ITPR1 Maintains Mitochondrial Redox Homeostasis to Drive Glioblastoma Progression Through Recruitment and Activation of DRP1

Background: Glioblastoma (GBM) exhibits marked cellular heterogeneity and resistance to therapy. Calcium (CA²⁺) signaling at endoplasmic reticulum (ER)-mitochondria contact sites has emerged as a key regulator of mitochondrial function and cell fate; however, its lineage-specific role and therapeutic relevance in GBM remain unclear. Methods: ITPR1 expression was analyzed using single-cell and bulk RNA Sequencing (RNA-seq) datasets and validated by immunohistochemistry and survival analyses. Functional studies were conducted using genetic silencing or CRISPR-mediated activation of ITPR1, combined with DRP1 knockdown, CA²⁺ imaging, transmission electron microscopy, co-immunoprecipitation, mitochondrial fractionation, and mitochondrial functional assays. Therapeutic efficacy was evaluated in orthotopic GBM xenograft models treated with 2-aminoethoxydiphenyl borate (2-APB), temozolomide (TMZ), or their combination. Results: ITPR1 was enriched in mesenchymal-like malignant cell states and associated with higher tumor grade, recurrence, and poor prognosis. ITPR1 knockdown suppressed GBM cell proliferation and tumor growth while promoting intrinsic Apoptosis. Mechanistically, loss of ITPR1 impaired ER-to-mitochondria CA²⁺ transfer, disrupted ER-mitochondria contacts, and altered mitochondrial ultrastructure. This was accompanied by reduced DRP1 Ser616 phosphorylation and mitochondrial recruitment, as well as decreased Autophagy and Mitophagy activity. Consequently, ITPR1 knockdown led to mitochondrial depolarization, increased mitochondrial Reactive Oxygen Species (ROS) accumulation, and activation of mitochondria-dependent Apoptosis. Conversely, DRP1 knockdown attenuated the mitochondrial and pro-survival effects induced by ITPR1 overexpression. In vivo, combined treatment with 2-APB and TMZ resulted in greater tumor suppression and prolonged survival compared with either treatment alone, accompanied by increased Apoptosis and reduced proliferation in tumor tissues. Conclusions: ITPR1 promotes GBM progression by sustaining ER-mitochondria CA²⁺ coupling and DRP1-dependent mitochondrial quality control, thereby maintaining mitochondrial homeostasis and cell survival. Targeting inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated CA²⁺ signaling with 2-APB enhances the therapeutic efficacy of TMZ, suggesting that ITPR1-centered CA²⁺ signaling may represent a potential therapeutic vulnerability in aggressive GBM.