Novel mechanism on the ischemic preconditioning : Role of AMP deaminase family for adenosine production

腺苷被认为是促进心脏缺血预处理的介质。腺苷可以通过胞外5′-核苷酸酶从细胞外的腺苷转化为5′-核苷酸酶，也可以通过胞内5′-核苷酸酶从细胞内的单磷酸腺苷（AMP）产生，表明腺苷浓度会受到细胞内AMP浓度的影响。AMP浓度不仅可以通过胞质5′-核苷酸酶降解为腺苷，还可以通过AMP脱氨酶降解为肌苷一磷酸（IMP）。因此，腺苷浓度会通过激活AMP脱氨酶而降低。AMP脱氨酶家族由肌型AMPD1、肝型AMPD2和血型AMPD3组成。然而，心脏AMP脱氨酶的分布和功能尚不清楚。在本研究中，我们研究了心脏AMP脱氨酶的定位和功能。在心力衰竭患者中，右心房表达AMPD1、2和3的信息和蛋白，左心房和双心室表达AMPD2和3。AMPD1具有肌球蛋白重链结合位点，包含PVEK的一致序列。根据氨基酸序列比对，AMPD2和ampd3也具有肌球蛋白结合位点。AMP脱氨酶家族和肌凝蛋白重链的异源表达研究表明，AMPD3可以像AMPD1一样结合肌凝蛋白重链，而AMPD2不与肌凝蛋白重链结合。肌凝蛋白重链结合的AMPD1活性显著高于未结合的AMPD1活性，而肌凝蛋白重链结合和未结合的AMPD3活性均未发生变化。缺血条件下心肌肌球蛋白结合的AMP脱氨酶活性（AMPD3为主表达）没有变化，而缺血条件下骨骼肌肌球蛋白结合的AMP脱氨酶活性（AMPD1为主表达）明显升高。此外，ampd3可以与ecto - 5'-核苷酸酶结合，正如AMPD1和ampd2可以与它结合一样。这些结果表明，心肌缺血促进肌球蛋白重链与AMPD3结合，使外泌体和胞质5′-核苷酸酶都能利用AMP转化为腺苷，从而激活心脏缺血预处理。少

Adenosine is known to be the mediator to facilitate the ischemic preconditioning of the heart. Adenosine is converted from extracellular AMP by ecto 5'-nucleotidase, and is also produced from intracellular adenosine monophosphate (AMP) by cytosolic 5'-nucleotidase, suggesting adenosine concentration will be influenced by intracellular AMP concentration. AMP concentration can be degradated not only by cytosolic 5'-nucleotidase into adenosine but also by AMP deaminase into inosine monophosphate (IMP). Therefore, adenosine concentration would be decreased by the activation of AMP deaminase. AMP deaminase family is composed of muscular AMPD1, hepatic AMPD2 and blood type AMPD3. However the distribution and function of cardiac AMP deaminase is not still characterized. In the present study, we studied the localization and the function of cardiac AMP deaminase. While the right atrium expressed the message and the protein of AMPD1, 2, and 3, the left atrium and both ventricles expressed AMPD2 … More and 3 in patients with heart failure. AMPD1 has the myosin heavy chain binding site which included the consensus sequence of PVEK.Based on the alignment for the amino acid sequence, AMPD2 and 3 possess the myosin binding site as well. The heterologous expression study of both AMP deaminase family and myosin heavy chain showed that AMPD3 can bind the myosin heavy chain as AMPD1, but AMPD2 did not bind to myosin heavy chain. While the activity of myosin heavy chain-bound AMPD1 was significantly higher than that of unbound AMPD1, the activity of AMPD3 did not alter under either myosin heavy chain bound or unbound condition. Under ischemic condition of the heart myosin bound AMP deaminase activity (AMPD3 dominantly expressed) did not change, although under ischemic condition of the skeletal muscle myosin bound AMP deaminase activity (dominantly AMPD1 expressed) significantly elevated. In addition AMPD 3 can bind to ecto 5'- nucleotidase, as AMPD1 and 2 can bind to it. These results suggest that cardiac ischemia facilitated myosin heavy chain to bind to AMPD3 in order to both ecto and cytosolic 5'-nucleotidase can utilize the AMP to convert into adenosine, which would lead to activate the ischemic preconditioning of the heart. Less