title: In situ force mapping of mammary gland transformation.
abstract: Tumor progression is characterized by an incremental stiffening of the tissue. The importance of tissue rigidity to cancer is appreciated, yet the contribution of specific tissue elements to tumor stiffening and their physiological significance remains unclear. We performed high-resolution atomic force microscopy indentation in live and snap-frozen fluorescently labeled mammary tissues to explore the origin of the tissue stiffening associated with mammary tumor development in PyMT mice. The tumor epithelium, the tumor-associated vasculature and the extracellular matrix all contributed to mammary gland stiffening as it transitioned from normal to invasive carcinoma. Consistent with the concept that extracellular matrix stiffness modifies cell tension, we found that isolated transformed mammary epithelial cells were intrinsically stiffer than their normal counterparts but that the malignant epithelium in situ was far stiffer than isolated breast tumor cells. Moreover, using an in situ vitrification approach, we determined that the extracellular matrix adjacent to the epithelium progressively stiffened as tissue evolved from normal through benign to an invasive state. Importantly, we also noted that there was significant mechanical heterogeneity within the transformed tissue both in the epithelium and the tumor-associated neovasculature. The vascular bed within the tumor core was substantially stiffer than the large patent vessels at the invasive front that are surrounded by the stiffest extracellular matrix. These findings clarify the contribution of individual mammary gland tissue elements to the altered biomechanical landscape of cancerous tissues and emphasize the importance of studying cancer cell evolution under conditions that preserve native interactions.
authors.affiliation: Department of Surgery and Center for Bioengineering and Tissue Regeneration, University of California at San Francisco, 513 Parnassus Ave, HSE 565, San Francisco, CA 94143-0456, USA.
authors.forename: Jose I
authors.initials: JI
authors.lastname: Lopez
authors.forename: Inkyung
authors.initials: I
authors.lastname: Kang
authors.forename: Weon-Kyoo
authors.initials: WK
authors.lastname: You
authors.forename: Donald M
authors.initials: DM
authors.lastname: McDonald
authors.forename: Valerie M
authors.initials: VM
authors.lastname: Weaver
mesh_terms: D000818:Animals; D057005:Bioengineering; D001696:Biomechanical Phenomena; D055592:Biophysical Phenomena; D002471:Cell Transformation, Neoplastic; D005109:Extracellular Matrix / Q000502:physiology; D005260:Female; D008321:Mammary Glands, Animal / Q000502:physiology; D008325:Mammary Neoplasms, Experimental / Q000209:etiology* / Q000503:physiopathology*; D008324:Mammary Tumor Virus, Mouse; D051379:Mice; D008822:Mice, Transgenic; D018625:Microscopy, Atomic Force; D009361:Neoplasm Invasiveness / Q000503:physiopathology; D012192:Retroviridae Infections / Q000209:etiology / Q000503:physiopathology; D013718:Tensile Strength; D014412:Tumor Virus Infections / Q000209:etiology / Q000503:physiopathology; D058989:Vitrification