Functional Significance of Ferritin Light Chain in Sepsis-associated Kidney Injury

脓毒症占重症监护室中急性肾损伤（阿基）的近50%， mortality.然而，脓毒症相关阿基（SA-AKI）的治疗仍然难以捉摸，因为 损伤的病理生理学还不清楚。证据强调了全身性细胞因子的致病作用 风暴和近端肾小管损伤（氧化应激和线粒体功能障碍）。细胞因子 在骨髓细胞（特别是巨噬细胞）中，由NFkB和HIF-1α信号转导介导的应答是一种主要的免疫应答。 脓毒症的致病机制在这种情况下，用铁蛋白轻链（FtL）处理巨噬细胞减少了 脂多糖（LPS）诱导NF κ B和HIF-1α及随后的促炎基因活化 表达（IL-6、TNFα）。另外，向野生型小鼠施用FtL减轻盲肠结扎和穿孔， (CLP)诱发炎症反应。对来自施用以下药物的小鼠的肾细胞群进行单细胞RNA测序： FtL（或生理盐水），然后进行LPS内毒素血症鉴定半胱氨酸蛋白酶抑制剂A（CSTA）是最显著的。 在FtL给药小鼠的骨髓细胞群中，表达上调的基因。CSTA是一种细胞内抑制剂， 组织蛋白酶虽然CSTA在脓毒症中的作用尚不清楚，但组织蛋白酶通过介导炎症反应而增强炎症反应。 NFκB的活化。因此，我们认为FtL通过CSTA-1阻止了炎症反应。 介导的组织蛋白酶和NFκB/HIF-1α信号转导抑制。与肾脏有关，而CLP 导致肾损伤标志物（NGAL和KIM-1）的显著表达，FtL给药阻止了这种表达。 过氧化物酶体增殖物激活受体γ辅激活因子1-α诱导和保留表达 （PGC-1α），线粒体生物发生和代谢的调节剂。近端小管（PT）是 脓毒症期间的最大损伤和FtL在该管段中表达。因此，我们建议确定 巨噬细胞和PT衍生的FtL在脓毒症期间的保护性反应中的不同作用。我们的研究结果是 临床相关，因为血清铁蛋白水平（主要是FtL）在炎症期间通常升高， 其在炎症中作用尚不清楚。我们认为，FtL的增加是一种适应性生理反应， 控制炎症和促进生存。在目的1中，使用两种脓毒症模型（CLP和LPS）， 新的工具删除或过表达FtL，我们将确定FtL是否诱导CSTA表达和抑制 巨噬细胞HIF-1α信号传导，从而防止线粒体功能障碍，糖酵解， 减轻细胞因子的过度产生。在目标2中，我们将确定巨噬细胞的不同功能作用， vs. PT特异性FtL表达在减轻肾功能丧失、肾脏炎症、氧化应激和 线粒体功能障碍使用体外和体内模型的综合方法，我们将确定 脓毒症期间FtL的功能。如果我们的假设得到验证，结果将证明开发一种新的 SA-AKI的治疗可以减轻脓毒症诱导的发病率、死亡率和 大量的医疗保健支出。

Sepsis accounts for nearly 50% of acute kidney injury (AKI) in the intensive care unit and significantly impacts mortality. However, therapy for sepsis-associated AKI (SA-AKI) has remained elusive because the pathophysiology of injury is not well understood. Evidence emphasizes the pathogenic role of systemic cytokine storm and proximal tubular damage (oxidative stress and mitochondrial dysfunction) in SA-AKI. The cytokine response, mediated by NFkB and HIF-1α signaling in myeloid cells (particularly, macrophages) is a dominant pathogenic mechanism in sepsis. In this context, treatment of macrophages with ferritin light chain (FtL) reduces lipopolysaccharide (LPS)-induced activation of NFkB and HIF-1α and subsequent pro-inflammatory gene expression (IL-6, TNFα). Additionally, administration of FtL to wildtype mice mitigates cecal ligation and puncture (CLP) induced hyperinflammation. Single cell RNA sequencing on renal cell populations from mice administered FtL (or saline) and then subjected to LPS endotoxemia identified cystatin A (CSTA) as the most significantly upregulated gene in the myeloid populations of FtL administered mice. CSTA is an intracellular inhibitor of cathepsins. While the role of CSTA in sepsis is unknown, cathepsins augment the inflammatory response via activation of NFκB. Therefore, we propose that FtL prevents the hyperinflammatory response via CSTA- mediated inhibition of cathepsin and NFκB/HIF-1α signaling during sepsis. Pertinent to the kidney, while CLP led to marked expression of kidney injury markers (NGAL and KIM-1), FtL administration prevented such induction and preserved expression of peroxisome proliferator-activated receptor gamma coactivator 1- alpha (PGC-1α), a regulator of mitochondrial biogenesis and metabolism. Proximal tubules (PT) are the sites of maximal injury during sepsis and FtL is expressed in this tubular segment. Thus, we propose to determine the disparate roles of macrophage- and PT-derived FtL in the protective response during sepsis. Our findings are clinically relevant because serum ferritin levels (predominantly FtL) are often elevated during inflammation but its role in inflammation is unknown. We propose that an increase in FtL is an adaptive physiological response to control inflammation and promote survival. In Aim 1, using two models of sepsis (CLP and LPS) combined with novel tools to delete or overexpress FtL, we will determine whether FtL induces CSTA expression and inhibits macrophage HIF-1α signaling, thereby preventing mitochondrial dysfunction, glycolysis and subsequently mitigating overproduction of cytokines. In Aim 2, we will determine the distinct functional roles of macrophage vs. PT-specific FtL expression in mitigating loss of kidney function, renal inflammation, oxidative stress and mitochondrial dysfunction. Using an integrative approach of in vitro and in vivo models, we will determine the function of FtL during sepsis. If our hypothesis is validated, the results will justify the development of a new treatment for SA-AKI that could alleviate the significant burden of sepsis induced morbidity, mortality and substantial health care expenditures.