Translational Research

2012-02-01

High points and hurdles in the translation of genomics

Jill Waalen — 2011-11-23

When the sequencing of the human genome was completed 8 years ago, it was the result of nearly 13 years of work by multiple groups using techniques that sequenced DNA base pairs at a rate of 115,000 (115 kbp) per day. As detailed by Marian in this issue of Translational Research, the technologic advances in DNA sequencing since then have been stunning. With next-generation, massively parallel methods, the rate of sequencing has increased 109-fold and the time required to sequence the 3.2 billion base pairs of a whole human genome has decreased from 3–4 months using 100 machines to 1 week with 1 machine. With the accompanying decrease in cost, the “$1000 genome” is now in sight.

Molecular genetic studies of complex phenotypes

Ali J. Marian — 2011-09-01

The approach to molecular genetic studies of complex phenotypes evolved considerably during the recent years. The candidate gene approach, which is restricted to an analysis of a few single-nucleotide polymorphisms (SNPs) in a modest number of cases and controls, has been supplanted by the unbiased approach of genome-wide association studies (GWAS), wherein a large number of tagger SNPs are typed in many individuals. GWAS, which are designed on the common disease-common variant hypothesis (CD-CV), identified several SNPs and loci for complex phenotypes. However, the alleles identified through GWAS are typically not causative but rather in linkage disequilibrium (LD) with the true causal variants. The common alleles, which may not capture the uncommon and rare variants, account only for a fraction of heritability of the complex traits. Hence, the focus is being shifted to rare variants–common disease (RV-CD) hypothesis, surmising that rare variants exert large effect sizes on the phenotype. In conjunctional with this conceptual shift, technologic advances in DNA sequencing techniques have dramatically enhanced whole genome or whole exome sequencing capacity. The sequencing approach affords identification of not only the rare but also the common variants. The approach—whether used in complementation with GWAS or as a stand-alone approach—could define the genetic architecture of the complex phenotypes. Robust phenotyping and large-scale sequencing studies are essential to extract the information content of the vast number of DNA sequence variants (DSVs) in the genome. To garner meaningful clinical information and link the genotype to a phenotype, the identification and characterization of a large number of causal fields beyond the information content of DNA sequence variants would be necessary. This review provides an update on the current progress and limitations in identifying DSVs that are associated with phenotypic effects.

Prematurity in mice leads to reduction in nephron number, hypertension, and proteinuria

2011-11-10

The nephron number at birth is a quantitative trait that correlates inversely with the risk of hypertension and chronic kidney disease later in life. During kidney development, the nephron number is controlled by multiple factors including genetic, epigenetic, and environmental modifiers. Premature birth, which represents more than 12% of annual live births in the United States, has been linked to low nephron number and the development of hypertension later in life. In this report, we describe the development of a mouse model of prematurity-induced reduction of nephron number. Premature mice, delivered 1 and 2 days early, have 17.4 ± 2.3% (n = 6) and 23.6 ± 2% (n = 10) fewer nephrons, respectively, when compared with full-term animals (12,252 ± 571 nephrons/kidney, n = 10). After 5 weeks of age, the mice delivered 2 days premature show lower real-time glomerular filtration rate (GFR, 283 ± 13 vs 389 ± 26 μL/min). The premature mice also develop hypertension (mean arterial pressure [MAP], 134 ± 18 vs 120 ± 14 mm Hg) and albuminuria (286 ± 83 vs 176 ± 59 μg albumin/mg creatinine). This mouse model provides a proof of concept that prematurity leads to reduced nephron number and hypertension, and this model will be useful in studying the pathophysiology of prematurity-induced nephron number reductions and hypertension.

The combined ratios of L-arginine and asymmetric and symmetric dimethylarginine as biomarkers in spontaneously hypertensive rats

Chien-Ning Hsu, Li-Tung Huang, Ying-Tung Lau, Ching-Yuang Lin, You-Lin Tain — 2011-09-29

Hypertension and hypertensive end-organ damage have been associated with decreased nitric oxide (NO) bioavailability. Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) both can inhibit NO availability by competition with L-arginine (L-Arg). However, whether a combined analysis of these 3 parameters can serve as an ideal biomarker of hypertension remains unclear. We measured the plasma and renal levels of L-Arg, ADMA, and SDMA in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) control rats at 3 stages: 4 weeks old (prehypertensive), 12 weeks old (hypertensive), and 24 weeks old (end-organ damage). The plasma and renal L-Arg/ADMA ratio (AAR) and the ADMA/SDMA ratio (ASR) were computed for all 3 age stages. Our results revealed an ADMA level increase, and an AAR decrease in plasma and kidneys may develop early on, even before the onset of hypertension in 4-week-old SHRs. The renal ADMA level and AAR were restored in SHRs at 24 weeks of age, which might protect SHRs against kidney injury. We found that the plasma AAR is superior to the levels of L-Arg and ADMA in plasma, and it predicted blood pressure and urinary NOx levels. Renal AAR is a strong independent marker of renal dimethylarginine dimethylaminohydrolase (DDAH) activity. The plasma ASR was correlated strongly to blood pressure. However, renal DDAH activity was related to the renal ASR but not the plasma ASR. In conclusion, the AAR and ASR may serve as better markers for disease activity and progression than each individual parameter. Clinical use of these ratios to elucidate the role of ADMA in hypertension awaits further validation.

