摘 要: 低氧誘導因子1(HIF-1)與微循環功能中的血管新生以及炎性反應密切相關。研究表明,HIF-1通過調控下游血紅素加氧酶及血管內皮生長因子影響血管生成。另外一方面,HIF-1通過調控白細胞介素8等細胞趨化因子影響血管炎癥狀態。目前急性心肌梗死及糖尿病中的微循環障礙越來越受到關注。深入了解微循環障礙的分子靶點,對微循環障礙的治療尤為重要。HIF-1作為低氧狀態下的適應性調節因子,通過影響血管新生、細胞凋亡、炎癥及氧化應激等多種環節參與微循環功能調節。鑒于HIF-1在微循環障礙中的地位,以HIF-1為靶點的微循環障礙治療越來越得到關注。
關鍵詞: 微循環障礙; 低氧誘導因子; 血管新生;
Abstract: Hypoxia inducible factor-1( HIF-1) is closely related to angiogenesis and inflammation response in the pathological process. Previous studies showed that HIF-1 affects angiogenesis by regulating the expression of heme oxygenase and vascular endothelial growth factor. Additionally,HIF-1 affects vascular inflammation by regulating chemokines such as interleukin-8. With the increasing evidences of microvascular dysfunction induced by acute myocardial infarction and diabetes,the microvascluar dysfunction treatment is getting important.A deep insight of HIF-1 is crucial in therapy of microvascular dysfunction.
Keyword: Microvascular dysfunction; Hypoxia inducible factor; Angiogenesis ;
低氧通常通過多種機制促進血管穩態失衡,包括血栓形成、動脈粥樣硬化、缺血再灌注損傷。缺血再灌注損傷、急性心肌梗死以及糖尿病缺血過程中的微循環障礙,與低氧誘導的炎性反應、氧化應激、血管新生和細胞生存密切相關。短期及中等程度的缺氧激活促生長及促增殖轉導途徑,而長期、持續的缺氧導致內皮細胞死亡[1,2,3]。在適度低氧狀態下,轉錄因子低氧誘導因子1(HIF-1)作為適應性反應調節因子[4]。在缺氧及復氧狀態下,HIF-1的轉錄活性及HIF-1α蛋白表達水平顯著增加。在心肌缺血及心肌梗死狀態下,HIF-1表達顯著增加。HIF-1通過調節血管新生以及血管功能,并通過將氧化應激轉化為糖酵解,改善局部微循環功能[5,6]。在長期及持續的缺氧狀態下,HIF-1信號轉導通路的過度激活可能參與內皮細胞死亡[7]。因此,HIF-1信號通路參與微血管狀態的調節,并可以作為微循環功能改善的重要作用靶點。
1、 HIF-1
HIF-1是一種異二聚體,由HIF-1α及HIF-1β兩種亞型組成[8,9]。其活性由HIF-1α的穩定性表達決定。脯氨酸羥化酶抑制劑和缺氧穩定HIF-1α,導致細胞核HIF-1α/β活性異二聚體增加[10];罨腍IF-1通過多種靶基因參與細胞自噬、能量代謝、離子平衡、血管重塑、細胞增殖以及血管新生[11,12,13]。HIF-1α的減少降低了細胞能量,低氧誘導的糖酵解,以及血管新生。在低氧誘導的代償反應中,HIF-1表達上調促進細胞生存,增加糖酵解酶基因的表達以及促血管生成因子的合成。而另外一方面,過度活化的HIF-1參與持續低氧誘導的內皮細胞死亡。
