The Erythrocyte Transcriptome: Global Characterization and Therapeutic Implication
A blood draw is one of the most readily accessible, commonly practiced medical procedures with biomarker utility. In particular, transcriptome signatures of blood cells provide valuable insights into the developmental history and adaptations of these circulating cells. The majority of cells within whole blood consist of erythrocytes, or red blood cells (RBCs) that are primarily responsible for the transport of gases throughout the bloodstream. Terminally differentiated and anucleate, RBCs were once thought to lack most RNAs. However, erythrocytes have been recently shown to contain select microRNAs that lend insight into erythrocyte pathophysiology. Erythrocyte RNAs possess the ability to both distinguish between erythroid disease subphenotypes, and provide insight into mechanisms contributing to these differences. We aim to further dissect the events controlling erythroid differentiation and pathophysiology with these readily-accessible genetic materials.
However, the complete repertoire of either small or large erythrocyte RNAs has not been determined. Based on this knowledge gap, my dissertation has two goals: 1) to define the comprehensive erythrocyte transcriptome, and 2) to utilize an in vitro erythroid differentiation model to elucidate the functions of these newly identified erythrocyte RNAs during development.
Using high-throughput sequencing, we show an extensive, diverse repertoire of both small-sized (short, 18-24 nt) and large-sized (long, >200 nt) RNA species in mature erythrocytes. Though many erythrocyte RNAs have known functions in erythroid cells, we describe several RNAs with unknown functions; these RNAs provide a wealth of genetic loci for further inquiry.
Additionally, several newly described, primate-specific RNAs were identified within the miR-144/-451 locus formerly involved in erythroid development. I performed a functional investigation of a previously uncharacterized microRNA, miR-4732-3p, within this locus. My study demonstrates that this microRNA is upregulated during erythroid development, represses SMAD2/4-dependent TGF-β signaling, and promotes proliferation during erythropoiesis. Thus, miR-4732-3p emphasizes the importance of balanced TGF-β signaling during primate erythropoiesis, and represents a key modulator with potential therapeutic utility.
These two studies highlight the advantage of venipuncture to provide a catalog of erythrocyte RNAs, both for an in vitro and in vivo understanding of erythrocyte biology. This in vitro approach functions as a continuous window into the erythrocyte development program, whereas this in vivo approach provides a snapshot of the mature erythrocyte population state in real-time. The integration of these two approaches provides a broad perspective covering the lifetime of erythroid cells.
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