Abstract

Pancreatic Ductal Adenocarcinoma (PDAC) is the most lethal solid malignancy with a 12% 5-year survival rate. Most tumors are detected at metastatic stages that are extremely resistant to therapy. PDAC recalcitrance is driven by a unique tumor microenvironment (TME) comprising dense collagenous fibrosis embedded with an abundance of cancer associated fibroblasts (CAFs) and infiltrating leukocytes. Preclinical studies have indicated that PDAC CAFs can have both pro- and anti-tumorigenic effects. This is likely owed to CAF phenotypic heterogeneity which was recently uncovered by single cell transcriptomics. Three major CAF subpopulations have been identified in mouse and human PDAC thus far: myofibroblastic (myCAF), inflammatory (iCAF), and antigen presenting (apCAF). Intriguingly, several studies have also identified PDAC CAF subsets with immune modulatory functions. However, the specific impact and phenotypic drivers of CAF heterogeneity in PDAC remain to be determined. Senescent CAFs have been shown to regulate fibrosis and anti-tumor immunity in skin and liver cancer models. Their effects are mediated by the senescence-associated secretory phenotype (SASP) comprising context-specific matrix and immune modulatory factors. Although a senescent CAF subset has not been investigated in PDAC, the characteristically harsh fibro-inflammatory pancreatic TME likely triggers senescence stress responses in CAFs. In this study, we identify and characterize a subpopulation of senescent myofibroblastic CAFs (SenCAFs) in mouse and human PDAC. We found that SenCAFs localize near tumors ducts and accumulate with PDAC progression. Transcriptomic characterization of the PDAC SenCAF phenotype revealed a matrisome-rich SASP with putative ECM and immune modulatory functions. We demonstrated that senescent pancreatic fibroblasts are pro-tumorigenic in transplantable PDAC models through a partially T cell dependent mechanism. To assess the impact of senescent CAFs in spontaneous PDAC, we crossed the KPPC genetic model of PDAC (LSL-KRASG12Dp53fl/flPdx1-CRE) with the INK-ATTAC (p16/INK4a Apoptosis Through Targeted Activation of Caspase) senescent cell depletion model. Senescence depletion with the KPPC-IA model or the senolytic drug ABT263/Navitoclax, delayed tumor progression, reduced fibrosis, and relieved immune suppression in macrophages and T lymphocytes. Our findings demonstrate that SenCAFs promote PDAC progression, fibrosis, and immune cell dysfunction. Modulating CAF senescence could be utilized clinically to shape a more permissive PDAC microenvironment that enhances immunotherapy efficacy.

Committee Chair

David DeNardo

Committee Members

Gregory Longmore; John Edwards; Maxim Artyomov; Sheila Stewart

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Molecular Genetics & Genomics)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

5-8-2025

Language

English (en)

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