Maternal undernutrition in late gestation increases IGF2 signalling molecules and collagen deposition in the right ventricle of the fetal sheep heart

Abstract

Key points: This study investigates the impact of decreased fetal plasma glucose concentrations on the developing heart in late gestation, by subjecting pregnant ewes to a 50% global nutrient restriction. Late gestation undernutrition (LGUN) decreased fetal plasma glucose concentrations whilst maintaining a normoxemic blood gas status. LGUN increased the mRNA expression of IGF2 and IGF2R. Fetal plasma glucose concentrations, but not fetal blood pressure, were significantly correlated with IGF2 expression and the activation of CAMKII in the fetal right ventricle. LGUN increased interstitial collagen deposition and altered the protein abundance of phospho-PLB and phospho-troponin I, regulators of cardiac contractility and relaxation. This study shows that a decrease in fetal plasma glucose concentrations may play a role in the development of detrimental changes in the right ventricle in early life, highlighting CAMKII as a potential target for the development of intervention strategies.

Abstract: Exposure of the fetus to a range of environmental stressors, including maternal undernutrition, is associated with an increased risk of death from cardiovascular disease in adult life. This study aimed to determine the effect of maternal nutrient restriction in late gestation on the molecular mechanisms that regulate cardiac growth and development of the fetal heart. Maternal undernutrition resulted in a decrease in fetal glucose concentrations across late gestation, whilst fetal arterial PO2 remained unchanged between the control and late gestation undernutrition (LGUN) groups. There was evidence of an up-regulation of IGF2/IGF2R signalling through the CAMKII pathway in the fetal right ventricle in the LGUN group, suggesting an increase in hypertrophic signalling. LGUN also resulted in an increased mRNA expression of COL1A, TIMP1 and TIMP3 in the right ventricle of the fetal heart. In addition, there was an inverse relationship between fetal glucose concentrations and COL1A expression. The presence of interstitial fibrosis in the heart of the LGUN group was confirmed through the quantification of picrosirius red-stained sections of the right ventricle. We have therefore shown that maternal undernutrition in late gestation may drive the onset of myocardial remodelling in the fetal right ventricle and thus has negative implications for right ventricle function and cardiac health in later life.

Keywords: IGF2; cardiac; fetus; fibrosis; heart; signalling; undernutrition.

Figure 1. Fetal mean PO2 (A) and plasma glucose concentrations (B) across late gestation

Data are expressed as mean ± SEM and analysed by unpaired t test. Control (n = 6), open bars; LGUN (n = 8), filled bars. ^* P < 0.05, effect of LGUN. Figure adapted, with permission, from Edwards & McMillen (2001).

Figure 2. Normalized mRNA expression of IGF1 (A), IGF2 (B), IGF1R (C) and IGF2R (D)

Data were analysed by unpaired t test. Data are expressed as mean ± SEM. Control, unfilled bars (n = 6); LGUN, filled bars (n = 8). MNE, mean normalized expression;^* P ≤ 0.05.

Figure 3. Relationship between fetal mean arterial pressure recorded at 115–125 and 135–145 days GA with mRNA expression of IGF2 (A, C) and IGF2R (B, D)

Each circle represents an individual data point. Control, open circles; LGUN, filled circles; MAP, mean arterial pressure; MNE, mean normalized expression; GA, gestational age.

Figure 4. Relationship between mean fetal plasma glucose concentration and the mRNA expression of IGF2 (A) and IGF2R (B)

Each circle represents an individual data point. Control, open circles (n = 5); LGUN, filled circles (n = 7); MNE, mean normalized expression.

Figure 5. Protein abundance of phosphorylated CAMKII (A) is increased as a result of LGUN and positively correlated to the mRNA expression of both IGF2 (E) and IGF2R (F)

Protein abundance of phospho‐PLB (B) and Troponin I (C) was increased and decreased, respectively, as a result of LGUN. Values are mean ± SEM. ^*Significantly different from control fetuses (P < 0.05). AU, arbitrary units. Control, open bars/circles (n = 6); LGUN, filled bars/circles (n = 8); MNE, mean normalized expression.

Figure 6. Normalized cardiac mRNA expression of COL1A (A), COL3A1 (B), TIMP‐1(D), TIMP‐2 (E) and TIMP‐3 (F)

Relationship between cardiac COL1A mRNA expression and mean fetal plasma concentrations in late gestation (C). Values are mean ± SEM. Control, open bars/circles (n = 6); LGUN, filled bars/circles (n = 8); MNE, mean normalized expression. ^*Significantly different from control fetuses (P < 0.05).

Figure 7. Interstitial collagen deposition (A) determined by picrosirius red staining in Control (B) and LGUN fetuses (C)

Stained slides scanned for whole slide images using a Nanozoomer at 40× magnification. Scale bar on representative images = 100 μm. Data analysed by unpaired t test. Data presented as mean ± SEM. P < 0.05 was considered significant. Control, unfilled bars (n = 4); LGUN, filled bars (n = 4). [Color figure can be viewed at http://wileyonlinelibrary.com]