Leptomeningeal anastomoses or pial collateral arteries are crucial for restoring cerebral blood flow (CBF) after an ischemic stroke. Vascular smooth muscle cells (VSMCs) are hypothesized to regulate the extent of this adaptive response, while the specific molecular mechanisms underlying this process are still being investigated. SNHG12, a long non-coding RNA, has been shown to influence several diseases related angiogenesis, including osteosarcoma and gastric cancer. However, the role of SNHG12 in contractile VSMC dedifferentiation during collateral arteriogenesis-related strokes remains unclear. Here we demonstrated that SNHG12 is a positive regulator of MMP9 and VSMC dedifferentiation, which enhances pial collateral arteriogenesis following cerebrovascular occlusion. Pial collateral remodeling is limited by the crosstalk between SNHG12-MMP9 signaling in VSMCs, which is mediated through repulsive guidance molecule a (RGMa) regulation. Thus, targeting SNHG12 may represent a therapeutic strategy for improving collateral function, neural tissue health, and functional recovery following ischemic stroke.