Division of Cardiovascular Sciences, School of Medical Sciences, University of Manchester, Manchester M13 9NT, UK.
School of Science, Engineering, & Environment, University of Salford, Salford M5 4NT, UK.
J Exp Biol. 2024 Oct 15;227(20). doi: 10.1242/jeb.247434. Epub 2024 Oct 30.
Oxygen deprivation during embryonic development can permanently remodel the vertebrate heart, often causing cardiovascular abnormalities in adulthood. While this phenomenon is mostly damaging, recent evidence suggests developmental hypoxia produces stress-tolerant phenotypes in some ectothermic vertebrates. Embryonic common snapping turtles (Chelydra serpentina) subjected to chronic hypoxia display improved cardiac anoxia tolerance after hatching, which is associated with altered Ca2+ homeostasis in heart cells (cardiomyocytes). Here, we examined the possibility that changes in Ca2+ cycling, through the sarcoplasmic reticulum (SR), underlie the developmentally programmed cardiac phenotype of snapping turtles. We investigated this hypothesis by isolating cardiomyocytes from juvenile turtles that developed in either normoxia (21% O2; 'N21') or chronic hypoxia (10% O2; 'H10') and subjected the cells to anoxia/reoxygenation, in either the presence or absence of SR Ca2+-cycling inhibitors. We simultaneously measured cellular shortening, intracellular Ca2+ concentration ([Ca2+]i), and intracellular pH (pHi). Under normoxic conditions, N21 and H10 cardiomyocytes shortened equally, but H10 Ca2+ transients (Δ[Ca2+]i) were twofold smaller than those of N21 cells, and SR inhibition only decreased N21 shortening and Δ[Ca2+]i. Anoxia subsequently depressed shortening, Δ[Ca2+]i and pHi in control N21 and H10 cardiomyocytes, yet H10 shortening and Δ[Ca2+]i recovered to pre-anoxic levels, partly due to enhanced myofilament Ca2+ sensitivity. SR blockade abolished the recovery of anoxic H10 cardiomyocytes and potentiated decreases in shortening, Δ[Ca2+]i and pHi. Our novel results provide the first evidence of developmental programming of SR function and demonstrate that developmental hypoxia confers a long-lasting, superior anoxia-tolerant cardiac phenotype in snapping turtles, by modifying SR function and enhancing myofilament Ca2+ sensitivity.
胚胎发育过程中的缺氧会永久性重塑脊椎动物的心脏，经常导致成年后的心血管异常。虽然这种现象大多是有害的，但最近的证据表明，发育性缺氧会在一些变温脊椎动物中产生应激耐受表型。在孵化后，长期处于慢性缺氧环境下的胚胎普通 snapping 龟（Chelydra serpentina）表现出更好的心肌缺氧耐受能力，这与心肌细胞（心肌细胞）中 Ca2+ 稳态的改变有关。在这里，我们研究了 Ca2+ 循环（通过肌浆网）的变化是否是 snapping 龟心脏发育编程表型的基础。我们通过从小龟（在正常氧浓度 21%O2 中发育的“N21”和慢性缺氧 10%O2 中发育的“H10”）中分离心肌细胞来研究这个假说，并将细胞置于缺氧/复氧条件下，同时存在或不存在肌浆网 Ca2+ 循环抑制剂。我们同时测量细胞缩短、细胞内 Ca2+ 浓度 ([Ca2+]i) 和细胞内 pH (pHi)。在正常氧条件下，N21 和 H10 心肌细胞的缩短程度相等，但 H10 Ca2+ 瞬变（Δ[Ca2+]i）比 N21 细胞小两倍，并且肌浆网抑制仅降低 N21 的缩短和 Δ[Ca2+]i。随后，缺氧抑制了对照 N21 和 H10 心肌细胞的缩短、Δ[Ca2+]i 和 pHi，但 H10 的缩短和 Δ[Ca2+]i 恢复到缺氧前水平，部分原因是肌球蛋白 Ca2+ 敏感性增强。肌浆网阻断消除了缺氧 H10 心肌细胞的恢复，并增强了缩短、Δ[Ca2+]i 和 pHi 的降低。我们的新结果首次提供了肌浆网功能发育编程的证据，并表明发育性缺氧通过改变肌浆网功能和增强肌球蛋白 Ca2+ 敏感性，赋予 snapping 龟持久的、优越的心肌缺氧耐受表型。
