Expression and localization of hepcidin in macrophages: a role in host defense against tuberculosis

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Hepcidin is a liver-produced antimicrobial peptide regulating iron homeostasis.
• It degrades ferroportin 1, controlling iron absorption and release.
• Its role in macrophage response to intracellular pathogens was previously unclear.

Purpose of the Study:

• To investigate hepcidin expression and function in macrophages infected with Mycobacterium avium and Mycobacterium tuberculosis.
• To determine if hepcidin exhibits direct antimicrobial activity against mycobacteria.

Main Methods:

• Macrophage cell lines (RAW264.7, THP-1) and primary bone marrow-derived macrophages were infected with mycobacteria.
• Hepcidin expression (mRNA and protein) was analyzed following stimulation with mycobacteria, IFN-gamma, IL-6, and IL-1beta.
• Iron loading and chelation effects on hepcidin expression were assessed.
• Hepcidin localization was visualized using confocal microscopy.
• Antimycobacterial activity of hepcidin was evaluated in vitro.

Main Results:

• Mycobacteria and IFN-gamma synergistically induced high levels of hepcidin mRNA and protein in macrophages.
• IL-6 and IL-1beta did not induce hepcidin expression.
• Iron loading inhibited IFN-gamma/M. avium-induced hepcidin, while iron chelation increased it.
• Hepcidin localized to mycobacteria-containing phagosomes in infected, IFN-gamma-activated cells.
• Hepcidin inhibited Mycobacterium tuberculosis growth in vitro and caused structural damage.

Conclusions:

• Hepcidin is expressed in macrophages upon infection with Mycobacterium species, particularly in response to IFN-gamma.
• Hepcidin localizes to phagosomes containing mycobacteria within infected cells.
• Hepcidin possesses direct antimycobacterial activity, inhibiting growth and causing structural damage to Mycobacterium tuberculosis.