Abstract

Breast cancer is the most frequently diagnosed cancer among women worldwide, and aging is the largest risk factor for breast cancer development. The process of aging is typically accompanied by a progressive accumulation of senescent cells, which are characterized by a series of markers such as p16INKA4 (p16) positivity and a distinctive profile of secretory factors including mitogens, cytokines, and extracellular matrix (ECM) proteins that are collectively recognized as senescence-associated secretory phenotype (SASP). Numerous data so far have shown that senescent stromal cells play critical roles in modulating tumor microenvironment and progression. For example, senescent fibroblasts induced in vitro could promote angiogenesis when co-implanted with human MDA-MB-231 breast tumor cells into immunocompromised mice, ultimately leading to accelerated tumor growth. Similarly, senescent skin fibroblasts established via ectopic p27 expression could suppress tumor immunosurveillance when co-inoculated with mouse skin tumor cells, which resulted in more robust tumor development. While these data provide compelling evidence of the pro-tumorigenic nature of senescent stroma, it remains understudied whether and how spontaneously arising senescent stroma contributes to breast cancer tumorigenesis. Clinically, high p16 positivity in stroma strongly correlates with ductal carcinoma in situ (DCIS) recurrence, raising the possibility that p16+ senescent stromal cells do contribute to breast cancer progression. To explore this hypothesis, we carried out single-cell RNA sequencing (scRNA-seq) analyses of human breast cancer samples and murine spontaneous mammary tumors. We found that senescence was restricted to a specific myofibroblastic cancer-associated fibroblasts (myCAFs) subpopulation that expresses numerous immune and extracellular matrix SASP factors that could impact tumor immunosurveillance. We refer to these cells as senescent CAFs (senCAFs). To investigate how senCAFs impact tumorigenesis, we crossed MMTV-PyMT (PyMT) mice that spontaneously develop mammary tumors to INK-ATTAC (INK) mice, which allows selective elimination of p16+ senescent cells. Depletion of senCAFs in PyMT/INK mice led to significantly delayed tumor onset and changes in various tumor-infiltrating immune cells including natural killer (NK) cells, both of which could be recapitulated by treating PyMT mice with a senolytic drug. Monoclonal antibody-mediated NK cell depletion in the PyMT model indicated that NK cells are required for senCAF’s tumor-promoting effect. Finally, we found that ECM deposited by senCAFs but not control fibroblasts that resembled non-senescent myCAFs directly inhibited NK cell killing of tumor cells. Together our data highlights that senCAFs contribute to mammary gland tumorigenesis by modulating tumor immunity and suggests that senolytic treatment may limit breast cancer progression.

Committee Chair

Sheila Stewart

Committee Members

David DeNardo; Gregory Longmore; Katherine Weibaecher; Li Ding; Maxim Artyomov

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Biochemistry)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

4-17-2025

Language

English (en)

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