A novel molecular classification method for osteosarcoma based on tumor cell differentiation trajectories

Subclassification of tumors based on molecular features may facilitate therapeutic choice and increase the response rate of cancer patients.However,the highly complex cell origin involved in osteosarcoma(OS)limits the utility of traditional bulk RNA sequencing for OS subclassification.Single-cell RNA sequencing(sc RNA-seq)holds great promise for identifying cell heterogeneity.However,this technique has rarely been used in the study of tumor subclassification.By analyzing sc RNA-seq data for six conventional OS and nine cancellous bone(CB)samples,we identified 29 clusters in OS and CB samples and discovered three differentiation trajectories from the cancer stem cell(CSC)-like subset,which allowed us to classify OS samples into three groups.The classification model was further examined using the TARGET dataset.Each subgroup of OS had different prognoses and possible drug sensitivities,and OS cells in the three differentiation branches showed distinct interactions with other clusters in the OS microenvironment.In addition,we verified the classification model through IHC staining in 138 OS samples,revealing a worse prognosis for Group B patients.Furthermore,we describe the novel transcriptional program of CSCs and highlight the activation of EZH2 in CSCs of OS.These findings provide a novel subclassification method based on sc RNA-seq and shed new light on the molecular features of CSCs in OS and may serve as valuable references for precision treatment for and therapeutic development in OS.

Pericytes may facilitate SARS-CoV-2 entry into the nervous system

Objective:Although the neurological and olfactory symptoms of coronavirus disease 2019 have been identified,the neurotropic properties of the causative virus,severe acute respiratory syndrome-associated coronavirus 2(SARS-CoV-2),remain unknown.We sought to identify the susceptible cell types and potential routes of SARS-CoV-2 entry into the central nervous system,olfactory system,and respiratory system.Methods:We collected single-cell RNA data from normal brain and nasal epithelium specimens,along with bronchial,tracheal,and lung specimens in public datasets.The susceptible cell types that express SARS-CoV-2 entry genes were identified using single-cell RNA sequencing and the expression of the key genes at protein levels was verified by immunohistochemistry.We compared the coexpression patterns of the entry receptor angiotensin-converting enzyme 2(ACE2)and the spike protein priming enzyme transmembrane serine protease(TMPRSS)/cathepsin L among the specimens.Results:The SARS-CoV-2 entry receptor ACE2 and the spike protein priming enzyme TMPRSS/cathepsin L were coexpressed by pericytes in brain tissue;this coexpression was confirmed by immunohistochemistry.In the nasal epithelium,ciliated cells and sustentacular cells exhibited strong coexpression of ACE2 and TMPRSS.Neurons and glia in the brain and nasal epithelium did not exhibit coexpression of ACE2 and TMPRSS.However,coexpression was present in ciliated cells,vascular smooth muscle cells,and fibroblasts in tracheal tissue;ciliated cells and goblet cells in bronchial tissue;and alveolar epithelium type 1 cells,AT2 cells,and ciliated cells in lung tissue.Conclusion:Neurological symptoms in patients with coronavirus disease 2019 could be associated with SARS-CoV-2 invasion across the blood-brain barrier via pericytes.Additionally,SARS-CoV-2-induced olfactory disorders could be the result of localized cell damage in the nasal epithelium.