Neoplastic and immune single-cell transcriptomics define subgroup-specific intra-tumoral heterogeneity of childhood medulloblastoma

BACKGROUND

Medulloblastoma (MB) is a heterogeneous disease in which neoplastic cells and associated immune cells contribute to disease progression. We aimed to determine the influence of neoplastic and immune cell diversity on MB biology in patient samples and animal models.

METHODS

To better characterize cellular heterogeneity in MB we used single-cell RNA sequencing, immunohistochemistry, and deconvolution of transcriptomic data to profile neoplastic and immune populations in patient samples and animal models across childhood MB subgroups.

RESULTS

Neoplastic cells cluster primarily according to individual sample of origin which is influenced by chromosomal copy number variance. Harmony alignment reveals novel MB subgroup/subtype-associated subpopulations that recapitulate neurodevelopmental processes, including photoreceptor and glutamatergic neuron-like cells in molecular subgroups GP3 and GP4, and a specific nodule-associated neuronally differentiated subpopulation in the sonic hedgehog subgroup. We definitively chart the spectrum of MB immune cell infiltrates, which include subpopulations that recapitulate developmentally related neuron-pruning and antigen-presenting myeloid cells. MB cellular diversity matching human samples is mirrored in subgroup-specific mouse models of MB.

CONCLUSIONS

These findings provide a clearer understanding of the diverse neoplastic and immune cell subpopulations that constitute the MB microenvironment.

EMBR-27. NEOPLASTIC AND IMMUNE SINGLE CELL TRANSCRIPTOMICS DEFINE SUBGROUP-SPECIFIC INTRA-TUMORAL HETEROGENEITY OF CHILDHOOD MEDULLOBLASTOMA

Medulloblastoma (MB) is a heterogeneous disease in which neoplastic cells and associated immune cells contribute to disease progression. To better understand cellular heterogeneity in MB we used single-cell RNA sequencing, immunohistochemistry and deconvolution of transcriptomic data to profile neoplastic and immune populations in childhood MB samples and MB genetically engineered mouse models (GEMM). Neoplastic cells clustered primarily according to individual sample of origin which is in part due to the effect of chromosomal copy number gains and losses. Harmony alignment of single cell transcriptomic data revealed novel MB subgroup/subtype-associated subpopulations that recapitulate neurodevelopmental processes and are associated with clinical outcomes. This includes photoreceptor-like cells and glutamatergic lineage unipolar brush cells in both GP3 and GP4 subgroups of MB, and a SHH subgroup nodule-associated neuronally-differentiated cell subpopulation. We definitively chart the spectrum of MB immune cell infiltrates, which reveals unexpected degree of myeloid cell diversity. Myeloid subpopulations include subgroup/subtype-associated developmentally-related neuron-pruning as well as antigen presenting myeloid cells. Human MB cellular diversity is recapitulated in subgroup-specific MB GEMM, supporting the fidelity of these models. These findings provide a clearer understanding of both the neoplastic and immune cell heterogeneity in MB and how these impact subgroup/subtype classification and clinical outcome.

Projected t-SNE for batch correction

MOTIVATION

Low-dimensional representations of high-dimensional data are routinely employed in biomedical research to visualize, interpret and communicate results from different pipelines. In this article, we propose a novel procedure to directly estimate t-SNE embeddings that are not driven by batch effects. Without correction, interesting structure in the data can be obscured by batch effects. The proposed algorithm can therefore significantly aid visualization of high-dimensional data.

RESULTS

The proposed methods are based on linear algebra and constrained optimization, leading to efficient algorithms and fast computation in many high-dimensional settings. Results on artificial single-cell transcription profiling data show that the proposed procedure successfully removes multiple batch effects from t-SNE embeddings, while retaining fundamental information on cell types. When applied to single-cell gene expression data to investigate mouse medulloblastoma, the proposed method successfully removes batches related with mice identifiers and the date of the experiment, while preserving clusters of oligodendrocytes, astrocytes, and endothelial cells and microglia, which are expected to lie in the stroma within or adjacent to the tumours.

AVAILABILITY AND IMPLEMENTATION

Source code implementing the proposed approach is available as an R package at https://github.com/emanuelealiverti/BC_tSNE, including a tutorial to reproduce the simulation studies.

CONTACT

aliverti@stat.unipd.it.

scRNA-seq in medulloblastoma shows cellular heterogeneity and lineage expansion support resistance to SHH inhibitor therapy

Targeting oncogenic pathways holds promise for brain tumor treatment, but inhibition of Sonic Hedgehog (SHH) signaling has failed in SHH-driven medulloblastoma. Cellular diversity within tumors and reduced lineage commitment can undermine targeted therapy by increasing the probability of treatment-resistant populations. Using single-cell RNA-seq and lineage tracing, we analyzed cellular diversity in medulloblastomas in transgenic, medulloblastoma-prone mice, and responses to the SHH-pathway inhibitor vismodegib. In untreated tumors, we find expected stromal cells and tumor-derived cells showing either a spectrum of neural progenitor-differentiation states or glial and stem cell markers. Vismodegib reduces the proliferative population and increases differentiation. However, specific cell types in vismodegib-treated tumors remain proliferative, showing either persistent SHH-pathway activation or stem cell characteristics. Our data show that even in tumors with a single pathway-activating mutation, diverse mechanisms drive tumor growth. This diversity confers early resistance to targeted inhibitor therapy, demonstrating the need to target multiple pathways simultaneously.

Although the hedgehog (HH) pathway is known to be deregulated in medulloblastoma, inhibitors of the pathway have shown disappointing clinical benefit. Using single-cell sequencing in a mouse model of the disease, the authors show that the response to the HH pathway inhibitor vismodegib is cell-type specific.

Neuropeptide-like immunoreactivities and carboxypeptide H activity associated with bovine brain clathrin coated vesicles

Chromatographically purified clathrin coated vesicles (CCV) from bovine brain gray matter were collected and analyzed for their adaptor protein profile via SDS-PAGE, for their carboxypeptidase H (CPH) activity via radioenzymatic assays and for their NP (NPY1-36, CCK-8 and SS-14) content by radioimmunoassays. The results reveal the expression of CPH and neuropeptide-like immunoreactivities (NP-Li: NPY-Li, CCK-Li and SS-Li) associated with CCV. CPH activity associated with CCV is stimulated by cobalt, inhibited by 5 microM GEMSA and has an acidic pH optimum (4.5-6.5). The Michaelis-Menten kinetics assay of CPH in CCV reveals a Km = 28.9 microM and Vmax = 1.88 nmol/min/mg at pH 4.5 using 3H.Bz-FAR as a substrate. The NP-Li and CPH were mainly associated with the ascending portion of the CCV peak suggesting that these molecules are found in the larger diameter CCV subpopulation associated with CCV of the trans Golgi network (TGN), endocytic or recycling CCV. Analysis of the adaptor protein profile of the material eluting from the Sephacryl S-1000 column demonstrates a wide distribution of the Golgi-associated AP-1 (HA-I) molecules (AP47 and AP19) in relation to the CCV peak, spanning both the ascending and descending portions of the CCV peak. This adaptor protein pattern is consistent with the inherent size microheterogeneity of TGN CCV, large diameter CCV of the regulated secretory pathway and smaller diameter CCV of the lysosomal pathway.