Sex-dependent effects of genetic upregulation of activated protein C on delayed effects of acute radiation exposure in the mouse heart, small intestine, and skin

Abstract

Accidental exposure to ionizing radiation may lead to delayed effects of acute radiation exposure (DEARE) in many organ systems. Activated protein C (APC) is a known mitigator of the acute radiation syndrome. To examine the role of APC in DEARE, we used a transgenic mouse model with 2- to 3-fold increased plasma levels of APC (high in APC, APCHi). Male and female APCHi mice and wild-type littermates were exposed to 9.5 Gy γ-rays with their hind-legs (bone marrow) shielded from radiation to allow long-term survival. At 3 and 6 months after irradiation, cardiac function was measured with ultrasonography. At 3 months, radiation increased cardiac dimensions in APCHi males, while decreases were seen in wild-type females. At this early time point, APCHi mice of both sexes were more susceptible to radiation-induced changes in systolic function compared to wild-types. At 6 months, a decrease in systolic function was mainly seen in male mice of both genotypes. At 6 months, specimens of heart, small intestine and dorsal skin were collected for tissue analysis. Female APCHi mice showed the most severe radiation-induced deposition of cardiac collagens but were protected against a radiation-induced loss of microvascular density. Both male and female APCHi mice were protected against a radiation induced upregulation of toll-like receptor 4 in the heart, but this did not translate into a clear protection against immune cell infiltration. In the small intestine, the APCHi genotype had no effect on an increase in the number of myeloperoxidase positive cells (seen mostly in females) or an increase in the expression of T-cell marker CD2 (males). Lastly, both male and female APCHi mice were protected against radiation-induced epidermal thickening and increase in 3-nitrotyrosine positive keratinocytes. In conclusion, prolonged high levels of APC in a transgenic mouse model had little effects on indicators of DEARE in the heart, small intestine and skin, with some differential effects in male compared to female mice.

Urinary Metabolomics for the Prediction of Radiation-Induced Cardiac Dysfunction

“…For all the mice included in this study, at 6 months after irradiation, cardiac ultrasound and histological staining were used to measure ejection fraction, mitral valve E/A, cardiac collagen deposition, and myocardial capillary density. Those results were published previously [15]. We defined heart dysfunction if any one of the following conditions was satisfied: (1) mitral valve E/A below 1.3 or above 2.3 (for this parameter, both low and high extreme values are an indication of cardiac dysfunction); (2) ejection fraction ≤40; (3) cardiac collagen content above 25% as an indicator of myocardial radiation fibrosis; or (4) the number of myocardial capillaries/areas ≤0.0038, a common manifestation of adverse myocardial remodeling in the irradiated heart [22].…”

“…Animal purchase, housing, irradiation, and assessment of cardiac function and histology were completed in a prior study [15]. All urine samples used in this study were collected from a previous publication, and no live mice were used or assessed.…”

“…All animal work was performed at the University of Arkansas for Medical Sciences (UAMS) under approved IACUC protocols (#3763 and 3982). A detailed description of the methods has been provided in a previous publication [15].…”

“…Dosimetry was performed with Gafchromic film (DOSE-MAP, Ashland Specialty Ingredients, Wayne, NJ, USA) and an ion chamber (Exradin A20, Standard Imaging, Middleton, WI, USA) and electrometer (X4000, Standard Imaging) that are calibrated for γ-rays once a year. Cardiac dysfunction was defined using previously published data based on the following criteria: mitral valve E/A ratio below 1.3 or above 2.3, ejection fraction ≤40, cardiac collagen content above 25%, or the number of myocardial capillaries/areas ≤0.0038 [15].…”

“…APC has previously been shown to have potent radiation mitigative effects in a mouse model of ARS [12]. We used a transgenic mouse model that constitutively overexpresses APC, hence being termed APCHi mice [13,14] to show the sex-dependent effects of APC upregulation on radiation-induced cardiac dysfunction [15]. In this prior study, we found that for a single dose of 9.5 Gy γ-rays, with hind-leg shielding from radiation to allow long-term survival, the APCHi genotype had no effect on radiation-induced changes in cardiac function but caused a more severe increase in radiation-induced cardiac collagen deposition compared to the WT genotype in female mice, while protecting female mice from a radiation-induced decrease in cardiac microvascular density.…”