Flanders Institute for Biotechnology (VIB) Center for Inflammation Research, Ghent, Belgium.
Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
Front Immunol. 2023 Mar 16;14:1124011. doi: 10.3389/fimmu.2023.1124011. eCollection 2023.
Polymicrobial sepsis causes acute anorexia (loss of appetite), leading to lipolysis in white adipose tissue and proteolysis in muscle, and thus release of free fatty acids (FFAs), glycerol and gluconeogenic amino acids. Since hepatic peroxisome proliferator-activated receptor alpha (PPARα) and glucocorticoid receptor (GR) quickly lose function in sepsis, these metabolites accumulate (causing toxicity) and fail to yield energy-rich molecules such as ketone bodies (KBs) and glucose. The mechanism of PPARα and GR dysfunction is not known.
METHODS & RESULTS: We investigated the hypothesis that hypoxia and/or activation of hypoxia inducible factors (HIFs) might play a role in these issues with PPARα and GR. After cecal ligation and puncture (CLP) in mice, leading to lethal polymicrobial sepsis, bulk liver RNA sequencing illustrated the induction of the genes encoding HIF1α and HIF2α, and an enrichment of HIF-dependent gene signatures. Therefore, we generated hepatocyte-specific knock-out mice for HIF1α, HIF2α or both, and a new HRE-luciferase reporter mouse line. After CLP, these HRE-luciferase reporter mice show signals in several tissues, including the liver. Hydrodynamic injection of an HRE-luciferase reporter plasmid also led to (liver-specific) signals in hypoxia and CLP. Despite these encouraging data, however, hepatocyte-specific HIF1α and/or HIF2α knock-out mice suggest that survival after CLP was not dependent on the hepatocyte-specific presence of HIF proteins, which was supported by measuring blood levels of glucose, FFAs, and KBs. The HIF proteins were also irrelevant in the CLP-induced glucocorticoid resistance, but we found indications that the absence of HIF1α in hepatocytes causes less inactivation of PPARα transcriptional function.
We conclude that HIF1α and HIF2α are activated in hepatocytes in sepsis, but their contribution to the mechanisms leading to lethality are minimal.
多微生物脓毒症引起急性厌食（食欲减退），导致白色脂肪组织中的脂肪分解和肌肉中的蛋白水解，从而释放游离脂肪酸（FFAs）、甘油和生糖氨基酸。由于肝过氧化物酶体增殖物激活受体 α（PPARα）和糖皮质激素受体（GR）在脓毒症中迅速失去功能，这些代谢物会积累（引起毒性），并且无法产生酮体（KBs）和葡萄糖等富含能量的分子。PPARα 和 GR 功能障碍的机制尚不清楚。
我们研究了假设，即缺氧和/或缺氧诱导因子（HIFs）的激活可能在 PPARα 和 GR 中发挥作用。在小鼠进行盲肠结扎和穿刺（CLP）导致致命性多微生物脓毒症后，大量肝脏 RNA 测序表明 HIF1α 和 HIF2α 的基因诱导，以及 HIF 依赖性基因特征的富集。因此，我们生成了肝细胞特异性敲除 HIF1α、HIF2α 或两者的小鼠，以及一种新的 HRE-荧光素酶报告小鼠品系。在 CLP 后，这些 HRE-荧光素酶报告小鼠在包括肝脏在内的几种组织中显示信号。HRE-荧光素酶报告质粒的水力注射也导致（肝脏特异性）在缺氧和 CLP 中的信号。然而，尽管有这些令人鼓舞的数据，但肝细胞特异性 HIF1α 和/或 HIF2α 敲除小鼠表明，CLP 后的存活率不依赖于肝细胞中 HIF 蛋白的存在，这一点通过测量血糖、FFAs 和 KBs 的血液水平得到了支持。HIF 蛋白在 CLP 诱导的糖皮质激素抵抗中也无关紧要，但我们发现迹象表明，肝细胞中 HIF1α 的缺失导致 PPARα 转录功能的失活减少。
我们得出结论，HIF1α 和 HIF2α 在脓毒症中被激活，但它们对导致致死的机制的贡献最小。
