The influence of tissue-specific heme oxygenase-1 (HO-1) deficiency on neuronal damage induced by subarachnoid hemorrhage in mice: the role of carbon monoxide (CO)

由血红素加氧酶1(HO-1)内源性产生一氧化碳(CO)是一种重要的细胞保护机制。1.人类HO-1缺乏会导致严重的疾病状态并导致过早死亡，2.经典的HO-1基因敲除会导致动物寿命显著缩短，3.HO-1的过度表达或诱导以及外源性CO在各种疾病模型中起到保护作用，这些事实突显了内源性CO产生的重要性。我们的实验室最近表明，外源性应用一氧化碳，无论是通过吸入或通过全身途径通过一氧化碳释放分子(CO-RM)发挥神经保护作用。有两个重要方面仍然不清楚：1.细胞特异性HO-1表达的独特作用是什么？2.就其保护作用而言，外源性CO应用是否等同于HO-1诱导内源性产生的CO？为了回答这些问题，我们将使用一个公认的脑损伤模型(蛛网膜下腔出血，SAH)，在该模型中，HO-1表达上调，并已被证明具有保护作用。对于HO-1基因敲除的小鼠，无论是在内皮细胞、神经元细胞还是小胶质细胞中，无论是全球HO-1缺陷还是条件性组织特异性HO-1缺陷，我们都想表征HO-1表达在这些细胞中所起的独特保护作用。因此，我们将研究以下假设：1.HO-1的表达可改善SAH后神经元的损伤。具体目的1：探讨全身性HO-1缺乏对蛛网膜下腔出血后神经细胞损伤的影响。2.内皮特异性HO-1对SAH所致小鼠脑血管痉挛和内皮功能障碍具有保护作用。特异性目的2：探讨内皮细胞HO-1缺陷在蛛网膜下腔出血后神经细胞死亡中的作用。3.神经元特异性HO-1可预防SAH小鼠细胞死亡。目的3：探讨组织特异性HO-1基因敲除对蛛网膜下腔出血后神经细胞死亡的影响。4.小胶质细胞特异性HO-1调节血红素清除和SAH诱导的神经炎性反应。具体目的4：评价小胶质细胞特异性HO-1基因敲除在蛛网膜下腔出血后神经细胞死亡中的作用。5.CO可以弥补上述整体和组织特异性HO-1基因敲除小鼠内源性CO产生的不足。具体目的5：探讨外源性应用CO对HO-1基因缺陷小鼠SAH后神经元损伤的潜在保护作用。

Endogenous production of carbon monoxide (CO) by heme oxygenase 1 (HO-1) represents an essential cellular protection mechanism. The importance of endogenous CO production is underlined by the facts that 1. deficiency of HO-1 in humans leads to a severe disease state with premature death, 2. classical genetic knockout of HO-1 in animals results in markedly reduced life span, 3. overexpression or induction of HO-1 and exogenous application of CO exerts protective effects in various disease models. Our lab has recently shown that exogenous application of CO, either inhalative or via systemic routes by a CO releasing molecule (CO-RM) exerts neuroprotective effects. Two important aspects remain unclear: 1. What is the distinct role of cell-specific HO-1 expression? 2. Does exogenous CO application equal endogenously generated CO by HO-1 induction regarding its protective effects? To answer these questions, we will use a well established model of cerebral injury (subarachnoid hemorrhage, SAH), in which HO-1 is upregulated and has been shown to be protective. With HO-1 knockout mice either with global HO-1 deficiency or conditional tissue-specific HO-1 deficiency in either endothelial, neuronal or microglial cells, we want to characterize the distinct protective role exerted by HO-1 expression in these cells. We therefore will study the following hypotheses: 1. HO-1 expression ameliorates neuronal injury after SAH. Specific aim 1: To evaluate the effect of global HO-1 deficiency on neuronal cell injury following SAH. 2. Endothelial-specific HO-1 is protective in SAH-induced cerebral vasospasm and endothelial dysfunction in mice. Specific aim 2: To evaluate the contribution of endothelial HO-1 deficiency to neuronal cell death following SAH. 3. Neuron-specific HO-1 prevents cell death following SAH in mice. Specific aim 3: To evaluate the effect of tissue-specific neuronal HO-1 knockout on neuronal cell death following SAH. 4. Microglia-specific HO-1 modulates heme removal and the SAH-induced neuroinflammatory response. Specific aim 4: To evaluate the contribution of microglia-specific HO-1 knockout to neuronal cell death following SAH. 5. CO can compensate for the deficiency of endogenous CO production in the above-described global and tissue-specific HO-1 knockout mice. Specific aim 5: To investigate the potentially protective effect of exogenous application of CO, either inhaled as gas or through the CO releasing molecule (CO-RM) ALF186 on neuronal damage after SAH in HO-1 deficient mice.