Association of regions on chromosomes 6 and 7 with blood pressure in Nigerian families

Quality Matters? The Involvement of Mitochondrial Quality Control in Cardiovascular Disease

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide. Multiple factors are known to affect the cardiovascular system from lifestyles, genes, underlying comorbidities, and age. Requiring high workload, metabolism of the heart is largely dependent on continuous power supply via mitochondria through effective oxidative respiration. Mitochondria not only serve as cellular power plants, but are also involved in many critical cellular processes, including the generation of intracellular reactive oxygen species (ROS) and regulating cellular survival. To cope with environmental stress, mitochondrial function has been suggested to be essential during bioenergetics adaptation resulting in cardiac pathological remodeling. Thus, mitochondrial dysfunction has been advocated in various aspects of cardiovascular pathology including the response to ischemia/reperfusion (I/R) injury, hypertension (HTN), and cardiovascular complications related to type 2 diabetes mellitus (DM). Therefore, mitochondrial homeostasis through mitochondrial dynamics and quality control is pivotal in the maintenance of cardiac health. Impairment of the segregation of damaged components and degradation of unhealthy mitochondria through autophagic mechanisms may play a crucial role in the pathogenesis of various cardiac disorders. This article provides in-depth understanding of the current literature regarding mitochondrial remodeling and dynamics in cardiovascular diseases.

Structure and Functions of Sidekicks

Many of the immunoglobulin superfamily (IgSF) molecules play pivotal roles in cell communication. The Sidekick (Sdk) gene, first described in Drosophila, encodes the single-pass transmembrane protein, Sdk, which is one of the largest among IgSF membrane proteins. Sdk first appeared in multicellular animals during the Precambrian age and later evolved to Sdk1 and Sdk2 in vertebrates by gene duplication. In flies, a single Sdk is involved in positioning photoreceptor neurons and their axons in the visual system and is responsible for dynamically rearranging cell shapes by strictly populating tricellular adherens junctions in epithelia. In vertebrates, Sdk1 and Sdk2 are expressed by unique sets of cell types and distinctively participate in the formation and/or maintenance of neural circuits in the retina, indicating that they are determinants of synaptic specificity. These functions are mediated by specific homophilic binding of their ectodomains and by intracellular association with PDZ scaffold proteins. Recent human genetic studies as well as animal experiments implicate that Sdk genes may influence various neurodevelopmental and psychiatric disorders, such as autism spectrum disorders, attention-deficit hyperactivity disorder, addiction, and depression. The gigantic Sdk1 gene is susceptible to erratic gene rearrangements or mutations in both somatic and germ-line cells, potentially contributing to neurological disorders and some types of cancers. This review summarizes what is known about the structure and roles of Sdks.

Emerging role of mitophagy in cardiovascular physiology and pathology

Healthy mitochondrial function is imperative for most tissues, but especially those with a high energy demand. Robust evidence linking mitochondrial dysfunction with cardiovascular disease has demonstrated that mitochondrial activity is highly relevant to cardiac muscle performance. Mitochondrial homeostasis is maintained through coordination among the processes that comprise the so-called mitochondrial dynamics machinery. The most-studied elements of cardiac mitochondrial dynamics are mitochondrial fission and fusion, biogenesis and degradation. Selective autophagic removal of mitochondria (mitophagy) is essential for clearing away defective mitochondria but can lead to cell damage and death if not tightly controlled. In cardiovascular cells such as cardiomyocytes and cardiac fibroblasts, mitophagy is involved in metabolic activity, cell differentiation, apoptosis and other physiological processes related to major phenotypic changes. Modulation of mitophagy has detrimental and/or beneficial outcomes in various cardiovascular diseases, suggesting that a deeper understanding of the mechanisms underlying mitochondrial degradation in the heart could provide valuable clinical insights. Here, we discuss current evidence supporting the role of mitophagy in cardiac pathophysiology, with an emphasis on different research models and their interpretations; basic concepts related to this selective autophagy; and the most commonly used experimental approaches for studying this mechanism. Finally, we provide a comprehensive literature analysis on the role of mitophagy in heart failure, ischemia/reperfusion, diabetic cardiomyopathy and other cardiovascular diseases, as well as its potential biomedical applications.

