Advisor(s)

Brant Wagener

Committee Member(s)

Igor Chesnokov
Kim Keeling
Pulin Che
Qiang Ding
Rui Zhao

Document Type

Dissertation

Date of Award

6-18-2026

Degree Name

Doctor of Philosophy (PhD)

School

Joint Health Sciences (Interdisciplinary)

Department

Biochemistry and Molecular Genetics

Abstract

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease characterized by persistent fibroblast activation, excessive extracellular matrix (ECM) deposition, and irreversible remodeling of lung architecture. A central feature of disease progression is the accumulation of fibroblasts that evade apoptosis and persist in a pathologically activated state. However, the molecular mechanisms that sustain this aberrant phenotype remain incompletely understood. The calcium-binding protein S100A4 has been implicated in fibrotic processes, but its role in orchestrating fibroblast fate and profibrotic behavior has not been fully defined, particularly with respect to its influence on fibroblast survival and activation in IPF. In the first part of this work, we examined S100A4 function in primary murine lung fibroblasts. Using a combination of cellular, molecular, and biochemical approaches, we demonstrated that S100A4 mediates fibroblast activation and survival through ERK-dependent signaling. We found that S100A4 promotes cytoskeletal remodeling, α-smooth muscle actin (α-SMA) incorporation into stress fibers, ECM contractility, migration, and resistance to apoptosis under perturbations. Pharmacological inhibition of ERK attenuated these responses, establishing ERK as a critical downstream mediator of S100A4-dependent fibroblast programs. In vivo, bleomycin-induced lung injury elicited robust upregulation of S100A4 and enhanced ERK signaling, consistent with persistent fibroblast activation during fibrotic remodeling. Extending these findings to human systems, we next analyzed primary lung fibroblasts from healthy donors and IPF patients using immunofluorescence and siRNA-mediated S100A4 knockdown. Normal fibroblasts exhibited low basal α-SMA incorporation and minimal stress fibers, whereas IPF fibroblasts displayed robust stress fiber formation and elongated morphology. Pharmacological inhibition of S100A4 or ERK partially reverted activated phenotypes, while combined inhibition shifted fibroblasts toward a quiescent-like morphology. We also found that S100A4 knockdown reduced α-SMA and COL1A1 expression, and recombinant S100A4 restored activation in normal cells. In IPF fibroblasts, ERK inhibition following S100A4 depletion significantly suppressed profibrotic markers, demonstrating pathway specificity within a disease-relevant context. Collectively, these studies support a mechanistic framework in which S100A4 functions upstream of ERK to coordinate fibroblast survival, cytoskeletal remodeling, myofibroblast differentiation, and ECM production. This work positions the S100A4–ERK signaling axis as a central regulator of fibroblast fate and ECM remodeling, highlighting its potential as a strategic target for therapeutic intervention.

Keywords

apoptosis;ERK;extracellular matrix;fibroblasts;idiopathic pulmonary fibrosis;S100A4

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