Ferritin functions as a proinflammatory cytokine via iron‐independent protein kinase C zeta/nuclear factor kappaB–regulated signaling in rat hepatic stellate cells†

TLDR

Ferritin levels rise with chronic liver inflammation, and although H‑ferritin has immunomodulatory effects, its role in hepatic stellate cell activation and fibrogenesis remains unclear. The authors hypothesize that ferritin functions as a cytokine that regulates proinflammatory activity in hepatic stellate cells via NF‑κB signaling. They treated hepatic stellate cells with tissue ferritin, apoferritin, recombinant H‑ and L‑ferritins to compare iron‑dependent versus iron‑independent effects and examined signaling through the proposed Tim‑2 receptor, PI3K, PKCζ, and MAPK pathways. Ferritin activates an iron‑independent cascade involving Tim‑2‑independent PI3K phosphorylation, PKCζ, and p44/p42 MAPK, leading to NF‑κB activation and upregulation of IL‑1β, iNOS, RANTES, IkappaBα, and ICAM‑1, establishing ferritin as a proinflammatory mediator in hepatic stellate cells and implicating it in liver fibrogenesis.

Abstract

Circulating ferritin levels reflect body iron stores and are elevated with inflammation in chronic liver injury. H-ferritin exhibits a number of extrahepatic immunomodulatory properties, although its role in hepatic inflammation and fibrogenesis is unknown. Hepatic stellate cells respond to liver injury through production of proinflammatory mediators that drive fibrogenesis. A specific receptor for ferritin has been demonstrated on activated hepatic stellate cells, although its identity and its role in stellate cell activation is unclear. We propose that ferritin acts as a cytokine regulating proinflammatory function via nuclear factor kappaB (NF-kappaB)-regulated signaling in hepatic stellate cell biology. Hepatic stellate cells were treated with tissue ferritin and iron-free apoferritin, recombinant H-ferritins and L-ferritins, to assess the role of ferritin versus ferritin-bound iron in the production of proinflammatory mediators of fibrogenesis, and to determine whether signaling pathways act via a proposed H-ferritin endocytosis receptor, T cell immunoglobulin-domain and mucin-domain 2 (Tim-2). This study demonstrated that ferritin activates an iron-independent signaling cascade, involving Tim-2 independent phosphoinositide 3 (PI3)-kinase phosphorylation, protein kinase C zeta (PKCzeta) and p44/p42-mitogen-activated protein kinase, resulting in p50/p65-NF-kappaB activation and markedly enhanced expression of hepatic proinflammatory mediators interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS), regulated on activation normal T cell expressed and secreted (RANTES), inhibitor of kappa Balpha (IkappaBalpha), and intercellular adhesion molecule 1 (ICAM1). This study has defined the role of ferritin as a proinflammatory mediator of hepatic stellate cell biology acting through the NF-kappaB signaling pathway, and suggests a potential role in the inflammatory processes associated with hepatic fibrogenesis.