Mapping genetic modifiers of radiation-induced cardiotoxicity to rat chromosome 3

Abstract

Radiation therapy is used in ~50% of cancer patients to reduce the risk of recurrence and in some cases improve survival. Despite these benefits, doses can be limited by toxicity in multiple organs, including the heart. The underlying causes and biomarkers of radiation-induced cardiotoxicity are currently unknown, prompting the need for experimental models with inherent differences in sensitivity and resistance to the development of radiation-induced cardiotoxicity. We have identified the parental SS (Dahl salt-sensitive/Mcwi) rat strain to be a highly-sensitized model of radiation-induced cardiotoxicity. In comparison, substitution of rat chromosome 3 from the resistant BN (Brown Norway) rat strain onto the SS background (SS-3BN consomic) significantly attenuated radiation-induced cardiotoxicity. SS-3BN rats had less radiation-induced cardiotoxicity than SS rats, as measured by survival, pleural and pericardial effusions, echocardiogram parameters, and histological damage. Mast cells, previously shown to have predominantly protective roles in radiation-induced cardiotoxicity, were increased in the more resistant SS-3BN hearts postradiation. RNA sequencing from SS and SS-3BN hearts at 1 wk postradiation revealed 5,098 differentially expressed candidate genes across the transcriptome and 350 differentially expressed genes on rat chromosome 3, which coincided with enrichment of multiple pathways, including mitochondrial dysfunction, sirtuin signaling, and ubiquitination. Upstream regulators of enriched pathways included the oxidative stress modulating transcription factor, Nrf2, which is located on rat chromosome 3. Nrf2 target genes were also differentially expressed in the SS vs. SS-3BN consomic hearts postradiation. Collectively, these data confirm the existence of heritable modifiers in radiation-induced cardiotoxicity and provide multiple biomarkers, pathways, and candidate genes for future analyses. NEW & NOTEWORTHY This novel study reveals that heritable genetic factors have the potential to modify normal tissue sensitivity to radiation. Gene variant(s) on rat chromosome 3 can contribute to enhanced cardiotoxicity displayed in the SS rats vs. the BN and SS-3BN consomic rats. Identifying genes that lead to understanding the mechanisms of radiation-induced cardiotoxicity represents a novel method to personalize radiation treatment, as well as predict the development of radiation-induced cardiotoxicity.

The Role of Mitochondrial Dysfunction in Radiation-Induced Heart Disease: From Bench to Bedside

“…The repressor protein Keap1 binds and sequesters Nrf2, promoting Nrf2 ubiquitin-mediated degradation. The protein phosphoglycerate mutase family member-5 (PGAM5) is attached to the mitochondrial membrane and can form a complex with Keap1 and Nrf2 (37,61,62). Under oxidative conditions, Nrf2 is released from the complex, allowing nuclear accumulation of Nrf2 (60,62).…”

“…One week after 24 Gy of localized cardiac radiation, changes in expression of numerous gene pathways, including mitochondrial function, were seen between the sensitive and resistant rat hearts. Nrf2 was found to be an upstream regulator of many of the enriched pathways (61). Other preclinical investigations have studied the protective role of the Nrf2 pathway on radiation injury to cardiomyocytes and other cell lines, including embryonic fibroblasts and breast and lung epithelial cells (37).…”

Emerging Challenges of Radiation-Associated Cardiovascular Dysfunction (RACVD) in Modern Radiation Oncology: Clinical Practice, Bench Investigation, and Multidisciplinary Care

“…Moreover, some molecules may play roles in the process of RACVD, such as peroxisome proliferator-activated receptor gamma (PPAR-γ) (155), Growth differentiation factor 15 (GDF15) (153), and RhoA GTPase (125) that is essential to mediate the irradiation inhibition of endothelial cell migration. More recently, by using RNA-seq, differential gene-expression profiles have been identified in mice models, such as Nrf2, PDK1, and sirtuins (156). However, despite these lines of evidence, the whole picture of RACVD development is still not well-demarcated.…”

Acquired Immunity Is Not Essential for Radiation-Induced Heart Dysfunction but Exerts a Complex Impact on Injury

“…Due to the increasing use of immune checkpoint inhibitors in cancer patients, as well as the variable state of adaptive immune cells in patients receiving chemotherapy and RT, it is important to better understand how adaptive immune cells alter the development and severity of RIHD. Using our previously published rat model of RIHD [26], we examined the role of T cells in cardiac radiation injury. We found that T-cell infiltration occurs in the heart after RT, and that localized heart irradiation leads to secretion of the T-cell-associated cytokines interleukin 2 (IL-2) and IL-13 [27,28].…”

“…This zinc-finger nuclease approach was also performed on inbred Salt-Sensitive (SS) rats to create IL2RG −/− rats [33,34]. The immune-competent SS rat strain previously demonstrated increased sensitivity to localized cardiac RT compared to the Brown Norway (BN) strain [26]. Here, we report that SS IL2RG −/− rats also developed RIHD after localized high dose irradiation, with worse heart function measured via echocardiogram at three months post-RT compared to the SS immunocompetent (SS WT) rats.…”