We observed that recombinant ciliary neurotrophic factor (CNTF) enhanced survival and neurite outgrowth of cultured adult
rat dorsal root ganglion (DRG) neurons. Among other neurotrophic factors (NGF and GDNF) and interleukin (IL)-6 cytokine members
[IL-6, LIF, cardiotrophin-1, and oncostatin M (OSM)] at the same concentration (50 ng/ml), CNTF, as well as LIF and OSM, displayed
high efficacy for the promotion of the number of viable neurons and neurite-bearing cells. CNTF enhanced the number of neurite-bearing
cells in both small neurons (soma diameter <30 μm) and large neurons (soma diameter ≥30 μm), whereas NGF and GDNF promoted
that in only small neurons. Western blot analysis revealed that CNTF induced phosphorylation of STAT3, Akt, and ERK1/2 in
the neurons. Furthermore, the neurite outgrowth-promoting activity of CNTF was diminished by co-treatment with Janus kinase
(JAK) 2 inhibitor, AG490; STAT3 inhibitor, STA-21; phosphatidyl inositol-3′-phosphate-kinase (PI3K) inhibitor, LY294002; and
mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, in a concentration-dependent manner. Its survival-promoting
activity was also affected by AG490, STA-21, and LY294002 at higher concentrations, but not by PD98059. These findings suggest
the involvement of JAK2/STAT3, PI3K/Akt, and MEK/ERK signaling pathways in CNTF-induced neurite outgrowth, where the former
two pathways are thought to play major roles in mediating the survival response of neurons to CNTF.
Keywords CNTF - Mature DRG neurons - Survival - Neurite outgrowth - gp130-mediated signaling pathways