Single-cell RNA sequencing reveals functional heterogeneity and sex differences of glioma-associated brain macrophages

Abstract

13Brain resident and infiltrating innate immune cells adapt a tumor-supportive phenotype in the 14 glioma microenvironment. Flow cytometry analysis supported by a single-cell RNA 15 sequencing study of human gliomas indicate considerable cell type heterogeneity. It remains 16 disputable whether microglia and infiltrating macrophages have the same or distinct roles in 17 supporting glioma progression. Here, we performed single-cell transcriptomics analyses of 18 CD11b+ cells sorted from murine syngeneic gliomas, indicating distinct activity of microglia, 19 infiltrating monocytes/macrophages and CNS border-associated macrophages. Our results 20 demonstrate a previously immeasurable scale of molecular heterogeneity in the innate 21 immune response in gliomas. We identified genes differentially expressed in activated 22 microglia from glioma-bearing mice of different sex, and profound overexpression of the 23 MHCII genes by male microglial cells, which we also observed in bulk human glioma 24 samples. Sex-specific gene expression in microglia in the glioma microenvironment may be 25 relevant to sex differences in incidence and outcomes of glioblastoma patients. 26 27 3 28 Introduction 29 Infiltrating immune system cells represent an abundant non-malignant component of the 30tumor microenvironment (TME). These cells play a pivotal role in tumor progression and 31 modulation of tumor responses to therapy 1 . A high number of macrophages within TME have 32 been associated with a poor prognosis in many cancers because those tumor-educated cells 33 suppress anti-tumor immunity, stimulate angiogenesis, and promote tumor invasion 2 . 34The central nervous system (CNS) is equipped with resident innate immune cells-microglia 35 and CNS border-associated macrophages (BAMs)-consisting of perivascular, meningeal, 36 and the choroid plexus macrophages. Those cells migrate to the CNS early in the prenatal 37 life and maintain a long-lasting population. In malignant gliomas, besides activation of local 38 microglia, circulating monocytes invade the brain from the periphery and differentiate within 39 the tumor; therefore, microglia and infiltrating monocytes/macrophages are commonly 40 referred to as glioma-associated macrophages (GAMs), due to the shortage 41 of immunocytochemical markers allowing their reliable identification 3 . Transcriptome profiling 42 of bulk CD11b+ cells isolated from human glioblastomas (GBMs) and rodent gliomas showed 43 a mixture of protumorigenic and antitumorigenic phenotypes and did not reveal consistent 44 markers and pathways 4-6 . Recent reports have demonstrated that GAMs consist of diverse 45 cell populations with likely distinct roles in tumor progression 7-10 . Dissecting the TME 46 composition and functional heterogeneity of tumor-infiltrating immune cells would extend the 47 understanding of the glioma immune microenvironment and allow to modulate functions of 48 distinct subpopulations for therapeutic benefits. 49Sex differences in incidence, transcriptomes, and patient outcomes in the adul...

Glioma-derived IL-33 orchestrates an inflammatory brain tumor microenvironment that accelerates glioma progression

“…8a, b, d). In addition and consistent with emerging descriptions of activated myeloid cell signatures in the glioma microenvironment, we also observed a population of glioma-associated microglia 107,109,110 (microglia 2 (cluster 2)) that express Ccl2, Ccl12, Ifitm3, and Il1β ( Fig. 10e and Supplementary Fig.…”

“…10g). As predicted, we observed a transition from IL-33 enriched inflammatory monocytes 100 (marked by expression of Ccr2, Ifitm2, and Ifitm3) to differentiating BMDM and then to glioma-associated BMDM 107,110,111 (marked by expression of Apoe, Hexb, and Cd81) consistent with a pro-tumorigenic environment. In addition, a gradual down regulation of ribosomal genes (e.g., Rpl and Rps) is seen within the trajectory, a feature akin to the myeloid lineage differentiation pattern observed by Athanasiadis and colleagues 112 and consistent with a recent study that has mapped the diversity of non-parenchymal brain macrophage 111 .…”

“…A comparable glioma-associated signature was also observed in microglia 5 (cluster 6 (e.g., Ccl3, Apoe, and Lpl) Supplementary Fig. 8a, b), and within these two microglial clusters, we observed a similar enrichment of GO terms related to cytokine secretion 107 and protein translation 110 (Fig. 10d).…”

Mitochondrial Dysfunction, Macrophage, and Microglia in Brain Cancer

“…Importantly, infiltration of blood-derived macrophages instead of microglia correlates with poor survival in low-grade glioma (Müller et al, 2017 ). ScRNAseq of mouse glioma shows that there are eight to nine clusters of microglia and three clusters of blood-derived macrophages (Ochocka et al, 2019 ). Among the microglia subsets, there are three major subgroups: one with high expression of homeostatic microglia signature genes, one with high transcriptional activity of gene that inhibit nuclear factor kappa B (NFκB) signaling, and one with increased expression of genes for antigen presentation (Ochocka et al, 2019 ).…”

Biological and Medical Importance of Cellular Heterogeneity Deciphered by Single-Cell RNA Sequencing

“…In recent years, scRNA-seq has been extensively used to understand the intratumoral genetic landscape in glioblastoma, medulloblastomas, kidney cancer, colorectal cancer, and other types of cancers [20,21,24,59,[77][78][79][80][81][82][83][84][85][86][87][88]. A recent scRNA-seq study provided a blueprint for glioblastoma and found that malignant cells exist in four primary cellular states, and the relative frequency of cells in each state varied according to the tumor microenvironment [89].…”