Metformin induces FOXO3-dependent fetal hemoglobin production in human primary erythroid cells.

Induction of red blood cell (RBC) fetal hemoglobin (HbF; α2γ2) ameliorates the pathophysiology of sickle cell disease (SCD) by reducing the concentration of sickle hemoglobin (HbS; α2ßS2) to inhibit its polymerization. Hydroxyurea (HU), the only US Food and Drug Administration (FDA)-approved drug for SCD, acts in part by inducing HbF; however, it is not fully effective, reflecting the need for new therapies. Whole-exome sequence analysis of rare genetic variants in SCD patients identified FOXO3 as a candidate regulator of RBC HbF. We validated these genomic findings through loss- and gain-of-function studies in normal human CD34+ hematopoietic stem and progenitor cells induced to undergo erythroid differentiation. FOXO3 gene silencing reduced γ-globin RNA levels and HbF levels in erythroblasts, whereas overexpression of FOXO3 produced the opposite effect. Moreover, treatment of primary CD34+ cell-derived erythroid cultures with metformin, an FDA-approved drug known to enhance FOXO3 activity in nonerythroid cells, caused dose-related FOXO3-dependent increases in the percentage of HbF protein and the fraction of HbF-immunostaining cells (F cells). Combined HU and metformin treatment induced HbF additively and reversed the arrest in erythroid maturation caused by HU treatment alone. HbF induction by metformin in erythroid precursors was dependent on FOXO3 expression and did not alter expression of BCL11A, MYB, or KLF1. Collectively, our data implicate FOXO3 as a positive regulator of γ-globin expression and identify metformin as a potential therapeutic agent for SCD.

Association of low-frequency and rare coding-sequence variants with blood lipids and coronary heart disease in 56,000 whites and blacks.

Low-frequency coding DNA sequence variants in the proprotein convertase subtilisin/kexin type 9 gene (PCSK9) lower plasma low-density lipoprotein cholesterol (LDL-C), protect against risk of coronary heart disease (CHD), and have prompted the development of a new class of therapeutics. It is uncertain whether the PCSK9 example represents a paradigm or an isolated exception. We used the "Exome Array" to genotype >200,000 low-frequency and rare coding sequence variants across the genome in 56,538 individuals (42,208 European ancestry [EA] and 14,330 African ancestry [AA]) and tested these variants for association with LDL-C, high-density lipoprotein cholesterol (HDL-C), and triglycerides. Although we did not identify new genes associated with LDL-C, we did identify four low-frequency (frequencies between 0.1% and 2%) variants (ANGPTL8 rs145464906 [c.361C>T; p.Gln121*], PAFAH1B2 rs186808413 [c.482C>T; p.Ser161Leu], COL18A1 rs114139997 [c.331G>A; p.Gly111Arg], and PCSK7 rs142953140 [c.1511G>A; p.Arg504His]) with large effects on HDL-C and/or triglycerides. None of these four variants was associated with risk for CHD, suggesting that examples of low-frequency coding variants with robust effects on both lipids and CHD will be limited.

Small dense low-density lipoprotein-cholesterol concentrations predict risk for coronary heart disease: the Atherosclerosis Risk In Communities (ARIC) study.

OBJECTIVE: To investigate the relationship between plasma levels of small dense low-density lipoprotein-cholesterol (sdLDL-C) and risk for incident coronary heart disease (CHD) in a prospective study among Atherosclerosis Risk in Communities (ARIC) study participants. APPROACH AND RESULTS: Plasma sdLDL-C was measured in 11 419 men and women of the biracial ARIC study using a newly developed homogeneous assay. A proportional hazards model was used to examine the relationship among sdLDL-C, vascular risk factors, and risk for CHD events (n=1158) for a period of ≈11 years. Plasma sdLDL-C levels were strongly correlated with an atherogenic lipid profile and were higher in patients with diabetes mellitus than non-diabetes mellitus (49.6 versus 42.3 mg/dL; P<0.0001). In a model that included established risk factors, sdLDL-C was associated with incident CHD with a hazard ratio of 1.51 (95% confidence interval, 1.21-1.88) for the highest versus the lowest quartile, respectively. Even in individuals considered to be at low cardiovascular risk based on their LDL-C levels, sdLDL-C predicted risk for incident CHD (hazard ratio, 1.61; 95% confidence interval, 1.04-2.49). Genome-wide association analyses identified genetic variants in 8 loci associated with sdLDL-C levels. These loci were in or close to genes previously associated with risk for CHD. We discovered 1 novel locus, PCSK7, for which genetic variation was significantly associated with sdLDL-C and other lipid factors. CONCLUSIONS: sdLDL-C was associated with incident CHD in ARIC study participants. The novel association of genetic variants in PCSK7 with sdLDL-C and other lipid traits may provide new insights into the role of this gene in lipid metabolism.

Whole exome sequencing identifies novel genes for fetal hemoglobin response to hydroxyurea in children with sickle cell anemia.

Hydroxyurea has proven efficacy in children and adults with sickle cell anemia (SCA), but with considerable inter-individual variability in the amount of fetal hemoglobin (HbF) produced. Sibling and twin studies indicate that some of that drug response variation is heritable. To test the hypothesis that genetic modifiers influence pharmacological induction of HbF, we investigated phenotype-genotype associations using whole exome sequencing of children with SCA treated prospectively with hydroxyurea to maximum tolerated dose (MTD). We analyzed 171 unrelated patients enrolled in two prospective clinical trials, all treated with dose escalation to MTD. We examined two MTD drug response phenotypes: HbF (final %HbF minus baseline %HbF), and final %HbF. Analyzing individual genetic variants, we identified multiple low frequency and common variants associated with HbF induction by hydroxyurea. A validation cohort of 130 pediatric sickle cell patients treated to MTD with hydroxyurea was genotyped for 13 non-synonymous variants with the strongest association with HbF response to hydroxyurea in the discovery cohort. A coding variant in Spalt-like transcription factor, or SALL2, was associated with higher final HbF in this second independent replication sample and SALL2 represents an outstanding novel candidate gene for further investigation. These findings may help focus future functional studies and provide new insights into the pharmacological HbF upregulation by hydroxyurea in patients with SCA.