Uncovering mediators of collagen degradation in the tumor microenvironment

Matrix Biol Plus. 2022 Jan 28:13:100101. doi: 10.1016/j.mbplus.2022.100101. eCollection 2022 Feb.


Increased remodeling of the extracellular matrix in malignant tumors has been shown to correlate with tumor aggressiveness and a poor prognosis. This remodeling involves degradation of the original extracellular matrix (ECM) and deposition of a new tumor-supporting ECM. The main constituent of the ECM is collagen and collagen turnover mainly occurs in a sequential manner, where initial proteolytic cleavage of the insoluble fibers is followed by cellular internalization of large well-defined collagen fragments for lysosomal degradation. However, despite extensive research in the field, a lack of consensus on which cell types within the tumor microenvironment express the involved proteases still exists. Furthermore, the relative contribution of different cell types to collagen internalization is not well-established. Here, we developed quantitative ex vivo collagen degradation assays and show that the proteases responsible for the initial collagen cleavage in two murine syngeneic tumor models are matrix metalloproteinases produced by cancer-associated fibroblasts and that collagen degradation fragments are endocytosed primarily by tumor-associated macrophages and cancer-associated fibroblasts from the tumor stroma. Using tumors from mannose receptor-deficient mice, we show that this receptor is essential for collagen-internalization by tumor-associated macrophages. Together, these findings identify the cell types responsible for the entire collagen degradation pathway, from initial cleavage to endocytosis of fragments for intracellular degradation.

Keywords: ATCC, American Type Culture Collection; CAF, cancer-associated fibroblast; CPM, counts per minute; CRC, colorectal cancer; Cancer-associated fibroblasts; Collagen degradation; Collagen endocytosis; ECM, extracellular matrix; ELISA, enzyme-linked immunosorbent assay; Extracellular matrix remodeling; FAP, fibroblast activation prot; FMO, fluorescence minus one; FSP-1, fibroblast-specific protein 1; IL, interleukin; LC, lung cancer; MMP, matrix metalloproteinase; MR, mannose receptor; Matrix metalloproteinases; NK, natural killer cell; OvC, ovarian cancer; PDGFR, platelet-derived growth factor receptor; TAM, tumor-associated macrophage; TME, tumor microenvironment; TNF, tumor necrosis factor; Tumor microenvironment; Tumor-associated macrophages; uPARAP, urokinase plasminogen activator receptor-associated protein; α-SMA, α-smooth muscle actin.