Ferritin Functions as a Proinflammatory Cytokine via Iron-Independent Protein Kinase C Zeta/Nuclear Factor KappaB–Regulated Signaling in Rat Hepatic Stellate Cells

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). Conclusions: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.