P2X7 signaling promotes microsphere embolism-triggered microglia activation by maintaining elevation of Fas ligand.
BACKGROUND
The cerebral microvascular occlusion elicits microvascular injury which mimics the different degrees of stroke severity observed in patients, but the mechanisms underlying these embolic injuries are far from understood. The Fas ligand (FasL)-Fas system has been implicated in a number of pathogenic states. Here, we examined the contribution of microglia-derived FasL to brain inflammatory injury, with a focus on the potential to suppress the FasL increase by inhibition of the P2X(7)-FasL signaling with pharmacological or genetic approaches during ischemia.


METHODS
The cerebral microvascular occlusion was induced by microsphere injection in experimental animals. Morphological changes in microglial cells were studied immunohistochemically. The biochemical analyses were used to examine the intracellular changes of P2X(7)/FasL signaling. The BV-2 cells and primary microglia from mice genetically deficient in P2X(7) were used to further establish a linkage between microglia activation and FasL overproduction.


RESULTS
The FasL expression was continuously elevated and was spatiotemporally related to microglia activation following microsphere embolism. Notably, P2X(7) expression concomitantly increased in microglia and presented a distribution pattern that was similar to that of FasL in ED1-positive cells at pathological process of microsphere embolism. Interestingly, FasL generation in cultured microglia cells subjected to oxygen-glucose deprivation-treated neuron-conditioned medium was prevented by the silencing of P2X(7). Furthermore, FasL induced the migration of BV-2 microglia, whereas the neutralization of FasL with a blocking antibody was highly effective in inhibiting ischemia-induced microglial mobility. Similar results were observed in primary microglia from wild-type mice or mice genetically deficient in P2X(7). Finally, the degrees of FasL overproduction and neuronal death were consistently reduced in P2X(7)(-/-) mice compared with wild-type littermates following microsphere embolism insult.


CONCLUSIONS
FasL functions as a key component of an immunoreactive response loop by recruiting microglia to the lesion sites through a P2X(7)-dependent mechanism. The specific modulation of P2X(7)/FasL signaling and aberrant microglial activation could provide therapeutic benefits in acute and subacute phase of cerebral microembolic injury.
Department of Neurobiology, Key Laboratory of Medical Neurobiology of Ministry of Health of China, Zhejiang University School of Medicine, Hangzhou, China.
Ying-mei
YM
Lu
Rong-rong
RR
Tao
Ji-yun
JY
Huang
Li-tao
LT
Li
Mei-hua
MH
Liao
Xiao-ming
XM
Li
Kohji
K
Fukunaga
Ze-Hui
ZH
Hong
Feng
F
Han
D000818:Animals; D016923:Cell Death; D002478:Cells, Cultured; D053222:Fas Ligand Protein / Q000096:biosynthesis* / Q000378:metabolism; D020766:Intracranial Embolism / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism*; D008863:Microspheres; D051381:Rats; D017208:Rats, Wistar; D058486:Receptors, Purinergic P2X7 / Q000502:physiology*
D053222:Fas Ligand Protein; D058486:Receptors, Purinergic P2X7