Sonic hedgehog regulates ischemia/hypoxia-induced neural progenitor proliferation.
OBJECTIVE
Sonic hedgehog (Shh) protein is required for the maintenance of neural progenitor cells (NPCs) in the embryonic and adult hippocampus. Brain ischemia causes increased proliferation of hippocampal NPCs. We therefore examined whether Shh regulates the increase in proliferation of NPCs after ischemia/hypoxia.


METHODS
Male SV129 mice were exposed to a 20-minute middle cerebral artery occlusion; hippocampi were then analyzed for Shh mRNA and protein expression by real-time polymerase chain reaction, immunoblot, and immunohistochemistry. Primary cell cultures of neurons, astrocytes, and NPCs were exposed to 16 hours of hypoxia (1% O(2)) and analyzed by real-time polymerase chain reaction and immunoblot for Shh expression. Proliferation of NPCs, in vivo and in vitro, was measured by bromodeoxyuridine incorporation.


RESULTS
Among the cell types examined in vitro, only NPC and neurons increased Shh mRNA under hypoxic conditions. Furthermore, hypoxia increased proliferation of NPCs and this proliferation was enhanced by the addition of recombinant Shh or blocked by the pathway-specific inhibitor, cyclopamine. Middle cerebral artery occlusion was associated with a transient 2-fold increase in the mRNA encoding both Shh and its transcription factor, Gli1, 0.5 days after ischemia. Within the hippocampus, Shh protein was increased approximately 3-fold 3 and 7 days after ischemia and was observed predominantly within cells in the CA3 and hilar regions. Shh was expressed only in mature neurons. In vivo, cyclopamine suppressed ischemia-induced proliferation of subgranular NPCs.


CONCLUSIONS
The Shh pathway plays a role in the proliferation of NPCs induced by ischemia/hypoxia and might participate in injury remodeling.
Sims
John R
JR
Department of Radiology and Neuroscience Center, Harvard Medical School, Massachusetts General Hospital, Stroke and Neurovascular Regulation Laboratory, Charlestown, Mass 02129, USA. jsims@partners.org
Lee
Sae-Won
SW
Topalkara
Kamil
K
Qiu
Jianhua
J
Xu
Jian
J
Zhou
Zhipeng
Z
Moskowitz
Michael A
MA
D000818:Animals; D049109:Cell Proliferation; D002478:Cells, Cultured; D053823:Hedgehog Proteins / Q000502:physiology*; D020925:Hypoxia-Ischemia, Brain / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D051379:Mice; D009434:Neural Pathways / Q000473:pathology / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000473:pathology*; D015398:Signal Transduction / Q000502:physiology*; D013234:Stem Cells / Q000473:pathology*
D053823:Hedgehog Proteins