基質金屬蛋白酶-2/-9在弓形蟲症致病過程之角色

先天性弓形蟲症（toxoplasmosis）的致病機轉主要是寄生蟲會通過胎盤的障壁感染胎兒。我們的研究分析26個臍帶血清，其中20個臍帶血清來自待產婦呈現抗弓形蟲免疫球蛋白 G (immunoglobulin G, IgG）抗體陽性反應，6個臍帶血清來自待產婦呈現抗弓形蟲免疫球蛋白 M（immunoglobulin M, IgM）抗體陽性反應（IgG低親和性）。經過免疫檢測，20個臍帶血清檢體中有18個呈現抗弓形蟲IgG抗體陽性反應，而抗弓形蟲IgM抗體檢測則全部呈現陰性反應，另外，6個臍帶血清檢體對弓形蟲IgG抗體全部呈現陰性反應，而其中3個臍帶血清檢體呈現抗弓形蟲IgM抗體陽性反應。進一步分析弓形蟲感染待產婦及胎兒的血清，結果顯示基質金屬蛋白酶（matrix metalloproteinase, MMP）-2及MMP-9明顯增加，且MMP-2及MMP-9蛋白可與纖維連結蛋白（fibronectin）互相作用，由這些結果我們推論MMP-2及MMP-9兩種酵素有參與纖維連結蛋白的降解及胎盤障壁功能喪失之過程，導致弓形蟲通過胎盤的障壁感染胎兒。我們進一步利用弓形蟲速殖子（tachyzoite）感染肥大細胞（mast cell）的細胞模式探討細胞外訊號調節激酶1/2（extracellular signal-regulated kinases 1/2, Erk1/2）、核轉錄因子-kappa B（nuclear factor-kappa B, NF-κB）、MMP-2和MMP-9之間的相關性。弓形蟲感染時肥大細胞的脫顆粒（degranulation）現象明顯增加。磷酸化（phosphorylated, p-）的Erk1/2及NF-κB在弓形蟲感染肥大細胞時明顯增加。以Erk激酶的抑制劑PD98059處理明顯降低p-Erk1/2、p-NF-κB、MMP-2和MMP-9的表現。以NF-κB間接抑制劑MG132處理，p-IκBα、p-NF-κB、MMP-2和MMP-9的表現也會顯著的減少。綜合上述實驗結果，抑制Erk1/2-NF-κB訊息傳遞路徑會降低MMP-2和MMP-9的酵素活性，進而控制弓形蟲的早期感染，由此可知肥大細胞產生MMP-2和MMP-9受到Erk1/2/NF-κB訊息傳遞作用所調節，阻斷此訊息傳遞路徑應可以做為宿主對抗弓形蟲症的策略。

It has been suggested that in congenital toxoplasmosis the parasite reaches the fetus by crossing the placental barrier. We studied 26 umbilical cord sera, 20 and 6 were derived from gravidas seropositive for anti-T. gondii IgG and seropositive for anti-T. gondii IgM (low IgG avidity), respectively. Eighteen of 20 cord blood samples were seropositive for T. gondii IgG, whereas all cord blood samples seronegative for T. gondii IgM. The other 6 sera were seronegative for T. gondii IgG, whereas 3 of 6 sera were seropositive for T. gondii IgM. Furthermore, T. gondii induced an increase in MMP-2 and -9 secretion in the sera of gravidas and umbilical cords. Moreover, MMP-2 and -9 were interacted with fibronectin. We propose that MMP-2 and -9 may be involved in ECM degradation and placental barrier dysfunction, which facilitates T. gondii transmission to the fetus. Further, we used mast cells infected with T. gondii as a cell model to investigate the associations among extracellular signal-regulated kinase (Erk)1/2, nuclear factor (NF)-κB, MMP-2, and MMP-9 in mast cells infected with T. gondii tachyzoites. Degranulation of mast cells was elevated markedly in T. gondii infection. Phosphorylated (p)-Erk1/2 and p-NF-κB were increased significantly in mast cells infected with T. gondii. Pretreatment with the Erk kinase inhibitor PD98059 significantly decreased the expression of p-Erk1/2, p-NF-κB, MMP-2, and MMP-9. Also, treatment with MG132, an indirect NF-κB inhibitor, effectively reduced p-IκBα, p-NF-κB, MMP-2, and MMP-9 expression. Collectively, our data demonstrated that suppression of an Erk1/2 / NF-κB signaling pathway caused a reduction in MMP-2 and -9 activities. Inhibiting this signaling pathway for MMP-2 and MMP-9 expression might offer a potential way to control early T. gondii infection. This pathway for the generation of MMP-2 and MMP-9 is important for mast cell secretion, and the Erk1/2 / NF-κB signaling pathway may be key in MMP-2 and MMP-9 production in host defenses against toxoplasmosis.