The blood-borne sialyltransferase ST6Gal-1 is a negative systemic regulator of granulopoiesis

Abstract

Responding to systemic demands in producing and replenishing end-effector blood cells is predicated on the appropriate delivery and interpretation of extrinsic signals to the HSPCs. The data presented herein implicate the systemic, extracellular form of the glycosyltransferase ST6Gal-1 in the regulation of late-stage neutrophil development. ST6Gal-1 is typically a membrane-bound enzyme sequestered within the intracellular secretory apparatus, but an extracellular form is released into the blood from the liver. Both human and murine HSPCs, upon exposure to extracellular ST6Gal-1 ex vivo, exhibited decreased proliferation, diminished expression of the neutrophilic primary granule protein MPO, and decreased appearance of CD11b cells. HSPC suppression was preceded by decreased STAT-3 phosphorylation and diminished C/EBPα expression, without increased apoptosis, indicating attenuated G-CSF receptor signaling. A murine model to raise systemic ST6Gal-1 level was developed to examine the role of the circulatory enzyme in vivo. Our results show that systemic ST6Gal-1 modified the cell surface of the GMP subset of HSPCs and decreased marrow neutrophil reserves. Acute airway neutrophilic inflammation by LPS challenge was used to drive demand for new neutrophil production. Reduced neutrophil infiltration into the airway was observed in mice with elevated circulatory ST6Gal-1 levels. The blunted transition of GMPs into GPs in vitro is consistent with ST6Gal-1-attenuated granulopoiesis. The data confirm that circulatory ST6Gal-1 is a negative systemic regulator of granulopoiesis and moreover suggest a clinical potential to limit the number of inflammatory cells by manipulating blood ST6Gal-1 levels.

Migration against the direction of flow is LFA-1-dependent in human hematopoietic stem and progenitor cells

“…Frozen aliquots of primary bone marrow HSPCs were obtained from the University of Pennsylvania Stem Cell and Xenograft Core. HSPCs were revived and cultured in Stemspan serum-free medium (Stem Cell Technologies, Vancouver, BC) overnight prior to experimentation (Dougher et al, 2017). Human umbilical vein endothelial cells (HUVECs) were maintained in EBM-2 growth medium with BulletKit supplement (Lonza, Wakersville, MD).…”

Blood-Borne ST6GAL1 Regulates Immunoglobulin Production in B Cells

“…The findings presented here extend the targets of extracellular ST6GAL1 to include the B cell lineage, demonstrating the importance of a systemic sialyltransferase to both the innate and adaptive branches of immunity. Collectively, findings by our group and others point to the ability of extrinsic sialylation to alter cellular sensitivity to exogenous ligands, including growth factors, cytokines, and antigens (14,15,17,30). Temporally, blood ST6GAL1 is diminished early in inflammation and rises above baseline at a time coinciding with the resolution of acute inflammation (4,6).…”

“…Recent studies suggest an unexpected role for blood ST6GAL1 in the direct enzymatic modification of cell-surface and soluble glycoproteins (11)(12)(13). Extracellular ST6GAL1 has been shown to directly sialylate bone marrow granulocyte/monocyte progenitors (GMP) to suppress G-CSF induced granulocyte differentiation (14)(15)(16)(17). Serum ST6GAL1 is also implicated in the sialylation of IgG, enabling binding to inhibitory FcγRIIb, the primary mechanism by which intravenous immunoglobulin (IVIG) alleviates autoimmune disease (18)(19)(20).…”

Don’t sugarcoat it: How glycocalyx composition influences cancer progression

“…Interestingly, ST6Gal-1 is also the only glycosyltransferase to date in which its soluble form can “extrinsically” glycosylate outside the cell (Manhardt et al, 2017). This mechanism describes how donor sugar from platelets (Lee-Sundlov et al, 2016; Lee et al, 2014) and ST6Gal-1 from B cells (Irons and Lau, 2018; Irons et al, 2019) can sialylate progenitors in the bone marrow (Nasirikenari et al, 2014) and prevent granulopoiesis (Dougher et al, 2017). In fact, this “extrinsic” sialylation mechanism has recently been implicated in colon cancer progression, as ST6Gal-1 loaded into exomeres can both sialylate β1 integrins and promote cancer organoid growth (Zhang et al, 2019).…”