Medical genetics and genomic medicine in Nigeria

Medical genetics and genomic medicine in Nigeria.

Analyzing Association Mapping in Pedigree-Based GWAS Using a Penalized Multitrait Mixed Model

Genome-wide association studies (GWAS) have led to the identification of many genetic variants associated with complex diseases in the past 10 years. Penalization methods, with significant numerical and statistical advantages, have been extensively adopted in analyzing GWAS. This study has been partly motivated by the analysis of Genetic Analysis Workshop (GAW) 18 data, which have two notable characteristics. First, the subjects are from a small number of pedigrees and hence related. Second, for each subject, multiple correlated traits have been measured. Most of the existing penalization methods assume independence between subjects and traits and can be suboptimal. There are a few methods in the literature based on mixed modeling that can accommodate correlations. However, they cannot fully accommodate the two types of correlations while conducting effective marker selection. In this study, we develop a penalized multitrait mixed modeling approach. It accommodates the two different types of correlations and includes several existing methods as special cases. Effective penalization is adopted for marker selection. Simulation demonstrates its satisfactory performance. The GAW 18 data are analyzed using the proposed method.

Vascular dysfunction precedes hypertension associated with a blood pressure locus on rat chromosome 12

We previously isolated a 6.1-Mb region of SS/Mcwi (Dahl salt-sensitive) rat chromosome 12 (13.4-19.5 Mb) that significantly elevated blood pressure (BP) (Δ+34 mmHg, P < 0.001) compared with the SS-12(BN) consomic control. In the present study, we examined the role of vascular dysfunction and remodeling in hypertension risk associated with the 6.1-Mb (13.4-19.5 Mb) locus on rat chromosome 12 by reducing dietary salt, which lowered BP levels so that there were no substantial differences in BP between strains. Consequently, any observed differences in the vasculature were considered BP-independent. We also reduced the candidate region from 6.1 Mb with 133 genes to 2 Mb with 23 genes by congenic mapping. Both the 2 Mb and 6.1 Mb congenic intervals were associated with hypercontractility and decreased elasticity of resistance vasculature prior to elevations of BP, suggesting that the vascular remodeling and dysfunction likely contribute to the pathogenesis of hypertension in these congenic models. Of the 23 genes within the narrowed congenic interval, 12 were differentially expressed between the resistance vasculature of the 2 Mb congenic and SS-12(BN) consomic strains. Among these, Grifin was consistently upregulated 2.7 ± 0.6-fold (P < 0.05) and 2.0 ± 0.3-fold (P < 0.01), and Chst12 was consistently downregulated -2.8 ± 0.3-fold (P < 0.01) and -4.4 ± 0.4-fold (P < 0.00001) in the 2 Mb congenic compared with SS-12(BN) consomic under normotensive and hypertensive conditions, respectively. A syntenic region on human chromosome 7 has also been associated with BP regulation, suggesting that identification of the genetic mechanism(s) underlying cardiovascular phenotypes in this congenic strain will likely be translated to a better understanding of human hypertension.

