Necroptotic astrocytes contribute to maintaining stemness of disseminated medulloblastoma through CCL2 secretion

BACKGROUND: Medulloblastoma (MB) with metastases at diagnosis and recurrence correlates with poor prognosis. Unfortunately, the molecular mechanism underlying metastases growth has received less attention than primary therapy-naive MB. Though astrocytes have been frequently detected in brain tumors, their roles in regulating the stemness properties of MB stem-like cells (MBSCs) in disseminated lesions remain elusive. METHODS: Effects of tumor-associated astrocytes (TAA)-secreted CCL2 on MBSCs self-renewal was determined by immunostaining analysis. Necroptosis of TAA was examined by measuring necrosome activity. Alterations in Notch signaling were examined after inhibition of CCL2. Progression of MBSCs-derived tumors was evaluated after pharmaceutical blockage of necroptosis. RESULTS: TAA, as the essential components of disseminated tumor, produced high level of CCL2 to shape inflammation microenvironment, which stimulated the enrichment of MBSCs in disseminated MB. In particular, CCL2 played a pivotal role in maintaining stem-like properties via JAK2/STAT3 mediated activation of Notch signaling. Loss of CCL2/CCR2 function repressed JAK2/STAT3-Notch pathway and impaired MBSCs proliferation, leading to a dramatic reduction of stemness, tumorigenicity and metastasizing capability. Furthermore, necroptosis-induced CCL2 release depended on RIP1/RIP3/MLKL activation in TAA, which promoted the oncogenic phenotype. Blockade of necroptosis resulted in CCL2 deprivation and compromised MBSCs self-proliferation, indicating MBSCs outsourced CCL2 from necroptotic TAA. Finally, CCL2 was upregulated in high-risk stages of MB, further supporting its value as a prognostic indicator. CONCLUSION: These findings highlighted the critical role of CCL2/CCR2 in Notch signaling activation in MBSCs, and revealed a necroptosis-associated glial cytokine microenvironment driving stemness maintenance in disseminations.