Search

Obesity is a major risk factor for COVID-19 severity; however, the mechanisms underlying this relationship are not fully understood. Since obesity influences the plasma proteome, we sought to identify circulating proteins mediating the effects of obesity on COVID-19 severity in humans. Here, we screened 4,907 plasma proteins to identify proteins influenced by body mass index (BMI) using Mendelian randomization (MR). This yielded 1,216 proteins, whose effect on COVID-19 severity was assessed, again using MR. We found that a standard deviation increase in nephronectin (NPNT) was associated with increased odds of critically ill COVID-19 (OR = 1.71,P= 1.63 × 10−10). The effect was driven by an NPNT splice isoform. Mediation analyses supported NPNT as a mediator. In single-cell RNA-sequencing,NPNTwas expressed in alveolar cells and fibroblasts of the lung in individuals who died of COVID-19. Finally, decreasing body fat mass and increasing fat-free mass were found to lower NPNT levels. These findings provide actionable insights into how obesity influences COVID-19 severity.

Obesity strongly increases the risk of cardiometabolic diseases, yet the underlying mediators of this relationship are not fully understood. Given that obesity has broad effects on circulating protein levels, we investigated circulating proteins that mediate the effects of obesity on coronary artery disease (CAD), stroke, and type 2 diabetes—since doing so may prioritize targets for therapeutic intervention. By integrating proteome-wide Mendelian randomization (MR) screening 4,907 plasma proteins, colocalization, and mediation analyses, we identified seven plasma proteins, including collagen type VI α3 (COL6A3). COL6A3 was strongly increased by body mass index (BMI) (β= 0.32, 95% CI: 0.26–0.38,P= 3.7 × 10-8per s.d. increase in BMI) and increased the risk of CAD (OR = 1.47, 95% CI:1.26–1.70,P= 4.5 × 10-7per s.d. increase in COL6A3). Notably, COL6A3 is cleaved at its C-terminus to produce endotrophin, which was found to mediate this effect on CAD. In single-cell RNA sequencing of adipose tissues and coronary arteries,COL6A3was highly expressed in cell types involved in metabolic dysfunction and fibrosis. Finally, we found that body fat reduction can reduce plasma levels of COL6A3-derived endotrophin, thereby highlighting a tractable way to modify endotrophin levels. In summary, we provide actionable insights into how circulating proteins mediate the effect of obesity on cardiometabolic diseases and prioritize endotrophin as a potential therapeutic target.

Many common and rare variants associated with hematologic traits have been discovered through imputation on large-scale reference panels. However, the majority of genome-wide association studies (GWASs) have been conducted in Europeans, and determining causal variants has proved challenging. We performed a GWAS of total leukocyte, neutrophil, lymphocyte, monocyte, eosinophil, and basophil counts generated from 109,563,748 variants in the autosomes and the X chromosome in the Trans-Omics for Precision Medicine (TOPMed) program, which included data from 61,802 individuals of diverse ancestry. We discovered and replicated 7 leukocyte trait associations, including (1) the association between a chromosome X, pseudo-autosomal region (PAR), noncoding variant located between cytokine receptor genes (CSF2RA and CLRF2) and lower eosinophil count; and (2) associations between single variants found predominantly among African Americans at the S1PR3 (9q22.1) and HBB (11p15.4) loci and monocyte and lymphocyte counts, respectively. We further provide evidence indicating that the newly discovered eosinophil-lowering chromosome X PAR variant might be associated with reduced susceptibility to common allergic diseases such as atopic dermatitis and asthma. Additionally, we found a burden of very rare FLT3 (13q12.2) variants associated with monocyte counts. Together, these results emphasize the utility of whole-genome sequencing in diverse samples in identifying associations missed by European-ancestry-driven GWASs.

