KEY TAKEAWAYS
- The study aimed to identify genetic signatures of elevated hemoglobin levels in Aymara using transcriptome analysis.
- Aymara-enriched NFKB1 SNPs and AS-NFKB1 link elevated hemoglobin levels to increased inflammation.
Tibetans, Ethiopians, and Andeans have been extensively studied for their evolutionary genetic adaptations to high-altitude hypoxia. Quechua and Aymara are the principal Andean ethnicities. At high altitudes, Tibetans and Ethiopians maintain hemoglobin levels similar to those at sea level, while Andeans exhibit higher hemoglobin levels than Europeans living at the same altitude.
Previous research determined that Tibetan selection of 2 genetic variants in the hypoxia-inducible factor pathway, EPAS1 (HIF-2a) and EGLN1 (prolyl hydroxylase 2) genes, correlates with their lower hemoglobin levels (Science 2010, Nat Gen 2014). The whole-genome sequencing study of Aymara (Am J Hum Genet. 2017) identified strong selection signals in BRINP3, NOS2, and TBX5 genes, linked to cardiovascular function and development, but failed to explain elevated hemoglobin levels.
Jihyun Song and the team aimed to identify genetic signatures associated with high hemoglobin levels in Aymara using transcriptome analysis.
Aymara and European samples were collected in La Paz, Bolivia (~4,000 m). Granulocytes were used for RNA sequencing (RNA-seq). Data were generated using a HiSeq system with 125 Cycle Paired-End Sequencing v4. Differential gene expression levels were determined using DESeq2, and differentially spliced exons were identified using rMATS.
The results revealed 2,601 differentially expressed genes and 1,922 spliced genes in Aymaras, associated with immune, inflammatory, and hypoxia-related pathways. Cis-genetic regulators were assessed as expression quantitative trait loci (eQTLs) and splicing quantitative trait loci (sQTLs).
Novel transcripts with exon 4 or 5, or both, skipped in NFKB1 (AS-NFKB1) were found. AS-NFKB1, a key part of the NF-κB pathway, contributes to the suppression of the inflammatory pathway and activation of HIFs. AS-NFKB1 without exon 4 or exons 4 and 5 is not translated into protein, while exon 5 skipped AS-NFKB1 is translated but improperly processed into p50, unable to correctly translocate into the nucleus.
Thus, AS-NFKB1 transcripts cause a partial loss of canonical NFKB1 function as the suppressor of NF-κB. These AS-NFKB1 transcript levels were associated with five sQTLs and enriched in Aymara compared to other populations. Among these five sQTLs, rs230511 was the most selected SNP in Aymara. AS-NFKB1 transcript levels and the T allele (Aymara-enriched allele) of rs230511 positively correlated with elevated hemoglobin in Aymara.
They also correlated with transcript and protein levels of NF-κB-regulated inflammatory genes, including interferon gamma and interleukin 6. Increased inflammation suppresses erythropoiesis through the upregulation of hepcidin, which also correlated with AS-NFKB1 transcript levels. AS-NFKB1 also correlated with marked upregulation of many HIF-regulated genes, the principal regulators of augmented erythropoiesis, explaining Aymara’s erythrocytosis.
These results indicated the increased HIF transcriptional activity, resulting in Aymara erythrocytosis, overcomes the suppression of erythropoiesis caused by inflammation modulated by AS-NFKB1.
The study concluded by identifying, for the first time, the elusive genetic signature of elevated hemoglobin in Andean Aymaras and its molecular basis. It demonstrated the association between Aymara-enriched NFKB1 SNPs and AS-NFKB1 with both elevated hemoglobin levels and heightened inflammation, elucidating a mechanism involving the loss of NFKB1 function due to AS-NFKB1. The evolutionary benefit of increased inflammation in Aymara remains to be identified.
No funding information was available.
Song J, Han S, Amaru R, et al. (2024). “ELEVATED HEMOGLOBIN OF ANDEAN AYMARAS IS CAUSED BY ALTERNATIVELY SPLICED NFKB1” Presented at EHA 2024. (LB3441)
