Apolipoprotein E promotes papillary thyroid carcinoma progression by activating PINK1/Parkin-mediated mitophagy

Increasing evidence supports a progression-related role of apolipoprotein E (APOE) in papillary thyroid carcinoma (PTC), yet a clear mechanistic explanation for this association is still lacking. Considering the pivotal role of mitochondrial homeostasis in tumorigenesis, the potential role of APOE in promoting PTC progression through mitophagy regulation was investigated. Additionally, the involvement of the PINK1/Parkin-associated pathway in this process was examined to provide insights into its contribution to tumor progression.

APOE in thyroid carcinoma was characterized in terms of its expression profile, diagnostic relevance, and potential biological functions, based on integrative evidence derived from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets. APOE and mitophagy-related protein expression were further examined in PTC tissues by immunohistochemistry. Further evaluation of APOE in PTC cell lines focused on its association with proliferation, apoptosis, and mitophagy, with bidirectional functional perturbation serving as the basis for assessment. Pharmacological inhibitors were used to assess the involvement of mitophagy-related signaling in the observed APOE-dependent phenotypes. Additionally, the in vivo impact of APOE on PTC tumor growth and mitophagy was further investigated through a nude mouse xenograft model, providing insight into its potential role in tumor progression.

A significant upregulation of APOE was observed in thyroid carcinoma tissues and PTC cell lines, supporting its potential relevance as a diagnostic biomarker. The modulation of APOE expression significantly influenced PTC cell proliferation and apoptosis, with overexpression promoting cell proliferation and inhibiting apoptosis, while knockdown led to the opposite effects. Mechanistically, APOE overexpression increased AMP-activated protein kinase (AMPK) phosphorylation and decreased mammalian target of rapamycin (mTOR) phosphorylation, accompanied by increased PINK1 and Parkin expression and mitophagy-related changes, including altered mitochondrial membrane potential, reduced overall reactive oxygen species levels, and increased autophagosome formation. Pharmacological inhibition of mitophagy attenuated the proliferative and antiapoptotic effects of APOE.

These findings demonstrate that APOE promotes PTC progression in association with PINK1/Parkin-related mitophagy and modulation of the AMPK/mTOR axis. The APOE-associated mitophagy axis may provide a rationale for future preclinical investigation in PTC.