# Heme synthesis, use and trafficking during erythropoiesis

> **NIH NIH R01** · UNIVERSITY OF WASHINGTON · 2024 · $475,997

## Abstract

Project summary/abstract.
An adult makes 2.4 million red cells per second and production can increase 5-10-fold in response to anemia.
Over 95% of red cell protein content is hemoglobin; each cell contains 270 million hemoglobin molecules;
each with 4 heme moieties; yet free-heme is toxic and must be tightly regulated. As expected from these rapid
kinetics, CFU-E/proerythroblasts are especially vulnerable to heme toxicity since this is when heme synthesis
intensifies but globin expression is low. FLVCR is critical and functions as a safety valve, exporting excess
heme. In prior studies, we demonstrated that mice lacking FLVCR develop profound macrocytic anemia.
Similarities between the clinical phenotype of Flvcr1-deleted mice and patients with Diamond Blackfan anemia
(DBA) prompted investigation of this disorder during our last grant cycle. DBA results from the
haploinsufficiency of any one of 19 different ribosomal proteins, poor ribosomal assembly and slowed or
aberrant translation. We hypothesized that although heme synthesis initiates normally, globin translation is
slowed. Heme exceeds the capacity of FLVCR and induces excess ROS and cell death. Sufficient synthesis
of globin, a protein, requires robust translation. However, the synthesis of heme, a chemical, proceeds
via an enzymatic process. It requires only small quantities of protein (enzymes) and thus minimal
translation. When translation is impaired, heme production surpasses globin production. Should the
quantity of intracellular heme overwhelm the export capacity of FLVCR, toxicity occurs.
We first derived data supporting this hypothesis that heme toxicity underlies DBA anemia by studying the
in vitro erythroid differentiation of marrow cells from DBA patients. We also fully characterized two
informative murine models - Flvcr1-deleted and Rpl11-haploinsufficient mice, models of heme excess
and DBA, respectively. More recently, we developed single cell methods to query individual cell
decision-making. By linking each cell’s surface protein expression to its unique transcriptome, then
analyzing pseudotime trajectories, we confirmed the primacy of heme excess in causing ineffective
erythropoiesis in DBA, and also unexpectedly showed that heme modulates the effectiveness of normal
erythropoiesis, suggesting that it functions as a physiological rheostat. The goals of this competitive
renewal application are to more completely define the molecular mechanisms which regulate red cell
differentiation and how excess heme leads to cell death. We will also use our cellular and murine models to
identify and test new therapies for DBA, recognizing that these may be applicable to other settings with
ineffective erythropoiesis, such as thalassemia and MDS. Since heme is synthesized from succinyl CoA (a
TCA cycle intermediate) and glycine (an amino acid) and functions as a sensor of energy and protein
availability, these studies may also provide insight into other metabolically-sensitive on-off proc...

## Key facts

- **NIH application ID:** 10837157
- **Project number:** 5R01HL031823-34
- **Recipient organization:** UNIVERSITY OF WASHINGTON
- **Principal Investigator:** Janis L Abkowitz
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $475,997
- **Award type:** 5
- **Project period:** 1986-12-01 → 2026-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10837157

## Citation

> US National Institutes of Health, RePORTER application 10837157, Heme synthesis, use and trafficking during erythropoiesis (5R01HL031823-34). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10837157. Licensed CC0.

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