Refined mapping of a hypertension susceptibility locus on rat chromosome 12

Previously, we found that transferring 6.1 Mb of salt-sensitive (SS) chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12(BN) background significantly elevated mean arterial pressure in response to an 8% NaCl diet (178±7 versus 144±2 mm Hg; P<0.001). Using congenic mapping, we have now narrowed the blood pressure locus by 86% from a 6.1-Mb region containing 133 genes to an 830-kb region (chr12:14.36-15.19 Mb) with 14 genes. Compared with the SS-12(BN) consomic, the 830-kb blood pressure locus was associated with a ∆+15 mm Hg (P<0.01) increase in blood pressure, which coincided with elevated albuminuria (∆+32 mg/d; P<0.001), proteinuria (∆+48 mg/d; P<0.01), protein casting (∆+154%; P<0.05), and renal fibrosis (∆+79%; P<0.05). Of the 14 genes residing in the 830-kb locus, 8 were differentially expressed, and among these, Chst12 (carbohydrate chondroitin 4 sulfotransferase 12) was most consistently downregulated by 2.6- to 4.5-fold (P<0.05) in both the renal medulla and cortex under normotensive and hypertensive conditions. Moreover, whole genome sequence analysis of overlapping blood pressure loci revealed an ≈86-kb region (chr12:14 541 567-14 627 442 bp) containing single-nucleotide variants near Chst12 that are unique to the hypertensive SS strain when compared with the normotensive Brown Norway, Dahl salt-resistant, and Wistar-Kyoto strains. Finally, the 830-kb interval is syntenic to a region on human chromosome 7 that has been genetically linked to blood pressure, suggesting that insight gained from our SS-12(BN) congenic strain may be translated to a better understanding of human hypertension.

Genetic epidemiology of type 2 diabetes and cardiovascular diseases in Africa

The burdens of type 2 diabetes (T2D) and cardiovascular diseases (CVD) are increasing in Africa. T2D and CVD are the result of the complex interaction between inherited characteristics, lifestyle, and environmental factors. The epidemic of obesity is largely behind the exploding global incidence of T2D. However, not all obese individuals develop diabetes and positive family history is a powerful risk factor for diabetes and CVD. Recent implementations of high throughput genotyping and sequencing approaches have advanced our understanding of the genetic basis of diabetes and CVD by identifying several genomic loci that were not previously linked to the pathobiology of these diseases. However, African populations have not been adequately represented in these global genomic efforts. Here, we summarize the state of knowledge of the genetic epidemiology of T2D and CVD in Africa and highlight new genomic initiatives that promise to inform disease etiology, public health and clinical medicine in Africa.

Genome-wide linkage analysis of carotid artery lumen diameter: the strong heart family study

BACKGROUND

A significant proportion of the variability in carotid artery lumen diameter is attributable to genetic factors.

METHODS

Carotid ultrasonography and genotyping were performed in the 3300 American Indian participants in the Strong Heart Family Study (SHFS) to identify chromosomal regions harboring novel genes associated with inter-individual variation in carotid artery lumen diameter. Genome-wide linkage analysis was conducted using standard variance component linkage methods, implemented in SOLAR, based on multipoint identity-by-descent matrices.

RESULTS

Genome-wide linkage analysis revealed a significant evidence for linkage for a locus for left carotid artery diastolic and systolic lumen diameters in Arizona SHFS participants on chromosome 7 at 120 cM (lod = 4.85 and 3.77, respectively, after sex and age adjustment, and lod = 3.12 and 2.72, respectively, after adjustment for sex, age, height, weight, systolic and diastolic blood pressure, diabetes mellitus and current smoking). Other regions with suggestive evidence of linkage for left carotid artery diastolic and systolic lumen diameter were found on chromosome 12 at 153 cM (lod = 2.20 and 2.60, respectively, after sex and age adjustment, and lod = 2.44 and 2.16, respectively, after full covariate adjustment) in Oklahoma SHFS participants; suggestive linkage for right carotid artery diastolic and systolic lumen diameter was found on chromosome 9 at 154 cM (lod = 2.72 and 3.19, respectively after sex and age adjustment, and lod = 2.36 and 2.21, respectively, after full covariate adjustment) in Oklahoma SHFS participants.

CONCLUSION

We found significant evidence for loci influencing carotid artery lumen diameter on chromosome 7q and suggestive linkage on chromosomes 12q and 9q.