Enhanced induction of heme oxygenase-1 suppresses thrombus formation and affects the protein C system in sepsis

2011-11-17

Heme oxygenase-1 (HO-1) displays anti-inflammatory and cytoprotective activities in sepsis. Here, we investigated the effects of HO-1 on thrombus formation and the protein C system in a septic C57BL/6 mouse model induced by cecal ligation and perforation (CLP). Septic mice were either preinjected with the vehicle, pretreated with hemin (an HO-1 inducer) or zinc protoporphyrin IX (ZnPP, an HO-1 inhibitor), or given a combination of hemin + ZnPP. CLP increased significantly the hepatic expression of HO-1; increased thrombosis in livers, kidneys, and lungs; shortened the prothrombin time (PT) and activated partial thromboplastin time (APTT); elevated the levels of tumor necrosis factor-1α (TNF-1α), interleukin-6 (IL-6), and thrombomodulin (TM); reduced the levels of protein C (PC) and activated protein C (aPC); and downregulated hepatic expression of PC and TM. The preadministration of hemin to septic mice increased the expression and activity of HO-1; inhibited thrombosis in the preceding 3 organs; prolonged PT and APTT; inhibited the production of TNF-α and IL-6; upregulated the expression of PC and TM in livers; elevated the plasma levels of PC and aPC; and reduced the plasma levels of TM. In contrast, ZnPP showed opposite effects to hemin and reversed the effects of hemin by inhibiting the activity of HO-1. The administration of tricarbonyl dichloro ruthenium (II) dimer (CORM-2), which is a CO-releasing molecule, had a similar effect to hemin on thrombosis and the protein C system. The data indicate that the enhanced induction of HO-1 inhibits thrombus formation and affects the protein C system in sepsis.

Mild hypothermia reduces ventilator–induced lung injury, irrespective of reducing respiratory rate

2011-11-14

In the era of lung-protective mechanical ventilation using limited tidal volumes, higher respiratory rates are applied to maintain adequate minute volume ventilation. However, higher respiratory rates may contribute to ventilator–induced lung injury (VILI). Induced hypothermia reduces carbon dioxide production and might allow for lower respiratory rates during mechanical ventilation. We hypothesized that hypothermia protects from VILI and investigated whether reducing respiratory rates enhance lung protection in an in vivo model of VILI. During 4 h of mechanical ventilation, VILI was induced by tidal volumes of 18 mL/kg in rats, with respiratory rates set at 15 or 10 breaths/min in combination with hypothermia (32°C) or normothermia (37°C). Hypothermia was induced by external cooling. A physiologic model was established. VILI was characterized by increased pulmonary neutrophil influx, protein leak, wet weights, histopathology score, and cytokine levels compared with lung protective mechanical ventilation. Hypothermia decreased neutrophil influx, pulmonary levels, systemic interleukin–6 levels, and histopathology score, and it tended to decrease the pulmonary protein leak. Reducing the respiratory rate in combination with hypothermia did not reduce the parameters of the lung injury. In conclusion, hypothermia protected from lung injury in a physiologic VILI model by reducing inflammation. Decreasing the respiratory rate mildly did not enhance protection.

Link between leptin and interleukin-6 levels in the initial phase of obesity related inflammation

2011-11-07

The mechanisms underlying the pathogenesis of obesity-related atherosclerosis remain to be clarified. To investigate the preclinical phase, interleukin-6 (IL-6) plasma levels were analyzed together with clinical, anthropometric, inflammatory, and metabolic variables in a well-defined cohort of 677 young and middle-aged overweight/obese and normal-weight subjects. In the juvenile and adult overweight/obese study group, IL-6 levels were increased significantly compared with normal-weight, age-matched controls (P < 0.001). In both juveniles and adults, higher levels of IL-6 were observed in obese compared with overweight participants. Subjects with metabolic syndrome (MS) had significantly higher IL-6 levels than those without MS. In juveniles, leptin, and in adults, the waist-to-height ratio, turned out to be the best predictor of IL-6 plasma levels in a multiple stepwise regression model. Taken together, in every age group, interleukin-6 is associated positively with the grade of overweight. Interestingly, leptin, which is the best known adipokine, is associated predictively with interleukin-6 plasma levels only in juveniles, which may indicate an important role of this molecule in the initiation of obesity-related inflammation.

Information for Readers

2012-02-01

Masthead

2012-02-01

Editorial Advisory Board

2012-02-01

Author Guidelines

2012-02-01

Translational Research

Contents

High points and hurdles in the translation of genomics

Molecular genetic studies of complex phenotypes

Prematurity in mice leads to reduction in nephron number, hypertension, and proteinuria

The combined ratios of L-arginine and asymmetric and symmetric dimethylarginine as biomarkers in spontaneously hypertensive rats

Enhanced induction of heme oxygenase-1 suppresses thrombus formation and affects the protein C system in sepsis

Mild hypothermia reduces ventilator–induced lung injury, irrespective of reducing respiratory rate

Link between leptin and interleukin-6 levels in the initial phase of obesity related inflammation

Information for Readers

Contents

Masthead

Editorial Advisory Board

Author Guidelines