Metabolic and Immunomodulatory Control of Stress Erythroid Progenitors Ensures Effective Erythroid Regeneration
Restricted (Penn State Only)
- Author:
- Ruan, Baiye
- Graduate Program:
- Pathobiology (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 03, 2022
- Committee Members:
- Andrew Patterson, Major Field Member
Robert Paulson, Chair & Dissertation Advisor
Xiaojun Lian, Outside Unit & Field Member
Kumble Prabhu, Major Field Member
Anthony Schmitt, Professor in Charge/Director of Graduate Studies - Keywords:
- stress erythropoiesis
inflammation
metabolism
nitric oxide
itaconate
immunomodulatory - Abstract:
- Hematopoiesis in adult bone marrow is the primary source of erythroid production during steady state conditions. However, in the course of infection or tissue injuries, elevated pro-inflammatory cytokines reshape the composition of hematopoietic lineages to increase the myeloid output at the expense of steady-state erythroid production. In addition, inflammation can directly inhibit the erythroid cell development and life span. To compensate for the reduction of steady-state erythropoiesis, an alternative response pathway, stress erythropoiesis, is induced. During inflammation, increased erythrophagocytosis produces chemokine CCL2 to recruit monocytes into the spleen where they form the early stress erythroid niche. Through cell-cell interactions, niche cells provide inflammatory cytokines and growth factors to promote the rapid expansion of early stress erythroid progenitors while inhibiting their erythroid differentiation potential. The subsequent increase of serum erythropoietin (Epo) level resolves the inflammatory signals in the niche, and changes of niche signals result in the transition of stress erythroid progenitors from proliferation to differentiation. In this dissertation, we applied integrated analysis between transcriptomics and metabolic profiling to examine the changes occurring at different stages of stress erythropoiesis. These analyses allow for identification of key signaling crosstalk between cell metabolism and immunomodulating molecules that involves in regulating the expansion and cell-fate transition of stress erythroid progenitors. The work described in Chapter 2 shows that the immature stress erythroid progenitors undergo profound metabolic changes during their rapid proliferation. These changes include a Warburg-like profile marked by increased engagement of glycolysis and decreased pyruvate entry into TCA cycle. This strategy provides sufficient glycolytic intermediates that are shunted into pentose phosphate pathway (PPP) and serine/glycine pathway to replenish biosynthetic precursors required for rapid cell proliferation. In addition, immature progenitors utilize the anaplerotic pathway referred to as glutaminolysis to replenish TCA cycle and generate substrates for nitric oxide (•NO) production. Similar to the niche cells, immature progenitors express robust levels of toll-like receptors (TLRs) and receptors for pro-inflammatory cytokines to sense inflammatory signals. This feature enables both niche and progenitors to respond to inflammation by increasing the inducible nitric oxide synthase (Nos2 or iNOS)-dependent •NO production. •NO serves as a critical metabolic regulator that maintains the glycolytic and anabolic metabolism to support the expansion of early progenitors. •NO-dependent metabolism also functions to inhibit the erythroid transcriptional program. In contrast, the cell-fate transition from proliferation to differentiation is marked by a decrease of iNOS-derived •NO production. This transition response is governed by the activation of nuclear factor erythroid 2-related factor 2 (Nfe2l2 or Nrf2), which removes •NO-dependent erythroid inhibition and allows the differentiation of stress erythroid progenitors. Built on abovementioned data, work in Chapter 3 further shows that the transition of progenitors from expansion to differentiation is contingent upon a switch of progenitor cell signaling from one dominated by inflammatory signals to one dominated by resolving signals. Furthermore, our data suggest that this signaling switch is tightly controlled by itaconate, an immunomodulatory metabolite. During the expansion stage, the production of itaconate is suppressed, allowing for the increased production of TNF-α-dependent reactive oxygen species (ROS) and iNOS-dependent •NO. These two inflammation-induced signaling molecules act synergistically to promote the expansion of immature progenitors. In contrast, the transition to differentiation couples with increased production of resolving signals itaconate and IL-10. These two immunomodulating mediators, via activating Nrf2, resolve inflammation-mediated erythroid inhibition, which in turn enables the commitment of stress erythroid progenitors. Collectively, these results suggest that the same inflammatory signals that suppress steady-state erythropoiesis serve to induce a compensatory stress erythropoiesis pathway by amplifying a large pool of immature progenitors prior to differentiation. A timely resolution of inflammatory signals in the subsequent differentiation stage is critical for an effective transition from immature progenitors to committed erythroid cells. The regulatory network that coordinates the expansion of early progenitors with differentiation of mature progenitors involves in dynamic changes of intracellular metabolism to support the growth as well as instruct the cell fate of stress erythroid progenitors. These data provide a foundation to appreciate the distinct responses between stress and steady-state progenitors to inflammatory stimuli, and may lead to new therapeutic targets to treat various types of anemia associated with inflammatory complications, such as anemia of chronic disease (ACD) and sickle cell anemia (SCA).