Tumor-Associated Macrophages Derived from Circulating Inflammatory Monocytes Degrade Collagen through Cellular Uptake

Cell Rep. 2017 Dec 26;21(13):3662-3671. doi: 10.1016/j.celrep.2017.12.011.


Physiologic turnover of interstitial collagen is mediated by a sequential pathway in which collagen is fragmented by pericellular collagenases, endocytosed by collagen receptors, and routed to lysosomes for degradation by cathepsins. Here, we use intravital microscopy to investigate if malignant tumors, which are characterized by high rates of extracellular matrix turnover, utilize a similar collagen degradation pathway. Tumors of epithelial, mesenchymal, or neural crest origin all display vigorous endocytic collagen degradation. The cells engaged in this process are identified as tumor-associated macrophage (TAM)-like cells that degrade collagen in a mannose receptor-dependent manner. Accordingly, mannose-receptor-deficient mice display increased intratumoral collagen. Whole-transcriptome profiling uncovers a distinct extracellular matrix-catabolic signature of these collagen-degrading TAMs. Lineage-ablation studies reveal that collagen-degrading TAMs originate from circulating CCR2+ monocytes. This study identifies a function of TAMs in altering the tumor microenvironment through endocytic collagen turnover and establishes macrophages as centrally engaged in tumor-associated collagen degradation.

Keywords: CCR2-derived TAMs; M2-polarized macrophages; cancer invasion; cathepsins; collagen endocytosis; collagenases; endocytic matrix turnover; extracellular matrix remodeling; tumor microenvironment; tumor-associated macrophages.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Movement*
  • Cell Polarity
  • Collagen / metabolism*
  • Endocytosis*
  • Extracellular Matrix / metabolism
  • Inflammation / pathology*
  • Lectins, C-Type
  • Macrophages / metabolism
  • Macrophages / pathology*
  • Mannose Receptor
  • Mannose-Binding Lectins
  • Mice, Inbred C57BL
  • Monocytes / pathology*
  • Neoplasms / genetics
  • Neoplasms / pathology*
  • Proteolysis*
  • Rats
  • Receptors, CCR2 / metabolism
  • Receptors, Cell Surface
  • Transcriptome / genetics


  • Lectins, C-Type
  • Mannose Receptor
  • Mannose-Binding Lectins
  • Receptors, CCR2
  • Receptors, Cell Surface
  • Collagen