N-glycosylation controls inflammatory licensing-triggered PD-L1 upregulation in human mesenchymal stromal cells

Abstract

Mesenchymal stromal cells (MSCs) are characterized by their multipotency, regenerative potential, and immunoregulatory properties. Nowadays, MSCs represent a promising cell-therapeutic option for hyperinflammatory conditions such as graft-vs-host disease following allogeneic hematopoietic stem cell transplantation. A better understanding of their biology is a prerequisite for improving their treatment efficacy.Emerging evidence suggests that immunosuppressive properties are not constitutively active in MSCs. Instead, microenvironmental inflammatory stimuli such as the cytokines interferon (IFN)-γ or tumor necrosis factor (TNF)-α license MSCs to acquire a tolerance-promoting phenotype. The immunological checkpoint molecule programmed death-ligand 1 (PD-L1) is an important regulator of T-cell responses.Binding of PD-L1 to the programmed cell death protein 1 (PD-1) receptor on T-cells suppresses their activation, proliferation, and induces apoptosis. Previous studies have revealed that cell surface expression and secretion of PD-L1 are part of the MSCs' immunomodulatory armamentarium. Here, we report that inflammatory licensing leads to an enhanced PD-L1 cell surface expression and secretion, which are both accompanied by an increased posttranslational protein N-glycosylation. These posttranslational modifications have been shown to be critical for key biological processes such as cell trafficking, receptor signaling, and immunohomeostasis. In fact, promoting N-glycosylation in MSCs yielded increased PD-L1 levels. We report for the first time that PD-L1 N-glycosylation plays a decisive role for its transport to the MSCs' cell surface and its subsequent secretion (in response to proinflammatory trigger). Our data offer insights into a novel regulatory mechanism with the potential to be exploited as a means to foster the immunosuppressive potency of human MSCs.

Exosomes, PD-L1 and aGvHD: Perspectives for WJMSCmediated Therapy

“…Like tumor-derived exosomes, recent studies have suggested that that MSC-derived exosomes can affect CD4+ and CD8+ T cells in the aGvHD patients. Lai et al reported that MSC exosomes effectively prolonged the survival of chronical GVHD mice and diminished the clinical and pathological scores [23]. They observed that activated CD4 T cells and their infiltration into the lung were reduced in these animals.…”

The expression mechanism of programmed cell death 1 ligand 1 and its role in immunomodulatory ability of mesenchymal stem cells

“… 82 In bone marrow derived-MSCs (BM-MSCs), glycosylation at the N-terminus of the protein upregulates PD-L1 expression. 83 Moreover, the phosphorylation of PD-L1 protein at Tyr112 will further promote the glycosylation of PD-L1 through STAT3 and enhance the stability of the protein. 84 However, metformin induces phosphorylation of PD-L1 protein at the S195 site, resulting in aberrant glycosylation of PD-L1 protein, which in turn induces protein degradation.…”

Glucose Metabolism: Optimizing Regenerative Functionalities of Mesenchymal Stromal Cells Postimplantation

“…Like MSCs requiring metabolic reprogramming for proliferation, MSCs undergo a metabolic shift to express immunosuppressive properties upon licensing 42,[109][110][111] . An increase in glycolysis is evidenced by increased surface expression of GLUT1, increased mRNA expression of several glycolytic genes (including enolase1 and HK2), higher glucose consumption, and higher ECAR 42,110 .…”

“…Protein glycosylation regulates the immunosuppressive properties of MSCs in at least two instances. First, N-glycosylation controls PD-L1 transport to hMSC surface and its subsequent release in response to MSC licensing 111 . Second, O-GlcNAcylation of signal transducer and activator of transcription 1 controlled the IDO mRNA and protein expression in licensed hMSCs 110 .…”