Abstract P1-08-05: Expression of the human APOE4 genotype modulates Doxorubicin cardiotoxicity in mice
Authors: Wang Guannan , Rebeck G. William , Rodriguez Olga , Lippman Marc E. , Bishopric Nanette H. 
Published: March 2022

Abstract
Background: The human apolipoprotein E (APOE) gene has three major allelic variants: APOE2, -E3 and -E4. Carriers of the E4 allele are at increased risk for Alzheimer’s and other age-related neurodegenerative disorders. Recently, APOE4 has been associated with risk for cancer-related cognitive decline following chemotherapy with Doxorubicin (DOX), a frequent component of adjuvant therapy for breast cancer. To date, the mechanisms for APOE4 neurotoxicity are unknown, but may greater vulnerability to oxidative stress. DOX also causes dose-dependent cardiotoxicity, but a role for APOE4 in heart damage has not been previously demonstrated. Objective: To determine whether APOE4 predisposes to DOX-induced damage to the myocardium. Methods: C57Bl/6 mice (5-7 mo and 14-18 mo, male and female) with human APOE3 or APOE4 homozygous knock-in (=hAPOE3 and hAPOE4, respectively) were subjected to a single IP injection of saline (Control) or DOX (10 mg/kg, or 5 weekly injections of 5 mg/kg, =DOX), and monitored between 3-45 days afterward. Left ventricular systolic function was quantitated using echocardiography (Vevo 3100) at baseline, during and at the end of each study. TUNEL assay was used to identify apoptotic cells. Collagen was imaged using Masson’s Trichrome staining. Myocardial protein and RNA were extracted from the left ventricle and was analyzed by immunoblotting, realtime PCR and RNASeq on an Illumina NexGen platform.Results: Aged female APOE4 mice had more myocardial collagen at baseline (8.93±1.23 vs. 6.06±1.44%). Baseline cardiac function were similar at baseline in the 2 mouse strains. Three days after DOX, apoptotic myocytes were more abundant in hAPOE4 vs hAPOE3 hearts (1.2 vs. 4.6 TUNEL+ cells per section, n= 5, p&lt;0.05). After DOX treatment, hAPOE4 mice had greater declines in left ventricular ejection fraction (EF, 46.9 vs 62.1%, p = hAPOE4 vs hAPOE3, p &lt; 0.001). Quantitative PCR, RNASeq and protein studies revealed multiple differences in the cardiac transcriptome between hAPOE3 and hAPOE4 mice both at baseline and after DOX treatment. Baseline expression of MEF2D, a key driver of the myocardial stress response, was increased in hAPOE4 vs APOE3, driven by a 3500x (p = 4.76E-17) in transcript variant 1. Robust differences were seen in expression of c-Jun, JunB, and myosin heavy chain genes Myh6 and Myh7 at baseline and following DOX treatment at day 3. Growth Arrest And DNA Damage Inducible Alpha(GADD45A) gene expression was ~2x higher in hAPOE4 mice at baseline, but was similar to hAPOE3 mice by day 14 after DOX. Protein levels of caspase-1, an essential regulator of inflammation and the innate immune response, increased with age in hAPOE3 mice. In contrast, levels of casp-1 were lower in hAPOE4 and did not increase with age (p= 0.002 for APOE4 vs APOE3 at 17 mo). Conclusions: These findings support a model in which the APOE4 allele increases vulnerability to DOX-induced cardiac damage through mechanisms that involve significant and complex alterations in the response to oxidative stress and/or damage signaling. Studies are ongoing to further elucidate transcriptional differences conferred by APOE4, to analyze substrates downstream of caspase-1 affected by APOE4, and to determine the extent to which APOE4 may contribute to DOX toxicity in patient populations.
Citation Format: Guannan Wang, G. William Rebeck, Olga Rodriguez, Marc E. Lippman, Nanette H. Bishopric. Expression of the human APOE4 genotype modulates Doxorubicin cardiotoxicity in mice [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-08-05.