Neuroprotective and immunomodulatory effects of leukemia inhibitory factor during neuroinflammatory responses in multiple sclerosis

Abstract

Leukemia inhibitory factor (LIF) is produced by infiltrating immune cells and glial cells during auto-immune and injury responses in the central nervous system (CNS). During these responses, LIF promotes survival of glial cells and neurons. While studies indicate that LIF has immunomodulatory potential, data on underlying events are lacking. Objective: (1) Study mechanisms of LIF-mediated protection of oligodendrocytes (OLG). (2) Determine the effect of LIF on macrophage function. Methods: LIF mediated effects were studied in primary rat OLG and macrophage cultures. Cell viability was measured by Annexin V/PI. Activation of signalling pathways was analyzed by Western blotting and RPA. Myelin phagocytosis was determined using DiI-labelled myelin and flow cytometry. Results: We show that LIF protects OLG selectively against the synergistic insult of the proinflammatory cytokines IFN-γ and TNF-α, while it does not protect against oxidative stress nor against staurosporine induced apoptosis. We further demonstrate that LIF protection is independent of suppressors of cytokine signalling and Bcl-2 mRNA expression levels. Our results indicate that LIF induces a shift in the cellular machinery towards a pro-survival execution program, illustrated by an enhanced expression of isoforms of the anti-apoptopic molecule 14-3-3 and an activation of the Jak/STAT3 and the phosphatidylinositol 3 kinase/Akt pathways. We further demonstrate that LIF modulates macrophage function by inhibiting the production of oxygen radicals and TNF-α, both mediators of CNS injury in neuroinflammatory diseases such as multiple sclerosis (MS). We show that LIF plays a role in myelin phagocytosis as it stimulates myelin uptake by macrophages. These effects of LIF on macrophage function are accompanied by activation of the JAK/STAT3 signalling pathway, without affecting AKT and ERK activation. Conclusions: These results demonstrate that LIF has both neuroprotective and anti-inflammatory properties and enhances myelin clearance, implicating it is an important factor in lesion modulation in immune mediated demyelinating diseases such as MS.