RIPK1 is a critical modulator of both tonic and TLR-responsive inflammatory and cell death pathways in human macrophage differentiation

Cell Death Dis. 2018 Sep 24;9(10):973. doi: 10.1038/s41419-018-1053-4.

Abstract

In this study, we took advantage of human-induced pluripotent stem cells (hiPSC) and CRISPR/Cas9 technology to investigate the potential roles of RIPK1 in regulating hematopoiesis and macrophage differentiation, proinflammatory activation, and cell death pathways. Knock-out of RIPK1 in hiPSCs demonstrated that this protein is not required for erythro-myeloid differentiation. Using a well-established macrophage differentiation protocol, knock-out of RIPK1 did not block the differentiation of iPSC-derived macrophages, which displayed a similar phenotype to WT hiPSC-derived macrophages. However, knock-out of RIPK1 leads to a TNFα-dependent apoptotic death of differentiated hiPSC-derived macrophages (iPS-MΦ) and progressive loss of iPS-MΦ production irrespective of external pro-inflammatory stimuli. Live video analysis demonstrated that TLR3/4 activation of RIPK1 KO hiPSC-derived macrophages triggered TRIF and RIPK3-dependent necroptosis irrespective of caspase-8 activation. In contrast, TLR3/4 activation of WT macrophages-induced necroptosis only when caspases were inhibited, confirming the modulating effect of RIPK1 on RIPK3-mediated necroptosis through the FADD, Caspase-8 pathway. Activation of these inflammatory pathways required RIPK3 kinase activity while RIPK1 was dispensable. However, loss of RIPK1 sensitizes macrophages to activate RIPK3 in response to inflammatory stimuli, thereby exacerbating a potentially pathological inflammatory response. Taken together, these results reveal that RIPK1 has an important role in regulating the potent inflammatory pathways in authentic human macrophages that are poised to respond to external stimuli. Consequently, RIPK1 activity might be a valid target in the development of novel therapies for chronic inflammatory diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport / metabolism
  • Apoptosis / physiology*
  • CRISPR-Cas Systems / genetics
  • Caspase 8 / metabolism
  • Cell Differentiation / physiology*
  • Gene Editing
  • Gene Knockout Techniques
  • Hematopoiesis / physiology
  • Humans
  • Induced Pluripotent Stem Cells / metabolism
  • Inflammation / metabolism*
  • Macrophages / metabolism*
  • Receptor-Interacting Protein Serine-Threonine Kinases / genetics
  • Receptor-Interacting Protein Serine-Threonine Kinases / metabolism*
  • Toll-Like Receptor 3 / metabolism*
  • Toll-Like Receptor 4 / metabolism*
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Adaptor Proteins, Vesicular Transport
  • TICAM1 protein, human
  • TLR3 protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 3
  • Toll-Like Receptor 4
  • Tumor Necrosis Factor-alpha
  • RIPK1 protein, human
  • RIPK3 protein, human
  • Receptor-Interacting Protein Serine-Threonine Kinases
  • Caspase 8