The Role of PGC-1α in Breast Cancer Liver Metastasis

Abstract

Breast cancer liver metastasis is a clinically devastating event associated with poor prognosis and limited treatment options, yet the metabolic determinants that govern whether disseminated breast cancer cells can successfully colonize the hepatic microenvironment remain poorly understood. Liver-tropic breast cancer cells exhibit unexpectedly low expression of PGC-1α, a master regulator of mitochondrial biogenesis and oxidative phosphorylation (OXPHOS), and instead rely predominantly on a glycolytic metabolic program. Whether this glycolytic phenotype constitutes a metabolic optimum for hepatic colonization, or alternatively reflects a suboptimal default state whose reprogramming through PGC-1α gain-of-function could enhance metastatic fitness, had not been directly tested. Equally unresolved is whether the PGC-1α-dependent oxidative metabolic state of host hepatocytes independently influences the permissiveness of the hepatic microenvironment for metastatic colonization.

This thesis addressed these questions through a dual-compartment seed-and-soil experimental strategy. Stable PGC-1α-overexpressing and matched empty-vector control variants of the liver-tropic 2792 murine breast cancer cell line were generated by lentiviral transduction and characterized by Seahorse extracellular flux analysis, genome-wide RNA sequencing, and targeted LC-MS/MS metabolomics. Hepatocyte-specific Ppargc1a knockout (KO) mice were generated using Alb-Cre-mediated loxP recombination and validated by PCR genotyping. Metastatic colonization efficiency was assessed using orthotopic mammary fat pad implantation and intrasplenic portal vein injection with blinded digital quantification of hepatic and pulmonary metastatic burden.

PGC-1α overexpression in liver-tropic breast cancer cells significantly increased basal and maximal mitochondrial ATP production rates and enlarged spare respiratory capacity, while concurrently reducing maximal glycolytic output. PGC-1α selectively increased the expression of Sod2 (manganese superoxide dismutase) and Uqcrc1 (respiratory Complex III subunit). Genome-wide RNA sequencing identified "Oxidative phosphorylation" as the overwhelmingly dominant activated KEGG pathway. Targeted metabolomics confirmed enrichment of serine-glycine one-carbon metabolism, tricarboxylic acid cycle (TCA), and OXPHOS metabolite sets, with O-phosphoserine and adenosine as the two metabolites elevated in PGC-1α-overexpressing cells, providing multi-omic convergence on the same core biological programs. In vivo, PGC-1α overexpression had no effect on orthotopic primary tumor growth yet increased pulmonary metastatic area more than threefold following spontaneous dissemination. In the intrasplenic liver colonization model, PGC-1α overexpression dramatically increased hepatic lesion number. In striking contrast, hepatocyte-specific Ppargc1a deletion produced no significant change in hepatic metastatic colonization efficiency across all host genotypes.

These findings establish that PGC-1α-driven metabolism in the tumor cell is a potent, cell-autonomous amplifier of breast cancer hepatic metastatic colonization competence, operating through enhanced mitochondrial bioenergetic reserve, antioxidant capacity, and serine-one-carbon metabolic flux. The metabolic state of the host hepatocyte is dispensable as a determinant of colonization efficiency, demonstrating that in the seed (breast cancer cell)–soil (liver tissue) PGC-1α-dependent metabolic duality, the seed’s PGC-1α metabolic programming is the decisive variable. This work resolves a previously unaddressed biological paradox, identifies PGC-1α-driven metabolic pathways as targetable vulnerabilities in metastatic breast cancer, and provides a molecularly grounded rationale for stratifying patients with PGC-1α-high metastatic disease for metabolically targeted therapeutic intervention.