Identification of hypertension susceptibility loci on rat chromosome 12

Previous studies have identified multiple blood pressure and renal disease quantitative trait loci located on rat chromosome 12. In the present study, we narrowed blood pressure loci using a series of overlapping Dahl salt-sensitive/Mcwi (SS)-12 Brown Norway (BN) congenic lines. We found that transferring 6.1 Mb of SS chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12BN background significantly elevated blood pressure on 1% NaCl (146±6 versus 127±1 mm Hg; P<0.001) and 8% NaCl diets (178±7 versus 144±2 mm Hg; P<0.001). Compared with the SS-12BN consomic, these animals also had significantly elevated albumin (218±31 versus 104±8 mg/d; P<0.001) and protein excretion (347±41 versus 195±12 mg/d; P<0.001) on a 1% NaCl diet. Elevated blood pressure, albuminuria, and proteinuria coincided with greater renal and cardiac damage, demonstrating that SS allele(s) within the 6.1 Mb congenic interval are associated with strong cardiovascular disease phenotypes. Sequence analysis of the 6.1 Mb congenic region revealed 12 673 single nucleotide polymorphisms between SS and BN rats. Of these polymorphisms, 293 lie within coding regions, and 18 resulted in nonsynonymous changes in conserved genes, of which 5 were predicted to be potentially damaging to protein function. Syntenic regions in human chromosome 7 have also been identified in multiple linkage and association studies of cardiovascular disease, suggesting that genetic variants underlying cardiovascular phenotypes in this congenic strain can likely be translated to a better understanding of human hypertension.

Pourcain B, Xiao Y, Timpson NJ, Smith GD, Reid IR, Ring SM, Sambrook PN, Karlsson M, Dennison EM, Kemp JP, Danoy P, Sayers A, Wilson SG, Nethander M, McCloskey E, Vandenput L, Eastell R, Liu J, Spector T, Mitchell BD, Streeten EA, Brommage R, Pettersson-Kymmer U, Brown MA, Ohlsson C, Richards JB, Lorentzon M. WNT16 influences bone mineral density, cortical bone thickness, bone strength, and osteoporotic fracture risk

We aimed to identify genetic variants associated with cortical bone thickness (CBT) and bone mineral density (BMD) by performing two separate genome-wide association study (GWAS) meta-analyses for CBT in 3 cohorts comprising 5,878 European subjects and for BMD in 5 cohorts comprising 5,672 individuals. We then assessed selected single-nucleotide polymorphisms (SNPs) for osteoporotic fracture in 2,023 cases and 3,740 controls. Association with CBT and forearm BMD was tested for ∼2.5 million SNPs in each cohort separately, and results were meta-analyzed using fixed effect meta-analysis. We identified a missense SNP (Thr>Ile; rs2707466) located in the WNT16 gene (7q31), associated with CBT (effect size of -0.11 standard deviations [SD] per C allele, P = 6.2 × 10(-9)). This SNP, as well as another nonsynonymous SNP rs2908004 (Gly>Arg), also had genome-wide significant association with forearm BMD (-0.14 SD per C allele, P = 2.3 × 10(-12), and -0.16 SD per G allele, P = 1.2 × 10(-15), respectively). Four genome-wide significant SNPs arising from BMD meta-analysis were tested for association with forearm fracture. SNP rs7776725 in FAM3C, a gene adjacent to WNT16, was associated with a genome-wide significant increased risk of forearm fracture (OR = 1.33, P = 7.3 × 10(-9)), with genome-wide suggestive signals from the two missense variants in WNT16 (rs2908004: OR = 1.22, P = 4.9 × 10(-6) and rs2707466: OR = 1.22, P = 7.2 × 10(-6)). We next generated a homozygous mouse with targeted disruption of Wnt16. Female Wnt16(-/-) mice had 27% (P<0.001) thinner cortical bones at the femur midshaft, and bone strength measures were reduced between 43%-61% (6.5 × 10(-13)<P<5.9 × 10(-4)) at both femur and tibia, compared with their wild-type littermates. Natural variation in humans and targeted disruption in mice demonstrate that WNT16 is an important determinant of CBT, BMD, bone strength, and risk of fracture.