Department of Medicine, University of Toledo College of Medicine and Life Sciences, Toledo, OH, USA.
Marshall Institute for Interdisciplinary Research, Marshall University, Huntington, WV, USA.
Nephrol Dial Transplant. 2018 Jul 1;33(7):1138-1149. doi: 10.1093/ndt/gfx334.
Recent studies have highlighted a critical role for CD40 in the pathogenesis of renal injury and fibrosis. However, little is currently understood about the regulation of CD40 in this setting.
We use novel Na/K-ATPase cell lines and inhibitors in order to demonstrate the regulatory function of Na/K-ATPase with regards to CD40 expression and function. We utilize 5/6 partial nephrectomy as well as direct infusion of a Na/K-ATPase ligand to demonstrate this mechanism exists in vivo.
We demonstrate that knockdown of the α1 isoform of Na/K-ATPase causes a reduction in CD40 while rescue of the α1 but not the α2 isoform restores CD40 expression in renal epithelial cells. Second, because the major functional difference between α1 and α2 is the ability of α1 to form a functional signaling complex with Src, we examined whether the Na/K-ATPase/Src complex is important for CD40 expression. We show that a gain-of-Src binding α2 mutant restores CD40 expression while loss-of-Src binding α1 reduces CD40 expression. Furthermore, loss of a functional Na/K-ATPase/Src complex also disrupts CD40 signaling. Importantly, we show that use of a specific Na/K-ATPase/Src complex antagonist, pNaKtide, can attenuate cardiotonic steroid (CTS)-induced induction of CD40 expression in vitro.
Because the Na/K-ATPase/Src complex is also a key player in the pathogenesis of renal injury and fibrosis, our new findings suggest that Na/K-ATPase and CD40 may comprise a pro-fibrotic feed-forward loop in the kidney and that pharmacological inhibition of this loop may be useful in the treatment of renal fibrosis.
最近的研究强调了 CD40 在肾损伤和纤维化发病机制中的关键作用。然而，目前对于这种情况下 CD40 的调节知之甚少。
我们使用新型的 Na/K-ATPase 细胞系和抑制剂，以证明 Na/K-ATPase 对 CD40 表达和功能的调节作用。我们利用 5/6 部分肾切除术以及直接输注 Na/K-ATPase 配体，证明了这种机制在体内的存在。
我们证明，Na/K-ATPase 的 α1 同工型的敲低导致 CD40 的减少，而 α1 的挽救而非 α2 的挽救恢复了肾上皮细胞中的 CD40 表达。其次，由于 α1 和 α2 之间的主要功能差异是 α1 形成与Src 功能信号复合物的能力，我们检查了 Na/K-ATPase/Src 复合物是否对 CD40 表达很重要。我们发现，获得 Src 结合的 α2 突变体恢复了 CD40 的表达，而丧失 Src 结合的 α1 降低了 CD40 的表达。此外，丧失功能的 Na/K-ATPase/Src 复合物也破坏了 CD40 信号转导。重要的是，我们发现使用特定的 Na/K-ATPase/Src 复合物拮抗剂 pNaKtide 可以在体外减弱强心甾醇 (CTS)诱导的 CD40 表达。
由于 Na/K-ATPase/Src 复合物也是肾损伤和纤维化发病机制中的关键参与者，我们的新发现表明，Na/K-ATPase 和 CD40 可能在肾脏中构成一个促纤维化的正反馈回路，并且该回路的药理学抑制可能对肾脏纤维化的治疗有用。
