Cheng Vanessa, Dasgupta Subham, Reddam Aalekhya, Volz David C
Department of Environmental Sciences, University of California, Riverside, CA, USA.
PeerJ. 2019 Nov 13;7:e8054. doi: 10.7717/peerj.8054. eCollection 2019.
Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor that regulates lipid/glucose homeostasis and adipocyte differentiation. While the role of PPARγ in adipogenesis and diabetes has been extensively studied, little is known about PPARγ function during early embryonic development. Within zebrafish, maternally-loaded pparγ transcripts are present within the first 6 h post-fertilization (hpf), and de novo transcription of zygotic pparγ commences at ~48 hpf. Since maternal pparγ transcripts are elevated during a critical window of cell fate specification, the objective of this study was to test the hypothesis that PPARγ regulates gastrulation and dorsoventral patterning during zebrafish embryogenesis. To accomplish this objective, we relied on (1) ciglitazone as a potent PPARγ agonist and (2) a splice-blocking, pparγ-specific morpholino to knockdown pparγ. We found that initiation of ciglitazone-a potent human PPARγ agonist-exposure by 4 hpf resulted in concentration-dependent effects on dorsoventral patterning in the absence of epiboly defects during gastrulation, leading to ventralized embryos by 24 hpf. Interestingly, ciglitazone-induced ventralization was reversed by co-exposure with dorsomorphin, a bone morphogenetic protein signaling inhibitor that induces strong dorsalization within zebrafish embryos. Moreover, mRNA-sequencing revealed that lipid- and cholesterol-related processes were affected by exposure to ciglitazone. However, pparγ knockdown did not block ciglitazone-induced ventralization, suggesting that PPARγ is not required for dorsoventral patterning nor involved in ciglitazone-induced toxicity within zebrafish embryos. Our findings point to a novel, PPARγ-independent mechanism of action and phenotype following ciglitazone exposure during early embryonic development.
过氧化物酶体增殖物激活受体γ（PPARγ）是一种配体激活的转录因子，可调节脂质/葡萄糖稳态和脂肪细胞分化。虽然PPARγ在脂肪生成和糖尿病中的作用已得到广泛研究，但对其在早期胚胎发育过程中的功能却知之甚少。在斑马鱼中，母源加载的pparγ转录本在受精后6小时（hpf）内就已存在，合子型pparγ的从头转录在约48 hpf开始。由于母源pparγ转录本在细胞命运决定的关键时期升高，本研究的目的是检验PPARγ在斑马鱼胚胎发育过程中调节原肠胚形成和背腹模式形成的假说。为实现这一目标，我们依赖于（1）吡格列酮作为一种有效的PPARγ激动剂，以及（2）一种剪接阻断的、pparγ特异性吗啉代寡核苷酸来敲低pparγ。我们发现，在原肠胚形成过程中无外包缺陷的情况下，在4 hpf开始暴露于强效人类PPARγ激动剂吡格列酮会对背腹模式形成产生浓度依赖性影响，导致24 hpf时胚胎腹化。有趣的是，与 dorsomorphin（一种骨形态发生蛋白信号抑制剂，可在斑马鱼胚胎中诱导强烈的背化）共同暴露可逆转吡格列酮诱导的腹化。此外，mRNA测序显示脂质和胆固醇相关过程受吡格列酮暴露的影响。然而，敲低pparγ并不能阻止吡格列酮诱导的腹化，这表明PPARγ对于斑马鱼胚胎的背腹模式形成并非必需，也不参与吡格列酮诱导的毒性作用。我们的研究结果指出了早期胚胎发育过程中吡格列酮暴露后一种新的、不依赖PPARγ的作用机制和表型。
