GDF1 Regulation of Ceramide Metabolism Restores Effective Hematopoiesis in Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) is a clonal hematopoietic disorder characterized by ineffective hematopoiesis, cytopenias, and an increased risk of transformation to acute myeloid leukemia. New studies are urgently needed to understand the underlying processes that govern MDS and related bone marrow failure disorders and to develop better therapeutic modalities. Sphingolipids are an extensive classification of lipids which play prominent roles in cellular signaling in addition to being essential components of membranes. The most well studied sphingolipid is ceramide, which serves as a hypothetical center of sphingolipid metabolism. Ceramide is an important cellular signal that can lead to apoptosis. Overall ceramide biology is significant because novel metabolic routes that persist in MDS may be exploited for therapeutic development. Interestingly, the gene encoding ceramide synthase 1 is encoded from a bicistronic transcript that also encodes for GDF1. Little is known about the roles of GDF1 outside of cardiac development. However, GDF1 is in the TGF-beta superfamily of which many members have been attributed roles in stem cell biology. Therefore, a better understanding of the role of GDF1 and its regulation of ceramide metabolism and hematopoiesis may lead to better treatment approaches for MDS and other bone marrow failure syndromes. The current study tested an overarching hypothesis that GDF1 regulates SMAD and STAT signaling to promote ceramide generation and restore effective myelopoiesis in MDS.

Initially, the expression of GDF1 was evaluated in hematopoietic cells isolated from transgenic murine models of MDS (Nup98-HoxD13; Srsf2^P95H-mutant) as well as myeloproliferation (Flt3^ITD). Interestingly, GDF1 expression was greatest in the bone marrow of MDS models. This was significant because we recently reported that nanoliposomal ceramide (Lip-C6), which delivers a bioactive ceramide analog, exerts unique therapeutic efficacy towards acute myeloid leukemia arising out of MDS (Barth et. al. Blood Advances 2019). Lip-C6 is a ceramide-based therapy that currently is in a clinical trial for solid tumor malignancies (ClinicalTrials.gov identifier: NCT02834611). Next, treatment of transgenic MDS mice with either recombinant GDF1 or Lip-C6 was shown to stimulate the expansion of erythroid progenitors. This was concomitant with a decrease in immature myeloid cells, which was revealed to be due to granulo-monocytopoietic differentiation. Mechanistic studies subsequently revealed that GDF1 increased SMAD2/3 phosphorylation while simultaneously down regulating STAT3 (Y705) phosphorylation, both in a TGF-beta receptor 1-dependent fashion. This dual effect was unique to GDF1, whereas TGF-beta or GDF3 only recapitulated individual the effects on SMAD2/3 and STAT3 signaling, respectively. Finally, STAT3 binding sites were identified in the promoter region of the ceramide detoxifying enzyme glucosylceramide synthase. This is important because glucosylceramide synthase expression was shown to be downregulated by recombinant GDF1 treatment. Therefore, GDF1-mediated downregulation of STAT3-dependent glucosylceramide synthase expression provides a mechanistic link where GDF1 can augment intracellular ceramide levels.

Overall, this study enhances our understanding of a fundamental hematopoietic process where GDF1 regulates ceramide metabolism and myelopoiesis. This is impactful because the effects of GDF1, which are unique from other related factors including TGF-beta and GDF3, are due to a novel mechanism of action that both upregulates SMAD2/3 signaling while downregulating STAT3 signaling. More so, this study demonstrated that GDF1, and/or ceramide, can exert an anti-MDS therapeutic role by restoring normal aspects of myelopoiesis.

This work was funded by NIH/NCI K22 CA190674 (B.M.B.) and University of New Hampshire COBRE Pilot Project Grant NIH/NIGMS P20 GM113131 (B.M.B.). The authors acknowledge US Provisional Patent 62/602,437, issued to B.M.B. and the University of New Hampshire.