Sphingolipid Modulation Activates Proteostasis Programs to Govern Human Hematopoietic Stem Cell Self-Renewal.

Cellular stress responses serve as crucial decision points balancing persistence or culling of hematopoietic stem cells (HSCs) for lifelong blood production. Although strong stressors cull HSCs, the linkage between stress programs and self-renewal properties that underlie human HSC maintenance remains unknown, particularly at quiescence exit when HSCs must also dynamically shift metabolic state. Here, we demonstrate distinct wiring of the sphingolipidome across the human hematopoietic hierarchy and find that genetic or pharmacologic modulation of the sphingolipid enzyme DEGS1 regulates lineage differentiation. Inhibition of DEGS1 in hematopoietic stem and progenitor cells during the transition from quiescence to cellular activation with N-(4-hydroxyphenyl) retinamide activates coordinated stress pathways that coalesce on endoplasmic reticulum stress and autophagy programs to maintain immunophenotypic and functional HSCs. Thus, our work identifies a linkage between sphingolipid metabolism, proteostatic quality control systems, and HSC self-renewal and provides therapeutic targets for improving HSC-based cellular therapeutics.E.L. is supported by Wellcome grant 107630/Z/15/Z and a core support grant from the Wellcome and MRC to the Wellcome-Medical Research Council Cambridge Stem Cell Institute. C.L. is supported by U.S. NIH, NCI Grant P01-CA097132. JED is supported by funds from the Princess Margaret Cancer Centre Foundation, Canadian Institutes for Health Research, Joint Canada-Israel Health Research Program, Terry Fox Foundation, and a Canada Research Chair

Human Embryonic Stem Cell-derived Cardiomyocytes with Ischemia Resistant Gap Junctions

Ischemic heart disease remains the number one killer worldwide, and no therapies are aimed at restoring lost muscle within patients’ hearts. Human pluripotent stem cell derived cardiomyocytes (hPSC-CMs) demonstrate engraftment and mediate beneficial effects on left ventricular contractile function in rodent and non-human primate models. Unfortunately, ventricular arrhythmias in large animal models post-transplantation prevent their clinical application. Loss of connexin-43 (Cx43) gap junctions (GJs) is hypothesized to contribute to hPSC-CM induced arrhythmias. Phosphomimetic mutations at casein kinase 1 (CK1) targeted residues that mimic the phosphorylated state of Cx43 reduced ischemia induced GJ remodeling and susceptibility to inducible arrhythmias in mice. hESC-CMs heterozygous for these CK1 mutations displayed ischemia resistant Cx43 GJs by immunofluorescence but were not protected from ischemia induced reentrant arrhythmias. Discovery of a frameshift mutation and a heterozygous genotype motivated production of homozygous CK1 hESC clones that merits further investigation as a potential solution to hPSC-CM graft-related arrhythmias.M.A.S

Sphingosine-1-Phosphate Receptor 3 Potentiates Inflammatory Programs in Normal and Leukemia Stem Cells to Promote Differentiation

Acute myeloid leukemia (AML) is a caricature of normal hematopoiesis, driven from leukemia stem cells (LSC) that share some hematopoietic stem cell (HSC) programs including responsiveness to inflammatory signaling. Although inflammation dysregulates mature myeloid cells and influences stemness programs and lineage determination in HSC by activating stress myelopoiesis, such roles in LSC are poorly understood. Here, we show that S1PR3, a receptor for the bioactive lipid sphingosine-1-phosphate, is a central regulator which drives myeloid differentiation and activates inflammatory programs in both HSC and LSC. S1PR3-mediated inflammatory signatures varied in a continuum from primitive to mature myeloid states across AML patient cohorts, each with distinct phenotypic and clinical properties. S1PR3 was high in LSC and blasts of mature myeloid samples with linkages to chemosensitivity, while S1PR3 activation in primitive samples promoted LSC differentiation leading to eradication. Our studies open new avenues for therapeutic target identification specific for each AML subset.J.E.D is supported by funds from the: Princess Margaret Cancer Centre Foundation, Ontario Institute for Cancer Research through funding provided by the Government of Ontario, Canadian Institutes for Health Research grants 130412, 89932, and 154293, International Development Research Centre Ottawa Canada grants 108401 and 109153, Canadian Cancer Society grant 703212, Terry Fox New Frontiers Program Project Grant 1047, University of Toronto’s Medicine by Design initiative with funding from the Canada First Research Excellence Fund, and a Canada Research Chair. E.L. is supported by Wellcome grant 107630/Z/15/Z and a core support grant from the Wellcome and MRC to the Wellcome-Medical Research Council Cambridge Stem Cell Institute. C.L. is supported by NIH, NCI grant P01-CA097132. W.W. was supported by the Swiss Initiative in Systems Biology Transition Postdoc fellowship