2、 HIF-1與血管新生
研究表明,低氧促進人微血管內皮細胞HIF-1α的核聚集,通過增加血管內皮生長因子(VEGF)的合成[14]及糖酵解代謝促進血管新生[15]。Tal等[16]研究發現,C端轉錄激活結構域的持續激活及HIF-1α分子的穩定性對于其介導的最佳轉錄活性和血管新生十分重要。Befani和Liakos[17]也證實,低氧可以促進微血管內皮整合蛋白基因的表達,從而增加微血管內皮細胞的遷移和毛細血管結構的形成。Kütscher等[18]研究發現,HIF-1α的過表達提高內皮前體干細胞的血管生成能力。低密度脂蛋白通過阻斷HIF-1α/VEGF信號通路從而抑制低氧誘導的血管新生[19]。
以骨髓間充質干細胞(BMMSC)轉染編碼突變型HIF-1α的載體(BMMSC-HIF),干預缺血再灌注損傷的羊,與對照組相比,在BMMSC-HIF治療7 d及60 d后,動物心肌中小血管及毛細血管密度顯著增加,BMMSC-HIF干預顯著降低缺血再灌注損傷后梗死面積,改善左心室功能[20]。Ríos-Navarro等[21]研究發現,與對照組相比,豬冠狀動脈結扎后90 min微循環密度顯著降低,表現為梗死區CD+31表達及微循環密度顯著減少。此外,微循環栓塞在再灌注1 min后發生。微循環密度減低和微循環栓塞在再灌注1周后達到高峰,于再灌注1個月后恢復。缺血后動物血清HIF-1α顯著增加,冠狀動脈血清促進體外培養冠狀動脈內皮細胞的血管新生,而HIF-1α的阻斷降低血清誘導的血管新生。
高糖狀態促發的低氧與缺血及微循環障礙密切相關,目前高糖對HIF-1表達的影響仍不明確,有研究表明,高糖狀態降低了HIF-1α的穩定性[22],此外在高糖狀態下,活性氧自由基被激活,是造成HIF-1α表達及轉錄減少的重要因素,從而使得低氧狀態下HIF-1、VEGF及血紅素加氧酶(HO-1)的表達減少,血管化減少,低氧誘導的血管新生的代償反應減低[23,24]。高糖抑制HIF-1的機制涉及多個方面。氧離子和一氧化氮的相互作用,導致穩態一氧化氮濃度降低,從而降低一氧化氮誘導的HIF-1α聚集和激活;钚匝踝杂苫ㄟ^激活脯氨酸羥化酶,增加泛素蛋白酶體活性降解HIF-1α。此外,腫瘤壞死因子途徑,血管緊張素及胰島素途徑參與高糖狀態下活性氧自由基對HIF-1α的抑制。Rho家族中小鳥苷酸三磷酸酶Rac1是細胞內氧化還原狀態的關鍵因素,在低氧誘導的HIF-1α表達及轉錄中起重要作用[25]。Rac1促進HIF-1α的表達和轉錄激活,活性氧自由基通過抑制Rac1的表達進而抑制HIF-1的表達[25]。Marfella等[26]研究表明,糖尿病大鼠HIF-1α及Rac1 mRNA表達降低與缺血后梗死面積增加密切相關,而這些效應可以被抗氧化劑谷胱甘肽拮抗。目前,高糖狀態對于HIF-1α的表達影響仍有不同的研究結果,在另外一些研究中,高糖能夠促進細胞中HIF-1α的表達以及穩定性[27,28]?傊,高糖對HIF-1α的影響取決于不同的細胞類型及不同的組織類型。
低氧狀態可以觸發HIF-1α/VEGF在內的一系列代償機制。去乙;(SIRT)是位于HIF-1α上游調控血管新生的因子。缺乏SIRT3表達的內皮細胞,其低氧誘導的血管新生能力顯著降低[29]。高糖狀態下,SIRT1、HIF-1α的表達降低,減低了低氧觸發的代償反應。Mi等[30]以低氧/高糖刺激大鼠腦微血管內皮細胞,模擬糖尿病狀態下的腦微循環障礙,結果表明,低氧及高糖狀態下,腦微血管內皮增殖和遷移顯著減少,二肽基肽酶4抑制劑拮抗低氧/高糖狀態下被抑制的SIRT1、HIF-1α,從而通過SIRT1/HIF-1α/VEGF通路發揮改善腦微循環的作用。
