SPARCL1 Enrichment at the Glioblastoma Invasive Front Is Consistent with Synaptogenic and Angiogenic Tumor Niches.

Astrocytes regulate key aspects of the neural microenvironment that can be co-opted by cancer to support tumor growth and invasion. Secreted protein acidic and rich in cysteine-like 1 (SPARCL1) is a matricellular glycoprotein expressed by astrocytes and stromal cells, whose expression varies across cancer types. While SPARCL1 is downregulated in many peripheral cancers, reports of its expression in gliomas, specifically glioblastoma (GBM), are inconsistent. The biological context underlying these divergent findings, and the role of SPARCL1 in GBM malignancy, remains unclear. Publicly available transcriptomic datasets from the Ivy Glioblastoma Atlas Project (Ivy GAP), GlioVis, and TCGA were analyzed to evaluate SPARCL1 expression across GBM cohorts. Spatially resolved gene expression data from Ivy GAP were used to assess SPARCL1 expression from defined tumor regions. Microarray and RNA sequencing datasets from GlioVis and TCGA, respectively, were used to assess SPARCL1 expression across whole-tumor samples. Spatial transcriptomics from Ivy GAP show SPARCL1 expression was upregulated along the leading edge and in infiltrating tumor regions. Microarray datasets showed greater SPARCL1 expression in tumors of astrocyte lineage as opposed to oligodendrocyte lineage. Bulk RNA sequencing showed high SPARCL1 expression in low-grade gliomas, which is consistent with astrocytic lineage, IDH mutation, and spatial averaging effects that might obscure regional associations. These findings demonstrate that SPARCL1 expression in GBM is shaped by tumor architecture, molecular classification, and microenvironment interactions. Enrichment of SPARCl1 at invasive tumor margins is consistent with prior studies linking SPARCL1 to neuron-glioma synapse formation and angiogenesis.