MicroRNA Function in Cellular Stress Response

MicroRNAs are key post-transcriptional regulators that have been found to play critical roles in the regulation of cellular functions. There is an emerging concept that microRNAs may be just as essential for fine-tuning physiological functions and responding to changing environments and stress conditions as for viability or development. In this dissertation, two studies are presented: The first study demonstrates a role for microRNA in the regulation of oxidative stress response in erythroid cells and the functional consequences of dysregulated microRNA expression in Sickle Cell Disease (SCD) pathobiology. The second study examines a functional role for microRNA in the cellular response to changes in cellular iron concentration. Together these studies illustrate the scope of importance of microRNAs in the coordination of cellular responses to diverse stresses.

Homozygous Sickle Cell (HbSS) erythrocytes are known to have reduced tolerance for oxidative stress, yet the basis for this phenotype has remained unknown. Here we use erythrocyte microRNA expression profiles to identify a subset of HbSS patients with higher miR-144 expression and more severe anemia. We reveal that in K562 erythroid cells and primary erythroid progenitor cells, miR-144 directly regulates NRF2, a central regulator of cellular response to oxidative stress, and modulates the oxidative stress response. We further demonstrate that increased miR-144 is associated with the reduced NRF2 levels, decreased glutathione regeneration, and attenuated antioxidant capacity found in HbSS erythroid progenitors, thereby providing a mechanism for the reduced oxidative stress tolerance and increased anemia severity seen in HbSS patients.

The post-transcriptional regulation of the IRP2 regulon in the cellular response to iron deficiency is well characterized. Here we examine the potential role for microRNA-mediated regulation in the coordinated response to cellular iron deficiency.