HIF-1α/Netrin-4 Axis Mediates RIPC-Induced Angiogenesis and Neurogenesis After Ischemic Stroke

Area of Science:

• Neuroscience
• Vascular Biology
• Regenerative Medicine

Background:

• Remote ischemic postconditioning (RIPC) shows neuroprotective potential in ischemic stroke.
• The exact molecular pathways of RIPC's reparative effects, including angiogenesis and neurogenesis, are not fully understood.
• Netrin-4 (NTN4) and Hypoxia-Inducible Factor 1α (HIF-1α) are implicated in cellular repair mechanisms.

Purpose of the Study:

• To investigate the role of Netrin-4 (NTN4) and its regulator Hypoxia-Inducible Factor 1α (HIF-1α) in mediating the neuroprotective effects of RIPC.
• To elucidate the molecular mechanisms by which RIPC promotes brain repair via the NTN4/HIF-1α axis.

Main Methods:

• Utilized endothelial-specific Ntn4 knockout (KO) mice subjected to middle cerebral artery occlusion (MCAO) and RIPC.
• Conducted in vitro assays with brain microvascular endothelial cells (BMECs) and neural stem cells (NSCs).
• Performed molecular interaction analyses, including DNA pull-down and chromatin immunoprecipitation (ChIP).

Main Results:

• RIPC significantly upregulated NTN4 expression in the ischemic penumbra of MCAO mice.
• Endothelial-specific Ntn4 knockout abolished RIPC's protective effects, impairing neurological recovery, angiogenesis, and neurogenesis.
• NTN4 promoted BMEC proliferation and tube formation via integrin β1-PI3K/AKT; enhanced NSC neuronal differentiation via integrin β1-MAPK/ERK.
• RIPC stabilized HIF-1α, which directly bound the Ntn4 promoter to drive its transcription.

Conclusions:

• RIPC orchestrates brain repair by stabilizing HIF-1α, which transcriptionally activates endothelial NTN4.
• Endothelial NTN4 signals through integrin β1 to activate parallel PI3K/AKT and MAPK/ERK pathways, driving angiogenesis and neurogenesis.
• The HIF-1α/NTN4 axis represents a key therapeutic target for stroke treatment.