Expression of TRPM6 and TRPM7 in the preterm piglet heart

Abstract

Preterm infants are at increased risk of death and disability, and cardiovascular instability after birth is a contributing factor. Immaturity of calcium handling in the preterm heart may limit myocardial contractility and cardiac output. Two transmembrane cation channels, TRPM6 and TRPM7, may regulate intracellular cardiac calcium in the neonatal period. The aim of this study was to determine TRPM6 and TRPM7 mRNA expression in piglet hearts in late gestation, and the effects of sex, maternal glucocorticoids, and the transition to extrauterine life. Left and right ventricular tissue was collected at a range of gestational ages from cesarean delivered piglets at birth and at 6 h old. Additional groups included piglets exposed to maternal glucocorticoid treatment and spontaneously born term piglets at 12-24 h old. TRPM6 and TRPM7 mRNA expression was measured using RT-qPCR. Males had significantly lower TRPM7 expression in the left ventricle across all gestational ages compared to females. At term, both ventricles had higher TRPM7 expression at 6 h old than at birth. In preterm piglets, TRPM7 expression only increased postnatally in the right ventricle following maternal glucocorticoid exposure. At 12-24 h old, TRPM7 expression in both ventricles was lower than levels in 6 h old term Caesar piglets (113 days). Male preterm piglets may have immature myocardial Ca²⁺ handling and this could contribute to their poorer outcomes. Increased TRPM7 expression is the mature response to birth that is missing in preterm neonates. TRPM7 could serve as a novel target to improve cardiac function in preterm neonates.

Keywords: TRPM7; cardiovascular function; cardiovascular instability; preterm; sex differences.

FIGURE 1

Cardiac TRPM6 mRNA expression in the left ventricle (LV; A,B) and right ventricle (RV; C,D) of piglets during late gestation. (A,C) Are combined sexes; (B,D) are females (open circles) and males (gray squares). Plot of median (IQR) of fold change (2^-ΔΔC_T) normalized to 113 d. N = 13 (91 d), 8 (97 d), 14 (100 d), 19 (113 d). *Indicates significantly lower expression at 110 d compared to 97 d and 113 d (P < 0.001).

FIGURE 2

Cardiac TRPM7 mRNA expression in the left ventricle (LV; A,B) and right ventricle (RV; C,D) of piglets during late gestation. (A,C) Are combined sexes; (B,D) are females (open circles) and males (gray squares). Plot of median (IQR) of fold change (2^-ΔΔC_T) normalized to 113 d. N = 13 (91 d), 8 (97 d), 14 (100 d), 19 (113 d). *Indicates significantly lower expression at 110 d compared to 97 d and 113 d (P < 0.005). ^†Indicates males at birth had lower TRPM7 expression in the left ventricle (P < 0.038).

FIGURE 3

Effect of postnatal age on cardiac mRNA expression of TRPM6 (A: LV is left ventricle, B: RV is right ventricle) and TRPM7 (C: LV, D: RV) in piglets at birth (0 h; closed circles) and 6 h old (open triangles). Plot of median (IQR) of fold change (2^-ΔΔC_T) normalized to 113 d + 0 h. GC is maternal glucocorticoid treatment. SVD is spontaneous vaginal delivery at term (12–24 h old; black triangles). *Indicates significant differences between groups (P < 0.05). ^†Indicates expression in the right ventricle of term SVD piglets was different to all other groups. n = 8 (91 d), 12 (91 d + 6 h), 12–13 (97 d + GC), 13 (97 d + GC + 6 h), 19–20 (113 d), 10 (113 d + 6 h), 10 (115 d + 24 h).

FIGURE 4

Effect of maternal glucocorticoids on cardiac mRNA expression of TRPM6 (A: LV is left ventricle, B: RV is right ventricle) and TRPM7 (C: LV, D: RV) of preterm piglets. Maternal glucocorticoid treatment (crosses) and no treatment (circles). Plot of median (IQR) of fold change (2^-ΔΔC_T) normalized to 113 d + 0 h. *Indicates significant differences between groups (P < 0.05). n = 13–15 (91 d + 0 h), 16 (91 d + 0 h + GC), 8 (97 d + 0 h), 13 (97 d + 0 h + GC), 12 (97 d + 6 h), 13 (97 d + 6 h + GC).