardiogram (ECG) in multiple zebrafish with controlled environment. The system helps minimize the effect of anesthetic drug and temperature to cardiac rhythm side effects as well as save time and efforts by 40-50 fold compared with the conventional approach. We further employed the system to study the Na+ sensitivity in the development of sinus arrest in Tg(SCN5A-D1275N) fish, a study model of the sick sinus syndrome, as well as the relationship between this variant and drug administration. The novel ECG system developed in this study holds promise to greatly accelerate other cardiovascular studies and drug screening using zebrafish.

Unique triad of shunts in a patient with paroxysmal palpitations!

We present the case of a 34-year-old woman with a rare constellation of congenital cardiovascular defects. She presented with new-onset dyspnoea on exertion and intermittent palpitations. Extensive cardiac workup revealed anomalous drainage of the inferior vena cava and a large secundum atrial septal defect. She underwent surgical repair. Intraoperatively, an additional congenital venous anomaly was discovered, a partial anomalous pulmonary venous connection. Specifically, the right inferior pulmonary vein connected to the inferior vena cava, and together, they drained into the left atrium. On conducting a thorough literature review, we believe this is the first reported case in an adult female.

Maternal iron deficiency perturbs embryonic cardiovascular development in mice

Congenital heart disease (CHD) is the most common class of human birth defects, with a prevalence of 0.9% of births. However, two-thirds of cases have an unknown cause, and many of these are thought to be caused by in utero exposure to environmental teratogens. Here we identify a potential teratogen causing CHD in mice: maternal iron deficiency (ID). We show that maternal ID in mice causes severe cardiovascular defects in the offspring. These defects likely arise from increased retinoic acid signalling in ID embryos. The defects can be prevented by iron administration in early pregnancy. It has also been proposed that teratogen exposure may potentiate the effects of genetic predisposition to CHD through gene–environment interaction. Here we show that maternal ID increases the severity of heart and craniofacial defects in a mouse model of Down syndrome. It will be important to understand if the effects of maternal ID seen here in mice may have clinical implications for women.

Msx1 Haploinsufficiency Modifies the Pax9-Deficient Cardiovascular Phenotype

Background Successful embryogenesis relies on the coordinated interaction between genes and tissues. The transcription factors Pax9 and Msx1 genetically interact during mouse craniofacial morphogenesis, and mice deficient for either gene display abnormal tooth and palate development. Pax9 is expressed specifically in the pharyngeal endoderm at mid-embryogenesis, and mice deficient for Pax9 on a C57Bl/6 genetic background also have cardiovascular defects affecting the outflow tract and aortic arch arteries giving double-outlet right ventricle, absent common carotid arteries and interruption of the aortic arch. Results In this study we have investigated both the effect of a different genetic background and Msx1 haploinsufficiency on the presentation of the Pax9-deficient cardiovascular phenotype. Compared to mice on a C57Bl/6 background, congenic CD1-Pax9−/− mice displayed a significantly reduced incidence of outflow tract defects but aortic arch defects were unchanged. Pax9−/− mice with Msx1 haploinsufficiency, however, have a reduced incidence of interrupted aortic arch, but more cases with cervical origins of the right subclavian artery and aortic arch, than seen in Pax9−/− mice. This alteration in arch artery defects was accompanied by a rescue in third pharyngeal arch neural crest cell migration and smooth muscle cell coverage of the third pharyngeal arch arteries. Although this change in phenotype could theoretically be compatible with post-natal survival, using tissue-specific inactivation of Pax9 to maintain correct palate development whilst inducing the cardiovascular defects was unable to prevent postnatal death in the mutant mice. Hyoid bone and thyroid cartilage formation were abnormal in Pax9−/− mice. Conclusions Msx1 haploinsufficiency mitigates the arch artery defects in Pax9−/− mice, potentially by maintaining the survival of the 3rd arch artery through unimpaired migration of neural crest cells to the third pharyngeal arches. With the neural crest cell derived hyoid bone and thyroid cartilage also being defective in Pax9−/− mice, we speculate that the pharyngeal endoderm is a key signalling centre that impacts on neural crest cell behaviour highlighting the ability of cells in different tissues to act synergistically or antagonistically during embryo development.