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

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.

Grant Number: 5R01DK122986-05
NIH Institute/Center: NIH
Principal Investigator: Subhashini Bolisetty