1,25D3 reprograms mitochondrial quality control via sirtuin and sensitizes glioblastoma to chemotherapy.

Tumor cells adapt to therapeutic stress by preserving mitochondrial integrity through mitophagy, but excessive mitophagy can overwhelm this adaptative mechanism and precipitate mitochondrial collapse. Here, we demonstrate that 1,25-dihydroxyvitamin D3 (1,25D3) reduces glioblastoma resistance to the standard chemotherapeutic temozolomide by driving mitophagic overload and mitochondrial dysfunction. We identified mitochondrial sirtuin SIRT4 as a key downstream effector of mitochondrial metabolism and quality control triggered by 1,25D3-induced mitochondrial stress. Pharmacological levels of 1,25D3 activate mitophagy by transcriptionally upregulating SIRT4 through vitamin D receptor (VDR) signaling. SIRT4, which is frequently downregulated in glioblastoma, suppresses glioblastoma glutamine metabolism by inhibiting glutamate dehydrogenase activity and limiting α-ketoglutarate availability, thereby integrating metabolic stress with enhanced mitophagy. This VDR-SIRT4 axis shifts mitophagy from a cytoprotective process to a lethal pathway, selectively sensitizing tumor cells while sparing normal astrocytes and brain tissue. By exploiting mitochondrial quality control as a metabolic vulnerability, 1,25D3 enhances chemotherapeutic efficacy and provides a translational rationale for repurposing 1,25D3 in resistant glioblastoma.