3 、HIF-1與炎癥及氧化應激
白細胞介素8(IL-8)介導血液中的中性粒細胞黏附、聚集、活化并遷移到炎癥部位,參與心血管損傷過程[30,31]。血清IL-8升高可以預測冠狀動脈介入手術后缺血復發,心肌梗死以及心源性死亡等不良心血管事件[31,32,33]。Ockaili等[34]研究表明,在體外,脯氨酸羥化酶抑制劑二甲基草酸甘氨酸上調人冠狀動脈微血管內皮細胞HIF-1的表達,進而增加HO-1表達,降低細胞因子誘導的炎癥細胞對人冠狀動脈微循環內皮細胞的遷移。在體內,脯氨酸羥化酶抑制劑促進缺血心肌HO-1表達,降低血清IL-8水平,減輕缺血再灌注損傷兔模型心肌梗死面積。此外,HIF-1的活化降低缺血后心肌細胞黏附因子的表達,減輕缺血再灌注損傷及梗死面積[35]。在持續低氧狀態下,HIF-1α的活化介導活性氧自由基對心臟微血管內皮的損傷。以siRNA抑制HIF-1α表達后,低氧誘導的活性氧自由基合成以及心臟微血管內皮凋亡顯著降低[36]。
4、 HIF-1與細胞自噬
適度的細胞自噬促進細胞存活,過度的細胞自噬促進細胞凋亡。如前所述,持續低氧觸發細胞死亡,而HIF-1參與細胞死亡信號轉導途徑。有研究表明,低氧通過誘導細胞過度自噬參與人臍靜脈內皮細胞死亡,而低氧誘導的HIF-1的過表達參與低氧觸發的細胞自噬小體形成。以siRNA敲除HIF-1的表達顯著降低自噬小體的形成。此外,LC3在自噬小體的聚集和裂解由HIF-1的過表達而增加,但隨著HIF-1的敲除降低。因此表明,在持續低氧狀態下,HIF-1的過表達可以誘導過度的細胞自噬,從而降低細胞活性[7,13]。
5、 HIF-1相關的微循環障礙治療
Xiao等[37]綜述了在高糖狀態下,以增加被抑制的HIF-1α為靶點的治療方案。二甲基草酸甘氨酸可以增加糖尿病動物的血管新生。此外,去鐵胺可以增加糖尿病缺血組織HIF-1α的轉錄活性以及VEGF表達。Feng等[38]發現金屬硫蛋白可以降低高糖誘導的活性氧自由基的產生,減輕高糖對心肌HIF-1α蛋白表達的抑制。
目前,中醫藥以及植物藥在以HIF-1α為靶點的微循環治療中得到關注。Chen等[39]研究發現,人參皂苷Rg1通過激活磷脂酰肌醇-3-激酶/蛋白激酶B/哺乳動物雷帕霉素靶蛋白信號轉導通路,進而活化HIF-1α和下游的VEGF,促進血管新生。Wang等[40]研究表明,芪藶強心可以通過上調HIF-1α/VEGF信號轉導途徑,增加心臟微血管內皮細胞的增殖以及血管新生能力。Wang等[41]研究發現,滸苔多糖通過上調HIF-1α降低大鼠心肌梗死面積。Dai等[42]報道,芪參益氣滴丸上調HIF-1α表達,進而提高大鼠微血管內皮血管新生能力。白藜蘆醇增加HIF-1α表達,從而改善冠狀動脈微循環功能[43]。
除藥物干預外,目前基礎研究發現基因治療在糖尿病動物中的治療潛能,應用表達HIF-1α活性的復合物(Ad2/HIF-α/VP16)的腺病毒載體促進糖尿病大鼠側支循環發育[24]。一種編碼HIF-1α活性形式的腺病毒可以有效阻斷高糖對VEGF蛋白表達的抑制[44]。Natarajan等[45]研究發現,以siRNA沉默小鼠脯氨酰-4-羥化酶-2表達,可以顯著增加HIF-1的轉錄活性,改善小鼠微血管內皮功能,發揮心臟保護效應。
6、 展望
急性缺血與糖尿病狀態均與低氧狀態誘發的微循環障礙密切相關。HIF-1作為低氧狀態下的適應性調節因子,通過影響血管新生、細胞凋亡、炎癥及氧化應激等多種環節參與微循環功能調節。未來以HIF-1為靶點的治療方式值得期待。
利益沖突所有作者均聲明不存在利益沖突
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