Chemotactic effect of ciliary neurotrophic factor on macrophages in retinal ganglion cell survival and axonal regeneration.
OBJECTIVE
To examine whether ciliary neurotrophic factor (CNTF) has a chemotactic effect on macrophages and whether macrophages are involved in CNTF-induced retinal ganglion cell (RGC) survival and axonal regeneration after optic nerve (ON) injury.


METHODS
Adult Fischer 344 rats received an autologous peripheral nerve graft onto transected ON for injured axons to grow. CNTF was applied intravitreally. When needed, clodronate liposomes were applied intravitreally or intravenously to deplete macrophages in the eye. A chemotaxis microchamber system was used to examine whether CNTF has a chemotactic effect on macrophages in vitro, whereas immunohistochemistry was used to identify the location of macrophages/microglia in the retina. The effects of CNTF on RGC neurite outgrowth and macrophage/microglia proliferation were tested in retinal explants.


RESULTS
Intravitreal CNTF significantly enhanced RGC survival and axonal regeneration as well as the number of macrophages in the eye. Removal of macrophages significantly reduced CNTF-induced RGC survival and axon regeneration. A chemotaxis assay showed a clear chemotactic effect of CNTF on blood-derived but not peritoneal macrophages. Immunohistochemistry revealed that local microglia was located in a region from the nerve fiber layer (NFL) to the inner nuclear layer, whereas blood-derived macrophages were in the NFL. In vitro experiments revealed that CNTF did not enhance neurite outgrowth or macrophage/microglia proliferation in retinal explants.


CONCLUSIONS
CNTF is a chemoattractant but not a proliferation enhancer for blood-derived macrophages, and blood-borne macrophages recruited into the eye by CNTF participate in RGC protection. This finding thus adds an important category to the existing understanding of the biological actions of CNTF.
Cen
Ling-Ping
LP
Joint Shantou International Eye Center of Shantou University and The Chinese University of Hong Kong, Shantou University Medical College, Shantou, Peoples Republic of China.
Luo
Jian-Min
JM
Zhang
Cheng-Wu
CW
Fan
You-Ming
YM
Song
Yue
Y
So
Kwok-Fai
KF
van Rooijen
Nico
N
Pang
Chi Pui
CP
Lam
Dennis S C
DS
Cui
Qi
Q
D000818:Animals; D001369:Axons / Q000502:physiology*; D001973:Bromodeoxyuridine / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000502:physiology; D002630:Chemotactic Factors / Q000494:pharmacology*; D002633:Chemotaxis / Q000187:drug effects; D020934:Ciliary Neurotrophic Factor / Q000494:pharmacology*; D008264:Macrophages / Q000502:physiology*; D009416:Nerve Regeneration / Q000502:physiology*; D009900:Optic Nerve / Q000502:physiology; D020221:Optic Nerve Injuries / Q000503:physiopathology; D051381:Rats; D011916:Rats, Inbred F344; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000502:physiology
D002630:Chemotactic Factors; D020934:Ciliary Neurotrophic Factor; D001973:Bromodeoxyuridine