Department of Internal Medicine, The University of Texas Medical Branch, Galveston, 77555-0562, USA.
Am J Physiol Renal Physiol. 2010 Sep;299(3):F536-44. doi: 10.1152/ajprenal.00108.2010. Epub 2010 Jun 16.
Bacterial infection and sepsis are associated with renal tubule dysfunction and dysregulation of systemic electrolyte balance but the underlying mechanisms are incompletely understood. Recently, we demonstrated that HCO(3)(-) absorption by the medullary thick ascending limb (MTAL) is inhibited by gram-negative bacterial LPS through activation of Toll-like receptor 4 (TLR4). Here, we examined whether MTAL transport is altered by activation of TLR2, the receptor predominantly responsible for recognizing gram-positive bacteria. Confocal immunofluorescence showed expression of TLR2 in the basolateral membrane domain of rat and mouse MTALs. The functional role of TLR2 was examined in perfused MTALs using Pam(3)CSK(4), a bacterial lipoprotein analog that specifically activates TLR2. Adding Pam(3)CSK(4) to the bath decreased HCO(3)(-) absorption by 25%. The inhibition by Pam(3)CSK(4) was eliminated in MTALs from TLR2(-/-) mice. HCO(3)(-) absorption was also inhibited by the TLR2 agonists lipoteichoic acid and peptidoglycan, two cell wall components of gram-positive bacteria. The MEK/ERK inhibitor U0126 eliminated inhibition of HCO(3)(-) absorption by bath LPS but had no effect on inhibition by Pam(3)CSK(4). The inhibition by Pam(3)CSK(4) was eliminated by the protein kinase C inhibitors chelerythrine Cl and bisindolylmaleimide. Moreover, the inhibition by Pam(3)CSK(4), lipoteichoic acid, and peptidoglycan was additive to inhibition by LPS. Thus, agonists of basolateral TLR2 and TLR4 inhibit HCO(3)(-) absorption independently through distinct signaling pathways. We conclude that bacterial components act directly through TLRs to modify the transport function of renal tubules. During polymicrobial sepsis, gram-positive bacterial molecules acting through TLR2 and gram-negative LPS acting through TLR4 can function through parallel signaling pathways to impair MTAL transport. The inhibition of luminal acidification may impair the ability of the kidneys to correct systemic acidosis that contributes to sepsis pathogenesis.
细菌感染和败血症与肾小管功能障碍和全身电解质平衡失调有关，但潜在机制尚不完全清楚。最近，我们证明，革兰氏阴性细菌 LPS 通过激活 Toll 样受体 4 (TLR4) 抑制髓质厚升支 (MTAL) 的 HCO3(-)吸收。在这里，我们检查了 TLR2 的激活是否会改变 MTAL 的转运，TLR2 是主要负责识别革兰氏阳性细菌的受体。共聚焦免疫荧光显示 TLR2 在大鼠和小鼠 MTAL 的基底外侧膜域表达。使用 Pam(3)CSK(4)（一种专门激活 TLR2 的细菌脂蛋白类似物）在灌流 MTAL 中检查 TLR2 的功能作用。向浴中添加 Pam(3)CSK(4)可使 HCO3(-)吸收减少 25%。TLR2(-/-) 小鼠的 MTAL 中消除了 Pam(3)CSK(4)的抑制作用。TLR2 激动剂脂磷壁酸和肽聚糖（革兰氏阳性菌细胞壁的两个组成部分）也抑制 HCO3(-)吸收。MEK/ERK 抑制剂 U0126 消除了浴中 LPS 对 HCO3(-)吸收的抑制作用，但对 Pam(3)CSK(4)的抑制作用没有影响。Pam(3)CSK(4)的抑制作用被蛋白激酶 C 抑制剂 Chelerythrine Cl 和 Bisindolylmaleimide 消除。此外，Pam(3)CSK(4)、脂磷壁酸和肽聚糖的抑制作用与 LPS 的抑制作用相加。因此，TLR2 和 TLR4 的激动剂通过不同的信号通路独立抑制 HCO3(-)吸收。我们得出结论，细菌成分通过 TLR 直接作用来改变肾脏小管的转运功能。在多微生物败血症中，通过 TLR2 作用的革兰氏阳性细菌分子和通过 TLR4 作用的革兰氏阴性 LPS 可以通过平行的信号通路起作用，从而损害 MTAL 转运。管腔酸化的抑制可能会损害肾脏纠正全身酸中毒的能力，而全身酸中毒有助于败血症的发病机制。
