Ryan Tewhey | PubMed Health

PubMed2026

Germline noncoding risk variants influence clonal hematopoiesis through altered hematopoietic enhancer activity.

Clonal hematopoiesis of indeterminate potential (CHIP) is a precursor condition characterized by the expansion of mutant hematopoietic stem and progenitor cell (HSPC) clones that increases the risk of hematologic malignancies. Although genome-wide association studies have identified multiple non-coding loci associated with CHIP susceptibility, their mechanisms remain unclear. We hypothesized that CHIP risk variants alter enhancer activity in HSPCs. To test this, we screened 1,374 non-coding variants from 51 CHIP-associated loci using a Massively Parallel Reporter Assay (MPRA) in the CD34+ fraction of MUTZ-3 cells. We identified 87 regulatory variants across 32 loci. Targeted genome editing in hematopoietic cells and complementary reporter assays in primary human HSPCs validated enhancer activity for variants regulating NKD2, FLT3, and MSI2. Functional studies demonstrated that increased MSI2 expression, modeling the effect of the CHIP risk allele, promotes clonal expansion of TET2-deficient HSPCs, providing a mechanistic link between inherited non-coding variation and CHIP clonal expansion.

Journal Article↗

PubMed2024

A systematic strategy for identifying causal single nucleotide polymorphisms and their target genes on Juvenile arthritis risk haplotypes.

BACKGROUND: Although genome-wide association studies (GWAS) have identified multiple regions conferring genetic risk for juvenile idiopathic arthritis (JIA), we are still faced with the task of identifying the single nucleotide polymorphisms (SNPs) on the disease haplotypes that exert the biological effects that confer risk. Until we identify the risk-driving variants, identifying the genes influenced by these variants, and therefore translating genetic information to improved clinical care, will remain an insurmountable task. We used a function-based approach for identifying causal variant candidates and the target genes on JIA risk haplotypes. METHODS: We used a massively parallel reporter assay (MPRA) in myeloid K562 cells to query the effects of 5,226 SNPs in non-coding regions on JIA risk haplotypes for their ability to alter gene expression when compared to the common allele. The assay relies on 180 bp oligonucleotide reporters ("oligos") in which the allele of interest is flanked by its cognate genomic sequence. Barcodes were added randomly by PCR to each oligo to achieve > 20 barcodes per oligo to provide a quantitative read-out of gene expression for each allele. Assays were performed in both unstimulated K562 cells and cells stimulated overnight with interferon gamma (IFNg). As proof of concept, we then used CRISPRi to demonstrate the feasibility of identifying the genes regulated by enhancers harboring expression-altering SNPs. RESULTS: We identified 553 expression-altering SNPs in unstimulated K562 cells and an additional 490 in cells stimulated with IFNg. We further filtered the SNPs to identify those plausibly situated within functional chromatin, using open chromatin and H3K27ac ChIPseq peaks in unstimulated cells and open chromatin plus H3K4me1 in stimulated cells. These procedures yielded 42 unique SNPs (total = 84) for each set. Using CRISPRi, we demonstrated that enhancers harboring MPRA-screened variants in the TRAF1 and LNPEP/ERAP2 loci regulated multiple genes, suggesting complex influences of disease-driving variants. CONCLUSION: Using MPRA and CRISPRi, JIA risk haplotypes can be queried to identify plausible candidates for disease-driving variants. Once these candidate variants are identified, target genes can be identified using CRISPRi informed by the 3D chromatin structures that encompass the risk haplotypes.

Humans↗