title: Hypoxic tumor microenvironments reduce collagen I fiber density.
abstract: Although the mechanisms through which hypoxia influences several phenotypic characteristics such as angiogenesis, selection for resistance to apoptosis, resistance to radiation and chemotherapy, and increased invasion and metastasis are well characterized, the relationship between tumor hypoxia and components of the extracellular matrix (ECM) is relatively unexplored. The collagen I (Col1) fiber matrix of solid tumors is the major structural part of the ECM. Col1 fiber density can increase tumor initiation, progression, and metastasis, with cancer cell invasion occurring along radially aligned Col1 fibers. Here we have investigated the influence of hypoxia on Col1 fiber density in solid breast and prostate tumor models. Second harmonic generation (SHG) microscopy was used to detect differences in Col1 fiber density and volume between hypoxic and normoxic tumor regions. Hypoxic regions were detected by fluorescence microscopy, using tumors derived from human breast and prostate cancer cell lines stably expressing enhanced green fluorescent protein (EGFP) under transcriptional control of the hypoxia response element. In-house fiber analysis software was used to quantitatively analyze Col1 fiber density and volume from the SHG microscopy images. Normoxic tumor regions exhibited a dense mesh of Col1 fibers. In contrast, fewer and structurally altered Col1 fibers were detected in hypoxic EGFP-expressing tumor regions. Microarray gene expression analyses identified increased expression of lysyl oxidase and reduced expression of some matrix metalloproteases in hypoxic compared with normoxic cancer cells. These results suggest that hypoxia mediates Col1 fiber restructuring in tumors, which may impact delivery of macromolecular agents as well as dissemination of cells.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Samata M
authors.initials: SM
authors.lastname: Kakkad
authors.forename: Meiyappan
authors.initials: M
authors.lastname: Solaiyappan
authors.forename: Brian
authors.initials: B
authors.lastname: O'Rourke
authors.forename: Ioannis
authors.initials: I
authors.lastname: Stasinopoulos
authors.forename: Ellen
authors.initials: E
authors.lastname: Ackerstaff
authors.forename: Venu
authors.initials: V
authors.lastname: Raman
authors.forename: Zaver M
authors.initials: ZM
authors.lastname: Bhujwalla
authors.forename: Kristine
authors.initials: K
authors.lastname: Glunde
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D024042:Collagen Type I / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D024022:Fibrillar Collagens / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020218:Response Elements; D014183:Transplantation, Heterologous
chemical_list: D024042:Collagen Type I; D024022:Fibrillar Collagens