SorLA restricts TNFalpha release from microglia to shape glioma-supportive brain microenvironment
SorLA, encoded by the gene SORL1, is an intracellular sorting receptor of the VPS10P domain receptor gene family. Although SorLA is best recognized for its ability to shuttle target proteins between intracellular compartments in neurons, recent data suggest that also its microglial expression can be of high relevance for the pathogenesis of brain diseases, including glioblastoma (GBM). Here we interrogated the impact of SorLA on the functional properties of glioma-associated microglia and macrophages (GAMs). In the GBM microenvironment, GAMs are re-programmed and in turn lose the ability to elicit anti-tumor responses. Instead, they acquire glioma-supporting phenotype, which is a key mechanism promoting glioma progression. Our analysis of scRNA-seq data from GBM patients revealed that the pro-tumorigenic and pro-inflammatory properties of GAMs are linked to high and low SORL1 expression, respectively. Using cell models, we confirm that SorLA levels are differentially regulated by the presence of glioma cells and by inflammatory cues. We further show that SorLA acts as a sorting receptor for the pro-inflammatory cytokine TNF to restrain its secretion from microglia. As a consequence, loss of SorLA enhanced the pro-inflammatory potential of microglia, having a remarkable impact on glioma progression. In a murine model of glioma, SorLA-deficient mice develop smaller tumors and show hallmarks of anti-tumor response including altered microglia morphology, enhanced necroptosis, and massive neutrophil influx into the tumor parenchyma. Our findings indicate that SorLA is a key player in shaping the phenotype of GAMs, and its depletion can unlock an anti-tumor response. Significance statementOur study provides insight into the mechanisms shaping the tumor microenvironment in glioblastoma (GBM), the most prevalent and aggressive brain malignancy in adults. Poor prognosis in GBM largely results from the properties of the glioma milieu that blocks the anti-tumor response. We show that SorLA restricts release of the pro-inflammatory cytokine TNF from microglia, thereby hampering their anti-glioma response. SorLA depletion reinforces the pro-inflammatory properties of tumor microenvironment and inhibits glioma growth. These findings have significant implications for our understanding of glioma biology, indicating SorLA-TNF interaction as a potential target in GBM therapies. They also offer a new perspective on SorLA activities in microglia which emerge as highly relevant not only for the pathogenesis GBM, but also of other brain diseases such as Alzheimers disease.