Modulation of Ceramide Content and Lack of Apoptosis in the Chronically Hypoxic Neonatal Rat Heart

Abstract

To assess the effect of chronic hypoxia on cardiomyocyte apoptosis, we used an animal model that mimics cyanotic heart disease. Rats were placed in a hypoxic environment at birth, and oxygen levels were maintained at 10% in an air-tight Plexiglas chamber. Controls remained in room air. Animals were killed, and the hearts were harvested at 1 and 4 wk. Significant polycythemia developed in the hypoxic rats at 1 and 4 wk. Right ventricular mass in the hypoxic rats was 192% and 278% that of controls, and hypoxic left ventricular mass was 140% and 178% that of the controls at 1 and 4 wk, respectively. The increase in cardiac mass was paralleled by only mild hypertrophy (10 to 20%). Contrary to previous reports showing increased apoptosis in response to hypoxia in cultured cardiomyocytes, there was no difference in the number of apoptotic cardiomyocytes between the chronically hypoxic rats and controls, as assayed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and Hoechst staining. We then examined the role of the sphingolipid ceramide because of its reported role in the stress response, growth suppression, and apoptosis. We found that the right ventricular ceramide content was significantly decreased in the hypoxic rats to 73% of control levels at the age of 4 wk. We suggest that the decrease in the ceramide content in the hypoxic right ventricular rat heart may be an adaptive response to chronic hypoxia and pulmonary hypertension. Lower ceramide levels may help suppress apoptosis and allow compensatory right ventricular cardiomyocyte proliferation. Apoptosis, or programmed cell death, is a mechanism of regulated cell death that plays a major role during development and homeostasis, and in many disease states. Apoptosis in cardiomyocytes has been demonstrated after injury caused by ischemia and reperfusion (1, 2), myocardial infarction (3, 4), cardiac aging (5), ventricular pacing (6), heart failure, and coronary embolization (7,8).Conflicting data regarding apoptotic changes, in response to hypoxia, have been described (9 -12). The failing myocardium is subject to regional ischemia and hypoxia, an abnormality that can trigger cardiomyocyte apoptosis (13). Long et al. (14) reported that cultured neonatal rat cardiomyocytes exposed to in vitro hypoxia for 48 h exhibited apoptotic changes. However, Bishopric et al. (15) found that induction of apoptosis of cardiac myocytes by hypoxia required acidosis, and that chronic hypoxia alone did not cause apoptosis of cardiomyocytes in culture. Hypoxia can induce cellular adaptive responses, such as c-Jun expression, that overcome apoptosis signals to minimize injury or damage (16). The in vivo effect of chronic hypoxia on the neonatal heart has not been investigated, and differentiating the effect of hypoxia and ischemia from that of hypoxia alone on apoptosis in the neonatal heart is important.Although no universal definition of apoptosis currently exists, morphologic and biochemical characteristics of apoptosis have been described that distinguis...

In vivo effect of chronic hypoxia on the neurochemical profile of the developing rat hippocampus

“…The animal model used in this study is well described for studies of chronic hypoxia and results in a similar degree of hypoxia present in human infants with CHD [8,26,32]. The body weight of the chronic hypoxia rats was decreased, as has been demonstrated in all studies that have used a similar model [8,12,26].…”

“…The body weight of the chronic hypoxia rats was decreased, as has been demonstrated in all studies that have used a similar model [8,12,26]. While the associated malnutrition may have played a role in the neurochemical alterations, the effects are likely to be minor.…”

“…The concentration of O 2 inside the chamber was maintained at 10% by mixing air and nitrogen and was monitored using an oxygen analyzer (Miniox II; Catalyst Research Corporation; Owings Mills, MD). The degree of hypoxia was based on rodent models of CHD [8,34]. Excess humidity from the chamber was eliminated using calcium bisulphate (Drierite; W.A.…”

Effect of chronic hypoxia on leptin, insulin, adiponectin, and ghrelin

“…As previously described, an animal model mimicking cyanotic heart disease was studied [23,24]. Animal cages were placed in temperature-controlled rooms (22°C) with constant 12-hour light/dark cycle.…”

p53 and Ceramide as Collaborators in the Stress Response

“…Many studies were conducted to determine the effects of hypoxia or hyperoxia on ceramide. First, it was shown that upon exposure to chronic hypoxia, the myocardial mass was increased in a rat and mouse models of cyanotic congenital heart disease due to compensatory cardiac proliferation in the right ventricle (RV) [28,29]. This phenotype was associated with the absence of apoptosis, the relative decrease in total ceramide, specifically N-palmitoyl-D-erythro-sphingosine (C16-Cer) levels [30], and the significant increase of the precursor dihydro-N-palmitoyl-D-erythro-sphinganine (DHC16) in the RV.…”