Date on Master's Thesis/Doctoral Dissertation

8-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Degree Program

Biochemistry and Molecular Biology, PhD

Committee Chair

Hill, Bradford G.

Committee Member

Jones, Steven P.

Committee Member

Clem, Brian

Committee Member

Smith, Melissa

Committee Member

Clark, Barbara

Author's Keywords

Metabolism; fibrosis; heart failure; myocardial infarction; PCK2; PKM2

Abstract

Cardiac fibroblasts are central effectors of cardiac repair after myocardial infarction (MI). In response to signaling cues, they differentiate to a range of phenotypes with robust capacities to synthesize and secrete extracellular matrix (ECM) and signaling molecules. Although activated fibroblast phenotypes are associated with pronounced changes in metabolism, it remains unclear how the metabolic network upholds the effector functions of fibroblasts in the post-infarcted heart. Here, we identified that critical enzymes in the phosphoenolpyruvate (PEP) cycle, i.e. pyruvate kinase muscle-2 (PKM2) and phosphoenolpyruvate carboxykinase-2 (PCK2), are elevated in the heart after MI and examined their role in regulating post-MI remodeling and fibroblast phenotype. Pck2 deletion had no effect on post-MI remodeling, suggesting that the PEP cycle is dispensable for post-MI cardiac repair; however, fibroblast-specific switching of Pkm2 to Pkm1 (fbPkm2→1) reduced ventricular dilation and wall thinning and enhanced ejection fraction. Despite these salutary effects, fbPkm2→1 splice variant switching did not affect cardiac fibrosis in vivo or myofibroblast differentiation, collagen production, inflammatory signaling, or transcriptional regulation in vitro. Nevertheless, vi fbPkm2→1 splice variant switching affected the metabolic phenotype of fibroblasts, as shown by increased pyruvate kinase (PK) activity, higher maximal mitochondrial respiratory capacity, and elevation in glycolytic intermediate abundance. Although stable isotope metabolomic studies in cardiac fibroblasts indicated minimal glucose-supported de novo glycine synthesis, they revealed that profibrotic ligands augment the activity of accessory pathways of glucose metabolism and that the hexosamine and glucuronate biosynthetic pathways carry high flux. Collectively, these findings reveal that, while the PEP cycle is dispensable for post-MI remodeling, fibroblast Pkm isoforms influence chronic post-MI remodeling, highlighting PK as a potential therapeutic target.

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