ObjectiveObservational studies on cognition found that vitamin D supplementation is associated with improved cognition. Further, recent Mendelian randomization (MR) studies have shown that increased vitamin D levels, as measured by 25-hydroxyvitamin D [25(OH)D], may protect against Alzheimer’s disease. Thus, it is possible that 25OHD may protect against Alzheimer’s disease by improving cognition.MethodsTo evaluate this hypothesis, we began by performing an observational study by testing the association of 25OHD levels with 5 cognitive outcomes related to memory and executive function, adjusting for age, sex, BMI, smoking status and nutritional risk index in 26,787 older individuals (median age 62). Since such observational analyses can be biased by confounding, we next performed two-sample mendelian randomization (MR) analyses testing the effect of 25(OH)D on cognitive outcomes, since this method helps to protect against bias from confounding.ResultsObservational studies suggested a strong protective association between 25(OH)D and cognitive measures. However, in MR analyses, we found no estimated effect of 25(OH)D on these outcomes.ConclusionThese findings suggest that associations between 25(OH)D levels and cognition are likely to be biased by confounding and that the relationship between 25(OH)D levels and Alzheimer’s disease is not due to the effect of 25(OH)D on cognition.

Deoxy-hemoglobin S polymerization into rigid fibers is the direct cause of the clinical sequelae observed in sickle cell disease (SCD). The rate of polymerization of sickle hemoglobin is determined primarily by intracellular hemoglobin concentration, itself dependent on the amount of sickle hemoglobin and on red blood cell (RBC) volume. Dense, dehydrated RBC (DRBC) are observed in SCD patients, and their number correlates with hemolytic parameters and complications such as renal dysfunction, leg ulcers and priapism. To identify new genes involved in RBC hydration in SCD, we performed the first genome-wide association study for DRBC in 374 sickle cell anemia (HbSS) patients. We did not find genome-wide significant results, indicating that variants that modulate DRBC have modest-to-weak effects. A secondary analysis demonstrated a nominal association (P=0.003) between DRBC in SCD patients and a variant associated with mean corpuscular hemoglobin concentration (MCHC) in non-anemic individuals. This intronic variant controls the expression of ATP2B4, the main calcium pump in erythrocytes. Our study highlights ATP2B4 as a promising target for modulation of RBC hydration in SCD patients.

Cas9-mediated, high-throughput, saturating in situ mutagenesis permits fine-mapping of function across genomic segments. Disease- and trait-associated variants from genome-wide association studies largely cluster in regulatory DNA. Here we demonstrate the use of multiple designer nucleases and variant-aware library design to interrogate trait-associated regulatory DNA at high resolution. We developed a computational tool for the creation of saturating mutagenesis libraries with single or combinatorial nucleases with incorporation of variants. We applied this methodology to the HBS1L-MYB intergenic region, a locus associated with red blood cell traits, including fetal hemoglobin levels. This approach identified putative regulatory elements that control MYB expression. Analysis of genomic copy number highlighted potential false positive regions, which emphasizes the importance of off-target analysis in design of saturating mutagenesis experiments. Taken together, these data establish a widely applicable high-throughput and high-resolution methodology to reliably identify minimal functional sequences within large regions of disease- and trait-associated DNA.

In a recent clinical trial, the metabolite l -glutamine was shown to reduce painful crises in sickle cell disease (SCD) patients. To support this observation and identify other metabolites implicated in SCD clinical heterogeneity, we profiled 129 metabolites in the plasma of 705 SCD patients. We tested correlations between metabolite levels and six SCD-related complications (painful crises, cholecystectomy, retinopathy, leg ulcer, priapism, aseptic necrosis) or estimated glomerular filtration rate (eGFR), and used Mendelian randomization (MR) to assess causality. We found a potential causal relationship between l -glutamine levels and painful crises (N = 1278, odds ratio (OR) [95% confidence interval] = 0.68 [0.52–0.89], P = 0.0048). In two smaller SCD cohorts (N = 299 and 406), the protective effect of l -glutamine was observed (OR = 0.82 [0.50–1.34]), although the MR result was not significant (P = 0.44). We identified 66 significant correlations between the levels of other metabolites and SCD-related complications or eGFR. We tested these correlations for causality using MR analyses and found no significant causal relationship. The baseline levels of quinolinic acid were associated with prospectively ascertained survival in SCD patients, and this effect was dependent on eGFR. Metabolomics provide a promising approach to prioritize small molecules that may serve as biomarkers or drug targets in SCD.