Smith Joshua A, Stallons L Jay, Collier Justin B, Chavin Kenneth D, Schnellmann Rick G
Department of Drug Discovery and Biomedical Sciences (J.A.S., L.J.S., J.B.C., R.G.S.) and Division of Transplant Surgery, Department of Surgery (K.D.C.), Medical University of South Carolina, Charleston, South Carolina ; and Ralph H. Johnson Veterans Administration Medical Center, Charleston, South Carolina (R.G.S.).
Department of Drug Discovery and Biomedical Sciences (J.A.S., L.J.S., J.B.C., R.G.S.) and Division of Transplant Surgery, Department of Surgery (K.D.C.), Medical University of South Carolina, Charleston, South Carolina ; and Ralph H. Johnson Veterans Administration Medical Center, Charleston, South Carolina (R.G.S.)
J Pharmacol Exp Ther. 2015 Feb;352(2):346-57. doi: 10.1124/jpet.114.221085. Epub 2014 Dec 12.
Although disruption of mitochondrial homeostasis and biogenesis (MB) is a widely accepted pathophysiologic feature of sepsis-induced acute kidney injury (AKI), the molecular mechanisms responsible for this phenomenon are unknown. In this study, we examined the signaling pathways responsible for the suppression of MB in a mouse model of lipopolysaccharide (LPS)-induced AKI. Downregulation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a master regulator of MB, was noted at the mRNA level at 3 hours and protein level at 18 hours in the renal cortex, and was associated with loss of renal function after LPS treatment. LPS-mediated suppression of PGC-1α led to reduced expression of downstream regulators of MB and electron transport chain proteins along with a reduction in renal cortical mitochondrial DNA content. Mechanistically, Toll-like receptor 4 (TLR4) knockout mice were protected from renal injury and disruption of MB after LPS exposure. Immunoblot analysis revealed activation of tumor progression locus 2/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (TPL-2/MEK/ERK) signaling in the renal cortex by LPS. Pharmacologic inhibition of MEK/ERK signaling attenuated renal dysfunction and loss of PGC-1α, and was associated with a reduction in proinflammatory cytokine (e.g., tumor necrosis factor-α [TNF-α], interleukin-1β) expression at 3 hours after LPS exposure. Neutralization of TNF-α also blocked PGC-1α suppression, but not renal dysfunction, after LPS-induced AKI. Finally, systemic administration of recombinant tumor necrosis factor-α alone was sufficient to produce AKI and disrupt mitochondrial homeostasis. These findings indicate an important role for the TLR4/MEK/ERK pathway in both LPS-induced renal dysfunction and suppression of MB. TLR4/MEK/ERK/TNF-α signaling may represent a novel therapeutic target to prevent mitochondrial dysfunction and AKI produced by sepsis.
尽管线粒体稳态和生物合成（MB）紊乱是脓毒症诱导的急性肾损伤（AKI）广泛认可的病理生理特征，但导致这一现象的分子机制尚不清楚。在本研究中，我们在脂多糖（LPS）诱导的AKI小鼠模型中研究了负责抑制MB的信号通路。过氧化物酶体增殖物激活受体γ共激活因子-1α（PGC-1α）是MB的主要调节因子，在肾皮质中，其mRNA水平在3小时时下调，蛋白质水平在18小时时下调，且与LPS处理后的肾功能丧失相关。LPS介导的PGC-1α抑制导致MB下游调节因子和电子传递链蛋白表达减少，同时肾皮质线粒体DNA含量降低。机制上，Toll样受体4（TLR4）基因敲除小鼠在LPS暴露后可免受肾损伤和MB破坏。免疫印迹分析显示，LPS可激活肾皮质中的肿瘤进展位点2/丝裂原活化蛋白激酶激酶/细胞外信号调节激酶（TPL-2/MEK/ERK）信号通路。MEK/ERK信号通路的药物抑制减轻了肾功能障碍和PGC-1α的丧失，并与LPS暴露后3小时促炎细胞因子（如肿瘤坏死因子-α [TNF-α]、白细胞介素-1β）表达减少有关。TNF-α的中和也可阻断LPS诱导的AKI后PGC-1α的抑制，但不能阻断肾功能障碍。最后，单独全身给予重组肿瘤坏死因子-α足以产生AKI并破坏线粒体稳态。这些发现表明，TLR4/MEK/ERK通路在LPS诱导的肾功能障碍和MB抑制中起重要作用。TLR4/MEK/ERK/TNF-α信号通路可能是预防脓毒症引起的线粒体功能障碍和AKI的新治疗靶点。
